types of protection of alternator

1. PROTECTION OF
ALTERNATER
Prepared By: Manavar Milan
1

2.  INDEX:
o Introduction
o Abnormalities and fault in alternator
o Differential protection
o Differential Protection for Alternator whose neutral
earthed through high resistance
o Negative phase sequence protection
o Balanced Earth fault protection
o Over current protection
o % Bias differential protection
o Application

3.  INTRODUCTION:
o The generating units, especially the larger ones are relatively
few in number and higher in individual cost then most other
equipments, therefore it is desirable and necessary to provide
protection to the alternators.
o In generating station ,as a continuous operation of generators
is much more necessary so the faulty part has to be cleared
very quickly for uninterruptable power supply.
o Unlike other apparatus, opening a breaker to isolate the faulty
generator is not sufficient to prevent further damage.

4.  ABNORMALITIES AND FAULT
IN ALTERNATOR:
(A) Abnormalities:
1. Failure of prime mover
2. Failure of exciter
3. Overloading
4. Unbalanced loading
5. Over voltage
6. Over speed

5. (B) Faults:
(b1) Stator faults:
1. Phase to phase faults
2. Phase to earth fault
3. Inter turn fault
(b2)Rotor faults:
1. Earth fault
2. Inter turn fault

6.  Differential Protection:

7. o It provide protection against phase to phase and phase to
ground
o When the stator winding (Armature winding) is healthy and
when there is no internal fault, equal currents flow the through
the secondary windings of CTs.
o So no currents flows through any winding of the relay.
o But the current balance is distributed when there is earth fault
in one phase or when there is phase to phase fault, current
flows through one or winding of the relay and the circuit
breaker is tripped.

8.  Differential Protection for Alternator
whose neutral earthed through high
resistance:

9. o Many times the neutral of alternator is earthed through high
resistance.
o Value of the earth fault current becomes less if the value of
earthling resistance is high.
o This means that some portion of the alternator winding will not get
protection.
o To overcome this difficulty, some change is made in the above
arrangement.

10. o In this two relay coils are used for the phase fault and the third
relay is used for earth fault.
o In the healthy condition the currents on the two sides of the
stator winding will be equal.
o So the currents balance is obtained as the secondary currents
of CT are equal no current will flow through the relay
winding.
o Current flow through the earth relay when there is earth fault
in any phase.

11. o If there is fault between two phases, the fault current will
circulate in the secondary winding of the two transformer
through two coils and no current will flow through the earth
relay.
o Thus the sensitive earth fault relay can be used so no difficulty
is encountered due to high earthing resistance.

12.  NEGATIVE PHASE SEQUENCE
PROTECTION:

13.  NEGATIVE PHASE SEQUENCE
PROTECTION:
o The negative sequence component is produced
when the load is become unbalanced.
o This component rotates with synchronous speed in
the direction opposite to that of the rotor.
o So, negative phase sequence filter is used to detect
the unbalanced loading.

14. BALANCED EARTH FAULT
PROTECTION:

15. BALANCED EARTH FAULT
PROTECTION:
o The value of the pickup current for the over current
relay is more so the relay cannot operate with low
value of the earth fault current.
o So, to give earth fault protection, an earth fault relay
is connected in the neutral circuit through CT as
shown in fig.

16.  OVER CURRENT PROTECTION:

17.  OVER CURRENT PROTECTION:
o The time setting of the over current relay is kept
higher then that of differential protection.
o Because the first differential protection should work
and if it fails to operate, after some time this over
current protection system will work.

18.  % BIAS DIFFERENTIAL
PROTECTION:

19.  % BIAS DIFFERENTIAL PROTECTION:
o When the alternator feeds the external fault, the
currents through the three windings increase to high
value so the CT saturate.
o Now the characteristics of the CTs on the two sides
may not be identical so some out of balance current
flows through the relay coil and the relay operate.
o To overcome this difficulty percentage biased
differential relay is used.

20. Application
 To detect the abnormality and fault condition.
 The protection system of alternator is provide
protection.

21. THANK YOU