The brake is to limit the voltage in the intermediate circuit when the motor acts as a generator. This occurs, for example, when the load drives the motor

and the power accumulates on the DC link. The brake is built up as a chopper circuit with the connection of an external brake resistor.

Placing the brake resistor externally offers the following advantages:

The brake resistor can be selected on the basis of the application in question.

The brake energy can be dissipated outside the control panel, i.e. where the energy can be utilized.

The electronics of the frequency converter will not be overheated if the brake resistor is overloaded.

The brake is protected against short-circuiting of the brake resistor, and the brake transistor is monitored to ensure that short-circuiting of the transistor

is detected. A relay/digital output can be used for protecting the brake resistor against overloading in connection with a fault in the frequency converter.

In addition, the brake makes it possible to read out the momentary power and the mean power for the latest 120 seconds. The brake can also monitor

the power energizing and make sure it does not exceed a limit selected in par. 2-12. In par. 2-13, select the function to carry out when the power

transmitted to the brake resistor exceeds the limit set in par. 2-12.

NB!

Monitoring the brake power is not a safety function; a thermal switch is required for that purpose. The brake resistor circuit is not earth

leakage protected.

Over voltage control (OVC)

The function ensures that a trip can be avoided if the DC link voltage increases. This is done by increasing the output frequency to limit the voltage from

the DC link. It is a very useful function, e.g. if the ramp-down time is too short since tripping of the frequency converter is avoided. In this situation the

ramp-down time is extended.