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ELECTRO-MECHANICAL METER FOR DISTRIBUTION UTILITY ENERGY MEASUREMENT

What is an electro-mechanical meter principle of operation?

In any electric distribution utility, energy is measured by means of the energy meter (watt-hour-meter) in most cases.  Energy meter which is an integrating instrument accounts the two main factors needed to measure energy, electrical quantities (v, i,) and time(t). The main principle used in watt-hour meters is the “Ferrari Principle”  formulated in 1884 while the induction watt-hour meters later was invented during 1889.
An electromechanical / induction-type energy meter, the most widely used energy meter in most utilities, for over a century, works on the principle that when a current carrying conductor is acted on by a magnetic field, the force which it experiences is proportional to the current and the field.
It was previously discussed that the operating principles of a watt-hour meter is mainly based on four major systems; the driving, moving, braking and registering.
• Driving system consisting of two electromagnets
• Moving system consisting of an aluminium disc
• Braking system consisting of a permanent magnet
• Registering system consisting of gear train and counter

Type of Meters
According to Connection
Bottom (A) type Meter
• A kWh meter where its terminal connection casing is attached parallel to the base of the meter. The suffix “A” means bottom type which usually found in meter form number and meter type number. (e.g. form 5A, VM63A)        

Socket Type Meter
• A kWh meter where its terminal jaws are located below the base of the meter that needs socket jaws for installation. The suffix “S” means socket type which usually found in meter form number and meter type number. (e.g. form 5S, VM63S)
According to Sensing Mechanism

Self-Contained (SC) Meter
• A kWh meter that measures energy in a certain loads and can sustain greater currents, such as 100 amps, 200 amps.
• Meter class: class 100 and class 200
• Larger current coil cross-section conductor.

Instrument Rated (IR) Meter
• A kWh meter that measures energy in a certain loads with the help of an instrument transformer such as current and potential transformer.
• Meter class: class 10, class 20.
• With pilot lamp for 3-phase meter.
• Smaller current coil cross-section conductor.

Maximum demand
The highest demand measured over a selected period of time, such as one (1) month.

Why utility charged maximum demand?
 The cost of supplying electricity to a customer can be separated into two broad categories.
• Cost of energy – oil, coal, gas, etc. to produce kilowatt-hours.
• Cost of equipment – generators, transmission & distribution lines and transformers.
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