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Instrumentation and
Automation of Power Plant

Instrumentation and Automation of Power Plant.pptx

Types of measurements
• Mechanical
• Pressure
• Temperature
• Air flow
• Coal handling
• Fluid flow
• Electrical
• Voltage
• Current
• Power
• Frequency
• Power factor

• Moving coil Instrument
• PMMC ( Permanent Magnet Type)
• Dynamometer Type
• Moving Iron-instrument
• Attraction Type Iron-Instrument
• Repulsion Type Iron-Instrument
• Thermal Instrument
• Hot wire Type Instrument
• Thermocouple Type Instrument
• Electronic Instrument
• Induction Instrument
• Rectifier Instrument
Classification of Voltmeter and Ammeter

Permanent Magnet Moving Coil (PMMC)

PMMC
• when the moving coil instrument is connected in the circuit, operating
current flows through the coil.
• This current carrying coil is placed in the magnetic field produced by the
permanent magnet and therefore, mechanical force acts on the coil.
• As the coil attached to the moving system, the pointer moves over the scale.
It may be noted here that if current direction is reversed the torque will also
be reversed since the direction of the field of permanent magnet is same.
• Hence, the pointer will move in the opposite direction, i.e it will go on the
wrong side of zero.
• In other words, these instruments work only when current in the circuit is
passed in a definite direction i.e. for d.c only.
• So it is called permanent magnet moving coil instruments because a coil
moves in the field of a permanent magnet.

MOVING IRON INSTRUMENT
• Attraction type moving iron instrument
• The current to be measured is passed through
the fixed coil. As the current is flow through
the fixed coil, a magnetic field is produced.
• By magnetic induction the moving iron gets
magnetized. The north pole of moving coil is
attracted by the south pole of fixed coil.
• Thus the deflecting force is produced due to
force of attraction.
• Since the moving iron is attached with the
spindle, the spindle rotates and the pointer
moves over the calibrated scale.
• But the force of attraction depends on the
current flowing through the coil.

• Repulsion type moving iron
instrument
• The basic principle behind the
working of repulsion motor is that
“similar poles repel each other.”
• This means two North poles will
repel each other. Similarly, two
South poles will repel each other.
• When the repulsion motor winding
is supplied with single-phase AC,
it produces a magnetic flux along
the direct axis

DYNAMAOMETER
• These instruments are the modified form of
permanent magnet moving coils type.
• Here operating field is produced by a
permanent but by another fixed coil.
• The moving system and the control system are
similar to those of permanent magnet type.
• Such instruments can be used for both a.c and
d.c circuits.
• They can be used as ammeters and voltmeters
but are generally used as wattmeters.

Construction of Dynamometer type instruments
• A dynamometer type instrument essentially consists of a fixed coil and a
moving coil.
• The fixed coil is split into two equal parts which are placed close together
and parallel to each other.
• The moving coil is pivoted in between the two fixed coils.
• The fixed and moving coils may be excited separately or they may be
connected in series depending upon the use to which the measurement is put.
• The moving coil is attached to the moving system so that under the action of
deflecting torque, the pointer moves over the scale.
• The controlling torque is provided by two springs which also serve the
additional purpose of leading the current into and out of the moving coil.
• Air friction damping is provided in such instruments.

Working of Dynamometer type instruments:
• When instrument is connected in the circuit, operating currents flow
through the coils.
• Due to this, mechanical force exists between the coils. The result is
that the moving coil moves the pointer over the scale.
• The pointer comes to rest at a position where deflecting torque is
equal to the controlling torque.by reversing the current, the field due to
fixed coils is reversed as well as the current in the moving coil, so that
the direction of deflecting torque remains unchanged.
• Therefore, such instruments can be used for both d.c and a.c
measurements.

Power Factor Meter
• The power factor meter measures the power factor of a transmission
system. The power factor is the cosine of the angle between the
voltage and current. The power factor meter determines the types of
load using on the line, and it also calculates the losses occur on it.

Power Factor Meter Working Principle
• The basic working principle of power factor meter is similar to that of
dynamometer type wattmeter i.e. when the field produced by moving
system tries to come in line with the field produced by the fixed coil,
deflecting torque is exerted on the moving system which deflects the
pointer attached to it (the moving system)

Electricity meter
• Electric meter or energy meter is a device that measures the amount of
electrical energy consumed. The most common unit of measurement
on the electricity measurement is the kilowatt hour [kWh], which is
equal to the amount of energy used by a load of one kilowatt hour over
a period of one hour.

Construction of Energy Meter
• Driving system
• It consists of a series magnet and a shunt magnet. The coil of the series magnet
is excited by load current while that of the shunt magnet is excited by a current
proportional to the supply voltage. These two coils are respectively referred as
current coil and potential coil (or pressure coil) of the energy meter.
• Moving system
• It consists of a freely suspended, light aluminum disc mounted on an alloy
shaft and placed amidst the air-gap of the two electromagnets.

• Braking system
• It consists of a position-adjustable permanent magnet placed near one edge of
the disc. When the disc rotates in the gap between the two poles of the brake
magnet, eddy currents are set up in the disc. These currents react with the
brake magnet field and provide the required braking torque damping out the
disc motion if any, beyond the required speed.. The braking torque can be
adjusted as required by varying the position of the braking magnet.
• Recording system
• It is a mechanism used to record continuously a number which is proportional
to the revolutions made by the disc. Thus it is the counter part of the pointer
and scale of indicating instruments. The shaft that supports the disc is
connected by a gear arrangement to a clock mechanism on the front of the
meter. It is provided with a decimally calibrated read out of the total energy
consumption in KWh.

Digital Frequency Meter
• A digital frequency meter is an electronic instrument that can measure
even the smaller value of frequency up to 3 decimals of a sinusoidal
wave and displays it on the counter display. It counts the frequency
periodically and can measure in the range of frequencies between 104
to 109 hertz. The entire concept is based on the conversion of
sinusoidal voltage into continuous pulses ( 01, 1.0, 10 seconds) along a
single direction.

Construction of Digital Frequency Meter

• The main components of digital frequency meter are
• Unknown Frequency Source: It is used to measure the unknown value of input signal frequency.
• Amplifier: It amplifies low-level signals to high-level signals.
• Schmitt Trigger: The main purpose of the Schmitt trigger is to convert the analog signal into a digital
signal in a pulse train form. It is also known as ADC and basically acts as a comparator circuit.
• And Gate: The generated output from AND gate is obtained only when the inputs exist at the gate. One
of the terminals of the AND gate is connected to Schmitt Trigger output, and another terminal is
connected to a flipflop.
• Counter: It operates based on the clock period, which starts from “0”. One input is taken from the
output of the AND gate. The counter is constructed by cascading many flip flops.
• Crystal Oscillator: When a DC supply is given to a crystal oscillator (frequency of 1MHz) it generates
a sinusoidal wave.
• Time-Based Selector: Depending on reference the time period of signals can be varied. It consists of a
clock oscillator which gives an accurate value. The clock oscillator output is given as input to Schmitt
trigger which converts sinusoidal wave into a series of a square wave of the same frequency. These
continuous pulses are sent to frequency divider decade which is in series that are connected one after
the another, where each divider decade consists of a counter decade and the frequency is divided by 10.
Each decade frequency divider provides respective output using a selector switch.
• Flip Flop: It provides output based on input.

Working Principle
• When an unknown frequency signal is applied to the meter it passes on to
amplifier which amplifies the weak signal.
• Now the amplified signal is now applied to Schmitt trigger which can convert
input sinusoidal signal into a square wave.
• The oscillator also generates sinusoidal waves at periodic intervals of time, which
is fed to Schmitt trigger.
• This trigger converts sin wave into a square wave, which is in the form of
continuous pulses, where one pulse is equal to one positive and one negative value
of a single signal cycle.
• The first pulse which is generated is given as input to the gate control flip flop
turning ON AND gate.
• The output from this AND gate count decimal value.
• Similarly, when the second pulse arrives, it disconnects AND gate, and when the
third pulse arrives the AND gate turns ON and the corresponding continuous
pulses for a precise time interval which is the decimal value is displayed on the
counter display.

Non electrical parameters
• Flow of feed water, fuel, air and steam with correction factor for
temperature
• Steam pressure and steam temperature
• Drum level measurement
• Radiation detector
• Smoke density measurement
• Dust monitor.

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Instrumentation and Automation of Power Plant.pptx

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