ABB 615 series Technical Manual page 764

Section 4
Protection functions
758
The starting times vary depending on motor design and load torque characteristics. The
time taken may vary from less than two seconds to more than 60 seconds. The starting time
is determined for each application.
When the permissible stall time is less than the starting time of the motor, the stalling
protection is used and the value of the time delay setting should be set slightly less than the
permissible stall time. The speed switch on the motor shaft must be used for detecting
whether the motor begins to accelerate or not. However, if the safe stall time is longer than
the start-up time of the motor, the speed switch is not required.
The failure of a motor to accelerate or to reach its full nominal speed in an acceptable time
when the stator is energized is caused by several types of abnormal conditions, including
a mechanical failure of the motor or load bearings, low supply voltage, open circuit in one
phase of a three-phase voltage supply or too high starting voltage. All these abnormal
conditions result in overheating.
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 start-up 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.
1MAC059074-MB A
615 series ANSI
Technical Manual