Energy Meter - Working Principle - Construction - Types of Energy Meter - Energy Meter Symbol - Applications of Energy Meter
Energy Meter
Energy meters are the integrated instruments which measures a quantity of electric energy supplying to the electric circuit in a specific time. These energy meters displays the quantity of electrical energy consumed by the user in Kilowatts/hour (KWH). Energy meters have its different names according to its function and working
principle. These meters are called as electricity meters, electric
meters, electrical meters, etc.
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| Energy Meter |
Symbol of Energy Meter
The Symbol of Energy Meter is a circle in which Kwh is written because Energy meter measures the electricity in Kwh like the image shown below. The Symbol of Energy meter is used in many electrical drawings and in many circuit diagrams of electrical and electronics to identify that this is a Symbol of Energy Meter and it is connected in this scheme so that the engineers come to know the symbol of energy meter and its connection scheme.
Types of Energy
Meters
Energy meters consist
of various types which are given below:
- Electric Motor Energy Meters
- Electrolytic Energy Meters
Electric Motor Energy
Meters
Electric Motor Energy
Meters are known by its name that these energy meters consist
of a small electric motor in it. Different kinds of electric motors are
used in these energy meters. Some energy meter uses mercury motor, commutator
motor, induction motor in it. The mercury motor energy meters are
only used on D.C Circuits whereas the induction motor energy meters
are used only on A.C Circuits and the commutator motor energy meters are
used on both A.C Circuits and D.C Circuits.
The energy meters
used for D.C circuits provides readings in the form of amp-hours or in watt
hours. In this mechanism of readings, moving system revolve continuously.
The speed of rotation is directly proportional to the current. The rotating
system is controlled by the permanent magnet which is placed nearly to
the moving system and produce eddy currents in some parts of rotating
system.
Ampere-hour Mercury
Motor Energy Meter
It consists of a
copper disc mounted on a spindle. The disc revolves between a pair of permanent
magnets and the free space is filled with mercury. One of the magnets is used
for braking for the rotation of disc.
Working Principle of
Ampere-hour Mercury Motor Energy Meter
The working principle of ampere hour mercury motor energy meter is that the measuring current
is led into the disc through the mercury and flows radially to the center of
the disc where it passes out to the external circuit through the spindle and
its bearings. The current flows only on right hand side of the disc. The magnetic
field of the permanent magnet M2 will exert a force on the right-hand side
of the disc which carries current. The direction of the force can be found by
the Fleming’s Left-hand rule (F= Bil Newton).The driving torque
Td is produced by the force. It cuts the field of left hand-side magnet M1 and
eddy current is produced in it.
Watt-hour Mercury
Motor Energy Meter
If the permanent
magnet M2 of the ampere hour meter is replaced by a wound electromagnet and
connect to the supply this results a watt hour energy meter. The exciting
current of this electromagnet is proportional to the voltage. The
disc has radial slot cuts in it.
Commutator Motor Energy
Meters
These energy meters are known as watt hour meters/watt hour
energy meters. These meters are also known as Elihu Thomson meters
according to its working principle. These meters consist of ironless motors
consists of a wound winding armature and a commutator.
Working Principle of Commutator Motor Energy Meters
The working principle of motor type energy meter is that there are two fixed coils (C1 and C2) placed on left- and
right-hand side of the armature. Each coil consists of a few turns of thick
copper wire connected in series with the supply. These two coils are connected
to the main supply in the circuit. The electromagnetic field is produced in
these two coils. This electromagnetic field is proportional to the
current to be measured. The armature rotates with the help of this
electromagnetic field. The armature coils produce current in it and provides
this current on its commutator. This current is proportional to the supply
voltage. The operating torque is produced due to the reaction of
electromagnetic field and the armature coils. Braking torque is produced due to
the eddy currents produced in a disc which is fixed on a spindle of the
same armature between the two brake magnets (permanent magnets). When the speed
of the disc reached on its steady position then the braking torque and
operating torque becomes equal to each other and the revolution of the disc is
proportional to
=
to the total energy in the circuit.
Induction Type Single Phase Watt-hour
Energy Meters/Single-Phase Energy Meters
Induction type energy meters, Single
phase energy meters are most commonly used as A.C meters in domestic and
industrial installations. These energy meters measures electric power in kilo-watthours.
These induction motor energy meters are designed for single phase electric circuits. In these energy meters, brake magnets make eddy currents in the disc
which revolves continuously through a fraction of changing.
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| Single Phase Energy Meter |
Construction
The construction of energy meter is that it consists of two electromagnets M1 and M2, one magnet M1 is
excited by line current and is known as series magnet. This electromagnet
produces alternating flux φ1. This flux is proportional to the phase with line
current whereas the second magnet M2 is known as shunt magnet. This
electromagnet is connected to the supply line and its current is proportional
to the supply voltage and produces a lagging flux φ2.Major portion of this flux
is useless and a few amount of this flux is useful and it passes through the
disc D.
Working Principle of Single-Phase
Energy Meters
The working principle of the induction type single phase energy meter is that the two fluxes φ1 and φ2 of the electromagnets M1 and M2
induce emf’s in the disc which produces eddy currents in the disc. These two
fluxes and the eddy current reacts each other and produces driving torque on
the disc. The braking torque is produced by the electromagnets M1 and
M2.The disc achieves a steady speed when the driving torque and braking torque
becomes equal to each other then,
The total number of uprisings in a given period
is
proportional to
(the
electric energy consumed).
Electrolytic Energy Meter
Electrolytic Energy meter
is an ampere-hour energy meter and is used in only D.C circuits. Their readings
are incorrect when these meters are used on other voltage readings. These
energy meters are not able to use on A.C circuits. These instruments can be
used on AC circuits by using a small rectifier unit in it. These
energy meters works according to the Faraday law of electrolysis. These energy
meters are simple, cheap, accurate in small loads. These energy meters are not
effected by stray magnetic fields and from friction errors.
Applications of Energy Meters
Energy meters
are widely used in domestic areas for the measurement of electric power
consumed by the customers and these energy meters are commonly used in industrial
sector for controlling the electric power of various machinery according
to its reading and for measurement of electric power.
