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Electromagnetic Measurements

Power and Energy Measurements, Low-Frequency

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Technical Contacts:
Thomas L. Nelson
Tel: 301-975-2986

Gerald J. FitzPatrick
Tel: 301-975-8922

Denise D. Prather
Administration and Logistics
Tel: 301-975-4221

Please contact the administration and logistics staff before shipping instruments or standards to the address listed below.

Mailing Address:
National Institute of Standards and Technology
100 Bureau Drive, Stop 8170
Gaithersburg, MD 20899-8170

Service ID
Description of Services Fee ($)
56110S Special Test of AC-DC Wattmeters, by Prearrangement At Cost
56200C Watt, Watthour, Var, Varhour Meter, Initial Two Determinations of Same Meter at 60 Hz 4240
56201C Each Additional Determination, Same Meter at 60 Hz 254
56202C Initial Two Determinations of One or Two Meters Run Simultaneously with the First (56200C) 3882
56210M Measurement Assurance Program for Watthour Meters 5507
56220S Special Tests of Watthour Meter with Pulse Output; 120 Volts, 5 Amperes, 60 Hz at 0.5 Lag, Unity and 0.5 Lead Power Factors 1790
Special Test of Phasor Measurement Units, PMUs At Cost
Fees are subject to change without notice.

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Special Tests of AC-DC Wattmeters (56110S)

Wattmeter calibrations at other than power frequencies are considered Special Tests and must be arranged on an individual basis. The following limitations apply:

A. Instruments must have separate voltage and current input terminals.

B. The instrument must have a self-contained power indicator, or provide a direct current or voltage signal which is proportional to power, or provide an output frequency which is proportional to the power.

C. Measurements are generally limited to sinusoidal signals at frequencies between dc and 100 kHz. Input signal levels should not exceed 240 V and 5 A.

D. Instruments will be tested in the as-received condition, and test uncertainties will be based in part on the performance of the

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Power and Energy Measurements, Low-Frequency (56200C-56202C)

Only standard electronic-type watt, watthour, var and varhour meters are accepted for test. Rotating types are no longer accepted except by special arrangement. If necessary, the meters should be cleaned or adjusted by the customer before they are shipped to NIST. NIST does not adjust meters and does not knowingly begin tests of faulty meters.

The test conditions must be specified by the customer. These include the current and voltage ranges to be tested, the frequency, the applied voltages, the applied currents, and the power factors. Values of these parameters which are available for routine testing are summarized in Table 9.12.

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Table 9.12 . Available Values of the Parameters for Routine Wattmeter, Watthour, Varmeter and Varhour Testing

Parameter Available Values
Voltage (V) 69 to 480
Current (A) 0.5 to 30
Power Factor 0 to 1.0
Phase Angle 0 to 360°
Frequency (Hz) 50*, 60, 400*
* Tests at 50 and 400 Hz are limited to voltages of 240 V or less and currents of 5 A or less.

If necessary, measurements can sometimes be made at other values of these parameters. These would, however, be considered special tests. Separate, specific arrangements and a higher fee will be charged than for a routine calibration.

Prior to the calibration, the meters are energized for between 1 h and 4 h at rated voltage and current on one range. A calibration consists of at least two sets of measurements taken over a minimum period of 2 d.

For wattmeters, the values of the reported corrections (in watts) generally have relative expanded uncertainties of 0.05% of the full scale range in volt-amperes. For watthour meters, the reported values of the percentage registration generally have relative expanded uncertainties of 0.05% of the indicated value. Special, higher accuracy tests can be arranged for an additional fee. The relative expanded uncertainties for power or energy measurements in these special tests may be as low as 0.005% if the short-term standard deviation of the device under test is appropriately small. For the highest accuracy, voltages are limited to 120 V and currents to 5 A.

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Measurement Assurance Program for Watthour Meters (56210M)

The Measurement Assurance Program for electric energy is designed to evaluate the performance of energy-measuring systems at the customer's laboratory. A NIST-owned, transport standard watthour meter of known stability is measured by NIST. It is then shipped to and measured by the customer, and shipped back to NIST. NIST analyzes the data and provides a report to the customer indicating the total uncertainty of the customer's measurement. This procedure enables the customer's standards to be measured relative to NIST standards without the downtime encountered when the customer's standards are shipped to and calibrated by NIST. In addition, and more important to those who calibrate standard watthour meters, the NIST MAP standard can be used by customers to evaluate their measurement process in a convenient and cost-effective way.

The uncertainty of a MAP includes the effects of the long-term and short-term instabilities of the NIST calibration system, the customer's calibration system, and the transport standard. Typically, the relative expanded uncertainty in a well-controlled comparison ranges between 0.03% and 0.05%. The Electricity Division maintains an active program of research and development in the area of electric power and energy measurements. This program often enables NIST to provide measurement support for watt and watthour meters beyond that listed in this section. Special tests will generally be conducted when the following conditions prevail:

A. The requested tests are fully developed and documented.

B. There is a significant technical or economic justification for traceability of the test on the item to national standards.

C. There has not been a routine or recurrent need for the test.

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Fast Turn-Around Energy Measurements, Low-Frequency (56220S)

This calibration service is offered for customers interested in a fast turn-around time, and reduced service cost for a limited number of specific test points. The three test points measured for this service are at 120 V and 5 A with power factors of unity, 0.5 lag, and 0.5 lead. These are the only test points offered for this service. If the customer requests additional test points, the price and turn-around time will be those for the routine calibration service (see Service ID Number 56200C). The relative expanded uncertainty assigned to a watthour meter for this service is 0.02%. This service will only accept standard watthour meters that have a pulse output. The turn-around time will be two weeks. Due to the short turn-around time of this service, the customer will need to schedule this calibration with the appropriate contact, and a purchase order must be submitted either with the instrument, or be received before the instrument arrives at NIST.

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Phasor Measurement Units, PMUs (56230S)

NIST is now providing calibration of Phasor Measurement Units, PMUs, to the IEEE Synchrophasor Standard C37.118-2205 performance requirements as a Special Test. Additional test conditions can also be performed by prearrangement.

The PMU test conditions are selected from the following:

Nominal Frequency  (50 Hz or 60 Hz)
Nominal Current  (up to 5 A rms)
Nominal Voltage  (up to 120 V rms)
Reporting rate    (one of 10, 12, 15, 20, or 30 readings per s for 60 Hz

 or one of 10 or 25 readings per s for 50 Hz)
Filter settings
 (specified by manufacturer)
Information to be provided with PMUs for test
  1. PMU model number and firmware version
  2. Simplified procedures for connecting to the device for testing
    a. parameters for the communication network, Ethernet information or RS 232 parameters
    b. Nominal frequency to be used for each test
    c. Nominal voltage and current values to use for each test (rms values)
    d. Procedure to check that the device is correctly reading the voltage and currents, that the three phase sequence is correct, that the PMU is responding to commands to send configuration information and start and stop data transmission
    e. Step by step procedure to make parameter changes necessary, such as, changing nominal frequency, changing reporting rates (tests must be done at 10, 12, 15, 20, and 30 readings per s for 60 Hz nominal frequency, and 10 and 25 readings per s for 50 Hz nominal frequency), and changing filter settings with each reading rate, if necessary
    f. other setting, such as reporting formats, phasors to be sent, etc. Note: we can only read one PMU, even if the PMU has multiple virtual PMUs per device
  3. Tests to be done and conditions for each including compliance level 0 or 1
    a. Initial setup - must be done on first testing of each PMU
    b. Message formats - must be done on first testing of each PMU
    c. Reporting rates
    d. Signal frequency
    e. signal magintude
    f. Phase angle - voltage versus current phasors
    g. Harmonic distortion
    h. Out-of-band interference - usually done at maximum and minimum reporting rates
    i. Unbalance
  4. Name and phone number of a contact person that will be available to help with questions during the testing period

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References-Power and Energy Measurements, Low Frequency

Digitally Synthesized Power Calibration Source, N. M. Oldham, O. B. Laug, and B. C. Waltrip, IEEE Trans. Instrum. Meas. IM-36 (2), 341 (June 1987).

NBS Wideband Sampling Wattmeter, G. N. Stenbakken, O. B. Laug, A. G. Perry, B. A. Bell, and T. H. Kibalo, Natl. Bur. Stand. (U.S.), Tech. Note 1221 (May 1987).

A Wideband Sampling Wattmeter, G. N. Stenbakken, IEEE Trans. Power Appar. Syst. PAS-103 (10), 2919 (Oct. 1984).

A Calibration Service for Wattmeters and Watthour Meters, J. D. Ramboz and R. C. McAuliff, Natl. Bur. Stand. (U.S.), Tech. Note 1179 (July 1983).

A Measurement Assurance Program for Electric Energy , N. M. Oldham, Natl. Bur. Stand. (U.S.), Tech. Note 930 (Sept. 1976).

Transfer of the Kilowatthour, S. R. Houghton, IEEE Trans. Power Appar. Syst. PAS-94 (4), 1232 (July-Aug. 1975).

Sampling Techniques for Electric Power Measurement, R. S. Turgel, Natl. Bur. Stand. (U.S.), Tech. Note 870 (June 1975).

A Current Comparator System to Establish the Unit of Electrical Energy at 60 Hz, K. J. Lentner, IEEE Trans. Instrum. Meas. IM-23 (4), 334 (Dec. 1974).

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Program questions: Calibrations
Phone: 301-975-2200, Fax: 301-975-2950
NIST, 100 Bureau Drive, Stop 8363, Gaithersburg, MD 20899-8363