How to Disable Field Supply of Lenze DC Drive 4903

One most simplest way is to connect some dummy load like filament lamps to field supply.

The drive is protecting the motor. It senses no field current so will not pass the armature current. As has been suggested you could apply a dummy load. But to be honest with you I think you are being foolish importing a separate field supply, if it fails the drive can't protect the motor.

Thank you Mr. Johny. My problem solved by 100%.

You are most welcome but do take note of TonyS's comments. Failure of the field supply will cause the armature to draw massive current. Can you tie the field supply into a drive disable somehow such that if the field supply is at least powered off the drive will not start?

Field windings are rated in current not voltage. The voltage rating means it needs around 110V DC to achieve the nominal rated field current. There is however some times an insulation issue (see below) You normally just need to set the field current in the drive to the nameplate to run at base speed, when you measure the volts it will be around 110V DC (depending on how good your multimeter is at dealing with harmonics)

I have run lower voltage DC motor field's from higher voltage Alstom/Cegelec/GEC field converters quite happily and have occassionally had to put in transformers on the AC supply to field converter section when I was concerned about the rating of the insulation - however in these instances (a) you need a separate AC supply (separate from the armature convertor) to the field convertor and (b) the transformer needs to be around 5 times higher rated as there will be a significant high frequency component that would cause a nominally rated transformer to over heat.

In YOUR case I would suspect that running a 110V DC motor field from a 340V DC rate field convertor to be fine, the insulation is very likely to be fine at that lowish voltage.

This way you will get the drive protection

Good point machine builder. If the drive allows you set set a given field current what not just set the correct field current from the motor specs and run it off the drives field supply?

To be quite honest I should have said that if you are dealing with a variable field then any issue with the voltage will be from the level of the AC supply rather than the average DC voltage. The AC supply will be switched by the field convertor and there will be voltage spikes well in excess of the average DC voltage so if the supply is for example 480V AC and the field is nominally 110V DC you will see could voltage spikes up to 1.414 times the rms value of 480V ie 679V. This might be too high for the field winding especially if it is an old motor that expected to see a smoother DC supply.

Strictly you should check with the motor manufacturer that it is suitable.

Unfortunately it is hard to get such data on older motors. The normal course is either just to try it but be prepared for a failure or if you really are too concerned to add the transformer as suggested earlier

Thanks to all for participating in this discussion.

Yes I do have protection system if external field supply has some problem, drive would be shut down.