POWER TRANSFORMER PROTECTION,GENERATR PROTECTION SCHEME,PILOT PROTECTION
POWER TRANSFORMER PROTECTION :
Faults occurring in transformer:
There are three main classes in which the faults are classified:
1. Faults in auxiliary equipment of the transformer.
2. Internal faults in the transformer windings.
3. External faults.
1. Faults in auxiliary equipment :
Faults in auxiliary equipment is –
· Due to Oil leakage in the transformer
· Due to Deterioration of dielectric strength of oil
· Due to Failure of ventilation system
· Due to Weakening of insulation
· Due to Improper joints or connections
· Due to Inter-turn faults
2. Internal faults in the transformer windings:
When the insulation between the windings and between the winding and the core fails,then the electrical fault occur. There may be phase to phase, phase to ground faults, H.V and L.V faults
3. External faults:
Faults that occur due to over loading or external short –circuit. When such faults occur, transformer must me disconnected from the supply.
If the transformer is greater than 5MVA then it can be protected by:
· Gas detector relay (Buchholz relay)
· Thermal relays
· Overcurrent protection
· Ground fault protection
· Differential protection
· Oil level monitor
If the transformer is less than 5 MVA then it can be protected by:
· Gas detector relay
· Over current protection
· Over voltage protection
· Ground fault protection
So the mostly used method for transformer protection is:
DIFFERENTIAL PROTECTION (MERGE PRICE PROTECTION)OF POWER TRANSFORMER:
Merge -price circulating current principle is commonly used for the protection of power transformers of 5MVA and above against earth and phase faults.
Any deviation of current from the normal ratio of the current intensity at input and output ends, that must be caused by a fault in the protected part , so that the unbalanced current can be employed directly for tripping and indicating the fault.
Faults occurred in generator:
1. Abnormal running conditions
2. Stator winding faults
3. Rotor faults
1. Abnormal running conditions:
Abnormal running conditions which are likely to occur in generator are:
· Failure of prime mover
· Failure of field
· Over current
· Over speed
· Over voltage
· Unbalanced loading
· Bearing over heating
· Voltage regulator failure
2. Stator winding faults:
Stator winding faults include-
· Phase-to-earth faults
· Phase-to-phase faults
· Inter-turn faults
Most of the fault occur in stator winding is due to the earth faults.
The effect of earth fault in stator winding is
· Arching to core , which welds laminations together causes eddy current and the repair of this involves considerable expenditure of time and money.
· Severe heating in the conductor causes damaging of insulator.
Basically the protection of stator is includes:-
The Percentage differential protection
· The Phase to earth fault protection
· The Protection against stator inter-turn fault
· The Stator overheating protection
· Field-ground fault
· Loss of excitation
· Rotor over-heating due to unbalanced three-phase stator currents
The protection of rotor mainly includes:
· Field ground fault protection
· Loss of excitation protection
· rotor overheating protection due to unbalanced three-phase stator currents
PILOT RELAYING SCHEME:
Relay: relay is mainly used to protect the electrical equipments from damage if fault occur.
PILOT PROTECTION: it is a form of line protection that uses a communication channel as a mean to compare electrical conditions at the terminals of a line.
· Pilot wire differential protection, used for very important and shorter length of lines.
· Carrier current pilot protection, where length of transmission is long and simultaneous opening of circuit breaker of both ends is necessary.
· Microwave pilot protection.
QUESTION AND ANSWERS
1. WHAT IS PILOT PROTECTION?
ANS:- it is a form of line protection that uses a communication channel as a mean to compare electrical conditions at the terminals of a line.
2.WHAT ARE THE DIFFEENT TYPES OF FAULT THAT OCCUR IN STATOR WINDING?
ANS:- Phase-to-earth faults
3.WHAT ARE THE FAULTS THAT OCCUR IN A GENERATO?
ANS:- Abnormal running conditions
Stator winding faults