Switchgear & Protection | List the difficulties experienced in differential relay in alternator protection. How are they overcome?

Difficulties Experienced in Differential Relay in Alternator Protection:

1. The differential protection provides very fast protection against phase to phase faults and phase to ground faults. If neutral is not grounded or grounded through resistance, error may cause. 

2. When differential relay is used for protection, the CT‟s should be identical in design, otherwise the ratio error may occur. 

3. There may be unequal length of leads of CT wire connections, causing error. 

4. Unequal secondary burden on CT. 

How are they overcome?

1. Additional sensitive earth fault relay should be provided. 

2. Use Biased Differential protection. 

3. Use Biased Differential protection 

4. Use Biased Differential protection