CR4 - The Engineer's Place for News and Discussion ®


Previous in Forum: Transformer 1 Phase to 3 Phase   Next in Forum: Energy Efficiency Calculations
Close
Close
Close
4 comments
Associate

Join Date: Sep 2013
Posts: 30

How To Interpret TAN DELTA Test Result In A Rotating Machine

03/15/2017 6:08 AM

Dear sir,

Greetings.

We are having an induction motor with following specifications. This motor is failed and the test details are given for your information.

INDUCTION MOTOR

Make: Crompton Greaves

KW: 2000

Amps: 223

M/C No: 2081741

Stater Volts: 6600

Rotor Volts: 1825

RPM: 993

Efficiency: 95.8

Year of mfd: 06/2009

Bearings

DE: NU234C3

NDE: 232C3 + 6232C3

Weight: 11000kg

Frame: 13TPR630G

The motor is failed and the primary observation report of the failed motor is as given below.

PRIMARY OBSERVATION

· Stator slot wedges are found opened at some slots.

· Rotor NDE side binding was found carbonized due to flash over occurred at overhang portion.

· Rotor main leads were fount burnt.

· Both DE & NDE side bearing housings were found loose to bearings.

· Rotor found slightly rubbed to stator core.

· DE side bearing inner race found damaged.

WINDING CONDITION ANALYSIS

· Rotor binding on both sides were removed to see for any physical damage to windings.

· Found one particular rotor top coil was burnt and melted due to heavy flash over creating a cavity in rotor core as well.

· Further, removed the connecting lugs to windings and tested each coil by isolating and found the bottom coil of the flashed area as well as the surrounding coil are also burnt,

· Confirmed the Rotor winding is burnt.

· Tested stator with SURGE COMPRASION TESTER and found the resultant waveforms were satisfactory, again tested the POLARIZATION INDEX(PI) value of the stator winding and found OK, resulting that the stator winding was found GOOD.

· But, found the stator insulation was found brittle at the portion(18-22 places Approx) where wedges were opened.

ROTOR WINDING FAILURE CAUSE

· Primarily, the bearings housings were worn out, causing to reduce the AIR GAP for stator and rotor.

· Which thereby rubbed stator core, erupting the wedges.

· While running at full RPM, the erupted wedge punctured the rotor insulation, causing the winding to fail at an early stage.

RECTIFICATION AND REMEDIAL WORKS TO BE CARRIED OUT

· Rotor is highly recommended to be completely re-winded as the flash has affected the whole area.

· Stator needs to be de wedged completely and using a standard procedure of re-insulating by providing H class insulation paper, liquid insulating and providing with new EPOXY GLASS wedges etc.

· Reconditioning of both DE & NDE bearing housings.

· Replacement of both side bearings with new onces.

After the primary observation, we have gone for the rewinding of rotor and repairing of stator and the scope of work by the motor rewinding party is as given below.

SCOPE OF WORK FOR ROTOR REWINDING

· De-brazing the end series jumper connections.

· Removing the wedges and stripping out the old burnt copper strip from the rotor core.

· Cleaning of slots with appropriate cleaning solvents.

· Fabricating of new rotor coils with 99.9% ELECTROLYTIC & DOUBLE FIBER GLASS COVERED COPPER CONDUCTOR.

· Providing of `H’ Class inter turn insulation to each strip with NOMEX and again a layer of POLY GLASS MICA INSULATION tape on the strip, Then providing slot insulation with `H’ CLASS HYPOTHERM(10 mill).

· Shaping the rotor strips as per the pitch and inserting into the rotor slots.

· Providing overhang insulation with VARNISHED GLASS TAPE.

· Providing of NEW CONNECTION LEADS made of tin coated copper conductor, insulated with DOUBLE FIBER GLASS & SILICON RUBBER and a layer POLY GLASS MICA AND TERLIN tape insulation along with copper lugs.

· Providing copper clips for series connections on both sides.

· Brazing of end series connections and jumper connections with leads on both sides with L&T MAKE 1805 GRADED SILVER BRAZING RODS.

· Insulating he brazed connections with a layer of KAPTON and two layers of PGMP & TERLIN insulations.

· Binding of overhang portions with unvarnished Resi glass yarn by applying Dr.Beck make HARDNER EH 408 and DEBKOT 505C resin bond insulation material for locking.

· Put into hot air circulated heat chamber for curing of Resi glass and getting proper IR values.

· Baking with Dr.Beck make ISONAL-51 J Varnish, again put into heat chamber for drying the varnish, applying Dr.Beck make Becktol red and gel coat to avoid the entry of moisture.

· DYNAMIC BALNCING OF ROTOR on computerized dynamic balancing machine along with cooling fans, slipring and accessories.

SCOPE OF WORK FOR STATOR REPAIR & OVERHAULING

· Motor complete dismantling including removing of air cooler, cooling Fans, slipring unit and slipring cover, both end Covers, bearings with housings on both sides.

· Threading out the rotor from the stator, checking the bearing seating dimensions on both sides on shaft with technical parameters.

· Carefully DE WEDGING of all slots by special tools, without damaging the windings.

· Cleaning of Burnt paper insulation and carbon deposits with CCL4.

· Keeping of stator in Hot air circulating heat chamber for 48Hrs to remove all moisture and then pouring DR.BECK make ISONEL71J liquid insulating varnish into each slot and again baking in oven upto drying @ 120 Deg.

· Providing PURE NOMEX insulation paper along with EPOXY slot liners into windings and then inserting new wedges made of TAPERED & EPOXY GLASS material.

· Again putting in to hot air circulated heat chamber for getting proper IR Values and firming up of windings

· Applying Dr.Beck make EPOXY GEL COAT red to avoid entry of moisture.

· After completion of work inserting the rotor into the stator, fixing of bearings on both sides, fixing of housings, end covers, Fans and air cooler, complete replacement of gaskets and fastners, assembling the motor in complete shape.

· Conducting all routine tests i.e. Insulations resistance, winding resistance, inductance, surge comparison and tan delta tests etc.

After completion of rewinding of rotor and repairing of stator,we did the tests before assembling and test results are given below.

ROTOR

1. INSULATION RESISTANCE(IR)

IN BETWEEN

APPLIDED

VOLTAGE

IR VALUES

BEFORE HV

AFTER HV

R PHASE - EARTH 1000V 656 MOhms 554 MOhms
Y PHASE – EARTH 1000V 656 MOhms 554 MOhms
B PHASE EARTHG 1000V 656 MOhms 554 MOhms

2. HIGH VOLTAGE TEST

IN BETWEEN APPLIED VOLTAGE DURATION LEAKAGE CURRENT TEST RESULT
PHASE –EARTH 4.6KV 60 SEC 0.3mA PASS

3. RESISITANCE & INDUCTION VALUES TEST

PHASES RESISTANCE IN OHMS INDUCTANCE IN mH
R –Y 17.8 mOhms 1.9mH
Y – B 17.8 mOhms 1.9mH
B -R 17.8 mOhms 1.9mH

4. POLARISATION INDEX(PI)

APPLIDED

VOLTAGE

DURATION T1-T2

IR AT T1

IR AT T2

PI

1000V 1-10 MIN 606 MOhms 1.89 GOhms 3.12

5. SURGE COMPARISON TEST( Testes with 15KV DC HIPOT Surge Test Kit)

· Applied Voltage 500V in between R,Y,B phases to Earth and the wave forms displayed in the Oscilloscope are found equal, Hence the results are satisfactory.

STATOR

1. INSULATION RESISTANCE(IR)

IN BETWEEN

APPLIDED

VOLTAGE

IR VALUES

R PHASE - EARTH 5000V 5.56 GOhms
Y PHASE – EARTH 5000V 5.56 GOhms
B PHASE EARTHG 5000V 5.56 GOhms

2. RESISITANCE & INDUCTION VALUES TEST

PHASES RESISTANCE IN OHMS INDUCTANCE IN mH
R –Y 199.5 mOhms 26.0mH
Y – B 202.5 mOhms 26.1 mH
B -R 199.8 mOhms 26.2 mH

3. POLARISATION INDEX(PI)

APPLIDED

VOLTAGE

DURATION T1-T2

IR AT T1

IR AT T2

PI

1000V 1-10 MIN 1.67 GOhms 5.13 GOhms 3.12

4. SURGE COMPARISON TEST (Testes with 15KV DC HIPOT Surge Test Kit)

· Applied Voltage 500V in between R,Y,B phases to Earth and the wave forms displayed in the Oscilloscope are found equal, Hence the results are satisfactory.

5. TAN DELTA

MODE VOLTAGE(V) CURRENT(mA) CAPACITANCE(nF) POWER(W) POWER FACTOR DISSIPATION FACTOR FREQ(Hz) INT.

CURRENT (%)

GST-G 3824 65.79 54.54 24.88 0.0994 0.0994 49.98 0.428
GST-G 3818 63.19 52.46 22.50 0.0937 0.0937 50.00 0.0078
GST-G 3887 63.50 51.78 24.11 0.0982 0.0982 49.98 1.036

I request members to kindly guide us about these test results and their opinions. It is observed that dissipation factor in TAN DELTA test is 0.09994, 0.0937 and 0.0982.Is there any guide line about this factor? Whether Tan Delta test is applicable for rotating machines? How much should be dissipation factor? Since, stator, all other tests , viz; PI test, Surge comparator test ,IR test ,HV test, Resistance and inductor values are OK, is there any need for TAN Delta test? Exactly what is the purpose and how the results can be inferred towards healthiness of motor, Kindly give your guidance. Give your comments about the other test results also. After rewinding, how much life I can expect for this motor?

I was told by the repairer, the insulation cost for the rotor is about 75% of the cost of the copper used for rotor. Can any body react on this statement? What is the advantage of going for silver brazing compared to copper brazing?How much cost difference will come for both brazings. Please help us.

Thanks and Regards,

NVRSrinivas

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain, and now disconnecting as Little England and Wales (not too sure about Wales bit, either). Kettle's on.
Posts: 26594
Good Answers: 697
#1

Re: How to interpretate TAN DELTA test result in a rotating machine.

03/15/2017 8:53 AM

<...Is there any guide line about this factor?...> There certainly should be one in the applicable test protocol document, otherwise there would be little point in carrying out the test in accordance with it and a pass/fail boundary would not be available to the individual(s) completing the test.

<...Whether Tan Delta test is applicable for rotating machines?...> As long as the equipment is connected electrically, the answer is yes. There would be no scope for applying the test to a wooden water wheel driving line-shafts and belt-take-off drives, for example, even though this style of thing is also a <...rotating machine...>.

<...How much should be dissipation factor?...> The answer is contained in the test protocol document, which has been withheld from the forum.

<...is there any need for TAN Delta test?...> As the motor has reportedly sustained internal damage as a result of stator/rotor impact following bearing failure, such a test would establish whether the insulation integrity remains at, or is tolerably lower, than the value(s) established on the original equipment manufacturer's newly-shipped machine. So the answer is "yes, provided the pass/fail boundary has been established beforehand". The criterion will be found within the test protocol document that is available to the individual(s) carrying out the test.

<...Exactly what is the purpose and how the results can be inferred towards healthiness of motor...> Its purpose is to establish the behaviour of the insulation. The inference towards the <...healthiness of motor...> is given in the test protocol document and the pass/fail boundary therein, which has been withheld from the forum.

All the above has been gathered following an internet search on the words "tan delta test" and its interpretation, which anyone might do.

<...After rewinding, how much life I can expect for this motor?...> The answer lies with the quality of the maintenance regime on the bearings. Not having a documented procedure to maintain the bearings, or not following it, would appear from the original posting above to have been the primary cause of a chain of failures. As the protocol for bearing maintenance cannot be seen from here, nor can the competence, skills and vigour of the individual(s) carrying it be assessed from here, it is not possible for the forum to answer the question any other way than "until the next bearing failure occurs".

<...the insulation cost for the rotor is about 75% of the cost of the copper used for rotor. Can any body react on this statement? What is the advantage of going for silver brazing compared to copper brazing?How much cost difference will come for both brazings...> Yes, indeed: "these are commercial considerations, which are outside the scope of this forum." However, the copper/silver brazing question is about material melting temperatures and material hardness, which cannot be assessed from here.

One might hope that the organisation has sufficient commonsense to have a spare standby new/refurbished motor available to allow for a further failure were the equipment duty to be critical to the success of the operation.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply Score 1 for Good Answer
Guru
Safety - Hazmat - New Member United States - US - Statue of Liberty - New Member Engineering Fields - Chemical Engineering - Old Hand

Join Date: Mar 2011
Location: Lubbock, Texas
Posts: 12366
Good Answers: 143
#2

Re: How to interpretate TAN DELTA test result in a rotating machine.

03/15/2017 10:36 AM

So your VFD test failed?

__________________
If it ain't broke, don't fix it. Just build a better one.
Register to Reply
Power-User

Join Date: Jul 2016
Posts: 350
Good Answers: 17
#3

Re: How To Interpret TAN DELTA Test Result In A Rotating Machine

03/16/2017 9:31 AM

You should realize that the test results you get are very specific to your exact motor design, so the best source of comparison is the identical tests run on a new identical motor from the manufacturer, or the results for your actual motor when tested. Or take your spare motor, that has been in service and still works, and test that one as well, to establish a population baseline.

It appears that your motor rebuilder is highly competent, organized and thorough enterprise, interested in your business, and especially interested in giving you the most assurance possible that the equipment you re-install will have at least the original service life, if not longer.

Register to Reply Score 1 for Good Answer
Power-User

Join Date: Jun 2010
Location: Kolkata, West Bengal, India
Posts: 164
Good Answers: 1
#4

Re: How To Interpret TAN DELTA Test Result In A Rotating Machine

03/29/2017 1:15 PM

The test results should be compared with OEM's test results at the time of procurement of the said motor. It is mentioned by OP that cavity is created due to flash over at the rotor core but there is no mention of repair of that portion and related electrical test of the rotor core; this issue may be looked into. This type of fault may be averted if there had been proper Planed Maintenance Programme ( PMP ) and condition monitoring system. This must be introduced as soon as possible. Regarding cost of repair this may be judged from comparative market rates.

__________________
Manindra
Register to Reply
Register to Reply 4 comments
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.

Comments rated to be "almost" Good Answers:

Check out these comments that don't yet have enough votes to be "official" good answers and, if you agree with them, rate them!
Copy to Clipboard

Users who posted comments:

James Stewart (1); manindra (1); PWSlack (1); rwilliams (1)

Previous in Forum: Transformer 1 Phase to 3 Phase   Next in Forum: Energy Efficiency Calculations

Advertisement