KEB Combivert F5 series Instruction Manual

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KEB Combivert F5 series Instruction Manual Manual pdf 26 page image

263. Accessories3.1 Braking ResistorAccessories3.1.1 Selection of theBraking ResistorThe COMBIVERT F5 inverter can be equipped with an external brakingresistor for limited 4 quadrant operation. The energy the motor regensinto the inverter during deceleration is dissipated through the internalbraking transistor to the braking resistor.The braking resistor heats up during braking. If it is installed inside acontrol cabinet, sufficient interior cooling must be provided! The resistorshould be mounted above and a minimum of 9 inches away from theinverter or in a separate enclosure!Different braking resistors are available from KEBCO. They are selectedaccording to their application requirements. The selection formulas andtechnical data of the resistors are listed on the following pages. Theprocedure for selecting a braking resistor is outlined below.1. Establish desired braking time.2. Calculate braking time without braking resistor (tBmin).3. If the desired braking time is shorter than the calculated brakingtime, it will be necessary to use a braking resistor. (tB < tBmin)4. Calculate braking torque (TB) taking the load torque (TL) intoaccount. TL is a positive value for friction and windage andnegative for overhauling loads.5. Calculate peak braking power (PB). This must always becalculated for the "worst case" (nmax to standstill).6. Selection of the braking resistors:a) The resistor should be selected so that PR > PB.b) PN is to be selected according to the duty cycle factor(d.c.f.).The braking resistors may only be used for the specified value.The maximum ON period of the braking resistor may not beexceeded.6 % d.c.f. = maximum braking time 8 s25 % d.c.f. = maximum braking time 30 s40 % d.c.f. = maximum braking time 48 sLonger ON periods require specially-designed braking resistors.Take into account the current through the braking transistor.7. Check whether the desired braking time is attained with theselected braking resistor (tBmin).Note: Consider the capacity of the braking resistor and motor. Thebraking torque may not exceed the rated torque of the motor by more than1.5 times. To realize maximum possible braking torque, the frequencyinverter must be sized for the increased motor current.