Measuring rotor current in slipring motors

[edison123]

We are interested in measuring the rotor current of a slipring motor from zero speed to full speed and also at full load. Given that the frequency of rotor current changes from power frequency at start to slip frequency at full speed, what type of current measuring instrument one must use ?

 

[DougMSOE]

I have done this numerous times on machines >1000HP.

What I found that works is a HALL effect clamp on amp meter.
If the rotor current is greater than the HALL effect clamp on amp meter, I have used current shunts. These work very well using the mV/amp conversion. The problem with the current shunts is an isolation issue, usually solved with battery powered equipment or isolation type probes on the osilloscope.

 

[GusD]

You have to have a Hall Effect amprobe.These instruments will measure down to 0 hz and anything in between.They are very common and reasonably inexpensive.I normally use HEMIs reading up to 1000 amps.Some types take multiple readings from 100/300/1000 amps .It is possible other scale combinations do exist in the market.

GusD

 

[jbartos]

Suggestion: It will depend on the HP size of the motor and accuracy of measurement. Is current monitoring also required?

 

[edison123]

What we have in mind to do online monitoring of rotor current during various phases of operation. This is for giving the vendor the data for slip power recovery systems to be supplied by them. The motor capacity is about 550 KW with a rotor voltage/current of 650 V / 500 A.

 

[jbartos]

Suggestion: Contact
C R Magnetics, Inc.
544 Axminister Dr.
Fenton, MO 63026 2902
USA
Tel: 636-343-8518
Fax: 636-343-5119

http://www.crmagnetics.com/

or equivalent

 

[GusD]

Hi edison123

We use some frequency converters in our WRMs.These devices are quite reliable to measure motor slip directly or speed if you so wish.They output a mA or mV signal for PLC control or any other required function.

GusD

 

[jbartos]

Suggestion: Visit

http://www.thomasregister.com

and type Monitors: Voltage & Current under Product or Service, which will return 73 companies to approach to