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DESIGN CONCEPTS OF 33/11kV NEW SUBSTATION. Planning 33/11kV Sub-Station. A- Decision of location a-The location should be best suited at the load centre of the 11kV net-work b-Load density and voltage-regulation.

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DESIGN CONCEPTS OF 33/11kV NEW SUBSTATION


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planning 33 11kv sub station
Planning 33/11kV Sub-Station
  • A- Decision of location
  • a-The location should be best suited at the load centre of the 11kV net-work
  • b-Load density and voltage-regulation.
  • c-Capacity of the substation should be decided keeping in view the future growth of the load for at least next 5years without needing any augmentation.
cont d
Cont’d
  • d- Selection of the site of sub-station
  • (i) Site should be free from all obstructions with the convenience of terminating H.V. lines.
  • (ii) Site should not be in a low-lying area otherwise it may get flooded during rainy seasons.
  • (iii) Site should be as near to the main roads as possible and easily approachable in all the seasons.
cont d4
Cont’d
  • (iv) As far as possible it should be near a town and away from garbage dumping ground to avoid vulture faults. Site should have drinking water facility. It should not be within 3 km from aerodrome. It should not be near military or police shooting ranges.
cont d5
Cont’d

(v) There should have adequate land keeping in view the requirements for installation of required equipments-

Land for 2x3MVA is approx 50x40metres

For staff quarters Approx 3 acres

(vi) Land should be in level and should not have any nallah or road crossing on it.

(vii) The site should be selected so as to accommodate the length of 11kv outgoing feeder to connect the existing net work. It should be possible to be taken out 4-5 numbers of 11kV feeders.

orientation of the sub station
Orientation of the Sub-Station
  • It should be such that the incoming and outgoing feeders are easily accessible to the sub-station structures.
  • Scope must be kept for future extension for additional feeders in future
planning the layout
Planning the Layout
  • Should be economical
  • Ease of operation and maintenance
  • Safety of operating professional
substation equipments
Substation Equipments
  • Structures
  • Power transformers
  • Circuit Breakers
  • H.T. Fuses
  • Isolating Switches
  • Bus bar Arrangement
  • Insulators
  • Lightning Protection equipments-LAs
cont d9
Cont’d
  • Instrument transformers -Current and Voltage transformers for –

(i) Protection System

(ii)Metering system

  • CONTROL Panels with Various types of relays and instruments
  • Control room
  • Cables-
  • Power cables
  • Control cables
cont d10
Cont’d
  • Batteries for D.C. supply
  • Station transformer
  • Fencing / boundary wall, approach road, security hut etc.
  • Earthing system

Facilities:

(i) Lighting

(ii) Fire-fighting equipment

(iii) Staff quarters

structures
Structures
  • Incoming – outgoing gantries
  • Mounting structures for Power Transformers, Station Transformers, breakers, isolators, HT fuses, insulator supports ( For Post Insulators), C.Ts & P.Ts.
  • Bus-bar structures to provide entry from the overhead line to the s/s and to extend required number of feeders (Bays). Similarly other structures required to mount the operating and other accessories. Minimum clearance from ground level and from any live part is to be maintained as per I.E. Rules.
continue
continue
  • Structure are fabricated from steel sections or rail and joist are used. P.C.C. poles cast in reduced length (up to 7 meters) with strength of 400kg are also being used for economy purposes.
power transformers
Power transformers
  • Power Transformers with different capacities are -

(i) 630kVA 33/11 step-down (Delta/Dy11)

(ii)1600kVA

(iii)3150kVA

(iv)5000kVA

Most of the Transformers are provided with off-circuit tap Changers.However On Load Tap Changers are being provided in the Power Transformers with capacity of more than 5MVA

protecting devices
Protecting Devices

A Circuit Breakers

  • (i) 33kV
  • Oil type circuit breakers. Now being replaced with vaccum/SF6 circuit breakers
  • Normal current - 630Amps voltage 36kV
  • Rated short circuit current 25 kA for 3 Sec
  • Metering and protection panel gets signals through 11kV/110V PTs and CTs which are provided with separate cores for metering and protection System.
cont d15
Cont’d

(ii) 11kV

  • Oil type circuit Breakers- Now being replaced with SF6 or Vacuum Circuit Breakers
  • Normal current-400Amps and 800Amps
  • Short circuit current-25kA for 3Secs
continue16
Continue
  • Breaker panel is provided with motor operated spring charging mechanism which operates at 230V single phase AC supply.
  • Circuit breakers for Transformers of more than 5MVA capacity are being provided. For lower capacity Transformers protection through HG fuses, on 33kV side are provided.
  • Outdoor type CTs and PTs are provided for 33kV system.
  • CTs and PTs are supplied with 11kV breaker Panel
ht fuse
HT Fuse
  • Normally drop out fuse cut outs for current rating of upto100Amps are being used. Fuses have insulated base / fitting arrangements with creep-age distance to earth not less than 320mm
isolating switches
Isolating Switches

Isolating Switches

-Switches are Used to isolate equipment for maintenance purposes

  • 33kV:
  • For 33kV system horizontal type isolating switches are used. Rated normal current - 630A at 36kV.
  • 11kV:
  • Two type IS Are being used
  • (i) suitable for horizontal mounting
  • (ii)suitable for vertical mounting ating
  • Normal rating- 400amps- At 12kV
bus bars
Bus Bars

Two types of bus bars - Rigid and Strain type

  • In rigid type- Pipes are used for bus-bar and also for making connections. These are supported on bus post insulators and requires large space.As the bus bars are rigid the clearance remain constant.
  • Minimum ground clearance 3660mm from ground. Since the clearance is not high, the maintenance is easy.
  • The strain type Bus bars are over head system of wires betn. Two supporting structures.
  • Material-ACSR Racoon for 33kV and 11kV bus-bars
cont d20
Cont’d
  • 33kV&11kV outgoing and incoming feeders kept at 6400mm for ground clearance. The other levels of live point in the s/s area are different heights but a minimum of 3660mm is to be maintained.
  • 11kV jumpers are kept at 4500mm height for ground clearance.
insulators
Insulators

Adequate insulation is required for reliability of supply, safety of personnel and equipment etc.

  • Number of insulators is kept minimum for aconomy reasons at the same time ensuring reliability and security of supply.
  • Special insulator with higher leakage resistance to be used, where problem of insulator pollution is expected
lightning protection
Lightning protection
  • Metal oxide lightning arresters are used as they have gapless construction and respond to over-voltage without any time delay. They have longer life and higher energy handling capacity.
  • Rated voltage 30kV for use on 33kV system and 9kV for use on 11kV. Nominal discharge current rating 10 & 5kA
instrument transformers
Instrument Transformers

Current Tranformers are required for protection & metering system

  • Standard ratings for 33/11kV S/S are
  • 300-150/5-5 or 5-5-1 Amps.
  • 200-100/5-5 Amps.
  • 100-50/5-5 Amps.
  • 50-25/5-5 Amps.
  • Accuracy class for protection - 5P10 and for metering Class 1
  • Oil filled or Resin cast CTs are being used depending upon application
cont d24
Cont’d
  • The CTs and PTs can be either Oil filled or resin cast depending upon the application
  • Standard voltage ratio for PTs is 33kV / 110V or 11kV / 110V .
control and relay panels
Control and Relay Panels

C&R Panels normally consist of

  • Ammeter with selector switch
  • Voltmeter with selector switch
  • Energy meter
  • IDMT Relays
  • Differential Relay or REF relay for Transformer protection
  • Various indications and Annunciations
control room
Control Room
  • While designing control room requirement of space for batteries, battery charger, ADLS, one small store room should also be considered in addition to space for 33kV C&R Panels and 11kV breaker panels along with sitting space for operating staff.
cables
CABLES
  • Care should be taken to segregate Power and control cables on separate racks so that in case of fire in power cables, control cables are not damaged and vice versa.
  • The trenches should be designed for easy entry of cables and properly sloped so as to avoid accumulation of water.
  • If possible segregation of AC and DC cables should also be considered.
  • All cables should be labeled for proper identification and sheath should be earthed .
battery and charger
Battery and Charger
  • Normally 24/30 Volt, 150 AH lead acid or NICAD Battery banks are used.
  • The Charger should be Single Phase AC operated Float cum Boost type having capacity of 5 Amps boost charging and 200 mA float Charging and should be fully automatic with alarm and indication system.
station transformer
Station Transformer
  • Station Transformer with a capacity of 63 or 100kVA capacity is normally sufficient to cater the needs of a 33/11kV substation.
  • However higher capacity station transformer may be considered if supply is considered to be provided to the staff Colony.
other facilities
Other Facilities
  • Boundary wall or Fencing
  • Illumination of control room and switch yard
  • Provision of Fire Extinguishers
earthing
Earthing
  • Provision of adequate Earthing in a substation is a must for safety of operating personnel and proper operation of the syetm and protective devices.The primary requirements are –
  • The earthing resistance should be as low as possible preferably less than 1 ohm.
earthing cont d
Earthing - cont’d
  • Provision of earthing for following is made in a substation –
  • Neutral point of each equipment / system such as transformer, capacitor bank, PT etc should have two independent earthings
  • Earthing of equipment enclosures and non current carrying parts
  • All metal frame works such as fencing wire mesh fencing pole illumination pole etc.
  • Lightening arresters should also have two independent earthings.
earthing cont d33
Earthing – cont’d
  • Factors considered while designing Earthing-
  • Duration of fault
  • Magnitude of fault current
  • Resistivity of underlying strata
  • Resistivity of surface material
  • Material of the earth electrodes
conductors loading capacity
ConductorsLoading Capacity

kW-km limit for Rabbit, weasel & squirrel conductors

0.8 P.F. 0.7 P.F.

  • a. Rabbit 11970 10800
  • b. Weasel 8100 7560
  • c. Squirrel 5760 5445
standardisation
STANDARDISATION :

WHILE DESIGINING THE 33/11 KV SUBSTATIONS, THE DESIGNOR HAS TO KEEP IN MIND THE NEEDS FOR STANDARDISATION.

WHY STANDARDISATION,

AVOIDING REPETATION OF DESIGN

REDUCTION IN DRAWING APPROVAL TIME

UNIFORMITY IN THE PRODUCTS

REDUCTION IN PROJECT IMPLEMENTATIONTIME

MINIMUM DOWN TIME

INTERCHANGEABILITY

COST EFFECTIVENESS

standardisation36
STANDARDISATION :
  • POTENTIAL AREAS FOR STANDARDISATION :
  • LAYOUT
  • STRUCTURES
  • EARTHING
  • CABLES & CABLE TRENCH
  • BATTERY SIZING
  • CLAMPS & CONNECTORS
  • BUSBARS
  • ILLUMINATION
  • CONTROL, PROTECTION & METERING
  • CONTROL ROOM
  • ALL FOUNDATIONS