1. SWITCHYARD OF
A 500MW POWER PLANT

2. ISOLATED PHASE BUSDUCT
3 NOS.GEN TRF 1  BANK
400 / 21 kV 200 MVA
ISOLATED PHASE BUSDUCT
FOR GENERATOR AND TRFS. LA
VT 4
UNIT TRF
21 / 11.5 KV
50 MVA
GCB A
UT - B SC
VT 1,2,3
LINE
CT’s
11 kV 1 BB SWGR
11 kV 1 BA SWGR
EARTH SWITCH OF
GENERATOR
GENERATOR
NEUTRAL
CT’s
400 KV
NGT & NGR
21KV / 220 V
175 KVA
0.212 OHMS 800 A
21 KV CT
11 KV
EARTH

3. Salient Features of the Project
Total Capacity MW
Generating Voltage - 21kV
Transmission Voltage kV & 220kV
400kV Switchyard - One & Half Breaker Scheme
220kV Switchyard - Two Main one Transfer Bus Scheme

4. What is a Switchyard ?
It is a switching station which has the following credits :
(i) Main link between Generating plant and Transmission system,
which has a large influence on the security of the supply.
(ii) Step-up and/or Step-down the voltage levels depending upon
the Network Node.
(iii) Switching ON/OFF Reactive Power Control devices, which
has effect on Quality of power.

5. Switchyard Type Conventional Air Insulated Type. Gas Insulated type.
Outdoor Gas Insulated type.

6. Switchyard layout Objective:
Substation layout consists essentially in arranging a number of switchgear components in an orderly pattern governed by their function and rules of spatial separation as described in electrical single line diagram.
Pre-requisites:
1) single line diagram
2) general layout plan of power plant
3) orientation of line evacuation
4) control room building

7. LAYOUT CONTD… Options / Alternatives
The layout will vary for the following:
Switching schemes
Type of insulation - Air Insulated/Gas Insulated.

8. SWITCHYARD EQUIPMENTS
Equipments commonly found in switchyard :
Lightening arrestor
Current transformer
Voltage transformer
Power transformers / I.C.T.
Bus bar and clamp fittings
Support structure
Isolators
Circuit Breaker
Wave traps
Earthing switch

9. Functions of various equipment :
* Transformers :
- Transforms the voltage levels from higher to lower level
or vice versa, keeping the power constant.
* Circuit breakers :
- Makes or automatically breaks the electrical circuits under Loaded condition.
* Isolators :
- Opens or closes the electrical circuits under No-load conditions.
* Instrument transformers :
- For stepping-down the electrical parameter (Voltage or Current) to a lower and safe value for Metering and Protection logics.
* Earth switch :
- Used to connect the charged body to ground to discharge the trapped charge to have a safe maintenance zone.

10. - Protects the O/H transmission line from Lightning strokes.
* Lightning arrestors :
- Safe guards the equipment by discharging the high currents due to Lightning.
* Overhead earth wire :
- Protects the O/H transmission line from Lightning strokes.
* Bus bar :
- Conductors to which a number of circuits are connected.
* Wave Traps/Line traps :
- Used in PLCC circuits for Communication and telemetering.
* Reactive Power control devices :
- Controls the reactive power imbalance in the grid by switching ON/OFF the Shunt Reactors, Shunt Capacitors etc.,
* Current Limiting Reactors :
- Limits the Short circuit currents in case of faulty conditions.

27. EXECUTION SEQUENCE:- Execution sequence for a substation Commissioning
Tower foundation
Equipment foundation
Laying of Cable trench
Laying of Earthmat
Support structure installation
High level stringing
Equipment installation
Equipment interconnection
Cabling layout
Commissioning

40. TABLE I: INSULATION LEVELS & CLEARANCE REQUIREMENTS AT DIFFERENT VOLTAGE LEVELS
NOMINAL SYSTEM VOLTAGE KV
INSULATION LEVELS
HIGHEST SYSTEM VOLTAGE KV
MINIMUM CLEARANCE
GROUND CLEARANCE
(MM)
SECTIONAL CLEARANCE (MM)
HEIGHT OF SUPPORTS (mm)
LIGHTNING IMPULSE LEVEL
(kVp)
SWITCHING SURGE LEVEL
POWER FREQUENCY IMPULSE LEVEL
(kVrms)
BETWEEN PHASE AND EARTH
BETWEEN PHASES 33 66
132
220
400
765
170
325
650
1050
1425
2100 -
1550
275
460
630
830 36
72.5
145
245
420
800
320
1300
3500 --
4000
3700
4600
5500
8000
2800
3000
4300
6500
10300
2500

41. Clearance contd… 5) Equipment spacing
a) Ease of maintenance/removal of equipment.
b) Equipment foundation & their cable trenches.
c) Distance between LA and equipment based on the protection reach of LA.
d) The spacings are generally kept in order to achieve various clearances specified at Table-I.

42. Clearance contd… 6) Bus bars: 7) Equipment Interconnection
The bus bars of 400 kV switchyard are generally made up 4 “IPS aluminum tube or Quad Moose rated for 3000 A”.
The bus bars of 220/132kV switchyard are generally made up of 3 “IPS aluminum tube or quad/ twin moose conductor”. Bus bars are placed at right angles to the feeders for tapping the power.
7) Equipment Interconnection
8) Spacer spans and locations
9) Connection Level
10) Land & Road Layout
11) Sequence and mounting of line traps

43. Clearance contd…. 12) Control Room Layout 13) Lighting System
14) Cabling Philosophy
15) Gravel Filling
16) Earthing System
17) Lightning Protection System

44. Selection of Bus Switching Scheme
PRE-REQUISITES
1)System security
2)Operational flexibility
3)Simplicity of protection arrangements
4)Ability to limit short circuit levels (ease of sectionalizing)
5)Maintenance – Its effect on system security
6)Ease of extension
7)Total land area
8)cost

45. EVOLVING A SUBSTATION LAYOUT
LAYING OUT A SUBSTATION INVOLVES STEP-BY-STEP PROCEDURE. MOST IMPORTANT POINTS TO BE CONSIDERED ARE BRIEFLY DESCRIBED BELOW:
THE IMPORTANT ELECTRICAL PARAMETERS ARE ESTABLISHED BY THE SYSTEM DESIGN. THE MAIN PARAMETERS ARE:
1) THE VOLTAGE AND BASIC INSULATION LEVEL OR SWITCHING SURGE LEVEL., THE SITE AND CLIMATIC CONDITIONS, THE METHOD OF CIRCUIT CONNECTION, AND SWITCHING OVER-VOLTAGE CONDITIONS.
2) THE BUS BAR SYSTEM DIAGRAM, THE NUMBER OF CIRCUITS AND THEIR PURPOSE I.E. THE CONTROL OF GENERATORS, TRANSFORMERS, FEEDERS, ETC.
THE DIAGRAM SHOULD INCLUDE DETAILS OF EXTENSIONS AND FUTURE CONVERSION TO A DIFFERENT BUS BAR SYSTEM, IF INTENDED.

46. EVOLVING A SUBSTATION LAYOUT
THE CONTINUOUS CURRENT RATING OF THE BUS BARS AND CIRCUITS.
THE SHORT CIRCUIT RATING OF BUS BARS AND EQUIPMENTS.
PARTICULARS OF REACTORS, NEUTRAL EARTHING EQUIPMENT AND REACTING, Interconnecting Transformers REQUIRED.
METHOD OF CONNECTION OF CIRCUITS, WHETHER BY OVERHEAD LINES OR BY CABLES.
DETAILS OF LIGHTNING PROTECTION EQUIPMENT.
DETAILS OF PROTECTIVE EQUIPMENT, DETERMINING THE INSTRUMENT TRANSFORMERS REQUIREMENTS, CARRIER CURRENT EQUIPMENT ETC.

47. EVOLVING A SUBSTATION LAYOUT
THE EXTENT TO WHICH CIRCUIT AND BUSBAR OUTAGES FOR MAINTENANCE WILL BE POSSIBLE.
SOME PARAMETERS WHICH INFLUENCE THE FORM OF THE LAYOUT ARE DETERMINED BY THE LOCAL CONDITIONS. THESE ARE:
THE AVAILABLE LAND AREA, SITE AND CLIMATE CONDITIONS, PLANNING AUTHORITY REQUIREMENTS AND AESTHETIC CONSIDERATIONS DETERMINE THE TYPE OF SUBSTATION.
THE DIRECTION OF OVERHEAD LINE ENTIRES POSITION AVAILABLE FOR TERMINAL TOWERS, LOCATION OF TRANSFORMERS AND REACTORS, ETC.
THE AVAILABILITY OF MATERIALS AND THE TRANSPORT AND ACCESS FACILITIES.
THE CAPABILITY AND SKILL OF THE MAINTENANCE STAFF DETERMINES THE IMPORTANCE OF CLARITY OF LAYOUT AND SIMPLICITY OF MAINTENANCE ZONING.

48. GUIDELINES FOR MAINTENANCE OF OIL PIT FOR TRANSFORMERS AND REACTORS
1.0 INTRODUCTION:
The layout for a transformer or reactor is planned in such away that there is adequate oil drainage facilities from underneath the equipment. This is essential in order to prevent catastrophic damage to nearby building/ equipments, if the transformer fire takes place and the oil is accumulated below the equipment due to explosion of the transformer/ reactor tank. The oil pit needs to be cleaned at a regular interval so that the oil drainage path is not blocked and in case of explosion, the oil is freely drained to the main oil pit. This regular cleaning is essential because at one of the site, although the oil pit was there below the transformer tank, its drainage was chocked and the transformer fire was accelerated since the accumulated oil in the pit also caught fire.
2.0 TYPES OF OIL PIT:
There are two types of oil pits in practice which are made below transformers/ reactors depending upon location, size and oil quantity etc. These are:
Soak Oil pit.
Drain and Retention Oil Pit.
SOAK OIL PIT:
If the oil pit provided below the transformer/reactor is not connected with the oil pit of any other equipment or main oil pit. it is classified as soak oil pit. The total volume of this individual soak oil pit is designed in such a way that volume of soak oil pit up to gravel filling level minus the volume of gravels should at least be equal to the oil volume in the transformer. The details of this type of soak oil pit are shown in figure-1.

49. SOAK OIL PIT

50. DRAIN AND RETENTION OIL PIT:
For the transformer or reactors located in the transformer yard i. e. unit aux. transformers/station aux. transformers/generator transformers and other transformers of 25 MVA and above rating, individual oil drain pits are provided and these individual oil pits are connected to one common retention oil pit for oil/water separation as these transformers are provided with mulsifire system and in case of fire, the mulsifire system will spray water, which will occupy the empty volume available in retention oil pi t. Also the transformers separated by fire walls and having oil quantity of more than 5000 liters are provided with individual oil drain pits which in turn are connected to one common retention oil pit. The drain oil pit is shown in figure-2.

52. RETENTION OIL PIT
The retention oil pit has two interconnecting chambers. The first chamber is called main chamber and the second chamber is called separation chamber. These two chambers are interconnected with a pipe. In case of fire, the oil-water mixture comes to the main chamber where the pipes from drain oil pit of individual transformers are connected. From here, by virtue of difference in specific gravity, the water is separated and flows to separation chamber. The separation chamber is connected to surface water drain to which the water is drained. The arrangement is shown in figure-3.

53. RETENTION OIL PIT

54. After the water is removed, the waste oil is pumped out to waste oil tankers. Under normal conditions, the retention oil pit is filled with water.
The total volume of main and separation chamber is sized to contain total oil volume of the largest transformer plus the volume of water sprayed during 10 minutes of mulsifire operation.
RECOMMENDATIONS:
Due to oil seepage and accumulation of dust in the oil pit, it becomes sticky substance like paste and has a tendency to clog the loose gravels in such a way that the oil/water cannot flow freely from the drain oil pit to retention oil pit. Further, due to such clogging, the designed volume of oil pit reduces, endangering into catastrophic fire. Under these circumstances, the purpose of oil pit for which it is designed is lost.

55. Design Philosophy / Practice
For designing a switchyard layout, various aspects are considered which are described here under:
Space around the switchyard. Adequate space should be provided for extension of the switchyard facilities when generating units or transmission lines are added in the future. The immediate surroundings should permit the routing of lines to the switchyard area from at least one direction without the need for heavy dead-end structures in the yard.
Switchyard location. The switchyard should be sited as near to the main plant as space permits, in order to minimize the length of control circuits and power feeders and also to enable use of service facilities located in the main plant.
Switchyard fencing. A chain link woven wire fence not less than 3.0 m height above toe wall, with lockable gates, should be provided to enclose the entire yard from safety point of view.

56. CLEARANCE:-
Clearance. The placement of equipment in EHV switchyard is greatly affected by the air clearances to be adopted. They are as follows:
Earth Clearance: this is the clearance between live parts and earthed structures, walls, screens and ground. A minimum height of live conductors above ground must also be maintained as per IE rules. Also there should be a certain minimum height of supports of various equipment (depending upon the fact that the bottom of any insulator has to be 2.5 meters above the ground level as statutory clearance).
Phase Clearance: this is the clearance between live parts of different phases.
Isolating Distance: this is the clearance between the terminals of an isolator and the connections thereto.
Section Clearance: this is the clearance between live parts and the terminals of a work section. The limits of this work section, or maintenance zone, may be the ground or a platform where a personnel has to carry out work.

57. Mounting of Line traps:-
Sequence and mounting of line traps
The sequence of installation of line traps, lightning arresters, coupling capacitors is given below for any line feeder:-
From line end: BPI, LA, CVT, Line Trap.
A bus post insulator is installed at line end to avoid mechanical forces on LA.
Mounting of the line trap shall be of pedestal type

58. Control room layout&lighting
A Control room building has to be built in the switchyard. Its location should be such as to minimize control cables between switchyard and main plant. Also it should have easy approach from main road and switchyard view should be possible from the control room. The control of the switchyard is either form the switchyard control room or the main plant control room. Al the panels for the purpose are to be located in this control room. For control of the switchyard please refer separate guidelines.
Lighting System
Switchyard lighting consist of outdoor lighting of the yard and lighting of Switchyard control room building. The outdoor lighting is to be done with 400W HPSV lamps. The various lighting fixtures complete with lamps and accessories shall be mounted only on Lightning Masts or Lighting poles. There should be no Lamp suspended on gantries or any live structure of the switchyard as per IE rules. The lighting along the road shall be achieved by providing suitable fixtures on lighting poles. Different illumination levels and type of lighting fixures and lighting design in Switchyard shall be as specified. Refer guideline on Lighting for more details

59. cable trenches. All cables used in switchyard are armoured type due to induced voltages. There are two types of cables used in a Switchyard viz. Power cables and control cables. The sizes for power cables vary from 3X 35mm2 to 2cX 6 mm2 and for control cables it varies from 5c X2.5 mm2 to 27cX2.5 mm2. Refer guideline on cable routing in switchyard for more details.
Gravel Filling
Gravel or surface material coverings, usually upto 150mm in depth, are useful in retarding the evaporation of moisture and thus in limiting the drying of topsoil layers during prolonged dry weather periods. Also covering the surface with gravel increase the surface resistance and thus reduces shock currents.

60. GRAVELS IN SWITCHYARD
1.The gravels with voids from a good insulating layer above the soil(Earthing) so that step potential is easily achieved.
It slows weeding in the soil
Gravels acts as a flame retardant in case of flaming oil being dropped from CT/CVT
It avoids snakes and other raptiles.

61. PREPARATION OF BASIC LAYOUT
WHILE MEETING ALL THE NEEDS ESTABLISHED THE FOLLOWING IDEALS SHOULD BE AIMED AT IN MAKING THE BASIC CIRCUIT LAYOUT.
MINIMUM GROUND AREA
MINIMUM QUANTITIES OF CONDUCTOR, JOINTS AND STRUCTURE
MINIMUM NUMBER OF INDEPENDENT INSULATORS, ESPECIALLY IN THE BUS BAR ZONE.
AFTER HAVING DETERMINED THE ELECTRICAL CLEARANCE BE USED A ROUGH CIRCUIT LAYOUT IS MADE. SEVERAL POSSIBLE ALTERNATIVES ARE PREPARED FROM WHICH THE MOST SUITABLE ONE WILL BE SELECTED. SOME VARIATION IS NEEDED, TO MEET THE REQUIREMENTS OF DIFFERENT TYPES OF CIRCUIT.
IT IS ALSO NECESSARY TO CALCULATE SHORT CIRCUIT AND ATMOSPHERIC FORCES TO DETERMINE THE STRESSES IN CONDUCTORS, INSULATORS AND STRUCTURES. THESE HELD IN DECIDING THE MOST OPTIMUM DIMENSIONS.

62. OPTIONS/ALTERNATIVES
1)Single sectionalised bus
2)Main and transfer bus
3)Sectionalised Main bus with transfer bus
4)Sectionalised double main and transfer bus
5)Double Bus Scheme
6)Ring bus
7)One and a half breaker
8)Double bus, double breaker

63. Single Sectionalized Bus-bar system
I/C Feeders CB
Bus-bar
Isolators
O/G Feeders

71. Double main bus & transfer bus system
Merits
Demerits
Remarks
Most flexible in operation
Highly reliable
High cost due to
three buses
Preferred by
some utilities for
400kV and
220kV
important
substations
Either main bus can be taken out
of service at any time for
maintenance

74. BASICS OF ONE AND HALF CIRCUIT BREAKER SCHEME

75. ONE & HALF BREAKER DESCRIPTION
BUS-1
3. THEY ARE DESIGNATED AS 1-52 CB, 2-52 CB, 3-52 CB.
1-52 CB
BUS-1
BUS-2
1-52 CB
3-52 CB
2-52 CB
2-52 CB
3-52 CB
BUS-2

76. ONE & HALF BREAKER DESCRIPTION
BUS-1
4. LINE - 1 IS CONNECTED IN BETWEEN 1-52 CB & 2-52 CB.
5. LINE - 2 IS CONNECTED IN BETWEEN 3-52 CB & 2-52 CB.
1-52 CB
BUS-1
BUS-2
LINE-1
1-52 CB
3-52 CB
2-52 CB
LINE-2
2-52 CB
3-52 CB
LINE-1
LINE-2
BUS-2

77. 400KV One and half Breaker Scheme

78. 400 KV BUS SECTIONALIZER

79. 220KV two main Bus one transfer Bus Scheme

80. One & half breaker scheme
Merits
Demerits
Remarks
Flexible operation for breaker in breaker maintenance
1)One and half
breakers per circuit,
hence higher cost
2) Protection and
auto-reclosing more
complex since
middle breaker must
be responsive to
both associated circuits
1. Used for 400kV
& 220kV
substations
2. Any breaker can be removed
from maintenance without
interruption of load.
3. Each circuit fed by two
4. All switching by breaker.
5. Selective tripping

81. Imp. considerations in substation design
 Safety of personnel and equipment
 Reliability and Security
 Adherence to
 Statutory obligations
– I.E. rules, Environmental aspects
 Electrical design considerations
 Structural design considerations
 Ease of maintenance
 Possibility to Expand