SHAILESH MODI, ASST. MANAGER,

ERDA (INDIA)

ONSITE ACCURACY VERFICATION OF ENERGY METER

WITHOUT DISCONNECTING

CTs AND PTs

ABSTRACT�ONSITE CALIBRATION OF ENERGY METER

�WITHOUT REMOVAL OF CT AND PT CONNECTIONS.

�REGULATION BY CENTRAL ELECTRICITY AUTHORITY

INTRODUCTION� Energy meters: One of the important element of an

electrical system� Energy Meter used in:

� Every electrical installation� From small houses to huge industries.

� All exchange points� Transmission, distribution and supply network

� Generation and power stations� Distribution transformers

� It acts as a link between consumer and utility.

Need of calibration

� It relates to the revenue of the utility

�The accuracy shall not exceed the permissible limits (as per standard)

�Required to have periodic calibration/accuracy check.

� If accuracy goes beyond the limits, replaced by calibrated meter having accuracy within prescribed limits.

Methods for calibration

Energy Meter: Onsite

� Meter is calibrated on actual load.

� Reference standard meter is connected in line with the test meter

� Accuracy is checked.

Methods for calibrationEnergy Meter: Using phantom load: � Meter is removed from the site � Accuracy is checked using phantom load generator.

� The voltage of the test meter is connected in parallel �The current circuit of test meter and reference meter is connected in series. � Check the accuracy of meter from lower load to maximum load at required power factor as per the requirement of standard.

Methods for calibration

Current Transformer (CT): � The primary of the test CT and standard CT are connected through a high current source

� Secondary of both the CT’s are compared and accuracy obtained.

Methods for calibrationPotential Transformer(PT): � The primary of the test PT and standard PT are connected to a voltage source

� Secondary of both the PT’s are compared and accuracy obtained.

DISADVANTAGES� Energy meter to be disconnected from site for calibration.

� CT’s and PT’s are required to be disconnected.

� All three are calibrated separately�Effect of lead from CT and PT to meter is accounted against rated burden

After measurement of accuracy of CT, PT and energy meter separately, one need to compute the overall compensation factor.

OBJECTIVE� Gazette notification no. 502/70/CEA/ DP&D

�Calibration & periodical testing of meters carried out at least once in five years �Consumer Meter: Meter above 650Volts should cover the entire metering system including CT and PT� Energy accounting and audit meters: The testing/ calibration must be carried out without removing CT’s and PT’s

OBJECTIVE

� Calibration/testing is to be done for the whole system which includes Energy Meter, CT and PT in actual loading condition.

� The main objective is to carry out the calibration of the Energy Meter with CT and PT with the actual burden connected to CT & PT.

METHODOLOGY

� LABORATORY EXPERIMENT The details of reference instruments used for calibration is:

� Energy Meter: 63.5V, 1A Class : 0.2

� PT: 11kV/63.5V Class : 1.0� CT: 200/5A Class : 0.2

METHODOLOGY

� LABORATORY EXPERIMENT The details of Instrument under test used for

calibration is:

� Energy Meter: 63.5V, 1A Class :0.5

� PT: 11kV/63.5V Class :3.0� CT: 200/1A Class :0.5

METHODOLOGY� The PT’s (standard as well as object) were

energized with high voltage source.

� CT’s were energized with high current source. � Secondary of the test CT and PT were connected to

the test meter

� Secondary of standard CT and PT were connected to the reference standard meter.

� Phase shifter is connected in the set up to change the power factor, when required.

METHODOLOGY

� Then both the energy meters are run for certain duration

� The % error of the test meter was taken.

� The pulses coming out from the test meter is sensed by the sensor of reference meter

� The % error of the test meter was displayed on standard meter.

TEST CIRCUIT FOR CALIBRATION OF ENERGY METER WITHOUT REMOVAL OF CT, PT CONNECTION

AT RATED CONDITIONS

RESULTS:

Calibration results separately for test objects:Energy Meter:

Sr. No.

Voltage CurrentPower Factor

%error

1 63.5V 1A UPF 0.06

RESULTSCalibration results separately for test objects:Current Transformer: Rating: 200/1 A

Sr. No.

% of CurrentRatio Error

(%)Phase error

1 100.5% 0.18 10.66min

RESULTSCalibration results separately for test objects:Potential Transformer: Rating: 11kV/63 .5V

Sr. No.

% of Voltage Ratio Error

(%)Phase error

1 101.2% 1.053 1.99min

RESULTS

Combine result for the setup (Energy Meter, CT, PT) :

Sr. No.

Voltage CurrentPower Factor

%error

1 63.5V 1A UPF 1.28

CONCLUSION� Our present method satisfies Gazette

Notification (de-energised condition)� The problem of the calibration of energy

meter with CT and PT online (or on actual load) is still an issue which is not yet resolved.

� No standard defines the procedure for the calibration of the same.

CONCLUSION� In this paper the problems related with the

aforesaid consideration were presented and discussed by mean of several experimental tests.

� Presently we have different methods for calibration of energy meter.

� But method suggested in this paper will be more reliable as compared to the earlier methods of onsite calibration of individual components.

THANK YOU