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BASICS OF METERING by Ramakrishna Perumal, Sr. Engineer, Technicas Reunidas

BASICS OF METERING

By : Ramakrishna Perumal, Sr. Engineer, Technicas Reunidas
Industry : Power
Keywords :

electrical metering

Activity:  11 comments  4804 views  last activity : 08 01 2012 09:03:08 +0000
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BASICS OF METERING

What is the basic difference between a Tri-Vector meter and multi function meter?

The basic difference between a Trivector meter and multi function meter is that a Trivector

meter cannot display the tariff it can display kWh and from that reading the tariff and cost has to

be calculated manually, where as a multi function meter can display tariff also if programmed

properly. Different tariff at different interval of time for normal and peak time load and also

different tariff at same time by two different display is possible in multi function meter.

What is accuracy class of meters?

Basic Current (I

b)

The value of current in accordance with which the relevant performance of the meter is fixed.

Rated Maximum Current (I

meet the accuracy requirements of relevant standard, when this current flows continuously in

the meter.

Now in the light of above two definitions accuracy class can be defined as A number which

gives the limits of the permissible percentage error, for all values of current between 0.1

max) The highest value of current at which the meter purports toIb and

I

meter is tested under reference conditions (including permitted tolerances on the reference

values) –as defined in IS 13779: INDIAN STANDARD AC STATIC WATTHOUR METERS,

CLASS 1 AND 2-SPECIFICATION (First Revision) & IS 14697: 1999 ac STATIC

TRANSFORMER OPERATED WATTHOUR AND VAR-HOUR METERS, CLASS 0.2 S, 0.5 S

AND 1.0 S — SPECIFICATION.

Accuracy class of 1,2 0.5S & 0.2S are available.

max for unity power factor (and in the case of polyphase meters with balanced loads) when the

Percentage Error

The percentage error is given by the following formula:

(Percentage error = Energy registered by the meter - True energy x 100)/True Energy

True energy

NOTE

uncertainty that can be traced to IS 12346 or standards agreed upon between manufacturer and

user.

- since the true value cannot be determined, it is approximated by a value with a stated

Percentage Error Limits (Single-Phase Meters and Polyphase

Meters with Balanced Loads)

Values Of Current

Power factor

Percentage Error limits for meters of

accuracy class:-

For direct

connected

meters

For Transformer

operated meters 1 2

0.05

0.1

0.1

0.8 Leading + & - 1.5 -

0.2

0.8 Leading + & - 1 -

When specially

requested by the

user:

0.2

Ib to 0.1 Ib 0.02 Ib to 0.05 Ib 1 + & - 1.5 + & - 2.5Ib to IMAX 0.05 Ib to IMAX 1 + & - 1 + & - 2Ib to 0.2 Ib 0.05 Ib to 0.1 Ib 0.5 Lagging + & - 1.5 + & - 2.5Ib to 0.2 IMAX 0.1 Ib to IMAX 0.5 Lagging + & - 1 + & - 2Ib to Ib

When specially

requested by the

user:

0.2

Ib to Ib

0.25 Lagging +3.5 & -3.5 -

0.5 Leading +2.5 & -2.5 -

What is current limit for meter being directly connected or being CT operated?

Usually direct connected meters are available for total current not exceeding 5 Amp but some

manufacturer provide 10 Amp also beyond which it will become essential to go for CT operated

meters. Any meter to be direct connected has to satisfy the following criteria:

·

rated frequency.

The meter shall be able to carry a short time over current of 30 IMAX for one half-cycle at

·

should not exceed 0.4 & 0.5 respectively.

After 5 Amps and for some manufacturers 10 Amps the meters have to be connected through

CT. Any meter to be connected through CT has to satisfy the following criteria.

Meters operating at unity power factor Percentage of basic current Ib for class 1 & 2

·

The meter shall be able to carry for 0.5 s a current to 20 times the maximum current.

·

should not exceed 0.2 & 0.3 respectively.

Meters operating at unity power factor Percentage of basic current Ib for class 1 & 2

What are the relevant standards and codes for meters?

IS 13779: 1999 AC STATIC WATTHOUR METERS, CLASS 1 AND 2-SPECIFICATION.

IS 14697: 1999 ac STATIC TRANSFORMER OPERATED WATTHOUR AND VAR-HOUR

METERS, CLASS 0.2 S, 0.5 S AND 1.0 S — SPECIFICATION.

What is initial start up time for meters?

The meter shall be fully functional within 5s after the rated voltage is applied to meter terminals.

 Top Comment : Devi Kaladeen   | 11 02 2009 20:10:11 +0000
Very informative. I have now increased my knowledge on metering. I do know a little in my line of work. As a matter of fact I monitor the reading on my meter regularly since we have so much power fluctuations here. I also use a lot of electrical item... even for cooking, so I guess you understand why I monitor the reading.
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11 comments on "BASICS OF METERING"
Sort by: Most Recent Top Rated
  Commented by  Nachiket D Sakinal, Design Engineer, Minilec India Pvt. Ltd.    | 08 01 2012 09:03:04 +0000 
what is the difference between AC STATIC WATTHOUR METERS  &  AC STATIC TRANSFORMER OPERATED WATTHOUR AND VAR-HOUR METERS..?
  Commented by  Ramakrishna Perumal, Electrical Specialist Engineer,    | 02 27 2012 15:39:27 +0000 
Remember that instrument errors add up to the errors of the transformers feeding them
  Commented by  Chirag Kakadiya, Commander in Chief, FBI – Federal Bureau of Investigation    | 02 27 2012 09:57:20 +0000 
Sir ,
All information are so helpful for understand metering and CT,
Now i have a question, 
If we have a ABT type Energy meter which is programmed for 0.2s class CT and If I feed this Meter by secondary of a 0.5s class CT , 
the Max. Current capacity of plant is 52.54 Amp(1 MW , at 11kv)& CT ratio is 125/1 Amp.
So my query is what will the difference in reading shown by ABT meter ??
  Commented by  Ramakrishna Perumal, Electrical Specialist Engineer,    | 02 21 2011 06:00:50 +0000 
The difference between whole current meter and CT meter is whole current meter is without current transformer and the CT meter is with current transformer (CT).
  Commented by  Ramakrishna Perumal, Sr. Engineer, Technicas Reunidas    | 02 21 2011 05:47:38 +0000 
Whole current meter will measure the actual current directly without using the transformer. 

CT meter will have current transformer to reduce the high current to low current and the meter connected to CT will give the reduce current reading equivalent to high current.
  Commented by  Jeyanthi, Sr. Design Engineer, Wallaby metering system    | 02 21 2011 05:19:30 +0000 
Sir,
     Its informative. I have one more doubt. What is mean by a whole current meter? and how it could be differed from normal CT meter?.. can you pls explain..?
  Commented by  Ramakrishna Perumal, Sr. Engineer, Technicas Reunidas    | 11 03 2009 09:39:52 +0000 
Mr. Ajay Good Kashimiri Joke.
  Commented by  Alka Thakur, Technical Support Manager, Vendio Services and a freelance German Translator    | 11 03 2009 05:49:33 +0000 
Thanks for sharing!!
  Commented by  Vineet Prakash, Sales/BD Manager, Tata Power    | 11 03 2009 04:49:00 +0000 
Nice article Mr.Perumal, it gives a lot of knowledge about metering. Thanks for sharing...
  Commented by  Ajay Ziz, Deputy Registrar, University of Jammu    | 11 03 2009 04:17:46 +0000
Rating : +1  
a kashmiri lands in new york ::
1 year and no elecricity rent is deposited by kashmiri..
the meter shows minimal reading ..
the FBI comes into action eventually requests the kashmiri to tell his secret ..which is the ingeniuous kundi ..
a red alert is sounded in US ..
a kashmiri has landed there ..
moral :: a alert mind can bypass any technology ..
  Commented by  Devi Kaladeen, Audit Manager, Health Sector Development Unit    | 11 02 2009 20:10:11 +0000
Rating : +1  
Very informative. I have now increased my knowledge on metering. I do know a little in my line of work. As a matter of fact I monitor the reading on my meter regularly since we have so much power fluctuations here. I also use a lot of electrical item... even for cooking, so I guess you understand why I monitor the reading.
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