Regen Braking - Conductor Rating

[human7]

When regenerative braking is used, it is my understanding that voltage on the motor conductors increases. I think the literature for our Seimens drive suggests the dc bus voltage could be well over 1000V during regen. For these applications I have always seen the wiring done using 600 VAC wire. To me this seems inadequate. Anyone want to weigh in on this?

 

[petersonra]

When regenerative braking is used, it is my understanding that voltage on the motor conductors increases. I think the literature for our Seimens drive suggests the dc bus voltage could be well over 1000V during regen. For these applications I have always seen the wiring done using 600 VAC wire. To me this seems inadequate. Anyone want to weigh in on this?

Think about a standard 460V sine wave. The peak voltage is about 650 V.

 

[richwaskowitz]

The voltage coming back from the motor will not be higher than what was put into it (conservation of mass and energy and all that science stuff). It is the DC bus which is behind the output transistors that will see a voltage rise during DB. Dynamic braking takes effect when the VFD senses the bus voltage rising above a threshold and turns on a transistor that connects a resistor to the bus, loading the "generator" and causing the motor to decelerate.
The insulation on the wiring to the DB resistor must be able to handle the 700-800 VDC, not the motor wiring.