2. Major Electrical Equipment
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• Generators
➢ Converts mechanical energy to
electrical energy. The size of the
generator determines the size of
the power plant.
Generator performance parameters:
i. Rated capacity
ii. Rated speed
iii. Rated voltage
iv. Power factor
v. Efficiency
vi. Temperature rise
vii. Cooling system
viii. Number of phases
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• Exciters and voltage regulators
➢ Excitation system provides field current to the rotor winding of a generator. Well-designed
excitation systems provide reliability of operation, stability and fast transient response.
Functions:
i. Excitation system builds up the necessary voltage on no load and then to keep it constant
on load condition.
ii. Star up, field flashing, and switching to the system by precise synchronizing.
iii. Protection of the generator for loss of excitation/asynchronous run.
iv. Protection of generator transformer from damage at frequency drops under no load
conditions by lowering the voltage regulator setting suitably.
v. Compensation for the step up transformer impedance.
7. Major Electrical Equipment
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Automatic Voltage Regulator (AVR):
To maintain terminal voltage of the generator under various operating conditions, provision of automatic
voltage regulation equipment is essential.
The main functions of an AVR are as follows:
• Control of system voltage within prescribed limits and have the operation of the machine nearer to the
steady state stability limit.
• Proper division of reactive load between the alternators operating in parallel.
• Prevention of dangerous over-voltages on the occurrence of sudden loss of load on the system.
• Increase of excitation under system fault conditions so that maximum synchronising power exists at the
time of clearance of fault, to prevent loss of synchronism.
8. Major Electrical Equipment
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• Power Transformers
➢ Power transformers are used for stepping-up the
voltage for transmission at generating stations and
for stepping-down voltage for distribution purpose.
Following factors need to be considered for a type of
PT for particular applications:
❖ Load factor
❖ Losses
❖ Initial cost
❖ Continuity of services
❖ Methods of cooling
❖ Percentage of impedance voltage
❖ Regulations of voltage
❖ Weight
❖ Floor area
9. Major Electrical Equipment
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• Switchgear
❖ During the operation of power system the
generating plants, transmission lines,
distributors and other electrical equipment
are required to be switched on and off under
both normal and abnormal conditions.
Therefore switchgears are used.
❖ All the protection equipment like switches,
fuse, Circuit breakers, relays are installed in
switchgear.
❖ Types 1. Outdoor type 2. indoor type.
❖ For the voltage above the 66KV outdoor
switchgears are installed Switchgear .
11. Major Electrical Equipment
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Plant Instrumentation
• Instruments are installed for efficient working and operation of a power plant by furnishing
continuous information about the conditions of pressure, temperature, and flow throughout
the plant.
• The conditions are monitored and results may be compared from time-to-time to achieve
the best performance possible of the plant or any part of the plant.
The functions of the instruments are thus summarized as:
(i) Operating guidance, (ii) Economical supervision, (iii) Performance calculations,
(iv) Cost and cost allocation, and (v) Maintenance/repair guidance.
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Mechanical instruments include temperature measuring devices, pressure measuring
instruments, flow-meters, fuel measuring instruments, gas analysis instruments, speed
measuring instruments, level recorders, gong alarms, steam calorimeters and fuel calorimeters
atmospheric measuring instruments (barometers, hygrometers, thermometers).
Electrical instruments include ammeters, voltmeters, wattmeters, kWh meters, kVARh
meters, synchroscope, power factor meters, reactive-volt-ampere meters, ground detectors.
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gong alarms
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Mechanical instruments
Pressure indicator Temperature indicator
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Mechanical instruments
Flow meter Level indicator
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Ground detector
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Electrical instruments
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Protective equipment
Protective equipment are very important in system to isolate
the abnormal conditions.
• Feature of protective equipment
greater reliability; High speed of operation; Simple and
withstand to large value of fault;
Various Protective equipment are: Fuse, Circuit Breakers,
Relays, Lightning arresters
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Protective equipment
Fuse
• Fuse is a wire of short length or thin strip
of material which melt with the flow of
excessive current.
• Under normal working conditions safe value
of current flows but during short circuit
load current increased which heat the wire
so wire melt and circuit break.
Advantages:- cheap in cost; needs no
maintenance; it interrupts short-circuit
current without noise, flame, gas or smoke.
Disadvantages of fuse:- wire should be
replaced after every operation.
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Protective equipment
Circuit breaker: A circuit
breaker is known as the
automatically operated electrical
switch that functions when a
fault detected by interrupting
the current flow. There are
various sizes of circuit breaker
which are from small devices up
to large switchgear that used to
protect low current circuit until
high voltage circuit.
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Operating principle of Circuit Breaker
• CB is consist of two contact one is moving contact and another
is fix contact, known as electrodes.
• These contacts are remain close under normal operating
condition.
• When fault is occur on any equipment of the system, the
tripping coil gets energized and the moving contact are pulled
by some mechanism and CB will operate, and circuit is open.
• Arc is induced between contact, when CB is operate under
faulty condition and current is able to continue until the
discharge.
• The production of Arc not only the delay the current but it also
generate heat which causes to damage CB and power system.
therefore production of Arc is main problem in CB. hence make
the CB as Arc production time is shortest as possible so heat
generated by it may be not more danger.
• During the arcing time, current flowing between the contacts
depends upon the arc resistance. if arc resistance is greater,
the smaller current flowing through contacts.
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Relays
A relay is an automatic device which senses an abnormal condition
of electrical circuit and closes its contacts. These contacts in
turns close and complete the circuit breaker trip coil circuit hence
make the circuit breaker tripped for disconnecting the faulty
portion of the electrical circuit from rest of the healthy circuit.
Relay has three essential elements:
Sensing element- it sense and measure the change;
Comparing element- compare the measured quantity to pre-
setted value;
Controlling element- it sends signal to circuit breaker Relays
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Types of circuit breakers
• Air circuit breaker (ACB)
➢ In an ACB, compressed air is stored air is stored in a tank and released
through a nozzle to produce a high velocity jet.
➢ It is used to extinguish the arc.
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Types of circuit breakers
• Oil circuit breaker
➢ In an Oil circuit breaker, oil is
worked as a dielectric or
insulating medium for arc
extinction.
➢ In oil circuit breaker the
contacts of the breaker are
made to separate within an
insulating oil. When the fault
occurs in the system the
contacts of the circuit
breaker are open under the
insulating oil, and an arc is
developed between them and
the heat of the arc is
evaporated in the surrounding
oil.
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Types of circuit breakers
• Vacuum circuit breaker (VCB)
➢ A breaker which used vacuum as an arc extinction medium is called a vacuum
circuit breaker.
➢ In this circuit breaker, the fixed and moving contact is enclosed in a
permanently sealed vacuum interrupter. The arc is extinct as the contacts
are separated in high vacuum.
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Earthing of power system
i. It provides lightning protection
ii. It greater safety of electrical equipment against over current.
iii. It improves service reliability.
iv. Greater safety of power system is achieved.
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Factors affecting power generation and distribution
i. Types of phase system (single or three phase)
ii. Types of fuel used
iii. Transmission voltage
iv. Cost of transmission and distribution system
v. Type of transmission (overhead or underground)
vi. Type of substation
vii. Auxiliary power consumption
viii. Capacity of the power plant
ix. Running cost of the power plant
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Power system stability
Whenever the speed of the alternator changes with respect to the synchronous speed, it
increases the variations in voltage and frequency. These variations further transmitted to the
lines and feeder connected to the alternator, thereby setting up the disturbances in the
connected equipment.
The stability of the power system can be achieved by the followings:
• Using lighting arrestors for protection of lines by using quick acting circuit breakers and
relays having minimum time lag.
• Voltage regulators connected on the line should be quick acting.
• Governors attached to the turbine driving alternators should be as quickly as possible so
that the generator input to the load is quickly adjustable.
• Stability is also improved mechanically by connecting to the synchronous motors to heavy
flywheel.
