GE L30 Instruction Manual page 448
Line current differential system, ur series
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10.2 CURRENT DIFFERENTIAL (87L) SETTINGS
•
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:
Choosing relay as a reference with a breakpoint value of 5.0 pu, breakpoints for relays 2 and 3 are calculated as follows:
To verify the calculated values, we have:
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.
10
10-6
Pickup relay 1
(
Pickup relay 2
(
Pickup relay 3
(
(
)
Breakpoint relay 2
Breakpoint relay 1
=
5.0
×
=
(
)
Breakpoint relay 3
Breakpoint relay 1
=
×
5.0
=
Breakpoint relay 1
(
)
×
CT
(
ratio
(
)
×
(
Breakpoint relay 2
CT
ratio
(
) CT
×
(
Breakpoint relay 3
ratio
L30 Line Current Differential System
)
0.4
=
)
0.2
=
)
0.8
=
(
CT
relay 1
ratio
(
)
×
--------------------------------------- -
(
CT
relay 2
ratio
1000 5 ⁄
------------------- -
2.5
=
2000 5 ⁄
CT
(
relay 1
ratio
(
)
×
--------------------------------------- -
(
CT
relay 3
ratio
1000 5 ⁄
------------------- -
10.0
=
500 5 ⁄
relay 1
)
5.0 1000 5 ⁄
×
1000
=
=
)
2.5 2000 5 ⁄
×
relay 2
1000
=
=
)
10.0 5000 5 ⁄
×
relay 3
=
=
10 APPLICATION OF SETTINGS
)
)
)
)
1000
GE Multilin
(EQ 10.11)
(EQ 10.12)
(EQ 10.13)
(EQ 10.14)
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