Multiple motor failures

[reactive]

A client of ours has had multiple LV (525V) motor failures since the plant was commissioned (a large smelter).

Our system measurements (over a two week period) show no abnormalities on the system.

Examination of 5 failed motors shows various symptoms (2 rust, 1 interturn, 2 insulation).

Does anyone have experience with problems associated with vacuum switching of LV machines. I have seen problems with travelling wave reflection and voltage doubling off the end of the windings on large MV machines but never on LV machines.

 

[rbulsara]

Provide more details


over what period motors failed.
HP rating of motors
Type motors
Type of starters
locations (indoor, outdoor, ambient conditions)
normal load on motors
Heavy duty starts?

What else is on the system, capacitors,

 

[advidana]

Are the motor all new, what horse power, are they the same brand, did they fail on one phase only, did they fail on the same day, (rust?)what type of motor enclosures are used in what type of area, when was the plant commissioned.

The old saying: It is bigger than a breadbox but smaller than an elephant.

 

[jbartos]

Suggestion: The LV will experience smaller traveling wave reflection effect since the capacitive charging or capacitive parameters of LV cable are lower

 

[reactive]

- Motors have failed over some months.
- Ratings vary from 10 kW to 250 kW.
- Induction motors.
- VSDs and DOL.
- Locations - various indoor, failures occurred during Winter, say max. 30 degC.
- Normal load varies per machine.
- Various types of load starts.
- There are no capacitors on the same network. Harmonics are normal.
- Motors are all new Weg.
- Motors are IP55.

We are talking about 25 failures so it is difficult to give exact details for all the machines, however suffice to say that the failures appear to be random, on various areas of the plant and not related to external system conditions.

There is at this stage a theory that the motors may have been badly stored for some time - yet to be confirmed.

 

[busbar]

Is the 525V bus ungrounded, or resistance or solidly grounded? {...not accounting for rust.}

 

[rbulsara]

What is the insulation class? H or F are desirable.

What is the significance of vaccume switching you mentioned in the original question?

This sounds like a issue that needs thorough investigation and documentation.

If you could make a spread sheet listing each failed motor that not only includes nameplate data, but items such a date of failure, source panel, type of starter, type of load, location, suspected and confirmed cause of failure, etc. then look for a trend or common element.

Also did a replace/repaired motor failed again at the same location. Such data gathering will be a good start. I would keep power quality monitoring a bit longer say a month.

 

[reactive]

Thanks for everybody's input so far.

We have now been informed by the client that he does not want us to investigate further at this stage (he just wants the qos measurements from us) and will not supply us with a complete list of all motors and other info. required.