GENERAL GUIDELINES FOR ESCOM WORKS IN KARNATAKA

GENERAL GUIDELINES FOR ESCOM WORKS IN KARNATAKA

(A) Usage of ACSR Conductor

1.      The Squirrel ACSR conductor shall not be used for any new works of KEB.

2.      The Average span for new 11 KV lines in Urban areas shall be 40 Mtr ,In Rural areas the average span length shall be 50 Mtrs. However the average span will be 60 Mtrs in respect of lines drawn to IP Sets.

Minimum size of the conductor to be used:

A.    11kV lines:

Minimum size of the conductor to be used for all new 11 KV lines shall be Rabbit ACSR only.

B.    LT lines:

a) Urban areas: Minimum size of conductor to be used for phases and neutral shall be Rabbit ACSR conductor.

b) Rural areas: The minimum size of conductor to be used shall be Weasel for phases and neutral.

c) Only Weasel Conductor shall be used for Street Light Control, Gangakalyana and water works.

(B)  Transformers:

a.       As per MOP directions, only Star 1(Previous 4 Star) rated transformers have to be used in Rural areas and

b.      Star 2 (Previous 5 Star) rated transformers have to be used in Urban/City areas.

c.       For Self-execution and layout works only Star 2 (Previous 5 Star) Transformers have to be provided.

 (C) Providing of GOS and HG Fuse unit:

All transformers above and inclusive of 25 KVA capacities are to be provided with GOS and HG fuse units.

(D) Providing Distribution Boxes and LT Protection Kit and DTCs:

As per the ESCOMS

1.      25/63/100 KVA transformer shall be provided with LT Protection Kit.

2.      Transformers with 250 KVA capacities and above shall be provided with LT Distribution Box with MCCB.

3.      In city limits transformers with 100 KVA capacities shall be provided with LT Distribution Box with MCCB.

(E) Guy set:

Guy set includes Anchor Rod, Turn buckle, Guy wire, Strain Insulator, Guy clamp with Bolts, Nuts and Washers

Note: As per the CEA guidelines, Transformers of capacity more than 25kVA have to be erected on DP structures/Plinth only.

Distribution Transformer with required CT Ratio in Trivector meter

Distribution Transformer Capacity	CT Ratio
15/25 kVA DTC	50/5 Amps
50/63 kVA DTC	100/5 Amps
100 kVA DTC	150/5 Amps
250 kVA DTC	400/5 Amps
500 kVA DTC	800/5 Amps

Calculate Lightning Protection for Building

Calculate Lightning Protection for Building

Fig-1-Conventional Type Lightning Arrester

Fig-2- Conventional Type Lightning Arrester installed to the particular building

  

Example: Calculate Whether Lightning Protection is required or not for following Building. Calculate No of Down Conductor for Lightning Protection

Area of Building / Structure:

• Length of Building (L) = 70 Meter.
• Width of Building ( W ) = 30 Meter.
• Height of Building (H) = 25 Meter.

Lightning Stock Flushing Density

• Number of Thunderstorm (N)= 80.00 Days/Year
• Lightning Flash Density   (Ng)=69 km2/Year
• Application of Structure (A)= Houses & Buildings
• Type of Constructions (B)= Steel framed encased without Metal Roof
• Contests or Consequential Effects (C)= Domestic / Office Buildings
• Degree of Isolation (D)= Structure in a large area having greater height
• Type of Country (E)= Flat country at any level
• Maximum Acceptable Overall Risk Factor =0.00001

Reference Table As per IS:2309
Thunder Storm Days / Year	Lightning Flash Density (Flashes to Ground /km2/year)
5	0.2
10	0.5
20	1.1
30	1.9
40	2.8
50	3.7
60	4.7
80	6.9
100	9.2

Application of Structure	Factor
Houses & Buildings	0.3
Houses & Buildings with outside aerial	0.7
Factories / workshop/ Laboratories	1
Office blocks / Hotel	1.2
Block of Flats / Residences Building	1.2
Churches/ Hall / Theaters / Museums, Exhibitions	1.3
Departmental stores / Post Offices	1.3
Stations / Airports / Stadium	1.3
Schools / Hospitals / Children’s Home	1.7
Others	1.2

Type of Constructions	Factor
Steel framed encased without Metal Roof	0.2
Reinforced concrete without Metal Roof	0.4
Steel framed encased with Metal Roof	0.8
Reinforced concrete with Metal Roof	1
Brick / Plain concrete or masonry without Metal Roof	1.4
Timber framed or clad without Metal Roof	1.7
Brick / Plain concrete or masonry with Metal Roof	2
Timber framed or clad with Metal Roof

Weighting Factors

Contests or Consequential Effects	Factor
Domestic / Office Buildings	0.3
Factories / Workshop	0.3
Industrial & Agricultural Buildings	0.8
Power stations / Gas works	1
Telephone exchange / Radio Station	1
Industrial key plants, Ancient monuments	1.3
Historic Buildings / Museums / Art Galleries	1.3
Schools / hospitals / Children Homes	1.7

Degree of Isolation	Factor
Structure in a large area having greater height	0.4
Structure located in a area of the same height	1
Structure completely Isolated	2

Calculation:

Collection Area (Ac)=(L x W) + 2 (L x H) + 2(W x H) +(3.14 x H²)

• Collection Area (Ac) = (70×30)+2x(70×25)+2x(30×25)+(3.14x25x25)
• Collection Area (Ac) =9063  Meter2

Probable No of Strikes to Building / Structure (P)= Ac x Ng x 10^-6 No’s / Year

• Probable No of Strikes to Building / Structure (P)= 9063x69x10^–6 No’s / Year
• Probable No of Strikes to Building / Structure (P)= 0.625347 No’s / Year

Overall Multiplying Factor (M) =A x B x C x D x E

• Application of Structure (A)= Houses & Buildings as per Table Multiplying Factor = 0.3
• Type of Constructions (B)= Steel framed encased without Metal Roof as per Table Multiplying Factor =0.2
• Contests or Consequential Effects (C)= Domestic / Office Buildings as per Table Multiplying Factor =0.3
• Degree of Isolation (D)= Structure in a large area having greater height as per Table Multiplying Factor =0.4
• Type of Country (E)= Flat country at any level so as per Table Multiplying Factor =0.3
• Overall Multiplying Factor (M) =0.3×0.2×0.3×0.4×0.3
• Overall Multiplying Factor (M) =0.00216

Overall Risk Factor Calculated (xc)= M x P

• Overall Risk Factor Calculated (xc)= 0.00216 x 0.625347
• Overall Risk Factor Calculated (xc)= 0.001350749

Note: Here we are getting the overall risk factor  > Maximum acceptable risk factor

         That is   0.001350749  >  0.00001

 Base Area of Structure (Ab) = (LxW)

• Base Area of Structure (Ab)=70 x 30
• Base Area of Structure (Ab)=2100 Meter2

Perimeter of Structure (P) =2x (L+W)

• Perimeter of Structure (P)=2x(70+30)
• Perimeter of Structure (P)=200 Meter

Lightning Protection Required or Not

• If Calculated Overall Risk Factor Calculated > Maximum Acceptable Overall Risk Factor than only Lighting Protection Required
• Here Calculated Overall Risk Factor is 0.001350749  > Max Acceptable Overall Risk Factor is 0.00001
• So Lightning Protection is Required for this building

 No of Down Conductor                                                                                                                  

• Down Conductors As per Perimeter of Structure (t)= P/30
• Down Conductors As per Perimeter of Structure (t)= 200/30
• Down Conductors As per Perimeter of Structure (t)= 7 No’s
• Minimum No of Down Conductor is 7 No’s

 Results:

• Lightning Protection is Required
• Down Conductors As per Perimeter of Structure (t)= 7 No’s
• Minimum No of Down Conductor is 7 No’s

Fig-3- The arrangement of Simple Lightning arrester installation with one down conductor