KWH METER READING WRONGLY

[kvkev]

I have a 2 element kwh meter connected to a delta balanced 3 phase system. It utilises 2 ct's (residually connected to red, and blue phases) and 2 vt's(connected with a common secondary earth). The meter is reading only 20% of the expected calculated kwh.
I suspect that one or both of the ct's have the wrong polarity. How do I verify the connections ? I have a power analyser instrument on which I have measured the upper and lower meter element voltage, current, power factor,and real power taken by the meter elements. The ct's are outputting the correct current.
Thanks
kvkev

 

[twosockets]

kvkev,

I realize that it has been a while since you posted your question. Are you still looking for an answer? I am new to this forum, so forgive me.

 

[kvkev]

Twosockets,
Yes, managed to crack it. The meter manufacturer went out of business some time ago, but luckily managed to contact an ex employee who was kind enough to forward some meter data.
Turns out that the CT's should not have been earthed, and the meter pulsing rate was set up wrongly at initial installation 10 years ago!!
Easy when you have the instructions !!

Regards,

kvkev

 

[twosockets]

kvkev,

I am glad you got it straightened out! One thing that you said makes me curious...what do you mean by "earthed?" I assume that you mean grounded. If so, I am curious as to why someone would advise you not to ground CT secondaries (again, I am assuming you mean the secondary side of the CTs).

For reasons of safety, and to bleed off any electrostatic charge in the case of higher voltages (>600 volt class), I always recommend that there be a ground reference on any instrument transformer secondary.

 

[kvkev]

Twosockets,
Yes I agree entirely, it is normal practice to ground one leg of CT's for metering and protection, and indeed this was how the original installation was configured.
However the manufacturer's handbook for this meter (which was later faxed to me, quotes:
"NB Neither side of any CT should be connected to earth, as this will upset the correct operation of the unit"
It gives no reasons as to why, but maybe other forum memebers may be able to shed some light on it.

Regards,

kvkev

 

[twosockets]

kvkev,

Who makes this meter?

 

[kvkev]

Twosockets,

Responder Company
Winchester
U.K.

No longer in business as such.

Regards,

kvkev

 

[twosockets]

kvkev,

I can't imagine why!

 

[WAT71]

I have been working with the Westinghouse ABB and Elster meters fro several years. As the IEC meters are now coming into play I am finding that they are showing isolated cts (no running x2 together and to the meter. The only thing I have had mentioined is the possiblitiy of stray voltage.
what the ANSI calls out for and the IEC calls out are different. Stay with ABB GE Sangamo and Landis for good true readings
Alex

 

[ScottyUK]

The problem of CT earthing causing wierd behaviour of electronic metering instruments isn't unique to Responder's products. I've observed products from GE Multilin, Yokogawa, and Bitronics all give peculiar results. As with most things, if you read the manual, you should be able to sort problems. The most common thing that really screws them up is the utility practice of earthing the yellow phase of the CT group rather than the star point.

For future reference, The Responder Company still exists as Polymeters Response International. Weblink below:

http://www.pri.co.uk/

----------------------------------

If we learn from our mistakes,
I'm getting a great education!

 

[kvkev]

Scottyuk
Thanks for the web link, I had an almighty job trying to obtain info on the unit. The factory that the meter is installed in, changed ownership some 5 years ago, and most of the original manufacturers data, manuals, etc were lost or destroyed when the initial owners moved out. Some of this equipment was installed 15 years ago, so chasing info is at times difficult.

Regards,

KVKEV