Schweitzer Engineering Laboratories SEL-387-0, Инструкция по эксплуатации

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3.59
Date Code 20050919
Instruction Manual SEL-387-0, -5, -6 Relay
Differential, Restricted Earth Fault, Thermal, and Overcurrent Elements
Overcurrent Element
51Nn Residual Inverse-Time Element
The 51N n element compares the magnitude of the calculated residual current,
IRW n , to the pickup setting, 51N n P. If calculated residual current 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, 51N n TC, determines the other
AND input. If 51N n TC is true, Relay Word bit 51N n asserts and the inverse
curve begins timing.
The settings defining the curve in this case are 51N n P for the pickup setting,
51N n C for the particular curve equation, 51N n TD for the time dial, and
51N n RS for the curve reset.
Curve time-out causes Relay Word bit 51N n T to assert. When the current
drops below pickup, 51N n deasserts and the element resets according to the
setting for 51N n RS. At the completion of the reset, Relay Word bit 51N n R
asserts. This bit normally is at logic state 1, when the element is at rest during
normal system operation. You can use the
TAR command to verify the state of
the bit. You can use the Level 2 serial port command RES or the front-panel
RESET51
function under the
{OTHER}
pushbutton to force the bit to a logical 1
during element testing.
51PCm and 51NCm Combined Overcurrent Element (m = 1, 2)
The combined overcurrent elements operate on summed input currents to two
windings. Elements 51PC1 and 51NC1 use phase and residual current from
Windings 1 and 2, while 51PC2 and 51NC2 use these currents from
Windings 3 and 4; see
Figure 3.27 .