This article will talk about the Energy Meters being used by the Distribution Companies, i.e. Energy Meters used essentially for the end users of electricity.
Broadly there are two types of Utility-scale Energy Meters being used for the end users, viz. CT operated meters and Whole meters.
Broadly meter technical specifications may be classified in below kinds:
- Service Condition
- Meter Construction
- Technical Particulars
- Parameters to be displayed
Let’s talk about these.
- Service Condition:
Generally, Utility requires compliance to below parameters for proper meter performance under its envisaged Service Condition:
- Maximum ambient temperature
- Maximum ambient temperature in shade
- Minimum temperature of air in shade
- Maximum daily average temperature
- Relative Humidity
- Annual rainfall
- Average number of tropical monsoon months per annum
- Seismic level
- Isokeraunic Level
- Maximum wind pressure
- Meter Construction
The meters are generally projection type, dust and moisture proof. The cover is made of Polycarbonate material so as to give it tough and non-breakable qualities. The meter body is type tested for IP51 degree of protection. All insulating materials used in the construction of the meter are substantially non-hygroscopic, non-ageing and of tested quality. All parts that are likely to develop corrosion under normal working condition are effectively protected against corrosion by a suitable method to achieve durable results. Independent sealing provision is made against an opening of the terminal cover and front cover. It is necessary to provide unidirectional screws with two holes for sealing purpose. The meters are pilfer-proof & tamper-proof.
The meters have Polycarbonate transparent base and the transparent cover of Polycarbonate material, which are ultra-sonically welded (continuous welding) so that once the meter is manufactured and tested at the factory; it would not be possible to open the cover at the site except the terminal cover. The meters are completely factory sealed except the terminal block covers. The provision is made on the Meter for at least two seals to be put by DISCOM. The Terminal cover is transparent with one side hinge with sealing arrangement.
A complete metering system does not get affected by the external electromagnetic interference such as the electrical discharge of cables and capacitors, harmonics, electrostatic discharges, external magnetic fields and DC current in AC supply etc. The Meters meet the requirement of CBIP Tech-report 88 (amended up to date). The meters withstand any type of High Voltage and High-Frequency surges, which are similar to the surges produced by induction coil type instruments without affecting the accuracy of the meter. Likewise, the accuracy of the meters do not get affected by the application of abnormal voltage/frequency generating device such as spark discharge of approximately 35 KV.
Generally, DISCOMs do expect Meters to comply below standards:
|Ingress Protection (IP)||Meter Body – IP 55
For outdoor use – Meter is to be sealed in an enclosure confirming IP 55
|IS 13779/ 1999||Specification of AC Static Watt-hour meters, class 1.0 & 2.0.|
|13947 /1993 & IS: 13410||Enclosure Box|
|IS 14697/1999||For CT operated Wh and VARh Meter, Class 0.2s and 0.5s|
|IS 2705/1992||For Transformer|
|IS 13947||Rated service short-circuit breaking capacity (KA) which is equal to ultimate breaking capacity|
- Technical Particulars
While publishing the requirements in the Tender, DISCOMs mention Guaranteed Technical Particulars (GTP) in a specific Annexure or section. Below are some of the key points of GTP:
|Type of meter||LT Whole Meter or CT Operated Meter|
|I-basic: 10 Amp (Generally)
I-max: 60 Amp (Generally)
|Overload capacity||600% of I-basic|
|Dynamic range||0.4% to 600% of I-basic|
|Power supply variation
· Operation Voltage
· Limit Range
|Generally through SMPS|
|Accuracy Class||Class 1 / Class 0.5s / Class 0.2s|
|Voltage Variation||+20% to +30%|
|Minimum Starting Current||–|
|Power Factor Range||–|
|Minimum Starting Current||–|
|Display||· Backlit display
· Continuous display
|Material||· For Base / Terminal Block
· For Meter Cover / Terminal Cover
|Communication Port||RS-232 or Optical Port|
|Real Time Clock (RTC)||RTC with backup battery and Battery life (maintenance free)
· Max drift per year
|Physical water Absorption||–|
|Modulus of Elasticity||–|
|Meter sealing mechanism||–|
|Magnetic Temper||Meter Immunity on AC / DC / Permanent Magnetic field all around the meter|
|No. of Time of the Day (TOD) Time Zones||–|
|MD Reset Mechanism||–|
|Parameters||· Instantaneous Parameters
· Load Survey
· Billing Data
· Temper Events
Generally, the meters are provided with two ports, viz.
- RS 232 or RS 485 (RJ 11 / RJ 45)
- Optical Port
These ports are important for data communication between the meter and any external data reading/storage mechanism.
Generally RS-232 port is used for communication between meter and modem ((GPRS / GSM / EDGE / CDMA / PSTN / LPR). Any Modem connected to this port establishes two-way communication (between Meter and Server) for data reading and changing the meter configurations.
The Optical Port is used for downloading the data locally via handheld unit (HHU) like CMRI, Laptop or PC. Sealing arrangement for both the communication ports is necessary. Optical Port also helps DISCOM officials for changing meter configurations such as TOD, Integration Period, Billing Date Resetting, etc.
The meter shall have 7 or 8 digits (with ± indication), parameter identifier, backlit Liquid Crystal Display (LCD) of minimum 8-10 mm height and wide viewing angle. Auto display cycling push button is also provided. LCD display is suitable to withstand 70 Deg C temperature. Generally, DISCOM specifies what all parameters and information are to be displayed on LCD display.
The meters are capable of performing complete self-diagnostic check to monitor the circuits for any malfunctioning to ensure the integrity of date memory location all the time. The meter shall provide information for unsatisfactory / non-functioning / malfunctioning of the following:-
- Time and date
- All display segments as per the requirement
- Real Time Clock (RTC)
- Non-Volatile Memory (NVM)
Following parameters are generally being displayed:
- Date and time
- Phase Currents
- Phase to Neutral Voltages
- Instantaneous Power Factors Phase wise
- Instantaneous Power Fact
- Cumulative kVAh TOD
- Cumulative kVArh lag/lead
- Maximum Demand (MD)
- Date & Time of last MD reset
- Parameters to be stored
Broadly there are found kinds of parameters being stored in the meter:
- Instantaneous parameters
- Billing parameters (both current billing and historic billing)
- Load Survey
In this post, we talk about the exhaustive list of these parameters, for reference.
Generally, below kinds of tests are necessary to be performed for DISCOM’s acceptance, as may be required by the DISCOM:
- Type Test
All the Type Tests specified in the technical specifications and as per IS: 14697 shall be carried out at laboratories which are accredited by the National Board of Testing and Calibration Laboratories (NABL) of Govt. of India such as CPRI Bangalore / Bhopal, ERDA Baroda, ERTL, etc.
- Acceptance and Routine Tests
- All acceptance tests as per IS: 14697 / 1999 shall be carried out on the meters
- Accuracy Tests
- All routine tests as per IS: 11731 shall be carried out on meter base & cover.
- Transportation Tests
As per a typical scenario
- at least 50% of the samples of the meters shall be tested for error at I-max, I-b and 5% I-b at unity power factor and 50% I-max and 10% I-b at 0.5 Lagging Power Factor besides checking them for starting current.
- This test shall be conducted on ready to install meter i.e. meter cover ultrasonically welded & sealed. After recording these errors, the meters be put in their normal packing and transported for at least 50 km in any transport vehicle such as pick up van, Jeep, etc. on uneven rural roads and then re-tested at all these loads after the transportation.
- The variation in errors recorded before and after transportation shall not exceed 1% at higher loads and 1.5% at loads below Ib.
Below are some of the standards being followed for Meter Testing:
|IEC 60695-10-2||Ball Pressure Test|
|IS 11731(Part-2) 1986||Flammability Test|
|IS:11000(part 2/SEC-1) 198||Glow Wire Test|
|ISO 75/Ae||Heat Deflection Temp (HDT)|
|IS: 15707||Specification for Testing, evaluation, installation & maintenance of AC Electricity Meters-Code of Practice|
Meter supplier is required to submit all obligatory Test Certificates to the DISCOM.
For CT Operated Meters, DISCOMs also specify the Technical Specifications of the Current Transformer.
Further to above, Meter manufacturers also embed Connection Diagrams on the Meter, for ease of Meter Connection.