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3.2 FULL LOAD CONTROL
The full load control is calibrated in % of phase CT rated amps.
It should be set to the maximum load rating of the motor being
protected. For example, a setting of 75% with 100:5 phase CTs
corresponds to a motor full load current of 75 amps. In the
time/overload curves of figures 3-2 the value of a multiple of
one full load is represented by the current set on this control.
When the current exceeds the full load control setting, the over-
load indicator light will flash to indicate an overload and the
relay will begin to time the overload according to the time/over-
load curves of fig. 3-2. If the condition persists the relay will
eventually trip.
When the motor is in a normal run state the internal memory
begins to discharge to simulate motor cooling. Overload trip time
will be reduced by the cumulative effect of previous overloads
and starting inrush unless the motor has not been overloaded
for a period of time in which case the memory is empty to simu-
late a cool motor.
Multiple start protection is provided by the memory which in-
tegrates the heating effect of each start. If power is lost and
reapplied or if the reset button is pressed after a trip, the memory
will be empty. Figures 3-3 shows how the thermal memory mod-
elling operates for typical motor operation.
Summary of Contents for PROTECT 4A-120
Page 1: ...MOTOR PROTECTION RELAY INSTRUCTION MANUAL ...
Page 5: ...2 FIGURE1 1 PROTECT 4A TYPICAL SYSTEM CONNECTION ...
Page 11: ...8 FIGURE 2 2 PHASE CT DIMENSIONS FIGURE 2 3 GROUND FAULT CT DIMENSIONS ...
Page 21: ...18 FIGURE 3 1 FRONT PANEL LAYOUT ...
Page 35: ...32 FIGURE 4 1 SINGLE PHASE INJECTION TESTING FIGURE 4 2 100 AMP CURRENT SOURCE ...
Page 39: ...36 FIGURE 4 3 GROUND FAULT EARTH LEAKAGE TEST ...
Page 44: ...41 FIGURE 5 1 HARDWARE BLOCK DIAGRAM ...
