How do you achieve 200% of rated motor torque from the motor at low speed?

The low speed flux boosting capability (FluxPlus) of the Zener MSC-3 will produce approximately 130% of rated torque at rated motor current. To get the remaining torque required, we need some extra amps. Choose an MSC-3 with a continuous rated current ofnot less than:
(Motor FLC/1.1) x (200/130) Amps (This is equivalent to Motor FLC x 1.4)

Please be aware that this current is beyond the contiuous capability of the motor, and the motor thermal protection (I2t, thermal overload relay or thermistors) should be set appropriately to protect the motor.

How does the DC choke help to protect the rectifier against line transients when the choke is after the rectifier?

It is effective in protecting the rectifier from current surges because it is series with the current flow. It is not effective in reducing the direct effect of volyage spikes, so we fit metal oxide varistors (MOVs) to all drives as standard.