ABB 615 Series ANSI, Technical Manual

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Section 6
1MAC050144-MB C
Supervision functions
468 615 series ANSI
Technical Manual
Repeated starts increase the temperature to a high value in the stator or rotor windings, or
both, unless enough time is allowed for the heat to dissipate. To ensure a safe operation it
is necessary to provide a fixed-time interval between starts or limit the number of starts
within a period of time. This is why the motor manufacturers have restrictions on how
many starts are allowed in a defined time interval. This function does not allow starting of
the motor if the number of starts exceeds the set level in the register that calculates them.
This insures that the thermal effects on the motor for consecutive starts stay within
permissible levels.
For example, the motor manufacturer may state that three starts at the maximum are
allowed within 4 hours and the startup situation time is 60 seconds. By initiating three
successive starts we reach the situation as illustrated. As a result, the value of the register
adds up to a total of 180 seconds. Right after the third start has been initiated, the output
lock of start of motor is activated and the fourth start will not be allowed, provided the time
limit has been set to 121 seconds.
Furthermore, a maximum of three starts in 4 hours means that the value of the register
should reach the set start time counter limit within 4 hours to allow a new start.
Accordingly, the start time counter reduction should be 60 seconds in 4 hours and should
thus be set to 60 s / 4 h = 15 s / h.
Figure 250: Typical motor-starting and capability curves
Setting of Cumulative time Lim
Cumulative time Lim is calculated by
(Equation 56)
n specified maximum allowed number of motor startups
t startup time of the motor (in seconds)
margin safety margin (~10...20 percent)
Setting of Counter Red rate
Counter Red rate is calculated by
t n t margin
si
∑
= − × +
( ) 1