Toshiba Adjustable Speed Drive H3 Operation Manual page 85

DYNAMIC BRAKING (Feature not available in H3 drives above 30 horsepower)
When a motor is mechanically forced to spin faster than the output frequency of the drive, the
motor acts as a generator. This regenerated energy forces current to flow into the drive's DC
bus. The bus capacitors will absorb some of the regenerative energy by charging and raising the
DC bus voltage. At high bus voltages, the drive can be programmed to fire the IGBT7 dynamic
braking transistor. This prevents a common drive fault, DC BUS OVERVOLTAGE. The dynamic
braking resistor, attached by the user to the "PA" and "PB" terminals, dissipates the bus energy
as heat when the IGBT7 fires. Two resistor values are of concern: resistance (ohms) and power
(watts). Insufficient resistance may lead to IGBT7 damage; too low of a wattage may result in
braking resistor damage from overheating.
Contact your Toshiba distributor for dynamic braking resistor part numbers and information.
Item 145, OVERVOLTAGE STALL PROTECTION - This function is turned on as a default setting.
Overvoltage stall protection causes the drive to automatically extend the decel time when the DC bus
voltage increases due to regeneration. The value stored in DECELERATION TIME #1 / DECELERATION
TIME #2 is not changed. The drive may still trip on overvoltage if the decel time is very small.
TOSHIBA
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