substation is part of a system and not an entity to itself. Normally, a power system is designed so
that the effects of an outage.
Substation planning considers the location, size, voltage, sources, loads, and ultimate function of a
substation.
Adequate engineering design provides direction for construction, procurement of material and
equipment, and future maintenance requirements while taking into account environmental, safety,
and reliability considerations.
Elements of a Substation
1. Primary power lines' side
2. Secondary power lines' side
3. Primary power lines
4. Ground wire
5. Overhead lines
6. Transformer for measurement of electric voltage
7. Disconnect switch
8. Circuit breaker
9. Current transformer
10. Lightning arrester
11. Main transformer
12. Control building
13. Security fence
14. Secondary power lines
TYPES OF SUBSTATIONS
Substations may be categorized as distribution substations, transmission substations, switching
substations, collector, converter, railway, mobile or any combination thereof
distribution substation is a combination of switching, controlling, and voltage step-down equipment
arranged to reduce subtransmission voltage to primary distribution voltage for residential, farm,
commercial, and industrial loads.
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
level suitable for local distribution.
A transmission substation is a combination of switching, controlling, and voltage step-down
equipment arranged to reduce transmission voltage to subtransmission voltage for distribution of
electrical energy to distribution substations.
Transmission substations function as bulk power distribution centers, and their importance in the
system often justifies bus and switching arrangements that are much more elaborate than
distribution substations.
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.
switching substation is a combination of switching and controlling equipment arranged to provide
circuit protection and system switching flexibility.
switching station is a substation without power transformers and operating only at a single voltage
level. Switching stations are sometimes used as collector and distribution stations. Sometimes they
are used for switching the current to back-up lines or for paralleling circuits in case of failure.
Converter substations may be associated with HVDC converter plants, traction current, or
interconnected non-synchronous networks. These stations contain power electronic devices to
change the frequency of current, or else convert from alternating to direct current or the reverse.
Electrified railways also use substations, often distribution substations. In some cases a conversion
of the current type takes place, commonly with rectifiers for direct current (DC) trains, or rotary
converters for trains using alternating current (AC) at frequencies other than that of the public grid.
mobile substation is a substation on wheels, containing a transformer, breakers and buswork
mounted on a self-contained semi-trailer, meant to be pulled by a truck.
Two of the most critical factors in the design of a substation are its location and siting
Public Safety: Substations should be safe for people who may have occasion to be near them. The
primary means of ensuring public safety at substations is by the erection of a suitable barrier such as
a metal fence.
Audible Noise: Sources of audible noise within a substation include transformers, voltage
regulators, circuit breakers, and other intermittent noise generators.
Site Selection: If the substation has to be located in or near a residential area, select a site with the
greatest distance from nearby residences, and, if possible, avoid a direct line of sight with them.
Layout Design: Good practice for noise control is to locate transformers the maximum possible
distance from the substation fence.
Electrostatic and Electromagnetic Effects: Consideration should be given to preventing radio
and television interference that could result from visible corona.
Weather
Temperature : It is necessary to design a substation for the extreme temperatures expected. Extreme
temperatures could affect circuit breakers, relay protection, or the bus.
Rain: A substation should be designed to be operable under predictable conditions of rainfall.
Additionally, it is desirable that substation drainage be sufficient enough to exhibit little standing
water within a few hours after a heavy rainfall.
Electrical Storms: The two measures normally employed for substation lightning protection are surge
arresters and shielding. Surge arresters provide little protection against direct strikes. Shielding is
provided by overhead wires, masts that are extensions of structures, or independent masts
Earthquakes
Substations subjected to intense earthquakes will most likely be damaged; however, seismic design
practices can minimize the damage. Although some substation equipment is inherently shock
resistant, the foundations, structures, equipment anchors, insulation, and conductors may not be.
SAFETY CONSIDERATIONS
It is paramount that substations be safe for the general public and for operating and maintenance
personnel. Practical approaches include the employment and training of qualified personnel,
appropriate working rules and procedures, proper design, and correct construction. The safeguarding
of equipment also needs to be considered in substation design
NEED FOR DOCUMENTATION
Documentation forms the basis for the expression and evaluation of engineering concepts. A
document serves as a vehicle for the cooperative and engineer to reach agreement on a particular
subject. In its final form, a document fulfills its primary role of establishing design and functional
requirements.
Transformer Primary Protective Devices
To prevent equipment damage from transformer or low-voltage bus faults, protective devices are
generally provided on the primary side of the transformer. These devices may also serve as primary
disconnects to enable isolation from the transmission system.
Voltage Regulation
To maintain voltage at a uniform level, voltage regulation equipment is usually required. The voltage
can be regulated by using either feeder or bus regulation. Feeder regulation may be used in multicircuit distribution substations, where the circuits are very diverse in load characteristics.
The bypass switches usually consist of three independently operated hook stick switches, but a
three-pole group-operated switch can also be used. In some applications, it may be desirable to
combine some of the switches to facilitate installation.
Surge Arresters
Transformers, regulators, and other substation equipment are particularly sensitive to transient
overvoltages. For the highest degree of equipment protection, surge arresters should be installed as
close as practical to the equipment being protected. In most instances, power transformers can be
furnished with surge arrester mounting brackets to facilitate installation.
Transmission substations are usually characterized by primary and secondary voltages of 69 kV or
higher. Since one transmission substation may supply several distribution substations and large loads,
reliability of service and flexibility of operation are extremely important.
Power circuit breakers in the three circuits help prevent complete substation shutdown for line
faults. The circuit breakers have disconnect switches on both source and load sides to permit
isolation during maintenance or other periods requiring complete de-energization.
A single bus configuration consists of one main bus that is energized at all times and to which all
circuits are connected. This arrangement is the simplest, but provides the least amount of system
reliability. Bus faults or failure of circuit breakers to operate under fault conditions results in
complete loss of the substation.
Sectionalized Bus
This arrangement is basically two or more single bus schemes, each tied together with bus
sectionalizing breakers. The sectionalizing breakers may be operated normally open or closed,
depending on system requirements. In this arrangement, a bus fault or breaker failure causes only
the affected bus section to be removed from service and thus eliminates total substation shutdown.
A main and transfer bus configuration consists of two independent buses, one of which, the main
bus, is normally energized. Under normal operating conditions, all incoming and outgoing circuits are
fed from the main bus through their associated circuit breakers and switches. If it becomes necessary
to remove a circuit breaker from service for maintenance or repairs, the integrity of circuit operation
can be maintained through use of the bypass and bus tie equipment.
A ring bus configuration is an extension of the sectionalized bus arrangement and is accomplished by
interconnecting the two open ends of the buses through another sectionalizing breaker. This results
in a closed loop or ring with each bus section separated by a circuit breaker. For maximum reliability
and operational flexibility, each section should supply only one circuit.
The breaker-and-a-half configuration provides for circuit breaker maintenance, since any breaker
can be removed from service without interrupting any circuits.
The double breaker–double bus configuration consists of two main buses, each normally energized.
Suspension insulators are used as insulation and support for strain buses in substations. Suspension
insulators are available in several forms to suit individual requirements. Distribution deadend-type
suspension insulators can be used at distribution voltages for substation strain buses. Distribution
deadend suspension insulators normally have clevis-type connections