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Generator Inspection 3
- Thread starter Fenix999
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Have a look at for a few ideas. Doble aren't the only company in this field by any means, but they are arguably the biggest and have a lot of historical data in their library. 6MW is a small machine by the standards of the typical generators they deal with, but all the tests are possible, whether they are economical is maybe the question. At 6MW some of the motor testing companies will probably be able to help. Post your location and maybe someone can give more help - my UK-based ideas won't help if you are in the US, and so on.
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If we learn from our mistakes I'm getting a great education!
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If we learn from our mistakes I'm getting a great education!
- Thread starter
- #7
No, I haven't heard of Bakker. I'll look them up.
Of the UK-based providers I would definitely suggest Doble, Dowding & Mills, and possibly Wyko (now part of Eriks). Power Technology at Ratcliffe might be worth a call too.
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If we learn from our mistakes I'm getting a great education!
Of the UK-based providers I would definitely suggest Doble, Dowding & Mills, and possibly Wyko (now part of Eriks). Power Technology at Ratcliffe might be worth a call too.
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If we learn from our mistakes I'm getting a great education!
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electrageek
Electrical
Usually the folowing tests can be done to help identify possible problems with a Generator. Disconnect the incoming cables and open the Y connection on the neutral. You now have three separate windings available for testing.
PI - Polarization Index Test
Consists of connecting a 1000V megger from Phase A to ground with the other two phases grounded. Run the 1000V test for 10 minutes and record the meg Ohms after each minute, take the 10 minute reading divided by the 1 minute reading to get the PI of the winding. Do the same test on each winding. The higher the PI value the better the insulation system is.
You should run this test on the Rotor as well.
Winding Resistance
Use a Ductor or DLRO (Digital Low Resistance Ohmmeter) unit. It measures the DC resistance of a circuit. Connect it to each winding one at a time and get a winding resistance for each winding. Can help identify shorted turns. Generally they should be fairly close to the same value.
Run this test on the Rotor as well.
DC Hipot (Can be a distructive test)
If your machine is 11Kv then the peak voltage is 11Kv X Sqrt(2) = 15.5Kv. You can use a DC Hipot to test the insulation system by applying a voltage above the 15.5Kv DC and take milliamp reading as you go up. The test is potenitally distructive because if you have an insulation problem with the Generator this will find it and probably make it much worse. (Rewind time) Some people still use this test at reduced levels.
PF (Power Factor Test).
This test is usually done at a voltage well under the rating of the Generator so is considered a nondistructive test. Most PF test sets designed to be used for testing Transformers but it can be adapted to test Generators. Generally it is the year to year comparisons that will mean something not necessarily the first time you run the test.
You met also check out the NETA website they provide testing specifications on most all electrical equipment.
PI - Polarization Index Test
Consists of connecting a 1000V megger from Phase A to ground with the other two phases grounded. Run the 1000V test for 10 minutes and record the meg Ohms after each minute, take the 10 minute reading divided by the 1 minute reading to get the PI of the winding. Do the same test on each winding. The higher the PI value the better the insulation system is.
You should run this test on the Rotor as well.
Winding Resistance
Use a Ductor or DLRO (Digital Low Resistance Ohmmeter) unit. It measures the DC resistance of a circuit. Connect it to each winding one at a time and get a winding resistance for each winding. Can help identify shorted turns. Generally they should be fairly close to the same value.
Run this test on the Rotor as well.
DC Hipot (Can be a distructive test)
If your machine is 11Kv then the peak voltage is 11Kv X Sqrt(2) = 15.5Kv. You can use a DC Hipot to test the insulation system by applying a voltage above the 15.5Kv DC and take milliamp reading as you go up. The test is potenitally distructive because if you have an insulation problem with the Generator this will find it and probably make it much worse. (Rewind time) Some people still use this test at reduced levels.
PF (Power Factor Test).
This test is usually done at a voltage well under the rating of the Generator so is considered a nondistructive test. Most PF test sets designed to be used for testing Transformers but it can be adapted to test Generators. Generally it is the year to year comparisons that will mean something not necessarily the first time you run the test.
You met also check out the NETA website they provide testing specifications on most all electrical equipment.
electrageek
Electrical
By the way Fenix999 you might have better luck by posting this in the Electrical Power Forum.
Cross-posting creates nothing but fragmented discussion. This forum is fine, and a 6MW 11kV machine has more in common with a large motor than a large utility class generator.
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If we learn from our mistakes I'm getting a great education!
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If we learn from our mistakes I'm getting a great education!
electrageek
Electrical
ScottyUK
I will respectfully disagree with where the post should have been originally posted. This is a Generator and no matter what size it is it belongs with the other forum. With that said I also agree it is better to leave it where it is now. I was trying to say it would have been better in the other forum for the future. The testing for a Generator is much different then for a motor.
I will respectfully disagree with where the post should have been originally posted. This is a Generator and no matter what size it is it belongs with the other forum. With that said I also agree it is better to leave it where it is now. I was trying to say it would have been better in the other forum for the future. The testing for a Generator is much different then for a motor.
eGeek,
Perhaps, but an 11kV synchronous generator has enough similarities with a synchronous motor to make the input from the people in this forum very worthwhile. Big utility class machines are a very different animal but that's not what we're looking at here, it's a small air-cooled set. The control and protection for a generator are considerably more complex, but the rotor and stator of an MV synchronous generator are virtually identical to those of an MV synchronous motor, except the generator is likely to have heavier bracing.
The tests you proposed would be typical for either a motor or generator while those I proposed earlier on could apply to either but are more commonly associated with generation where the cost is easier to justify, although PD monitoring is becoming more mainstream and is increasingly seen on larger MV motors. Of those we have collectively put forward I think the most useful from a routine diagnostic point of view is the PD monitoring, with the other tests being better suited to outage works. The tests you proposed would be a good starting point for the resident maintenance team to carry out in house, where the likes of an RSO or El-Cid need specialised equipment and a fair mount of experience in interpreting the results and are normally contracted out or dealt with by a machine diagnostics specialist within a larger organisation.
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If we learn from our mistakes I'm getting a great education!
Perhaps, but an 11kV synchronous generator has enough similarities with a synchronous motor to make the input from the people in this forum very worthwhile. Big utility class machines are a very different animal but that's not what we're looking at here, it's a small air-cooled set. The control and protection for a generator are considerably more complex, but the rotor and stator of an MV synchronous generator are virtually identical to those of an MV synchronous motor, except the generator is likely to have heavier bracing.
The tests you proposed would be typical for either a motor or generator while those I proposed earlier on could apply to either but are more commonly associated with generation where the cost is easier to justify, although PD monitoring is becoming more mainstream and is increasingly seen on larger MV motors. Of those we have collectively put forward I think the most useful from a routine diagnostic point of view is the PD monitoring, with the other tests being better suited to outage works. The tests you proposed would be a good starting point for the resident maintenance team to carry out in house, where the likes of an RSO or El-Cid need specialised equipment and a fair mount of experience in interpreting the results and are normally contracted out or dealt with by a machine diagnostics specialist within a larger organisation.
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If we learn from our mistakes I'm getting a great education!
- Thread starter
- #14
First of all Thanks for the replys from both, I will check out the sites soon.
recently it came to my knowledge a machine in the spanish market that cought my attention. it is called EDAIII from unitronics.
Check also the attachment, for me, it seems interesting, until the part where they say in page 9 "When EDA test gives evidences of one or more insulation problem, it’s the time to confirm this issue with 2nd instance techniques".
The advantages seems to be that the machine can be operated by a non-expert guy and if evidences problems are found then it should be used other techniques.
If you guys have time, give it a look and give me your opinion.
Thanks and regards,
recently it came to my knowledge a machine in the spanish market that cought my attention. it is called EDAIII from unitronics.
Check also the attachment, for me, it seems interesting, until the part where they say in page 9 "When EDA test gives evidences of one or more insulation problem, it’s the time to confirm this issue with 2nd instance techniques".
The advantages seems to be that the machine can be operated by a non-expert guy and if evidences problems are found then it should be used other techniques.
If you guys have time, give it a look and give me your opinion.
Thanks and regards,
eGeek; Just for your info, I don't know of anyone who only looks at the Power Forum. 99% of the EE members look at both so no participants are likely missing.
Keith Cress
kcress -
Keith Cress
kcress -
electrageek
Electrical
itsmoked,
You are probably right but I am part of the 1%. I don't get a chance to get to the forum very often so usually just visit the power section. Just happen to check the motors one this time. I guess the proof is in the responses.
Fenix999,
If you get all the information you need then fine if not then you can always check out the other forums. My only point was that the Power forum would be the best place for this thread not that it is the only forum. A 6MW Generator is exactly like a 60MW generator and only similar to a 5000Hp Synchronous Motor. It isn't really a competition between forums.
You are probably right but I am part of the 1%. I don't get a chance to get to the forum very often so usually just visit the power section. Just happen to check the motors one this time. I guess the proof is in the responses.
Fenix999,
If you get all the information you need then fine if not then you can always check out the other forums. My only point was that the Power forum would be the best place for this thread not that it is the only forum. A 6MW Generator is exactly like a 60MW generator and only similar to a 5000Hp Synchronous Motor. It isn't really a competition between forums.
- Thread starter
- #17
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hi, i´m technician from Indar Electrical Machines in Spain, and we use EDA, for testing generators... and near Portugal there´s other companies like EMENASA in Vigo that they could help you. If you are interested I could tell you the typical testings for this machines, our main market are this machines.....
in anyway this forum is not for selling, for this i prefer to say you the ussual testings.....
in anyway this forum is not for selling, for this i prefer to say you the ussual testings.....
- Thread starter
- #19
I don't want to buy, but I was trying to verify the reliability of the EDA machine in comparison with other tests.
Perhaps since you are a user, you can tell me how many times did EDA accurately found a problem and you could act accordingly.
Thanks
Perhaps since you are a user, you can tell me how many times did EDA accurately found a problem and you could act accordingly.
Thanks
Ok, like user I have to say EDA, is a good tool but too much expensive if you only wants to check one generator or two.... in this way best thing is to subcontract... and yes, sometimes I see EDA find problems like short turns in the rotor... and the most important thing, it´s a good way to know if the winding is wet,dirty... or only old...this will give you a better idea how to deal with the machine...
what´s the manufacturer of the generator.... ? sometimes for a 6,6 kv machine, it´s a good idea to do IP and megger it, and to measure winding resistance... on my opinion the idea of doing high potencial test is no so good.... cause it could be destructive... in example, one spanish company that rules with test in generators, go to a power plant.. it was a ALCONZA generator, 6 kv, 3 MW, on hydro unit with 20 years old... this guys do high potential test, on the beginning they said that everything was ok, so the guy start up generator and when the excitation goes on.... black smoke come from inside of generator..... now the generator is at the repair office, we have done ELCID test and the core is dead, we need to take new one.. and the same for the winding... and you know the long wait for the new windings... and core..... we are giving them 3 months waiting.... and a huge bill...
Tomorrow i fly to Turkey but i hope to stay in contact from there
what´s the manufacturer of the generator.... ? sometimes for a 6,6 kv machine, it´s a good idea to do IP and megger it, and to measure winding resistance... on my opinion the idea of doing high potencial test is no so good.... cause it could be destructive... in example, one spanish company that rules with test in generators, go to a power plant.. it was a ALCONZA generator, 6 kv, 3 MW, on hydro unit with 20 years old... this guys do high potential test, on the beginning they said that everything was ok, so the guy start up generator and when the excitation goes on.... black smoke come from inside of generator..... now the generator is at the repair office, we have done ELCID test and the core is dead, we need to take new one.. and the same for the winding... and you know the long wait for the new windings... and core..... we are giving them 3 months waiting.... and a huge bill...
Tomorrow i fly to Turkey but i hope to stay in contact from there
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