Online Motor Health Analysis for 6000HP DC Motor

1. Connect the 0-10V signal into a galvanically-isolated input on some telemetry device.
2. Send the signal to some central point via telemetry radio, satellite, fibre-optic, ethernet or whatever signal.
3. Convert the incoming signal into a scale range of 0-6.5kA for display and recording purposes.

What is wrong with measuring the [0 to 75 millivolt full-scale?] shunt voltage with a digital voltmeter? Usually drives have a panel meter indicating current, connected to the shunt.

I would approach a 6,5kA 750VDC motor with extreme care. An inductive kicback - should anything happen can be in the 10kVolt range. I would not like be there, nor my instrumentation. Neither would live to tell about it.

What I do not understand is MM's original question. It said, that Hall effect cannot be used. Why? Hall effect devices are made exactly to measure from DC up with decent response to higher frequencies. Calibration is not needed, as there an Ammeter for DC power. I see absolutely no problem.

I guess the shunt is already fitted and in use and part of the closed loop current control for the motor. What undertakes this control?

Modern systems use digital DC drives, earlier used analogue DC drives, very early used magnetic amplifiers/mercury arc rectifiers/mg sets.

It is highly likely that you can pick up a suitable current feedback signal from somewhere in part of this current "control circuitry". It is FAR better to do this than directly off the shunt but make sure the input impedance of what you are connecting doesn't unduly load the current control circuits otherwise you will have big problems with your motor/drive system. This would be the case if you connected directly to the shunt as well.

Hope this helps

You never said you wanted to record anything automatically, hence my reference to a DVM connected to shunt. As PW Slack wrote, if you actually mean you want to transfer a current value into a data logger, there are many suppliers of DC amplifiers - even with isolation - but 750V is challenging.

1. You have not explained what frequency response you need. DC to ??
2. What tests do you want to do? How many currents and voltages to record?
3. Do you want a permanent connection for recording?

I have recorded 110V DC 800A peak starter motor voltage and current, without isolation, by using USB data logger and laptop computer [on battery power] standing on plastic crate using direct connect to existing shunt and 10:1 oscilloscope probe to the (fused) existing voltmeter terminal. But you have to work with the existing connections (shunt in positive - negative going input signals), and make ways to get wiring out of control board.

750V obviously needs even more care! I would advise installing fused outputs, within the control board, for common, shunt voltage and motor voltage feeds out to a recorder.

But more info about what you really need to do is required.

Dear friends,

Very sorry. Due to my health problem, i can't able to give any reply and i check CR4 only through my mobile.

My problem is to log (record) the data like current harmonics, Pole pass amplitude comparison etc., for interpreting the armature health of the 6000HP DC Motor. We don't have Hall Effect current clamp for measuring 6.5 Kilo Ampere DC current directly. Using 0-10 V from the converter how I can record current harmonics data and other parameters. No, I don't want permanent connection.

From what you say, you do not need DC recording - any DC values at time of measurement can be written down on paper.

Say 600 rev/min [= 10 Hz] motor with 20 commutator segments gives 10 x 20 = 200 Hz minimum switch frequency - please describe your actual values.

So a computer sound card ( 16 bit, 15 kHz max) looks adequate. The so called "microphone" input has about 100 mV rms sine sensitivity for full scale - fine for 75 mV max from current shunt - please describe actual shunt mV and rated current.You probably will not need simultaneous recording of current and voltage - so laptop [usually just a microphone input] on battery power will be OK as I suggested.

Sorry guys

I now think, that MM is milking us only. He is not capable of designing and doing your contact / current bypass, neither my noncontact sensor setup. By now, I do not even believe, he knows what to do with it. Too bad. I am sure, I am his grandfather, or at least his grandfather's friend. He can come to him or me with any problem. But not this behaviour. Not acceptable.

Very sorry.