Medium Voltoage Motor Rotation Check 4

[MJJBEE]

I have a 4160 V 1000 HP Motor I want to check the rotation on. However we recently had a failure and would prefer not to do a bump test. Is there another solution?

 

[Skogsgurra]

There is usually enough residual magnetic field in the rotor to induce a voltage in the stator winding. If it is possible to rotate the shaft, you can connect a recorder to the motor, rotate the shaft (right direction!) and see what phase sequence you get on the recorder. If same as your 4160 V, you are all set.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MJJBEE]

Gunnar,

Do you have any Idea of the amount of voltage we can get out of this motor? It has been sitting for 2-3 months. Also what would it do if we hooked up 480 V to this motor while it was uncoupled? Thanks for your help

 

[aolalde]

For around US$200 buy a Phase sequence and rotor rotation tester from Amprobe, hand rotaing the shaft will be enough. See picture.
Safer, clean and cheap.

 

[aolalde]

The details are:
Amprobe Model MN1604.

It test the line 3-phase sequence or the de-energized 3-phase motor leads squence for a desired motor rotation.The rotor is test rotated by hand.

http://www.amprobe.com

 

[aolalde]

Sorry the model number is PRM-1, actually replaced by PRM-3

http://www.amprobe.com/cgi-bin/pdc/viewprod.cgi?pid=2109&tid=1&type=elec

 

[MJJBEE]

yes but that meter is only rated 600V and we are dealing with a 4160V motor. What voltage is that motor going to produce? I know it will be less then 4160 but will it be less then 600V?

 

[jraef]

That just means that you can't use it as a line voltage rotation tester above 600V. For the motor rotation check, you must disconnect it from the line anyway so there is no voltage to consider (other than making sure the motor leads have been grounded to discharge any remaining capacitance).

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[Skogsgurra]

Q: " Do you have any Idea of the amount of voltage we can get out of this motor? It has been sitting for 2-3 months. Also what would it do if we hooked up 480 V to this motor while it was uncoupled?"

I have no idea what voltage you get. It depends on remanence and how fast you rotate. Most recorders work down to millivolts, so you should be able to see the phase sequence. There is no risk that you get hundreds of volts.

Connecting 480 V is a very good test if you run uncoupled. I would call that a "bump test" and you said you would avoid that. But, of course, at 480 V, you get about 1 percent torque - so the "bump" will not be very "bumpy". You may even find that the motor doesn't start. It depends on what bearings you have. But you will absolutely be able to find out rotation. Just turn the shaft. The way it turns easier is the way it will rotate when you connect 4160 V.

I like the Amprobe tester that aoalde referred to. But (I know that you will not do it, but have to say it) do not test the 4160 V with it. It will explode.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MJJBEE]

Ok we will try that first. I will know tomorrow if it works thanks for your help

 

[jraef]

But you will absolutely be able to find out rotation. Just turn the shaft. The way it turns easier is the way it will rotate when you connect 4160 V.

Very clever. A PLS for you!

JRaef.com
"Engineers like to solve problems. If there are no problems handily available, they will create their own problems." Scott Adams
For the best use of Eng-Tips, please click here -> faq731-376

 

[itsmoked]

do not test the 4160 V with it. It will explode.

Don't you mean you will explode?

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

do not test the 4160 V with it. It will explode.

Don't you mean you will explode?

My guess; All of the above!!
LOL
Respectfully

 

[MJJBEE]

Ok so we have a final plan. We had a tester overnighted to us. We will try to turn the shaft by hand However because of the Bering configuration we are not sure we can get enough speed to actually get test data from that tester. So our second plan is to hook up a 300 KW 480 V Diesel to each motor and check the rotation that way. we have one motor attached to this bus already that we know is properly connected. Thanks for your help

 

[aolalde]

Certainly the instrument handles only up to 600 Volts. If it is connected to the line 4160 Volts it will melt. If you want to test the line phase sequence connect it trough PT’s 4160/110 V.
An induction motor could become a generator. On a rough estimation, it will require full field intensity and full speed (assume 890 rpm) to generate 4160 Volts. Induced voltage will be reduced proportional to flux and shaft speed.
If we are lucky the residual magnetism will be 1% of the nominal and by hand you barely will get 10 rpm.

The expected voltage will be; V = 4160 X.01X10/890 = 0.467 Volts.

 

[waross]

I have seen usable test results from motors in the 20 hp. to 50 hp. range with a quarter turn of the motor shaft.
Let us know how your tester performs.
Thanks.

 

[Skogsgurra]

I have both a motor and a recorder close in my little shop. So I hooked up the recorder and turned the motor (5,5 kW, 4 pole, 400 V) by hand. This is the recording I got.

As it happened, this motor was doing CW rotation when connected A - B - C (or L1, L2, L3 as we say in EU). The voltage is no more than around 100 mV RMS. A larger motor and/or a higher speed will produce higher voltages.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[MJJBEE]

We have hooked up a tester and have gotten the phasing of these motors. It really didn't take much turning to get the information we needed thanks for your help.

 

[waross]

Thanks for the feedback.
Respectfully