Minimum Electrical Clearance.

Minimum Electrical Clearance As Per BS:162.

INDOOR
Voltage in KV	Phase to earth in mm	Phase to phase in mm
0.415	15.8	19.05
0.600	19.05	19.05
3.3	50.8	50.8
6.6	63.5	88.9
11	76.2	127.0
15	101.6	165.1
22	139.7	241.3
33	222.25	355.6

Minimum Electrical Clearance As Per BS:162.

OUTDOOR
Voltage in KV	Phase to earth in mm	Phase to phase in mm
6.6	139.7	177.8
11	177.8	228.6
22	279.4	330.2
33	381	431.8
66	685.8	787.4
110	863.6	990.6
132	1066.8	1219.2
220	1778	2057.4

 Minimum Working Clearance:

OUTDOOR SWITCHYARD
Voltage in KV	To ground in mm	Between section(mm)
11	2750	2500
33	3700	2800
66	4000	3000
132	4600	3500
220	5500	4500

 Minimum Ground Clearance As Per IE-1956(Rule 77)

Voltage in KV	To ground in mm
132	6.10
220	7.00
400	8.84
800	12.40

Minimum Clearance between Lines Crossing Each Other (IE-1957)

System Voltage	132KV	220KV	400KV	800KV
Low & Medium	3.05	4.58	5.49	7.94
11-66KV	3.05	4.58	5.49	7.94
132KV	3.05	4.58	5.49	7.94
220KV	4.58	4.58	5.49	7.94
400KV	5.49	5.49	5.49	7.94
800KV	7.94	7.94	7.94	7.94

Minimum Height above Railway As Per IE-1957

Voltage	Broad Meter & Narrow Gauges
Above 66KV up to 132KV	14.60 Meter
Above 132KV up to 220KV	15.40 Meter
Above 220KV up to 400KV	17.90 Meter
Above 400KV up to 500KV	19.30 Meter
Above 500KV up to 800KV	23.40 Meter

Various Air clearances to be provided as per IE rule 64

Voltage KV	33KV	66KV	110KV	220KV	400KV
BIL (Kvp)	170	325	550	1050	1425
P-E (cm)	30	63	115	240	350
P-P(cm)	40	75	135	210	410
P-G (Meter)	3.7	4.0	4.6	5.5	8.0
Section Clearance(Mt)	2.8	3.0	3.5	4.3	6.5

Clearances from Buildings of HT and EHT voltage lines IE Rule 80

Vertical Distance
High voltage lines up to 33KV	3.7 Meter
Extra High Voltage	3.7 Meter + Add 0.3 meter for every additional 33KV
Horizontal clearance between the conductor and Building
High Voltage Up to 11 KV	1.2 Meter
11KV To 33KV	2.0 Meter
Extra High Voltage	2.0 Meter + Add 0.3 meter for every additional 33KV

Clearance above ground of the lowest conductor As per IE Rule 77

Over head Line Across Street
Low and Medium Voltage	5.8 Meter
High Voltage	6.1 Meter
Over head Line Along  Street (Parallel To Street)
Low and Medium Voltage	5.5 Meter
High Voltage	5.8  Meter
Over head Line Without Across or Along  Street
Low/Medium /HT line up to 11KV If Bare Conductor	4.6 Meter
Low/Medium /HT line up to 11KV If Insulated Conductor	4.0 Meter
Above 11  KV Line	5.2 Meter
Above 33KV Line	5.8 Meter + Add 0.3 meter for every additional 33KV

Clearance between conductors and Trolley / Tram wires (IE Rule 78)

Low and Medium Voltage	1.2 Meter
High Voltage Line Up to 11KV	1.8 Meter
High Voltage Line Above to 11KV	2.5 Meter
Extra High Voltage Line	3.0 Meter

 Clearances from Buildings of low & medium voltage lines(IE Rule 79 )

For  Flat roof, Open Balcony, Verandah Roof and lean to Roof
Line Passes Over Building Vertical Clearance	2.5 Meter
Line Passes Adjustment of Building Horizontal Clearance	1.2 Meter
For pitched Roof
Line Passes Over Building Vertical Clearance	2.5 Meter
Line Passes Adjustment of Building Horizontal Clearance	1.2 Meter

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
	D

 NORMS OF PROTECTION FOR EHV CLASS POWER TRANSFORMERS

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

Typical Limiting Values of SubStation Equipments.

Typical Limiting Values of Sub Station Electrical Equipments.

1. Transformer / Reactor:

Sr. No.	Equipment / test data	Permissible limits	Reference
A)	Transformer oil
	a) BDV
	-At the time of first charging	600 kV (Gap – 2.5 mm) – Minimum	IS – 1866
	-During O&M	50 kV (Gap – 2.5 mm) – Minimum	IS – 1867
	b) Moisture content		IS – 1868
	-At the time of first charging	15 PPM (Max.)	IS – 1869
	-During O&M	25 PPM (Max.)	IS – 1870
	c) Resistivity at 90 degree C	0.1-1012 Ohm-CM (Min.)	IS – 1871
	d) Acidity	0.2 mg KOH/gm (Max.)	IS – 1872
	e) IFT at 27 degree C	0.018 N/M (Min.)	IS – 1873
	f) Tan delta at 90 degree C	0.20 (Max.)	IS – 1874
	g) Flash point	126 Deg. C (Min.)	IS – 1875
B)	Vibration level for reactors	200 Microns (Peak to Peak)	IS – 1876
		60 Microns (Average)	IS – 1877
C)	Tan delta for bushing at 20 Deg. C	0.007*	IEC – 137
D)	Capacitance for bushing	+ 5% variation	IEC – 138
E)	IR value for winding	1000 M-Ohm By 5.0/10.0 kV Megger	IEC – 139
F)	Tan delta for windings at 20 Deg. C	0.007*	IEEE/C57.12.90.1980
G)	Contact resistance of bushing terminal connectors	10 M. Ohm / Connector	NGC.UK Recommendations
H)	Turret Neutral CT ratio errors	39	IS – 2705

 2. Circuit Breakers 

Sr. No.	Equipment / test data	Permissible limits	Reference
A)	Dew point of SF6 gas	Dew point values as per Annexure – II
B)	Dew point of operating air	-45 Deg. C at ATM. Pressure
C)	CB Operating timings	400 kV               220KV
	a) Closing time (Max.)	150 MS              200MS
	b) Trip time (Max.)	25 MS                35MS
	c) Close/trip time, Pole discrepancy
	– Phase to Phase (Max.)	3.33 MS            3.33MS
	-Break to break (Max.) of same phase	2.5 MS              2.5MS
D)	PIR time
	BHEL make	12-16 MS	Manufacturers Recommendations
	ABB make	8-12 MS	Manufacturers Recommendations
	NGEF make	8-12 MS	Manufacturers Recommendations
	M&G make	8-12 MS	Manufacturers Recommendations
	TELK make	8-12 MS	Manufacturers Recommendations
	ABB make (HVDC)	8-12 MS	Manufacturers Recommendations
E)	PIR opening time prior to opening of main contacts (ABB, CGL, NGEF make CBs)	5 MS (Min.) at rated pressure	Manufacturers Recommendations
F)	Pir and main contacts overlap time [BHEL, M&G, ABB (imported) make CBs]	6 MS (Min.) at rated pressure	Manufacturers Recommendations
G)	Tan delta of grading capacitors	0.007 at 20 Deg. C
H)	Capacitance of grading capacitors	Within + 10% / -5% of the rated value	IEC 359
I)	Contact resistance of CB	150 M. Ohm
J)	Contact resistance of CB terminal connector	10 M. Ohm per connector	NGC, UK recommendations
K)	IR value:
	1. Phase – earth	1000 M Ohm (Min.) by 5.0 / 10.0 kV Megger
	2. Across open contacts	1000 M Ohm (Min.) by 5.0/10.0 kV Megger
	3. Control cables	50 M Ohm (Min.) by 0.5 kV Megger
L)	Pressure switch settings
	-SF6 gas pressure switches	Within + 0.1 Bar of set value
	-Operating air pr. Switches	Within + 0.1 Bar of set value
	-Operating oil pr. Switches	Within + 0.1 Bar of set value
M)	BDV of oil used for MOCB
	-At the time of filling	40 kV at 2.5 mm Gap (Min.)	Mfgs. Recommendation
	-During O&M	20 kV at 2.5 mm Gap. (Min.)	Mfgs. Recommendation

 3. Current Transformer

Sr. No.	Equipment / test data	Permissible limits	Reference
A)	IR value
	1. Primary – earth	1000 M – Ohm (Min.) by 5.0/10.0 kV Megger
	2. Secondary – earth	50 M – Ohm (Min.) by 0.5 kV Megger
	3. Control cables	50 M-Ohm (Min.) by 0.5 kV Megger
B)	Tan delta value	0.007* at 20 Deg. C
C)	Terminal Connector	10 M-Ohm per connector	NGC, UK Recommendations
D)	CT ratio errors	+ 3% -Protection cores	IS – 2705
D)	CT ratio errors	+ 1% -Metering cores	IS – 2706

 4. Capacitive Voltage

Sr. No.	Equipment / test data	Permissible limits	Reference
A)	Tan Delta	0.007* at 20 Deg. C
B)	Capacitance	Within +10%/-5% of the rated value	IEC – 358
C	Contact resistance of terminal connector	10 M-Ohm per connector	NGC, UK Recommendations
D)	IR Value	IR Value
	1. Primary – earth	1000 M – Ohm (Min.) by 5.0/10.0 kV Megger
	2. Secondary – earth	50 M – Ohm (Min.) by 0.5 kV Megger
	3. Control cables	50 M-Ohm (Min.) by 0.5 kV Megger
E)	EMU tank oil parameters	EMU tank oil parameters
	a) BDV (Min.)	30 kV (Gap. –2.5 mm)	IS – 1866
	b) Moisture content (Max.)	35 ppm	-do-
	c) Resistivity at 90 Deg. C	0.1 – 1012 Ohm. – CM	-do-
	d) Acidity	0.5 mg kOH /gm (Max.)	-do-
	e) IFT at 27 Deg. C	0.018 N/M (Min.)	-do-
	f) Tan delta at 90 Deg. C	1.0 Max.	-do-
	g) Flash point	125 Deg. C (Min.)	-do-
F)	CVT voltage ratio errors	+ 5% protection cores	IEEE/C93.1.1990
F)	CVT voltage ratio errors	+ 0.5% metering cores	IEC 186

 5. Isolators

Sr. No.	Equipment / test data	Permissible limits	Reference
A)	Contact resistance	300 M-Ohm. (Max.)
B)	Contact resistance of terminal connector	10 M – Ohm per connector	NGC, UK Recommendations
C)	IR value
	1. Phase – earth	1000 M – Ohm (Min.) by 5.0/10.0 kV Megger	NGC, UK Recommendations
	2. Across open contacts	1000 M – Ohm (Min.) by 5.0/10.0 kV Megger	NGC, UK Recommendations
	3. Control cables	50 M-Ohm (Min.) by 0.5 kV Megger

 6. Surge Arrester

Sr. No.	Equipment / test data	Permissible limits	Reference
A)	Leakage current	500 M-Amp. (Resistive)	Hitachi, Japan Recom.
B)	IR value	1000 M-Ohm. (Min.)	Hitachi, Japan Recom.

 7. Miscellaneous

Sr. No.	Equipment / test data	Permissible limits	Reference
A)	Station earth resistance	1.0 Ohm (Max.)
B)	Thermo vision scanning
	Temp. up to 15 Deg. C (above ambient)	Normal
	Temp. above 15-50 Deg. C (above ambient)	Alert
	Temp. above 50 Deg. C (above ambient)	To be immediately attended
C)	Terminal connectors – Contact resistance	10 M-Ohm per connector	HGC, UK Recommendations
D)	IR values
	1. All electrical motors	50 M-Ohm (Min.) by 0.5 kV Megger
	2. Control cables	50 M-Ohm (Min) by 0.5 kV Megger
	3. Lt. Transformers	100 M.-Ohm (Min.) by Megger
	4. Lt. Switchgears	100 M – Ohm (Min.) by 0.5 kV Megger

 8. Batteries

Sr. No.	Equipment / test data	Permissible limits	Reference
A)	Terminal connector resistance	10 M – Ohm + 20%	ANSI/IEEE – 450 1989
B)	Specific gravity	1200 + 5 GM/L at 27 Deg. C

 Temperature Correction Factor for Tan Delta Measurement

Sr. No.	Oil temperature Deg. C	Correction factor(K)
1	10	0.8
2	15	0.9
3	20	1.0
4	25	1.12
5	30	1.25
6	35	1.40
7	40	1.55
8	45	1.75
9	50	1.95
10	55	2.18
11	60	2.42
12	65	2.70
13	70	3.00

If Tan Delta of bushing/winding/CVT/CT is measured at oil temperature T Deg. C. Then Tan Delta at 20 Deg. C shall be as given below:

Tan Delta at 20 Deg. C = Tan Delta at Temp T Deg. C / Factor K.

Dew Point Limits for SF6 Gas in EHV Circuit Breakers

Sr. No	Make of C.B	Dew point at rated Pr. Deg. C	Corresponding dew point at Atmospheric .Pr.	Remarks
1	BHEL	-15	-36	At the time of commissioning
		-7	-29	During O&M
		-5	-27	Critical
2	M&G	—	-39	At the time of commissioning
			-32	During O&M
3	CGL	-15	-35	At the time of commissioning
		-10	-31	During O&M
4	ABB	-15	-35	At the time of commissioning
		-5	-26	During O&M
5	NGEF	-15	-36	At the time of commissioning
		-7	-29	During O&M

 Note: Dew point of SF6 gas varies with pressure at which measurement is carried out. So it is to be ensured that if measurement is done at pressure other than atmospheric pressure, it needs to be converted to the atmospheric pressure.