Regulation 7(1)(a)
1.—(1) he following tests shall not be carried out until the voltage circuits of meters under test and the voltage circuit of the working standard integrating meters have been energised for a period of one hour or half an hour if a current of not less than either 10% of basic current or 5% of marked current is applied to the current circuit of the meters, save that the non-registration test may be carried out during the pre-heating period.
(2) Sub-paragraph (1) shall not apply to a meter which the examiner is satisfied is capable of full operation as soon as it is energised.
2.—(1) Induction meters shall be tested to ensure that when the current circuits are open and a voltage of 110% of the marked voltage is applied to the voltage circuits, rotors cease to rotate before completing one revolution.
(2) Static meters shall be tested for non-registration by one of the following methods—
(i)When subjected to the test conditions specified in paragraph 2(1), the meter shall not emit more than one output pulse over the minimum test period determined in paragraph (ii);
(ii)the minimum test period (t) shall be computed by the formula:
No math image to display
where:
k = number of pulses per kWh emitted by the meter
m = number of elements
V = declared system voltage
Im = marked maximum current.
(b)When static meters are fitted with inhibiting circuits, they may be tested for non-registration with a current, which is less than the threshold current in respect of a meter of that type, applied to the current circuits and a voltage of 100% of the marked voltage applied to the voltage circuits of the meters under test. Meters shall not emit more than one output pulse over a minimum test period (t) determined as follows—
No math image to display
where:
V = declared system voltage
I = total current of all phases
k = number of pulses per kWh emitted by the meter
pf = power factor.
3.—(1) Apparatus used for determining the errors of meters during these tests shall comply with directions.
(2) The rate of advance of a meter over a test period shall be obtained by reading the electro-mechanical register or electronic display on or connected to the meter or by monitoring the rotation of the disc or pulse output of meters.
(3) For any test load applied to the meters under test, the load applied to a working standard integrating meter shall not be less than 25% or more than 125% of its full load rating.
(4) For a working standard wattmeter, the applied load shall not be less than 40% or more than 100% of its full scale or range reading.
4. Method A test
(1) A long period dial test where the advance of a kWh display, which is part of or connected to a meter under test, is compared with the advance of a precision kilowatt-hour meter.
(2) A short period test where the rate of advance of a meter under test is compared to the rate of advance of a precision kilowatt-hour meter.
(3) A short period test where the actual rate of advance of a meter, when tested under constant power conditions over a specified test period is compared to the calculated rate of advance for those conditions.
5.—(1) The tests shall be carried out in accordance with Table 1.
(2) Tests may be carried out at a temperature outside the temperature range given in Table 1, but within the range 15°C to 30°C, providing a correction is made in relation to the reference temperature by using the mean temperature co-efficient of the meters under test and of the working standard meter(s) used for determining meter errors.
(3) The meter position requirement given in Table 1 applies to induction meters only. Tolerance applies to the vertical wall on which the meter base is mounted and a horizontal reference line or edge on the meter such as lower edge of the terminal block.
(4) (a) The order of the phases shall correspond to the sequence shown on the connection diagram.
(b)The voltages shall be balanced so that the voltage between any line and neutral or between any two lines shall not differ by more than 1.5% from the mean of the corresponding voltages.
(c)The currents shall be balanced so that the current in any conductor shall not differ by more than 2.5% from the mean of these currents.
(d)The phase displacement between the current and corresponding phase to neutral voltage shall not differ from other current and voltage phase displacements by more than 3° at any power factor under any specified load conditions.
(5) The test given in Table 1 in respect of external magnetic induction shall be carried out during commissioning or after major modification or refurbishing of a meter testing system. The test consists of determining the errors at 0.1 Ib unity power factor with the meters normally connected and then determining the errors—
(a)for single phase meters, after reversing both current and voltage connections, for which half the difference between the two errors is the value of the variation;
(b)for polyphase meters, by making two additional measurements after each of the connections to the current circuits and to the voltage circuits are changed over 120° but with the phase sequence unaltered, for which the greatest difference between each error determined and the mean of the three errors is the value of the variation.
(6) Where all the errors of meters are determined by Method B or Method C test, an additional test in accordance with Method A shall be carried out. The Method A test shall be carried out at one of the loads used for the Method B or Method C test. The error obtained by the Method A test shall not differ by more than 0.6% from the error obtained at the same load value by the Method B or Method C test.
(7) The tests described in paragraph 4 shall continue until the error of meters can be calculated within a tolerance of not greater than plus or minus 0.2%.
(8) Method A tests may be used for intermediate and high loads, at unity power factor and at 0.5 power factor, and Method B or Method C tests for the low load, provided that an additional Method B or Method C test is carried out at one of the test load values used for the Method A tests.
6.—(1) Every meter shall be tested at each of the loads specified in Table 2.
(2) The ratio errors shall be determined for voltage transformers intended for use with meters but not tested with a meter.
(3) Current transformers intended for use with meters but not tested with a meter shall be tested from 5% to 120% of rated current.
7. Induction meters
(1) (a) All induction meters with more than one register shall be tested on one register in accordance with paragraphs 5 and 6, and on each and every other register at a low load using Method A, Method B or Method C tests and at an intermediate or high load using Method A test.
(b)For the same load conditions the maximum permitted difference between the error on one register (expressed as a percentage) and the error on any other register (expressed as a percentage) is one.
(c)Every register change mechanism shall be tested for correct operation with an applied voltage of 90% of the declared system voltage.
(2) (a) All static meters with more than one register shall be tested on one register in accordance with paragraphs 5 and 6.
(b)On static meters with more than one register, where the total units are the sum of all the registers, a further test shall be carried out on each and every other register using Method A.
(c)On static meters with more than one register, where the total units are recorded on one register, only this register is required to be tested in accordance with paragraphs 5 and 6.
8.—(1) Every polyphase meter shall be tested on a circuit having a phase relationship for which that meter is designed. However, three phase, four wire polyphase meters may be tested without current in the neutral conductor.
(2) Polyphase meters shall be tested by using—
(a)a polyphase kilowatt-hour energy standard;
(b)2 or 3 single phase kilowatt-hour energy standards; or
(c)2 or 3 single phase wattmeters.
9.—(1) The maximum error permitted for—
(a)single phase and polyphase whole current meters; and
(b)single phase and polyphase transformer operated meters when tested with transformers connected
shall not exceed plus or minus 1.9% for test numbers 1, 2, 3 and 4 in Table 2.
(2) The maximum error permitted for both single phase and polyphase transformer operated meters, when tested without transformers connected, shall not exceed plus or minus 1.4% for test numbers 1, 2, 3 and 4 given in Table 2.
(3) The maximum error permitted for polyphase whole current meters and transformer operated meters, when tested with transformers connected, shall not exceed plus 2% or minus 3% for test numbers 5 and 6 given in Table 2.
(4) The maximum error permitted for polyphase transformer operated meters, when tested without transformers connected, shall not exceed plus 1.5% or minus 2.5% for test numbers 5 and 6 given in Table 2.
(5) Where current and voltage transformers, which are intended to be used with meters, are not tested connected to a meter then the total error of the transformers at any load point throughout the rated range shall not exceed 0.5%.
| Influence Quantities | Reference Value | Tolerance |
|---|---|---|
| Ambient temperature | Reference temperature or, if not indicated, 23°C. | ± 2° |
| Meter Position | Vertical | ± 3° |
| Voltage | Reference voltage | ± 1.5% |
| Frequency | Reference frequency 50Hz | ± 0.5% |
| Voltage and current waveform | Sinusoidal form | Distortion factor <5% |
| External magnetic induction at the reference frequency | Zero | Induction value that does not produce a relative error variation of more than ±0.3% |
| Test load in terms of marked current | |||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Test Number and Load | Power Factor | Basic/Maximum | Maximum continuous | Long Range | Short Range | Meter Type | Polyphase Meter Load | ||||||
| |||||||||||||
| 1 (high) | 1 | Imax | 100% | 100%-200% (Note 1) | 100%-125% (Note 1) | Single and polyphase | Balanced | ||||||
| 2 (intermediate) | 1 | Ib or 125% Ib | Any load between 25%-75% of the value specified for Test Number 1 | Single and polyphase | Balanced | ||||||||
| 3 (low) | 1 | 5% Ib | 1,67% (Note 2) | 5% | 5% | Single and polyphase | Balanced | ||||||
| 4 (inductive) | 0.5 (Note 3) | Ib or Imax | 100% | The same value selected for Test Number 1 | Single and polyphase | Balanced | |||||||
| 5 (element) | 1 | Ib | 100% | The same value selected for Test Number 1 | Polyphase | One phase loaded in turn | |||||||
| 6 (inductive) (element) | 0.5 (Note 3) | Ib | 100% | The same value selected for Test Number 1 | Polyphase | One phase loaded in turn | |||||||