the current fails to fall below the current threshold before the stall time delay has elapsed, a trip is
initiated.
2.2 Number of Starts Limitation (66)
Repeated starting or intermittent operation of a motor may generate high temperatures within the
motor, unless sufficient time is allowed for cooling between two or more starts. The P253 motor
protection relay incorporates a number of starts limitation facilities, fully programmable and applicable
to both hot and cold start conditions.
2.2.1 Starts Inhibition
Motors can be started a limited number of times in a defined period without exceeding the permitted
winding temperatures. The settings in the Limit NB STARTS protection menu monitor these starts.
Two types of starts are supervised:
• Hot Starts are defined by an initial thermal state greater than 50%
• Cold Starts are defined by an initial thermal state lower than 50%
The maximum allowable number of starts per period is an auto-reset inhibit function. This function
monitors the number of motor starts in the set period. At the end of the period the number of starts is
decremented.
Starts are detected using the 52a status from the breaker. Once the number of starts equals the user-
defined setting, the start inhibit is enabled for the set period (Inhibit Strt Time).
Start inhibition function is explained with the help of following examples:
Start inhibition example 1:
The maximum number of starts within the Supervising Time has been reached so the Inhib. Strt
Time is initiated. The remaining time Supervising Time – tn is greater than the Inhib. Strt Time, so the
start inhibition remains for a duration equal to Supervising Time – tn. Therefore, with the default
settings and a tn of 8 mins for example, the inhibition time before a new start is 52 mins.
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