EHV SWITCHYARD
EQUIPMENTS, SWITCHING
SCHMES & LAYOUTS
Switchyard Type
Conventional Air Insulated Type.
Gas Insulated type.
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
DESIGN GUIDELINES CONTD…
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
CONTD…
DESIGN PRACTICES/PHYLOSOPHY
1) Consideration in Selection of Bus
Switching Scheme
2) Comparison of Schemes
a) Sectionalized main bus with transfer bus
(Scheme-I)
b) Sectionalized double main and
transfer bus (Scheme-II)
c) One and a half breaker (Scheme-
III)
DISCUSSIONS OF SCHEMES
SCHEME 1
SCHEMES CONTD…
SCHEME 2
SCHEMES CONTD…
SCHEME 3
System Security (Reliability
i) feeder fault
ii) Bus fault
iii) Redundancy in design
Main & Transfer
i) require
operation of one breaker
ii) supply would be interrupted until all the feeders are transferred to the healthy bus iii) No alternate path (Offline redundancy available)
Double Main & Transfer
i) require
operation of one breaker
ii) supply would be interrupted until all the feeders are transferred to the healthy bus iii) No alternate path (Offline redundancy available)
One & Half Breaker i)require operation of two breakers ii) continuity of supply is maintained because each circuit gets fed through two paths
iii) Alternate path is available
(Online redundancy available)
Operational Flexibility: Simplicity of Protection Arrangements Ability to limit Short Circuit Levels (Ease of Sectionalizing) Switching operation to take out the breaker from the bay more extensive Protection arrangement involves AC & DC switching . Sectionalising of bus bars or introduction of reactors in buses with a view to limit short circuit level is adoptable.
Switching operation to take out the breaker from the bay more extensive
Protection arrangement involves AC & DC switching & bus differential protection is complicated as it involves CT switching. Sectionalising of bus bars or introduction of reactors in buses with a view to limit short circuit level is adoptable.
A breaker can be taken out of service without the need for additional switching Protection
arrangement is simplified as no AC & DC switching involve and Bus differential protection is simple. Sectionalising of bus bars or introduction of reactors in buses with a view to limit short circuit level is adoptable.
Ease of extension
Total land area
Cost Switchyard shall be suitable for future extension without loss of feeders. This scheme is flexible for such future additions
This scheme occupy more or less the same land area as of the other two
schemes.
one breaker per feeder is required Switchyard shall be suitable for future extension without loss of feeders. This scheme is flexible for such future additions
This scheme occupy more or less the same land area as of the other two
schemes.
one breaker per feeder is required Switchyard shall be suitable for future extension without loss of feeders. This scheme is flexible for such future additions
This scheme occupy more or less the same land area as of the other two
schemes.
Three breaker per 2 feeder is
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
LAYOUT CONTD…
Options / Alternatives
The layout will vary for the
following:
1)
Switching schemes
2)
Type of insulation - Air
Insulated/Gas Insulated.
LAYOUT CONTD…
Design Philosophy / Practice
1) Space around the switchyard
2) Switchyard location
3) Switchyard fencing.
4) Clearance.
i) phase to earth clearance
ii) phase to phase clearance
iii) section clearance
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 (kVp) POWER FREQUENCY IMPULSE LEVEL (kVrms) BETWEEN PHASE AND EARTH (MM) BETWEEN PHASES (MM) 33 66 132 220 400 765 170 325 650 1050 1425 2100 -1050 1550 70 140 275 460 630 830 36 72.5 145 245 420 800 320 630 1300 2100 3500 6400 320 630 1300 2100 4000 9400 3700 4000 4600 5500 8000 --2800 3000 3500 4300 6500 10300 2500 2500 2500 2500 2500 2500
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
Clearance contd…
6) Bus bars:
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
Clearance contd….
12) Control Room Layout
13) Lighting System
14) Cabling Philosophy
15) Gravel Filling
16) Earthing System
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.
EVOLVING A SUBSTATION
LAYOUT
1)
THE CONTINUOUS CURRENT RATING OF THE BUS BARS
AND CIRCUITS.
2)
THE SHORT CIRCUIT RATING OF BUS BARS AND
EQUIPMENTS.
3)
PARTICULARS OF REACTORS, NEUTRAL EARTHING
EQUIPMENT AND REACTING, Interconnecting Transformers
REQUIRED.
4)
METHOD OF CONNECTION OF CIRCUITS, WHETHER BY
OVERHEAD LINES OR BY CABLES.
5)
DETAILS OF LIGHTNING PROTECTION EQUIPMENT.
6)
DETAILS OF PROTECTIVE EQUIPMENT, DETERMINING THE
INSTRUMENT TRANSFORMERS REQUIREMENTS, CARRIER
CURRENT EQUIPMENT ETC.
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:
1) THE AVAILABLE LAND AREA, SITE AND CLIMATE
CONDITIONS, PLANNING AUTHORITY REQUIREMENTS AND AESTHETIC CONSIDERATIONS DETERMINE THE TYPE OF SUBSTATION.
2) THE DIRECTION OF OVERHEAD LINE ENTIRES POSITION
AVAILABLE FOR TERMINAL TOWERS, LOCATION OF TRANSFORMERS AND REACTORS, ETC.
3) THE AVAILABILITY OF MATERIALS AND THE TRANSPORT AND
ACCESS FACILITIES.
4) THE CAPABILITY AND SKILL OF THE MAINTENANCE STAFF
DETERMINES THE IMPORTANCE OF CLARITY OF LAYOUT AND SIMPLICITY OF MAINTENANCE ZONING.
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.
PURPOSE OF EARTHING
THE OBJECT OF EARTHING IS TO MAINTAIN A
LOW POTENTIAL ON ANY OBJECT.
THE PURPOSE OF A EARTHING SYSTEM IN A
SUBSTATION AREA IS TO
LIMIT THE POTENTIAL
GRADIENT WITHIN AND IMMEDIATELY OUTSIDE
THE AREA
IS A VALUE, SAFE FOR THE WORKING
PERSONNEL. SAFETY IS TO BE ENSURED UNDER
NORMAL AS WELL AS ABNORMAL OPERATING
REQUIREMENTS OF A GOOD
EARTHING SYSTEM
FOLLOWING BASIC REQUIREMENTS ARE TO BE SATISFIED SO AS TO
ENSURE A PROPER AND SOUND EARTHING SYSTEM.
1)
THE EARTH RESISTANCE FOR THE SWITCHYARD AREA
SHOULD BE LOWER THAN A CERTAIN LIMITING VALUE
“RA” IN ORDER TO ENSURE THAT A SAFE POTENTIAL
GRADIENT IS MAINTAINED IN THE SWITCHYARD AREA
AND PROTECTIVE RELAY EQUIPMENT OPERATE
SATISFACTORILY. FOR MAJOR SWITCHYARDS AND
SUBSTATIONS IN INDIA, THIS LIMITING VALUE OF EARTH
RESISTANCE (RA) IS TAKEN TO BE LESS THAN 0.5 OHM.
2)
THE GROUNDING CONDUCTOR MATERIAL SHOULD BE
CAPABLE OF CARRYING THE MAXIMUM EARTH FAULT
CURRENT WITHOUT-OVERHEATING AND MECHANICAL
DAMAGE. THE MAXIMUM FAULT LEVEL IN THE 400 KV
SYSTEM HAS BEEN ESTIMATED TO BE 40 KA AND THIS
VALUE OF FAULT CURRENT TO USED IS THE DESIGN OF
EARTH MAT FOR THE 400 KV SUBSTATION.
REQUIREMENTS OF A GOOD
EARTHING SYSTEM
ALL METALLIC OBJECTS WHICH DO NOT CARRY
CURRENT AND INSTALLED THE SUBSTATION SUCH
AS STRUCTURES, PARTS OF ELECTRICAL
EQUIPMENTS, FENCES, ARMOURING AND SHEATHS
OF THE LOW VOLTAGE POWER AND CONTROL
CABLES SHOULD BE CONNECTED TO THE
EARTHING ELECTRODE SYSTEM.
.
THE DESIGN OF THE GROUND CONDUCTOR
SHOULD TAKE CARE OF THE EFFECT OF
CORROSION FOR THE TOTAL LIFE SPAN OF THE
PLANT.
Switchyard Equipments.
Circuit Breaker.
Disconnectors (Isolators)
Current Transformers.
Capacitor Voltage Transformers
(CVT).
Lightning Arrestors.
Post Insulators.
General Parameters
Dielectric Parameters .(IEC 694)
- Power Frequency Voltage.
- Lightning Impulse Voltage.
- Switching Impulse Voltage.
- Corona Extinction Voltage.
- RIV Level.
General Parameters (Contd.)
Rated Current.
Short Time Current.
400kV Equipments
a.
Rated voltage
420 kV
b.
Rated frequency
50 Hz
c.
Rated short time withstand
current capacity
40 kA rms for one (1) second
d.
Insulation levels for 420kV Circuit
breakers and Disconnecting
Switches
e.
i) Rated one minute power
Frequency withstand
voltage
a) 520 kV rms between live
terminals and earth.
b) 610 kV rms across isolating
distance.
ii) Rated lightning impulse
withstand voltage
a) +/ - 1425 kVp between live terminals
and earth.
b) +/- 1425 kVp impulse on one
terminal and 240 kVp po
wer
frequency of opposite polarity on
other terminal (across isolating
distance).
iii) Rated switching impulse
withstand voltage
a) +/- 1050 kVp between live
terminals and earth.
b) +/- 900 kVp impulse on one
terminal and 345 kVp power
frequency of opposite p
olarity on
other terminal (across isolating
distance).
f.
Max. Radio interference voltage
at 266kVrms
1000 micro volts for frequency
between 0.5 Mhz and 2.0 Mhz for all
equipment. However, for insulator
strings the measurement would be
at 305 kV .
Circuit Breakers Type (IEC: 62271-100)
MOCB.
ABCB.
SF6
Rated operating duty cycle- O-0.3 sec-CO-3
min.-CO
Operating mechanism
Total Break Time
Disconnectors
HCB Type.
Double Break Type
.
Pantograph type.
Vertical Break type.
Provision of Earth Switches.
Motor / manual operated.
Current Transformer ( IEC 60044, IS
2705)
Dead tank/Live tank type.
Bar Primary type.
Ring Type.
No. of Cores.
Ratio.
Accuracy.
rated primary current
Rated burden for metering
Knee Point voltage
Capacitor Voltage Transformer (IEC
60044, IS 3156)
Capacitance.
Voltage Ratio.
No. Of Cores.
Accuracy.
Output Burden
Lightning Arrestor ( IEC 60099)
Gap Type / Gapless Type.
Voltage Rating.
Energy Capability.
Monitoring.
Location.
Post Insulators
Voltage Rating.
Cantilever Strength.
Fixing Details.
Wave Trap (IEC 60353)
Rated Inductance(0.5/1.0 mH).
Rated current.
Band Width.
SWITCHYARD AUXILIARY SYSTEMS
CONTROL ROOM
HVAC FOR CONTROL ROOM
A RELIABLE 415V AC SUPPLY ( LT SWGR)
220 V & 48 V DC SUPPLY( BATTERY & BATTERY
CHARGER)
POWER & CONTROL CABLE
LIGHTING ( Yard lighting & indoor lighting of control
room)
Other items-Clamps, connectors , Insulator strings , BMK
192 69 ~10% 400kV GIS 275kV GIS Trfr 1 Trfr 2 Trfr 3 Trfr 4 SVC Trfrs 400kV AIS 275kV AIS
COMPARASON BETWEEN AIS AND GIS SUBSTATION
FOOTPRINT FOR HECTOR
Conductor Phase Spacing
9,81.m
if
sSAG DUE TO CONDUCTOR
f
s= 9,81.mi.Lc2
8.T
f
s= maximum conductor sag (m)
m
i= mass of conductor (kg/m)
L
c= conductor span length (m)
T = tension per conductor (N)
T
M
M
M
Attraction
Repulsion
CANTILEVER FORCES DUE TO FAULT CURRENT
COMBINATION SUPPORT STRUCTURE FOR 3 PHASES
F
S
TUBE
Upgradation of transmission voltage
from 400kV AC to 765kV AC.
Presently the highest AC Transmission voltage is 400kV only.
NTPC is fully geared up for implementing next AC voltage of
765kV.
Advantages:
Step up from generation voltage to 765kV.
High Capacity Transmission to the order of 2500MW per line
with lower right of way requirement.
765kV Transmission system is techno economically better
option whenever power transmission system requires multi
point tapping at various location for catering the load
requirement of high growth area.
765kV system offers low transmission losses, resulting in
higher utilisation of generating capacity and optimises the
resource required for capacity addition.
765kV Major Parameters
Highest system voltage : 800 kV rms
Lightning Impulse voltage : ± 2100 kVp Switching impulse voltage : ± 1550 kVp
Power frequency withstand : 830kV(rms) for 1 min. (rms) :
Max. fault level (1 sec.) : 40 kA
Minimum creepage distance : 20000 mm
Max. Radio Interference Voltage : 2500 micro volts. level at 508kV (rms).
Corona extinction voltage : 508kV (rms minimum) Phase to earth clearance : 4900 mm Conductor to Structure
: 6400 mm Rod to Structure Phase to phase clearance : 7600 mm Conductor to Conductor
: 9400 mm Rod to Conductor Section clearance : 10300 mm
Average electric field at 1.8 m from ground 10kV/m Average magnetic field 500 micro tesla
