Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

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4.38
SEL-700G Relay Instruction Manual Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
REF Current Pickup Level
The minimum acceptable REF element pickup value, 50REF1P, must meet the
following criteria and be set at the greater of the two criteria values.
1. 50REF1P must be greater than any natural residual current
imbalance caused by load conditions.
2. 50REF1P must be greater than a minimum value determined by
the relationship of the CTRn (where n = N, X, or Y) values
used in the REF function.
Calculate the pickup for the application shown in Figure 4.20, where the
REF1 element is applied to the step-up transformer. To determine the pickup
value per the first criteria, use 10% of full load as the highest expected
unbalance. This can be calculated as
The resulting pickup using criterion one is 0.28 pu.
Now apply criterion two. The second criterion of 50REF1P is related to the
relative sensitivity of the phase CTs compared to the neutral CT. Based on the
X_CUR_IN setting, use the corresponding phase CT ratio (CTRX if
X_CUR_IN = TERM, CTRY if X_CUR_IN = NEUT). Because
X_CUR_IN = NEUT in this application, use CTRY to determine the pickup
value.
The resulting setting per criterion two is 0.17 pu. Because 50REF1P must be
set at the greater of the two criteria values, you would select a setting of
0.28 pu.
100% Stator Ground Protection Elements
The SEL-700G provides a two-zone function designed to detect stator
winding ground faults on resistance and high-impedance grounded generators.
The Zone 1 element, 64G1, uses a fundamental-frequency neutral overvoltage
element that is sensitive to faults in the middle and upper portions of the
winding. The Zone 2 element, 64G2, uses a third-harmonic voltage
differential function to detect faults in the upper and lower portions of the
winding. By using the two zones together, the relay provides 100 percent
stator ground fault coverage.
10% Full Load Current (Primary Amps)
100 MVA
3 138 kV
  
------------------------------------ 10%

41.84 A = =
10% Full Load Current (Secondary Amps)
41.84 A
CTRN
-------------------
41.84 A
30
------------------- 1.39 A = = =
10% Full Load Current (per unit)
1.39 A
INOMN
---------------------
1.39 A
5 A
---------------- 0.28 pu = = =
50REF1P 0.05 CTRY INOMY
  
CTRN INOMN
       
50REF1P 0.05 100 5
  
30 5
       
50REF1P 0.17
