1. STANI MEMORIAL COLLEGE OF ENGINEERING & TECHNOLOGY
POWER SYSTEM DESIGN LAB
EXPERIMENT NO. 7
Aim: - Substations: Types of substations, various bus-bar arrangements, and Electrical equipments for
substations.
Apparatus Requirements: - Circuit Breaker, Insulator, Power Transformer, Conductor, Bus-bar,
Power supply.
Theory: - A substation is a part of an electrical generation, transmission, and distribution system.
Substations transform voltage from high to low, or the reverse, or perform any of several other important
functions like switching’s of lines, change in power factor etc. Electric power may flow through several
substations between generating plant and consumer, and its voltage may change in several steps.
A substation that has a step-up transformer increases the voltage while decreasing the current, while a
step-down transformer decreases the voltage while increasing the current for domestic and commercial
distribution. The word substation comes from the days before the distribution system became a grid.
TYPES OF SUBSTATIONS:1. TRANSMISSION SUBSTATION: - A transmission substation connects two or more
transmission lines. The simplest case is where all transmission lines have the same voltage. In
such cases, the substation contains high-voltage switches that allow lines to be connected or
isolated for fault clearance or maintenance. A transmission station may have transformers to
convert between two transmission voltages, voltage control/power factor correction devices such
as capacitors, reactors or static VAR compensators and equipment such as phase shifting
transformers to control power flow between two adjacent power systems.
2. DISTRIBUTION SUBSTATION: - A distribution substation transfers power from the
transmission system to the distribution system of an area. It is uneconomical to directly connect
electricity consumers to the main transmission network, unless they use large amounts of power,
so the distribution station reduces voltage to a value suitable for local distribution.

2. 3. COLLECTOR SUBSTATION: - In distributed generation projects such as a wind farm, a
collector substation may be required. It somewhat resembles a distribution substation although
power flow is in the opposite direction, from many wind turbines up into the transmission grid.
Usually for economy of construction the collector system operates around 35 kV and the collector
substation steps up voltage to a transmission voltage for the grid. The collector substation can also
provide power factor correction if it is needed, metering and control of the wind farm. In some
special cases a collector substation can also contain an HVDC static inverter plant.
4. SWITCHING SUBSTATION: - A switching substation is a substation which does not contain
transformers and operates only at a single voltage level. Switching substations are sometimes used
as collector and distribution stations. Sometimes they are used for switching the current to back-up
lines or for parallelizing circuits in case of failure.
BUS-BAR: - Bus-bars are conductor from which many tapings can be taken to connect the different lines.
Current and Voltage along with its whole length are same i.e. constant.
In GSS mainly, two types buses are provided one bus is called "MAIN" bus and the other "AUXILIARY"
or "TRANSFER" bus. Incoming or Outgoing feeders are connected from these buses. The Main buses
remains in work permanent and the Auxiliary or Transfer bus works in failure condition of main bus.
ELECTRICAL EQUIPMENTS FOR SUBSTATION
1. CIRCUIT BREAKER: - A circuit breaker is an automatically operated electrical switch
designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic
function is to detect a fault condition and, by interrupting continuity, to immediately discontinue
electrical flow. Unlike a fuse, which operates once and then has to be replaced, a circuit breaker
can be reset (either manually or automatically) to resume normal operation. Circuit breakers are
made in varying sizes, from small devices that protect an individual household appliance up to
large switchgear designed to protect high voltage circuits feeding an entire city.
 Oil Circuit Breaker (OCB)
 Air-Blast Circuit Breaker (ABCB)
 Sulphur Hexafluoride Circuit Breakers (SF6)
 Vacuum Circuit Breakers (VCB)
2. TRANSFORMER: - A transformer is a device that transfers electrical energy from one circuit to
another without changing the frequency. A varying current in the first or primary winding creates

3. a varying magnetic flux in the transformer's core and thus a varying magnetic field through the
secondary winding. This varying magnetic field induces a varying electromotive force (EMF), or
"voltage", in the secondary winding. This effect is called mutual induction.
3. CONDUCTORS: - The conductor is a very essential part of transmission and distribution system
of electrical power, the cost of the conductor material accounts for a major part of the total cost.
So proper choice of conductor material and size of the conductor is of utmost importance.
4. ISOTATORS: - Isolator or a dis-connector switch is used to de-energise an electrical circuit for
maintenance purpose. It is an off load device. They are not equipped with arc quenching devices.
Isolators are employed in addition to circuit breakers, and are provided on each side of every
circuit breaker to provide isolation. While opening a circuit, if the circuit breaker is opened
carelessly, when carrying a heavy current, the resulting are could easily cause a flash over to
ground. This may shatter the supporting insulators and may even cause a fatal accident to the
operator. While closing a circuit, the isolator is closed first, then the circuit breaker.
5. INSULATOR: - An insulator, also called a dielectric, is a material that resists the flow of electric
charge. In insulating materials valence electrons are tightly bonded to their atoms. These materials
are used in electrical equipment as insulators or insulation. Their function is to support or separate
electrical conductors without allowing current through themselves. The term also refers to
insulating supports that attach electric power transmission wires to utility poles or pylons.
Circuit Diagrams:-
Figure 7.1 Bay of Bus bar

4. Figure 7.2 Typical Single bus arrangements
Precautions:1) Do not touch any live conductor.
2) Please keep distance from electrical equipments because voltage level very high i.e. 132
kV, 220 kV, and 400 kV.
Procedure:-

5. Observation Table:-
Calculation:-
Result: - We have successfully studied about the substations, bus- bar, and Equipments of substations.

6. Viva- Voice:Ques. 1 Name of different types of Substation.
Ques. 2 What is the functioning of Switching Substation?
Ques. 3 Types of Bus-Bar used in Substation?

7. Ans 1. Transmission Substation,
Distribution Substation,
Collector Substation,
Switching Substation
Ans 2. A switching substation is a substation which does not contain transformers and operates only at a
single voltage level. Sometimes they are used for switching the current to back-up lines or for
parallelizing circuits in case of failure.
Ans 3. Two Types arrangements of bus bar are used in substation: MAIN bus bar and AUXILIARY bus
bar.