Electrical Clearance in Substation

Minimum Clearance in Substation:

Voltage Highest Voltage Lighting Impulse Level (Kvp) Switching Impulse Level (Kvp) Minimum Clearance Safety Clearance(Mt) Ground Clearance(Mt)
Phase-Earth Phase-Phase
11KV 12KV 70   0.178 0.229 2.600 3.700
33KV 36KV 170   0.320 0.320 2.800 3.700
132KV 145KV 550   1.100 1.100 3.700 4.600
650   1.100 1.100 2.700 4.600
220KV 245KV 950   1.900 1.900 4.300 5.500
1050   1.900 1.900 4.300 5.500
400KV 420KV 1425 1050(P-E) 3.400 4.200 6.400 8.000 

 Electrical Clearance in Substation:

Voltage Height of I Bay From Ground (Mt) Height of II Bay From Ground (Mt) Bay Width (Mt) Phase-Phase (Mt) BetweenEquipment Earth Wire From Ground
132KV (Single) 8.0 11.0 3.0 3.0 10.5
220KV (Single) 12.5 18 4.5 4.5 15.5
220KV (Double) 18.5 25 25 4.5 4.5 28.5
400KV 15.6 22 22.0 7.0 >6.0 30.0

Standard Bay Widths in Meters:

Voltage Bay Width (Meter)
11KV 4.7 Meter
33KV 4.7 Meter
66KV 7.6 Meter
132KV 12.2 Meter
220KV 17 Meter
400KV 27 Meter

 Standard Bus and Equipment Elevation

Voltage Equipment live Terminal Elevation (Meter) Main Bus Take of Elevation (Meter)
Low High
11 KV/33KV 2.8To 4 5.5  To6.5 9 6.5To8.5
66KV 2.8To 4 6To8 9To 10.5 9.5
132KV 3.7To5 8To9.5 13.5To14.5 12To12.5
220KV 4.9To5.5 9To13 18.5 15To18.5
400KV 8.0 15.5 23

 Phase spacing for strung Bus:

Voltage Clearance
11KV 1300 mm
33KV 1300 mm
66KV 2200 mm
132KV 3000 mm
220KV 4500 mm
400KV 7000 mm

 Minimum Clearance of Live Parts from Ground:

Voltage Minimum Clearance to Ground (Mt) Section Clearance (Mt)
11KV 3.700 2.600
33KV 3.700 2.800
66KV 4.600 3.000
132KV 4.600 3.500
220KV 5.500 4.300
400KV 8.000 7.000

 Insulator String:

 Voltage No of Suspension String Length (mm) No of Disc for Tension String Length in (mm)
66KV 5 965 6 1070
132KV 9 1255 10 1820
220KV 14 1915 15 2915
400KV 23 3850 2 X 23 5450

 Nominal Span:

Voltage Normal Span (Meter)
66KV 240-250-275
132KV 315-325-335
220KV 315-325-335
400KV 315-325-335

 Minimum Ground Clearance:

Voltage Ground (Meter)
66KV 5.5
132KV 6.1
220KV 7.0
400KV 8.0
800KV 12.4

 Indoor Substation Minimum Clearances


Distance Descriptions
0.9 Meter Horizontally between any item of equipment and thesubstation wall
0.6 Meter Horizontally between any Two items of equipment
1.2 Meter Horizontally in front of any HV switchgear

 Clearance of Conductor on Tower

Voltage Tower Type Vertical Space (Mt) Horizontal Space(Mt) Total Height From Ground(Mt)
66KV A 1.03 4.0 15.91
  B 1.03 4.27 15.42
  C 1.22 4.88 16.24
132KV A 7.140 2.17 23.14
  B 4.2 6.29 22.06
  C 4.2 7.15 22.68
  D 4.2 8.8 24.06
220KV A 5.2 8.5 28.55
  B 5.25 10.5 29.08
  C 6.7 12.6 31.68


Voltage ratio & capacity HV Side LV Side Common relays
 132/33/11KV up to 8 MVA   3 O/L relays + 1 E/L relay 2 O/L relays + 1 E/L relay Buchholz, OLTC Buchholz, OT, WT
 132/33/11KV above 8 MVA and below 31.5 MVA   3 O/L relays + 1 dir. E/L relay 3 O/L relays + 1 E/L relay Differential, Buchholz, OLTC Buchholz, OT, WT
 132/33KV, 31.5 MVA & above   3 O/L relays + 1 dir. E/L relay 3 O/L relays + 1 E/L relay Differential, Over flux,Buchholz, OLTC PRV, OT, WT
 220/33 KV, 31.5MVA & 50MVA 220/132KV, 100 MVA   3 O/L relays + 1 dir. E/L relay 3 O/L relays + 1 dir. relay Differential, Over flux,Buchholz, OLTC PRV, OT, WT
 400/220KV 315MVA   3 directional O/L relays (with dir. High set) +1 directional E/L relays. Restricted E/F relay + 3 Directional O/L relays for action 3 directional O/L relays (with dir. High set)+1 directional E/L relays. Restricted E/F relay Differential, Over flux,Buchholz, OLTC PRV, OT, WT and overload (alarm) relay

 The bottom most portion of any insulator or bushing in service should be at a minimum height of 2500 mm above ground level.

 Location of L.A (From T.C Bushing):

Voltage BIL KV Peak Distance (Mt)
11KV 75 12
33KV 200 15
66KV 325 24
132KV 550 35
220KV 900 To 1050 Close To T.C
400KV 1425 To 1550

About Jignesh.Parmar
Jignesh Parmar has completed M.Tech (Power System Control), B.E(Electrical) from Gujarat University. He has more than 14 years experience in Power Transmission-Power Distribution-Electrical energy theft detection-Electrical Maintenance-Electrical Projects(Planning-Designing-coordination-Execution). He is Presently associate with one of the leading business group as a Deputy Manager at Ahmedabad,India. He is Freelancer Programmer of Advance Excel and design useful Excel Sheets of Electrical Engineering as per IS,NEC,IEC,IEEE codes. He is technical Author for "Electrical Mirror" and "Electrical India" Magazines. He is Technical Blogger and Familiar with English, Hindi, Gujarati, French languages. He wants to Share his experience & knowledge and help technical enthusiasts to find suitable solutions and updating themselves on various Engineering Topics.

48 Responses to Electrical Clearance in Substation

  1. kathiresan krishnamoorthy says:

    I am a chief engineer attached to Ceylon Electricity Board Srilanka.I conduct lecture for CEB
    engineers,electrical superintendents,technical staff therefore i need tecnical information for overhead lines,substation and ddlo,lighting arrester installation etc
    thanking you

  2. abu monsur ali says:

    Could i have the various references for clearnace w.r.t National/International standard, for indoor s/s upto 33 kv level also……….

  3. P.Rajasekaran says:

    Can you please explain me the difference between ground clearance and earth clearance

  4. Karma Wangdi says:

    i am from Bhutan and i would like to know that my small land is near to the 66KV transmission line, And will there be safe enough for me to construct building near to the line and will there be no problem as such in the longer duration.

  5. zulkif li othman says:

    Dear Jignesh,

    Excellent compilation! What is the difference between ‘min clearance to ground’ and sectional clearance?

    thank you and regards.

  6. axonkerala says:

    Really Helpful Notes

  7. sue song says:

    May i know when operating the 11kV OR 33kV Air Break Isolator from ground how to determine which class of insulation glove to wear for the safety protection.

  8. Moorthi says:

    Dear sir.
    I am Electrical sr engineer.we using 11KV/0.415KV substation for construction supply.
    1.There four substations in various area.when we charging the transformers one bye first time no any problem.but next day we are charging the transformers.first transformer will charging with any problem but we go charge the second trans that incoming surge arrest er will burst.

    2.what is reason sure arrester will burst.

    • I have observed following possibility in past for blasting of LA at DP structure.
      (1) May be Phase to ground Fault ( May be touch branches of tree with phase in distribution Line)
      (2) Failure of PIN Insulator of Distribution Line
      (3) wrong connection of LA (You face problem while charging System so Recheck LA connection with Ground)
      (4) Due to heavy Lighting Strock.
      (5) Fault in HT/LT Cable.
      (6) Selection of wrong size of LA.

      • Dwight R. Machica says:

        i have expeirence that the primary line 13.2kv after energizing in 8hrs more or less the Lightning Arrester blown or fuse Line1& Line2, what findings could you advise? & solution
        this problem.

        Thank you

  9. Sivakumar says:

    Halo Jignesh,

    as part of my job, i would like to verify space adequacy of HVDC substation. can you please clarify below points. Thanks,

    (1) what is the clearance to be followed for 400 kV HVDC substation?
    (2) for indoor substation, is it sufficient to consider phase-ground, phase-phase and section clearances (i.e. ground clerances not considered) only? will it be enough to maintain adequate creepage distance between phase and ground & phase-phase if the live conductors are beyond the reach of working personnel?
    (3) Is there any specific earthing design to be followed for HVDC substation?

  10. Vijay Kumar Harsh says:

    Dear Jignesh
    Thank you very much for such a nice updated details provided by you on this blog.
    Er Vijay Kumar Harsh
    Project Manager ,Yemen

  11. murthy says:

    Dear sir
    In which IS standard will i find these details it is very urgent


  12. RAJEEV JAKHAR says:

    Dear Jignesh,

    Please share your Email ID and contact nos..
    Regards RAJEEV JAKHAR (09810386806)

  13. gokul says:


    can u please explain about that lightning impulse 550 & 650 since for the 1st one 132kv sectional clearance is 2.7 & for the second one 3.7 please explain

  14. suganya says:

    Hi Sir,
    Am a Diploma EEE Student.i want to kow what is the ground,sectional,clearances.?

  15. sonakshi says:

    hello jignesh,
    could you please tell what is ground clearance & safety clearance?

  16. Ahmed says:

    could you please mention standard for these clearance?

  17. idhan says:

    Hi Jignesh

    There is a horizontal clearance between phases and fences. I’m referring to those fences protecting the substation. However, is there a clearence norm when wires are coming out of the substation? (Basically when the wires are connected to some tower or to some another equipment, in which moment there is only a vertical distance between wires and fences)

    Is there any documentation about this specific topic?

    Thank you in advance!

  18. sundaram says:

    all these clearances based on which iec… pls tell me

  19. sanjeev Pareek says:

    Good job.

  20. dav says:

    i love it

  21. dav says:

    i live where we use 330kv. what is the clearances for the substation? do i assume the values for 400kv?

  22. shivkanth says:

    I am shivkanth Vijayan from Bhoruka Power, Bangalore. I would like to know the IE standard for 66KV bus height in substation which is 4.6mtrs vertical????

  23. Mahesh says:

    can i have minimum clearances required for 66KV equipments in switchyard? CB to Bus Isolator, CB to CT, CT to Line Iso, Line Iso to Cable sealing end to LA, PT?

  24. Srikanta Ghosh says:

    Dear Jignesh Sir,
    Myself srikanta Ghosh B.tech Electrical engineer from west bengal. Recently working in a MNC company and posted in bangladesh. I work as site engineer in 132/33KV S/S. I want to be your assistant in any of your project or want a training from you. Is it possible sir ?

  25. Kuldeep Singh says:

    Dear Jignesh,

    my self is Kuldeep Singh advocate by profession and Manager in Land acquisition & Liaison department in a company who going to enter in new business related to solar or wind energy parks in various states, i just check some of courses which help me to understand batter in electrical line, can you assist me to find any course .

    Kuldeep Singh

  26. Mudasir Ahmad says:

    Dear Jignesh.Parmar
    Can u determine causes of bursting a Lightning Arrestor in 33kV end of a Transformer, used in dusty area.?

  27. Biplob Roy says:

    what’s the clearance would be phase to ground for 240 kv 1050 kv BIL. At the disconnect switch (240 kv 1050 kv BIL) point there is expansion type connector with corona ring. Now to calculate phase to ground clearance from edge of ring to ground point of ds whats distance need to consider. There is two types of distance given 1. rod to structure (2100mm) and 2. conductor to structure which is 1900mm. In this situation I believe we should consider 1900mm. Any comments is appreciated.

  28. Raj Kumar says:

    sir, Can I know what is the minimum ground clearance for a 230kv twin zebra conductor in a 230/110 kv air insulated Sub station.

  29. tha zaw says:

    sir,I want to know safety clearance for 36KV alive part and switch gear panel.

  30. Sivi Samuel says:

    I want to know the Bus arrangement reliable and costlier for a indoor substation of 33KV.

  31. Sivi Samuel says:

    I am Looking for a career in uae. can you tell me about some standards of uae

  32. Sreenu says:

    dear sir,
    how to calculate minimum clearance , is there any formula?

  33. Lidia says:

    what is it that you call “bay” in here?

  34. Palak Gandhi says:

    What is the difference between safety clearance and ground clearance in an EHV substation???
    I have been trying to understand the same from long time.

    e.g. for 132kV S/s at 550kVp safety clearance is 3.7 m and ground clearance is 4.6 m.

    Please help


  35. Winlaekhing says:

    Dear sir,
    I may known the phase to phase distance of line’s and substation’s Disconnecting switch(12kv DS, 33kV and 66kVDSE)

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    I am regular visitor, how are you everybody? This piece of writing posted at
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  39. Melvin Robles says:

    How about clearance between CT and PT for 230KV outdoor substation?

  40. jignesh patel says:

    Hi ,
    In switchyard we are using hand gloves to open or close isolator and give a earth switch in 66 KV,132 kv and 220 kv but the rating of gloves is maximum 40 kv then why we using that gloves .
    Please guide me about that .

  41. Kumail says:

    Do you know what should be minimum clearance distance between a tree and a 500 kV DC transmission line.

  42. Kumail says:

    How can we use air gap between a tree and a 500 kV dc transmission line in electrical modelling?

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