GE 369, Быстрый старт

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CHAPTER 4: KEYPAD SETPOINTS S4 CURRENT ELEMENTS
369 MOTOR MANAGEMENT RELAY – QUICKSTART GUIDE 4–41
still responds very fast, but rides through normal operational disturbances. Normally, the
Phase Short Circuit time delay will be set as quick as possible, 0 ms. Time may have to be
increased if nuisance tripping occurs.
When a motor starts, the starting current (typically 6 × FLA for an induction motor) has an
asymmetrical component. This asymmetrical current may cause one phase to see as
much as 1.6 times the normal RMS starting current. If the short circuit level was set at 1.25
times the symmetrical starting current, it is probable that there would be nuisance trips
during motor starting. As a rule of thumb the short circuit protection is typically set to at
least 1.6 times the symmetrical starting current value. This allows the motor to start
without nuisance tripping.
Note
Both the main Short Circuit delay and the backup delay start timing when the current
exceeds the Short Circuit Pickup level.