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Title:
WORLDWIDE COMMONWEALTH ELECTRICITY BY HVDC SYSTEM
Document Type and Number:
WIPO Patent Application WO/2022/084728
Kind Code:
A2
Inventors:
OLAOMI ANTHONY ADEDAPO (NG)
Application Number:
PCT/IB2020/060006
Publication Date:
April 28, 2022
Filing Date:
October 24, 2020
Export Citation:
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Assignee:
OLAOMI ANTHONY ADEDAPO (NG)
International Classes:
H02J1/00; E02B3/00; G06Q50/06; H02J13/00; H02K7/18
Download PDF:
Claims:
The Claims

WORLDWIDE COMMONWEALTH ELECTRICITY BY HVDC SYSTEM

I, Engr. Dr. Olaomi, Anthony Adedapo, hereby declare that the above-named invention is my personal and intuitive discovery during my Ph.D endeavoured research work. This invention has three subtitles which are regarded as unity of three inventions as they are interdependent, interconnected with worldwide application. The drive and focus are the same, that is, to provide cheap, constantly available, reliable electricity to the worldwide consumers intercontinentally.

This inventional title, that is, “Worldwide Commonwealth Electricity By HVDC System”, breeds the following subtitles:

1. Intercontinental Commonwealth of Electricity by HVDC System, that is, HVDC worldwide network with HVDC coordinative circuit breakers for continental, intercontinental and worldwide haulage and wheeling of enormous electrical energy from the annually flowing run-of-river serial dams.

2. HVAC and HVDC Transmission Losses Economic Reduction, that is, reduction in the wheeling of enormous electrical power losses to the barest minimum even of 2% for any distance of transmission. This is the reason why HVDC system with the absence of reactances will make bilateral intercontinental power supply and worldwide HVDC network with coordinative circuit breakers practical, economical, and profitable.

3. Commonwealth Hydroelectricity from Run-of-river Serial Dams, that is, siting of many dams serially on annually flowing rivers like Niger River, Congo River, Nile River, Tigris River, Mississippi River and so on for generation of enormous electrical power to be wheeled continentally and intercontinentally by HVDC system of transmission network with coordinative circuit breakers.

4. I also declare that this invention with its subtitles is for competitive sale to any utility company(ies) or govemment(s) for worldwide utilization.

Description:
WORLDWIDE COMMONWEALTH ELECTRICITY BY HVDC SYSTEM

GENERAL INTRODUCTION

The inauguration and presentation of these three unity of inventions compressedly titled: Worldwide Commonwealth Electricity By HVDC System envisions to power the energy economies of the world through cheap, stable and reliable means of carriage of electric power thousands of kilometers with low losses even as low as 2%. Siting of 50 dams serially on Niger River will provide electric power in the range of 101.850 - 156.300 GW. Similar number of run-of-river serial dams can be sited worldwide along the annually flowing rivers of the world for generation of enormous hydroelectricity for worldwide electric power transmission through HVDC system. The main title crystallised from the following subtitles:

1 ) Intercontinental Commonwealth of Electricity By HVDC System

2) HVAC And HVDC Transmission Losses Economic Reduction

3) Commonwealth Hydroelectricity From The Run-of-river Serial Dams

The descriptions, tables and drawings (figures) associated with these three unity of inventions are presented sequentially in a successive manner as itemized numerically here.

INTERCONTINENTAL COMMONWEALTH OF ELECTRICITY BY HVDC SYSTEM

BACKGROUND OF THE WORK

The establishment of the intercontinental commonwealth of electricity by HVDC system is practicable because the system can be utilized for the carriage of enormous electricity over long distances in the range of thousands of kilometers with low losses even as low as 2%. Therefore, HVDC system can be bilaterally utilized for the carriage of enormous electric power continentally, intercontinentally, and worldwide and can be centrally controlled because of the availability the HVDC coordinative circuit breakers.

In the contemporary time, the haulage of enormous electric energy over long distances is effected by high voltage direct current (HVDC) transmission line system. This is possible because the inductive reactance (ωL = X L ) is zero as a result of the fact that the angular frequency, ω , in radians per second is zero. Hence, the voltage drop, IX L , along the line is zero. Also, the shunt capacitive reactance along the transmission line is infinite and that drastically reduces the leakage/charging current to an infinitesimal level. This is the reason why “Ferranti Effect" (appearance of a spurious higher voltage at the receiving end than at the sending end of an AC transmission line) is absent in the HVDC transmission system (Nagrath I.J., Kothari D.P., 2002)

As a result of the above fact of absence of inductive and capacitive reactances on the HVDC transmission lines and cables, HVDC system is capable of carriage of enormous power in the range of megawatts and gigawatts over long distances even above a distance of 5,000 km. Presently, apart from HVDC wheeling of power over long distances, the system is extensively used to interconnect AC utility stations of different voltage magnitudes, phase angles, frequencies, and phase sequences. This is usually referred to as back-to-back interconnection of zero distance as a firewall to forestall instability and high current level faults during electricity bilaterial trading between utility companies. Because of its high transmission efficiency, HVDC system is normally employed to evacuate power from the remote super power stations to the local centers situated over one thousand kilometers away accomplished with insignificant losses.

It can be easily established that the transmission capacity of a bipolar HVDC system is about 3 times that of 3-phase high voltage alternating current (HVAC) system for the same peak voltages, the same conductor size and at 0.800 power factor while the power factor of HVDC system is always 1.00. Because of the absence of skin effect in the HVDC line, I 2 R loss in the HVDC system is lesser than that of HVAC system. As a result of reduced phase-to-phase clearance, phase-to-ground clearance, and the number of conductors of HVDC system is of HVAC system, the tower size of the HVDC system is smaller than that of the HVAC system. The HVAC right-of-way is wider and more complex than that of the HVDC system because of the environmental concern such as corona, aestheticism and heavier load. In order words, because of lesser load on the supporting structure, tower design is smaller, cheaper and narrower for HVDC than for HVAC systems. By bipolar mode, HVDC insulation level is about 47% of that of 3-phase HVAC system of the same power capacity (Gupta J.B, 2004).

The HVDC converter stations which were formally costlier than the HVAC substations are now progressively less expensive because of the advancement of the technology of semiconductors (Vijay K.S., 2004). In general, the cost structure of HVDC transmission depends on many factors such as power capacity for transmission, transmission distance, transmission voltage, environmental conditions, regulatory requirements, cost of labour in the siting country, transmission medium (overhead, underground, and underwater through sea medium), and the cost of the equipment.

THE SUPERIORITY OF HVDC OVER HVAC FOR LONG DISTANCE HAULAGE OF

HUGE POWER

In the demonstration of the superiority of HVDC over HVAC, the application of HVDC is presented as:

• A 765 kV HVAC line can typically transmit 2000 MW, while a single bipolar HVDC line can transmit about 4000 MW at ±500 kV, 4800 MW at ±600 kV and 6400 MW at ± 800 kV. For the same voltage, HVDC system can transmit three times the capacity of the HVAC system. For instance, transmitting 4800 MW may require three 765 kV HVAC lines, but a single bipolar HVDC line at ±600 kV. From the reliability point of view, one HVDC bipolar line can be regarded as two AC lines (Lubini I.E., 2000).

• A 3500 km point-to-point ± 800 kV HVDC transmission system of 3000 MW would cost 1.8 billion US Dollars at 10% losses on the line, compared to four 800 kV AC lines costing 3.5 billion US Dollars (Lubini I.E., 2000). • Likewise, a 3500 km point-to-point, + 800 kV HVDC transmission system of 6000 MW costs 3 billion US Dollars at 10% losses, compared to seven 800 kV AC lines costing 6 billion US Dollars. The above costs include the converter station equipment, the lines and control systems (Lubini I.E., 2000).

It has been amply established that HVAC and HVDC power can be transmitted to any distance at the losses of 2%, or 4%, or 6%, or 8%, or 10% and or any other tolerable loss level can be computed by using the formulated expressions for HVAC and HVDC system losses. Since HVDC is free from reactive losses except resistance losses, the system (HVDC system) can now be bilaterally used for haulage of enormous electric energy from continent to continent of any distance at low loss level even as low as 2%. Through inventive and intuitive design, HVDC coordinate circuit breakers are now available for manufacturing so that HVDC network is presently practicable.

DIFFERENT TYPES OF MODERN HVDC CONVERTERS

There are majorly three types of modem HVDC converters namely:

• The conventional HVDC converter is a line commutated current source converter (LCCSC) or HVDC line commutated converter (HVDC-LCC) which conducts when the anode is more positive than the cathode or when the cathode is more negative than the anode. It uses a stack of thyristors as the conversion valve device. It is mostly applicable to strong power systems whose effective short circuit ratio (ESCR) is high, low impedance source, large short circuit capacity, and high stability margin for HVDC high power conversion of rectification and inversion (Mohan, et al, 2003; Baoliang, et al, 2007).

• HVDC capacitor commutated converter (HVDC-CCC) uses a stack of thyristors as the conversion valve device but with a capacitor connected between the valve and the transformer leakage inductance. It is utilized mainly to ameliorate the weak power systems of low ESCR to forestall commutation failures (Vijay, 2004); Qian, et al, 2008).

• The most recent HVDC converter is a voltage source converter (VSC) that is a voltage source through a parallel capacitor and is acronymously referred to as HVDC -VSC or HVDC-Light or HVDC-PLUS (PLUS means: power link universal system) (Siemens, 2011). This is also referred to as self-commutated converter in that it can switch on or off without the reversal of the commutation voltage. It uses GTO (gate turn off) thyristor or IGBT (insulated gate bipolar transistor) or IGCT (insulated gate commutated thyristor) as the conversion valve device. It is capable of handling medium power procession up to 200 MW. This is due to the present technological, commercial, economic and practical limitations of GTO, IGBT and IGCT valve devices (Vijay S.K., 2004; Arrillaga, et al, 2007).

For carriage or transmission of huge power to long distances, HVDC-LCCSC system has been established to be more reliable, safer, more economical and of lower losses than the HVAC counterpart. It is useful for the haulage of enormous power from remote hydroelectric dams, large- scale wind-power farms to the load centers. Hence, the HVDC-LCCSC system is identified and devoted to the haulage of enormous power for long distances in the range of hundreds and thousands of kilometers with low losses.

RELATIONSHIP BETWEEN HVAC AND HVDC POWER SYSTEMS

The modem electricity power system will be a mix of AC and DC as shown in Figure 1. The two systems shake hands fraternally in order to give each other assistance. The AC power system is superior in power generation, voltage and current transformations using transformers, distribution of electric power, and utilization of the same. The DC power is superior in long distance transmission but it is not transformable for lack of variation with time and induction (Kimbark, 1971).

ONE-LINE DIAGRAM OF HVAC AND HVDC TRANSMISSION LINES

The one-line diagram in Figure 2 shows the pictorial diagrams of HVAC and HVDC systems. The HVAC system experiences only voltage and current transformations from the sending end to the receiving-end load. But HVAC-HVDC-HVAC system undergoes conversion from HVAC to HVDC and is then inverted back to HVAC for utilization at the load centre. THE DESIGN OF COORDINATIVE CIRCUIT BREAKERS FOR HVDC SYSTEM

NETWORK

In the HVAC system of 50Hz or 60Hz, the current zeros 100 or 120 times respectively in a second, so that an AC circuit breaker can operate at any current natural zero when the magnetic field energy, is zero and the electric field energy, is maximum. But for the HVDC system, current and voltage are non-zero parameters so that the circuit breaker suitable for AC circuit breaking is not straightforwardly applicable to HVDC breaking. Forced arc interruption or chopping would produce high rate of rise of restriking voltage (RRRV) and transient restriking voltage (TRY) and eventual arc restriking without interruption and ultimate damaging of the breaker contacts.

Most of the present HVDC links are two-terminal links which do not need circuit breakers because their currents are brought to zero by the control of the firing angles of the converters. However, multi-terminal HVDC networks need circuit breakers. These circuit breakers must be able to convert

DC to AC for existence of current zero so that the breaker is enabled to break the circuit at current zero.

For the design of HVDC circuit breaker to be effective or functional, there are three cardinal problems that must be resolved visavis;

• generation of artificial AC across the SF 6 circuit breaker for current natural zero to occur.

• stopping of arc voltage build-up for restriking in the SF 6 circuit breaker.

• removal of stored energy by rapid cooling and deionization in the SF 6 circuit breaker.

All these phenomena are achievable through the circuit breaker in Figure 3.

The artificial alternating current is created by the LC circuit. Under normal condition, S 2 is closed and opened and capacitor, C, is charged fully to the voltage through R 2 . When a fault occurs, the switching mechanism opens S 2 and closes S 1 so that C discharges through L and SF 6 circuit breaker in an oscillatory manner as in Figure 3(b).

It is always optimally desirable to break the circuit at the first current natural zero. The active filter (AF) or passive filter (PF) is for the cancellation of the sundry and spurious harmonics that may be generated. Switches Si and S2 may be built by using semiconductor devices such as GTO (gate turn off) thyristor or IGBT (insulated gate bipolar transistor) or IGCT (insulated gate commutated thyristor) for fast and accurate switching.

Various timing of circuit breaking can be achieved by varying the frequency of oscillation through the variation of L or C. Assuming that the value of L is kept constant at 10 mH, as the frequency is increased, the values of capacitance vary according to Table 1 vis-à-vis

(1)

If the circuit breaker is designed to open at the first current natural zero, then

(2) and (3)

Table 1 shows results obtained using equations connecting C n and T n for the various frequencies indicated in column one.

As the circuit breaker interruption period decreases, the rate of rise of restrike voltage increases rapidly to the end that interruption may not take place in the first half cycle of current natural zero. To forestall this occurrence, a resistance of = is connected across the SF 6 CB. In addition a spark gap of silicon carbide (Sic) or zinc oxide

(Zno) arrester is also connected across the SF 6 CB for the control of completely abnormal voltage rise and for dissipating the accrued energy. Sic has a non-linear resistance of such that I = kv 4 which means that Sic arrester resistance decreases rapidly as the voltage rise exceeds the design value. L s is a saturable core reactor that aids the HVDC circuit breaker. Under normal working condition, its inductance Ls = is zero. But when the artificial AC is switched in, the inductive reactance becomes prominent and chokes up TRV and RRRV and high frequency harmonics generated

Table 1 emanates from the design of HVDC coordination circuit breakers. The Table shows the various generative frequencies with the sequential breaking times so that HVDC circuit breakers could be coordinated such that some circuit breakers will serve as immediate breakers and others as remote or backup breakers. The availability of HVDC coordinated circuit breakers makes HVDC network practicable as it has been in the AC system. With the available practicality of HVDC network, the HVDC engineer can now co-ordinately pick the safe operating period for the level of protection desired at each HVDC circuit breaker location.

THE COORDINATIVE PROTECTION SCHEME FOR HVDC POWER NETWORK

The HVDC network consists of HVAC sources and HVAC terminal ends, that is, AC generators and AC loads sandwiched with HVDC system made up of converters and HVDC transmissions lines or underground cables or undersea cables. The whole network comprises of hybrid circuit breakers, that is, HVAC and HVDC circuit breakers. The HVDC protection scheme can utilize the HVDC circuit breaker developed in Figure 3 and timing in Table 1. The HVDC circuit breaker does not need any relaying scheme since it generates its own artificial AC to effect its operation. The use of semiconductor devices for switches and S 2 will aid fast operation of the circuit breaker.

The HVDC circuit breaker operations can be time coordinated as shown in Table 1 and Figure 4. The HVDC at inverter stations are more prone to fault than the transmission link and the rectifier stations because of incessant switching of the loads. Therefore, the HVDC circuit breakers at the extreme right can be denoted as the primary protection device and the operating time can be adjusted according to Table 1. The circuit breakers in the transmission link can be the immediate backup and the HVDC circuit breakers in the extreme left can constitute the remote backup. The operating times for the circuit breakers can be adjusted according to the Table 1

POWER TAPPING (TEE-ING) ALONG THE HVDC TRANSMISSION LINE

The modem electricity power system will be a mix of AC and DC as shown in Figure 1. The AC power system is superior in power generation, voltage and current transformations using transformers, distribution of electric power, and utilization of the same. The DC power is superior in long distance transmission but it is not transformable for lack of variation with time. Hence tapping principle is applicable to HVAC/HVDC/HVAC long distance transmission network as shown in Figure 5. Four bipolar converters are parallel connected on the AC side and serially connected on the DC side for power and current boosting for HVDC transmission. The network has been intuitively designed to have simultaneous converter of rectification at the generation station and converter of inversion at the tapping points along the HVDC transmission line. The power tapping system is bipolar and hence has two lines of positive and negative polarities. Only one line is shown for clarity. Also, each HVDC transmission branch is bipolar and has DC circuit breakers and AC circuit breakers and inversion to 3- phase AC system.

HVDC POWER NETWORKS FOR LONG DISTANCE TRANSMISSION: NIGERIA AND

AFRICA AS THE CASE STUDY

The Nigerian HVDC network traverses the country with six tappings at strategic locations. The HVDC network for Africa consists of 4 axes i.e Sokoto axis, Bauchi axis, Garbon axis and Lagos axis. The design of these axes is similar to the format of HVDC network for Nigeria including the tappings for inversions at various concerned nations in Africa. Each network consists of 4 bipolar mode-connected converter stations of rectification and the power tappings along each axis for HVDC inversion to HVAC for further transmission, distribution and utilization.

HVDC NETWORK FOR NIGERIA DESIGN

The network is as shown in Figure 6. The network consists of 4-bipolar mode-connected converter station of rectifier for conversion from AC to DC. The HVDC transmission line emerging from the converter station consists of power tappings for inversion from HVDC to HVAC for further AC subtransmission and distribution to the consumers.

All the 4 bipolar systems are connected in parallel om the AC side with a common operating voltage of 600 kV on the DC side and a current of 5 kA per bipole per line. That is the total line current is 20 kA.

The total power derivable and transmissible from the rectifier converter network will be:

The transmissible power

= 2 X 20,000 X 600,000

= 2.4 x 10 10 Watts

= 24 GW According to Jos Arrillaga, the total power loss in the electrical components such as transformers, valves, filters, and reactive power sources in a converter station is about 0.8% of the total power derivable from that converter station.

Hence, the total power extractable from the AC power source.

= DC power + the power loss

= 24 X 1.008

= 24.192 GW (3)

There are 16 power transformers in the converter station. Therefore the power rating of each transformer is:

(4) where

S = complex power rating of each transformer cosθ = ac system power factor.

The normal operational delay angle, a, is 15° and the corresponding minimum commutation or overlap angle, μ, is also 15° . With these angles, V dor , the ideal no load direct voltage at the rectifier converter can be calculated, i.e.

(5)

But

V dr = 300kV for one, three-phase, 6-pulse, full-wave Graetz bridge.

Hence, μhere V dor = ideal no-load rectifier direct voltage

V dr = direct voltage from the rectifier conveter for transmission a = delay angle /ignition angle /control angle μ = commuatation /overlap angle

5 = a + μ, extinction angle

Now

S = 1.0472(ideal no-load direct voltage)(rated direct current) (Kundur P, 1994) (6)

= 1.0472 x V dor x I d

= 1.0472 x 327.52 x 5

= 1714.90 MV A

But,

Scosθ = 1512 MW

Therefore, θ = cos -1 (1512/1714.52) = 28.13° where θ = power factor angle for AC system

Here , cosθ ≠ α as stipulated by many authors and their theories. This disparity occurs because the authors assume lossless situation in the converter station and zero commutation angle in equating cosθ and cos a.

The total complex power , S T , for the converter station is

S T = 165

= 16 x 1714.52 = 27.43232 GVA

The total real power P supplied to the station is

P = 27.43232 cos28.13°

= 24.192 GW

This power is equal to the stipulated transmissible power plus Jos Arrillaga 0.8% loss per converter station.

POWER EXTRACTION AT THE TAPPING STATIONS

If there are 6 tapping stations in Nigeria and 24 GW transmissible power is to be equally distributed among the 6 tapping stations, then the law of compound depreciation can be used. With tolerable transmission loss of 2% and Arillaga converter loss of 0.8% , the equal power extractable at each tapping point, using the law of compound depreciation, is given by

(7) where

P s = tapping station power

P T = total transmissible power

N% = percentage tolerable transmission loss

3.8887 GW is the power available for inversion at each tapping station. The frequency of the inverted power will depend on the existing AC system frequency at the tapping station or the frequency of the synchronous generator for provision of commutation voltage if AC system does not exist at the tapping station. THE HVDC POWER NETWORK FOR AFRICA

These HVDC networks consist of 4 axes i.e. Sokoto axis, Bauchi axis, Garbon axis and Lagos axis as shown in Figures 7a to 7d. Each network consists of 4 bipolar mode- connected converter station of rectification. All the 4 bipolar systems are connected in parallel on the AC side with common operating DC voltage of 600 kV and current of 5 kA. Therefore, the total power available from each converter station is

P T = 8IV (8)

P T = 8 x 5000 x 600000

P T = 24 GW

The total power transmissible by the 4 networks is 96 GW. If the networks are designed for tolerable losses of N = 2%, the total power receivable at the various inverter stations transformable to AC is

Receivable power = Transmissible power (1 - N% pu - 1.6% pu ) (9)

= 96(1 - 0.02 - 0.016)

= 96 X 0.964

= 92.544 GW

POWER TRANSMISSIBLE AND RECEIVABLE THROUGH HVDC BIPOLAR SYSTEM

Table 2 shows the transmissible and receivable Powers at N% losses and at 5 kA. Modem thyristors are able to carry a current of 5 kA each. The table shows the transmissible powers and the various receivable powers at the various loss levels at the HVDC voltages indicated. The losses include the line losses and the two converter station losses of 0.8% each of the transmissible power and the receivable power.

The expression/mathematical algorithm for finding the parameters in Table 2 is given by: Receivable Power = Transmissible power (1 — (N% + 1.6%))(Eugene, et al, 1970) (10)

HVDC TRANSMISSIBLE AND RECEIVABLE POWER AND LOSSES FOR 4000 KM AT

2% OVERALL LOSS AND AT 3% LOSS PER 1000 KM

Table 3 shows the power transmissible and receivable through various HVDC voltages from 330 to 1200 kV for a distance of 4000 km. The last column shows the various annual energy savable by selecting 2% overall loss for the 4000 km transmission line rather than 3% loss for every 1000 km. The savable energy runs into millions of dollars annually. Any other tolerable loss can be selected from Table 3.

The parameters in Table 3 were calculated by the following mathematical algorithms:

• Receivable power = Transmissible power (1- N% - 1.6%) at 2% overall loss for overall distance of 4000 km.

• Receivable power = Transmissible power at 3% loss per 1000 km for overall distance of 4000 km (Eugene, et al, 1970). (11)

POSSIBLE ANNUAL REVENUE ACCRUABLE TO NIGERIA AND OTHER SIMILAR

INVESTORS

If the average power made available to the African consumers through HVDC network is 92.544 GW annually, then the number of electrical energy units available to the consumers will be:

= 92.544 x 10 9 x 24 x 365/1000

= 8.1068544 x 10 11 kWh

= 8.1068544 x 10 11 units of electrical energy

The total amount accruable to Nigeria annually will be

= 8.1068544 X 10 11 X 0.121 (Dollar/kWh, 2019 USA Average)

= 98.09293824 x 10 9 Dollars = 98.09293824 billion USA Dollars

WORLDWIDE CONTINENTAL HYDROELECTRICITY GENERATION AND HVDC

BILATERAL TRANSMISSION NETWORKS

All the continents of our planet, i.e. Africa, Asia, Europe, North America, South America and Antarctica, are richly and naturally endowed with many dammable rivers for irrigation, portable water supply and generation of hydroelectricity. Many of these rivers that flow all the year round can be serially dammed for generation of enormous electricity. This enormous electricity generated from all the dammable rivers within a continent can be converted to HVDC power and HVDC network with coordinative HVDC circuit breakers and can be used to transmit the power to all the nations or states within the continent. The HVDC network can be upfront designed for a particular percentage tolerable loss from 2 to 10 percent on the transmission line and 0.08 % station loss of the transmission power according to J. Arrilaga (Arrillaga, J., et al, 2007)

In some cases, the excess of power generated in a particular continent, as a result of availability of abundant flow rate of water, can be transmitted to another continent through the HVDC link at a low loss. This is practicable because HVDC power is capable of being transmitted to any distance at a loss as low as 2% of the transmissible power.

Adaptation of hydroelectricity generation of enormous electricity and haulage of the same by HVDC system continentally and intercontinentally with tappings for inversion to HVAC system for local distribution will go a long way in powering the energy economies of the world and at the same time reduce the greenhouse gas emissions effect in this planet. The outline and features of the continental dammable rivers and HVDC converters, transmission networks with tappings for HVDC inversion to HVAC for local power distribution are demonstrated for each continent and the world as follows:

AFRICA CONTINENT

The major dammable rivers in Africa for hydroelectricity generation and conversion to HVDC for continental HVDC transmission network and tappings for inversion to HVAC for local power distribution are:

Nile River

• Niger River • Senegal River

• Volta River

Benue River

• Congo River

• Zambezi River

• Limpopo River

• Orange River

The dammable rivers listing for Africa continent is not exhaustive. See figure 8.

ASIA CONTINENT

Likewise, the major dammable rivers in Asia for hydroelectricity generation and HVDC system network:

Amur River

• Huang River

• Yangtze River

• Mekong River

• Irrawaddy River

• Ganges River

• Godavari River

Indus River

• Tigris River

• Euphrates River

The dammable rivers listing for Asia continent is not exhaustive. See figure 9.

AUSTRALIA CONTINENT

The major dammable rivers in Australia for hydroelectricity generation and HVDC system network: Murchison River

Diamantina River

• Darling River

• Murray River

• Coopers Creek River

The dammable rivers listing for Australia continent is not exhaustive. See figure 10.

EUROPE CONTINENT

The dammable rivers in Europe for hydroelectricity generation and HVDC system network:

Volga River

Vistula River

Oder River

Elbe River

Rhine River

Seine River

Thames River

Loire River

Rhone River

Po River

Tagus River

Danude River

The dammable rivers listing for Europe continent is not exhaustive. See figure 11.

NORTH AMERICA (USA and CANADA)

The endowed and dammable rivers in North America for hydroelectricity generation and HVDC system network are as below: Mackenzie River

Yukon River

Fraser River

Churchill River

Columbia River

Colorado River

Missouri River

Mississippi River

Ohio River

Rio Grande River

St. Lawrence River

The dammable rivers listing for North America continent is not exhaustive. See figure 12.

SOUTH AMERICA

The naturally endowed and dammable rivers in South America for hydroelectricity generation and

HVDC system network are as below:

Orinoco River

Magdalena River

Negro River

Amazon River

Madeira River

Trapajos River

Paraguay River

Parana River

Xingu River

Tocantins River

Sao Francisco River

The dammable rivers listing for South America continent is not exhaustive. See figure 13. CONCLUSION

The HVDC network system was hitherto impracticable because of absence of DC circuit breaks this research work has designed workable coordinative circuit breakers which implies that HVDC network is now practicable. See Figure 14 for worldwide hydroelectricity generation scheme and allied intercontinental HVDC system network. The HVDC system operating voltages could be: 600kV, 700kV, 800kV, 900kV, 1000kV, 1100kV, 1200kV, 1300kV, 1400kV, and 1500kV. 1200kV, 20kA might be acceptable for worldwide transmission.

(2) HVAC AND HVDC TRANSMISSION LOSSES ECONOMIC REDUCTION

BACKGROUND OF THE WORK

The beneficial and economic breakthrough emanating from reduction of HVAC and HVDC transmission line and cable losses can be made clearly obvious. The transmission line losses of high voltage alternating current (HVAC) and high voltage direct current (HVDC) systems can be technically reduced to the barest minimum thereby minimizing the needed power generation for a particular electric load. Lower generation of electricity implies lower consumption of fuel and lesser current and losses for the same voltage, and hence, lesser expenses for the same electric load. With I 2 R loss in the transmission line conductors reduced to the barest minimum, HVDC system can now be the means of cross-continental and intercontinental carriage of enormous electric energy.

Energy losses are generally encountered because of underfunding of transmission lines, distribution infrastructural networks, and operation with low power factors. Energy losses are colossal in most developing countries; the average loss has been greater than 18%. Typical transmission line losses are on the order of 7-10% in the United States and the other developed countries (Roberto Rudervall, et al, (2000)). The minimum average energy losses of 7% in the US amount to 466.032 billion kWh per annum These losses can be reduced to 133.152 billion kWh per annum (71.43% reduction) by using precise conductor size of 2% loss as stipulated in this intuitive research work. These figures are based on the US electricity installed capacity of 760 GW (Hadi Saadat, 2006). Transmission line conductors range in the cross-sectional area size according to voltage, line length, and power carriage demand. Lowering transmission line losses results in reduced generation requirements, with subsequenent reductions in greenhouse gas emissions (GHGE), (Mitigation Handbook, 1999).

Pertinent efforts should be made to reduce losses to the barest minimum possible because an insignificant percentage loss in the electricity transmission could culminate in billions of kilowatt- hours (kWh) of waste electricity. For instance, if the total power of 100 GW is generated in Nigeria for sale at the transmission efficiency of 82%, the total energy units lost is 157.68 billion kWh per annum which translates to 3.641 trillion naira (19.07928BUSD) loss per annum at the present utility rate of 23.09 naira per energy of kWh unit at 18% losses.

Therefore, transmission line losses are economic problems that must be technically tackled. Table 4 shows the electricity energy losses scenario in the Nigerian power network from 1990 to 1999.

Table 4 depicts Nigerian power system installed capacity from 1990 to 1999. The table also shows the total energy generation, consumption and losses. The percentage losses are very colossal. These losses could be reduced to 2% through this research effort.

DESIGN OF TOLERABLE LOSS CONDUCTOR SIZES FOR TRANSMISSION LINE AND

CABLE SYSTEMS

Copper and aluminum conductors are the most acceptable conductors for carriage of electric energy at both distribution and transmission levels. The International Standard of 100% conductivity is that of annealed copper. The commercial hard-drawn copper wire has 97.3% and aluminum has 61% of the conductivity of the standard annealed copper. At 20 °C, the hard-drawn copper has resistivity, p, of 1.77 X 10 -8 Q-m, while the resistivity of aluminium at the same temperature is 2.83 X 10 -8 Ω- m (Stevenson, 1982).

The conductor constants or parameters, for both copper and aluminum, are resistance, inductance, capacitance, and shunt conductance. The shunt conductance is generally due to leakage of charges over insulation and is so small that it can be ignored. The series inductance mainly dictates the power transmission line capacity and the shunt capacitance causes charging and leakage of current along the line. The resistance of the transmission line conductors (both copper and aluminum) is the most important cause of power loss ( I 2 R) in a transmission line (Gupta, 2004). The ohmic resistance, R, ( R = ρL/a) for a fixed distance, L, is inversely proportional to the cross-sectional area, a, or size. As the size, a, increases, the resistance decreases and so I 2 R loss decreases. The I 2 R 4 loss constitutes an economic loss which may run into billions of US dollars every year. This research work focuses on I 2 R loss reduction even down to 2% can be achieved. At present, the average I 2 R loss in the advanced nations is about 7-10% while the average loss in the developing nations is about 18% (Roberto Rudervall, et al, 2000). Thus, a tolerable loss based on conductor size is designed in order to reduce the loss in the transmission line.

The reasons for the necessity of tolerable loss conductor size design are (Roberto Rudervall, et al, 2000):

• Transmission line losses are economic problems that must be technically tackled

• The losses involve waste generations of power, increase of greenhouse gas emissions into the atmosphere thereby causing a rise in the climate temperature change.

The losses are due to chronic under-investment in transmission lines and distribution infrastructures and operation with inappropriate power factors

• The losses are averagely 18% in the 88 developing nations and 7-10% in the technologically advanced nations.

Figure 15 shows n generating stations through n three-phase transmission lines and feeding a central load.

The total power loss in the 3-phase network is given by:

P L = P L1 + P L2 + P L3 + ... + P Ln (12) where

P L = total network losses

= P L1 + P L2 + P L3 + ... + P Ln

(13) where

V 1 , V 2 , ... , V n = line to line voltages

P 1 , P 2 , ... , P n = line transmissible powers

I 1 , I 2 , ..., I n = line currents pƒ 1 , pƒ 2 , •••, pƒ n = power factors

= cosine of the angle between voltage and current

That is, each line has its own corresponding three-phase transmission loss or energy waste (3I 2 R i t ).

If the line voltages, power factors, and active power from the lines are correspondingly given as:

V 1 ,V 2 , V 3 , ..., V n ; Pƒ 1 , Pƒ 2 ,Pƒ 3 . ..Pƒ n1 ; P 1 , P 2 , P 3 , ... , P n , then the losses are

(14)

If the same type of transmission line conductor is used, then the resistances may be written as

(15) where a i = cross sectional area or size in m 2 L i = transmission line length in m ρ = resistivity in ohm-meter (Q-m)

= 2.83x10 -8 Ω-m at 20°C (aluminum conductor)

Therefore, the total loss could also be written in terms of resistivity with the various cross-sectional area sizes as in equation (16)

(16)

Now, if each line loss is to be limited to a maximum of 2% of the real power (Pi) generated and transmitted from each generating station, then the total network loss remains at 2% of the total power at the load center. Therefore, each line loss can be intuitively and independently equated, i.e.

(17)

Substituting the values for ρ (aluminum conductor) and = 98%, the cross-sectional areas ( a i ) in square meters for 2% network line transmission losses, are:

(18) where a i = wire cross-sectional area or size in m 2

L i = transmission line length in m because the resistance is measured in ohms/metre

P i = power transmission in MW

V i = line voltage in kV i = 1, 2... n

Generalizing the percentage loss, for N% loss on each line at any power factor, pƒ i , from equation (17)

(19)

Substituting for the resistivity, ρ, as usual, for aluminum

(20)

(20) where

N can take any value such as: N = 1, 2, 3, 4, 5, ... according to the percentage loss that can be tolerated.

HVAC CONDUCTOR SIZES FOR N% TOLERABLE LOSSES

The generalized formula for the calculation of the cross-sectional areas, a, for desirable loss in electrical power transmission in AC is given by

(21)

Area for equivalent copper conductor = a X 0.61 mm 2 (22) where

L = transmission line length in m P = power in MW

V L = line voltage in kV pƒ = power factors (usually 0.8 for sustenance of reactive power and voltage on a transmission line)

N = tolerable percentage power loss a = cross-sectional area in mm 2 for AC

HVDC CONDUCTOR SIZES FOR N% TOLERABLE LOSSES

The suitable conductor sizes for HVDC transmission line can also be derived. For a bipolar transmission system, the total loss, PL, in the line is given by

(23)

(24)

The loss on one of the two conductors is

(25)

(26) where

P L2 , P L1 = power loss in the two conductors or a single conductor respectively

P = power transmissible in MW

V = DC voltage of transmission in kV ρ = resistivity (Ω-m)

L = transmission length in m

A = cross-sectional area in m 2 P is proportional to P L , therefore, for N% tolerable loss on the line

For an Aluminum conductor,

(27)

Area for copper conductor = A X 0.61 mm 2

(the conductivity of aluminum is 61% of that of copper) i.e. the equivalent copper size

(28) where

V = DC voltage in kV

P = transmissible power in MW

L = transmission length in m

N = tolerable percentage loss

For HVDC systems, the power factor is 1.

The cable/wire sizes for aluminum and copper conductors for tolerable losses from N = 2% to N = 10% with the corresponding AC and DC voltages from 330 kV to 1200 kV and the relevant transmissible power are shown in Table 5. HVAC AND HVDC TRANSMISSION LINE CONDUCTOR SIZES FOR N% TOLERABLE

LOSSES

Table 5 shows the results of the MATLAB simulation program obtained for tolerable transmission losses for transmission line conductor sizes of aluminum and copper conductors for HVAC and HVDC power systems. The extra-high voltages (EHV) and the ultra-high voltages (UHV) used for both HVAC and HVDC systems are the standard transmission voltages averagely common with the present worldwide transmission systems for haulage of enormous power from generation station to substation or electric energy wheeling between interconnected utilities and progressive near future utilization of voltages in the realm of UHV as predicted by researchers (Gunnar Asplund, et al, 2005; Siemens, 2011). The transmissible real power for each voltage is also listed in the Table. The HVAC power system is assumed to be 3-phase transmission line, while the HVDC power system is to be regarded as a bipolar link. The corresponding apparent power for each HVAC can be easily calculated by simply dividing the relevant active power by power factor 0.800. In any case, only the real power is needed to calculate the wire/cable size for any particular tolerable loss on any particular transmission line because voltages and currents are always in phase for resistances.

The voltage spectrum intuitively ranges from 330 kV to 1200 kV (for both HVDC and HVAC systems) according to the present utilization of voltages for main transmission and sub-transmission lines for wheeling or haulage of enormous power in megawatts (MW) and gigawatts (GW). The power spectrum ranges from 500 MW to 6612 MW according to the principle of proportionality of square of voltage to power and as empirically expressed by ( P. Kundur, 1994).

Also, Table 5 contains tolerable transmission conductor sizes for tolerable or permissible losses. The wire size dimensional units are in mm 2 . N represents the percentage losses. The percentage losses are calculated specifically for N = 2%, 4%, 6%, 8% and 10%. Any other size of interest not presented in the Table can be computed utilizing equations (21) and (22) for HVAC aluminum and copper conductors respectively and equations (27) and (28) for HVDC aluminum and copper conductors respectively.

Table 5 wire sizes cater for a distance of 1000 km for transmission or wheeling of AC and DC powers. Other distances, voltages, and powers can be interpolated or extrapolated as the situations demand using the proffered equations. The HVDC system can normally be utilized for haulage or wheeling of enormous power for a distance far greater than 1000 km because of absence of inductive and capacitive reactances. For the HVDC system, the only voltage drop is IR and the power loss is I 2 R which Table 5 tries to reduce to the barest minimum.

The main application of Table 5 is to aid power transmission line designers and investors to choose wire sizes that will minimize losses to tolerable and permissible levels. Reduction of losses on the transmission lines and the distribution infrastructures will reduce waste generations and greenhouse gas emissions into the atmosphere. Of course, there will be a meagre increase in the costs of the wires but the law of cost diminishing retur principle still applies as the wire sizes increase. The usage of bundle conductors will further facilitate reduction of losses on the lines as the voltages increase.

Furthermore, bigger conductor sizes with stranding and bundle installations will reduce corona, skin, and spiraling effects.

From the diligent observations of the bar charts or graphs in Figures 16 to 19 for HVAC and HVDV for aluminum and copper conductors derived from Table 5, the choice of tolerable 4%-loss level for any transmission line for any voltage, power, and distance will bring profitable leverage between costs and losses. This is purely advisory.

The resulting bar charts of aluminum and copper conductor sizes for HVAC and HVDC low-loss transmission systems are as depicted in Figures 16 to 19. There are five bar charts per voltage for each tolerable loss level of 2%, 4%, 6%, 8% and 10% for both HVAC and HVDC transmission lines of both aluminum and copper conductors.

The colours of the bar charts are:

2% Tolerable Loss Level- Deep Blue 4% Tolerable Loss Level- Light Blue

6% Tolerable Loss Level - Lemon

8% Tolerable Loss Level- Orange

10% Tolerable Loss Level- Brown

The bar charts vertical lengths indicate the magnitude of the cross-sectional areas or sizes of the transmission wires in mm 2 as tabulated in Table 5 for the various indicated transmissible voltages and the relevant power.

Figures 16 shows the bar charts for the HVAC aluminum tolerable conductor sizes for N% tolerable losses from N= 2% loss to N =10% loss for each voltage and power indicated. The voltage range is from 330 kV to 1200 kV while the power varies from 500 to 6612 MW. The aluminum conductor cross-sectional areas or sizes vary from 10151.23 mm 2 for 2% tolerable loss level at 330 kV, AC, 500 MW to 1842.45 mm 2 for 10% tolerable loss 1200 kV, AC, 6612 MW. The corresponding diameters for 2% loss and 10% loss are 113.69 mm and 48.44 mm respectively. Other aluminium conductor cross-sectional areas for AC are equally easily identifiable either from the table or from the bar charts. The bar charts assume the varying physical lengths because the sizes are directly proportional to the transmission line length and the power but inversely proportional to the square of voltage, square of power factor and loss level percentage. Hence, it should be noted that higher the loss level percentage, N%, smaller the wire size.

Figure 17 shows the bar charts for HVDC aluminum tolerable loss conductor sizes for N% tolerable losses. The power factor for HVDC is always unity, hence the conductor sizes are smaller for the same length of transmission, power, voltage and tolerance loss level. The aluminum conductor sizes vary from 6496.79 mm 2 for 2% tolerable loss level, 330 kV, DC, 500 MW to 1179.17 mm 2 for 10% tolerable loss level, 1200 kV, DC, 6612 MW. The corresponding diameters are 90.92 mm for 2% loss and 38.74 mm for 10% loss.

Figures 18 and 19 show the bar charts for HVAC and HVDC for copper tolerable loss conductor sizes for N% tolerable losses respectively. The conductivity of copper conductor is about 39% superior to that of aluminum conductor even though aluminum conductor is more useful for overhead transmission because of lower cost, lighter weight, lower voltage gradient at the conductor surface because of greater diameter which lowers surface ionization and the consequent corona loss. Figure 18 has AC copper conductor size of 6192.25 mm 2 at 2% tolerable loss for 330 kV, AC, 500 MW and 1123.89 mm 2 at 10% tolerable loss for 1200 kV, AC, 6612 MW. The corresponding diameters are 88.80 mm at 2% tolerable loss and 37.83 mm at 10% tolerable loss.

From Figure 19, the first bar chart at 2% tolerable copper conductor loss, 330 kV, DC, 500 MW has an area size of 3963.04 mm 2 while the area size at 10% loss level, 1200 kV, DC, 6612 MW is 719.29 mm 2 . The corresponding diameters are 71.03 mm at 2% copper conductor loss and 30.20 mm at 10% copper conductor loss. Other loss level conductor sizes can be similarly read either from the table or from the bar charts.

Moreover, Figures 20 to 29 depict bar graphs of aluminium and copper conductor cross-sectional areas or sizes for 2% to 10% tolerable loss levels with their corresponding HVAC and HVDC voltages from 330 kV to 1200 kV. The purpose of the bar graphs is to create visual impression of their sizes when aluminium and copper conductors are used for HVAC and HVDC transmission of electrical power at the indicated tolerable loss levels. The bar graphs also showcase the physical and differential features between the HVAC and the HVDC conductor sizes from 2% - loss level to

10%- loss level. It is also evident from the bar graphs that haulage of enormous power over distances is more economical with HVDC than with HVAC.

Summarily:

• Figures 20, 22, 24, 26, and 28 graphically demonstrate conductor sizes for 2%, 4%, 6%, 8%, and, 10% tolerable losses using aluminum conductor as the mode of transmission for HVAC and HVDC voltages from 330 kV to 1200 kV for the various power tabulated in Table 5

• On the other hand, Figures 21, 23, 25, 27 and 29 also depict conductor sizes for 2%, 4%, 6%, 8% and 10% tolerable losses using copper conductor as the mode of transmission for HVAC and HVDC voltages form 330 kV to 1200 kV for the various power indicated in Table 5. CONCLUSION

The cardinal focus of this research endeavour is to reduce the economic challenge associated with the colossal losses when wheeling enormous power from the generating stations to the long distance substations and distribution centres. Reduction of losses will also facilitate the carriage of huge power internationally and intercontmentally. HVDC transmission system can now be utilized magnificently and significantly for international and intercontinental wheeling of enormous power with desirable tolerable losses even as low as 2% because HVDC system can wheel power along limitless long distances because of absence of inductive stability limit and Ferranti effect which are very prominent in the HVAC transmission system. The presence of these elements, i.e inductive reactance stability and Ferranti effect, in the HVAC system makes HVAC long distance carriage of power impractical.

(3) COMMONWEALTH HYDROELECTRICITY FROM THE RUN-OF-

RIVER SERIAL DAMS

BACKGROUND OF THE WORK

The energy stored in the stationary or flowing water which eventually turns to falling water is called potential and kinetic energy respectively and this energy is used to turn a hydraulic turbine linked to an electric synchronous generator thereby converting water energy to mechanical energy which is converted to electrical energy through the synchronous alternator. The hydroelectricity which depends ultimately on the natural evaporation and precipitation of water by the sun’s solar energy is the present renewable energy source for generation of electricity on a large scale. Presently, the hydroelectric power system provides about 30 percent of the total world electric power supply. This percentage will be on the great increase if further utilization of the available hydroelectricity resources in the world embarkation is earnestly resumed.

There is a great number of countries in the world that have developed their hydrological resources to the level that greater part of their electricity needs is being catered for mainly by hydroelectricity. Some of such countries are listed in Table 6 (D.S. Chauhan, S.K. Srivasfava, 2007). The versatility of the hydroelectricity cannot be over emphasized. It is able to reliably satisfy the three types of load demand by consumers namely:

• Base-load demand: - which is expected to be continuous for 24 hours every day.

• Peak-load demand: - which is the highest load demand occurring for a period of time in a day or occurring occasionally, monthly, or yearly.

Intermediate-load demand: - which is the sporadic or steady load demand increase between the base load and peak load.

RELEVANT FACTS ON HYDROLOGY, HYDROGRAPHY, AND HYDRAULICS OF WATER

Hydrology is the engineering science that deals with occurrence, circulation, and properties of the water on the earth and the earth’s atmosphere. Sun is the major player in these activities. The solar energy from sun warms the water of oceans, rivers, lakes, land, and green vegetation which leads to evaporation and transpiration of water vapor carried by wind into the atmosphere. After sufficient cooling, the vapor condenses leading to precipitation as snow, rain, hail, and sleet on the land, lakes, and oceans as shown in Figure 30.

Part of the precipitation on the land discharges as surface run-off to rivers, lakes, oceans, and the remaining part seeps into the ground as underground water which sometimes emanates as water springs, streams, and rivers that empty themselves into the seas, oceans and lakes.

The run-off is the precipitation minus the consistent atmospheric evaporation. Hence, the total runoff is equal to the direct run-off over the land surface plus the run-off through the seepage. Generally, the total run-off is influenced by rainfall pattern, geology, topography and vegetation of the area. Thus the hydrological cycle continues (J.B. Gupta, 2004).

In the hydrological cycle processes, water molecules exhibit themselves in the following five phases: (Larry W. Mays, 2005)

• Liquid to vapor leading to evaporation • Vapor to liquid resulting in condensation to water

• Vapor to solid or solid to vapor resulting in state transition

• Solid to liquid i.e. melting to water

• Liquid to solid i.e. freezing to ice

The physical properties of water are unique among the substances with similar molecular mass. Water has the highest specific heat than any known substance which means that temperature change within it occurs very slowly. Water also has a high viscosity and a high surface tension as a result of hydrogen bonding which in turn makes rain to fall in spherical droplets. Water vapor as it is in a gaseous state exerts pressure in the atmosphere called vapor pressure or relative humidity.

Hydrography is the engineering science of measurement, description, and mapping of the surface waters of the earth with special reference to their use for navigation, irrigation, and hydroelectricity. It is an act of hydrographical representation of discharge or flow rate of a river/stream with time at a particular location. The hydrograph is an integral expression of the physiographic and climatic characteristics that govern the relationship between rainfall and runoff of a particular drainage basin/catchment area/watershed. It is often referred to as stream flow hydrograph or discharge hydrograph. It is usually plotted with flow rate (discharge) as the ordinate and the time interval as the abscissa. A hydrograph gives information about maximum/minimum discharge average runoff value of discharge as related to a river within a certain period of time and at a particular location.

The term “hydraulics" is derived from a Greek word meaning waters and is fundamentally the science of dealing with water at rest, in transition and in motion. These states are known as hydrostatics and hydro-dynamics. Hydraulic engineering, therefore, involves the application of engineering basic principles and methodology for the control, conservation, and utilization of water.

Hydraulics is also essentially the study of liquid (water state) in pipe and open channel, referred to as closed-channel/pipe flow and open-channel flow respectively. Closed-channel flow and openchannel flow are similar in many ways but have one major difference. Open-channel flow occurs when there is a free surface whereas closed-channel flow does not have a free surface. Closed- channel flow here refers to pressurized flow in pipes as long as there is not a free surface. THE PROGRESSIVE PROMINENCE OF HYDROELECTRICITY IN THE WORLD

Water had been of prime importance since the inception of humanity on this planet. Apart from its sustenance of life, it had been progressively used for running mills in various forms and for transportation even from early Egyptian and Babylonian civilizations which dated back to about 2500 B.C. By the sixteenth century of the present era, water power had been adopted to many industrial processes to alleviate human drudgery.

The technological breakthrough of late nineteenth century paved the way for the large scale utilization of water for generation of electricity. Today, hydraulics, (science of water), had metamorphosed into many divisions of application such as irrigation, hydrologic flood and erosion control, pipe line waterways, drainage, sanitary and water-power engineering (M.Morris, 2005)

Water-power engineering is the development of hydroelectric power by means of dam construction across a water-flow channel thereby producing a high-head reservoir. The high-head reservoir creates an enormous potential energy with the available gravitational force of falling or flowing water. The amount of potential energy in the water reservoir is proportional to the effective head and the flow rate in the connected pipe as shown Figure 31. The potential energy in the reservoir is converted to kinetic energy in the pipe called penstock, the kinetic energy is converted to mechanical energy in the water turbine, and the mechanical energy is converted to the electrical energy in the electrical generator by the joint power shafts of the water turbine and the generator (G.L. Asawa, 2005)

THE NATIONS WITH GREAT CAPACITY HYDROELECTRIC POWER PLANTS

Hydroelectricity generation is spreading wide among many nations of the world. In many parts of Canada for instance, the word “hydro” is often synonymous to electric energy delivered by a power utility company in that country. The total installed hydroelectric capacity in Canada is 88,974 MW. A single generating station called “Hydro-Quebec” has a total installed hydroelectric capacity (2005) of 31,512 MW. This should generate an inspirational spirit in the hearts of electric energy investors with respect to the enormous volumes of water flowing in the rivers in the world.

Table 7 shows the largest hydroelectric power stations in operation in the world. A hydroelectric power plant does not always operate at its full power rating all the time in a year; the ratio between the annual average power generated and the installed capacity rating is called the capacity factor of that plant. The installed capacity of a hydroelectric power plant is the sum of all the generator nameplate power ratings (Wikipedia, 2008)

THE PROSPECTS OF GENERATING MORE ABUNDANT HYDROELECTRICITY IN

THE WORLD - NIGER RIVER AS A CASE STUDY

At present, Nigeria has three hydropower plants which are Kanji, Jebba, and Shiroro with their corresponding installed capacities. Year 2006 annual average power generated and availability factor are shown in Table 8

The present total installed hydropower capacity in Nigeria is 1938.40 MW, yet hydroelectricity resources in Nigeria that are untapped and undeveloped are enormous. One of such resources is the Niger/Benue confluence run-of-basin from Lokoja to the estuaries at Niger Delta. There is a great treasure of hydroelectricity hiding in this river basin which if judiciously tapped and developed will electrically lift up Nigeria and many other African countries from the present epileptic energy position to buoyancy. This fact is informed and aided by the Niger River flow rate data collected from the ministry of Transport, Inland Waterways as in Table 9. Assuredly, 50 hydroelectric dams can be sited serially along the river as shown in Figure 32.

THE HYDROELECTRICITY POWER EXTRACTABLE FROM DAMMING

NIGER/BENUE RIVER (USUALLY REFERRED TO AS NIGER RIVER)

The maximum extractable power from the Niger River after the confluence can be simply expressed as

P m = ωQH × 10 -6 MW (29) where

P m = maximum electrical power available in MW ω = specific weight, which is the gravitational force per unit volume of water. The specific weight of water at 4°C is 9810 N/m 3 Also, ω = ρg (30) where ρ = mass density, simply referred to as density, is the mass per unit volume i.e. kg/m 3 .The density of water at 4°C is 1000 kg/m 3 . For many applications involving hydrologic or hydraulic processes, the density is assumed constant so that water is regarded as incompressible. g = gravitational acceleration in m/s 2

Q = flow rate or discharge of water in m 3 /s

H = potential elevation of water available in the dam and is simply referred to as waterhead in metres, m

The effective hydroelectric power denoted by, P eƒƒ , is expressed as P eƒƒ = ω QHζ × 10 -6 MW (31) where ζ = overall efficiency coefficient of the hydro-power plant. ζ = ζ h × ζ t × ζ g (32) where ζ h = coefficient of head losses in the pressure tunnel, penstock and draft tube, whichmay be empirically taken as 90% ζ t = the coefficient of efficiency associated with water turbine and could be empirically taken as 95% because of present advancement in water turbine technology most especially when Kaplan water turbine is employed. ζ g = generator efficiency coefficient which could be empirically taken as 98% because the excitation DC power of the rotor field winding is about 2% of the salient synchronous generator power output.

Hence, ζ = 0.9 X 0.95 X 0.98 = 0.8379 Table 8 shows the Niger River flow rate data for sixteen years covering both dry and rainy seasons. The effective power, P eƒƒ will be calculated for the minimum flow rate from the dry season data base which coincides with the year 2004 flow rate (i.e. 2816 m 3 /sec) and the minimum flow rate from the rainy season data base which in this case coincides with year 2006 (i.e. 4322 m 3 /s).

The water turbine recommended here is Kaplan because of its few but adjustable blades whose load could vary from 30% to 110% of the maximum load yet maintaining high efficiency with this load variation.

The optimal elevation head variation recommended here is 88 m as this height has been constructed for a Kaplan turbine located in Italy: “the highest head installation using a Kaplan turbine has a 290-ft head” approximately, 88-m head, (Penner S.S., Icerman L, 1977)

For dry season, the effective and derivative power is given by P eƒƒ = ωQHζ × 10 -6 MW (33) where Q = 2816 m 3 /s

□ P eƒƒ = 9810 x 2816 x 88 x 0.8379 x 10 -6 MW

= 2037 MW or 2.037 GW

For rainy season P eƒƒ = ωQHζ × 10 -6 MW, where Q = 4322 m 3 /s

□ P eƒƒ = 9810 x 4322 x 88 x 0.8379 x 10 -6 MW

= 3126.29 MW

= 3.126 GW

The hydroelectric power extractable from a single dam on Niger River after Niger/Benue confluence will vary from 2.037 GW to 3.126 GW

The length of Niger River from the point of the confluence to the Atlantic Ocean through the estuaries is 822.21 km (Source: PHCN). There is abundant wealth of hydroelectricity along the run- of-river Niger waiting for tapping. This wealth will emanate by construction of hydroelectric dams along the river. 50 serial dams can be effectively sited along the River at a space of every 15 km apart from the confluence to the estuaries leaving a distance of 72 km from the start of the estuaries to the Atlantic Ocean.

With the 15-km space between the dams, it has been watchfully observed that the turbulent flow created by a particular dam would have become streamline or laminar flow before reaching the next dam so that interference or disturbance between the dams will not exist. Moreover, since dams don’t consume water, the volume of water available at the preceding dam will be increasingly available at the succeeding dam because of possible availability of tributaries between the dams. Any run-of- river serial dams anywhere in the world can be of any constructible number for effective hydropower generation.

When the 50 serial dams are constructed, the power that will be available to Nigeria and possibly other African countries will vary from 2.037x50 to 3.126x50 GW i.e. 101.85 to 156.30 GW (from the 50 serial dams) every moment.

THE COMMON TYPES OF HYDROELECTRIC DAMS IN USE TO DATE

There are many types of hydroelectric dams in the world today but they could be majorly classified into four groups as follows (G.L.Asawa, 2005; Larry W. May, 2005)

Run-of-river reservoir dam

• Run-of-river reservoir with pondage/impoundment dams

• Storage/pump reservoir dam

• Storage type dam

The run-of-river reservoir dam principle is applicable to the Niger River hydropower design process being undertaking here.

Hydroelectric dams are also classified according to availability of the elevation head of water as follows:

• High head dams - 500 m and above Medium head dams - 45 to 500 m

Low head dams - 30 to 100 m

• Very low head dams - 1.5 to 25 m

There is no definite demarcation between the heads as they interweave or intermingle each other.

TYPE AND CHOICE OF HYDRAULIC TURBINES

The hydraulic turbines could be classified into two groups namely impulse turbines and reaction turbines. The modem example of impulse turbine is Pelton wheel or Pelton turbine. It is also called tangential or peripheral flow turbine whereby the water potential energy is converted to kinetic energy through the nozzle before impinging on the hemispheric buckets attached to the runner shaft for the rotation of the turbine runner shaft. It is usually employed for high heads and moderate discharges.

The reaction turbines are mostly Francis, Propeller, Kaplan, Bulb, and Tubular turbines. Francis turbine is a mixed flow turbine with radial inlet and axial outlet flow. It is suitable for a medium head and medium discharge. Propeller and Kaplan turbines are both axial flow turbines. The major difference between them is that propeller has fixed blades while the blades of Kaplan are variable. Kaplan has adjustable runner blades which can be rotated about pivots fixed to the shaft of the runner. This Kaplan turbine, because of its adjustable pitch of blades, is capable of operating in the wide range of heads, yet maintaining high efficiency of about 90%. One of the characteristic features of Kaplan is that the gate opening and blade angle are adjusted simultaneously by the governing mechanism. Another special capability of Kaplan turbine is its ability of reverse operation as a pump and hence, is ideally suitable for pumped storage dams. The installation features of the Kaplan turbine are shown in Figure 33. (G.B. Gupta, 2004; S.S. Pennur and L. Icerman, 1977)

The Bulb turbine and the tubular turbine are similar in application because both are installed in the centre of water passageway. The Bulb turbine is a horizontal axial-flow turbine with the runner connected directly or indirectly (i.e. through a speed-changer accessory) to a generator as in Figure 34. The tubular turbine as an axial-flow turbine may be vertically, horizontally, and slantiy installed with a link to the generator located outside water as in the Figure 35.

The head applications and power generation capacities of the major hydroelectric power plants are shown diagrammatically in Figure 36 (Larry W. May, 2005). It is clearly seen that head application ranges and power generations are interwoven (S.S. Pennur, L. Icerman, 1977).

Both the Bulb and Tubular turbines are very appropriate for very low-head dams and have economic advantages in that some of the devices such as spiral/semi-spiral scroll cases and elbow draft tubes prominent in Francis and Kaplan installations are not required (Larry W. May, 2005).

THE EFFICIENCY CURVES OF COMMERCIAL TURBINES

The efficiency curves of the most commercial turbines, i.e. Pelton, Francis, Kaplan, and fixed blade propeller are shown in Figure 37. The curves are plotted as functions of the operating capacities expressed as percentages of the design load capacities. The Kaplan turbine curve shows that the Kaplan turbines have efficiency of about 90 % or more in the operating range from about 40 to 85 % of the design load capacity (Larry W. May, 2005, R.K. Rajput, (2006)).

THE TYPICAL DESIGN OF ONE OF THE 50 EQUAL CAPACITY DAMS

Gravity dams are most suitable for run-of-river reservoir dams like the ones to be sited between the Niger/Benue confluence and the estuaries. This type of dam is the most conversantly utilized one, it requires little maintenance for a long time (B.C Punmia, B.B.L. Pande, 1992). A gravity dam is usually straight in plan and construction although it may be slightly curved in plan and construction.

THE FORCES THAT ARE OPERATING ON A GRAVITY DAM

The forces operating on a gravity dam may be summarily stated as:

• Water thrust

• Weight or thrust of the dam • Uplift pressure

• Wave pressure or thrust

• Silt pressure or thrust

These operating forces acting on gravity dam are diagrammatically shown in Figure 38.

The analysis of the dam forces is as follows:

• The water thrust could be resolved into the horizontal component, F H , and vertical component, F V , as indicated in Figure 38. The total thrust is F H + F V + = F T (34)

Now, the highest discharge, Q = 8693 m 3 /s (from Table 8)

Therefore,

F T = 8693 x 1000 x 9.81 (Mass of 1 m 3 of water is 1000 kg)

F T = 85.28 MN

• Weight or dam thrust is the major resisting force of the dam and must be such that the dam is immune to failure for all its years of operation. For the purpose of analysis, the dam may be divided into many triangles and rectangles of weights w 1 , w 2 ,w 3 ... w n The total weight may be W so that

W= w 1 + w 2 + w 3 + ... + w n (35)

In essence, the water thrust should not be more than 40% of weight of the dam for a wide margin of safety for the operating life of the dam.

Hence,

W= 85.28 X 100/40 = 213.20 MN

The uplift pressure is the upward pressure of water as it seeps through the pervious body of the dam. The accumulation of this water causes upward pressure under the dam in opposition to the vertical pressure thereby weakening the stability of the dam. This pressure could specifically contribute to the overturning or sliding of the dam. To safeguard the dam against uplift pressure, the dam design and construction may include the following:

• Inclusion of toe beam or apron of about 30m deep

• Provision of drainage galleries in the body of the dam

• Masonry concreting of the reservoir foundation to make it impervious to water seepage

• Spillways for constant evacuation of excess water to limit the dam water weight pressure to the maximum of 85.28 MN.

According to the U.S.B.R recommendation, the uplift pressure at different parts of the dam under consideration may be calculated as follows: a) The uplift pressure at heel A = ωH = pgH = 1000 X 9.81 X 88 = 863.28 kN/m 2 b) The uplift pressure at the drainage gallery= ω [H' + (H — H')] (36)

The tail water height is about 10 m. therefore, the gallery = 9810 [10 + (88 10)]

353.16 k N/m 2 c) The uplift pressure at toe F = ωH' = 9810 X 10 = 98.10 kN/m 2

• Wave Pressure of waves are generated on reservoir water surface because of wind storms passing over the dam. The height of wave pressure, according to Molitor D.A is given by: h w = 0.032√V.F + 0.763 - 0.271(F) 025 ƒ or F < 32 km (37) and h w = 0.032√V.F ƒ or F > 32 km (38) where h w = height of waves in meters between trough and crest.

V = wind velocity in km per hour

F = ƒ etch or straight length of water expanse. At Lokoja, the average wind velocity is 11.4 km/hr (from internet). The pressure intensity due to waves is given by

P w = 2.4wh w ( N/m 2 ) at 0.125h w metres (39)

For the dam under consideration here, F will be about 1km. Hence, h w = 0.032√11.48 X 1 + 0.763 - 0.271(l) 0.25 = 0.6004 m

Therefore,

P w = 2.4 x 9810 x 0.6004 x 0.125 = 1.767 kN/m 2

This wind storm could be minimized by planting tall trees around the dam.

• Silt Pressure: Every river normally brings silt and debris along with it. The silt load deposit becomes appreciably troublesome after a while along the life of the dam. The dam is therefore subjected to silt pressure in addition to water pressure. If Y is the submerged unit weight of the silt and 0 is the angle of integral friction and h is the height of silt deposit in the dam, the silt pressure is given by

(40)

Siltation problems can be reduced to the bearest minimum by the following methods

• Regular dredging of the dam (Dr. Ojoawo, LAUTECH) +

• Construction of trash barrier upstream of the dam.

+ (Dr. Ojoawo is a professor of civil engineering, LAUTECH, Ogbomoso, Nigeria)

MODES OF FAILURE OF A DAM

• Overturning Failure is the tumbling or capsizing of the dam if the beam/ apron is weak and eventually fails.

• Sliding Failure is the tilting of the dam or part of the dam to an angle due to the failure of the toe beam/ apron or part of it. • Compressive Failure is due to mounting of water pressure due sudden flood increase if the spillways are not available or inadvertently closed.

• Tension Failure is the deformation due to cracks in the body of the dam. These cracks could possibly expand by travelling to different parts of the dam body leading to eventual shearing.

The dams must be comprehensively designed and constructed by experienced dam engineers to avoid any catastrophic failure throughout the life span of the dams.

THE CONTROL OF HYDROELECTRIC POWER PLANTS

For optimal performance of the hydroelectric power plants between the Niger/Benue confluence and the estuaries of Niger River into the sea, all the 50 serial dam plants should be automation centrally controlled by a control system. And at the same time, each dam plant will be under a subsystem control. In general, an automation system often referred to as a process control system (PCS) or supervisory control and data acquisition (SCADA) system, is critical to the safe, reliable, and efficient operation of many physical processes such as electrical power generation, transmission, and distribution, water, petroleum, natural gas, and sensitive manufacturing industries. Computerized automation of control systems enables orderly, fast, coordinated system management compared to human ability with his inevitable drudgery (Jason Stamp, et al, 2003).

The hydroelectric parameters for monitoring, processing, and data collation are usually water head, intake gate opening, speed of the turbine, water flow rate in m 3 /s and velocity in the penstock, synchronous generator output voltage, real power, reactive power, complex power, power factor, tie- line/isolated frequency, turbine/generator temperatures.

The hydroelectric plant governing instrumentation devices, according to the modem trend, will be optimal and adaptive control systems based on their various attached parameter sensors. The optimal and adaptive control systems have capability for handling linear and non- linear responses of the governing devices. As adaptation is a fundamental characteristic of living organisms because they are able to adapt themselves to maintaining physiological equilibrium and stability in the midst of changing environmental conditions and in the same vein, an adaptive control system is capable of accommodating unpredictable environmental changes, whether they arise within the system or external to it. Moreover, adaptive control system would also accommodate moderate engineering design errors and uncertainties and would compensate for the aging of system components, thereby maintaining system reliability.

For the 50-hydroelectric dam plants, PCS or SCADA will consist of 50 minicomputer-based local terminal units (LTU) and one mainframe terminal unit (MTU) as shown in Figure 6. Each LTU computer system will control and process all the peripheral local governors, interface transducers/sensors, and data logger outputs. These data from each plant will be multiplexed for microwave signal transmission to the MTU system for storage and further processing. The MTU system will use the acquisitive data for the supervisory control of the 50 serial dam plants from a central control point. The MTU system will serve as the main energy control centre while the 50 LTU systems will act as the supplementary energy control centre. Each dam plant will also be equipped with computer-based automatic generation control (AGC) including speed changer or speeder motor that will divide power generation proportionately among the 7- working dam plant units and will remove the steady-state frequency error offset. If any of the turbine generator units at any plant station defaults, LTU computer actuates a tripping action, initiates a changeover to one of the two standby units and sends information to MTU for a request for repair or maintenance. Each of the 50 hydroelectric dam plants may be installed with 9 turbine generating units, each of 500 MW capacity as stated in Table 11, 4th row. 7 units will be put to operation while 2 units are utilized as standby.

THE CUMULATIVE SERIAL DAM POWER ON NIGER RIVER

Table 10 shows the cumulative serial dam power summary of the hydroelectric power that could be generated on the Niger River from Niger/Benue confluence to the Niger estuaries. The maximum power generated becomes 171.93 GW if the Kaplan turbines operate at 110% efficiency.

It is here established that 50 serial dams can be conveniently sited along Niger River. The dams could be located 15 km apart whereby turbulent flow would have given way to steady flow. Some other world rivers may be able to accommodate more than 50 serial dams, others may accommodate less, e.g, Nile River is likely to be able to accommodate more than 50 serial dams of different power capacities. AN OVERVIEW OF THE COST OF POWER GENERATION

Embarkment on power plant design and construction will advisorily and economically depend on the availability of fuel, (waters, for hydroelectricity) the cost of the fuel and plant construction cost. The Energy Information Administration has furnished the Federal Government of Nigeria with the power generation costs scenario (2006) as distilled from Tell, November 23, 2009, page 25. (The information here was distilled and put in the tabular form and the last column was calculated by the author)

It is easy to decipher or infer from Table 11 that nuclear, hydroelectric, gas/oil, and integrated coal-gasification plants will be presently most affordable to Nigeria and other nations with similar water fuel providence. Moreover from row 4 of Table 11 the total cost of the generating 156,300 MW from the Niger River 50 dams will be about 426.3864 billion US dollars.

Similar serial dams could be constructed along Congo and Nile Rivers and the 3 sets of serial dams on Niger, Congo, and Nile Rivers could complement each other through HVDC transmission lines to supply cheap and uninterruptible electricity to the continent of Africa. A duplication of similar scenario of hydroelectricity power generation could be made for the continents of Europe, Asia, Australia, South and North America utilizing their dammable rivers with the aid of HVDC transmission lines for power wheeling.

CONCLUSION

The methodology of construction of the 50 serial run-of-river dams along Niger River in Nigeria can be made adaptable to the construction of various numbers of serial run-of-river dams utilizing the untapped energy resources of many rivers all over the world for electricity generation whereby the modem world will depend more on hydroelectric and wind turbine electric generations. This adaption will reduce worldwide dependence on fossil-fuel plant electricity generation whereby green-house gas emissions reduction is fostered.

Enlargement of hydroelectricity supply by construction of more dams will also reduce the utilization of nuclear reactors which generate harmfill radioactive particles which are hazardous to living beings and injurious to our biosphere. Moreover, a dam may be designed to have tripartite applications and utilization, that is, (i) generation of electricity, (ii) irrigation for nearby farmlands, and (iii) supply of domestic and industrial water to urban cities. In addition, the space of about 15 km between the dams can be used for fishery where fishing activities can be carried out consistently.

At this juncture, it is pertinent to declare that the present power need of Nigeria is about 40 GW. The excess power generated through the 50 serial run-of-river dams can be commercially transmitted to the other African nations through the engagement of high voltage direct current (HVDC) transmission haulage which can carry electrical enormous power to long distances of thousands of kilometers with low and tolerable losses.

For overwhelming availability of electricity in Africa, similar serial run-of-river dams can be sited along Nile and Congo Rivers. These three sets of dams can supplement each other so that the African nations can be illuminated and economically powered without electricity blinking for many years. This electricity supply scenario for Africa is adaptable to the other continents of the world.

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