try to make a basic information to design a sub-station and components of sub-station. please comment and give me solution if I had any wrong information.

1. Sub-Station Design

2. Components of Sub-Station
Major Components
• Transformer
• HT Meter Unit
• LT Switchgear
• SDB
• PFI Panel
• HT Cable
• G.I Pipe for HT Cable Laying
• Cable Pit
• LT Cable
• Earthing System
• lightning Arrester
• Drop Out Fuse
Minor Components
• Earthing Boring
• Earthing Inspection pit
• Equalizer Bar
• Shock Treatment Charts
• Single Line Diagram
• First Aid Box
• Rubber hand Gloves

3. Transformer Selection
• Suppose total load = 80KW
• Note:
Available Transformer rating in market, 100, 200, 250, 315, 400,
500, 630, 750, 800, 1000, 1250 KVA.
• So, Our required Transformer - 100KVA

4. HT (High Tension) Panel & Switchgear
• HT panel is a metal enclosure fitted with HT Circuit Breakers, relays & metering
that is used to receive 11KV/33KV supply (from one or more source) & distribute
the power through its outgoing feeders. Outgoing feeder may be one or more it
depends on the load of the building.
• HT Panel & Switchgear components are –
1) Ampere meter 8) Volt meter
2) Ampere selector switch 9) Voltmeter switch
3) Circuit Breaker 10) Panel Heater
4) Solid State Programmable KWH Meter
5)Supporter / Insulator
6) Indicating Lamp
7) TP Cast Resin CT & PT

5. LT (Low Tension) Panel & Switchgear
• Transformer Power × 1.6 = 100KVA * 1.6 =160A
• LT Panel is an electrical distribution board that receives power from generator or
transformer and distributes the same to various electronic devices and distribution
boards.
• LT Switchgear components are –
1) Ampere meter 3) Volt meter
2) Ampere selector switch 4) Voltmeter switch
5) Circuit Breaker 6) Bus bar
7) LTCT 8)Supporter / Insulator
9) Connector 10) Cable Lux
11) Indicating Lamp 12) KT Fuse / Controller Fuse

6. LT(Low Tension) Panel & Switchgear (Cont.)
1) Ampere meter
Show measurement how many current flows on the loads.
Available Ampere meter Ratings , (
𝐴𝑚𝑝
5
)
30
5
,
60
5
,
100
5
,
150
5
,
200
5
,
300
5
,
400
5
,
630
5
,
800
5
,
1000
5
,
1250
5
,
1500
5
,
1600
5
,
2000
5
2500
5
,
3000
5
,
3500
5
,
4000
5
,
4500
5
,
5000
5
,
6000
5
.
2) Ampere selector switch
Show measurement, how many current flows on the Three Phase loads Like R Y B .

7. LT(Low Tension) Panel & Switchgear (Cont.)
3) Volt meter
It measures voltage across the loads (400V – 500V ).
4) Voltage Selector switch
It measures voltage across the every phase .
5) Circuit Breaker
SP- Single Phase Circuit Breaker
DP- Double Phase Circuit Breaker
TP- Three Phase Circuit Breaker MCB
Example – MCB, MCCB, ACB, VCB, SF6 CB, LBS.

8. LT(Low Tension) Panel & Switchgear (Cont.)
Ratings of Circuit Breakers :
• SP/DP : 6A, 16A, 20A, 26A, 32A, 40A, 60A, 63A. MCCB
• TP/ MCB (Miniature Circuit Breaker) : 6A, 16A, 20A,
26A, 32A, 40A, 60A, 63A.
• MCCB (Molded Case Circuit Breaker) : 25A, 32A, 40A,
60A, 63A, 75A, 80A, 100A, 125A, 150A, 160A, 200A, ACB
250A, 300A, 320A, 400A, 500A, 630A, 800A, 1000A,
1250A, 1600A.
• ACB (Air Circuit Breaker) : 800A, 1000A, 1250A,
2000A, 2500A. VCB
• VCB (Vacuum Circuit Breaker) : 630A, 800A, 1250A.

9. LT(Low Tension) Panel & Switchgear (Cont.)
LTCT (Low Tension Current Transformer)
• It depends on secondary current or LT switchgear ratio.
• LTCT and LT switchgear have same Amp.
Ratings:
30
5
,
60
5
,
100
5
,
150
5
,
200
5
,
300
5
,
400
5
,
630
5
,
800
5
,
1000
5
,
1250
5
,
1500
5
,
1600
5
,
2000
5
,
2500
5
,
3000
5
,
3500
5
,
4000
5
,
4500
5
,
5000
5
,
6000
5
.
• Supporter / Insulator
We can use supporter or Insulator till 600A.
More than 600A we need to use Fibre.

10. PFI Selection
• PFI Rating/ Capacity = Transformer Capacity × 0.6
=100 × 0.6 = 60KVAR
• Capacitor Bank Value =
KVAR ∗10^9
2π ∗f ∗V^2
uf
=
160 ∗10^9
2π ∗50 ∗440^2
uf
= 2630.65 uf, total
= 2630.65 / 3 uf, per phase of Three Phase
= 876.88 uf

11. Bus bar Selection
• For Copper 1Sqmm = 1.5A ~ 2A
• For Aluminium 1Sqmm = 0.5A~ 1.5A
• Suppose total load current = 196 A + 25% = 246 A
• So, Bus bar Size = 246 / 1.6 = 154 Sqmm
If thickness of bar is 7 mm , then high = 154 / 7 = 22 m

12. Cable Selection
• Cable selection depends on three factors.
1 . Load Current
2. Temperature or Correction Factor
3. Voltage Drop
Always we take 20% extra load with total load. Let total load 80KW.
So Total load + 20% of load = 80 + 16 = 96 KW
1. Load Current Calculation
For Single Phase Connection , IL = Power / Voltage × cosƟ
For three Phase Connection, IL = Power / √3 Voltage × cosƟ

14. Cable Selection (Cont.)
2. Correction Factor 0r Temperature or Current Carrying Capacity (C.C.C.)
In our House hold and many industrial wiring is conduit wiring .
There is no air inside of the conduit wiring that’s why Temperature of Cable Increase.
So, Current Carrying Capacity is changing.
Let Our Load Current is 50A.
From Chart , we can choose 16Sqmm wire which carries 61A.
But C.C.C of this Wire is (61A*0.71) = 43.31 A, Which is Less than IL .
If we Choose 25Sqmm wire which carries 80A.
CCC of this wire =( 80*0.71)= 56.8A .
So, we can choose this wire (25Sqmm wire which carries 80A).

15. Cable Selection (Cont.)
3. Voltage Drop
There is no voltage Drop within 10m to 15m. If we use 100m wire than we
definitely get voltage drop.
Voltage drop of this wire 1.80 mV/A/m .
So, the total voltage Drop of this Wire = (1.80 *56.8*100)/1000 =10.224
Note:
There is no problem If the voltage drop will be 3% to 5% of nominal voltage.
3% of 220V = 6.6V
For 25Sqmm wire we get more than 6.6V voltage drop.
So, We use 35Sqmm wire for system.

16. Other Equipment of Sub-Station
Lightning Arrester & Drop Out Fuse
We always use same rating for lightning arrester and Drop Out Fuse as
DESCO input Connection Rating.
Drop out Fuse Lightning Arrester