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9/19/12 Substation Main Functions and Classification | EEP
1/6electrical-engineering-portal.com/substation-main-functions-and-classification
electrical-engineering-portal.com
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a n d-cla ssifica t ion
Substation Main Functions and Classification
An
electrical substation is an assemblage of electrical components including busbars, switchgear, power
transformers, auxiliaries etc. These components are connected in a definite sequence such that a ckt. can be
switched off during normal operation by manual command and also automatically during abnormal
conditions such as short-ckt.
Basically an electrical substation consists of number of incoming ckt. and outgoing ckt. connected to a
common Bus-bar sy stems. A substation receives electrical power from generating station v ia incoming
transmission lines and delivers elect. power v ia the outgoing transmission lines.
“Substation is integral part of a power sy stem and form important links between the generating station,
transmission sy stems, distribution sy stems and the load points.”
Main tasks of major sub-stations in the T&D
Main tasks associated with major sub-stations in the transmission and ditribution sy stem include following:
1 . Protection of transmission sy stem.
9/19/12 Substation Main Functions and Classification | EEP
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2. Controlling the Exchange of Energy .
3. Ensure steady State & Transient stability .
4. Load shedding and prevention of loss of sy nchronism. Maintaining the sy stem frequency within
targeted limits.
5. Voltage Control; reducing the reactive power flow by compensation of reactive power, tap-changing.
6. Securing the supply by prov ing adequate line capacity .
7 . Data transmission v ia power line carrier for the purpose of network monitoring; control and
protection.
8. Fault analy sis and pin-pointing the cause and subsequent improvement in that area of field.
9. Determining the energy transfer through transmission lines.
10. Reliable supply by feeding the network at various points.
11 . Establishment of economic load distribution and several associated functions.
Types of substation
The substations can be classified in several ways including the following:
1 Classification based on voltage levels
e.g. : A.C. Substation : EHV, HV, MV, LV; HVDC Substation.
2 Classification based on Outdoor or Indoor
Outdoor substation is under open skv . Indoor substation is inside a building.
3 Classification based on configuration
Conventional Air insulated outdoor substation or
SF6 Gas Insulated Substation (GIS)
Composite substations hav ing combination of the above two
4 Classification based on application
Step Up Substation – Associated with generating station as the generating voltage is low.
Primary Grid Substation – Created at suitable load centre along primary transmission lines.
Secondary Substation – Along secondary transmission line.
Distribution Substation – Created where the transmission line voltage is step down to supply
voltage.
Bulk supply and industrial substation – Similar to distribution sub-station but created separately for
each consumer.
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Mining Substation – Needs special design consideration because of extra precaution for safety
needed in the operation of electric supply .
Mobile Substation – Temporary requirement.
Important Notes:
Prim ary Substations receive power from EHV lines at 400KV, 220KV, 132KV and transform the voltage
to 66KV, 33KV or 22KV (22KV is uncommon) to suit the local requirements in respect of both load and
distance of ultimate consumers. These are also referred to ‘EHV’ Substations.
Secondary Substations receive power at 66/33KV which is stepped down usually to 11KV.
Distribution Substations receive power at 11KV, 6.6 KV and step down to a volt suitable for LV
distribution purposes, normally at 415 volts.
Substation parts and equipment
Each sub-station has the following parts and equipment:
1 Outdoor Switchyard
Incoming Lines
Outgoing Lines
Busbar
Transformers
Bus post insulator & string insulators
Substation Equipment such as circuit-beakers, isolators, earthing switches, surge arresters, CTs,
VTs, neutral grounding equipment.
Station Earthing sy stem comprising ground mat, risers, auxiliary mat, earthing strips, earthing
spikes & earth electrodes.
Overhead earthwire shielding against lightening strokes.
Galvanised steel structures for towers, gantries, equipment supports.
PLCC equipment including line trap, tuning unit, coupling capacitor, etc.
Power cables
Control cables for protection and control
Roads, Railway track, cable trenches
Station illumination sy stem
2 Main Office Building
Administrative building
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Conference room etc.
3 Switchgear and Control Panel Building
Low voltage a.c. Switchgear
Control Panels, Protection Panels
4 Battery Room and D.C. Distribution System
D.C. Battery sy stem and charging equipment
D.C. distribution sy stem
5 Mechanical, Electrical and Other Auxiliaries
Fire fighting sy stem
Diesel Generator (D.G.) Set
Oil purification sy stem
Secondary Distribution
Distribution Substation
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Secon da r y su bsta t ion - V ila lon g a V LG 6 6 /2 0 kV
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Distr ibu t ion su bsta t ion - 2 0/04 kV MCset m eta l-cla d sw itch g ea r (Sch n eider Electr ic)