GE Digital Energy L30, Instruction Manual, Page: 445 / 644

GE Multilin L30 Line Current Differential System 10-5
10 APPLICATION OF SETTINGS 10.2 CURRENT DIFFERENTIAL (87L) SETTINGS
10
• For relay 3, channel 1 communicates to relay 1 and channel 2 communicates to relay 2
Consequently, to achieve the maximum sensitivity of 0.2 pu at the terminal with a CT ratio of 2000/5 (400 amps line primary
differential current), the following pickup values are chosen:
(EQ 10.17)
Choosing relay as a reference with a breakpoint value of 5.0 pu, breakpoints for relays 2 and 3 are calculated as follows:
(EQ 10.18)
(EQ 10.19)
To verify the calculated values, we have:
(EQ 10.20)
This satisfies the equality condition indicated earlier.
During on-load tests, the differential current at all terminals should be the same and generally equal to the charging current
if the tap and CT ratio settings are chosen correctly.
Pickup relay 1
 
0.4
Pickup relay 2
 
0.2
Pickup relay 3
 
0.8
Breakpoint relay 2
 
Breakpoint relay 1
 
CT
ratio
relay 1
 
CT
ratio
relay 2
 
----------------------------------------

5.0
1000 5

2000 5

--------------------

2.5
Breakpoint relay 3
 
Breakpoint relay 1
 
CT
ratio
relay 1
 
CT
ratio
relay 3
 
----------------------------------------

5.0
1000 5

500 5

--------------------

10.0
Breakpoint relay 1
 
CT
ratio
relay 1
  
5.0 1000 5
 
1000
Breakpoint relay 2
 
CT
ratio
relay 2
  
2.5 2000 5
 
1000
Breakpoint relay 3
 
CT
ratio
relay 3
  
10.0 5000 5
 
1000