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SWITCHGEAR Presentation Transcript
1.SWITCHGEAR
2.Presentation outline
Basics of switchgear
Components and Classification
Basic design aspects
Breakers, relays and fuses
Typical parameters
Basics of switchgear
Components and Classification
Basic design aspects
Breakers, relays and fuses
Typical parameters
3.What is a Switchgear ?
“The apparatus used for Switching, Controlling and Protecting the Electrical Circuits and equipment”.
Need of Switchgear :
* Switching during normal operating conditions for the
purpose of Operation and Maintenance.
* Switching during Faults and Abnormal conditions and
interrupting the fault currents.
“The apparatus used for Switching, Controlling and Protecting the Electrical Circuits and equipment”.
Need of Switchgear :
* Switching during normal operating conditions for the
purpose of Operation and Maintenance.
* Switching during Faults and Abnormal conditions and
interrupting the fault currents.
4.SWITCHGEAR
Historical background :
up to 1875 : knife switches
1885 : Bulk Oil circuit breaker
1900 : Arc extinction devices, MOCB
1930’s : ABCB
1950’s : SF6
1960’s : Vacuum CB
Historical background :
up to 1875 : knife switches
1885 : Bulk Oil circuit breaker
1900 : Arc extinction devices, MOCB
1930’s : ABCB
1950’s : SF6
1960’s : Vacuum CB
5.Switching devices :
Circuit breakers / contactors
Isolators
Earthing switch
Control Circuit :
service / test /isolated position selectors
Tripping and closing circuit
Spring charging, anti pumping arrangement
Supply monitoring , space heaters , indications
Measurement :
Ammeter, voltmeter, energy meter
Protection :
Relays, CT, PT,
Circuit breakers / contactors
Isolators
Earthing switch
Control Circuit :
service / test /isolated position selectors
Tripping and closing circuit
Spring charging, anti pumping arrangement
Supply monitoring , space heaters , indications
Measurement :
Ammeter, voltmeter, energy meter
Protection :
Relays, CT, PT,
6.SWITCHGEAR Various symbols :
7.CLASSIFICATION OF SWITCHGEARS :
Method of arc quenching :
Bulk oil, Min. oil, Air Break, Air Blast, SF6 , Vacuum
Working voltage :
440 v, 6.6 kV, 11 kV, 400 kV etc.
Indoor / out door
SOME INTERLOCKS :
Check synchronisation for closing
Master relay contacts for trip and close
HV & LV Breaker interlocks
Main / Reserve supply change over
Method of arc quenching :
Bulk oil, Min. oil, Air Break, Air Blast, SF6 , Vacuum
Working voltage :
440 v, 6.6 kV, 11 kV, 400 kV etc.
Indoor / out door
SOME INTERLOCKS :
Check synchronisation for closing
Master relay contacts for trip and close
HV & LV Breaker interlocks
Main / Reserve supply change over
8.Swgr: Basic Design Aspects
The Auxiliary power system in a power plant must form a RELIABLE source of power to all unit and Station auxiliaries. The basic function of Switchgear is to control supply of electric power and to protect the equipment in the event of abnormal conditions.Hence the Switchgears have to be RELIABLE , SAFE, and ADEQUATE .
Defining the reliability, safety aspects and adequacy aspects in terms of Quantitative parameters forms the essential part in “SPECIFICATIONS”
The Auxiliary power system in a power plant must form a RELIABLE source of power to all unit and Station auxiliaries. The basic function of Switchgear is to control supply of electric power and to protect the equipment in the event of abnormal conditions.Hence the Switchgears have to be RELIABLE , SAFE, and ADEQUATE .
Defining the reliability, safety aspects and adequacy aspects in terms of Quantitative parameters forms the essential part in “SPECIFICATIONS”
9.Swgr: Basic Design Aspects
33 KV, 11 KV, 6.6 KV and 3.3 KV Switchgears
Indoor, metal clad single front and fully Compartmentalized , with degree of protection IP42 and IP52 for metering compartments. For 33 KV the switchgears can be metal enclosed either.
Circuit Breakers of either SF6 or Vacuum type. They shall comprise of three separate identical single pole interrupting units operated through a common shaft by a sturdy mechanism.
33 KV, 11 KV, 6.6 KV and 3.3 KV Switchgears
Indoor, metal clad single front and fully Compartmentalized , with degree of protection IP42 and IP52 for metering compartments. For 33 KV the switchgears can be metal enclosed either.
Circuit Breakers of either SF6 or Vacuum type. They shall comprise of three separate identical single pole interrupting units operated through a common shaft by a sturdy mechanism.
10. Basic Design Aspects
Breakers are suitable for Switching transformers and motors at any load and also for starting 3.3 KV - Above 200 KW to 1500 KW , 11 KV- above 1500 KW for 500 MW units and 6.6 KV- above 200 KW for 210 MW units.
Surge arresters are provided for all motor feeders to limit the over voltages
For Coal handling plant Motors where frequent start/stop of motors is called for HRC fuse backed contactors are provided.
Suitable Interlocks are provided to ensure that Breaker is off before opening the rear doors/covers.
Breakers are suitable for Switching transformers and motors at any load and also for starting 3.3 KV - Above 200 KW to 1500 KW , 11 KV- above 1500 KW for 500 MW units and 6.6 KV- above 200 KW for 210 MW units.
Surge arresters are provided for all motor feeders to limit the over voltages
For Coal handling plant Motors where frequent start/stop of motors is called for HRC fuse backed contactors are provided.
Suitable Interlocks are provided to ensure that Breaker is off before opening the rear doors/covers.
11. Basic design features: Control and Safety
VSTPP -II onwards all Circuit Breakers/contactors are being controlled normally from remote through DDCMIS/PLC. The control Switch located on the Switchgear is normally used only for testing.
All the logic for incomers, buscouplers , ties, transformer feeders and motor feeders is being generated in DDCMIS only . The reverse blocking schemes are still incorporated in Swgr(hardwired)
In earlier projects these logics were generated in Swgr / remote panel (HARDWIRED).
Such a type of control has facilitated Flexibility ,simpler wiring and helped in standardizing interface requirements . A typical Control scheme being implemented in Talcher-II is as displayed.
Isolation Transformers for Lighting distribution to limit the fault of lighting Boards to 9 KA.
Safety Measures for Switchgear include provision of insulated mats in front.
VSTPP -II onwards all Circuit Breakers/contactors are being controlled normally from remote through DDCMIS/PLC. The control Switch located on the Switchgear is normally used only for testing.
All the logic for incomers, buscouplers , ties, transformer feeders and motor feeders is being generated in DDCMIS only . The reverse blocking schemes are still incorporated in Swgr(hardwired)
In earlier projects these logics were generated in Swgr / remote panel (HARDWIRED).
Such a type of control has facilitated Flexibility ,simpler wiring and helped in standardizing interface requirements . A typical Control scheme being implemented in Talcher-II is as displayed.
Isolation Transformers for Lighting distribution to limit the fault of lighting Boards to 9 KA.
Safety Measures for Switchgear include provision of insulated mats in front.
12.Typical Control Scheme
13.Unit Supply One Line Diagram
14. Relays
15. The relay detects the abnormal conditions in the electrical
circuits by constantly measuring the electrical quantities
which are different under normal and faulty conditions.
16.
Requirements of Protecting relaying :
Selectivity
- Ability to select the faulty part and isolate that part
without disturbing the rest of the system.
Speed
- Ability to disconnect the faulty part at the earliest
possible time.
Sensitivity
- Ability of the relay to operate with low value of
actuating quantity.
Reliability
- Ability of the system to operate under pre-determined
conditions
17. Simplicity
- Should be simple so that it can be easily maintained.
- The simpler the protection scheme, the greater is the
reliability
Economy
- Availability at lower cost.
- Generally, the protective gear should not cost more than 5% of the total cost. However, when the apparatus to be protected is of utmost importance (e.g. Generator, GT
etc) economic conditions are subordinated to reliability.
circuits by constantly measuring the electrical quantities
which are different under normal and faulty conditions.
16.
Requirements of Protecting relaying :
Selectivity
- Ability to select the faulty part and isolate that part
without disturbing the rest of the system.
Speed
- Ability to disconnect the faulty part at the earliest
possible time.
Sensitivity
- Ability of the relay to operate with low value of
actuating quantity.
Reliability
- Ability of the system to operate under pre-determined
conditions
17. Simplicity
- Should be simple so that it can be easily maintained.
- The simpler the protection scheme, the greater is the
reliability
Economy
- Availability at lower cost.
- Generally, the protective gear should not cost more than 5% of the total cost. However, when the apparatus to be protected is of utmost importance (e.g. Generator, GT
etc) economic conditions are subordinated to reliability.
18. Classification of Relays based on Design :
19. Basic classification of Relays based on Function :
* Current based, with and without directional feature.
* Voltage based
* Impedance based
* Frequency based
* Power based, with and without directional feature
20. Circuit Breakers
* Current based, with and without directional feature.
* Voltage based
* Impedance based
* Frequency based
* Power based, with and without directional feature
20. Circuit Breakers
21.Main Parts of a Circuit Breaker :
* Fixed Contact * Movable Contact
* Operating Mechanism and control circuit
* Arc extinguishing medium
* Fixed Contact * Movable Contact
* Operating Mechanism and control circuit
* Arc extinguishing medium
22. Basic trip circuit
23. Few definitions
24
Fault clearing process : During any Fault…..
* Fault impedance will be low, so fault current will
increase and relay senses this increase in current.
* Relay contacts closes and sends trip signal to circuit
breaker and the trip coil of the circuit breaker will get
energized.
* Operating mechanism of the circuit breaker will
operate and separate the contacts.
* Arc will be initiated between the contacts and it is
extinguished by suitable methods.
Fault clearing process : During any Fault…..
* Fault impedance will be low, so fault current will
increase and relay senses this increase in current.
* Relay contacts closes and sends trip signal to circuit
breaker and the trip coil of the circuit breaker will get
energized.
* Operating mechanism of the circuit breaker will
operate and separate the contacts.
* Arc will be initiated between the contacts and it is
extinguished by suitable methods.
25. Arcing phenomenon :
- When a fault occurs, heavy current flows through the contacts of the circuit breaker before they are opened by the protective system.
- At the instant when the contacts begin to separate, the contact area decreases rapidly and current density (I/A) increases and hence rise in temperature.
-The heat produced is sufficient to ionise the medium between the contacts. This ionised medium acts as conductor and an arc is struck between the contacts.
- The potential difference between the contacts is very small and is sufficient to maintain the arc.
- The current flow depends upon the Arc resistance.
- When a fault occurs, heavy current flows through the contacts of the circuit breaker before they are opened by the protective system.
- At the instant when the contacts begin to separate, the contact area decreases rapidly and current density (I/A) increases and hence rise in temperature.
-The heat produced is sufficient to ionise the medium between the contacts. This ionised medium acts as conductor and an arc is struck between the contacts.
- The potential difference between the contacts is very small and is sufficient to maintain the arc.
- The current flow depends upon the Arc resistance.
26. Events/Timings
during fault clearing process
during fault clearing process
27. Various types of CBs :
28. Air Break CB :
29. ABCB- Principle of arc quenching
30. Bulk Oil CB :
31. Minimum Oil CB :
32.Advantage of SF6
Inert gas with high dielectric strength.
* Colour less and odour less.
* Non-toxic and non- inflammable.
* Sf6 is blown axially to the arc, hence it removes the heat by axial convection and radial dissipation. As a result the arc dia reduces and comes to zero at current zero.
* Gas pressure in the chamber is at 5 ksc.
* SF6 is filled at a pressure of 12 ksc in the tank and maintained by means of an individual or a common compressor.
* The decomposition products of arcing are not explosive hence no chance of fire.
Disadvantages
* SF6 gas condensates at low temperature & high pressure
Inert gas with high dielectric strength.
* Colour less and odour less.
* Non-toxic and non- inflammable.
* Sf6 is blown axially to the arc, hence it removes the heat by axial convection and radial dissipation. As a result the arc dia reduces and comes to zero at current zero.
* Gas pressure in the chamber is at 5 ksc.
* SF6 is filled at a pressure of 12 ksc in the tank and maintained by means of an individual or a common compressor.
* The decomposition products of arcing are not explosive hence no chance of fire.
Disadvantages
* SF6 gas condensates at low temperature & high pressure
33.Advantage of vacuum CB
* Used up to 66 KV.
* Vacuum is of the range of 10¯6 to 10¯8 torr.
* Vacuum is highly dielectric, so arc can’t persists.
* Separation of contacts causes the release of metal vapour from the contacts, the density of vapour depends on the fault current.
* At current zero the vapour emission will tends to zero and the density will becomes zero and dielectric strength will build up and restriking will be prevented.
* No emission to atmosphere, hence pollution free.
* Non- explosive and silent operation.
* Compact size.
* Used up to 66 KV.
* Vacuum is of the range of 10¯6 to 10¯8 torr.
* Vacuum is highly dielectric, so arc can’t persists.
* Separation of contacts causes the release of metal vapour from the contacts, the density of vapour depends on the fault current.
* At current zero the vapour emission will tends to zero and the density will becomes zero and dielectric strength will build up and restriking will be prevented.
* No emission to atmosphere, hence pollution free.
* Non- explosive and silent operation.
* Compact size.
34.Disadvantage of vacuum CB
* High initial cost.
* Surge suppressors (R or RC combination) are to be connected at load side for limiting switching over-voltage while switching low pf loads.
* High initial cost.
* Surge suppressors (R or RC combination) are to be connected at load side for limiting switching over-voltage while switching low pf loads.
35.Fuses
36. Few definitions :
Rated current :
- Current which can be carried without fusing
Minimum fusing current :
- Min value of the rms current at which the fuse melts.
Fusing factor :
- FF = Min fusing current / Rated current
Prospective current :
- Current which would have flown if the fuse is absent.
Cut-off current :
- Maximum value of fault current actually reached
before the fuse elements melts.
Rated current :
- Current which can be carried without fusing
Minimum fusing current :
- Min value of the rms current at which the fuse melts.
Fusing factor :
- FF = Min fusing current / Rated current
Prospective current :
- Current which would have flown if the fuse is absent.
Cut-off current :
- Maximum value of fault current actually reached
before the fuse elements melts.
37. Characteristics of Fuse :
38.Characteristics of Fuse element :
39.HV fuses
(i) Expulsion type :
- consists of hollow tube made of synthetic-resin
bonded paper in which fuse wire is placed
- when fuse element melts, it causes decomposition of
the inner coating of the tube resulting in formation
of gases which extinguishes the arc.
- used in the level of 11 KV, 250 MVA and generally
used for protection of distribution transformers.
(ii) Drop-out fuse :
- Expulsion type fuse.
- when fuse melts, the fuse element carrying tube drops
down due to gravity, so that, can be spotted easily.
(i) Expulsion type :
- consists of hollow tube made of synthetic-resin
bonded paper in which fuse wire is placed
- when fuse element melts, it causes decomposition of
the inner coating of the tube resulting in formation
of gases which extinguishes the arc.
- used in the level of 11 KV, 250 MVA and generally
used for protection of distribution transformers.
(ii) Drop-out fuse :
- Expulsion type fuse.
- when fuse melts, the fuse element carrying tube drops
down due to gravity, so that, can be spotted easily.
40.Coordination between Fuses and a O/C
protection devices:
protection devices:
41.Details of various CBs in RSTPS
42. SF6 gas pressures of CBs : (bar)
43.Operating medium parameters of CBs : (bar)
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