Bump Testing 3

[JonnyWill]

What are the requirements to bump test a Meduim Voltage Motor directly coupled to a reciprocating compressor?
Does one need to have all the utilies operational, cooling water, air, lube oil, (flushed) ???
An answer in the simplest form would be appreciated, required for planning purposes.
Thanks in advance.

 

[PWR]

It is normally done uncoupled so none of the points you raise are an issue.

 

[JonnyWill]

I realise it is normally done uncoupled, but because its coupled machine .You can't bump test the motor uncoupled unless I push the motor back away from the hub of the compressor shaft ... Then one must do an alignment all over again..

 

[Barry1961]

Many large reciprocating compressors have a separate oil pump with a pressure switch interlock to prevent starting the compressor before oil pressure has time to build. If this is the case I would strongly recommend hooking it up.

You could probably get away with running without cooling water for a few minutes. If you do not have the outlet connected, unload the discharge valves or remove the discharge valve assemblies you should be able to run it even longer.

Barry1961

 

[abcd3286]

Could you get away without support utilities for a 2 second test - more than likely.

To get pragmatic though
The bump test is generally done to ensure you got phase rotation on the motor correct ie motor turns the right direction. After this we generally put it on line and if ran OK put it in service.
SO the answer is yes you should have the thing ready to go in all respects before bump test.

Dan Bentler

 

[jraef]

Barry1961 is right. Lube is important for sure, even for a simple rotation bump test, unless maybe you have a VFD that can start ever so slowly. Once you bump for rotation, the entire drive train will turn (in your case since you can't disconnect), and any unlubed components are subjected to stress as the motor accelerates and then coasts to a stop. With the load connected it may coast to a stop quickly, but a lot of that is because of friction, and friction without lube is bad.

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[stardelta]

Why the need to bump test is it just to determine rotation? Can you find someone who owns one of these, or beg/borrow/steal one and eliminate all the effort and risk?

http://www.fluke.co.uk/comx/show_product.aspx?locale=uken&pid=35297

 

[jraef]

stardelta,
I believe that device, and ones like it, are used to tell you what direction the motor is spinning while already running. You hook up the device to the motor, you bump it, and it tells you which direction it is spinning. It does not tell you which direction it is GOING to spin when you first hook it up. Only a bump test will tell you that. If you can't see a shaft during the bump test, these are very usefull. I've been trying to get sumersible pump people to use these on the pumps above ground before dropping them because once they are under water, you can't tell rotation directiona any longer except by flow differences.

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[aolalde]

Hello JonnyWill.

A “Bump Test” is made to find the “Resonant Frequencies” or “Natural Frequencies” of a system.

If you want to analyze the motor alone, it will be uncoupled and excited by an impact, like “ringing a bell”. The whole vibration spectrum is recorded and the peak vibration found will identify the natural frequencies. If the system; motor- load- base is analyzed, do not uncouple the driven machine.
The motor and/or system do not need to rotate and I will leave the lubricants, cooling water etc close to the operating quantities since their mass could affect the results.
The most important result of this test is to show that the operating or forced exciting frequencies are far apart of the natural frequencies.

 

[abcd3286]

I don't know about the test unit from Fluke - never used it.

I have used Ideal (?) and I believe Greenlee has version also. Have two parts
one is same old phase rotation for supply conductors that has been used for eons. once you know phase rotation of supply the neat part (the second unit) comes in.
It can be hooked to motor leads then hand spin motor in desired rotation direction and this unit will tell you phase rotation of motor leads itself. Now all you have to do is match motor leads to supply leads and it should go right direction.

Pretty slick BUT be careful of which end you referance to -0 you GOTTA read the directions.

Dan Bentler

 

[stardelta]

Appologies for my earlier comment which in retrospect was very vague. It can done with a suitable phase rotation indicator without having to power up the motor. We use an old but very reliable and easy to use instrument made by Biddle. Firstly the instrument is connected to the motor, The three leads from the Biddle are marked U V W and they must be connected to the corresponding phase circuits of the motor. The motor is lightly spun in a clockwise direction at the shaft. The biddle will then indicate phase rotation of the winding via a center reading meter, if it is also clockwise the phases are correctly marked for clockwise rotation at the shaft end with U/red V/yellow W/blue. If the biddle indicates anti-clockwise it will rotate anti-clockwise if fed U/red V/yellow W/blue. It is a requirement of IEC standards that motors rotate clockwise at the shaft end when fed U/red V/yellow W/Blue. We see many that have been rewound without phase direction being determined and the leads have marked wrongly as a result. The only downside is that the motor must be lightly spun by hand, not always possible if it is in situ. The link shows the latest version of the instrument we use.

http://www.inotek.com/Catalog/biddle2pm.html