Sub Station Abstracts

Sub Station Equipments and Safety Clearance

Rating of Lighting Arrestor:

• Size of L.A = 1.5 X Phase to Earth Voltage    OR   

    =1.5 X system Voltage/1.732       OR

   = 0.81 X highest System Voltage

Lighting Arrestor Protection Radius:

• Protection Radius (Rp) = Sqrt (H X (2D-H)+L(2D+L))

H= Actual Height of L.A

D= 20 meter, 40 meter or 60 meter

L= V X T (T=Discharge Time & V= 1m/ms)

Creepage Distance:

• 18 mm to 22 mm /KV for Moderate Polluted Air.
• 25 mm to 33 mm /KV for Heavily Polluted Air.
• In HVDC System The value is double from above value.

Lighting Arrestor Rating:

Rated Voltage	Highest Voltage	L.A Rating
132kv	145kv	120kv To 132kv
220kv	245kv	198kv To 216kv
400kv	420kv	336kv

Location of Lighting Arrestor:

Rated Voltage	Max Distance from Equipment
132kv	35 meter To 45 meter
220kv	Closed To Transformer
400kv	Closed To Transformer

 Size of Corona Ring:

Rated Voltage	Size of Corona Ring
Less than 170 KV	160mm Ring Put on HV end
170KV To 275KV	350mm Ring Put on HV end
More than 275KV	450mm Ring Put on HV end
More than 275KV	350mm Ring Put on HV end

 Capacity of Sub Station as per GERC:

Size of S/S	Electrical Load
66 KV	80 MVA
132 KV	150 MVA
220 KV	320 MVA
400 KV	1000 MVA

 Breaking / Short Circuit Capacity of Sub Station:

Size of S/S	Short Circuit Current
66 KV	25 KAmp  for 1 or 3 sec
132 KV	31.5 KAmp  for 1 or 3 sec
220 KV	40 KAmp  for 1 or 3 sec
400 KV	40 KAmp  for 1 or 3 sec

 Fault Clear Time:               

Size of S/S	Fault Clear Time
66 KV	300 mili Sec
132 KV	160 mili Sec
220 KV	120 mili Sec
400 KV	100 mili Sec

 Normal Type of Conductors:

Voltage	Main Bus	Auxiliary Bus
11KV	Twin ACSR Zebra	ACSR Zebra
33KV	ACSR Zebra	ACSR Zebra
132KV	ACSR Zebra	ACSR Panthers
220KV	Twin ACSR Zebra	ACSR Zebra
400KV	1/14.2 mm Dia Alu Pipe	Twin ACSR Moose

 Number of Disc Insulator:

System	Number	Strength (KN)
11KV	4	120KN
33KV	4	120KN
132KV	10	120KN
220KV	14	70KN
220KV (Anti  Fog)	2 X 15	120KN
400KV (Anti  Fog)	2 X 25	120KN

 Minimum Clearance:

Voltage	Phase to Earth Wire	Phase to Phase	Section Clearance
2.2KV	28cm	33cm	27.45cm
33KV	380cm	43cm	27.7cm
132KV	107cm	12cm	25cm
220KV	178cm	20.6cm	42.8cm
400KV	350cm	40cm	65cm

 Ground Clearance:

Voltage	Meter
33KV	3.7meter
66 KV	6.1meter
132 KV	6.1meter
220 KV	7.0meter
400 KV	8.8meter

 Conductor Spacing:

Voltage	Highest Voltage	Lighting Impulse Level (Kvp)	Min Clearance		Ground Clearance	Safety working Clearance
			Phase to Earth	Phase to Phase
11KV	12kv	70	178mm	229mm	3700mm	2600mm
33KV	36kv	170	320mm	320mm	3700mm	2800mm
132 KV	145kv	550	1300mm	1300mm	4600mm	3700mm
220 KV	245kv	950	2100mm	2100mm	5500mm	4300mm
400 KV	420kv	1425	3400mm	4200mm	8000mm	6400mm

  Earthing Resistance Value:

Particular	Max Earthing Resistance
Power Station	0.5Ω
EHT Sub Station	1Ω
33KV Sub Station	2Ω
Double Pole Structure	5Ω
Tower foot Resistance	10Ω
Distribution Transformer	5Ω
220KV Sub Station	1Ω To 2Ω
400KV Sub Station	0.5Ω

 Losses in 11 kv Transformer at 75c (As per CBIP):

Transformer	No Load Loss(kw)	Load Loss (kw)	% Impedance
3.15MVA	2.9	20	6.25
4MVA	3.2	27	7.15
5.3MVA	3.9	31	7.15
6.3MVA	4.5	37	7.15

 Losses in 66 kv Transformer at 75c (As per CBIP):

Transformer	No Load Loss(kw)	Load Loss (kw)	% Impedance
6.3MVA	6	40	8.35
8MVA	7.1	48	8.35
10MVA	8.4	57	8.35
12.5MVA	9.7	70	8.35
20MVA	13	102	10.0

 Standard Rating of 66KV Transformer (As per CBIP):

Transformer	KV	Type of Cooling
6.3MVA	66KV/11KV	ONAN
8MVA	66KV/11KV	ONAN
10MVA	66KV/11KV	ONAN
12.5MVA	66KV/11KV	ONAN / ONAF
20MVA	66KV/11KV	ONAN / ONAF

 % Impedance for Transformer (As per IS 2026):

33KV Transformer		66KV Transformer
MVA	%Impedance	MVA	%Impedance
1MVA	5%	6.3MVA	8.35%
1.6MVA	6.25%	8MVA	8.35%
3.15MVA	6.25%	10MVA	8.35%
4MVA	7.15%	12.5MVA	8.35%
5MVA	7.15%	20MVA	10%
6.3MVA	7.15%	16MVA	10%
8MVA	8.35%	25MVA	10%
10MVA	8.35%	31.5MVA	12.5%

 

MVA	%impedance
Less Than 1MVA	5%
1MVA To 2.5MVA	6%
2.5MVA To 5MVA	7%
5MVA To 7MVA	8%
7MVA To 12MVA	9%
12MVA To 30MVA	10%
More Than 30MVA	12.5%

  Bus Bar Materials:

Description	Bus Bar and Jumper Material
400 kV Main Bus	114.2 mm dia. Aluminium pipe
400 kV equipment interconnection	114.2 mm dia. Aluminium pipe
400 kV overhead bus & droppers in all bays.	Twin ACSR Moose
220 kV Main Bus	Quadruple / Twin ACSR Zebra / Twin AAC Tarantulla
220 kV Auxiliary Bus	ACSR Zebra
220 kV equipment interconnection	Twin ACSR Zebra / Single ACSR Zebra
220 kV overhead bus & droppers in all bays.	Twin ACSR Zebra / Single ACSR Zebra
132 kV Main Bus	ACSR Zebra
132 kV Auxiliary Bus	ACSR Panther
132 kV equipment interconnection	ACSR Zebra / ACSR Panther
132 kV overhead bus & droppers in all bays.	ACSR Panther
33 kV Main Bus	ACSR Zebra
33 kV Auxiliary Bus	ACSR Zebra
33 kV equipment interconnection, overhead bus and droppers:
(i) Bus coupler & transformer bay	ACSR Zebra
(ii) Feeder bay.	ACSR Panther
11 kV Main Bus	Twin ACSR Zebra
11 kV Auxiliary Bus	ACSR Zebra
11 kV equipment interconnection, overhead bus and droppers:
(i) Transformer bay	Twin ACSR Zebra / Single ACSR Zebra
(ii) Bus coupler	ACSR Zebra