Conventional Meters used to read only one parameter – either Current or Voltage or Power Factor (essentially phase angle). Fundamentals of Current measurement, voltage measurement and PF measurement lead to the invention of “Energy Meters”. After Electricity got commercialised in 1880, DC Energy Meters were introduced into the market in 1888 by General Electric Company. Later in 1894, AC Energy Meters were introduced by the Westinghouse Electric Company. The largest source of long-term errors in the meter is a drift in the preamp, followed by the precision of the voltage reference. Both of these vary with temperature as well and vary wildly because most meters are outdoors. Such characteristic and meter design pushed for the need of more efficient Electronic Meters (essentially solid state).

Today, metering and instrumentation have evolved to a great extent. Meter standards, accuracy, error logs, data logs, relay tripping – all such functionalities have been embedded meticulously.

What all different kinds of purposes do the Energy Meters serve?

  • Energy accounting
    • Electricity bill reconciliation
      • Demand
      • Total Energy consumption
      • Power factor
    • Specific Energy Consumption
  • Network performance
    • Network loss calculations
    • Phase balancing
    • Feeder loading
  • Asset performances
    • Asset-level energy consumption benchmarking
    • Trend-line for seasonality impact
    • Trend-line for production impact
    • Asset up time
    • Asset maintenance

 

 

 

Energy Meters are meant to read various electrical parameters (RMS values) such as

  • Voltage (L-L and L-N)
  • Current (Phase-wise)
  • Power (Phase-wise KW, KVA & KVAr)
  • Maximum Demand (KW & KVA)
  • Energy (Import/Export KWh, KVAh & KVARh)
  • Power Factor (both Leading and Lagging)
  • Frequency
  • Phase Angle
  • Harmonics (Individual and Total Harmonic Distortion)

Further to above, they can also read below parameters:

  • Load ON/OFF Hours
  • Power ON/OFF Hours

Below are configurable inputs to the Energy Meters:

  • CT Ratio
  • PT Ratio
  • Baud Rate
  • Parity
  • Meter ID

 

So, how do we connect these meters?

 

 

Brief note on Multifunction Meters (Panel Meters)

  • They are generally 1-Phase, 2-wire and 3-Phase, 4-wire
  • Smaller in size
  • Easy to install in a panel
  • Do not follow any standards/guidelines for the list of reading parameters
  • Available off-the-shelf in the market
  • Cost effective
  • Available for accuracy class 1, 0.5s and 0.2s
  • They cannot read tariff data
  • They cannot store billing related data
  • Generally these meters are CT operated
  • Generally, they are either 96×96 or 48×96 in size
  • Front facia is IP 54 and terminal side is IP 20
  • Commonly, it’s burden is 3-5 VA
  • It can be operated over Auxiliary power supply of 80-300 V AC or 24-60 V DC
  • communicate over RTU ModBus protocol via RS-485 or RS-232 port

 

Brief note on Utility Meters

  • They are available in configuration of – 1-Phase, 2-wire; 3-Phase, 3-wire; and 3-Phase, 4-wire
  • Larger in size
  • Costly
  • Follows IS 15959 standards
  • Build in sync with the required parameter inclusion and guidelines by the DISCOMs
  • They can store Billing Data for 12 billing cycles
  • They are designed to provide and store tariff related data
  • It has configurable tariff slots
  • Both CT operated and whole-current meters are available
  • Communicate over ASCII or DLMS (Device Language Message Specification) protocol via RS-232 and optical reader
  • It can give a log details of the stored data

 

Meters are being instruments, they require to be calibrated periodically. Energy meters also poses complexities in terms of its microcontroller firmware that reads various electrical parameters and the board that is capable to stores a certain amount of thus read data, and in many cases command the relay for load disconnect function. Utilities/DISCOMs publish their requirements for various applications (domestic consumers, commercial consumers, industrial consumers, energy accounting, etc.). Meter manufacturers are required to adhere to these criteria.

 

Similar to Energy Meters, in the subsequent posts, we shall talk about other such assets.

 

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