What is Electric Meter

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What is Electric Meter ?
An electric meter or energy meter is a device
that measures the amount of electrical energy
supplied to or produced by a residence, business
or machine.The most common type is more properly
known as a kilowatt hour meter or a joule meter.
When used in electricity retailing, the utilities
record the values measured by these meters to
generate an invoice for the electricity. They may
also record other variables including the time
when the electricity was used.The most common
unit of measurement on the electricity meter is
the kilowatt hour, which is equal to the amount
of energy used by a load of one kilowatt over a
period of one hour, or 3,600,000 joules.
ElectroMechanical Meters
The electromechanical induction meter operates by
counting the revolutions of an aluminium disc
which is made to rotate at a speed proportional
to the power. The number of revolutions is thus
proportional to the energy usage. It consumes a
small amount of power, typically around 2
watts. The metallic disc is acted upon by two
coils. One coil is connected in such a way that
it produces a magnetic flux in proportion to the
voltage and the other produces a magnetic flux in
proportion to the current. The field of the
voltage coil is delayed by 90 degrees using a lag
coil. This produces eddy currents in the disc and
the effect is such that a force is exerted on the
disc in proportion to the product of the
instantaneous current and voltage. A permanent
magnet exerts an opposing force proportional to
the speed of rotation of the disc - this acts as
a brake which causes the disc to stop spinning
when power stops being drawn rather than allowing
it to spin faster and faster. This causes the
disc to rotate at a speed proportional to the
power being used.The type of meter described
above is used on a single-phase AC supply.
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SOME PHOTOS OF KWH METERS
FIGURE 1
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ELECTROMECHANICAL METER
VOLTAGE COIL
Voltage coil should have 220V(110V) othervise
rotor wouldnt spin.
ROTOR
CURRENT COIL
Rotor speed depens on how much current passes
through between nodes 2 and 1 current coil)
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2
3
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FIGURE 1
NEUTRAL LINES COME FROM HOME AND NEUTRAL LINE
COMES FROM ELEC. COMPANY. THEY ARE CONNECTED TO
SAME NODE
HOT LINE COMES FROM ELECTRIC COMPANY
HOT LINE COMES FROM HOME DISTRUBITION (FUSE) BOX
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Reading KWH Meters
The aluminium disc is supported by a spindle
which has a worm gear which drives the register.
The register is a series of dials which record
the amount of energy used. The dials may be of
the cyclometer type, an odometer-like display
that is easy to read where for each dial a single
digit is shown through a window in the face of
the meter, or of the pointer type where a pointer
indicates each digit. It should be noted that
with the dial pointer type, adjacent pointers
generally rotate in opposite directions due to
the gearing mechanism. The amount of energy
represented by one revolution of the disc is
denoted by the symbol Kh which is given in units
of watt-hours per revolution. The value 7.2 is
commonly seen. Using the value of Kh, one can
determine their power consumption at any given
time by timing the disc with a stopwatch. If the
time in seconds taken by the disc to complete one
revolution is t, then the power in watts is
. For example, if Kh 7.2,
as above, and one revolution took place in 14.4
seconds, the power is 1800 watts. This
method can be used to determine the power
consumption of household devices by switching
them on one by one. Most domestic electricity
meters must be read manually.
How does your electric company biils you ?

• As I mentioned above, the register is a series of
  dials which record the amount of energy used.
• Reading example
• Consider your counter (register) is 35200 for
  this month.
• Your counter (register) was 34800 last month.
• That means 35200- 34800 400 kWh you used.
• Electric companies have money constant for 1 KWH.
  In my country it is 0.2. you can see it on the
  bill.
• If you multiply kWh used by this constant and add
  standard taxes (you can see on the bill) you will
  get the exact bill amount.
• In this situation, 400x0.2 80 taxes

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BASIC ELECTRIC PRINCIPLES
There are two elertrical currents.First one is
Alternating current (AC) and the second one is
Direct Current (DC). Home appliances and KWH
meter use AC as power source. But AC is more
complicated than DC. Thats why i will explain
only DC. We would use only estimation not the
exact values.
Ohms Law
V Voltage Source ( your electric company
power source) - Volt I Current passes through
load and come back to the voltage source -
Amps R Resistor (ohmic load) - Ohm P Power
Watt (1000W 1kW)
V I X R P V x I

• Some countries use 110V voltage level
• Some countries use 220V voltage level

Example If you use five standard light bulbs
(100W) at your home. The current I would be
100x5220xI ? I500/220 2.27 Amps. This is not
exact value but estimation. That means 2.27Amps
pass through your meters current coil.
Another Example If you use 3000W electric
heater at your home. The current of electric
heater would be 3000/22013.6Amps. And the
resistance of electric heater is R220/13.616.1
ohms.
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Some Electrical Components You Should Know
This is double pole circuit breaker. It will be
in fuse box or meter cupboard. It is used for
protection of main cables. It will be in Meter
cupboard or Fuse Box. If it is in Fuse box, the
E.L.C.B has to be in meter cupboard or vice versa.
This is one pole circuit breaker. It is used for
protection of cables. It will be in Fuse Box.
Note If E.L.C.B is in meter cupboard, Double
pole circuit breaker should be in fuse box or
vice versa.
This is E.L.C.B means Earth Leakage Circuit
Breaker. This component is used for prevention of
hazard electric shock. It will be in Meter
cupboard or Fuse Box. In old technologies it is
larger. Now its smaller.
This is E.L.C.B means Earth Leakage Circuit
Breaker. This component is used for prevention of
hazard electric shock. It will be in Meter
cupboard or Fuse Box. This is new technology
E.L.C.B. Its same but smaller.
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KWH Meter Wiring Diagram
Main Hot line comes from electric comany
Main Circuit Breaker
E.L.C.B or Double pole circuit breaker
A
Kwh meter
Main Neutral line comes from electric comany
Neutral line comes from home fuse box
Hot line comes from home fusse box
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What is Transformer ?
Transformer is a device that transfers electrical
energy from one circuit to another through
inductively coupled electrical conductors. A
changing current in the first circuit (the
primary) creates a changing magnetic field. This
changing magnetic field induces a changing
voltage in the second circuit (the secondary).
This effect is called mutual induction. If a load
is connected to the secondary circuit, electric
charge will flow in the secondary winding of the
transformer and transfer energy from the primary
circuit to the load. In an ideal transformer, the
induced voltage in the secondary winding (VS) is
a fraction of the primary voltage (VP) and is
given by the ratio of the number of secondary
turns to the number of primary turns
Core
Primary winding
Secondary winding