Blocked motor, reduction of the residual hazards

Question:
How can the residual hazard of an overheated motor be reduced when the motor is blocked at the 9300 servo controller?

Answer:
The motor temperature of the 9300 servo controller is generally monitored by means of a temperature sensor in the motor winding. When the maximum temperature is reached, the controller is inhibited in order to avoid further overheat and consequently to protect it. In unfavourable cases, e. g. when the motor is suddenly mechanically blocked, the motor can be overheated, although the motor temperature is monitored by the temperature sensor (residual hazard).

Function description:
If the motor is blocked, detections can also be made by means of the function block interconnection described below, and the controller can be switched off, overheating is avoided. Under the following circumstances a motor blocking is detected, and after an adjustable time (DIGDEL1, DIGDEL2) has run out, an error message (Trip) is activated:

• The drive is almost in standstill (actual speed nact < speed limit C0472/1) and the servo controller operates at the current limit, which is adjusted for the motor (Imax = high)
•  The drive is almost in standstill (actual speed nact < speed limit C0472/1) and the speed setpoint nSet2 is > speed limit C0472/1.

Settings:

• CMP2, C0685 = 6 (/IN1/</IN2/)
• CMP2, C0686 = 0 (hysteresis = 0)
• CMP2, C0687 = 0 (window = 0)
• CMP3, C0690 = 5 (/IN1/>/IN2/)
• CMP3, C0691 = 0 (hysteresis = 0)
• CMP3, C0692 = 0 (window = 0)
• FCODE C0472/1 = 0.5 % (speed limit)
• DIGDEL1, C0720 = 0 (On-delay)
• DIGDEL1, C0721 = 6 (Imax-delay= 6 s)
• DIGDEL2, C0725 = 0 (On-delay)
• DIGDEL2, C0726 = 3 (nSet2-delay = 3 s)

Boundary conditions:

• The above values are suggestions and must be adapted to the existent motor type.
• Parameter setting of the motor data Imax (C0022) and the motor rated current (C0088) must absolutely be correct. The motor must be able to conduct the current Imax at least for the set delay.
• Consider the heating of the motor when it is blocked in standstill and several times tried to be driven.

Function block interconnection: