in a substation busbars are one of the most critical elements in a power system, if the fault is not cleared or isolated it will not only damage the busbar but also it will create a loss of supply to the customers who are depending upon that substation for the electricity so the busbar protection must be done
The circuit breaker must be tripped and not subject to any auto reclosure because the fault that occurs in the substation busbars are usually of permanent nature. In a fault condition, the current in the busbar will be high and it would result in mechanical destruction and it would affect all the feeder.
If fast bus fault clearance is not needed for the system then overcurrent relays can be used for this kind of protection
DIFFERENTIAL BUSBAR PROTECTION
- CURRENT DIFFERENTIAL PROTECTION
- VOLTAGE DIFFERENTIAL PROTECTION
CURRENT DIFFERENTIAL PROTECTION
This type of protection involves the Kirchoff’s current law that is total current entering the is the total current that leaves the node basic principle of this method is the phasor sum of all currents that enters and leaves the bus protection zone is zero if not then there a fault in the protection zone, the bus problem may arise from large circuits which are involved and the different energization level which is encountered in these circuit for external faults
If there is any external fault in a circuit of a six-circuit bus, five of them may supply varying amount of current but the sixth and the faulted one will balance the rest of them and it will result in high false differential currents.
VOLTAGE DIFFERENTIAL PROTECTION
In this method, the CT’s of all incoming and outgoing feeders are connected in series instead of parallel. The differential relay and the secondary’s of all CT’s will create a closed loop. If all the CT’s polarity matched then the total sum of CT’s secondary’s is zero and there won’t be any voltage across the differential relay
If any fault occurs then the sum of the CT’s secondary voltage is not zero and due to the resultant voltage a current circulates in the loop and when it flows through the differential relay it will trip all the circuit breaker which is associated with the bus zone