Previous in Forum: Power Factor Correction   Next in Forum: Nexys4 DDR Board
Close

Comments Format:






Change Mode
Close

Subscribe to Discussion:

CR4 allows you to "subscribe" to a discussion
so that you can be notified of new comments to
the discussion via email.

Close

Rating Vote:







Add Vote
6 comments
Rate this Comments: Nested
Anonymous Poster #1

Electrical Motor 13, 8 KV Low Insulation Resistance Test Result

11/27/2018 8:56 AM

I have a problem with my motor 13, 8 KV, When we start, there's ground fault 105 Ampere, and we found there's differential current on phase C 147 Ampere. After we perform Insulation Resistance Test with 5 KV (3 minutes) we found result:

Phase A to ground: 115 Kohm (voltage inject 350 VDC)

Phase B to ground: 1, 5 Mohm (voltage inject 2500 VDC)

Phase C to ground: 2, 1 Mohm (voltage inject 2500 VDC)

Phase A to Phase B: 1, 5 MOhm (voltage inject 2500 VDC)

Phase A to phase C: 1, 8 Mohm (voltage inject 2500 VDC)

Phase B to Phase C: 4, 5 Mohm (voltage inject 2500 VDC)

1. What happens with the motor? Is the motor short to the ground on phase A?

2. Why is the Megger Test just 2500 KV while we are setting 5000 V?

3. When we perform Insulation Resistance Test with analog Megger Test, 5 KV, the result shows 0 Ohm. Why?

I hope I can hear a good answer soon, thank you
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 Good Answers:

These comments received enough positive ratings to make them "good answers".

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!
PWSlack
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. Kettle's on.
Posts: 30581
Good Answers: 822
#1

Re: Electrical motor 13,8 KV low insulation resistance test result

11/27/2018 9:03 AM

A1) It looks that way, though the fault is not linear with respect to applied voltage.

A2) The question is best directed towards the individual actually carrying out the test and the test protocol, rather than a global, international, anonymous internet forum: what <...we...> are doing depends also upon the boundary of the <...we...>, which hasn't been shared with the forum.

A3) The measurement seems to reinforce A1)

__________________
 "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Reply
Tornado
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21012
Good Answers: 783
#2

Re: Electrical Motor 13, 8 KV Low Insulation Resistance Test Result

11/27/2018 8:09 PM

Maybe you could use CR4 to organize a prayer circle to make this pesky ground fault go away.

__________________
 In vino veritas; in cervisia carmen; in aqua E. coli.
Reply
4
Panta SD
Associate

Join Date: May 2007
Location: Serbia
Posts: 42
Good Answers: 4
#3

Re: Electrical Motor 13, 8 KV Low Insulation Resistance Test Result

11/28/2018 6:16 AM

1. The motor has a poor resistance between all phases and ground so that a complete coil was damaged .

2. Digital instrument has a current limit , 350V/115 Kohms is 3mA so that when it reaches it, it will not increase the output voltage.

3. Analog instrument has no current limit and it shows zero
Reply Good Answer (Score 4)
No more Good Answers. Go to first "Almost" Good Answer
Jose1
Commentator

Join Date: May 2017
Posts: 70
Good Answers: 1
#4

Re: Electrical Motor 13, 8 KV Low Insulation Resistance Test Result

11/28/2018 8:56 AM

ANSEWRS

1) Phase A: is groundwall insulation shorted (kilo-scale); 41 m-A current.

Recommendation: clean the stator and perform a new Megger test. If results will be similar, then phase-A has a groundwall failure and phases B-C have a poor insulation.

Other two questions already answered by Panta.
Reply Score 1 for Good Answer
No more "Almost" Good Answers.
brich
Guru

Join Date: Oct 2009
Location: sometimes Wales,UK.. was Libya, now Oman!
Posts: 1715
Good Answers: 116
#5

Re: Electrical Motor 13, 8 KV Low Insulation Resistance Test Result

11/28/2018 11:00 AM

I am assuming that your motor is star connected?

If so yes, A phase is showing signs of insulation fatigue maybe due to heat and/or harmonics.

You have two options

1. run it until it blows up
2. rewind it now

__________________
 The square root of nothing is what you make it!
Reply
Jose1
Commentator

Join Date: May 2017
Posts: 70
Good Answers: 1
#6

Re: Electrical Motor 13, 8 KV Low Insulation Resistance Test Result

11/28/2018 11:15 AM

INSPECT stator lead(s): cracks.....
Reply
Reply to Forum Thread 6 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 Good Answers:

These comments received enough positive ratings to make them "good answers".

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:

brich (1); Jose1 (2); Panta SD (1); PWSlack (1); Tornado (1)

Previous in Forum: Power Factor Correction   Next in Forum: Nexys4 DDR Board

Advertisement

Got Something to Say?
Ask a Question
Start a Discussion

Search this Forum
Electrical Engineering:
Go

CR4 Sections
Aerospace
BioMech & BioMed
Chemical & Material Science
Civil Engineering
Communications & Electronics
Education and Engineering Careers
Electrical Engineering
General
Instrumentation
Manufacturing
Mechanical Engineering
New Technologies & Research
Software & Programming
Sustainable Engineering
Transportation

Site Directories
Forum Directory
Blog Directory
User Group Directory
RSS Feeds

CR4 Rules of Conduct
CR4 FAQ
Site Glossary

Who's Online (60 right now)
Show Members
Advertisement