Prolong Trip signal is generated if the current fails to fall below the starting current threshold before
the end of the Prol.Start Time delay.
2.1.3 Locked Rotor During Starting – (stall time < start time)
For applications, such as motors driving high inertia loads, the stall withstand time can be safely
exceeded during starting. This can be done without an over temperature condition within the motor.
The stall withstand time is less than the start time, therefore time alone cannot be used to distinguish
between a start and a stall condition.
The P253 relay overcomes this problem by using a contact from a speed sensing device wired into a
specified opto input. Change of state of this contact indicates successful acceleration of the motor. If
the line current exceeds the value set in the Starting current and the speed of the motor is equal to
zero, the relay trips following the programmed Stall Time.
Note: The breaker status must be mapped for this function and the breaker must be closed (52a input
high) for the relay to operate if a locked rotor is detected.
Figure 2 shows the principle of this feature:
Figure 2: Locked rotor detection
2.1.4 Stall During Running
A stall during running is given by a current exceeding the programmed current threshold,(Stall Setting)
following a successful start. The Successful Start signal is issued if the current decreases below the
starting current and/or CB still close (depending on start criteria) when Prol. Start Time is timed out. If
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