Design of EHV Switchyard Renewable Energy Engineering.pdf

Design Of EHV Switchyard.

1. “Design of EHV Switchyard”

2. Agenda
Introduction
Design Considerations
Design Parameters
Switchyard Electrical Clearances
Transmission Line Clearances
Switchyard Design Calculations
Comparison of rigid and flexible buses
Point on wave switching
Porcelain vs Polymer Composite Insulators
Proposal Implementations For Future Project

3. Introduction
400kV Switchyard
400kV Systems is designed to cater for evacuation of generated power
from 2x700 MWe units of KAPP-3&4.
The power generated at 21kV is stepped up to 400kV level by three single
phase 285MVA, 21kV/420/√3kV GTs located adjacent to Electrical Bay
building and connected to 400kV switchyard through overhead lines.
400kV Systems also provide start-up power through GT-UT circuit by the
provision of GCB between the generator and GT.

Description KAPP-3&4 RAPP-5 to 8
Breaker Scheme
and configuration
One and half with I type One and half with I type
Number of Bays 4 line + 2 GT + 1 BR + 1 future
bays
4 line + 3 lines with line
reactor + 4 GT + 1 BR bays
Conductor size 4.5” Al. tube (EH) main bus,
4” Al. tube (EH) / Triple AAAC
/ Twin AAAC or ACSR
equipment connections.
4” / 4.5” Al. tube (EH) main
bus, 4” Al. tube /4” Al. tube
(EH)/ Twin AAAC or ACSR
equipment connections.

4. Introduction Contd..
220kV Switchyard
220kV System is common for both KAPS-1&2 and KAPP-3&4.
Two additional bays for SUT-3A & 3B and SUT-4A & 4B have been
added to the existing 220kV switchyard to provide off site power
supply to station auxiliaries through start-up transformers.


Description KAPP-1 to 4 RAPP-5 to 8
Breaker Scheme and
configuration
Two main bus with by-pass
isolators
Two main bus with by-pass
isolators
Number of Bays 8 line + 2 GT + 4 SUT + 1 BC 2 lines+1 line under
construction + 4 SUT +
2Colony T/F + 1BC
Conductor Size 4” Al. tube (EH) for Main,
Twin Moose ACSR / 2.5” Al.
tube (EH) for equipment
connections.
Triple Moose ACSR for Main,
Twin Moose ACSR / 2.5” Al.
tube (EH) / 3” Al. tube for
equipment connections.

5. Design Considerations
Safety of personnel and equipment
Reliability and Security
Quality
oManufacturing
oConstruction
Adherence to
Statutory obligations
– CEA rules
– AERB regulation
Electrical design considerations
Structural design considerations
Ease of maintenance
Possibility to Expand

6. Design Parameters
Sr. Description 400kV 220kV
1 Nominal system voltage 400kV 220kV
2 Max. operating voltage 420kV 245kV
3 Rated frequency 50Hz 50Hz
4 Number of phases 3 3
5 System neutral earthing Effectively earthed
6 Maximum power transfer capacity of
switchyard MVA
2000 500
7 Switching scheme for air insulated
switchyard
One & half
breaker
Two main with
bypass
8 Circuit Breaker
Rating kA
Maximum break time
PIR
1ᴓ auto reclo
50 or 63/1s
40msec
>200km line
1ᴓ auto reclo
40/3s
60msec
--
Based on CEA regulations on technical standard for construction of electrical plants and electrical lines

7. Design Parameters Contd..
Sr. Description 400kV 220kV
9 Corona Extinction voltage kVrms (ph to
earth)
320kV 156kV
10 Max. Radio interference voltage at
1MHz for phase to earth voltage
1000 μV
@ 267kV
1000 μV
@ 156kV
11 Min. Creepage distance
For heavy pollution area
For very heavy pollution area

25mm/kV
31mm/kV

25mm/kV
31mm/kV
12 i) Min. duration for computation of
capacity of battery (if stand by)
3h for steady & continuous
1h emergency light load
ii) Min. duration for computation of
capacity of battery (without stand by
battery)
6h for steady & continuous
2h emergency light load

8. Design Parameters Contd..
Sr. Description 400kV 220kV Remarks
13 Rated insulation levels
i) Full wave impulse
withstand voltage (1.2/50μs)
-- for other equipments
-- for reactor/ X’mer (Winding)
-- for lines



1425kVp
1300kVp
1550kVp



1050kVp
950kVp
1050kVp
ii) Switching impulse
withstand voltage (dry/wet)
1050kVp
iii) One min. power freq.
withstand voltage (dry/wet)
-- for lines
-- for other equipments


680kV
630kV


460kV
460kV

9. Outdoor Switchyard Electrical Clearances
Sr. Description 400kV 220kV
1 Phase to Phase 4200 mm 2100 mm
2 Phase to Earth 3400 mm 2100 mm
3 Ground Clearance 8000 mm 5500 mm
4 Height of insulator bottom from
ground
2440mm
5 Safe working clearance 6400 mm 4300 mm
Adopted Minimum Electrical Clearances for KAPP-3&4 and RAPP-7&8.
Based on CBIP Substation Manual

10. Safe working clearances

11. Safe working clearances

12. Transmission Line Electrical Clearances
Sr. Description 400kV 220kV
1 Transmission line Corridor 52 m 35 m
2 Vertical clearance from building 3.7 m+0.3m for every
additional 33kV
3 horizontal clearance from building 2 m+0.3m for every
additional 33kV
4 Ground clearance 5.2 m+0.3m for every
additional 33kV
5 Mid span clearance between
conductor and earth wire
9 m
6 Spacing between sub conductors 450 mm 300 mm
CEA regulations on measures relating to safety and electric supply and
CBIP Manual on Transmission Lines.

13. Bus Arrangements
 Single Bus scheme
 Single Bus with Sectionaliser scheme
 Main and Transfer Bus scheme
 Double Bus with Single Breaker scheme

 Double Bus and Transfer bus scheme
 Ring Bus scheme

 Double Bus with Two Breaker scheme

14. Design Calculations
Bus bar sizing – (IEEE 605 & IEC 60865)
Sag Tension Calculations – (IS: 802 (Part-1/section-1)
1995, IS: 5613, Generation, Transmission &
Utilisation of electrical power by A.T.STARR)
Short Circuit Force calculation as per IEC 60865
Earthing Design (FEM of ETAP / IEEE- 80)
Lightning Protection design (High Voltage
Engineering by Razveig)
Switchyard Lighting design as IS 6665/3646
Equipment sizing design and its cantilever strength
calculation

15. Bus bar design
Start
Calculate solar heat gain
(q
s)=ε’Q
sA’Ksin(θ)
Check
I
L<I &
I
f<I
swc
No
Yes
No
Yes
System parameters (V, f, I
L, I
f, t
f)
Ambient temperature (θ
a), Solar
radiation (Q
s), Wind speed,
Emissivity constant (ε), Solar
absorption constant(ε’)
Layout details (h, phase spacing),
Conductor details (A, D,
Conductor temperature before
fault (θ
bf), after fault (θ
af)), Skin
effect coefficient, DC resistance
Calculate convection loss
(q
c)=3.561D
-0.4
A(θ
bf-θ
a)
Calculate radiation loss
(q
r)=5.6697*10
-8
εA[(θ
bf+273)
4
-
(θ
af+273)
4
]
From heat balance equation
I=sqrt( (q
c+q
r-q
s)/(RF)
Short time with stand current



Stop
Corona
shall be
checked

16. Comparison of Rigid and Flexible Bus
Rigid Bus Strain Bus
Conductor Extruded Structural or seam
less tube
Stranded bundled conductors
Broken conductor
faults
Conductors are not under
strain
Conductors are under strain
Seismic Less reliable More effective
Bus height Main Bus 8.8 m & Crossing of
bus 13.8m
Jack Bus 22.3m
Main Bus 15.8 m
Jack Bus 23.3m
Mounting structure
for 2 bays & one bus

13 BPI+4 HPI =
(13*0.3MT+4*0.86MT) = 7.34
MT
2 X 15.8m ht towers
(2*4.8MT)+ 2 X 27m long
beam (2*4MT) =17.6 MT
Foundation More (13 nos) Less (2 nos)
Insulators 13 nos Post Insulators 6 nos String Insulators & its
hardware
Time Higher man hours Fewer man hours

17. Contd..

18. Gantry Structure Design
Sag / Tension calculation :
Sr. Temp Wind Pressure Limits
1. Min. 36%
2. Every Day Temperature 100% T <= 70% of UTS
3. Every Day Temperature No wind T <= 22% of UTS for
conductor
T <= 20% of UTS for
ground wire
4. Max.
(ACSR 75
0
C/ AAAC 85
0
C)
No wind Clearances
5. At every 5
0
C (up to 50
0
C) No wind

19. Contd..
Start
Conductor data (n, A, w, E, UTS),
Spacer data & insulator data
Calculate vertical sag and
inclination sag
Check
clearances
within limits
Stop

Check T
2, T
1 value
within as per IS-
802 (Previous
slide)

Note: Repeat the above procedure
for achieving the conditions as
mentioned in previous slide.
No
Yes
No
Yes
Environmental details (wind,θ1,
θ2), Min. clearances
Layout details (span length,
height) & Initial tension
Calculate equivalent weight of
conductor & force due to wind

20. Short Circuit Force Calculations
System data, Layout,
Conductor, Static
tensile force at Min. /
Max. Temperature
Electromagnetic Force (Fm) per
unit length of conductor
Calculate Drop force (Fd)
Calculate
minimum air
clearances
Stop
Calculate direction of force,
resulting period, swing out angle
Tensile force during short circuit
(Ft)
Swing out angle
<60 deg, Ratio of
Fm & Gravitational
Force < 0.6

Number of
conductors>1
Calculate pinch force (Fpi)
Max.(Ft, Fd & Fpi)
No
Yes
No
Yes
Yes
No

21. Earthing Design

Guiding standards – IEEE 80, IS:3043, CBIP-302.
Switchyards are designed for the system fault level . However
for optimal earthing design actual fault current may be
considered.
Basic Objectives:
Step potential within tolerable
Touch Potential limit
Ground Resistance
Adequacy of Ground conductor for fault current (considering
corrosion)

22. Earthing Design
Description KAPP-3&4 RAPS-5&6
Area 352 m*160 m 107.5 m*254 m
Soil resistivity 41ohm-m @ 2m depth
800 ohm-m
1450 ohm-m
Gravel resistance 2500 ohm-m 5000 ohm-m
Conductor size 195.1 sqmm Cu 40mm dia MS rod
Total length of ground
conductor
9040 m 39746.5 m
Total length of ground rods 372 m 180 m
depth 0.6 m 1 m
Touch potential 563.3 V < 583.9 V 1445.12 V < 1645.27 V
Step potential 748.1 V < 1886.2 V 1500.26 V < 5902.27 V
Ground resistance 0.99 ohm 1.91 ohm (Isolated)
Calculation methodology FEM - ETAP IEEE-80

23. FEM
Finite Element Method (FEM) solves partial differential equations by
discretizing the volume-space (usually with triangular vertices)
The analysis using FEM has four steps
Discretization of the geometry to sub-region or element (triangular ).
Attainment of the field equation as Governing equation in surface of element
Assembly of all the elements in the solution region by matrices.
Solve the matrices obtained

24. Touch and Step potential

25. Lighting Design
Adequate lighting is necessary for safety of working personnel and O&M activities

Recommended value of Illumination level
–Control desks - 400 Lux
–Protection panel - 200 Lux
–Battery room - 150 Lux
–Cable gallery - 100 Lux
–Other areas of control building - 200 Lux
–Switchyard - 50 Lux (main equipment)
- 20 Lux (balance Area / road @
ground level)
20% light fixtures shall be provided as AC emergency lighting in switchyard and
control building
DC lighting in control building

26. LED vs General Lighting Service
Description LED FTL
Principle of
operation
LED is made up of a semiconductor
material. LED bulbs are grouped in
clusters with diffuser lenses.
It made up with long glass tube with metal
fittings on each end by filling small amount
of mercury and an inert gas and coated
inside phosphorous powder
Direction of light 110 deg. (Directional) 360 deg.
Initial Cost More Less
Running cost Up to 50000 hours 10000 hours
Noise Do not have this problem
After significant amount of time FTL used to
make buzzing noise
Instant on Instantly Time required to flicker before staying on
Colour
It provides different colours (depends on
chip material and colour temperatures
for any purpose. It requires feedback
loop systems with colour sensors, to
actively monitor and control the colour
output of multiple colour mixing LEDs
Warm white (2700 K) for residential lighting/
Neutral-white (3500 K) / Cool-white (4100 K)
for office lighting / Daylight (5000 K to 6500
K) which is bluish-white
Heat Generation Heat sink is required Small amount of heat produced
Sensitivity for
heat
Sensitive to excessive heat, like most solid
state electronic components No sensitivity

27. LED vs General Lighting Service
Description
Watts (LED)

Watts
(Incandescent)
Watts (CFL)

Watts (FTL)

450 Lumen 4-5 40 9-13 --
800 Lumen 6-8 60 13-15 --
1,100 Lumen 9-13 75 18-25 --
1,600 Lumen 16-20 100 23-30 --
2600 Lumen 25-28 150 30-55 40W + 12W
Heat Emitted
(1Btu = 0.55 deg.C)
3.4 btu's/hour
(6-8 watts)
85 btu's/hour
(60 watts)
30 btu's/hour
(13-15 watt)
Life Span 50000 hours 1200 hours 8000 hours 20000 hours

28. Contd..

29. Contd..

30. Lightning Protection – Ground Wire FIG-4bFIG-4a
Zone of protection by
single ground wire

bx=1.2H(1-Hx/(0.8H)) for
Hx<2/3H
bx=0.6H(1-Hx/H) for
Hx>2/3H

Zone of protection by
two ground wire
H0=H-S/4

31. Lightning Protection – Lightning Mast FIG-2a
FIG-2b FIG-3.0
Zone of protection by single LM
rox=1.5h(1-hx/(0.8h)) for hx<2/3h
rox=0.75h(1-hx/h) for hx>2/3h
If h>30m, P=5.5/sqrt(h) shall be multiplied with above equations.
Distance bewteen two LM: S<=7(h-h0)
Maximum diameter of three LM: D<=8(h-h0)

32. 220kV Cable Selection Process
LOAD, VOLTAGE LEVEL,
SCC, LAYING CONDITION
CABLE TYPE & DESIGN
CONDUCTOR MATERIAL
EARTHING METHOD OF
SHEATH
CONDUCTOR CROSS
SECTION
SELECTION OF CABLE
ACCESSORIES
LAYING CONDITION

33. 220kV Cable Manufacturing Process
CONDUCTOR RODS
BETWEEN EACH LAYER WATER
SWEALLABLE TAPE IS PROVIDED
COMPLETE COMPACTED
CONDUCTOR
CONDUCTOR SCREEN (Semi
Conducting tape)
CURING
SEMICONDUCTING & WATER
SWELLABLE TAPE OVER
INSULATION
COPPER WOVEN TAPE
STRANDS
TRIPLE EXTRUSION PROCESS
DEGASFYING
METALLIC SHEATH
BITUMINUS COMPOUND
OVER SHEATH (Extruded HDPE
(Type ST7)

34. Cross section view of single core 500sqmm 220kV
Cable used in RAPP-7&8 and KAPP-3&4

35. 220kV Cable Design Calculations
Reference standard IEC 62067 & IEEE 635
Heating of cables
Core loss (Wc=I
2
R)
Dielectric loss (Wd=ωCV
2
tanδ)
Sheath loss (Ws=λWc)
Charging current (I
c=V/X
c=ωCV)
 Dielectric stress calculation at conductor and at insulation
Sheath Induced Voltage
Continuous and Short Circuit Current rating of cable
Effect of charging SUT with cable feeder.

36. Earthing of 220kV Cable
Both end bonding Single end bonding
Cross bonding

37. 220kV Cable Accessories
Air termination
 Link box without SVL
Link box with SVL
Bonding Cable
Earthing Continuity Cable (ECC)

38. Point on Wave Switching
Reference standard IEC 62271-302
 Principal
Alternative to PIR
It introduces a suitable time delay between the instant it receives an input command for operating
the switchgear.
Application
Shunt Reactor Switching
Transformer Switching
Capacitor banks switching
Transmission line switching
System Requirement
Individual pole operated CB
Mechanism of the CB
Bus voltage for reference
CT input
Temperature input

39. Point on Wave Switching

40. Point on Wave Switching

41. Porcelain vs Polymer Composite Insulators
Description Porcelain Polymer Insulators
Material Clay, feld spar, quartz and
alumina
Glass fiber reinforced epoxy resin rod shaped
core (FRP rod) over seamless sheath of
silicone elastomeric or silicone alloy
compound.
Hydrophobic Forms water film on the
surface making easy path
leading to more flashovers
Prevents the formation of conductive film on
its surface without the need of washing
Strength Good Better due to crimping, but high crimping
force leads FRP rod damage
Resistance to
breakage
High fragile Flexible hence high resistance to breakage
Leakage current Higher Lower
Tracking Poor tacking resistance Excellent tracking resistance avoids erosion or
tracking of the housing material
Draw backs Porosity Parrots, which loves to chew on polymeric
insulators.
Moisture may enter in the core if any
unwanted gaps b/w core & weather sheds
Standard IEC 60383 IEC 61109

42. Polymer Composite Insulator Cross Section

43. Seismic Design
The switchyard and towers are be designed for earthquake as per IS: 1893 Part-4
with an importance factor of 1.75.
Horizontal seismic coefficient (Ah) for structure = (Zone factor(Z)/2)*(Importance
factor/Response reduction factor) *(Average response acceleration
coefficient(Sa/g)).
Shear force = Ah*(m*g) Newton
Seismic design force for higher floors shall be computed as per the provision of
clause 13.3 of ASCE 7-05

44. Future Implementations (proposed)
Lightning cum lighting mast
Point on wave switching for Circuit Breaker
Butterfly tower in Transformer yard
LED fixtures in switchyard control building
Bay Control Room
Switchyard Seismic Design - IEEE Std 693-2005

45. Butterfly tower
Specially designed tower
for tapping connection
to GTs.
Avoid snapping of
conductor on GTs (MAPS
GT-2 incident).
Proposed for new
projects

46. Bay Control Rooms

47. THANKS for attention!