ENERGY SUPPLY SYSTEM AND METHOD RELATED THERETO

Field of invention

The present invention in a first aspect relates to an energy supply system for providing auxiliary electrical energy to equipment on a high voltage platform. in a second aspect, the invention relates to a high voltage platform provided with such an energy supply system.

Sn a third aspect, the invention relates to an electric network provided with such a platform. Sn a fourth aspect, the invention relates to a method for providing auxiliary electric energy to equipment on a high voltage platform.

Background of the invention

For equipment on high voltage platforms along high voltage transmission lines, a problem is to assure an auxiliary power supply even when the power lines are without power. Today laser light is transmitted from the ground through fibre optics up to the platform, but with this method it is not possible to transmit more than approximately 0,5 W per optical fibre. The equipment must be able to operate even when the power Sines are without power, such as during service or when a fault has occurred along the power lines, to protect equipment from damage caused by stroke of lightning. Existing systems for supplying energy are not able to meet these demands.

DE 1807 591 discloses a high voltage breaker arranged on a platform.

The breaker is provided with an actuator powered by an effectuating capacitor. The effectuating capacitor is charged by an energy converter, converting chemical or mechanical energy into electric energy, As an example the energy converter can be a fuel cell.

A problem with a supply device of this kind is that a conventional capacitor of this kind leaks energy such that it repeatedly has to be recharged. Furthermore when the capacitor has been in use it has to be recharged. The power from a fuel cell is normally to low to allow recharging within reasonable time. Alternatively a particular powerful and costly fuel ceil has to be used.

Summary of the invention

The object of the present invention is to overcome the above identified problem and aϋow energy suppiy to the effectuating capacitor within a reasonable time and at iow cost. This object has according to the first aspect of the invention been achieved in that an energy supply system of the kind in question includes the specific features that the system contains an intermediate storage and suppiy unit for storing energy from the fue! ceϋ and supplying energy to the effectuating capacitor and an electric transforming unit for feeding energy from the intermediate storage and supply unit to the effectuating capacitor.

By such an intermediate storage and suppiy unit ful! energy is supplied to the effectuating capacitor at a short time, while electric energy is supplied to the intermediate storage on a longer time basis. Thus the energy suppiy to the intermediate storage unit can be made at a low power, whereas the energy supply from the intermediate storage unit takes place at much higher power. The electric transforming unit allows a iow voltage of the intermediate storage and supply unit to be adapted to a higher voltage of the effectuating capacitor.

The power supply from the fue! ceil to the intermediate storage and supply unit is allowed to be fairly iow so that a fuel cell of low power can be used. The power of the fuel cell is much lower than the power the electric transforming unit has to handle for charging the effectuating capacitor within a limited time.

The fuel cell wili require relatively few operating hours yearly if the number of actuations is limited. The lifetime of the system therefore will not be limited to the lifetime of the fuel ceil. According to a preferred embodiment of the invented system the intermediate storage and suppiy unit comprises at least one low voltage capacitor having high energy storage capacity and low leaking effect.

Using one or more iow voltage capacitors of this type optimizes the requirements for being charged by the fuel cell, for charging the effectuating capacitor and for obtaining a low volume.

According to a further preferred embodiment the intermediate storage and supply units include at least one electric chemical double-layer capacitor.

This type of capacitor, often referred to as ultracapacitor or supercapacitor is particularly usable for the intermediate storage and supply unit due to its high

capacitance and large energy storage capacity. Typically, an uJtracapacitor has a capacitance of hundreds or thousands Farads, whereas the voltage normally is low, only a few volts. The energy storage capacity is normally about 10 - 20 kJ/kg.

Since an ultracapacitor has very low energy leakage, there is practically no need for recharging due to leakage. Recharging is only required to compensate for energy supplied therefrom.

According to a further preferred embodiment, the voltage is in the range of 1 to 4 V, preferably in the range of 2 - 3 V and the energy storage capacity is in the range of 5 to 50 kJ per kg, preferably in the range of 10 to 20 kJ per kg. According to a further preferred embodiment, the storage means includes a plurality of ultracapacitors in series.

Providing a plurality of uStracapitors is a convenient way to reach the necessary voltage level.

According to a further preferred embodiment, the fuel ceil has a charging power in the range of 15 to 100 W, preferably in the range of 30 to 50 W.

Thereby the fuel ceil is designed to be able to charge the intermediate storage means within a time that is required, normally about one hour.

The low charging power of the fuel ceil means that it can be small and cheap. According to a further preferred embodiment the fuel cell and the intermediate storage and supply means are located in an insulated cabinet.

Thereby it is possible to provide an environment for these components that assures conditions regarding e.g. temperature that are required for a proper functioning. According to a further preferred embodiment the cabinet is provided with a tempered air supply duct arranged to supply tempered air into the cabinet.

The supply of tempered air is a convenient way of keeping the temperature within the cabinet within an appropriate range.

According to a further preferred embodiment the fuel ceil has an air supply duct which air supply duct is located within the tempered air supply duct.

By arranging the air supply to the cathode side of the fuei cell in this way the temperature of also this air supply can be held within appropriate range thanks to heat exchange with the supplied tempered air.

According to a further preferred embodiment the system includes at least one fan arranged to blow air into the cabinet.

This offers an additional or alternative way to maintain the temperature in the cabinet at an adequate ievei. According to a further preferred embodiment the fuei cell is provided with a cathode drain duct arranged to drain water to the bottom of the cabinet.

By draining the water from the cathode side of the fue! cei! to the bottom of the cabinet which is located on the platform any high potential problems that could arise by draining the water to the ground is avoided. According to a further preferred embodiment the system includes a fuei cell controller located on the platform and a microprocessor located on the ground which are arranged to control the operation of the system.

Through this arrangement the system can automatically adapt to prevailing conditions and the starting and stopping of the components in the system can be arranged to be performed automaticaily in response to sensed parameters. The above described preferred embodiments are specified in the dependent claims of the invented system.

According to a further preferred embodiment the system includes measuring means for measuring the voltage across the intermediate storage and supply unit and/or the at least one effectuating capacitor.

Thereby the charging level status can be controlled and required measures for initiating recharge can be taken.

According to a further preferred embodiment the system includes first signa! means arranged to start operation of the fuei cell in dependence of the measuring means and/or second signal means arranged to start discharging of the intermediate storage and supply unit in dependence of said measuring means.

This, in an easy way allows automatic initiating of required operation measures for maintaining the system at appropriate stand-by condition.

Sn the second aspect of the invention, the object is met in that a high volt- age platform has the specific feature that it is provided with a system according to the invention and in particular according to any of the preferred embodiments thereof.

in the third aspect of the invention, the object is met in that an eiectricai network has the specific feature that it is provided with a high voltage platform according to the invention, in the fourth aspect of the invention, the object is met in that the method for providing auxiiiary electric energy to equipment on a high voltage piatform includes the specific measures of supplying energy from the fue! ceii to an intermediate storage and supply unit and supplying energy from the intermediate storage and supply unit to the at least one effectuating capacitor.

According to a preferred embodiment of the invented method energy is supplied to the intermediate storage and supply unit only when the voltage across the intermediate and storage and supply unit is below a predetermined Sevei.

Thereby the fuel ceii is required to operate only when necessary thus saving operating time for the fue! cell.

According to further preferred embodiments of the invented method, the method is performed with the use of a system according to the invention and in particular according to advantageous embodiments thereof.

The invented high voitage platform, the invented electrical network and the invented method and the preferred embodiments of these inventions solve corresponding problems and have the corresponding advantages as have been de- scribed above for the invented system and the preferred embodiments thereof.

The invention wiil be explained more in detail by the foiiowing description of advantageous examples thereof and with reference to the accompanying drawing.

Brief description of the

Figure 1 schematically illustrates an energy suppiy system according to the invention.

Figure 2 is a scheme illustrating the functions of the system of fig. 1.

Description of advantageous examples of the invention

Fig. 1 schematicaiiy depicts a high voitage piatform 1 , On the platform 1 , equipment 10 connected to a high voltage transmission iine 4 is provided. The equipment 10 is actuated by one or more effectuating capacitors 3, in case need

shouid arise, After the capacitor 3 has been fully discharged from its energy content, e.g. 15 kJ it has to be recharged.

Recharging of the effectuating capacitor 3 is accomplished by charging it from the intermediate storage and supply unit 5 via the electric transforming unit 31 , e.g. an inverter.

The intermediate energy storage and supply unit 5 consists of a number, e.g. six, of uStracapacitors 6 mounted in series. Each ultracapacitor 6 has a capacitance of 5000 F and a maximum voltage of 2.5 V. Each ultracapacitor 6 thus can store 15.6 kJ, resulting in a total of 94 kJ. This is sufficient to charge the effectuating capacitor 3 in 1 minute at a power of approximately 250 W.

After the uStracapacitors 8 in the intermediate energy storage and supply unit 5 has been activated and has charged the effectuating capacitor, the ultracapacitors have to be recharged. Since the expected need for charging the effectuating capacitor 3 is only about ten times a year, a iong time is available for charging the uStracapacitors 6.

The uitracapacitors 6 are charged by a fuel ceil 7. Due to the Song time available for charging the uStracapacitors, the power of the fuel cell can be moderate. The power can e.g. be about 30-50 W, which will allow charging the ultracapacitors to an energy of 50-100 kJ within one hour. The output of the fuel eel! gives approximately 15 V DC in output voltage, which corresponds to six uitracapacitors of 2.5 V.

The fueS ceii 7 is running on pure hydrogen and is via a polymer tube 8 connected to a hydrogen bottie 9 located on ground level.

A more detailed explanation of the system is made with reference to fig. 2, which is a scheme illustrating the various functions of an electric energy supply system according to the invention.

The fuel ceil 7 is located in an insulated cabinet 11. The system shouid be able to work within a temperature in the range e.g. -4O ⁰ C to +40 ⁰ C and at a reSative humidity up to 100 %. The temperature range within the cabinet 11 should be kept within the range of +5 ⁰ C to +45 ⁰ C. A Sow humidity should prevaiS in order to minimize corrosion due to condensation.

Tempered air is supplied to the cabinet 11 in order to keep the temperature therein above +5 ⁰ C.

The temperature within the cabinet 11 is measured and if the temperature is beiow O ⁰ C the fuel cell has to be heated up before starting it.

For cooling purposes two fans 12, 13 are arranged to blow cold air into the cabinet 11. In the disclosed example the hydrogen for the fuel eel! is supplied to the anode side from a bottle at ground level.

A tube 19 leads air to the fuel cell to provide oxygen supply to the cathode side of the fuel ceil 7. An air pump 20 on the ground gives the air pressure and amount of air needed. The amount of air needed depends on the output power from the fuel cell 7. The amount of air is governed by the speed of the air pump 20 which is controlled by the microprocessor 17. Normally the air pump speed can be constant.

Air for tempering the cabinet 11 is supplied through a tube 22. Preferably the air supply tube 19 supplying air to the cathode side is located inside the tempered air tube 22. The fuel cell generates water when operating. 90 % of the water comes from the air exit port on the cathode side. This water is drained through the cathode drain tube 23 into the cabinet 11 on the high voltage platform 1. Most of this water is ventilated away by the recirculated air and normally no droplets are formed that has to be drained away. About 10 % of the water comes down with the hydrogen purge pipe 24.

This water leaves as moist air and normally no droplets are formed.

The hydrogen purge pipe 24 is provided with a solenoid purge valve 25 which is periodicaliy opened to allow hydrogen gas, impurities and eventual water to be purged off from the anode side. The solenoid purge valve 25 is located at ground level and is controlled by the microprocessor 17.

The operation of the system is controlled by a fuel cell controller 27 located on the platform 1 and by a microprocessor 17 located on ground. The main tasks of the fuel cell controller 27 and the microprocessor 17 are to control charging of the effectuating capacitor 3 and charging of the ultracapacitor bank. The voltage of the effectuating capacitor 3 is monitored, When the measured voltage of the effectuating capacitor 3 is below a certain limit, due to operation or energy leakage, the relay 30 is closed and energy is supplied from the uStracapitors 5 via the inverter 31 , provided that the voltage of the ultracapitors is above a certain limit e.g. 11 ,5 V.

The voltage of the uitracapitors 5 is also monitored. When the measured voltage is below a certain limit the fuel cell is started thereby charging the uitracapitors 5. When exceeding a certain voltage, e.g. 14,4 V of the uitracapitors 5, the fuel cell 7 is shut off.