In September issue of Electrical India, Part – I of this article was published. The remaining portion of the article has been cited here as Part II. The introduction to this part has been kept unchanged in order to give an instant cue to the reader.
Test Requirements For Smart Meters
Type tests cover verification of the following requirements.
Schedule of Type Tests as per IS 16444 (Part 1) & IS 16444 (Part 2)
- Test of Insulation properties:
i) Impulse voltage test
ii) AC High voltage test
iii) Insulation resistance test
- Test of Accuracy Requirements:
i) Test on limits of error
ii) Interpretation of test results
iii) Test of meter constant
iv) Test of starting condition
v) Test of no-load condition
vi) Test of ambient temperature influence
vii) Test of repeatability of error
viii) Test of influence quantities
- Test of Electrical Requirement:
i) Test of power consumption test
ii) Test of influence of supply voltage
iii) Test of influence of short-time over currents
iv) Test of influence of self-heating
v) Test of influence of heating
vi) Test of influence of immunity to earth fault
- Test for Electromagnetic Compatibility:
i) Radio interference measurement
ii) Fast transient burst test
iii) Test of immunity to electrostatic discharges
iv) Test of immunity to electromagnetic HF field
v) Surge Immunity Test
- Test for Climatic Influences:
i) Dry heat test,
ii) Cold test and
iii) Damp heat cyclic test
- Test for Mechanical Requirements:
i) Vibration test,
ii. Shock test.
iii. Spring hammer test,
iv. Protection against penetration of dust and water and
v. Test of resistance to heat and fire
- Test for Load Switch [Applicable only for A.C. Static Direct connected Watt-hour Smart Meter as per IS 16444 (Part 1)]
a. Performance requirements for load switching utilization category UC1 (Test requirements are mentioned in Clause 188.8.131.52.1 of IS 15884).
Category UC1 is applicable to smart meters rated at maximum current up to 100A.
b. Performance requirements for load switching utilization categories UC2 and UC3 (Test requirements are mentioned in Annex G of IS 15884): i. Normal operation, ii. Electrical Endurance, iii. Line to Load Voltage Surge withstand, iv. Fault current making capacity, v. Short-circuit current carrying capacity, vi. inimum Switched current, vii. Dielectric strength
- Test for Data Exchange Protocol
- Tests for Smart Meter Communicability and Smart meter functional requirements are cross referred to IS 15959 (Part 2) / IS 15959 (Part 3).
Significance Of Tests
- Test of Insulation properties: This test shall confirm the design and construction of meter for safety of personal and equipment in normal use and under normal conditions.
i)Impulse voltage test – This test determines the effect of voltage surge due to atmospheric disturbances of very short duration on electrical installation and their individual part. Lightning may produce over voltage on overhead transmission line by direct or indirect stroke.
ii)AC High voltage test – This test verifies the dielectric properties of smart meter.
This test verifies the dielectric properties of smart meter.
- Test of Accuracy Requirements: This tests will verify the metrological requirements of smart meters under normal conditions of use and under the influence of influencing quantities. This test in turn confirms the accurate billing.
i)Test on limits of error – This test ensures the smart meter class of accuracy due to variation of current and power factor.
ii)Interpretation of test results – During Test on limits of error, if the % error of smart meter obtained at various current and different power factors are within the limits, there is no need to displace the zero line to bring the errors within the limits.
iii)Test of meter constant – This test confirms the relation between the test output and the indication in the display shall comply with the marking on the name plate of smart meter.
iv)Test of starting condition – The smart meter shall start and continue to register at the lowest value of current mentioned in the standard.
v)Test of no-load condition – During the test, the test output of the smart meter shall not produce more than one output pulse when 115% of reference voltage applied to the meter and current circuit in open circuit
vi)Test of ambient temperature influence – This test will verify the smart meter is capable of operating at higher or lower temperature without any change of characteristic of component and during this influence the % error of the meter is verified at different load current and power factor. The mean temperature coefficient is computed i.e., the ratio of the variation of the percentage errors to the change of temperature at the reference temperature shall be within the permissible limits.
vii) Test of repeatability of error – This test confirms the smart meter accuracy is repeatable or not at 5% Basic current, Basic current at UPF.
viii)Test of influence quantities – This test will confirm that the smart meter accuracy and variation in % error are within the specified limits under the following influence conditions: – a. Voltage variation, b. Frequency variation, c. Waveform: 10% of third harmonic in the current, d. Reversed phase sequence, e. Voltage unbalance, f. DC component in AC current circuit / DC and even harmonic test (applicable as per IS 13779), g. Auxiliary voltage (applicable as per IS 14697), h. Phase of auxiliary supply voltage by 120º (applicable as per IS 14697), i. Continuous magnetic induction (AC & DC) of external origin
- Test of Electrical Requirement: To verify the electric strength properties of the smart meter and withstand capacity of the smart meter under abnormal conditions.
i)Test of power consumption – To verify the power consumption of the smart meter in the voltage and current circuits are within the permissible limits as per standard.
ii)Test of influence of supply voltage – This test verifies when the smart meter is subjected to influence of supply voltage variations, the meter shall operate correctly and the accuracy and variation in % error shall be within the permissible limits.
iii)Test of influence of short-time over currents – The Short-time over currents may happen to be experienced by the smart meters due to short circuit faults occurred at the consumer premises. Short-time overcurrent shall not damage the meter and the switch shall remain operative. The surroundings of the meter shall not be endangered and protection against indirect contact shall be assured in all cases. After the test, variation of error shall not exceed the specified value as per standard.
iv)Test of influence of self-heating – This test will confirm that the current carrying capacity of cables, size of terminal block, screws used for cables are not over heated during full load condition for longer duration. The variation in error of the smart meter during twenty minutes shall not exceed the specified limits and variation between the minimum and maximum error of the meter shall be within the limit specified in the standard.
v)Test of influence of heating – This test is to confirm the proper operation of meter at different seasons. This test verifies the temperature rise of the meter due to excessive heating and restores the dielectric properties. Test of influence of immunity to earth fault – This test applies to three phase four wire meters. Earth fault condition is simulated in one of the 3 lines – all voltages increased to 1.1 times Vref during 4 hrs. Neutral of MUT is disconnected from Ground terminal of Meter Test Equipment (MTE) & is connected to line of MTE at which Earth fault has to be simulated. In this way 2 voltage terminals of MUT which are not affected by Earth fault are connected to 1.9 times Vref, Current= 0.5Ib & UPF. After the test, smart meter shall show no damage & shall operate correctly.
- Test for Electromagnetic Compatibility (EMC): The smart meter shall be designed in such a way the conducted or radiated electromagnetic disturbance shall not interfere functionally or metrologically with the operation of the meter.
To ensure that the smart meter is electromagnetically compatible, it shall comply with the two following test requirements: 1) Emission tests and 2) Immunity tests Radio interference measurement (Emission): This test ensures the RF emission disturbance (EMI) by conduction or by radiation shall not exceed the permissible limits mentioned in the standard.
Depending upon the way the EMI escapes from the equipment, there are two emission tests as per standards – the conducted emission (CE) test, which measures the EMI that couples on to the other equipment via the power lead of the meter under test, and covers the frequency range from 150kHz to 30MHz; and the radiated emission (RE) test, that measures the EMI which escapes into the free space from the meter under test. It covers the emission over the frequency range 30 MHz to 1000 MHz.
Immunity tests: The immunity tests confirm that the meter is susceptible to both conducted and radiated RF electromagnetic disturbances. The conducted disturbances are – Fast transient burst, Electrostatic discharge and Surge and the radiated disturbances are Electromagnetic HF fields.
Fast transient burst test: The purpose of this test is to verify the immunity of the smart meters against Fast transient bursts of very short transients generated by the switching of small inductive loads, relay contact bouncing (conducted interference) or switching of HV switchgear – particularly SF6 or vacuum switchgear (radiated interferences). This test ensures proper functioning and operation of the smart meter, when the Fast transient burst generated from source is coupled into the meter via power lines.
Test of immunity to electrostatic discharges: The Electrostatic Discharge (ESD) scenario is experienced when an operator is walking across a carpet of artificial fiber in a low humidity condition, a person can build up a charge of several thousand volts and also the ESD is generated from the moving objects. This disturbance simulates the type of high voltage interference that occurs when an operator touches the user accessible parts of smart meter after being charged to a high potential. This test ensures proper functioning and operation of the smart meter, when the ESD generated from one or another source is passed into the meter via user accessible parts.
Surge Immunity Test: The purpose of this test is to verify the immunity of the smart meter subjected to transient caused by over voltages from switching in the power network and lightning strokes (direct or indirect). This test ensures proper functioning and operation of the smart meter, in case Surges generated from the source and is passed into the meter via power lines.
Test of immunity to electromagnetic HF field: Electromagnetic (EM) radiations generated by sources like small handheld radio transceivers, fixed station radio and TV transmitters, vehicle radio transmitters etc.
This test ensures the proper operation and functioning of the smart meter under Electromagnetic HF fields present in the surrounding environment.
- Test for Climatic Influences: This test is to ensure proper functioning of the meters in different locations and under climatic conditions.
i)Dry heat test – This test determines the ability of components used in the meter at high temperature.
ii)Cold test – This test determines the ability of components used in the meter at low temperature.
iii)Damp heat cyclic test – This test determines the ability of components used in the meter under high humidity conditions when combined with cyclic temperature changes.
After each of the climatic tests, the meter shall show no damage and change of the information. These tests should not affect the functioning and operation of the smart meter.
- Test for Mechanical Requirements:
i)Vibration test – The smart meter is likely to be subjected to vibration environment during transportation and during operating condition. Hence the immunity of vibration is important to prove the reliability and performance of smart meter. The acceptance criteria for this test are that the smart meter shall show no change of information and variation in % error shall be within the permissible limits as per standard.
ii)Shock test – This test simulates the effects of relatively infrequent non-repetitive mechanical shocks likely to encounter by the smart meter in operating condition or during transportation. The acceptance criteria for this test are that the smart meter shall show no change of information and variation in % error shall be within the permissible limits as per standard.
iii)Spring hammer test – The purpose of this test is determine the ability of the meter to withstand a kinetic energy of 0.22 Nm on the outer surfaces of the meter cover (including windows) and on the terminal cover.
iv)Protection against penetration of dust and water – The smart meter shall have adequate degree of protection against ingress of dust and water. This test should not affect the functioning of the meter.
v)Test of resistance to heat and fire – The terminal block, the terminal cover and the meter case shall ensure reasonable safety against spread of fire. They should not be ignited by thermic overload of live parts in contact with them. The smart meter shall confirm to the requirements of the standard.
- Test for Load Switch [applicable only as per IS 16444 (Part 1)]
The load switch test ensures the performance of the load switch used for remote connect/disconnect. Load switch tests shall be carried out as per the utilisation category.
a.Performance requirements for load switching utilization category UC1 – This test verifies that the smart meter is capable of make and break at Vref, Imax with a linear resistive load for 3000 operations and at Vref, Ib, 0.4 inductive power factor for 3000 operations.
b.Performance requirements for load switching utilization categories UC2 and UC3 – The smart meter load switches shall be rated to carry maximum current continuously under normal operating conditions and to withstand the switching transients during make and break operations. The following tests on the smart meter shall be carried out as per the standard.
iii)Line to Load Voltage Surge withstand
iv)Fault current making capacity
v)Short-circuit current carrying capacity
vi)Minimum Switched current
The above said tests will confirm the following properties of load switch.
- Capable of making and breaking negligible currents of specified values – Capable of making, breaking and carrying rated currents of specified values;
- Capable of making into fault currents with specified value and under specified conditions;
- Capable of carrying short-circuit currents of specified value for a specified time period and under specified conditions;
- Not required to provide safety isolation properties in the open contact position. These are requirements for the installation mains isolation switch; and
- Not required to break overload currents or short-circuit currents. These are the requirements for fuses and circuit breakers that are normally used to protect the installation.
- Data exchange protocol
The DLMS data exchange protocol is chosen for smart meters including specific requirements for Smart Meters for the application layer as per IS 15959 (Part 1, 2 & 3). This helps in interoperability of meters with different makes of meters.
The purpose of DLMS protocol test is to ensure that the protocol is implemented in the meter and data from various object identification systems (OBIS) are as per standard. The data exchange protocol chosen for Smart Meter shall be as per IS 15959 (Part 2 for direct connected Smart meters & Part 3 for transformer operated Smart meters).
- Tests for Smart Meter Communicability – The communication modules for WAN/NAN/IHD shall be approved by designated agency authorized by DoT and shall have Equipment Type Approval (ETA) as mentioned in the smart meter standards. The standard provides for use of suitable communication technologies in the design of smart meters. However, to assess the communication capability of smart meter a few tests including a test for end to end communication capability and functional requirements are identified and included in relevant standard of smart meter.
Necessity of Testing
Testing will ensure the following: i) Insulation properties, ii) Accuracy, iii) Reliability, iv) EMC, v) Environment hardness, vi) Mechanical durability and vii) Safety
Independent testing ensures that all Smart meters are subject to the same standards and requirements which gives confidence both to consumer and utility. Also allows the interoperability of the meters of different manufacturers.
CPRI Laboratory is accredited by NABL as per ISO/IEC 17025 and BIS recognised.
Considering the importance and necessity of Smart meters, it is required to install tested and proven meters in the field to carry out the required intended functions accurately, reliable operation, safety of personnel, equipment and also minimise the revenue losses to the utilities.
The authors wish to thank the management of Central Power Research Institute (CPRI), Bangalore for permitting to publish this paper. The facility provided by Metering and Utility Automation Division, CPRI is greatly acknowledged.
V. Suresh holds Bachelor’s degree in Electronics & Communication Engineering and Master of Business Administration in Finance from Bangalore University. He is with Central Power Research Institute for 30.5 years and presently working in Metering & Utility Automation Division.
V. Harinath Babu holds Bachelor’s degree in Electronics. He is having experience of 35 years in academic and Central Power Research Institute and is heading Metering & Utility Automation Division there.