Standard Parameters of 800 kV Class Transmission Systems in India

Prof. Robert B. Laughlin
Department of Physics
Stanford University, Stanford, CA 94305

http://www.cea.nic.in/power_systems/Design_&_Engg/Standard_Parameter_of_800_KV_Class_Transmission_System_in_India.htm
(Copied 1 Aug 09)

STANDARD PARAMETER OF 800 KV CLASS TRANSMIISSION SYSTEM IN INDIA

PREFACE

Earlier in the year 1990 Central Electricity Authority (CEA) brought out a report detailing parameters of the 800 kV class equipment and transmission line material based on the recommendations of Working Groups constituted following the decision of Government of India to select 800 kV (with 765 kV as the nominal voltage) as the next higher AC Transmission voltage in the country. Following this, a good number of lines were identified at this voltage. Though some of these lines have been installed maintaining 800 kV class parameters, they are being operated at 400 kV level for want of adequate power development. Accordingly associated substations continue to be at      400 kV level.

But with the initiative taken to have electricity for all by the year 2012, coinciding with the end of 11th five-year plan, now it is a near-reality to charge the above mentioned lines at 765 kV and construct few more intra-regional and inter-regional lines at that level with a dozen or so number of substations. Keeping this in mind and the progress that has been further made and as experienced in few countries that have this class of transmission system, it was felt necessary to revive the Standing EHV Committee of CEA with representations from leading power utilities and manufacturers in the country. As per order of Ministry of Power it was reconstituted in the year 2000. A few meetings took place for revising the salient parameters of 800 kV class of equipment and transmission material and reviewing those for 400 kV level through separate groups. The present report is an outcome of the deliberations in the meetings and inputs received from the members concerned. It is expected that the contents would serve power utilities as the basis of design and engineering of 800 kV transmission system in the country.

New Delhi

(Dr. S.Mukhopadhyay)

December 31, 2002

Chief Engineer (SETD), CEA

 

BASIC SYSTEM PARAMETERS OF 800 KV SYSTEMS

1.    Rated voltage                                             kV    :    800

2.    Nominal Voltage                                        kV   :    765

3.    Rated frequency                                         Hz   :    50

4.   System Neutral Earthing                                    :   Effectively earthed

5.    Rated current                                             A     :    2000

6.    Short circuit current and duration              kA   :    40 for one second

7.   Creepage distance                        

Pollution site severity

Specific creepage distance mm/kV*

Low

16

Medium

20

Heavy

25

Very Heavy

31

* These are the values suggested in IEC- 815, 1986, which is applicable to System Voltage of up to 525kV. As the pollution withstand characteristics is known to be non-linear for higher voltages, requiring increased creepage distance in proportion to the non-linearity factor.  Studies by ENEL, EPRI, CIGRE suggest that this factor may be as high as 20% for 800 kV System.  Hence creepage distances presented in the Table are to be appropriately increased.  Further, these values may not be suitable for station insulation since the influence of diameter is considerable on the pollution performance.

8.    Insulation Levels
a)    Substation equipment

  Reactors/  CBs/Isolators/CVTs/CTs     Transformers                                                           

Basic Insulation level              kV(peak)   1950                         2400 

Basic switching level               kV(peak)  1550                         1550 

Power frequency                      kV (rms)     -                                830 

RIV at 508 kV rms                  Micro         -                          1000(Max.)
                                                 volts                                  
b)    Transmission lines

 Basic Insulation level              kV(peak)           2400 

Basic Switching level               kV(peak)           1550 

Power frequency                     kV(rms)               830 

RIV at 508 kV (rms)                Micro volts        500(Max.)

                TRANSFORMER

Generator Transformers 
1.  Ratings:                               

Three phase rating
MVA(Generally
Single phase units
are envisaged)
Voltage
ratio
Tapping range
percent  
Percent
Impedance
Voltage
 Cooling
630 MVA,800 MVA  21/765 A-off ckt
taps/links
 +2
-6  
(8 steps)  
alternatively
 
B-On load  taps
+2
-6 
   (16 steps)
15.0
(tolerance
allowed  
=  + 10%)
ONAN/OFAF
or
OFAF or OFWF
or
ONAN/ODAF or
ODAF/ODWF

Maximum   flux density in any part
of core and yoke at rated MVA,                   tesla          :                             1.9
voltage and frequency.

Withstand capability for 25%                       minutes    :                               1
above the rated voltage

Withstand capability for 40%                        seconds    :                               5
above rated voltage

2.  Connections :  HV Star, Neutral effectively earthed
                              LV Delta

3.    Connection symbol       :    YN, dll (in 3 phase bank)

4.     Terminals:

       a)  LV Terminals

36 kV, 12500 amps. oil filled type bushing mounted on turrets, suitable for connections to bus bars in isolated phase bus ducts which shall have spacing of 1500 mm for each   210 MVA single-phase unit of the 630 MVA three phase bank.

For each of 266.6 MVA single phase unit of 800 MVA, 3 phase bank, 2 Nos. 36 kV, 12500 Amp bushings per termination shall be used (Total 4 Nos. bushings).

b)  HV Terminal line end :

800 kV oil filled 1250 amps. condenser bushing with test tap.  No arcing horns shall be provided.

Neutral ends : 36 kV porcelain bushing.  No arcing horns shall be provided.

Auto Transformers

1.    Ratings

Three phase rating Voltage Tapping   Percent     Impedance
Voltage
Cooling
HV/IV/LV
MVA       
ratio range   percent HV 
IV    
HV   
LV
IV
LV
 
 315/315/105 765/220/ 
33       
+ 4.5%   
-7.5%
24 steps   
12.5      40   25  ONAN/OFAF
or ONAN/
  ODAF  or
ODAF 
630/630/210 765/400/33 + 4.5  %  |
-7.5%   
24 steps
12.5   60     40  -do-
800/800/266.6   -do- -do- -do- -do- -do-
1000/1000/333.3 765/400/
33     
+4.5%
-7.5%
 24 steps
14.0  65             45   -do-

                                                           tolerance    10%        15%       15%

Max. flux density in any part of core and
yoke at rated MVA, voltage and frequency                            tesla        :    1.9
 

Withstand   capability for 25% above the                               minutes   :     1
rated voltage 

Withstand capability for 40% above the                                seconds   :     5    
rated voltage.

2.  Connection   :    HV/IV Star auto with neutral effectively earthed
                          :    LV-Delta 

3.  Connection Symbol  :    YNa0,  dll  

4.  Short Circuit Level  :      

     800 kV                  -       40 kA  (rms)  for 1 second     

     420 kV                  -      40 and 63 kA(rms) for 1 second 

     245 kV                  -      40 kA (rms) for 1 second 

5.  Terminals: 

a)  LV Terminals      -       52 kV oil filled condenser bushings.  The bushings shall be
                                          arranged in a line with 1000 mm spacing to allow mounting of                                           phase to phase barriers.  No arcing horns shall be provided. 

b)  IV terminal         -        245/420 kV oil filled condenser bushings with test tap.  No
                                          arcing horns shall be provided.

c)  HV Terminal      -        800 kV oil filled condenser bushing with test tap.  No
     Line end                        arcing horns shall be provided. 

     Neutral end           -        36 kV porcelain bushing.  No arcing horns shall be provided. 

Insulation Levels:

                   Lightning, switching Impulse and Power frequency voltage level.

Highest voltage
for equipment.  
 Um kV (rms)
Rated withstand
   lightning   
Impulse voltage  
switching  (kV peak)  
Rated power frequency
short duration withstand
voltage kV(rms)
kV(peak)          
17.5(Neutral) 95     -  38
24(LV of GTs) 125 -         50
52 (LV of Auto Transformer) 250     -       95   
245   950 - 395
420 1300 1050 -
800  1950 1550 -

                 In the event when transferred surges are higher than 250 (kV peak) the insulation level of tertiary winding and bushing are to be chosen accordingly. 

Partial discharge                

At    1.5 x Um  kV,  pico coloumbs             500 (Max.)
               v 3

BUSHINGS :

1)    The voltage and current ratings, basic insulation level and creepage distance of the
       bushings shall be as follows:              

Voltage Ratingk
V(rms)
Current  Rating
(Amp)
Creepage    Distance (mm) Basic Impulse Level   kV(peak)    Switching Impulse
Level kV(peak)
800 1250    16,000    2100   1550 
420 1250  
   
2000 
10,500       1425       1025
245 1250 6,125      1025  
 52 2000
5000
1,800   250      -
2)     RIV at 508 kV (rms)          micro volts           :     1000 (Max.) 
3)      Corona Extinction voltage    kV(rms)          :   508 (Min.)
4)      Partial discharge level     pico coloumbs   :  500 (Max.)

                                                                  

CIRCUIT BREAKERS 

1.      Type :     SF6
2.      Installation :    Outdoor
3.      No. of poles   :    3
4.      No. of trip circuits  :    2 (independent)
5.      Rated short circuit
        making current.  kA peak
:    100
6.      Value of pre-insertion
       resistor    ohm
:    450    To limit switching surge
               over voltage to 1.9 p.u.
7.      Pre- insertion time         ms :     10  
8.      Rated operating duty cycle     :     0-.3 second-CO-3 min.-CO
9.      Rated break time   ms :      40
10.   Closing time                                     ms   :      100
11.   Difference in the instants of opening of contacts
            - within a pole  ms
           
- between poles   ms

:       2.5
 :       3.33
12.   Difference in the instants of
       closing of contacts between poles   ms
:       10
13.    Rated line charging current  

      

Sl.No. Line Length(km) Typical Line Charging current at bus voltage of             1.4 pu (kA)
    No shunt    reactor in the line With one of the two shunt reactors failed Both shunt reactors in service
1 100 0.262 0.197 0.131
2 150 0.393 0.295 0.197
3 200 0.542 0.393 0.262
4 250 0.655 0.491 0.328
5 300 0.786 0.590 0.393
6 350 0.917 0.688 0.459
14.    Small inductive current     :        0.5 A to 10 A without
          switching over voltage exceeding 1.9 p.u.
15.    Type of operating mechanism    :      Pneumatic or hydraulic spring charged or           combination of these.
      Anti  pumping and trip free
16.    First pole to clear factor :         1.3
17.    Type of auto reclosing   :        Single phase and 3-Phase. 
18.    No. of auxiliary contacts :         10 NO and 10 NC on each pole, exclusively for  purchaser’s use.Continuous current 10 A DC. Breaking capacity shall be 2 Amp. min. with circuit time constant not less than 20 ms at 220 V DC.  Contacts should be reversible type at site.

DISCONNECTS/EARTHING SWITCHES 

1.    Type of disconnect         :         Vertical Break
2.    No. of poles   :         3
3.    Installation           :         Outdoor
4.    Rated peak withstand current                 kA :         100
5.     Rated magnetising current/
       capacitive breaking & making
       current.            A           
:          0.7
6.     Type of operating mechanism     :         Electrical/Manual

INSTRUMENT TRANSFORMERS

Current Transformers

1.    Rated primary currents                                      A   :       2000 

2.    Rated secondary current                                    A   :       

3.    Number of cores                                                      :       

4.    Rated continuous thermal                                        :       120%
      current.     

5.    Parameter Core  I    Core  II    Core  III Core  IV Core  V
Utilistation Line/
Equipment 
Protection  
Main- I  
Line/
Equipment 
Protection  
Main- II
Metering   Bus bar
  Protection  
Bus bar
 Transformation ratio 2000-  
1000-  
500/1
2000-   
1000-
500/1  
2000-   
1000-
500/1  
2000-   
1000/1
2000-   
1000/1
Accuracy Class PS   PS   0.2   
   ISF <10
PS   PS  
Rated Burden - - 15 VA      
Min.knee point 
voltage
Vk
4000-    
2000-
1000 volts 
4000-    
2000-
1000 volts 
- 2000-    
1000
volts
2000-  
1000
volts
Maximum Exciting
Current at Rated Vk/2
10-50-100
  mA        
25-50-100
  mA        
- 25-50
  mA        
25-50
  mA        
Maximum Secondary
Winding Resistance.
15-5-2.5
ohm
10-5-2.5
ohm
-   10-5   
ohm
  10-5   
ohm

      Data for TPY/TPX Core(Alternative to Core I & Core II)

 i)    Duty cycle     :   Single/Double energization CO/CO-t-CO 
ii)    Ratio applicable :    2000/1A
iii)   Rated symmetrical short circuit current factor :   20
iv)    Rated primary time   constant.         ms :    80
v)    Duration for flow of current
      Single energistation                     ms    
  
  Double energisation                      ms

 
:     240 for CO duty
:     100 & 40 for CO-t-CO duty 
vi)  Time interval  between two successive short
       circuit current.   ms
:      1000 
vii)  Rated burden                              ohm :      7.5


Bushing CTs                                                            Not yet finalised. 
Capacitor Voltage Transformers
1.   Number of secondary windings                     :      3  
2.  Rated secondary voltage, burden, accuracy and utilisation

Winding Rated Voltage Volt Rated burden  VA Accuracy   Purpose
I 110 /v3 50     3P   Main I  
Protection  
II 110 /v3   50 3P   Main II
Protection
III 110 /v3 50   0.2   Metering.

                                                                                               

3.    Transformation Ratio 765 / v3  kV     
110 / v3 V
 4.    Voltage factor 1.5 for 30 seconds
5.    Rated Capacitance      pF 4400 
6.     Stray conductance of the low Voltage terminal over
        entire carrier frequency range micro-Siemens
50
7.    Corona extinction voltage            kV(rms) 508(Min.) 
8.     Partial discharge level at 508 kV(rms)  
           
Pico   coulombs
Less than 10 

Protection Schemes

Line Protection

1)    Main I 

       Carrier aided distance protection suitable for use with different carrier modes. 

2)     Main II 

        Carrier aided protection based on directional comparison using wave detection or     
        phase comparison principles.

3)      Directional Earth fault Scheme

         Two sets of directional earth fault relays, one for each main protection to cover high
          resistance faults.

4)        Over-voltage Protection

          The relay to have two stages and shall be able to monitor phase to neutral voltage
          for all the three phases.   

Auto Transformer Protection

1)       Differential Protection
          (Percentage Biased)

2)       High impedance differential protection

3)       Over fluxing protection.

4)       Back-up directional over current protection.

5)       Overload protection.

6)        Neutral standby earth protection

7)         Delta circulating current protection.

Shunt Reactor  Protection

1)          Differential  protection

2)          Restricted earthfault protection 

3)           Back-up protection 

Bus Bar Protection 

High speed differential protection with features for checking the security as required. 

Circuit Breaker Failure Protection

In the event of circuit breaker failure, all circuit breakers connected to the Bus Section to which the fault circuit  breaker is connected shall be tripped with minimum possible time delay. 

Other Equipments

a)   Distance to Fault Locator 

Distance to Fault Locator shall be installed for identifying the location of faults and for taking preventive measures against fault prone areas.

b)   Disturbance Recording Equipment

i)     Disturbance Recorder 

      Disturbance Recorder shall be micro-processor based and shall be used to record the
      graphic form of instantaneous value of voltage and current in all three phases, open
      delta voltage and neutral current, open or closed positions of relay contacts and
      breaker during the system disturbance condition.

ii)    Event Logging Equipment

       The Event Logger is recommended to record the status of 800 kV Switchyard
       equipment and relays and occurances of alarms.  It shall be possible to accommodate
       about upto 500 points.   Whenever input status change occurs, an immediate printed
       record would be provided by the equipment.

POWER LINE CARRIER COMMUNICATION

A.    Coupling Devices.

       1.     Method of coupling      :    Phase to phase/3-phase coupling 
       2.       Nominal line side Impedance   ohms   :     480 (phase to phase) 
     3.        Nominal equipment side
                  Impedance   ohms
  :     150 (balanced)
:       75(unbalanced) 
     4.         Bandwidth                 kHz  :       50-150 

       B.     Line Traps 

       1.          Rated inductance at system
                   frequency    mH 
:       
        2.        Blocking resistance           ohms  :      430 
        3.        Rated Bandwidth            kHz      :     50-150 
        4.        Radio Interference    Voltage at 508                      kV(rms)  Micro    volts      :      500(Max.) 
        5.         Nominal discharge current
                    of  protective device connected
                    across main coil   kA
:        10

      
      C.     PLC Terminal

        1.           Carrier frequency range   kHz    :        50-500 
        2.           Carrier frequency band                       kHz   :        4.0/2.5 or integral multiple thereof   
      3.          Nominal Impedance at carrier
                     frequency output  ohms  
:        75 (unbalanced) 
       4.           Return loss within the nominal
                     carrier frequency band.      db   
:       Not less than 10 
       5.           Peak envelope power    W  :       Upto 80 
       6.             Speech frequency band      Hz :   300-2000 or  300-2400
       7.            Speech levels
                     Four wire transmit
                     
Four wire receive  
                    
Two wire transmit  
                     Two wire receive   


 :         +8 dB    -3.5   dB 
:         0 dB 
 
:         7 dB  

       

D.  VF Protection Signalling

      1.       Transmission time        msec   :    20 (max.) 
      2.       PLC Channel No.1                     Speech + data 
      3.       PLC  Channel No.2                  :    Protection 1 +
Express speech
      4.       PLC Channel No.3               :     Protection 2
      5.       PLC Channel No.4          :   Protection 3

    E.  Coupling Capacitors

      1.       Installation                 :      Outdoor
      2.       Rated capacitance            Pico Farad :      8800
      3.       Switching Impulse
               withstand voltage           kV(peak)             
:       1550
      4.        Voltage factor                   :        1.5 for 30 secs.
      5.         Equivalent series resistance
                 over the entire carrier
                 frequency range.                       Ohms      
   :        less than 40
    6.           Radio Interference
                 voltage at
                 508 kV(rms)           Micro volts       
:         2500  (max.) 
   7.            Partial discharge
                 level                  Pico Couloumbs 
:         Less than 10 
  8.           Corona extinction
                  voltage          kV(rms)       
  :         508 (Min.)

     

SURGE ARRESTERS

1.    Type Arrester                                       :     Gapless (Metal Oxide) 
2.     Nominal discharge current                           kA        :      20 
3.     Rated Arrester voltage                                 kV(rms)    :      624 
4.    Continuous operating voltage                       kV(rms)      :      485   
5.     Maximum residual voltage
       at lighting impulse
       current of 20 KA                                         kV(peak)    
  :     1430
6.     Maximum switching impulse
       residual voltage at 2 kA                               kV(peak)  
  :     1280
7.      Maximum steep current
        impulse residual voltage
        at 20 kA                                             kV(peak)    
:     1630
8.      Dynamic over voltage
        withstand capability
        for 3 peaks
        0.3 sec.                                                        kV(peak)  
|        0.1 sec.                                                        kV(peak)     
        1.0 sec.                                                        kV(peak)     
      
10.0 sec.                                                       kV(peak)    



     1240
:    1045
:    920
:     865   
9.     Discharge capability
       A- Transmission line class            
      
B-  Minimum energy capability   kj/kV                  
   
:       4
   :    28 
NOTE:-  This energy takes into account
                      occurence of two successive
                      line discharges followed by
                      TOV profile as given at
                      Sl.No.(8).
10.   Maximum radio interference/
        partial discharge at   508 kV (rms)  micro volts/      pico-coloumbs
   :       250/50

  

SWITCHYARD  LAYOUT 

1.     Switching Scheme                 :   Double bus Double breaker.  Depending on  the requirement of purchaser, one and a half breaker scheme can also be adopted.However, the bays arrangements shall be so selected that the rated current of 2000 A   for different equipments is not exceeded under any contingency.     
2.     Clearance (Minimum) 
        Phase to earth                        m  
        Phase to Phase                       m       
    
     Section clearance                   m  

  :     6.4 
:    10.0 
:    10.0       
3.      Bay details
        i)   Bay width                          m     
        ii)      Bus size (Tentative) 
            a)  Rigid bus/equipment
                 Inter connecting bus        
          
b)   Strung bus/Crossover bus    
 
:     45 

:     6" IPS tubular Aluminium pipe

:    Quad All Aluminium Tarantulla

             iii)      Bay Dimensions      

    Low level   
  
(Above ground) 
(Meters)     
High level
(Above ground) 
(Meters)     
  Bus level   12      27 
Equipment Interconnecting level 12   12 
Crossover bus level      27           39
Span length               15      
(Rigid bus)
  90

TRANSMISSION LINE

             

Conductor:

1.    Code Name                                 :   ACSR Bersimis
2.    Number of sub-conductor /phase           :   4
3.    Spacing  between conductors              mm        :   450
4.    Bundle arrangement                                     :   Horizontal Square
5.    Nominal Aluminium area                   sq.mm       :   690
6.    Stranding and Wire Diameter              :   42/4.57 mm Al + 7/2.54 mm St.
7.    Overall Diameter                                  mm     :   35.04
8.     Approximate mass                             kg /km      :   2187
9.      Ultimate Tensile strength                         kN    :    146.87
10.     D.C.  Resistance at 20  C     ohms/km    :    0.04242
11.     Corona extinction        kV(rms)    
         voltage phase to ground
:     560
12.    Modulus of Elasticity                        kg/cm2     :  0.6320 x 106
13.    Coefficient of linear expansion     per degree C :  21.5 x 10 -6
14    Maximum allowable temperature      degree C  :  95

Earthwire :

1.    Size                                         :   7/3.66 mm G.S.S. wire of   95 Kgf/ sq.mm ( 1GPa) quality
2.   Number of earthwire           :   2
3.    Overall Diameter                                  mm   :    10.98 
4.    Quality of groundwire                   kgf/sq.mm    :    95 
5.  Ultimate Tensile strength                     kgs.    :     6972 
6.    D.C. Resistance at 20  C               ohms/km     :     2.5 
7.     Shield angle for towers        
       
(i)   Outer phase               
     
(ii)   Middle phase                        

  :     15
:     The middle phase shall fall below the circle drawn with twoground wire points as diameter.
8.     Modulus of Elasticity                        kg/cm2     :  1.933 x 106
9.     Coefficient of linear expansion     per degree C :   11.5 x 10 -6       
10.    Maximum allowable temperature      degree C :  53

Disc Insulators and Insulator Strings:

  Insulator strings   Suspension  string Tension  string Pilot string
1.  Configuration    V-90   Quadruple     4 strings
in parallel
Single   I
 2.    Number of discs         per string(Size    
     
280x170 mm,
     EMS=210 KN   
      creepage distance=
     
370 mm)
2 x 35   
(Each limb
35 discs)
  4 x 35       
(Each limb   
35 discs)     
1 x 35
(35 discs)
3.     No deformation load  
       (67% of mechanical
       failing load of 210 KN) 
2  x  140   KN   4    x   140  KN 1   x  140 KN
4.     Maximum voltage
       across any disc
       across any disc
       phase to ground
       voltage of 462 kV(rms) 
Not more than 25 kV(rms)  

 Towers  :

1.      Number of circuit          :     Single circuit 
2.      Configuration                     :     Horizontal 
3.       Normal span                     m             :     400
4.      Wind span                                       :     1.0 x normal span (For plain terrain)
5.        Weight span  
         i)  Suspension tower, max.     
 
                                             min.    


    ii)   Angle tower,   Downward     
                                   Upward      
   
:      1.5 x Normal span
:      0.8 x Normal span (for plain terrain)
        (For hilly terrain, the minimum
          weight span be fixed suitably).
  :     2 x  Normal span
:      200 m Net span
6.         Maximum temperature of      
          
current carrying power
           conductor exposed to sun
    95 C   
7.         Maximum temperature of      
           
groundwire exposed to sun
:      53 C

8.          Clearances: 

  i)     Minimum ground                     mm
   clearances as per Indian
             Electricity rules.
12,400
ii)       As per interference   
limitations                                 mm
15,500
iii)        Live conductor to
             grounded metal
 

     

   Swing      Clearance
'V' Suspension string (V- 90) Nil        5,000   mm      
‘I’ Suspension string         
Zone I & II          Nil      5,100    mm   
  22        4,400    mm   
    45     1,300    mm   
Zone III & IV        Nil        5,100    mm   
    27         4,400    mm   
  55       1,300    mm  
Zone V & VI    Nil     5,100    mm  
  30 4,400    mm
  60      1,300    mm   

        
            Quadruple tension string              

             Jumper         

Zone I & II                                        Nil                                  5,100    mm   
                    
                                                15                                  4,400    mm   
                                                                     30                                  1,300    mm   

Zone III & IV                                   Nil                                  5,100    mm   
                                                                  20                                  4,400    mm   
                                                                  40                                  1,300    mm   

Zone V & VI                                     Nil                                  5,100    mm   
                    
                                                22                                  4,400    mm   
                                                                     45                                  1,300    mm   

           Pilot string                                                     Nil                                   5,100     mm                                                                                  20                                    4,400      mm

   iv)        Mid span separation               mm    :     12,400

    v)       For  ground  undulation,         mm      :          300
             extra over ground
             clearance

   vi)     Creep compensation for                      :        Height of tower may be increased
            conductor through                                        instead of considering reduction in                             over
           tensioning at the time of                                      temperature
             stringing

9)    Loadings  :

      Loadings shall be determined for the
     two loading combinations including
     wind on tower as given below :

       -  Combination  I      
                                                   As per IS: 802 -Part I-1995       
       -  Combination II                                      

 

SHUNT REACTORS

1.    Rating (single phase)       MVAR                :  50, 80, 110 in three phase banks.
2.    Winding connection                     :  Star
3.     Neutral earthing                        :  Earthed through Neutral Grounding Reactor.
4.    Magnetisation characteristic     :   Linear upto 1.4 p.u.    
 :   Slope of the characteristic in the saturated region         shall be 0.3 to 0.5. 
5.    Permissible unbalance current %  
      among single phase reactors of a
      three phase bank. 
 :   2
6.     Ratio of zero sequence reactance      
      to positive sequence reactance. 
  :   1.0 (single phase)
7.     Noise level at rated voltage          dB   
       and frequency            
:    81 for 50  MVAR
    83 for 80 MVAR
     85 for 110 MVAR 
8.     Clearances of terminals in            mm    
        air (phase to earth) 
 :      5800
9.      Type of cooling                    :       ONAN 
10.     Type of cooling medium                      :       Mineral oil to IS:335  (and as standardised for
        800kV Power Transformers)       
11.    Terminals
     Line Terminals

        
Neutral Terminal        

 
:       800 kV oil filled condenser  bushing with test             tap. No arcing horns shall be provided 
   :        145 kV oil filled condenser oil/ SF6 bushing

     

145 kV NEUTRAL GROUNDING REACTOR FOR GROUNDING SHUNT REACTOR.

1.  Number of  phases                                          :      1
2. Maximum   continuous current            A(rms)  :      15
3. Short time current Rating                    A(rms)  ) To be specified by purchaser after system studies.
4. Rated Impedance                                  ohms   ) To be specified by purchaser after system studies.
5. Magnetisation characteristics                 :    Linear upto short time current.
6. Terminals
     a)   Line end            

     
b) Earth end                                 

:    145 kV condenser bushing (as  standardised for          neutral of 800 kV shunt reactor)
   :     36 kV porcelain bushing 
7.     Type of cooling              :       ONAN 
8.      Type of cooling  Medium         :      Mineral oil to IS:335 (and asstandardized for          "800 kV Power Transformers") 
9.      Phase to earth air clearances
        a)   Line end                                     mm      
       
b) Neutral end                                  mm              

   :       1050
   :         230
10.     Insulation  levels
         a)   Lightning impulse          kV(peak) 
              voltage withstand of the
               line terminal

       b)   One minute power frequency     kV(rms)  
             voltage withstand of the
              earth terminals.


:        550

:         38
11.     Whether full or graded insulation.                  :      Graded insulation           

 

SHUNT REACTOR

(Connected to tertiary of power transformer to provide back-up reactive compensation)

1.  Rated voltage                                    kV     :    36
2.  Number of phases                     :      3
3.  Rating (three phase)                    MVAR     :    31.5, 50, 63, 80
4.  Winding connection     :   Star with neutral left inside.
5.    Whether full or graded insulation       :   Full insulation
6.  Basic insulation level (for line
     and neutral end of winding and
     bushings) 

     a)  1.2/50 microsecond
          lightning impulse
          withstand voltage           kV(peak)   
     b)  One minute power frequency
           withstand voltage        kV(rms)    




:      250 


  :        95 
7.    Magnetisation characteristic              :  Linear upto 1.3 p.u. voltage 
8.     Minimum clearance in air 
        Phase-phase                     mm           
       
Phase-earth                      mm           

  :     530 
   :     480
9.      Noise level at rated          dB    
      voltage and frequency.         
:      74 for 31.5 MVAR
75 for 50 MVAR
 
77 for 63 MVAR
 
77 for 80 MVAR
10.   Terminals
       a)  Line Terminals                   
 :        52 kV, 800/2000 A oil filled condenser bushing with test tap. No arcing horn shall be provided.
11.   Type of cooling                          :         ONAN with tank mounted or separately mounted radiator bank.
12.   Type of cooling medium                     :           Mineral oil to IS:335(and as standardised  for"800 kV Power Transformers"). 

INTERFERENCE  LEVELS

Transmission Lines

1.     RI should not exceed 50 dB for   80% of the time duration during the year.

2.     TVI- The minimum signal to noise ratio should be 30.

3.      Audio noise level for 800 kV system should be less than 55 dB(A).

4.      Electrostatic field  should  be less that 10 kV/m below the outermost phase
        (2 m above the ground) and less than 2 kV/m at the edge of the right of way(45 m).

PTCC:

1.      Maximum value of induced                 volts        -    650
        electromagnetic voltage for
        fault duration of equal to or
        less than 200 ms.

2.      Maximum value of induced
        noise(noise interference)                Micro volts  -     2000 (measured)   |
      
to be taken cognizance if
        noise is persistent).