Find the Root Cuase in this situation of Motor Insulation Damage

[pakblogger2012]

Hi,
I hope all of you would be in good state of health.
Recently a situation has been reported to me .I thought it better to put it here on this forum for root cause analysis by worthy forum fellows also.
Situation is as under.

Two chillers (TRANE ERTWA model) were in operation when suddenly D-link of electric pole ( 2 out 3 )blew.Electrical personnel were called by chiller operator and they restored d-link wire and electricity was restored.
Right at the time when operator observed heavy sound in compressor then he rushed to breaker of control supply to chillers and turned it off.It is further mentioned that from chiller to electrical pole there is chiller breaker then transformer and its breaker then electric pole.But in first situation only last protection( d-link of pole) actuated.
On restoration of power supply in 3 phase ,operator again started chillers (02 ) again and put load on it.But after one hour again same happened as written above.
Again electrical personnel came and replaced wire of d-link of electrical pole.They were of view that some thing is happening somewhere that is again again blowing it.It may be short circuiting or overloading somewhere .
However they asked to operate one chiller first and see whether same happens or not.If same happens then problem may be in same chiller ,if not then start 2nd chiller and check same.They suspected chiller for possible faults.It is worthy to mention that besides chiller load there is also lighting etc load of building on transformer. Normal load of building is 100 A while chiller draw 300 A usually. But when above incident happened ,one person observed total current on transformer meter to about 1000 A that was abnormally high and caused pole link to blow.

One chiller was operated and link did not blew first and on next day only 2nd chiller was operated and link blew .Then again link was installed and first chiller was operated and again link blew .I mean to say that pole link blew on both chillers .

Electrical personnel were confused and inspected whole line from pole to chiller for possible fault.
Electric motors of chiller compressors were meggered and insulation of 3/4 motors wer found grounded with resistance in kilo ohms. However winding to winding results were satisfactory only winding to ground resistance was too low,motors were almost grounded.Further ,cables in the lines were meggered and found ok.

I request honorable members to analyze above situation for root cause ,please.

[nike123]

Root cause is inadequate power capacity in power supply transformer for required power consumption of connected equipment at that transformer station, and lack of under-voltage and phase loss protection on chillers.

[pakblogger2012]

Root cause is inadequate power capacity in power supply transformer for required power consumption of connected equipment at that transformer station, and lack of under-voltage and phase loss protection on chillers.
When later on chiller history was checked, alarms were found related to phase loss phase unbalance, power loss and overloading.All protections were also found activated.
Does it mean that chiller would not start if any of above faults exists, when during operation when any such fault comes then what happens?

[pakblogger2012]

grid data did not show any undervoltage at that time sir.

[nike123]

When later on chiller history was checked, alarms were found related to phase loss phase unbalance, power loss and overloading.All protections were also found activated.

If protections are activated and chillers are still working without intervention of service personell, then someone has override built in protections.


Does it mean that chiller would not start if any of above faults exists,

Correct!


when during operation when any such fault comes then what happens?

Chiller stops and then it should be examined by service personnel prior returning it in to operation.

[nike123]

grid data did not show any undervoltage at that time sir.
Who is recording that data? If that was power supply company, i tend to suspect in validity of such data.
It should be recorded at consumer, as near as possible to chillers.

[pakblogger2012]

Who is recording that data? If that was power supply company, i tend to suspect in validity of such data.
It should be recorded at consumer, as near as possible to chillers.

Grid personnel take readings on pre determined time and also when any under/over voltage is observed .Grid is almost 01 Km away from chillers.

[pakblogger2012]

If protections are activated and chillers are still working without intervention of service personell, then someone has override built in protections.



Correct!



Chiller stops and then it should be examined by service personnel prior returning it in to operation.

In this case ,what are chances that motor insulation might have damaged.
I mean ,chiller cannot start if any of above mentioned fault exists ,but when during operation any above fault appears then chiller control system senses that fault and stops that motor. But obviously it takes some time from sensing fault to stopping that motor, and if surge is very high then it might have damaged insulation.

your comments please sir.

[pakblogger2012]

If protections are activated and chillers are still working without intervention of service personell, then someone has override built in protections.

please sir explain ,how one can override built in protections?

[pakblogger2012]

which of following can be suspected most for insulation damage.
1.phase loss
2.phase unbalance
3.power loss
4.overloading

[mikeref]

Might the resistance to Earth be a clue?

Electric motors of chiller compressors were meggered and insulation of 3/4 motors wer found grounded with resistance in kilo ohms. However winding to winding results were satisfactory only winding to ground resistance was too low,motors were almost grounded. (Quote.)

[pakblogger2012]

Might the resistance to Earth be a clue?

Resistance of winding to ground was measured and found too low ( in one motor it was 10 K ohm).
Yest it may be clue of what happened inside motor.It indicates that damage has occurred to insulation of motor,that indicates that there was heating environment somehow which caused insulation to get weak,further,cause of heating may be over current flow in windings ,that means cause of over current may be overloading ,further ,cause of overloading may may be phase loss .Overheating may also be due to phase unbalance greater than 5 % or such that.
Overloading may also be because of mechanical seizure of compressor of which no clue was found.

Your comments ,please

[mikeref]

Compressor motors are normally drawing 300 amps ( Quote) and there was a recorded 1,000 amp spike...regardless of one or the other...or both compressors in service at that time right?

If that is the case, then i would run compressor 1 with data loggers in continuous...or one second intervals to record voltage and amps on the incoming phases.:)

[nike123]

please sir explain ,how one can override built in protections?

I done it myself many times in test purpose! Depending on protection there is always mean to alter settings or override digital inputs etc...

[nike123]

Resistance between windings is hard or impossible to measure if windings are not separately connected to terminal box.

[nike123]

Damaged compressors motors should bee examined for burning cause by specialist. Here is example:
http://www.academia.edu/7289446/Typical_three_phase_winding_failures_and_possible_causes

That will reveal root cause of what damaged compressor motor. After that, it is posible to deduct what protection (if any) has failed to do its job.