Does anyone have experience with using LIRA (Line Impedance Resonance Analysis) for cable testing & has compared the results with TDR, VLF tan delta & partial discharge?
We are doing the latter & client wants a comparison. To my understanding, LIRA can detect physical damage to the cable but...
We use a DC Hipot tester (Phenix) as well as a power frequency tan delta tester (Tettex + Eltel) & a PD analyzer (PD Tech + HVPD). We have wondered about purchasing a VLF source to avoid the resonators; but I am unsure if the tan delta values plus PD values & patterns at power frequency would be...
I think the more important questions are:
1. What is the coupler rating - 80 pF, 500 pF, 1 nF, 2 nF or 8 nF? - The higher the coupler rating; the larger the measured signal will be.
2. What is the frequency band in which the measurement is taken? - A lower "low cut-off" frequency will give you...
I have added it as a PDF now, should work.http://files.engineering.com/getfile.aspx?folder=dea3bb2b-ac7b-4fb5-b56c-7760bb6142c8&file=P43_October-10_R8_IR_&_PI_Draft_Standard.pdf
I would agree with EPete that extremely high P. I. values do indicate insulation degradation. I have attached data of two identical 9.2 MW, 13.8 kV motors that I tested some months ago. These have been examined and visual indications of degradation & PD observed. A spare motor is being planned...
Here’s an explanation of Dielectric Discharge Ratio from Metrel’s “Guide to Modern Insulation Testing”:
The dielectric discharge test is very useful for testing a multi-layer insulation. This test can identify excess discharge currents that occur when one layer of a multi-layer insulation is...
Here another case; this one does worry me. These are identical 30 MW, 11 kV, 2-pole gas turbine generators; commissioned in 1995. The P. I. values for two phases increased drastically for GTG 1. We've opened the generator; cleaned it (solvents + dry ice), dried it & varnished it. The P. I...
The motors are all of 6.6 kV. I do not know for sure that stress grading coatings are present; but this is quite standard for 6.6 kV motors (certainly for the first two; which are of BHEL make).
The top row is for October 2012, bottom row for October 2011.
Why the query about stress grading...
ElectricPete,
I have seen this kind of behaviour & have seen the correlation in the capacitance & tan delta tip-ups (see the attached document). The top reading for each motor is of 2012 & the bottom reading is for 2011. Couple of these are planned for rewinds. These motors are 6.6 kV with VPI...
There is no way that the rotor retaining rings don't have locks, just need to find them. Some have external nuts; other have circlips. Some have both. Often; the circlip won't release till you cross 200 C. I've always used gas torches, work just fine. Induction heating equipment is a lot more...
PD locations based on PD Tech guidelineshttp://files.engineering.com/getfile.aspx?folder=1ad79eaa-9f45-428a-a090-da168abb6897&file=Partial_Discharge_Locations.pdf
PD Interpretation based on PD Tech guidelineshttp://files.engineering.com/getfile.aspx?folder=0d4e69dd-0766-4457-ae54-bbbb3229306a&file=Partial_Discharge_Interpretation.pdf
Hi EPete,
Thanks for the slides. So, I understand that you do TVA probe checks only if the Iris system shows high values. Is that correct?
I have attached a presentation explaining the cause of +ve & -ve pulses, by Cutler-Hammer. It is most logical. I get confused at times as PD Tech uses...
EPete,
Thanks for the feedback. A few questions please:
1. I have been recommending swapping the line & neutral leads to many clients in India but no one takes it seriously. Is this a standard practice in USA?
2. For these particular 13.2 kV motors; do you have a phase-resolved PD pattern...
