Sel 411L - Page 431

P.3.323
Date Code 20151029 Protection Manual SEL-411L Relay
Protection Functions
Protection Application Examples
E32 := AUTO Directional Control (Y, AUTO)
ECOMM := N Comm. Scheme (N, DCB, POTT, POTT2, POTT3,
DCUB1, DCUB2)
EBFL1 := N Breaker 1 Failure Logic (N, 1, 2)
EBFL2 := N Breaker 2 Failure Logic (N, 1, 2)
E25BK1 := N Synchronism Check for Breaker 1 (Y, N)
E25BK2 := N Synchronism Check for Breaker 2 (Y, N)
E79 := N Reclosing (Y, Y1, N)
EMANCL := N Manual Closing (Y, N)
ELOP := Y1 Loss-of-Potential (Y, Y1, N)
EDEM := N Demand Metering (N, THM, ROL)
EADVS := N Advanced Settings (Y, N)
87 Current Differential Protection
In this application, the relay measures the currents directly from both
breakers. Each of the CTs has the proper polarity, meaning that primary
current flowing into the breaker and onto the line is in phase with the current
leaving the CT terminal with the polarity mark. Therefore, include both the W
and X current inputs and choose P for polarity.
We would have the following at both terminals:
87CTWL := 1 Terminal W permanently included in 87L Element
(SEL
OGIC control equation)
87CTPWL := P CT Polarity of Terminal W (P = Pos., N = Neg.)
87CTXL := 1 Terminal X permanently included in 87L Element
(SEL
OGIC control equation)
87CTPXL := P CT Polarity of Terminal X (P = Pos., N = Neg.)
We would have the following at Terminal S:
87CTP1R := 2000 Max. CT Primary Current Remote Relay 1 (1–50000)
We would have the following at Terminal R:
87CTP1R := 1600 Max. CT Primary Current Remote Relay 1 (1–50000)
The CT ratios are different at each end of the line. The following calculation
helps to determine the TAP settings.
Automatic calculation of TAP values is as follows:
Equation 3.110
We would have the following at Terminal S:
Equation 3.111
CTP
BASE
= max (Remote CT Primary, Local CT Primary) = max
(1600, 2000) = 2000
TAP
CTP
BASE
CTR
LOCAL
-----------------------------
2000
320
------------ 6.25===