On-site megger

[Manse]

Hi

I am looking for a solution for an on-site megger. The product should be connected permanent to a generator, when the generator is turned off, i would like to do the insulation measurements remotley from a computer. I have been searching the internet, but all i can find is handheld meggers!

Please help

BR
Manse

 

[Engineer54]

Hi

I am looking for a solution for an on-site megger. The product should be connected permanent to a generator, when the generator is turned off, i would like to do the insulation measurements remotley from a computer. I have been searching the internet, but all i can find is handheld meggers!

Please help

BR
Manse

What the hell for???

 

[Marvo]

Yeah, more details would be good. I can only assume this is an IT system maybe. I've also seen insulation monitoring on underground borehole pumps.

Insulation monitors are better known as IMD's or IMS's, motor insulation monitors are MIM's . As far as feeding the data to a pc you're in the realms of DAQ and SCADA systems unless you fancy writing your own database and graphinh application which isn't as bad as it sounds but without further info I couldn't advise any further.

 

[Former Sponsor TM]

Hi Manse, I've done some research for you and it is definitely something we can supply to you and offer a 5% discount on. I'll PM you with further details....

 

[Engineer54]

Hi Manse, I've done some research for you and it is definitely something we can supply to you and offer a 5% discount on. I'll PM you with further details....

It would also be interesting to us here, on the type of unit your suggesting. Any chance of giving us the details too??

 

[Former Sponsor TM]

Yes of course, it's not normally a sort of tester we have a massive amount of interest in due to the specifics of this application, but the unit that I've suggested is the Clare HAL 104. It's a tester that can be operated remotely from a PC or laptop, for example behind a test screen in a labatory.

There is a PDF datasheet available online if anybody is interested in the actual specifics of the tester.

 

[Manse]

Hmm im not sure if the Clara HAL 104 is right for my application. The idea is to locate it in a turbine. When the turbine is off, i would be nice to se the insulation "level" in the generator, and then keep monitoring it. Lower resistance, lower lifetime of insulation.

 

[Marvo]

So you're trying to predict time to failure. Wouldn't you be better monitoring the bearings if it's a wind turbine. I'm guessing the MTBF for the bearings would be shorter than the time for the windings.

 

[Engineer54]

Having read a bit of the spec, (but by all means no-where near all), this Hal unit, is more of a specialised Pat Tester than an IR monitor...

 

[oldtimer]

I dont want to throw a spanner into this but operating a megger should be done by a competent person not sure if doing it remotely would be a good thing. (I speak as a person who has worked with BMS systems over the past 26 years and yep bearing monitoring via vibration yes but injecting 500vdc remotley you would have to put interlocks in to ensure the generator would not start during the test period also just how critical is the plant you are monitoring plus if it is that critical then you need duty share generators ie power cut 2 gennies kick in and if one fails the other takes up the slack

 

[Engineer54]

Hmm im not sure if the Clara HAL 104 is right for my application. The idea is to locate it in a turbine. When the turbine is off, i would be nice to se the insulation "level" in the generator, and then keep monitoring it. Lower resistance, lower lifetime of insulation.

The generator side of a turbine (of any description be it gas, wind or whatever) are far more robust than the drive side of things. The weakest point would probably be add-on's like voltage control/stabilisers and the diode sets etc!! Unless totally abused, the actual windings will probably out live the turbine or engine....

As for bearing wear, yes a possibility there, after long periods of time. The biggest failure of bearings is caused lack of maintenance or by leaving them sitting in the same position for extended periods without use. That can cause ''Flats'' on the shaft surface, which will reduce the life of any bearing even when new ones are fitted as the damage is on the shaft itself!!

 

[Engineer54]

I dont want to throw a spanner into this but operating a megger should be done by a competent person not sure if doing it remotely would be a good thing. (I speak as a person who has worked with BMS systems over the past 26 years and yep bearing monitoring via vibration yes but injecting 500vdc remotley you would have to put interlocks in to ensure the generator would not start during the test period also just how critical is the plant you are monitoring plus if it is that critical then you need duty share generators ie power cut 2 gennies kick in and if one fails the other takes up the slack

Typical IR monitoring don't work on the same basis as an electricians megger unit. Take a look at these two links, to get the idea. Also think about an insulation monitor for a medical room IT system...

MONITORING INSULATION RESISTANCE

US Patent # 6,794,883. Method and system for monitoring winding insulation resistance - Patents.com

 

[Marvo]

I can see there would be advantages to monitoring insulation, bearings and even regulator temperatures but I think the crunch comes with the costs involved. It's not unusual in monitoring systems that the cost of the monitoring far outweighs the cost of the item being monitored. The main factor is how important is it that failures be predicted in advance. Many times it's cheaper to actually keep a complete spare unit or component on standby if it's a mission critical application.

 

[Manse]

Yes the bearings is also monitored. But we would like to monitor the insulation as well

 

[Manse]

I was actually thinking about 1000vdc. Ofcourse it should be connected correctly. It is not critical, but when the generator is placed in a windturbine fare away. Then it is not easy just to go yourself and make the measurements.