Reactors on output side of A-B 1336 Drives

[1mick1]

Hello all,
We use a large number of A-B 1336 drives at our facility and we use line reactors on the output side of our drives but not the input,is this the industry standard as i would have thought that on the input side it would have made the drive less likely to have trouble from peaks and transients from the incoming supply.

 

[jraef]

Rectors on the output side is generally for the protection of the motor. It also protects the VFD output transistors from some damaging shorts inthe load, because the dampening of any current rise tends to give the VFD's protection systems time to react (although not guaranteed). Reactors on the input side can help with that as well, and offer similar protection for the front-end too but are mainly to aleviate harmonics issues.

"Venditori de oleum-vipera non vigere excordis populi"

 

[Mstrvb19]

I would think that a reactor in the input side would degrade the peformance of the VFD. Someone correct me if I am wrong, but the current demand of a VFD changes quickly (i.e. most harmonics on the input are harmonic currents) while the output is more likely to have harmonic voltages. Thus a reactor on the input side would resist the changes in current that are necessary for the drive to perform. Of course, most of these harmonics should already be bypassed from the input, but, if this is the case, then a reactor would set up a resonance with the input filtering. Sound right?

 

[Dopler]

Input transformers for VFD are intended for some reasons, some are
Voltage transformation, adequate voltage input for VFD
Phase shifts, depending number of VFD pulses
Electrical isolation, between power source and VFD
Harmonic reduction, impedance between power source and VFD
Fault current limit to the converter, impedance does

There is another problem, Neutral Shift, in VFD current source with isolation reactors or without isolation transformer, the motor windings insulation is subject to double the nominal phase to neutral voltage stress.
This may not cause an immediate motor failure, but life is shortened, is important because standard existing motors can not be safely applied to current source VFD.
If an isolation transformer, delta-wye not grounded is installed, the voltage generated is shared between isolation transformer secondary neutral and motor neutral.
Because the motor winding capacitance is bigger than transformer winding capacitance, almost all the voltage appear on the transformer, good thing, because transformer's secondary isolations much higher than motor winding isolation.

 

[jraef]

Yes but the 1336 is not a current source inverter, it is a PWM drive.

"Venditori de oleum-vipera non vigere excordis populi"

 

[Dopler]

It is correct, PWM.