Power Meters

TABLE OF CONTENTS
• POWER METER
• POLYPHASE POWER MEASUREMENT
• VAR(VOLT-AMP. REACTIVE) METER
• ENERGY(KILOWATT/HOUR) METER
• POWER FACTOR METER
4

POWER(WATT)
METER & POLY-
PHASE POWER
MEASUREMENT
5
P R E P A R E D B Y : -
M U S H A R R A F A Z I Z
F A 1 7 - B E E - 0 2 6

POWER
• Power is defined as the work performed in a specific time or simply a
rate of doing work.
• Electric power is defined as the electric work done or electric energy
dissipated per unit time. It is product of voltage and current i.e. P=VI.
• It is measured in Joules per second, i.e., watts.
6

POWER MEASUREMENT IN
DC CIRCUITS
• As I said earlier, the DC power is the
product of voltage across the load and
current through the load.
• Therefore, the power can be
determined by using voltmeter and
ammeter , by connecting them in any
one of the given arrangements as
shown in figure and hence the power
can be calculated by the product of
these parameters.
7

• In figure (a), the ammeter measures the total current through the circuit and this
current is the sum of current through the load and current through voltmeter. So the
measurement of power includes the power absorption by the meter.
• This is avoided in arrangement (b), but the voltmeter measures the voltage drop
across the ammeter in addition to voltage across the load and hence the error in the
measurement. These errors are called as insertion errors.
• However, these errors can be neglected when 𝑰 𝑽 is compared with I and 𝑽 𝑨
compared with V. So the measured power will coincide with true power.
• Since the voltmeter and ammeter are more sensitive than a wattmeter, the measured
value is more accurate than that obtained by a wattmeter. Therefore, power can be
calculated by the reading obtained by the meter. P = V × I watts
8

POWER MEASUREMENT IN
AC CIRCUITS
• The above method needs two
measuring devices and also requires
some calculations.
• It is also possible to measure the
power directly by a single meter,
called wattmeter.
• It is an electrodynamic instrument
consisting of fixed coils and a
moving coil.
9

WHAT IS POWER(WATT) METER?
• A wattmeter is an electrical instrument which is used to measure the
electric power (in watts) of any electrical circuit.
10

TYPES OF POWER METERS
Single Phase Power
Meter
Such a power meter which is
used to measure the power of
single phase system.
Poly Phase Power Meter
Such a power meter which is
used to measure the power of
poly-phase system i.e. three
phase system.
11

CONSTRUCTION OF WATTMETER
• The internal construction of a wattmeter consists of two coils.
• One of the coil is in series and the other is connected in parallel. The coil that
is connected in series with the circuit is known as the current coil and the one
that is connected in parallel with the circuit is known as the voltage coil.
• These coils are named according to the convention because the current of
the circuit passes through the current coil and the voltage is dropped across
the potential coil, also named as the voltage coil.
• The needle that is supposed to move on the marked scale to indicate the
amount of power is also attached to the potential coil. The reason for this is
that the potential coil is allowed to move whereas the current coil is kept
fixed.
• The mechanical construction of a wattmeter is shown in the previous slide.
14

WORKING OF WATTMETER
• When the current passes through the current coil, it creates an electromagnetic field around the coil.
The strength of this electromagnetic field is directly proportional to the amount of current passing
through it.
• In case of DC current, the current is also in phase with its generated electromagnetic field. The
voltage is dropped across the potential coil and as a result of this complete process, the needle
moves across the scale.
• The needle deflection is such that it is according to the product of the current passing and the
voltage dropped, that is, P = VI.
• This was the case of DC power. We know that the AC power is given by the formula P = VIcosθ, and
we know that this cosθ factor is because of the fact that the current and voltage are not in phase.
• But the question that arises here is that how will a wattmeter measure the AC power and this power
factor? So the wattmeter simply measures the average power in case if AC power is required.
• The measurement principle of wattmeter is shown in the figure below:
15

W O R K I N G O F
P O W E R ( WAT T )
M E T E R
Wattmeter usually consists of two
coils known as Current coil and
Potential coil. The Current coil is
connected in series with the electric
circuit whereas the movable Potential
coil is connected in parallel. The
current flows through the Current coil
generating an electromagnetic field
around the coil. A needle connected
to the potential coil indicates
measurement of the electric power.
16

COILS OF WATTMETER
CURRENT COIL
• A coil which is connected in
series with the load, carries full
load current and produces
indicating torque in
proportional to the current of
measuring quantity, is known
as current coil. It is made of
few turns of thick wire.
POTENTIAL (PRESSURE) COIL
• A coil which connected in
parallel with the load and
produces indicating torque in
proportional to the potential
difference of the measuring
quantity, is known as pressure
coil. It is made of many turns
of fine wire.
17

POLY-PHASE
POWER
MEASUREMENT
18
M U S H A R R A F A Z I Z
F A 1 7 - B E E - 0 2 6

Delta Configuration
(three wire system)
Wye Configuration
(four wire system)
THREE PHASE TYPES
20

POLY PHASE POWER MEASUREMENT
• 2 Elements (watt-meters), Three
Phase Power Measurement
• 3 Elements (watt-meters), Three
Phase Power Measurement
21

THREE PHASE POWER (WATT)
METERS
• Polyphase watt-meter consists of 2 or 3 single-phase watt-meters mounted in the
same package.
• A dual element wattmeter will measure power in a 3 phase 3-wire system regardless
of power factor, voltage or current variations between phases.
• In 3 phase 4-wire system the 3 element types is mostly used.
• If there is unbalanced voltage, only the 3 element is suitable.
22

POLY PHASE POWER MEASUREMENT
• The total power in 2 elements (watt meters) is WT = W1+W2 .
• The total power in 3 elements (watt meters) is WT = W1+W2+W3 .
23

APPLICATIONS OF WATTMETER
As other measuring instrument, watt meters are also used extensively in electrical
circuit measurement.
They are also used in industries to check the power rating and consumption of
electrical appliances.
Electromagnetic watt meters are used to measure utility frequencies.
They are used with refrigerators, electric heaters and other equipment to measure
their power ratings.
24

VAR METER
26
E H T I S H A M
F A 1 7 - B E E - 1 3 4

VAR (VOLT AMPERE REACTIVE) METER
DEFINATION:
The instruments which measure
the reactive power of the circuit are called
varmeter
Reactive Power:
When the voltage and current
are out of phase to each other, such type of
power is known as the reactive power. Reactive
power exists in AC Circuit .The circuit having
inductive or capactive, impedence.

REACTIVE POWER
• Reactive power depends on phase angle between the voltage and the
current.
• Reactive power in the circuit mathematically can be described as
•

REACTIVE & ACTIVE POWER
The active power is the product of the voltage, current and the cosine of the
angle between them. The active power is the real power, and it is measured in watts.
The reactive power is the product of voltage and current and the sine of the angle
between them. The reactive power is the useless power.
Reactive power is symbolized by the letter Q and is measured in the unit of Volt-Amps-
Reactive (VAR).

CLASSIFICATION OF VAR METER
• The var meter can be classified as
1-Single phase var meter
2-Polyphase var meter
• a

1-SINGLE PHASE VARMETERS
Pressure coil
Current coil
load I

1-SINGLE PHASE VARMETERS
(CONSTRUCTION)
The var meter is in which the pressure
coil of the meter is made highly
inductive.
The terms “highly inductive” means, the
voltage of the pressure coils lags at an
angle of 90° with that of the current coil.
Presure coil
Current coil
load current

1-SINGLE PHASE VAR METERS
(WORKING)
• The current which passes through the current coil is the load
current. The load current has a phase difference of 90°
concerning that of the supply voltage, and it is given by the
equation shown below.

ADVANTAGES OF SINGLE PHASE VAR
METER.
It is use for measuring reactive power for single phase
systems.
It can be used for measuring reactive power where
circuit is operating at low voltages.
It can be used in industries where power factor
correction is required.

DRAW BACK OF SINGLE PHASE VAR
METER
• The Single Phase Varmeter gives the incorrect result because of
the presence of harmonics.
• It can not used for measuring reactive power where circuit is operating at
high voltages
• It can not measure reactive power of unbalanced three phase system

2-POLY PHASE VAR METERS
(CONSTRUCTION )
• The two auto-transformers are used to create the phase shifting (which is necessary for
the measurement of reactive power), when connected in open delta configuration.
• Current coils of both the wattmeter are connected in series with supply line 1 and 3.
• While pressure coils are connected in parallel.

WORKING
• 1- Both the auto-transformers can produce maximum of 115.4% of the line voltage.
• One of the end of the pressure coil of wattmeter (marked as one) is connected to 115.4
% of tapping of auto-transformer-2 while other end is connected to 57.7 % tapping of
auto-transformer-1.
• Due to this connection voltage produces across the pressure coil of wattmeter one is
equal to line voltage but shifted by an angle of 90o. The power shown by wattmeter
thus equal to reactive power.

WORKING OF VAR METER
• Similarly the pressure coil of wattmeter 2 is connected
showing same voltage equal to line voltage but differ in phase
and this difference in phase is equal to again 90o. Now the
arithmetic sum of both readings of the watt meters is equal to
total reactive power of circuit

REACTIVE POWER MEASUREMENT IN
THREE-PHASE CIRCUIT
• The single wattmeter method is
used for measuring the power
of the three-phase circuit.
• The current coil of the
Wattmeter is connected to one
phase, and the pressure coil is
connected to the other phase of
the line.

POLY PHASE VAR METER
(ADVANTEGES)
It is useful for measuring reactive power in balance as well as unbalanced three phase
system.
It can used for measuring reactive power where circuit is operating at high voltages
It has massive applications in heavy industry where power factor correction is a major issue.

OVER TO TALHA SAEED
•THANKYOU

ENERGY
(KILOWATT/HOU
R) METER
44
T A L H A S A E E D
F A 1 7 - B E E - 1 0 2

WHAT IS ENERGY WATT-HOUR
METER?
• Energy Meter or Watt-Hour Meter is an electrical instrument that
measures the amount of electrical energy used by the consumers.
Utilities are one of the electrical departments, which install these
instruments at every place like homes, industries, organizations,
commercial buildings to charge for the electricity consumption by loads
such as lights, fans, refrigerator, and other home appliances.

USAGE:
• The basic unit of power is watts and it is measured by using a watt meter. One
thousand watts make one kilowatt. If one uses one kilowatt in one-hour duration,
one unit of energy gets consumed. So energy meters measure the rapid voltage and
currents, calculate their product and give instantaneous power. This power is
integrated over a time interval, which gives the energy utilized over that time period.

TYPES:
• The energy meters are classified into two basic categories, such as:
1-Electromechanical Type Induction Meter
2-Electronic Energy Meter
Electromechanical type Induction meter is the type of Single Phase
Electronic Energy Meter is the type of Three Phase
But today our concern is only with single phase.

CONSTRUCTION:
• The energy meter has four main parts. They are the
1.Driving System
2.Moving System
3.Braking System
4.Registering System

• 1. Driving System – The electromagnet is the main component of the
driving system. It is the temporary magnet which is excited by the
current flow through their coil. The core of the electromagnet is made
up of silicon steel lamination. The driving system has two
electromagnets. The upper one is called the shunt electromagnet, and
the lower one is called series electromagnet.
• The series electromagnet is excited by the load current flow through
the current coil. The coil of the shunt electromagnet is directly
connected with the supply and hence carry the current proportional to
the shunt voltage. This coil is called the pressure coil.
• The centre limb of the magnet has the copper band. These bands are
adjustable. The main function of the copper band is to align the flux
produced by the shunt magnet in such a way that it is exactly
perpendicular to the supplied voltage.

2. Moving System – The moving system is the aluminium disc mounted on the shaft of
the alloy. The disc is placed in the air gap of the two electromagnets. The eddy current
is induced in the disc because of the change of the magnetic field. This eddy current is
cut by the magnetic flux. The interaction of the flux and the disc induces the deflecting
torque.
• When the devices consume power, the aluminium disc starts rotating, and after some
number of rotations, the disc displays the unit used by the load. The number of
rotations of the disc is counted at particular interval of time. The disc measured the
power consumption in kilowatt hours.

3. Braking system – The permanent magnet is used for
reducing the rotation of the aluminium disc. The aluminium
disc induces the eddy current because of their rotation. The
eddy current cut the magnetic flux of the permanent magnet
and hence produces the braking torque.
• This braking torque opposes the movement of the disc,
thus reduces their speed. The permanent magnet is
adjustable due to which the braking torque is also adjusted
by shifting the magnet to the other radial position.

4. Registration (Counting Mechanism) – The main function of
the registration or counting mechanism is to record the
number of rotations of the aluminium disc. Their rotation is
directly proportional to the energy consumed by the loads in
the kilowatt hour.
• The rotation of the disc is transmitted to the pointers of the
different dial for recording the different readings. The
reading in kWh is obtained by multiply the number of
rotations of the disc with the meter constant. The figure of
the dial is shown below.

WORKING:
• The energy meter has the aluminium disc whose rotation determines
the power consumption of the load. The disc is placed between the air
gap of the series and shunt electromagnet. The shunt magnet has the
pressure coil, and the series magnet has the current coil.
• The pressure coil creates the magnetic field because of the supply
voltage, and the current coil produces it because of the current.
• The field induces by the voltage coil is lagging by 90º on the magnetic
field of the current coil because of which eddy current induced in the
disc. The interaction of the eddy current and the magnetic field causes
torque, which exerts a force on the disc. Thus, the disc starts rotating.
• The force on the disc is proportional to the current and voltage of the
coil. The permanent magnet controls Their rotation. The permanent
magnet opposes the movement of the disc and equalises it on the
power consumption. The cyclometer counts the rotation of the disc.

CONCLUSION:
• This type of energy meter is simple in construction and the accuracy is somewhat less
due to creeping and other external fields. A foremost problem with these types of
energy meters is their proneness to tampering, which necessitates an electrical-
energy-monitoring system. These series and shunt type meters are widely used in
domestic and industrial applications.
• Electronic energy meters are accurate, precise and reliable type of measuring
instruments when compared to electromechanical induction type meters. When
connected to loads, they consume less power and start measuring instantaneous.

POWER FACTOR
METER
56
T A L H A S A E E D
F A 1 7 - B E E - 1 0 2

WHAT IS POWER FACTOR METER?
• THE POWER FACTOR METER MEASURES THE POWER
FACTOR OF A TRANSMISSION SYSTEM. THE POWER
FACTOR IS THE COSINE OF ANGLE BETWEEN THE
VOLTAGE AND CURRENT.

TYPES OF POWER FACTOR METER:
• THE POWER FACTOR METER IS OF TWO TYPES:
1.ELECTRODYNAMOMETER
• SINGLE PHASE ELECTRODYNAMOMETER
• THREE PHASES ELECTRODYNAMOMETER
1.MOVING IRON TYPE METER
• ROTATING IRON MAGNETIC FIELD
• NUMBER OF ALTERNATING FIELD

SINGLE PHASE ELECTRODYNAMOMETER
POWER FACTOR METER:
CONSTRUCTION:
MATHEMATICALLY:
The power factor of a circuit can be found out from the wattmeter reading and voltmeter
and ammeter readings suitably connected in the circuit.
Power factor = Wattmeter reading / (Voltmeter reading x ammeter reading).
Power factor = True Power / Apparent Power
This method involves mathematical calculations. Sometimes it is required to measure
the power factor of the circuit instantaneously when the power factor of the load is varying
continuously.

A dynamometer type power factor
meter consists of two fixed
coils FF connected in series carrying
the load current (or a definite
fraction of it) forming the current
circuit, and two identical moving
coils A and B fixed at the nearly
right angle to each other pivoted on
the same spindle forming the
pressure circuit as shown in the
figure.

The current coils FF are wound with thick wire whereas pressure coils A and B are wound with
fine wire. The pressure coils fixed on the same spindle, to which a pointer is attached,
constitutes the moving system.
The pressure coil A is connected across the supply through a non-inductive resistant and
pressure coil B is connected across the supply through highly inductive choke coil of
inductance L. The value of resistance R and inductance L are so chosen that for the main
supply frequency, the current in the two pressure coils A and B is the same.
Thus the fields produced by the two coils are of the same strength. The field produced by the
coil B lags behind the field produced by the coil A slightly less than 90° because of resistance
of the coil. Accordingly while fixing the coil B the plane of this coil is displaced from the plane
of the coil A by the electrical angle which is slightly less than 90°.
However while discussing the action (working) of the instrument it will be assumed that the
phase difference between the two currents flowing through the coils A and B is 90° and same
is the angle between the planes of the coils.
Though power factor meter is an indicating instrument but no controlling torque is provided in
this instrument. The currents are being led into the moving coils A and B by fine ligaments
which exert no control.

WORKING:
Since no controlling torque is provided in this instrument, therefore, when
it is not connected in the circuit, the moving coils will remain in the
position in which these are turned. This will only happen when the
moving system is perfectly balanced.
When the instrument is connected to the load circuit, current flows
through the fixed coils FF and Moving coils A and B, flux is set by the
fixed coils and moving coils.
By the alignment of two fields, torque develops i.e. the resultant field
produced by the moving coils tries to come in line with the field
produced by the fixed coils and torque develops till both of them come
in line with each other. There are three extreme conditions in which this
instrument is connected in the circuit.

1. When power factor of the circuit is unity: In this case, current is in phase with
circuit voltage. The current flowing through potential coil A is in phase with the
voltage which is also in phase with the current flowing through current coil FF.
At the same time, the current flowing through potential coil B lags behind voltage
as well as the current flowing through current coil FF by 90o. Thus pressure
coil A will experience a turning moment so its plane will come in position a parallel
to the plane of the current coil FF. The torque acting on the pressure coil B is zero.
Thus, the pointer indicates unity power factor on the scale.
2.When power factor of the circuit is zero lagging: In this case, current lags behind
the circuit voltage by 90°. Therefore, the current flowing through pressure
coil B will be in phase with the current in current coils FF, both being lagging
behind the circuit voltage by 90°.
The current flowing through pressure coil A will lead the current in current
coil FF by 90°. Thus a turning moment acts on the pressure coil B and brings its
plane parallel to the plane of current coil FF and pointer indicates zero power
factor lagging.

3.When power factor of the circuit is zero leading: In this case current
leads the circuit voltage by 90o. Therefore, the current flowing through
pressure coil A lags the current in current coil FF by 90° and the current
flowing through pressure coil B lags the current in current coil FF by 180°.
Thus field produced by the moving system is just reversed to that in the
case (2). Thus an opposite turning moment acts on the pressure
coil B and brings its plane parallel to the plane of current coil FF and
pointer indicates zero power factor leading.

• For intermediate power factors the moving system of power factor
meter takes up intermediate positions and the pointer indicates the
power factor accordingly.

Power Meters

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Power Meters

Similar to Power Meters (20)

Recently uploaded

Recently uploaded (20)

Power Meters