Electromagnetic MeasurementsPrecision Ratio MeasurementsInductive DividersTechnical Contact: Denise D. Prather Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
back to top of page | back to index of electromagnetic measurements Special Ratio Measurements and Tests of Inductive Voltage Dividers, by Prearrangement (54110S)This service category provides for the measurement and/or evaluation of prototype ratio devices and inductive voltage dividers based on new principles, and for unique ratio measurements at the highest accuracy levels, such as the determination of the ratios of Hamon resistance transfer devices or Silsbee-type voltage ratio standards. Such measurements are undertaken at the discretion of NIST technical staff and only when the need for them can be clearly demonstrated. back to top of page | back to index of electromagnetic measurements Inductive Voltage Dividers (54120C-54131C)Inductive voltage dividers (decade transformer dividers) are accepted for calibration only at (50, 60, 100, 120, 400, 1000, 5000, and 10 000) Hz. The most significant dial only can be calibrated at 15 kHz and 20 kHz. Calibration voltages may be specified up to 100 V or the manufacturer's specified limit, whichever is lower. The largest contribution to instability in undamaged inductive voltage dividers is wear or dirt in the decade switches. Variable contact resistance in these switches sometimes affects the stability of voltage-ratio measurements to a significant extent but is most evident by its effect on the phase angle. When a decade inductive voltage divider exhibits large changes in phase angle for repeated measurements after the switches have been disturbed, the divider should no longer be considered satisfactory for use as a voltage-ratio reference standard. Inductive voltage dividers that use pushbutton switching or incorporate a resistive divider as a fine adjustment usually are not accepted for calibration. Corrections to the separate decades of an inductive divider, in general, cannot be simply combined. However, the correction to a step setting of one of the higher decades usually is independent of the setting of the lower decades. The effects of stray impedances must be corrected by connecting the case to the divider at one point, and unless otherwise specified, the case will be connected to one of the "common" terminals, typically marked "GRD," "Case GND," or "Case GRD." Decade inductive voltage dividers are calibrated at NIST at room temperature (22 °C to 24 °C) by comparison with a two-stage, three-decade transformer of known ratios. back to top of page | back to index of electromagnetic measurements References-Inductive DividersAmerican National Standard for Decade Transformer Dividers (Voltage Type), ANSI C100, 1-1972 Amer. Natl. Stand. Inst., New York, NY (Jan. 1972). Instructions for the Use of the NBS Reference Inductive Divider, Wilbur C. Sze, Natl. Bur. Stand. (U.S.), NBSIR, unpublished (1970). (Available from NIST.) Two-Stage, Guarded Inductive Voltage Divider for Use at 100 kHz, D. H. Hamon and T. L. Zapf, ISA Transactions, 9, 3, Instrum. Soc. of Amer. Res. Triangle Park, NC (1970). Comparator for Calibration of Inductive Voltage Dividers from 1 to 10 kHz, W. C. Sze, ISA Transactions 6,4, Instrum. Soc. of America, Res. Triangle Park, NC (1967). back to top of page | back to index of electromagnetic measurements Resistive DividersTechnical Contact: Denise D. Prather Please contact the administration and logistics staff before shipping instruments or standards to the address listed below. Mailing Address:
back to top of page | back to index of electromagnetic measurements Resistor and Resistive Dividers, DC Measurements (54210C-54211S)
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| Service ID Number |
Description of Services | Fee ($) |
|---|---|---|
| 54310S | Special Test of Capacitive Dividers at 60 Hz, by Prearrangement | At Cost |
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Capacitive Dividers, 60-Hz Measurements (54310S)
Determinations of capacitive divider ratios at 60-Hz ac employ the same equipment used for the calibration of ac resistive dividers. The same limitations pertain to shielding (proximity and pickup effects). The NIST measurement system imposes a negligible burden on the divider if its output voltage is 100 volts or less. Otherwise, the burden is equivalent to a 1000-pF capacitor.
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References-Capacitive Dividers
Comparative High Voltage Impulse Measurement, G. J. FitzPatrick and E. F. Kelley, J. Res. Natl. Inst. Stand. Technol. 101(5), 639 (1996).
High-Voltage Divider and Resistor Calibrations, M. Misakian, Natl. Bur. Stand. (U.S.), Tech. Note 1215 (July 1985).
Evaluation of a Multimegavolt Impulse Measurement System, R. E. Hebner, D. L. Hillhouse, and R. A. Bullock, Natl. Bur. Stand. (U.S.), NBSIR 79-1933 (Nov. 1979).
Calibration of High-Voltage Pulse Measurement Systems Based on the Kerr Effect, Natl. Bur. Stand. (U.S.), NBSIR 77-1317 (Sept. 1977).
Special Shielded Resistor for High-Voltage Measurements, J. H. Park, J. Res. Natl. Bur. Stand. (U.S.), 66C (1), 19 (Jan.-Mar. 1962).
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Voltage and Current Transformers
Technical Contacts:
Gerald FitzPatrick
Tel: 301-975-8922
E-mail: gfitzpatrick@nist.gov
Thomas L. Nelson
Tel: 301-975-2986
E-mail: thomas.nelson@nist.gov
Denise D. Prather
Administration and Logistics
Tel: 301/975-4221
E-mail: denise.prather@nist.gov
Please contact the administration and logistics staff before shipping instruments or standards to the address listed below.
Mailing Address:
National Institute of Standards and Technology
100 Bureau Drive, Stop 8170
Gaithersburg, MD 20899-8170
| Service ID Number |
Description of Services | Fee ($) |
|---|---|---|
| 54510C | Voltage Transformer, Ratio & Phase Angle, at 60 Hz on 1 Range, 1 Secondary Voltage, 1 Burden primary Vrms <= 150 kV | At Cost |
| 54520C | Current Transformer, Ratio & Phase Angle, 1 Range at 1 Frequency, 1 Burden, Secondary Currents (0.5, 1, 2, 3, 4, 5) A, Primary Current Not Over 12 000 A | 4653 |
| 54521C | Current Transformer, Ratio & Phase Angle, 1 Secondary Current, Additional Combination of Range, Frequency, and Burden, Primary Current Not Over 12 000 A | 438 |
| 54522C | Current Transformer, Ratio & Phase at Each additional Secondary Current, Same Combination of Range, Frequency, and Burden as 54520C or 54521C | 356 |
| 54600S | Special Tests of Dividers and Transformers, by Prearrangement | At Cost |
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Voltage Transformers (54510C)
NIST provides routine services for the measurement of complex voltage ratios (magnitude and phase angle) of transformers for primary voltages up to 150 kV; and for secondary voltages above 50 V, subject to some constraints as to the maximum physical size of the device. Results of these routine tests are reported with expanded uncertainties of 0.03 % for ratio and 0.3 mrad (1 mrad = 3.438 min) for phase angle. If the test conditions and the device under test warrant, special tests with smaller uncertainties can be performed. These special tests may require an extra fee. The customer must specify the secondary voltage and the secondary burden for each transformer or for each range of a multirange transformer. Ambiguity can be avoided if the impedance and power factor, or the resistance and reactance, are specified, rather than the volt-ampere rating of each burden.
The customer should note that the NIST calibration system represents a minimum burden of 1000 pF for routine calibrations. The customer should give some care to the specification of a burden recognizing that the use of the transformer with a burden different from that used in the calibration can result in significant error.
Calibrations of voltage transformers are performed routinely only at 60 Hz. Measurements are made with one side of both the primary and secondary windings connected together and to ground.
NIST does have some capability to perform measurements at voltages, frequencies, and burdens outside of the ranges described above. Calibrations can occasionally be provided at these nonroutine test points as a special test for an increased fee.
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Current Transformers (54520C-54522C)
Normally NIST calibrates only current transformers of high quality for use as reference standards. The NIST equipment is designed to test current transformers with a rated secondary current of 5 A, with test points chosen to be one or more of the following values: (0.5, 1, 2, 3, 4, 5) A.
Routine tests are carried out at 50 Hz, 60 Hz, and 400 Hz. For measurements at 50 Hz or 60 Hz, the results are generally reported with expanded uncertainties of 0.01% in ratio and 0.1 mrad in phase angle. For measurements at 400 Hz, the reported expanded uncertainty is 0.03% in ratio and 0.3 mrad in phase angle.
The customer must specify the test frequency, the secondary currents, and the secondary burdens for each transformer or for each range of a multirange transformer. Current transformers should be tested with burdens equivalent to those which are imposed when the device is used as a transfer standard. Routine calibration using the burdens specified in the American National Standards Institute (ANSI) Standard C-57.13 is not recommended unless these burdens are subsequently used in the customer's factory or laboratory. Large errors can result if the values of ratio and phase angle obtained with an ANSI recommended burden are used for the transformer when it is connected to a different burden.
The burden is preferably specified in terms of the measured resistance and inductance. These values should include the effects of the leads used to make a connection to the transformer secondary. An alternative, which is sometimes feasible, is to submit the transformer together with its normal leads and connected burden for calibration as a unit. If neither of the above are possible, the burden may be stated in terms of the voltampere product and the power factor of the secondary circuit at the test frequency. For reference, it should be noted that the test equipment regularly used at NIST represents a minimum test burden of about 0.03 Ω with a inductance of about 10 µH.
Because of contact resistance and current rectification, loose or dirty primary and secondary terminations may affect the measurement results. These surfaces should be tight and clean when the transformer is shipped to NIST to minimize this source of error.
Unless otherwise specified, current transformers are demagnetized prior to calibration. If it is desired to have a transformer tested as submitted (without de-magnetization), this requirement should be stated on the purchase order and NIST staff should be informed by telephone before the transformer is shipped.
Many current transformers are not designed to be used as transfer standards, and most of these do not require calibration at NIST. NIST staff can provide some assistance in the assessment of the appropriateness of the device for NIST calibration and in the identification of alternative calibration sources. If NIST is required to perform laboratory measurements to determine whether or not a particular device can be calibrated, a charge for the cost of these measurements will be made.
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Special Tests of Dividers and Transformers (54600S)
NIST maintains an active program of research and development in the area of electrical measurements at high-voltage levels. For this reason, NIST often is able to provide measurement support for high-voltage devices other than those listed above in this section. Special tests will generally be conducted by NIST, if the following criteria are met:
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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References-Voltage and Current Transformers
A Calibration Service for Current Transformers, J. D. Ramboz and O. Petersons, NIST Spec. Publ. 250-36 (June 1991).
A Calibration Service for Voltage Transformers and High-Voltage Capacitors, W. E. Anderson, Natl. Bur. Stand. (U.S.), Spec. Publ. 250-33 (June 1988).
An Electronic Ratio Error Set for Current Transformer Calibrations, R. L. Kahler, IEEE Trans. Instrum. Meas. IM-28 (2), 162 (June 1979).
A Wide-Range High-Voltage Capacitance Bridge with One PPM Accuracy, O. Petersons and W. E. Anderson, IEEE Trans. Instrum. Meas. IM-24 (4), 336 (Dec. 1975).
Wide-Band Two-Stage Current Transformers of High Accuracy, T. M. Souders, IEEE Trans. Instrum. Meas. IM-21 (4), 340 (Nov. 1972).
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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