FC 300 Design GuideIntroduction to FC 300" Control with Brake FunctionThe 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 DClink. 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 braking energy can be dissipated outside the control panel, i.e., where the energy can be utilized.- The electronics of the adjustable frequency drive will not overheat if the brake resistor is overloaded.The brake is protected against short-circuiting of the brake resistor, and the brake transistor is monitored toensure that short-circuiting of the transistor is detected. A relay/digital output can be used for protectingthe brake resistor against overloading in connection with a fault in the adjustable frequency drive.In addition, the brake makes it possible to read out the momentary power and the mean powerfor the last 120 seconds. The brake can also monitor the power energizing and make sure it doesnot exceed a limit set in par. 2-12. In par. 2-13, select the function to carry out when the powertransmitted to the brake resistor exceeds the limit set in par. 2-12.NOTEMonitoring the braking energy is not a safety function; a thermal switch is required forthat purpose. The brake resistor circuit is not ground leakage protected.Over-voltage control (OVC) (excluding the brake resistor) can be selected as an alternative brake functionin par. 2-17. This function is active for all units. The function ensures that a trip can be avoided if theDC link voltage increases. This is done by increasing the output frequency to limit the voltage fromthe DC link. It is a very useful function, e.g., if the ramp-down time is too short since tripping theadjustable frequency drive is avoided. In this situation, the ramp-down time is extended.49MG.33.B6.22 - VLT is a registered Danfoss trademark
