One and half scheme High Impedance Busbar protection -1
This is normal One and half scheme bus bar protection.
1A and 1B bus bar scheme will operate separately irrespective of middle breaker or DS close or open. In this scheme the middle breaker CTs are over lapped to protect the middle breaker. Consider the 1A side breaker CT connected with 1A bus scheme and 1B side breaker CT connected with 1B bus scheme. If any fault in middle breaker it will consider as the out zone fault for both protection schemes. So the breaker is proteded by overlapping the CTs. The Disconnecter Switch (DS) contact is no need in the CT secondary circuit as like Double bus scheme.
One and half scheme High Impedance Busbar protection -2
This circuit special one and there is no middle breaker and CT. The middle DS is separate the 1A &1B bus.
There is no separate incoming line for 1B bus and energaized through 1A bus only.
There are two condition for protection operation
1. When middle DS closed , both relay will coming into picture. Both 1A & 1B Relay will operate for fault in any bus. A disconnector 'NC' contact will open one CT earth point to maintain the single point earthing.
2. When middle DS open, 1B relay will be disconnected from the circuit and a disconnector 'NO' contact will open the CT secondary circuit in 1B side to avoid the relay operation for 1A bus fault.
Double Bus High Impedance Busbar protection -3
The CT secondary current will select the relay by DS contacts status.
1. When 1A DS closed and current will go to 1A relay through Early make and Late break 1A DS contact. If 1B DS closed current will go to 1B relay through Early make and Late break 1B DS contact.
2. If both DS are closed and current will go to both relays. If both DS are open CT will shorted through DS 'NC' contacts.
3. During fault condition trip also selected through DS contacts to trip the particular breakers connected in faulty bus.