A substation is a high-voltage electric facility used to switch generators, equipment, and circuits in and out of a system. It also changes AC voltages and converts between AC and DC. Substations can be classified by their service, mounting, function, type of apparatus, and control. They include transformers, switches, circuit breakers, and other equipment to distribute power at appropriate voltages for transmission and utilization.

2. PURPOSE AND GENERAL
CLASSIFICATION
A substation is a high-voltage electric system facility. It
is used to switch generators, equipment, and circuits
or lines in and out of a system. It also is used to change
AC voltages from one level to another, and/or change
alternating current to direct current or direct current
to alternating current. Some substations are small with
little more than a transformer and associated switches.
Others are very large with several transformers and
dozens of switches and other equipment.

4. SUBSTASTION can classified according to:
Service
Alternating current
Alternating to direct current
Mounting
Indoor
Outdoor

5. Function
Tap
Distributing
Industrial
Sectionalizing
Transmission-line supply
Power- factor correction
Frequency changer
Railway, portable
Direct current for light and power

6.  Type of apparatus
Transformer
Rotary converter
Motor generator
Frequency changer
Synchronous condenser
Power rectifier
Control
Manual
Semiautomatic
Automatic
Supervisory

7.  High voltage (HV) ac:
69 kV, 115 kV, 138 kV, 161 kV, 230 kV
 Extra-high voltage (EHV) ac:
345 kV, 500 kV, 765 kV
 Ultra-high voltage (UHV) ac:
1100 kV, 1500 kV
 Direct-current high voltage (dc HV):
±250 kV, ±400 kV, ±500 kV

8.  to be economical, transmission of large amounts of power
over long distances must be done at voltages above 110,000
volts. Such substation between the 110- and 44-kv. Lines is
known as a “ tap sub-station”.
-Equipment may comprise high and low tension
switching equipment, transformers, and lightning
arresters.
A. TAP

9. B. Distribution
 Any substation that is used to transform electrical
energy to a potential that is low enough for general
distribution and utilization is a – distributing
substation
 for local dist, 2 400 volts has been recognized as a
standard voltage;
 Distribution at 6 600, 13 200 and 22 000 volts is used
for longer distances and larger blocks of power.

10.  DISTRIBUTION SUBSTATION

11. C. Industrial
 Large blocks of power are required by industrial
plants, it often becomes necessary and advisable to
install an individual substation to supply such a load
direct from the main high-voltage line or secondary
line of lower voltage.
 Equipment may comprise only switching equip, in
most cases a voltage transformation is probably
needed

12. D. Sectionalizing
 In very long high-voltage large capacity lines,
particularly when several circuits are run in parallel, it
is often necessary to split the lines into sections, in
order that proper protection to the line and service be
obtained.
 Equipment comprise only switching equipment. In
long lines it may also serve to supply power factor
correcting equipment

13. E. Transmission-line supply
It is becoming more and more common to install
the high-tension equipment of a power plant outdoors,
the installation becoming nothing more than a step-
up substation receiving its power at generator voltage,
then stepping up its voltage and finally sending it out
over high-voltage transmission lines.

14. F. Power factor Correction
 Long transmission lines will reveal the fact that the
voltage at the end of the line tends to increase as the
load supplied is decreased, while on the other hand it
tends to decrease as the load is increased.
 It is necessary to use synchronous condensers, so to
control it power factor and voltage regulation may be
had at the end of a long transmission line.

15. Synchronous Condensers
 synchronous condenser is a synchronous machine
running without mechanical load and supplying or
absorbing reactive power to or from a power system.
Also called a synchronous capacitor, synchronous
compensator or rotating machinery.

16. G. Frequency Changer
 To interconnect two systems of different frequencies it
is absolutely necessary that the frequency changers be
used.
This type will necessitate transformers to step-
down or step up the voltage supplied to or delivered
from the frequency changer.

17. H. Railway
 Substations supplying railways may be generally
classified under two heads, namely, as
Alternating current and Direct current
Alternating current – power can be more
economically generated and controlled from the
three – phase units than single phase generators.
Direct current – is has been generally recognized
that direct current is better suited to city railway
service. the substation are generally supplied with
3-phase power and converted to direct current by
means of rotary converters, motor generator
sets, or power arc rectifiers.

18. I. Direct Current for Light and Power
 There are still a few sections in some of our large cities
which are supplied with direct current three wire
systems. Such a supply is invariably obtained from
synchronous converters.
E.g.; certain types of motor loads in industrial plants,
for electrolytic work, low voltage DC is absolutely
essential.

19. Outdoor Substation
 The necessary clearances b/w conductors and the
space required for switches, circuit breakers,
transformers, and other equipment become so great
for voltages above 22 000 volts that it is generally more
economical to install all such equipment outdoors.

20. Indoor Substation
 Indoor Electrical Power Substation:
In Indoor Substations is installed within the
substation building. Such substations are usually for
the rating of 22 kV below . Indoor Substations are
preferred in heavily polluted areas and Power
Substations situated near the seas (saline atmosphere
causes Insulator Failures results in Flashovers)

21. Indoor substation

23. Transformer
 Power transformers raise or lower the voltage as
needed to serve the transmission or distribution
circuits.

24. Potential transformers
 Potential transformers are required to provide accurate
voltages for meters used for billing industrial
customers or utility companies.

25. Current transformers
 Current transformers can be used to supply
information for measuring power flows and the
electrical inputs for the operation of protective relays
associated with the transmission and distribution
circuits or for power transformers.

26.  These current transformers have the primary
winding connected in series with the conductor
carrying the current to be measured or controlled. The
secondary winding is thus insulated from the high
voltage and can then be connected to low-voltage
metering circuits.

27. Grounding Transformer
 A grounding transformer is intended primarily to
provide a neutral point for grounding purposes. It may
be provided with a delta winding in which resistors or
reactors are connected.

28. Rectifier
 A rectifier is a device used to convert alternating
current to direct current.

29. Rotary Converter
 A rotary converter is a type of electrical
machine which acts as a
mechanical rectifier or inverter. It was used to
convert alternating current (AC) to direct
current (DC), or DC to AC power, before the advent of
chemical or solid state power rectification. They were
commonly used to provide DC power for commercial,
industrial and railway electrification from an AC power
source.

30. Frequency Changer
 A frequency changer is a motor-generator set that changes
power of an alternating current system from one frequency
to one or more different frequencies, with or without a
change in the number of phases, or in voltage. Sometimes a
converter is used to accomplish this.

31. Lightning Arresters
 Lightning arresters are protective devices for
limiting surge voltages due to lightning strikes or
equipment faults or other events, to prevent damage to
equipment and disruption of service. Also called surge
arresters.

33. A. Manual
This type of control is applicable only to small-
capacity substations. All the disconnecting switches,
circuit breakers, and other equipment are manually
controlled.

34. B. Semi-automatic
The majority of stations fall under this class.
Control is obtained from a switchboard through
mechanically or electrically remote methods, but all
control is dependent upon the operator in charge at
the substation.

35. C. Automatic
Full automatic substations have obtained a
considerable favor for various purposed, particularly
among railway engineers. Such substations are entirely
unattended; they are started up automatically when a
train comes into the range of the particular station and
stopped when the train passed out of the range of the
station.

36. D. Supervisory
In a many good cases it is desirable that the
operation of a substation be under the direct control of
an operator located at a considerable distance away.
This can be accomplished by what us known
supervisory control. By means of only three or four
control wires running b/w the operator and the
substation , it is possible to operate the substation very
satisfactorily.