The present invention relates with LT switchgear system used for collecting electrical power from string inverters used in solar industry and more particularly to a solution providing increased redundancy and less heat and busbar material without compromising the electrical safety, protection aspects and system requirements.
BACKGROUND
The apparatus used for switching, controlling, and protecting the electrical circuits and equipment is known as switchgear. The term 'switchgear' is a generic term encompassing a wide range of products like switches, fuses, circuit breakers, isolators, relays, current and potential transformers, indicating instruments, lightning arresters and control panels and the said products are examples of the switchgear devices.
The switchgear system is directly linked to the supply system. It is placed in both the high and low voltage side of the power transformer. It is used for controlling the equipment for testing and maintenance and for clearing the fault. When the fault occurs in the power system, heavy current flow through equipment due to which the equipment gets damaged, and the service also gets interrupted. Hence, to protect the lines, generators, transformers, and other electrical equipment from damage automatic protective devices are installed in switchgear.
The present LT Switchgear system in solar industry is used to collect the power from string inverter and pool total power in common bus bar and then feed to LV winding of Inverter transformer for stepping up the voltage level. Such systems generally collect power of 3-4 MW in a common bus bar with high current Air Circuit Breaker at LV side of transformer.

The automatic protective switchgear mainly consists of the relay and circuit breaker. When the fault occurs in any section of the system, the relay identifies the fault of that section and comes into operation and gives command to the trip circuit of the breaker which disconnects the faulty section. The healthy section continues supplying loads as usual, and thus there is no damage to equipment and no complete interruption of supply.
Switchgear can be classified on basis of voltage level into the following:
1. Low voltage (LV) Switchgear: up to 1KV
2. Medium voltage (MV) Switchgear: 3 KV to 33 KV
3. High voltage (HV) Switchgear: Above 33 KV
Components of LT Switchgear: The term LT Switchgear includes low voltage Circuit Breakers, Switches, off load electrical isolators, HRC fuses, Earth Leakage Circuit Breaker, Miniature Circuit Breakers (MCB) and Molded Case Circuit Breakers (MCCB) etc i.e. all the accessories required to protect the LV system.
In a typical solar power plant with string inverter used as power conditioners for converting DC to AC, LT AC collection board (ACCB) is used as a power collection center from string inverters in a DC field block. The power is further fed to step up transformer. Normally in LT System fuses are best device for short circuit currents. MCCBs are good for overload, earth fault and Isolations. The LT AC system voltage in case of string inverter is 800Vac which is unconventional & hence components are monopolistic and costly.
LT Switchgear is used as a power collection center from string inverters. The power is further fed to step up transformer in LT System. Normally, the

LT switchgear consists of the fuses & Circuit breakers. The fuse is best device for short circuit currents & MCCBs are good for overload, earth fault and Isolations. Typical Solar string inverters LT voltage is 800Vac. The ACCB (AC Combiner Box or AC Collector Box) is used as protective device of down the line cables to string inverters and for cable faults. Also, it feeds LV winding of MV transformer. In big solar PV power plants where a number of inverters are present, ACCB is used in its place. ACCB possesses one MCCB for each inverter and a master ACB (Air Circuit Breaker) at the outgoing part.
The LT Switchgear for high amperage is constructed with common bus bar and a final outgoing connection with required current rating breaker. In LT switchgear with a smaller number of feeders handling high current (Generally between 3000-4000A), the heat generation and dissipation become a major challenge.
The problem become still larger if switchgear is installed outdoor as heat dissipation becomes a major challenge and due to radiation is still falling on switchgear, this results in major derating and temperature rise causing failure of switchgear and its components.
Problems Due to Common Busbar:
• 4000A common busbar. Producing more heat in the panel.
• Redundancy is less. A fault at downstream will trip the entire AC collection box through ACB.
• Cost approx. INR 15 lacs/panel
• Heat generation is high ventilation system is required.

SUMMARY OF THE INVENTION
Accordingly, an LT Switchgear bus baring for high amperage system is disclosed herein which is cost effective, redundant, reliable, and innovative solution of high amperage LT switchgear. The LT Switchgear bus baring as disclosed herein gives a unique solution to optimization of heat generation losses and bus bar materials, along with switchgear and its components by dividing the common bar system into separate sub-systems without compromising the electrical safety and protection aspects and meeting system requirements. Furthermore, the LT Switchgear bus baring as disclosed herein reduces the bus bar material by 55% and heat generation losses by 60% with increased redundancy of the system.
The LT Switchgear bus baring for high amperage system as disclosed herein comprises of more than one sub-system of busbar, trip bus, transformer JB, one or more fuses, one or more circuit breakers, one or more ACCB's and a master ACB (Air Circuit Breaker), wherein the circuit breaker is MCCB (Molded Case Circuit Breaker) or MCB (Miniature Circuit Breaker) and wherein the ACCB possesses one circuit breaker for each inverter.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig.1 illustrates the conventional ACCB Circuit diagram.
Fig.2 illustrates the ACCB Circuit diagram of the LT Switchgear system.
DESCRIPTION OF THE INVENTION
As a solution a bus baring system was developed where is maximum current handling is reduced to 1/5th by dividing the Common Busbar into 8 nos. sub systems of 500A. This also results in the reduction of the busbar material by 55%. As heat generation is proportional to square of current, the heat reduced to 1/25th by reducing the maximum current to 1/5th and thereby decreasing the heat

generation by 60%. This also reduced the copper/aluminium busbar requirement and cost.
Accordingly, herein disclosed is an LT Switchgear bus baring for high amperage system comprising of more than one sub-system of busbar, trip bus, transformer JB, one or more fuses, one or more circuit breakers, one or more ACCB's and a master ACB (Air Circuit Breaker), wherein the circuit breaker is MCCB (Molded Case Circuit Breaker) or MCB (Miniature Circuit Breaker) and wherein the ACCB possesses one circuit breaker for each inverter.
According to one embodiment the LT Switchgear bus baring for high amperage system comprises of sub-systems of 500A. The common bus bar of amperage capacity of 4000A is divided into 8 sub-systems of 500A busbar. It reduces the bus bar material by 55%. As higher current results in higher I2R losses so we get reduced current in bus bars and less heat generation losses by the LT Switchgear bus baring as disclosed herein.
To take care of protection part a LV system was formed where in a trip bus is created. According to one embodiment all the circuit breakers trip coil is connected to the trip bus and a fault at downstream will trip only the associated circuit breaker, i.e. 1 out of 8 sus systems as time and current grading is done between the circuit breaker relay and main relay. In case of call from protection relay system all sub circuit breakers trip simultaneously resulting in effective isolation of system.
The LT Switchgear bus baring as disclosed herein decreases heat generation losses by approximately 60% and also no ventilation and ventilation control is required. However, we still achieve protection feature by common simultaneous trip command keeping amperage per bus bar lesser by not making common bus thus allowing as to connect circuit breaker with decreased making and breaking capacity with increased redundancy of the system.

CLAIMS

1. An LT Switchgear bus baring for high amperage system comprising of more than one sub-system of busbar, trip bus, transformer JB, one or more fuses, one or more circuit breakers, one or more ACCB's and a master ACB (Air Circuit Breaker), wherein the circuit breaker is MCCB (Molded Case Circuit Breaker) or MCB (Miniature Circuit Breaker) and wherein the ACCB possesses one circuit breaker for each inverter.
2. The LT Switchgear bus baring as claimed in claim 1 wherein the said LT Switchgear bus baring comprises of 8 sub systems of 500A.
3. The LT Switchgear bus baring as claimed in claim 1 wherein all circuit breakers' trip coil is connected to trip bus.
4. The LT Switchgear bus baring as claimed in claim 1 wherein a fault at downstream will trip only associated circuit breaker.
5. The LT Switchgear bus baring as claimed in claim 1 wherein in case of call from protection relay system all sub circuit breakers trip simultaneously resulting in effective isolation of system.
6. The LT Switchgear bus baring as claimed in claim 1 wherein no Ventilation and ventilation control is required.