points at 0.5 power factor on a base range and one scale point at other combinations of ranges, followed by tests at unity power factor at one scale point on one or more ranges, depending upon the results obtained. Item 201.304a Description Determination of the difference between the reading on reversed Fee (*) 201.304b 201.304c Determination of this difference at one scale point on an additional (*) 201.304z For frequencies greater than 70 Hz and for special tests not covered (*) *For current fees, see Appendix C. 201.305 Watthour meters. Except under unusual circumstances, only portable standard watthour meters (rotating standards) will be accepted for test. Tests consist of determinations of the percentage registration of the meter "as received." If meters are to be cleaned and adjusted this must be done before they are submitted for test. The Bureau does not undertake the cleaning and adjustment of meters and does not knowingly begin tests on faulty meters. Before tests can be started the test conditions must be completely specified by the user as to current and voltage ranges to be tested, frequency, applied voltage and current, and power factor. A guide listing a limited yet adequate schedule of tests is available at no charge. Test voltages should be chosen from the following values: 1, 2, or 4 times 110, 115, 120, 125, and 130 V. Test currents should be chosen from the following values: 1, 10, or 100 times 0.25, 0.5, 0.75, 1, 1.25, 1.5, 2, 2.5, 3, 3.75, 4, 5, 7.5 A (but not to exceed 100 A). Tests at other voltages or currents, or at power factors other than 1.0 and 0.5 current lagging, will be considered as special tests, because rearrangements of circuits are required (see 201.305z). Unless otherwise specified, test runs on portable standard watthour meters (rotating standards) are of approximately 100 sec duration. The meters are energized for at least 30 min at rated voltage and current on one range before starting the test. Item Description Fee 201.305a Test at 60 Hz on one combination of range, applied voltage, and (*) 201.305b Additional tests on the same or an additional combination of range, (*) See footnote at end of table. 201.305c Test of one or two additional meters simultaneously with the first, (*) 201.305d Test of each additional meter simultaneously with the first, under the (*) 201.305z For special tests not covered by the above schedule, advance arrange- *For current fees, see Appendix C. 201.306 Current transformers. (a) Calibration: The Bureau normally calibrates only current transformers of high quality for use as reference standards. The Bureau may decline requests for tests which are not to be used for establishing or checking a reference standard. If the transformer quality is stated in terms of ASA accuracy classes, calibration will normally be limited to transformers stated to be in the 0.3 percent class for one or more ASA burdens. Bureau equipment is primarily designed for testing current transformers whose rated secondary current is 5 A. Results obtained at frequencies near 60 Hz (c/s) will normally be reported to an accuracy of 0.05 percent in ratio and 1 min in phase angle. However, in some instances the ratio can be reported to an accuracy of 0.02 percent and the phase angle to 0.5 min. (b) Test information: Tests cannot be started until information is furnished concerning the following conditions: (1) test frequency, (2) secondary test currents, (3) secondary burdens, (4) ranges to be tested. It is customary to make tests at secondary currents of 0.5, 1, 2, 3, 4, and 5 A. (c) Transformer burden: (1) Current transformers should be tested with burdens equivalent to the impedance imposed when the transformer is used as a reference standard. Inclusion of tests at ASA burdens in not recommended. The burdens listed in the American Standard for Instrument Transformers, C-57.13, are for rating purposes only and differ from the instrument burdens imposed on a reference standard. Large errors in measurement can result if the values of ratio and phase angle obtained with an ASA burden are used for the transformer when it supplies only an instrument burden. (2) Preferably the burden should be specified in terms of the measured resistance and inductance, including the leads to connect the instruments to the secondary of the transformer. If this measurement cannot be made conveniently, it will suffice in most cases to state the name of the maker, the type, range, and serial number of each instrument used in the burden, and the length and size of the wire of the leads used in the secondary circuit. Alternatively the burden may be stated in terms of the volt-amperes and power factor of the secondary circuit at the test frequency. (3) The test equipment regularly used at the Bureau imposes a minimum test burden of about 0.16 ohm with a minimum inductance of about 10μH (if the burden inductance is larger than 10μH, the minimum resistance is increased above 0.16 ohm). Special test equipment and procedures must be used for burdens lower than 0.16 ohm, so that advance arrangements must be made and higher fees must be charged. In planning for the tests of a transformer it is therefore desirable to select a low burden, but one larger than this minimum, preferably not less than 0.2 ohm. The required total may be made up by incorporating resistance in the leads to the instruments. (d) Multirange current transformers, in which the same sections of primary windings are used in series and in parallel, usually have phase angles and ratio factors which are equal on the several ranges to within the accuracy needed for almost any measurement purpose. Hence a test at six values of secondary current on one range is nearly always sufficient to determine the chracteristics of the transformer. Further tests, often made at 0.5 and 5 secondary amperes on each additional range, merely serve as a safeguard by means of which mistakes in winding may be detected. When the various ranges of a multirange transformer are obtained by taps on either winding, this relation does not necessarily hold, particularly in the case of secondary taps; and tests in addition to the initial six-point test on one range should be made, using two values of secondary current on each of the ranges so obtained. Transformers of some designs, however, show very little difference in ratio factor and phase angle on the various ranges, and the Bureau should be consulted before tests on a large number of ranges are requested. (e) Demagnetization: Unless otherwise specified, current transformers will be demagnetized before being tested. If it is desired to have a transformer tested as submitted (without demagnetization), this fact should specifically be stated. (f) Test limitation at frequencies greater than 60 Hz: At 400 Hz, the maximum current range for which tests are made is about 200 A and the phase angle values are normally reported to an accuracy of 3 min; at 800 Hz there is a further reduction in the current range and accuracy. If the burdens at these higher frequencies are specified in terms of volt-amperes and power factor, the frequency for which these values are stated must be clearly indicated so that the proper burden resistance and inductance can be duplicated. (g) Recalibration: At room temperature the ratio and phase angle under a specified test condition should be repeatable unless the core is magnetized. Once stability has been demonstrated, a current transformer should not require recalibration at intervals less than 5 years. Item Description Fee 201.306a-1 Determinations of the ratio and phase angle of a current transformer (*) 201.306a-2 Same as a-1 except primary current greater than 500 A but not to (*) 201.306b-1 Determinations of the ratio and phase angle at one value of secondary (*) 201.306b-2 Same as b-1, except primary current greater than 500 A but not to (*) 201.306c Determinations of ratio and phase angle at an additional value of See footnote at end of table. 201.306z For tests of current transformers at frequencies other than 25, 50, or *For current fees, see Appendix C. 201.307 Current transformer comparators (testing sets). Item 201.307a 201.307b 201.307z Determination of the values of current ratio and phase angle for For special tests not covered by the above schedule, advance arrange- (*) (*) (a) A general discussion of magnetic principles and methods used in magnetic testing is given in NBS Monograph 47, Basic Magnetic Quantities and the Measurement of the Magnetic Properties of Materials. Price 30 cents. Available from Superintendent of Documents, U.S. Government Printing Office, Washington, D.C., 20402. See p. 135 for order blank. (b) Tests in this field are for the most part made on samples which serve as standards to coordinate work in various laboratories and thus secure uniformity in commercial testing. For this purpose it is essential that the standard bars be very uniform in their magnetic properties. The Bureau does not normally make routine acceptance tests of magnetic materials unless these specimens are to be used, at least temporarily, as standards. The standard dimensions of magnetic test specimens are given in 201.401 and 201.402. It is occasionally possible to test specimens of unusual materials or shapes where the services of the Bureau are needed in the development of new test procedures which are likely to be of importance in the industry. In such cases a full understanding of the problem should be developed by correspondence, or preferably by a visit which will permit direct discussion between the engineers concerned and the Bureau staff. 201.401 General magnetic measurements; normal induction and hysteresis. Specimens submitted for test should be of rectangular cross section, width not to exceed 3.0 cm (1% in.); thickness not to exceed 1.0 cm (% in.); for magnetizing forces from 0 to 300 or 0 to 5,000 oersteds (Oe), length to be not less than 25.4 cm (10 in.); for magnetizing forces in the range 100 to 5,000 Oe, length to be not less than 7 cm (2% in.). Specimens whose permeability is not greater than 4 may be of circular cross section, diameter not to exceed 1.27 cm (1⁄2 in.), but in any event cross-sectional area must be not less than 0.2 cm2 (0.031 in.2). Item Description Fee 201.401a Determination of data for normal induction curve in the range 0 to (*) 201.401b Determination of data for normal induction curve in the range 100 to (*) 201.401c Determination of data for normal induction curve in the range 0 to (*) 201.401d Determination of data for demagnetization curve, one value of mag- (*) 201.401e Same as 201.401d, each additional value of maximum magnetizing (*) 201.401f Determination of permeability for specimens whose permeability is (*) 201.401g Each additional specimen submitted at the same time. (*) 201.401z For examination of material found to be unsuitable for test, or for *For current fees, see Appendix C. 201.402 Magnetic materials: a-c permeability and core loss. Test specimens should consist of the proper number of strips 3 cm (16 in.) wide and either 28 cm (112 in.) to 30.5 cm (12 in.), or 50 cm (1916 in.) long, prepared in accordance with the specifications of the American Society for Testing and Materials, A-34. |