An electrical substation uses components like circuit breakers, busbars, and insulators to control the transmission, transformation, and distribution of power. There are two main types of substation insulation systems: air insulated (AIS) and gas insulated (GIS). AIS uses air as insulation between live components, while GIS uses sulfur hexafluoride gas to insulate live components within a sealed metal enclosure. GIS systems require less space than AIS but have higher installation costs. Protective devices in substations include circuit breakers, disconnectors, earthing switches, and surge arresters, which work to isolate faulty sections of the electrical network to prevent damage.

1. BHARAT HEAVY ELECTRICALS LIMITED
5th FLOOR, ADVANT NAVIS BUSINESS PARK,
SECTOR-142, NOIDA(UP)-201305
UNDER GUIDENCE OF: DIPAK KUMAR MANDAL
(SR. DY. GENERAL MANAGER)
TRAINING PERIOD: FROM 27.05.2019 TO 15.07.2019
SUBMITTED BY: SIDDHARTH SHARMA (JIIT – 128 , NOIDA)
SANYAM JAIN (ADGITM , DELHI)

2.  Substation is an electrical installation where power
is controlled for transmission, transformation and
distribution purpose.
 Main Components: circuit breakers, bus-bar,
insulators, lightning arrestor
 Process includes Generation (in 22kV)
Transmission (in 400kV) Consumption/Load
center (in 230V)
 Two primary substation insulation system:
 AIS System
 GIS system

3.  The air insulated substation (AIS) uses air as the
primary dielectric from phase to phase, and phase
to ground insulation.
 Advantages:
 Low construction cost and time
 Easy maintenance
 Disadvantages:
 More space required as compared to GIS
 Poor dielectric property of air
 Directly exposed to humidity, pollutant and
moisture

5.  Gas insulated substation (GIS) primarily uses sulphur
hexafluoride (SF6) gas for insulation of all components
 All the live components are enclosed in grounded
metal enclosure.
 Whole system is sealed with chamber full of gas
 Advantages:
 Less space required as compared to AIS (about 25% of
AIS)
 Protection against external environmental factors
 Disadvantages:
 High installation cost
 High level maintenance is required

6.  OUTDOOR GIS  INDOOR GIS

9. SNO SPECIFICATIONS VALUES
1 Rated Voltage 400 Kv
2 Rated Power Frequency withstand voltage
1. 650 kV rms btw live
terminals and earth
2. 815 kV rms across
isolating distance
3 Rated Lightning Impulse withstand voltage
1425 kVp btw live terminals
4 Rated switching Impulse withstand voltage
1. 1575 kVp (between
phases)
2. 900 (+345) (across
isolating distance)
5 Rated Frequency 50 Hz
6 Max/Min Ambient Temperature 50 Deg C/-5 Deg C
7 Rated Short time withstand current 63 kA (for 1 sec)

10. 1. Circuit Breakers
2. Disconnecting Switches(isolator)
3. Earthing Switch
4. Fast-Acting Earth Switch
5. Current Transformer
6. Voltage Transformer
7. Cables and Boxes
8. Surge Arresters
9. Gas supply and Monitoring Equipments

13.  Protect
electrical circuit
from damage
caused by
overload or
short circuit
 Uses SF6 to
extinguish the
arc
 Clear a fault to
protect
equipment and
human life!

14.  Colorless, odourless, non-toxic, non-flammable
 Highly electronegitive, means free electrons
can be removed easily
 Excellent insulating
 Performance is not effected due to
environmental conditions
 Noisless operation and no over-voltage
problem

15.  Used to isolate different elements of the
substation, such as circuit breakers,
transmission lines, transformer banks, buses,
and voltage transformers.
 Advantages:
 safety for the people working on the high voltage
network,
 providing visible and reliable air gap
 isolation of line sections and equipment

16.  Used to earth different substation elements,
such as circuit breakers and voltage
transformers.
 .It can be combined with any type of
disconnector or installed independently with
their own insulator.
 Electrically interblocked between isolator and
circuit breaker
 Only closed if both isolator and circuit breaker
are in open position

18.  Extra capability of closing an energized conductor,
creating a short circuit without experiencing major
damage to the switch or the enclosure.
 Used earth substation elements like, transmission
lines, transformer banks and main buses.
 Used get rid of DC trapped charges on a
transmission line.
 Used to break electrostatically induced capacitive
currents and electromagnetically induced
inductive currents

19.  Reduce high voltage currents to a much lower
value for safely monitoring the actual electrical
current flowing in an AC transmission line
 Have electromagnetic shield to protect high
frequency transient (1 – 30 MHz) caused by
inductive loads and lightening.

21.  Used to decrease the bus high voltage to lower
control levels of 120/208volts for protective
relays, control and metering and
synchronisation.
 Secondary winding protected by HRC fuse.
 HRC Fuse: Fuse wire carry short circuit heavy
current for short time period, for fault to get
removed, if not it blows off.

23.  Interfaces between utility and GIS equipments.
 User has the possibility to install control or
monitoring devices within the cabinet.
 Marshalling box:
(a)Marshalling boxes are used in substation
switchyards provided with Terminal Blocks to
which control cables are connected.
(b)Marshalling means grouping of I/Os.

25.  A surge arrester is a device to protect electrical
equipment from over-voltage transients caused
by external or internal events.
 Also called a surge protection device or
transient voltage surge suppressor, this class of
device is used to protect equipment in power
transmission and distribution systems

27.  An electrical power system consists of generators,
transformers, transmission and distribution lines, etc.
 Short circuits and other abnormal conditions cause
damage to equipment if suitable protective relays and
circuit breakers are not provided for the protection of
each section of the power system.
 Short circuits are usually called faults by power
engineers. For example, the failure of conducting path
due to a break in a conductor is a type of fault.
 If a fault occurs in an element of a power system, an
automatic protective device is needed to isolate the
faulty element as quickly as possible to keep the
healthy section of the system in normal operation. The
fault must be cleared within a fraction of a second.
 A heavy short circuit current may cause a fire.

28.  The system voltage may reduce to a low
level and individual generators in a
power station or groups of generators in
different power stations may lose
synchronism. Thus, an uncleared heavy
short circuit may cause the total failure of
the system.
 A circuit breaker can disconnect the
faulty element of the system when it is
called upon to do so by the protective
relay.
 Relay is a device which senses abnormal
conditions on a power system by
constantly monitoring electrical
quantities of the system, which differ
under normal and abnormal conditions.
 The basic electrical quantities which are
likely to change during abnormal
conditions are current, voltage, phase-
angle (direction) and frequency.

30.  Faults are caused either by insulation failures or by
conducting path failures.
 Most of the faults on transmission and distribution
lines are caused by overvoltages due to lightning or
switching surges, or by external conducting objects
falling on overhead Iines.
 Sometimes, dirt in general accumulates on the
surface of string and pin insulators. This reduces
their insulation strength and causes flashovers.
 Short circuits are also caused by tree branches,birds
or other conducting objects falling on the overhead
lines.

31.  The opening of one or two of the three phases
makes the system unbalanced. Unbalanced
currents flowing in rotating machines set up
harmonics, thereby heating the machines in short
periods of time. Therefore, unbalancing of the
lines is not allowed in the normal operation of a
power system.
 The causes of faults are: failure of the solid
insulation due to aging, heat, moisture or
overvoltage, mechanical damage, accidental
contact with earth or earthed screens, flashover
due to over-voltages, etc.
 Certain faults occur due to the poor quality of
system components or because of a faulty system
design. Hence the occurrence of such faults can
be reduced by improving the system design, by
using components and materials of good quality
and by better operation and maintenance.

32.  Two broad classifications of faults are:
(i) Symmetrical faults
(ii) Unsymmetrical faults
 Symmetrical Faults :- In a (3 ph) or symmetrical fault, all the
three phases are short circuited. They may be short circuited to the
ground or they may be short-circuited without involving the
ground. It is used to determine the system fault level.
 Unsymmetrical Faults :-Single phase to ground, two phase to
ground, phase to phase short circuits; single phase open circuit
and two phase open circuit are unsymmetrical types of faults.
 Single phase to ground (L-G) fault:- A short circuit between any
one of the phase conductors and earth is called a single phase to
ground fault. It may be due to a phase conductor breaking and
falling to the ground.
 Two phase to ground (2L-G) fault :-A short circuit between any
two phases and the earth is called a double line to ground or a two
phase to ground fault.

33.  Line to line (L-L) fault :-A short circuit between
any two phases is called a line to line or phase to
phase fault.
 Open circuited phases:- This type of fault is
caused by a break in the conducting path. Such
faults occur when one or more phase conductors
break or a cable joint or a joint on the overhead
lines fails. Such situations may also arise when
circuit breakers or isolators open but fail to close
one or more phases. Due to the opening of one or
two phases, unbalanced currents flow in the
system, thereby heating rotating machines.
 Winding faults :- Faults also occur on the
alternator, motor and transformer windings. In
addition to these types of faults, there is one
more type of fault, namely the short circuiting of
turns which occurs on machine windings.

36.  For the design and application of a protective scheme, it is
very useful to have an idea of the frequency of occurrence
of faults on various elements of a power system. Usually
the power stations are situated far away from the load
centres, resulting in overhead lines being exposed to
atmospheric conditions. The chances of faults occurring,
are greater for overhead lines than for other parts of the
power system.

37.  50% of the total faults occur on overhead lines.
Overhead lines require more attention .Table shows
the frequency of occurrence of different types of
faults on overhead lines.
 L-G fault occurs most.
 In the case of cables, 50% of the faults occur in cables
and 50% at end junctions.

38.  There is a separate protective scheme for each piece
of equipment or element of the power system, such
as generator protection, transformer protection,
transmission line protection, bus bar protection, etc.
Thus, a power system is divided into a number of
zones for protection.
 A protective zone covers one or at the most two
elements of a power system. The protective zones are
planned in such a way that the entire power system is
collectively covered by them, and thus, no part of the
system is left unprotected.

40.  Relays are the primary protection as well as switching devices in most of
the control processes or equipments, which works to isolate or change the
state of an electric circuit from one state to another.
 Different Types of Relays Classification:
 Protective relays continuously monitor these parameters: voltage, current,
and power; and if these parameters violate from set limits they generate
alarm or isolate that particular circuit. These types of relays are used to
protect equipments like motors, generators, and transformers, and so on.
 Reclosing relays are used to connect various components and devices
within the system network, such as synchronizing process, and to restore
the various devices soon after any electrical fault vanishes, and then to
connect transformers and feeders to line network.
 Monitoring relays monitors the system conditions such as direction of
power and accordingly generates the alarm. These are also called
directional relays.

42. •When power flows through the first circuit (1),
it activates the electromagnet (brown),
generating a magnetic field (blue) that attracts a
contact (red) and activates the second circuit (2).
When the power is switched off, a spring pulls
the contact back up to its original position,
switching the second circuit off again.
•This is an example of a "normally open" (NO)
relay: the contacts in the second circuit are not
connected by default, and switch on only when a
current flows through the magnet. Other relays
are "normally closed" (NC; the contacts are
connected so a current flows through them by
default) and switch off only when the magnet is
activated, pulling or pushing the contacts apart.
Normally open relays are the most common.

44.  Electromagnetic Relays
 Induction Type Relay
 Static Relay
 Numerical Relay

45.  These relays are constructed with electrical,
mechanical and magnetic components, and
have operating coil and mechanical contacts.
 Therefore, when the coil gets activated by
a supply system, these mechanical contacts
gets opened or closed. The type of supply can
be AC or DC.

47.  These are used as protective relays in AC
systems alone and are usable with DC systems.
 The actuating force for contacts movement is
developed by a moving conductor that may be
a disc or a cup, through the interaction of
electromagnetic fluxes due to fault currents.

49.  It uses analogue electronic devices instead of
magnetic coils and mechanical components to
create the relay characteristics.
 The measurement is carried out by static
circuits consisting of comparators, level
detectors, filter etc
 While in a conventional electromagnetic relay it
is done by comparing operating torque (or
force) with restraining torque (or force).

51.  Numerical protection relays protect power
transformers and distribution systems from
various types of faults
 For power transformers, these faults include
protection from distance, line differential, pilot
wire, low-impedance busbar, high-impedance
differential, frequency, voltage, failure of circuit
breaker, auto reclosing, and synchronism faults.
 For power distribution systems, these faults
include protection from overcurrent, under or
overvoltage, directional overcurrent’s, and feeder
manager relay faults.

53. Characteristic El. Mech. Relay Static Relay Digital Relay
Numerical
Relay
Relay Size Bulky Small Small Compact
Speed of
Response
Slow Fast Fast Very fast
Timing
function
Mechanical
clock works,
dashpot
Static timers Counter Counter
Time of
Accuracy
Temp.
dependant
Temp.
dependant
Stable Stable
Reliability High Low High High
Vibration Proof No Yes Yes Yes
Characteristics Limited Wide Wide Wide
Requirement of
Draw Out
Required Required Not required Not required
CT Burden High Low Low Low
CT Burden 8 to 10 VA 1 VA < 0.5 VA < 0.5 VA

54. Characteristic
El. Mech.
Relay
Static Relay Digital Relay
Numerical
Relay
Reset Time Very High Less Less Less
Auxiliary supply Required Required Required Required
Range of settings Limited Wide Wide Wide
Isolation Voltage Low High High High
Function Single function Single function Multi function Single function
Maintenance Frequent Frequent Low Very Low
Resistance 100 mille ohms 10 Ohms 10 Ohms 10 Ohms
Output Capacitance < 1 Pico Farad
> 20 Pico
Farads
> 20 Pico
Farads
> 20 Pico
Farads