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Anonymous Poster #1

Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/14/2014 2:45 AM

Dear Sir,

We have Installed 3 Nos. of 1910 kW, 6.6 kV , VPI processed M/s CGL Make, CLASS 'F" Insualtion, Max I = 212 Amps, CACA Type Cooling, Vertical Mounted for Cooling water Pumps.

The problem we are facing of is that the Motor Winding temperatures are always in the range of 110 -125 degree Celcius even in the winter season and will reach 138 Deg in summer season. This motor is used for the purpose of Circulated Water Pumps which is always loaded to 98-100% of Full load current i.e 212 Amps, for our thermal Unit of Capacity 250 MW. This is for service of Continious duty.

As the winding temperatures are always high we request you to suggest remedial measures to reduce the winding temp and reasons for higher winding temperatures

Pump details are:

Discharge - 18250 M3/ hour

Head - 30 MWC

speed - 496 RPM

Power - 1910 kW

Please treat the matter as most urgent and reply is awaited at the earliest.

MAINTENANCE ELECTRICAL ENGINEER

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Commentator
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#1

Re: Excessive WINDING TEMPERATURES OF 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/14/2014 4:40 AM

Is this temp for all 3 Motors ?

Has it been increased recently? or from the Installation ?

Please check if the motor is Overloaded..

If the motor is not overloaded, then check the colloing circuit of this motor. Check if any blockages in the cooling circuit.

Best way is to contact CGL experts for analysis..

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#2
In reply to #1

Re: Excessive WINDING TEMPERATURES OF 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/14/2014 7:11 AM

Thanks for the early response and follwoing are some of the additional details.

The temp of all the three motors are same.

It has been the same condition since the installation of the motors

The motors have been almost fully loaded i.e up to 212 Amps.

We have observed that the whole motor body temp is very hot even though the ventilation systems & the air circulation in the Motor room is good and all the exhaust fans are in working condition and Hot air is coming out of Coolers of the motor

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#7
In reply to #2

Re: Excessive WINDING TEMPERATURES OF 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/14/2014 3:33 PM

So, if it was ok on day 1, why is it a problem now?

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#15
In reply to #7

Re: Excessive WINDING TEMPERATURES OF 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/17/2014 12:00 AM


THANK YOU VERY MUCH FOR FEEDBACK

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#3

Re: Excessive WINDING TEMPERATURES OF 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/14/2014 8:21 AM

has your temperature testing device been calibrated and verified?

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#4

Re: Excessive WINDING TEMPERATURES OF 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/14/2014 8:58 AM

What have the manufactures had to say about this?

In the recent past I've had several new motor run far hotter than their predecessors only to be told it was perfectly normal. I can't say I was happy about it but I'm not going to argue with the guys that made the motor.

Out of interest what are the PF and efficiency figures for the motor? I use a spreadsheet for motor calculations, I had to put some pretty horrible figures in to get 212A.

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#5

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/14/2014 11:08 AM

Before you waste a lot more of our (and your) time, by insisting on an immediate solution from unpaid volunteers, do you even understand what "Class F insulation" means? Unless there is a huge difference in IEC and NEMA classifications, Class F means it is rated for use up to 155 degrees C. Your worst case is 138 degrees C and most of the time it is much lower than that. I do not see that this is a problem to begin with.

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#6
In reply to #5

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/14/2014 11:23 AM

And just to confirm, Class F means the same thing everywhere.

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#8

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/15/2014 12:04 AM

Dear Friend,

First of all you should be contect with CGL M7 Div. regarding high temprature problem so that they will be check and analisys.

I would like to know that you have only 3 motors in your pump house or only these 3 motors getting heated. Please check inlet / outlet Air temprature and internal Air temprature of the motor body which may help for analisys. I assumed that this VTPC 1700 Frame motor which might be supply with M&P and KBL Pump. As my previous visit and expiriance with other customers that this is common problem in CGL motors and the Temprature always reach in summer as 140c.

The only way to change cooling with unidirection and increase the cool are in motor body.

Robbin

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#16
In reply to #8

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/17/2014 12:01 AM


THANK YOU VERY MUCH OF THE FEEDBACK

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#9

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/15/2014 12:41 AM

May be please check the FAN direction , also please check the FAN circuit ..if everything is fine, contact Motor vendor.. they may suggest something ....

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#10

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/15/2014 1:39 AM

These motors are hot sure, but they are hot within their operating limits and have, as you say, been working that way since first installation.

I'm not sure why you are worried.

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#11

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/15/2014 3:07 AM

A fully load motor running at this temperature looks to me like a normal running temp. All our motors are class F and operate between 90- 140degress dependent on pump loading

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#12

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/15/2014 4:01 AM

Such motors are alwsys specified with clF insulation with hot spot limited to clB . Better run extra cwp during summer till a solution can be implemented.

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#13

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/16/2014 3:23 AM

First of all I think the jraef is right: the winding temperature is less than insulation rated and then it is not an overload problem. I don't know how the temperature is measured and it could be some "spot" more elevated temperature.

Second, you can check the voltage at motor terminals. Less voltage could conduit to overload. Nevertheless at medium voltage the voltage drop is usually insignificant, the common cable could be a problem for 3*2000=6000 kVA if it is a long cable and small cross-section.

However I agree with Cabtree:

"So, if it was ok on day 1, why is it a problem now?"

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#14
In reply to #13

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/16/2014 11:59 PM

THANK YOU VERY MUCH FOR THE FEEDBACK

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#17

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/17/2014 6:27 AM

For Insulation class F, continuous duty, allowable AVERAGE temperature rise is 105 Deg C over 40 Deg C ambient.

That means maximum allowable operating temperature = 145 Deg C

You are measuring with RTD so that is not average but hot spot temperature - so 138 Deg C is safe but not desirable when we look to 15 to 20 years life for continuous operation of a motor.

Specially the summers are long in India ( it is also my country).

Yours is a CACA (outdoor motor). When ambient is 40 Deg C, the cold air leaving air to air cooler is 15 Deg more.

That means at 40 Deg ambient, temperature of cooling air inside is minimum 55 Deg C - also at higher temperature lower density of air - resultant low mass of cooling air and expected higher temperature of motor.

I will suggest that in summer you can cool the ambient air entering motor.

If it is an indoor location you can install water curtain at air entering the supply fan. This will lower ventilation air in to pump room by 8 to 10 Deg C (depending upon dry and wet bulb temperatures in summer).

If the motor is located outdoor - water curtain around the motor at a distance of 1.5 meter shall cool the air entering the motor or you can also install mist cooling at air inlets. (No risk to winding as it CA CA type design).

Above cooling aid to be used only in Summer (ambient above 35 Deg C).

This shall increase life of your motor, both of stator winding and Bearings (note with inside air being higher by 15K, bearings will also run hotter. Requires use of special grease meant for the duty temperature - Shell Alvania G3 or equivalent)

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#18
In reply to #17

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/17/2014 6:53 AM

THANK YOU VERY MUCH FOR YOUR VALUABLE SUGGESTIONS

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#19
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Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/18/2014 12:22 AM

Best way to thank him is to give him a GA (good answer) rating.

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#20
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Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/18/2014 10:38 AM

Thanks Wal, appreciate your encouraging comments.

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#21

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/19/2014 3:01 AM

Dear Friend,

You have not mentioned anything about POWER FACTOR

The speed is indicated as 496 RPM and hence Synchronous Speed is 500 RPM.

Lower and lower the speed of Motor means Higher and higher the Inductance Effect in the Motor Winding , and hence the Line Current will be more and more which leads to higher heating effect with in the winding. The Power Factor will be Poor. Hence capacitors to be added to compensate for less power factor, and this will certainly reduce the heating effect with in the winding.

Pl. check PF and if it is less than 0.85, try to improve it to 0.85 Level. The Winding Heating Problem will come under control.

DHAYANANDHAN.S

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#22
In reply to #21

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/19/2014 3:14 AM

PFC effects towards the source not the load. It just makes the reactive power billable by the utility so they can recover the losses (or save on diesel costs if you make your own juice)

Of course the current goes up with more load ie more slip. It's doing mechanical work...unless it's jammed and then it's just working to make itself hot.

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#23
In reply to #22

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/19/2014 8:40 AM

Dear Mr.Wal,

You are right.

I have my experience with, 11 KV, 1500 KW Motor, 600 RPM Sync.Speed Motor, where the winding Temp. was higher than indicated, in the manual. We connected capacitor additionally and the Current came down by 45 Amps, and temp of winding has come down by 7.5 Deg.C

Based on that I have suggested.

DHAYANANDHAN.S

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#24
In reply to #23

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/19/2014 8:58 AM

Sir Great!! - You have designed a capacitor which when connected external to motor can reduce the current inside the motor.

May be you open the text book again, study the equivalent circuit/circle diagram and find that Power Factor inside motor is function of torque (combination of basic inductance and variable Resistance) Resistance is proportional to load Torque.

Capacitor might have helped in your case in following ways:

1. Shunting some harmonics if waveform is not sinusoidal (reducing core losses).

2. Reduce voltage drop in cable and hence slightly higher voltage at terminals and correspondingly reduce current for given load on its shaft. (provided it is long cable between panel and motor)

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#25
In reply to #24

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/19/2014 9:56 PM

I like your two possible explanations for why the external cap helped.

Cures are funny things sometimes.....

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#29
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Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

04/08/2014 4:54 AM

Isn't true that the capacitor bank if connected across the motor,will reduce the motor input current & hence heating.?

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#31
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Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

04/08/2014 2:25 PM

No Sir,

Capacitor connected across Terminals of Induction Motor (Asynchronous motor) will only reduce the Inductive burden on up-stream (that is cables, switchgear and Utility).

Only you can adjust Power Factor of Synchronous Motors (No need of capacitors - this is done by adjusting Excitation - the reason that Synchronous Motors once were installed in Receiving Stations to provide Capacitive load during high loads period to balance Reactive demand of load and Inductive load at night - when due to Captive Leakage of Line Insulators the receiving end voltage used to exceed sending end voltage). For more please open books of your Engineering Course.

Best regards,

Ramesh

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#32
In reply to #31

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

04/09/2014 1:11 AM

You are qouted here:Reduce voltage drop in cable and hence slightly higher voltage at terminals and correspondingly reduce current for given load on its shaft.This means the current input to motor is reduced.Thats what I learned.!But the reduction in heat loss may not be significant.

The power factor is a fucntion of load as the magnetistion current remains almost same throughout the load.Please correct me if i am worng.

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#33
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Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

04/09/2014 1:29 AM

You are correct when -

1. if cable is long enough for inductive current will cause sufficient voltage drop. For 3 core cable (in trifoil shape) voltage drop is mainly due to resistance of cable

2. And Capacitors are at Terminals of the motor.

And term used in latest post by me is "....INDUCTIVE BURDEN.......".

Enough inputs have been provided by all on this subject and please refresh your engineering course to understand and sought out the problem.

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#26

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/21/2014 4:59 AM

Hello,

I tend to agree with the majority here, the machines ar ok and running within class F rises. If you actually ordered Class B temperature rise motors with class F insulation then your motors are running within their capability but you certainly are not getting what you paid for. The data sheets for the motors should give you this. It used to be the norm for motors to have be designed for a lower temperature class than the insulation can cope with. But more motors are being purchased using the full thermal capability of the insulation which may be what you have - this gives a hotter motor, lower efficiency, shorter life but lower purchase price.

Have you measured the air into the motors, (entering the fan), check there may be some recirculation.

Also, check the voltage at the motor terminals, the power factor is quite poor on a 12 pole machine (you have three in parallel) and you may be getting a significant voltage drop through the transformer due to the reactive current, lower voltage would give more current and heat. This can be corrected.

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#27

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/22/2014 6:04 AM

If motor insulation is Class-F, the temperature is expected to be limited to Class-B level. Hence, 138degC is not OK. It is a real problem. Here, the poster to confirm the Class-F is the allowable temperature rise (i.e. insulation of Class-H) or is it the insulation class (as stated).

May good answers as to why the motor is running hotter and I agree with

1) The effect of harmonics

2) The effect of reduced voltage at the motor terminals

Hope the poster would come back to the forum and share the findings

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#28
In reply to #27

Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

03/26/2014 9:23 AM

Unbalance voltage across the motor terminals will increase the negative sequence current as well as decrease kW capacity of the motor, may result increase in winding teperature.

Manindra

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#30
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Re: Excessive Winding Temperatures of 1910 kW Motor, 6.6kV VPI Insulation, HT Motor

04/08/2014 5:52 AM

THANK YOU FOR YOUR VALUABLE SUGGESTION/FEEDBACK

BYE

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