The Measuring Instruments Regulations 2016 SCHEDULE 1E — ACTIVE ELECTRICAL ENERGY METERS (MI-003) (Annex V to the Directive)

Accuracy

1

The manufacturer shall specify the class index of the meter. The class indices are defined as: Class A, B and C.

Rated operating conditions

2

The manufacturer shall specify the rated operating conditions of the meter; in particular: The values of f n , U n , I n , I st , I min , I tr and I max that apply to the meter. For the current values specified, the meter shall satisfy the conditions given in Table 1; 1 For Class B electromechanical meters I min ≤ 0.4 ∙ I tr shall apply. The voltage, frequency and power factor ranges within which the meter shall satisfy the MPE requirements are specified in Table 2. These ranges shall recognise the typical characteristics of electricity supplied by public distribution systems. The voltage and frequency ranges shall be at least: 0.9 ∙ U n ≤ U ≤ 1.1 ∙ U n 0.98 ∙ f n ≤ f ≤ 1.02 ∙ f n power factor range at least from cosφ = 0.5 inductive to cosφ = 0.8 capacitive.

MPEs

3

The effects of the various measurands and influence quantities (a, b, c,…) are evaluated separately, all other measurands and influence quantities being kept relatively constant at their reference values. The error of measurement, that shall not exceed the MPE stated in Table 2, is calculated as: When the meter is operating under varying-load current, the percentage errors shall not exceed the limits given in Table 2. – 10 °C … + 5 °C or + 30 °C … + 40 °C – 25 °C … – 10 °C or + 40 °C … + 55 °C – 40 °C … – 25 °C or + 55 °C … + 70 °C Single phase meter; polyphase meter if operating with balanced loads Polyphase meter if operating with single phase load I tr ≤ I < I max , see exception below When a meter operates in different temperature ranges the relevant MPE values shall apply. The meter shall not exploit the MPEs or systematically favour any party.

MPEs

4

Permissible effect of disturbances

4

General As electrical energy meters are directly connected to the mains supply and as mains current is also one of the measurands, a special electromagnetic environment is used for electricity meters. The meter shall comply with the electromagnetic environment E2 and the additional requirements in paragraphs 4.2 and 4.3. The electromagnetic environment and permissible effects reflect the situation that there are disturbances of long duration which shall not affect the accuracy beyond the critical change values and transient disturbances, which may cause a temporary degradation or loss of function or performance but from which the meter shall recover and shall not affect the accuracy beyond the critical change values. When there is a foreseeable high risk due to lightning or where overhead supply networks are predominant, the metrological characteristics of the meter shall be protected.

Effect of disturbances of long duration

4

In the case of electromechanical electricity meters, no critical change values are defined for harmonic contents in the current circuits and for DC and harmonics in the current circuit.

Permissible effect of transient electromagnetic phenomena

4

The effect of an electromagnetic disturbance on an electrical energy meter shall be such that during and immediately after a disturbance: — any output intended for testing the accuracy of the meter does not produce pulses or signals corresponding to an energy of more than the critical change value, and in reasonable time after the disturbance the meter shall: — recover to operate within the MPE limits, and — have all measurement functions safeguarded, and — allow recovery of all measurement data present prior to the disturbance, and — not indicate a change in the registered energy of more than the critical change value. (m being the number of measuring elements of the meter, Un in Volts and Imax in Amps).

4

For overcurrent the critical change value is 1.5 %.

Suitability

5

Below the rated operating voltage the positive error of the meter shall not exceed 10 %.

5

The display of the total energy shall have a sufficient number of digits to ensure that when the meter is operated for 4,000 hours at full load (I = I max , U = U n and PF = 1) the indication does not return to its initial value and shall not be able to be reset during use.

5

In the event of loss of electricity in the circuit, the amounts of electrical energy measured shall remain available for reading during a period of at least 4 months.

Running with no load

5

When the voltage is applied with no current flowing in the current circuit (current circuit shall be open circuit), the meter shall not register energy at any voltage between 0.8 ∙ U n and 1.1 U n .

Starting

5

The meter shall start and continue to register at U n , PF = 1 (polyphase meter with balanced loads) and a current which is equal to I st .

Units

6

The electrical energy measured shall be displayed in kilowatt-hours or in megawatt-hours.

Putting into use

7

(a) Subject to sub-paragraph (b), measurement may be performed by means of any active electrical energy meter provided that the temperature range to which an active electrical energy meter is exposed is not wider than the range specified by the manufacturer in relation to that active electrical energy meter in accordance with paragraph 1.3.1 and Table 1 in Schedule 1A to these Regulations. (b) Class A active electrical energy meters may not be used when operating outside the temperature range of an upper temperature limit of 30°C to a lower temperature limit of 5°C. (c) The person responsible for installing the active electrical energy meter must determine the correct current range and assess the climatic environment. CONFORMITY ASSESSMENT The conformity assessment procedures specified in the modules in Schedule 1B applicable to active electrical energy meters that the manufacturer can choose between are: (a) B and F; (b) B and D; or (c) H1.