Clearances required for substation up to 800 kV ( According to CBIP ) Minimum clearance $ Highest Lightning Switching system impulse impulse voltage Voltage ( kV ) voltage ( kVp ) ( kVp ) 36 72.5 123 170 325 450 550 550 650 950 1050 1425 1050 (Ph- E) 1575 (Ph-Ph) 1550 (Ph-E) 2550 (Ph-Ph)

safety clearances (mm)

Phase -toPhase -to- Phase earth ( mm ) ( mm ) 320 320 630 900 1100 1100 1300 1900 2100 3400 * 6400 * 630 900 1100 1100 1300 1900 2100 4200 ** 9400 **

2800 3100 3400 3700 3700 3800 4300 4600 6400

145

245

420

800

2100

10300

* Based on Rod - structure air gap ** Based on Rod - conductor air gap $ This value of air clearances are the minimum values dictated by electrical consideration and do not include any addition for construction tolerances, effect of short circuits, wind effects and safety of personnel, etc.

Minimum Electrical clearance for outdoor switchgear According to IS : 10118 ( part III ) Voltage rating Impulse (Highest System Withstand Voltage) Level kV (rms) 12 kV (peak) 60 75 36 145 170 325 450 550 450 550 650 650 750 850 950 1050 Minimum Min clearance Sectional clearance to Earth clearance between phases mm 90 120 320 630 900 1100 900 1100 1300 1300 1500 1600 1900 2400 mm 90 120 270 320 630 900 1100 900 1100 1300 1300 1500 1700 1900 2100 mm 2600 2600 2750 3000 3500 3500 4000 3500 4000 4000 4000 4500 4500 5000

72.5 123

145

245

CORRELATIONS BETWEEN INSULATION LEVELS AND

Minimum clearances in air- Voltage range I ( 1kV < Um 245 kV ) ( Table 1 of IEC 61936-1 ) Rated short duration power- Rated lightning Minimum phase-to-earth and phasefrequency impulse withstand to-phase clearance,N c withstand voltage a voltage 1.2/50 s ( peak value ) kV 10 Indoor installations mm 60 60 60 90 90 120 160 120 160 160 220 270 270 320 480 630 900 1100 900 1100 1300 1100 1300 1500 1300 1500 1700 1900 2100 Outdoor installations mm 120 120 120 120 150 150 160 160 160

Nominal voltage of system Voltage range Un r.m.s kV 3

Highest voltage for equipment

Um r.m.s kV

r.m.s

kV 20 40 40 6 7.2 20 60 60 10 12 28 75 95 75 15 17.5 38 95 95 20 24 50 125 145 145 30 36 70 170 45 52 95 250 I 66 72.5 140 325 450 185 b 110 123 230 550 185 b 450 b 132 145 230 550 275 650 b 230 550 b 150 170 275 650 325 750 b 275 650 b 325 b 750 b 220 245 360 850 395 950 460 1050 a. The rated lightning impulse is applicable to phase- to-phase and phase- to earth. 3.6

b. If values are considered insufficient to prove that the required phase-to-phase withstand voltages are met, additional phase-to-phase withstand tests are needed. c. For rod-structure.

Minimum clearances in air- Voltage range II ( Um> 245 kV ) ( Table 2 of IEC 61936-1 ) Rated lightning impulse withstand voltage a Rated switching impulse withstand voltage Phase-tophase 250/2500 s (peak value) kV 1900 1700 b 950/1050 330 362 950/1050 1050/1175 1050/1175 II 380 420 1175/1300 1300/1425 525 480c

Nominal Voltage of System Voltage range Un r.m.s kV

Highest Voltage for equipment c

Rated switching impulse withstand Minimum phase-to-earth clearence voltage Rod structure N mm 1600

Minimum phase-to-phase clearence Rod Conductor conductor conductor parallel mm 2300 2600 2600 3100 2900 3100 3600 3700 3900 4200 6100 7200 7600 2600 3100 3100 3600 3400 3600 4200 4300 4600 5000 7400 9000 9400

Um r.m.s kV

1.2/50 s (peak value) kV 850/950

Phase-to-earth 250/2500 s (peak value) kV 750 850 850 950 850 950 1050 950

Conductor structure

1125 1275 1275 1425 1360 1425 1575 1615 1680 1763 2210 2423 2480

275

300

1800 1900 b 1800 1900 b 2200 1900 2200 b 2200 2400 b 2600 2200 2400 b 2600 3100 3600 4200 4900

2400 2400 2900 2400 2900 3400 2900

1175/1300

1300/1425 1050 3400 (550) 1425/1550 1175 4100 1675/1800 1300 4800 765 700 1800/1950 1425 5600 (800) c 1950/2100 1550 6400 a. The rated lightning impulse is applicable phase- to-phase and phase- to earth. b. Minimum clearance required for upper value of rated lightning impulse withstand voltage. c. The introduction of Um = 550 kV (instead of 525 kV): 800 kV(Instead of 765 kV): 1200 kV, of a value between 765 kV

and 1200kV, and of the associated rated withstand voltages, is under consideration.

Clearences practice used within UK Section 5 of BS 7354 : 1990 Safety working clearence (horizontal) (see note 1) m 2.3 2.3 2.3 2.5 2.9 3.9 4.6

Nominal system voltage/BIL/SIL kV 6.6/75 11/95 33/170 66/325 132/550/650 275/1050/850 400/1425/1050

Basic Electrical Safety Working clearence clearence (phase-to-earth) (Vertical) m 0.5 2) 0.5 2) 0.5 2) 0.7 1.1 2.1 2.8 m 2.9 2.9 2.9 3.1 3.5 4.8 5.5

Insulation Height (pedestrian access) (see note 2) m 2.1 2.1 2.1 2.1 2.1 2.4 2.4

Phase- to-phase clearence m 0.25 0.25 0.43 0.78 1.4 2.4 3.6

Note: 1. The safety working clearences(horizontal) in column 4 are regarded as minimum clearences. For systems where the predominant volatges are higher (275 kV and 400 kV) it is practice in the UK that the horizontal and vertical clearences are equal, conforming to the minimum figures in column 3. Note: 2. The insulation height(pedestrain access)figures in column 5 are shown in respect of the appropriate system voltage as follows: (a) for systems predominantly involving distribution voltages,i.e. upto and including 132 kV,2.1 m is the recommended minimum requirement: (b) for systems where the predominant voltages are higher,i.e. 275 kV and 400kV, 2.4 m is the recommended minimum requirement. The above figures are regarded as minimum clearences. Users and operators may wish to allow further clearence greater than that shown for the voltage level in column 5, particularly for equipment at the higher distribution voltages situated in a single compound with higher voltage equipment present in a compound subject to a greater clearence. In these circumstances, it might be convenient to design and operate to the clearence for the highest voltage equipment.

Clearances required for different voltage levels as per TCE standard

Switching Highest system Basic insulation insulation level ( Voltage ( kV ) level ( kVp ) kVp ) 36 72.5 123 170 325 450 550 550 650 950 1050 -

Minimum clearance Phase Phase -Phase Earth ( mm ) ( mm ) 320 320 630 900 1100 1100 1300 1900 2100 3400 ** 4200 *** 630 900 1100 1100 1300 1900 2100

Sectional clearance ( mm ) 2800 3000 3500 4000 4000 4000 4500 5000 6500

Ground clearance mm ) *

(

3700 4000 4600 4600 4600 4600 5500 5500 8000

145

245

420

1425 1050 (Ph- E) 1575 (Ph-Ph)

* This is defined by IE rules ** Based on Rod - structure air gap *** Based on Rod - conductor air gap

As per IE rules ( Rule 64) Highest system voltage (kV) 12 36 72.5 145 245 420 800 Safety working clearance (m) 2.6 2.8 3.1 3.7 4.3 6.4 10.3