Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

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4.36
SEL-700G Relay Instruction Manual Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
The operating current, IOP, is simply the neutral CT current divided by
nominal rating of the neutral CT, I
NNOM
. The REF1 element calculates the
real part of IPOL times IOP* (IOP complex conjugate). This equates to |IPOL|
times |IOP| times the cosine of the angle between them. The result is positive
if the angle is within ±90 degrees, indicating a forward or internal fault. The
result is negative if the angle is greater than +90 or less than –90 degrees,
indicating a reverse or external fault. The relay compares the output of the
REF1 element to positive and negative thresholds, to ensure security for very
small currents or for an angle very near +90 or –90 degrees. If the REF1
output exceeds the threshold test, it then must persist for at least 1.5 cycles
before the Relay Word bit REF1F (forward) or REF1R (reverse) asserts.
Assertion of REF1F constitutes a decision to trip by the REF1 function.
You can perform tripping directly by inclusion of the Relay Word bit REF1F
into one or more of the trip variables (TRX, TR1, TR2, TR3), as appropriate.
If you want additional security, the relay is programmed to use REF1F to
torque control an inverse-time curve for delayed tripping, as discussed in the
following text. Figure 4.19 shows the output of the REF1 protection function.
Timing is on an extremely inverse time-overcurrent curve (Curve U4) at the
time-dial setting (0.5) and with 50REF1P as the pickup setting.
Figure 4.19 REF Protection Output (Extremely Inverse-Time O/C)
Relay Word bit REF1F (forward fault) torque controls the timing curve, and
IN operates the timing function. The curve resets in one cycle if current drops
below pickup or if REF1F deasserts. When the curve times out, Relay Word bit
REF1P asserts. The default trip logic uses REF1P to shut down the generator.
When REF protection is enabled (EREF := Y), the relay automatically
configures the protection to use the appropriate phase CT based on
X_CUR_IN setting for SEL-700G1 relays. For other relay models, locate the
phase CTs on the terminal side of the generator for the REF elements to be
effective (as shown in Figure 2.18).
The setting REF1TC is a SEL
OGIC
control equation setting that defines the
conditions under which the relay enables REF1.
You can set the neutral current sensitivity threshold, 50REF1P, to as low as
0.05 times nominal current for a 1 A CT (0.25 A for a 5 A nominal CT
Table 4.5 Restricted Earth Fault Settings
Setting Prompt Setting Range
Setting Name :=
Factory Default
REF ENABLE Y, N EREF := N
REF1 CURR LEVEL 0.05–3.00 pu 50REF1P := 0.25
REF1 TRQCTRL SEL
OGIC
REF1TC := 1
52AX BYPASS EN Y, N REF52BYP := Y
50REF1P*INNOM
(RW = Relay Word bit)
|IN|
_
+
REF1P
(RW)
REF1F
(RW)
50REF1P (pickup)
U4 Curve
TD 0.5
Reset 1 cycle
Timing
1/INNOM