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Program features 119

 Thermal protection of motor cable

The control program contains a thermal protection function for the motor cable. This

function should be used, for example, when the nominal current of the drive exceeds

the current-carrying capacity of the motor cable.

The program calculates the temperature of the cable on the basis of the following

data:

• Measured output current (parameter 01.07 Motor current)

• Nominal continuous current rating of the cable, specified by 35.61 Cable nominal

current, and

• Thermal time constant of the cable, specified by 35.62 Cable thermal rise time.

When the calculated temperature of the cable reaches 102% of the rated maximum,

a warning (A480 Motor cable overload) is given. The drive trips on a fault (4000 Motor

cable overload) when 106% is reached.

Settings

Parameters 35.60…35.62 (page 332).

 User load curve

The user load curve provides a function that monitors an input signal (eg. motor

torque or motor current) as a function of drive output speed or frequency. The

function includes both high limit (overload) and low limit (underload) monitoring.

Overload monitoring can, for example, be used to detect a pump becoming clogged

or a saw blade hitting a knot. Underload monitoring can detect the load being lost, for

example because of the snapping of a transmission belt.

The monitoring is effective within a motor speed and/or frequency range. The

frequency range is used with a frequency reference in scalar motor control mode;

otherwise, the speed range is used. The range is defined by five speed (parameters

37.11…37.15) or frequency (37.16…37.20) values. The values are positive, but the

monitoring is symmetrically active in the negative direction as the sign of the

monitored signal is ignored. Outside the speed/frequency range, the monitoring is

disabled.

An underload (37.21…37.25) and overload (37.31…37.35) limit is set for each of the

five speed or frequency points. Between these points, the limits are interpolated

linearly to form overload and underload curves.

ABB ACS880-04XT User Manual

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