LOW VOLTAGE

FIELD OF INVENTION

The present invention generally relates to a low voltage electrical protection relay and an low voltage distribution board (LV DB) vacuum circuit breaker. More particularly, the present invention relates to an integrated overload and earth fault protection system, which protects the load / electrical appliances from overload and earth fault. Advantageously, the present invention monitors normal or overload stages to prevent fire in real time.

BACKGROUND ART

Power-system protection is a branch of electrical power engineering that deals with the protection of electrical power systems from faults through the isolation of faulted parts from the rest of the electrical network. The power-system protection keeps the power system stable by isolating only components that are under fault, whilst leaving as much of network as possible still in operation.

Generally, overload protection requires a current transformer which simply measures the current in a circuit. There are two types of overload protection namely instantaneous overcurrent and time overcurrent (TOC). Instantaneous overcurrent requires that the current exceeds a pre-determined level for the circuit breaker to operate. The TOC protection operates based on a current vs time curve. Based on the curve if the measured current exceeds a given level for the preset amount of time, the circuit breaker or fuse will operate. Earth fault protection again requires current transformers and senses an imbalance in a three-phase circuit. Normally the three phase currents are in balance. If one or two phases become connected to earth via a low impedance path, their magnitudes will increase dramatically, as will current imbalance. If this imbalance exceeds a pre-determined value, a circuit breaker will operate.

Electrical faults are the major cause of domestic, commercial, and industrial fires around the world. An electrical short circuit is reported to be the most likely cause of all such fire and associated disasters. Conventional protection system is insufficient to monitor the normal or overload stages to prevent fire.

Known in prior art is protecting a single phase short circuit using a single phase Miniature Circuit Breaker (MCB) as shown in Figure 1.

Another known in prior art is protecting a three phase short circuit using a three phase MCB.

Another known in prior art is using Residual current detectors (RCD) for detection of residual current between phase and earth or neutral and earth as shown in Figure 2. However, the circuits protected with RCD will not detect any over load.

Yet another known in prior art is using single phase overall Earth Leakage Circuit Breaker (ELCB) for detecting earth leakage as a common in any individual circuit's phase to ground fault as shown in Figure 3.

Another known in prior art is using three phase overall Earth Leakage Circuit Breaker (ELCB)for detecting earth leakage as a common in any individual circuit's phase to ground fault. Disadvantages of the prior art are:

• The conventional single or three phase MCBs will not detect earth fault and the conventional ELCB will not detect short circuit.

• The conventional protection system does not protect the circuit from overload.

• In conventional protection system using the single or three phase MCBs, a leakage between phase and neutral is referred as a load only, and continue to supply till short circuit associated with fire.

• In conventional protection system using the single or three phase ELCB at the incoming side will trip on ground fault only, which delays clearing of electrical fault and that leads to a fire and disaster.

• Conventionally, both short circuit and earth fault are not available in single unit, therefore during a single phase earth fault, ELCB will create Blackouts until physical repair of faulty part.

• The conventional protection system does not disconnect power supply when short circuit associated with fire is detected.

• The conventional protection system requires stabilizers for protecting appliances / load from frequent power failures, which increases cost and power loss.

Accordingly, there exists a need for an integrated overload and earth fault protection system for low voltage, which protects the load / electrical appliances from overload and earth fault. Further there exists a need for an overload and earth fault protection system, which monitors normal or overload stages to prevent fire in real time. OBJECTS OF INVENTION

One or more of the problems of the conventional prior art may be overcome by various embodiments of the system of the present invention.

It is the primary object of the present invention to provide an integrated overload and earth fault protection system for low voltage, which protects the load / electrical appliances from overload and earth fault.

It is another object of the present invention to provide an integrated overload and earth fault protection system for low voltage, which monitors normal or overload stages to prevent fire in real time.

It is another object of the present invention to provide an integrated overload and earth fault protection system for low voltage, which detects unbalance or leakage between phase and neutral in a single or three phase circuit during operation of load.

It is another object of the present invention to provide an integrated overload and earth fault protection system for low voltage, which eliminates use of stabilizers in the load connected.

SUMMARY OF INVENTION

Thus according to the basic aspect of the present invention, there is provided an integrated overload and earth fault protection system for low voltage comprising:

a Vacuum Circuit Breaker ( CB);

a Protection Relay;

a Phase Current Transformer (PCT); a Unbalance Current Transformer (UCT); and

a Load,

wherein said protection relay includes an Over Load (OL) element and Earth Fault (EF) element,

wherein the load is connected to a single/three phase AC power supply through the VCB, PCT and UCT,

wherein the UCT is positioned in between phase and neutral terminal to detect unbalance current due to earth fault,

wherein output from the PCT and UCT is fed to the OLEF protection relay, wherein during fault in protected zone of the load, the VCB opens to remove potential from the load, and

wherein the VCB automatically controls the power supply to the system based on the output from the OLEF protection relay, which protects the load from overload and ■ earth fault. other aspect of the present invention, wherein the VCB further comprising:

at least two fixed contacts;

one moving contact;

solenoid assembly; and

spring,

wherein the solenoid assembly includes a solenoid coil and solenoid plunger, wherein the fixed contact is directly connected to bus side terminal post and the fixed contact is directly connected to load side terminal post, said terminal posts maintains vacuum inside chambers of the VCB,

wherein the moving contact is connected to end of the solenoid plunger,, and wherein the moving contact actuates between the fixed contacts with a pre-defined air gap.

It is another aspect of the present invention, wherein one end of the solenoid coil is connected to a neutral terminal post and other end of the solenoid coil is connected to a switched phase terminal post, said terminal posts maintains vacuum inside the chambers of the VCB.

It is another aspect of the present invention, wherein the VCB is optionally provided with a local ON/OFF switch to provide security during maintenance or repair of faulty electrical circuit.

It is another aspect of the present invention, wherein during a low voltage VCB closing function, the moving contact actuates between the fixed contacts, the solenoid coil magnetizes and pushes the solenoid plunger outward against the spring when ON/OFF switch is ON which is based on phase potential that passes through a programmable Binary output of the protection relay.

It is another aspect of the present invention, wherein the VCB remains in closed condition until the ON/OFF switch or the protection relay contacts or the removal or failure of grid supply.

It is another aspect of the present invention, wherein during VCB opening function, the Binary output changes status from Normally Close (NC) to Normally Open (NO) and removes the solenoid supply and the return spring pulls the moving contact to the open status. It is another aspect of the present invention, wherein the VCB remains in the open position until a manual reset command is initiated from the HMI.

It is another aspect of the present invention, wherein the OLEF protection relay is programmable to allow user to make settings to match the actual load/ connected load.

It is another aspect of the present invention, wherein an input from fire alarm system / lightning device could be given as one of the input to the OLEF protection relay for latched tripping of the main supply.

It is another aspect of the present invention, wherein the OLEF protection relay output control signal to the VCB with pre-programmed time delay, which eliminates use of stabilizers in the load connected.

It is another aspect of the present invention, wherein the PCT has primary current rated approximately 30 A and secondary current rated approximately 0.1 A or 100 mA.

It is another aspect of the present invention, wherein the UCT has primary current approximately 10 A and secondary current rated approximately 0.1 A or 100 mA.

It is another aspect of the present invention, wherein the system records real time measurement of voltage, current, frequency, real power, reactive power, power factor and energy. It is another aspect of the present invention, wherein the system is configurable for each Over Load (OL) and Earth Fault (EF) detection, warning, recording, tripping and isolation in less than 100ms time delay.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: illustrates the single phase short circuit protection using single phase Miniature Circuit Breaker (MCB) according to the prior art.

Figure 2: illustrates the detection of residual current using Residual current detectors (RCD)according to the prior art.

Figure 3: illustrates the single phase overall Earth Leakage Circuit Breaker (ELCB) according to the prior art.

Figure4: illustrates the integrated overload and earth fault protection system for low voltage according to the present invention.

Figure 5: illustrates the construction of Vacuum Circuit Breaker (VCB) according to the present invention.

Figure 6: illustrates the Vacuum Circuit Breaker (VCB) circuit according to the present invention.

Figure 7: illustrates the view of Over Load (OL) and Earth Fault (EF) Protection Relay according to the present invention.

DETAILED DESCRIPTION OF DRAWINGS WITH REFERENCE TO ACCOMPANYING DRAWINGS

The invention as herein described relates to an integrated overload and earth fault protection system for low voltage, which protects the load / electrical appliances from overload and earth fault. The system of the present invention monitors normal or over load stages to prevent fire in real time.

Referring to Figure 4, the overload and earth fault protection system for low voltage comprises of a Vacuum Circuit Breaker (VCB) [A]; Protection Relay [B], said protection relay includes Over Load (OL) element [B.2] and Earth Fault (EF) element [B.3];a Phase

Current Transformer (PCT) [C.l]; a Unbalance Current Transformer (UCT) [C.2]; and a load

[LI]. The load [LI] is connected to a single/three phase AC power supply [M] through the

VCB [A], PCT [C.l] and UCT[C.2]. The UCT [C.2] is positioned in between phase [M.3] and neutral [M.4] terminal to detect unbalance current due to earth fault. The output from the

PCT [C.l] and UCT [C.2] is fed to the OLEF [B.2, B.3] protection relay [B]. The VCB [A] automatically controls the power supply to the system based on the output from the OLEF

[B.2, B.3] protection relay [B], which protects the load [L.l] from overload and earth fault.

Referring to Figures 5 and 6, the VCB [A] is preferably a box with bottom and four sides preferably made up of insulated materialand the top cover is a metallic plate.The box is divided into three chambers [A.16, A.17 and A.18] by insulated vertical walls. The VCB [A] has two fixed contacts namely bus side fixed contact [A.1.1] and feeder side fixed contact

[A.1.2] and one moving contact [A.2]. The fixed contacts [A.1.1 and A.1.2] are assembled in the wall [A.21], said fixed contact [A.1.1] is directly connected to Bus side terminal post

[A.3] and the fixed contact [A.1.2] is directly connected to Load side terminal post [A.4]. The terminal posts [A.3 and A.4] are capable of maintaining vacuum inside the VCB chambers

[A.16, A.17 and A.18]. The chambers are namely power circuit vacuum chamber [A.16], moving contact vacuum chamber [A.17] and solenoid assembly vacuum chamber [A.18]. The moving contact [A.2] is assembled on an insulated plate at the end of a solenoid plunger [A.6]. A solenoid coil [A.5] is fixed between the bottom side of the box and the top metal cover in such a way that the heat from the solenoid coil [A.5] will be dissipated through the metal cover. The solenoid plunger [A.6] is a cylindrical body of magnetic material. The plunger body inside the solenoid is bigger and the outer body is smaller in size. The air gap between the inner of the coil and the plunger is as low as possible to create a free movement inside the solenoid coil [A.5]. A spring [A.7] is fitted to the solenoid plunger body [A.6] by a cotter pin [A.23]. The solenoid coil [A.5] has two coil ends [A.8 and A.9]. The solenoid coil end [A.8] is connected to a neutral terminal post [A.10], which could maintain the vacuum inside the chamber. The phase from the bus is passing through a terminal post [A.11], said terminal post [A.11] is capable of maintaining vacuum inside the chamber. The solenoid coil end terminal [A.9] is connected to a switched phase terminal post [A.12], said terminal post [A.12] is capable of maintaining vacuum inside the chamber. The VCB [A] is provided with a valve [A.15] installed on the side wall of the insulated box, said valve is used for creating vacuum inside chambers [A.16, A.17, and A.18]. The valve [A.15] will be closed and sealed after the completion of vacuum inside the chambers [A.16, A.17 and A.18]. The components terminal post [A.10, A.11, A.12], valve [A.15], ON LED [A.14], and local ON/OFF switch [A.13] are covered by a side box [A.20]. The LED lamp [A.14] is provided on the side box to indicate the status of the VCB [A].

Working of the Vacuum Circuit Breaker [A]:

The VCB close function:

During a low voltage VCB closing function, the moving contact [A.2] actuate or firmly touches between the fixed contacts [A.1.1 and A.1.2]. The closing movement of the contact

[A.2] is achieved by the outward movement of the solenoid plunger [A.6] inside the solenoid coil [A.5] by applying single phase supply to the coil. The single phase control supply of the VCB [A] is directly wired from the source/bus side of the circuit to be protected by VCB [A]. The neutral wire is directly connected to the end terminal [A.7] through the terminal post [A.10]. The phase from the Bus is connected to the terminal post [A.l 1], said terminal post [A.l l] is directly wired to a Binary output [B.6.1] of the protection relay [B]. The Binary output [B.6.1] is a programmable output contact and is used as Normally Closed (NC) or failsafe contact. The phase potential pass through the Binary output [B.6.1] and enter in to the local ON/OFF switch [A.13]. If the local control/On-Off switch [A.13] is in ON position the solenoid coil [A.5] will magnetize and push the solenoid plunger [A.6] outward against the spring [A.7]. The VCB [A] remain in closed condition until the local switch [A.13] or the protection relay [B] contacts [B.6.1] or the removal or failure of grid supply.

The VCB open function:

The VCB [A] is always in closed position with grid supply and protection system in healthy mode. A local opening of VCB [A] could be initiated by manually opening the local ON/OFF switch [A.13]and the VCB [A] will remain in open status till the manual switch return to the ON position. An open command could be generated from the protection relay and [B.6.1] will change status from Normally Close (NC) to Normally Open (NO) and remove solenoid supply and the return spring [A.7] will pull the moving contact to the open status. The binary output contact [B.6.1] will remain in latched position until a reset command initiated from the protection relay [B].

The VCB trip function:

The trip and latch function is used for opening the VCB [A] during a faulty situation. The trip command is initiated by the protection relay [B] with respect to the internal settings. The trip is a command linked to the binary output contact [B.6.1] along with other contacts used for warning/annunciation. This contact will remain in open until a manual reset command initiated except for under voltage trip or power failure trip, the binary output contact [B.6.1] will remain in tripped position. A reset from the under voltage will be initiated by restoring the power supply and a pre-assigned time delay. After a grid supply failure this presetting will automatically close the VCB [A] and deliver the load [LI].

Referring to Figures 4 and 7, the PCT [C.l] is preferably a bar type CT, which has a primary phase wire passing through a secondary coil without any physical connection, said PCT has primary current rated approximately 30 A and secondary current rated approximately 0.1 A or 100 mA. The analogue input for Over Load (OL) to the Protection Relay (PR) [B] is directly wired from the secondary of the PCT [C.l] in location [B.2]. The UCT [C.2] is preferably a bar CT, which has a primary phase and neutral passing through the secondary coil without any physical connection, said UCT has primary current approximately 10 A as it receives higher secondary values during an unbalanced fault or ground fault and secondary current rated approximately 0.1 A or 100 mA chosen. The analogue input for Earth Fault (EF) to [B] is directly wired from secondary of the UCT [C.2] in location [B.3]. More preferably, the PCT and UCT class 1.0 with burden 2.5 VA are used. The mains voltage either single phase or three phase is directly wired to the [B] in location [B.l] as shown in Figure 7. The auxiliary supply to [B] is derived from the mains connected at [B.l] and distributed internally.

An external input from fire alarm system [B.4] is directly wired to the location [BI.l]. The input from fire alarm system could be given as one of the input to the OLEF protection relay

[B] for latched tripping of the main supply. Another external input from a lightning device

[B.5] is directly wired to the location [BI.2], said input could be given as one of the input to the OLEF protection relay [B] for instantaneous tripping of the mains and re-closing it after a set time delay. A hard wiring from [A.11] is directly connected to the incoming of [B.6.1] and the outgoing from [B.6.1] is directly connected to the local ON/OFF switch [A.13]. The output [B.6.2] is readily available for wiring to an external incoming source to trip during a fire alarm initiation or lightning device function. The output [B.6.3] is readily available for wiring to an external annunciation facility. An LCD screen [B.7] is provided on the front panel for displaying real time parameters, fault values, and to read internal setting parameters. A Human Machine Interface (HMI) [B.8] is provided on the front panel below the LCD screen [B.7]. A communication port [B.9] for USB/ Ethernet/ RS 232/RS 485is provided at the bottom of the front panel and the back plate of the [B].The type of the port is decided by third party communication software. In one embodiment, the VCB is actuated by the OLEF protection relay during fault and open by command from the HMI [B.8] .In another embodiment, the VCB is actuated by the OLEF protection relay during fault and open by command from remote through third party software.

Working of the protection relay [B] :

In normal working condition the VCB [A] .protection relay [B], PCT [C.l] and UCT [C.2] satisfactorily deliver load [LI]. The output contact [B.6.1] remain closed and allow to pass current to the solenoid coil [A.5] and VCB [A] remain in closed position. The PCT [C.l] or

UCT [C.2] sends an AC analogue signal to the corresponding protection element of the protection relay [B]. The signal will be received as an input to the operational amplifier[OPAMP] circuit to filter and process an analogue equivalent output. The equivalent analogue output from the OP AMP circuit is sent to the analogue to digital converter (ADC) to convert it into binary form so that the microprocessor or the microcontroller could understand the data. The binary output from the ADC is sent into the input terminal of the microcontroller. By the comparison of this table of data it can infer an output. This output is actually inferred by the microcontroller by comparing the data processed with the stored table of data. Each entry in the table of data has an outcome instruction stored with respect to it. It compares the input data and receives a value that is equivalent to OL or EF state. The microcontroller checks that data with stored table of data and find out which matches to it. If the comparison matches any set protection condition, the central processing unit [CPU] sends an output through the data bus to the relay output contacts. On detection of any set protection condition, the relay also begins recording the data for that period. The signals are continuously monitored. In the event of the fault in the load circuit of [LI], the protection relay [B] will detect precisely and trip output [B.6.1]. By tripping [B.6.1] the solenoid coil [A.5] de energize and the return spring [A.6] will open the VCB [A] to remove potential from the load [LI]. The VCB [A] will remain in the open position until a manual reset command is initiated from the HMI [B.8] of the [B]. Before resetting, it is possible to read the fault data from the LCD screen [B.7] through the HMI [B.8] and decide the repair or reset. This way each and every low voltage (LV) load circuit could be protected from electrical faults and electrically generated fire.

The OLEF [B.2, B.3] protection relay [B] is programmable to allow user to make settings to match the actual load / connected load. The OLEF protection relay output control signal to the VCB with pre-programmed time delay, which eliminates use of stabilizers in the load connected. The OLEF protection relay [B] operation can be monitored and recorded in real time from a remote location through a software, said software includes but limited to Supervisory Control And Data Acquisition (SCADA).The OLEF is connected to a single / three phase power supply for its operation. For illustration, in said OLEF protection relay 12 numbers independent single phase circuits are protected by 12 numbers phase CT inputs for overcurrent protection and 12 numbers unbalance CT inputs for ground current protection are directly wired to the relay from the corresponding CT circuits. In case of three phase equipment protection, three separate phases of 120 degree phase difference will be used with common neutral. In said three phase equipment UCT will be connected through all phases for ground fault detection. The mains voltage either single or three phase is directly connected to the relay for voltage measurements and derives auxiliary supply from it.

The following are the faults covered by the OLEF protection relay:

• Overload in a protective circuit.

• Short circuit between phase and neutral in a circuit.

• Unbalance or leakage between phase and neutral in a circuit during load.

• Earth fault current between phase and ground.

• Earth fault current between neutral and ground.

• Electric spark/ loose contact detection during normal load.

• Detection of harmonics developed by the appliances during its operation.

• Trip command via external input from fire alarm system of third party device.

• Trip command via lightning arrestor of third party device.

The following are the advantages of the system of the present invention:

• Performs circuit monitoring, displaying on HMI, and recording real time measurement of voltage, current, frequency, real power, reactive power, power factor, and energy. • The system is configurable for Over Load (OL) detection, warning, recording, tripping and isolation in less than 100ms time delay.

• The system is configurable for Earth Fault (EF) detection, warning, recording, tripping and isolation in less than 100ms time delay.

• The system provides sparks/ loose detection warning, recording, tripping, isolation, and event and fault recording with fault pickups or trips.

• Provides ease in maintenance and rectification on the faulty circuits.