Date Code 20020129
Differential, Restricted Earth Fault,
3-37
Overcurrent, Voltage, and Frequency Elements
SEL-387E Instruction Manual
If the curve times out, Relay Word bit 51PnT asserts. When all phase currents drop below
pickup, with or without a curve time-out, 51Pn deasserts and the element resets according to
setting 51PnRS. At the completion of the reset, Relay Word bit 51PnR asserts. This bit normally
will be at logic state 1, when the element is at rest during normal system operation. Use the
TAR
command via a serial port or the front panel to verify the state of this bit. You can use the
Level 2 serial port command
RES
or the front-panel RESET51 function under the OTHER button
to force this bit to logical 1 during element testing. This saves time if you have chosen
electromechanical reset.
50Qn1 and 50Nn1 – Sequence Current Definite-Time Element Logic
Figure 3.19 shows the logic for the definite-time 50Qn1 negative-sequence element and the
definite-time 50Nn1 residual element.
Figure 3.19: 50Qn1 and 50Nn1 Sequence Definite-Time O/C Element, Torque Controlled
50Qn1 Negative-Sequence Definite-Time Element
The 50Qn1 element logic compares the magnitude of calculated negative-sequence current
3I2Wn to pickup setting 50Qn1P. If the calculated negative-sequence current magnitude exceeds
the pickup level, a logical 1 asserts at one input to the AND gate at the center. The torque-control
SEL
OGIC
control equation, 50Qn1TC, determines the other AND input. If 50Qn1TC is true,
Relay Word bit 50Qn1 asserts and the timer starts. After the time specified by delay setting
50Qn1D has expired, a second Relay Word bit, 50Qn1T, asserts. The 50Qn1T bit asserts only if
the 50Qn1 bit remains asserted for the duration of 50Qn1D. When 50Qn1 deasserts, the timer
resets without delay, along with 50Qn1T if it has asserted.
50Nn1 Residual Definite-Time Element
The 50Nn1 element logic compares the magnitude of the calculated residual current, IRWn,
to the
pickup setting, 50Nn1P. If the calculated residual current magnitude exceeds the pickup level, a
logical 1 asserts at one input to the AND gate at the center. The torque-control SEL
OGIC
control
equation, 50Nn1TC, determines the other AND input. If 50Nn1TC is true, Relay Word bit
50Nn1 asserts and the timer starts. After the time specified by delay setting 50Nn1D has expired,
a second Relay Word bit, 50Nn1T, asserts. The 50Nn1T bit asserts only if the 50Nn1 bit remains
asserted for the duration of 50Nn1D. When 50Nn1 deasserts, the timer resets without delay,
along with 50Nn1T if it has asserted.
Содержание SEL-387E
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