Differential Element Settings
13-11
SEL-300G Instruction Manual
Date Code 20060731
Differential Element Tripping
The 87U and 87R differential elements detect faults and usually are used to trip the main
generator breaker, the field breaker, the prime mover, and the generator lockout relay. Refer to
Section 4: SEL
OGIC
Control Equations
for more detail and examples of tripping SEL
OGIC
control equations.
S
ETTINGS
F
OR
U
NIT
P
ROTECTION
Setting Description
For unit current differential applications similar to those shown in Figure 5.15, the SEL-300G
offers differential protection that can compensate correctly for the ratio and phase shift of the
generator step-up transformer.
Enable Differential Protection (G, T, N)
E87 = T
Set E87 = T to enable differential protection elements when the generator step-up
transformer is included in the differential zone. If differential protection is not required,
set E87 = N. When E87 = N, the 87B, 87BL1, 87BL2, 87BL3, 87R, 87R1, 87R2,
87R3, 87U, 87U1, 87U2, and 87U3 Relay Word bits are inactive and the following
relay settings are hidden and do not need to be entered.
XFMR High-Side Winding L-L Voltage (OFF, 1.0–1000.0 kV)
VWDGD = 13.8
XFMR Connection (GEN, YY, YDAC, YDAB, DACDAC,
DABDAB, DABY, DACY)
TRCON = DABY
87 Input CT Connection (Y, DAB, DAC)
CTCON = DAB
Phase Input TAP Value
TAP1 = Derived Quantity
87 Input TAP Value
TAPD = Derived Quantity
Unrestrained Element Pickup, multiple of TAP (1.0–20.0)
U87P = 10.0
Restrained Element Pickup, multiple of TAP (0.04–1.00)
O87P = 0.30
Restraint Slope 1 Percentage (5–100%)
SLP1 = 40
When a generator step-up transformer is included in the differential zone, set VWDGD equal
to the transformer rated high-side voltage in line-to-line kilovolts. If you are setting E87 =
T, but not including a power transformer in the differential zone, either set VWDGD equal to
the generator rate line-to-line voltage or set VWDGD = OFF.
The TRCON setting is defined by the step-up transformer connections. The CTCON setting
is defined by the connection of the 87 input current transformers.
As you enter the relay settings, the relay will display the derived values of TAP1 and TAPD.
If you enter a setting for VWDGD, you do not need to enter settings for TAP1 or TAPD
when E87 = T. When you set VWDGD = OFF, you will need to calculate and enter settings
for TAP1 and TAPD using the instructions below.
The unrestrained differential element pickup is defined by the U87P setting. The 87U Relay
Word bit asserts if any of the measured differential operate quantities, IOP1, IOP2, or IOP3,
exceeds the U87P setting. The restrained differential element pickup is defined by the O87P
Summary of Contents for SEL-300G
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