2. SUBSTATION
•SUBSTATION - A station in the power transmission
system at which electric power is transformed to a
conveniently used form. The station may consist of
transformers, switches, circuit breakers and other
auxiliary equipment. Its main function is to receive
energy transmitted at high voltage from the
generating station, by either step-up or step-down
the voltage to a value appropriate for local use and
provide facilities for switching. Substations have
some additional functions. Its provide points where
safety devices may be installed to disconnect circuits
or equipment in the event of trouble.
Some substation, such as power plant
switchyard are simply switching stations where
different connections can be made between various
transmission lines.
5. Rated Voltage/ Maximum Voltage
Rated Current
Rated Frequency
BIL or Basic Insulation Level
1 minute power frequency with stand voltage
Short time current for 3 sec
Auxiliary Operating supply
Basic & Common Specification of Substation Equipment's
6. Rated Voltage/ Maximum Voltage
The voltage value of electrical equipment for which it is designed to be
used is called nominal voltage or rated Voltage.
The voltage that can be applied to equipment to operate safely is called
Maximum voltage. The maximum tolerance value that we can apply
Rated Current
This is the maximum rms current the equipment can continuously operate
at, under normal conditions. This rating is based on an , within an
allowable maximum temperature rise. For temperatures above 40°C,
switchgear rated current must be derated
Rated Frequency
This is the rated test frequency of the switchgear and must match the
operating frequency of the installation. Two medium voltage mains supply
frequencies are used globally:
7. BIL or Basic Insulation Level
When lightning impulse over voltage appears in the system, it is
discharged through surge protecting devices before the equipment's of
the system gets damaged.
Hence, the insulation of such equipment must be designed to withstand a
certain minimum voltage before the lightning impulse over voltage gets
discharged through surge protecting devices.
Therefore, operating voltage level of surge protecting devices must be
lower than the said minimum voltage withstanding level of the
equipment. This minimum voltage rating is defined as BIL or basic
insulation level of electrical equipment.
9. 1 Minute Power frequency with stand voltage
This is the maximum rms voltage that the equipment can withstand at mains
frequency for 1 minute. It simulates power surges originated from within a
power system from such events as switching transients, resonance, etc.
Short time current for 3 sec
This is the period of time that the equipment is rated to carry the short-time
withstand current. IEC 62271-1 specifies a standard rating of 1 second,
although durations of 0.5, 2 and 3 seconds are allowed
This is the level of symmetrical rms fault current the switchgear can carry in
the closed position for a short time period (typically 1 second), without
temperature rise exceeding predefined levels. IEC 62271-1 specifies standard
ratings as base 10 multiples of 1, 1.25, 1.6, 2, 2.5, 3.15, 4, 5, 6.3, 8
10. Short time current for 3 sec
This is the period of time that the equipment is rated to carry the short-time
withstand current. IEC 62271-1 specifies a standard rating of 1 second,
although durations of 0.5, 2 and 3 seconds are allowed
This is the level of symmetrical rms fault current the switchgear can carry in
the closed position for a short time period (typically 1 second), without
temperature rise exceeding predefined levels. IEC 62271-1 specifies standard
ratings as base 10 multiples of 1, 1.25, 1.6, 2, 2.5, 3.15, 4, 5, 6.3, 8
12. A. BUSBAR
BUSBAR (or bus, for short) – is a term we use for a
main bar or conductor carrying an electric current to
which many connection may be made.
Buses are merely convenient means of
connecting switches and other equipment into
various arrangements. The usual arrangement of
connections in most substations permit working on
almost any piece of equipment without interruption
to incoming or outgoing feeders. In the switchyard or
substation, buses are open to the air. Aluminum or
copper conductors supported on porcelain insulators,
carry the electric energy from point to point.
14. B. DISCONNECTS
DISCONNECT – is an easily removed piece of the
actual conductor of a circuit.
The purpose of disconnects is to isolate equipment.
Disconnects are not used to interrupt circuits; they
are no-load devices.
A typical use of disconnects is to isolate a circuit
breaker by installing one disconnect on either side of
the circuit breaker (in series with the breaker).
Operation of disconnects is one of the most
important and responsible jobs of a power plant
operator.
One error in isolation of equipment, or the accidental
grounding of line equipment, can be a fatal mistake.
ACSR Conductor IEC 61089 Standard.
18. C. CIRCUIT BREAKER
CIRCUIT BREAKER – is used to interrupt circuits while
current is flowing through them. The making and
breaking of contacts in a Oil type circuit breaker are
done under oil, this oil serves to quench the arc when
the circuit is opened. The operation of the breaker is
very rapid when opening. As with the transformer, the
high voltage connections are made through bushings.
Circuit breakers of this type are usually arranged for
remote electrical control from a suitably located
switchboard.
Some recently developed circuit breakers have
no oil, but put out the arc by a blast of compressed
air; these are called air circuit breakers. Another type
encloses the contacts in a vacuum or a gas (sulfur
hexafluoride, SF6) which tends to self maintain the
arc.
https://youtu.be/ncQYYTXgB28
24. WHAT IS THE DUTY CYCLE/ OPERATING SEQUENCE OF
CB?
IT IS THE MECHANICAL DUTY REQUIREMENT TO BE
FULFILLED BY THE OPERATING MECHANISM OF THE
BREAKER AND SPECIFIED ON THE NAME PLATE OF THE
BREAKER BY THE MANUFACTURER.
IT IS MAINLY USED DURING CIRCUIT BREAKER AUTO
RECLOSING.
IT SPECIFIED AS: O-T-CO-T’-CO AND GENERALLY
GIVEN AS O-0.3 SEC-CO-3 MIN-CO, WHERE O IS CB
TRIPPING, T IS THE DEAD TIME, CO IS RECLOSE WITH
IMMEDIATE TRIPPING (AR UNSUCCESSFUL) AND T’ IS
THE RECLAIM TIME AND THEN THE CYCLE
CONTINUOUS, IF ITS A MULTISPORT AR OR THE
FAULT RECOURSE.
25. Sequence of Operation:
1. When there is a fault, the concerned relay operates, which inturn
operates the Master Trip Relay (86).
2. CB Trip initiates and at the same time Auto Reclose Initiates.
3. CB Trips in about 30ms, which is indicated by “O” in the Duty Cycle.
4. Then CB will remain open for some time (0.3 sec) to complete the Arc
Quenching which is called as Dead Time and is indicated by “0.3Sec” in
the Duty Cycle.
5. After 0.3 sec, if AR is in Service, a Reclose will be attempted, and if the
fault persists, CB Trips immediately ( AR Unsuccessful ) which is
indicated by “CO” in the duty cycle.
6. If its a Single Shot Auto-reclose, the Breaker will go into Auto Reclose
Lockout, that means , the Auto Reclose Relay will not give any further
Reclose Command to the Breaker.
7. After CO, there is a Reclaim Time of 3 Minutes, in which the CB gets
ready for Closing, which includes CB Spring Charging Time, indicated by
“3 Min” in the Duty Cycle.
8. After the Reclaim Time has completed, Second Reclose will be attempted
in following two cases:
26.
27.
28. D. CURRENT TRANSFORMER
CURRENT TRANSFORMER – Current transformer are
used with ammeters, watt meters, power-factor
meters, watt-hour meters, compensators, protective
and regulating relays and the trip coil of circuit
breakers. One current transformer can be used to
operate several instruments, provided that the
combined burden does not exceed that for which the
transformer is designed and compensated. The
current transformer is connected directly in series
with the line.
29.
30.
31.
32.
33.
34.
35.
36.
37. E. VOLTAGE TRANSFORMER
VOLTAGE TRANSFORMER – also know as potential
transformer, are used with volt-meters, wattmeters,
watt-hour meters, power-factor meters, frequency
meters, synchroscopes and synchronizing apparatus,
protective and regulating relays and the no-voltage
and over-voltage trip coils of automatic circuit
breakers. One transformer can be used for a number
of instruments at the same time if the total current
taken by the instrument does not exceed that for
which the transformer is designed and compensated.
The ordinary voltage transformer is connected across
the line, and the magnetic flux in the core depends
upon the primary voltage
38.
39.
40.
41. F. EARTHING SWITCH
EARTHING SWITCH – also known as ground
disconnect, which used to connects the equipment to
a grid of electrical conductors buried in the earth on
the station property. It is intended to protect people
working on the grounded equipment. It does this by
completing a circuit path, thereby reducing the
voltage difference between the equipment and its
surroundings. For safety reasons, it is important that
ground disconnects and all associated connections
have good contact and low resistance. It is also
important that the protective ground not be
accidentally remove, that is why all the earthing
switches, disconnect switches and circuit breakers are
all interlocked to each other and proper/correct
sequencing must be followed.
42. G. SURGE ARRESTOR
SURGE ARRESTOR – are devices used to provide the
necessary path to ground for such surges, yet prevent
any power current from following the surge. An ideal
arrester must therefore have the following properties:
1. Ability to remove the surge energy from the line in a
min. time.
2. High resistive to flow of power current.
3. A valve action automatically allowing surge to pass
and then closing up so as not to permit power
current to flow to ground.
4. Always ready to perform.
5. Performance such that no system disturbances are
introduced by its operation.
6. Economically feasible
43.
44.
45. OVERHEAD GROUND WIRE – by a ground wire is
meant a wire, generally of steel, supported from the
top of transmission-line towers and solidly grounded
at each tower. It is considered a preventive device,
but it does not entirely prevent the formation of
travelling waves on a line. Furthermore, those lines
which are not equipped with ground wires will be
subjected to disturbances which produce surges that
must be allowed to escaped to ground, or the
apparatus connected to the line must be strong
enough to reflect or absorb these surges until they
are entirely damped out.
46.
47. PREVENTIVE MAINTENANCE
BUSBARS & OVERHEAD GROUND WIRE
At least once a year
Visual Inspection & Examination of all wiring connectors.
Check Insulator , clean or apply HVIC if necessary.
Check the physical condition of bus (cables or bars)
For ground wire, check or test the grounding system.
DISCONNECT & EARTHING SWITCHES
At least once a month
Visual Inspection.
Check heating resistor located at its control panel for proper
functioning.
At least once a year
Clean contacts of disconnectors as well as earthing switches and apply
electrical contact grease , if necessary.
48. Check disconnectors and earthing switches, joints and bearings of the
operating linkages for deformed bearing points.
Check flexible connections of earthing switches.
Check all screwed joints for tight fit.
Clean insulators if necessary, when an excessive amount of dirt has
accumulated.
Carry-out the maintenance of operating mechanism.
VOLTAGE TRANSFORMER
At least once a month
Inspect the voltage divider to be sure that no oil leak or serious
accumulation of soot, dust or salt composite is present.
Inspect the intermediate voltage transformer and check the minimum
permissible oil level.
At least once a year
Check all screwed joints & contact for tight fit.
Clean insulators if necessary, when an excessive amount of dirt has
accumulated.
49. CURRENT TRANSFORMER
At least once a month
Visual Inspection to check oil level and defects or possible oil leaks.
At least once a year
Check all screwed joints & contact for tight fit.
Clean insulators if necessary, when an excessive amount of dirt has
accumulated.
Check primary and secondary connectors and conduct necessary
tightening.
Note: Never open a secondary winding of a CT while on service.
SURGE ARRESTOR
At least once a year
Visual Inspection & Examination of all wiring connectors.
Check Insulator and metal circular ring, clean or apply HVIC if
necessary.
Check the physical condition of bus (cables or bars)
50. For ground wire, check or test the grounding system.
Note: Arrestors should never be touched unless completely
disconnected from all live lines and equipment and effectively
connected to ground at the line side of the arrestor.
