Home / Dictionary Glossary & Useful Equations for Electrical Engineering

Dictionary Glossary & Useful Equations for Electrical Engineering

Cable Capacity

  • For Cu Wire Current Capacity (Up to 30 Sq.mm) = 6X Size of Wire in Sq.mm
  • Ex. For 2.5 Sq.mm=6×2.5=15 Amp, For 1 Sq.mm=6×1=6 Amp, For 1.5 Sq.mm=6×1.5=9 Amp
  • For Cable Current Capacity = 4X Size of Cable in Sq.mm ,Ex. For 2.5 Sq.mm=4×2.5=9 Amp.
  • Nomenclature for cable Rating = Uo/U
  • where Uo=Phase-Ground Voltage, U=Phase-Phase Voltage, Um=Highest Permissible Voltage

Current Capacity of Equipment’s:

  • 1 Phase Motor draws Current=7Amp per HP.
  • 3 Phase Motor draws Current=1.25Amp per HP.
  • Full Load Current of 3 Phase Motor=HPx1.5
  • Full Load Current of 1 Phase Motor=HPx6
  • No Load Current of 3 Phase Motor =30% of FLC
  • KW Rating of Motor=HPx0.75
  • Full Load Current of equipment =1.39xKVA (for 3 Phase 415Volt)
  • Full Load Current of equipment =1.74xKw (for 3 Phase 415Volt)

 

Earthing Resistance:

  • Earthing Resistance for Single Pit=5Ω ,Earthing Grid=0.5Ω
  • As per NEC 1985 Earthing Resistance should be <5Ω.
  • Voltage between Neutral and Earth <=2 Volts
  • Resistance between Neutral and Earth <=1Ω
  • Creepage Distance=18 to 22mm/KV (Moderate Polluted Air) or
  • Creepage Distance=25 to 33mm/KV (Highly Polluted Air)

Minimum Bending Radius:

  • Minimum Bending Radius for LT Power Cable=12xDia of Cable.
  • Minimum Bending Radius for HT Power Cable=20xDia of Cable.
  • Minimum Bending Radius for Control Cable=10xDia of Cable.

Insulation Resistance:

  • Insulation Resistance Value for Rotating Machine= (KV+1) MΩ.
  • Insulation Resistance Value for Motor (IS 732) = ((20xVoltage (L-L)) / (1000+ (2xKW)).
  • Insulation Resistance Value for Equipment (<1KV) = Minimum 1 MΩ.
  • Insulation Resistance Value for Equipment (>1KV) = KV 1 MΩ per 1KV.
  • Insulation Resistance Value for Panel = 2 x KV rating of the panel.
  • Min Insulation Resistance Value (Domestic) = 50 MΩ / No of Points. (All Electrical Points with Electrical fitting & Plugs). Should be less than 0.5 MΩ
  • Min Insulation Resistance Value (Commercial) = 100 MΩ / No of Points. (All Electrical Points without fitting & Plugs).Should be less than 0.5 MΩ.
  • Test Voltage (A.C) for Meggering = (2X Name Plate Voltage) +1000
  • Test Voltage (D.C) for Meggering = (2X Name Plate Voltage).
  • Submersible Pump Take 0.4 KWH of extra Energy at 1 meter drop of Water.

    Lighting Arrestor:

  • Arrestor have Two Rating=
  • (1) MCOV=Max. Continuous Line to Ground Operating Voltage.
  • (2) Duty Cycle Voltage. (Duty Cycle Voltage>MCOV).

    Transformer:

  • Current Rating of Transformer=KVAx1.4
  • Short Circuit Current of T.C /Generator= Current Rating / % Impedance
  • No Load Current of Transformer=<2% of Transformer Rated current
  • Capacitor Current (Ic)=KVAR / 1.732xVolt (Phase-Phase)
  • Typically the local utility provides transformers rated up to 500kVA For maximum connected load of 99kW,
  • Typically the local utility provides transformers rated up to 1250kVA For maximum connected load of 150kW.
  • The diversity they would apply to apartments is around 60%
  • Maximum HT (11kV) connected load will be around 4.5MVA per circuit.
  • 4No. earth pits per transformer (2No. for body and 2No. for neutral earthing),
  • Clearances, approx.1000mm around TC allow for transformer movement for replacement.

    Diesel Generator:

  • Diesel Generator Set Produces=3.87 Units (KWH) in 1 Litter of Diesel.
  • Requirement Area of Diesel Generator = for 25KW to 48KW=56 Sq.meter, 100KW=65 Sq.meter.
  • DG less than or equal to 1000kVA must be in a canopy.
  • DG greater 1000kVA can either be in a canopy or skid mounted in an acoustically treated room
  • DG noise levels to be less than 75dBA @ 1meter.
  • DG fuel storage tanks should be a maximum of 990 Litter per unit Storage tanks above this level will trigger more stringent explosion protection provision.

Current Transformer:

  • Nomenclature: CT
  • Ratio: input / output current ratio
  • Burden (VA): total burden including pilot wires. (2.5, 5, 10, 15 and 30VA.)
  • Class: Accuracy required for operation (Metering: 0.2, 0.5, 1 or 3, Protection: 5, 10, 15, 20, 30).
  • Accuracy Limit Factor:
  • Nomenclature of CT: Ratio, VA Burden, Accuracy Class, Accuracy Limit Factor.Example: 1600/5, 15VA 5P10  (Ratio: 1600/5, Burden: 15VA, Accuracy Class: 5P, ALF: 10)
  • As per IEEE Metering CT: 0.3B0.1 rated Metering CT is accu­rate to 0.3 percent if the connected secondary burden if imped­ance does not exceed 0.1 ohms.
  • As per IEEE Relaying (Protection) CT: 2.5C100 Relaying CT is accurate within 2.5 percent if the secondary burden is less than 1.0 ohm (100 volts/100A).

Size of Capacitor for P.F Correction:

For Motor

Size of Capacitor = 1/3 Hp of Motor ( 0.12x KW of Motor)

For Transformer

< 315 KVA 5% of KVA Rating
315 KVA to 1000 KVA 6% of KVA Rating
>1000 KVA 8% of KVA Rating

 Earthing Resistance value:

Earthing Resistance Value

Power Station 0.5 Ω
Sub Station Major 1.0 Ω
Sub Station Minor 2.0 Ω
Distribution Transformer 5.0 Ω
Transmission Line 10 Ω
Single Isolate Earth Pit 5.0 Ω
Earthing Grid 0.5 Ω
As per NEC Earthing Resistance should be <5.0 Ω

 Voltage Limit (As per CPWD & Kerala Elect.Board):

Voltage Limit (As Per CPWD)

240V < 5 KW
415V <100 KVA
11KV   MVA
22KV <6 MVA
33KV <12 MVA
66KV <20 MVA
110KV <40 MVA
220KV >40 MVA

Voltage Variation

> 33 KV (-) 12.5% to (+) 10%
< 33 KV (-) 9% to (+) 6%
Low Voltage (-) 6% to (+) 6%

 Insulation Class:

Insulation

Temperature

Class A

               105°C

Class E

120°C

Class B

130°C

Class F

155°C

Class H

180°C

Class N

200°C

 Standard Voltage Limit:

Voltage IEC (60038) IEC (6100:3.6) Indian Elect. Rule
ELV < 50 V
LV 50 V to 1 KV <=1 KV < 250 V
MV <= 35 KV 250 V to 650 V
HV > 1KV <= 230 KV 650 V to 33 KV
EHV > 230 KV > 33 KV

 Standard Electrical Connection (As per GERC):

As per Type of Connection

Connection

Voltage

LT Connection

<=440V

HT connection

440V to 66KV

EHT connection

>= 66KV

As per Electrical Load Demand

Up 6W Load demand

1 Phase 230V Supply

6W to 100KVA(100KW)

3 Phase 440V Supply

100KVA to 2500KVA

11KV,22KV,33KV

Above 2500KVA

66KV

HT Connection Earthing

H.T Connection’s Earthing Strip

20mmX4mm Cu. Strip

CT & PT bodies

2Nos

PT Secondary

1Nos

CT Secondary

1Nos

I/C and O/G Cable+ Cubicle Body

2Nos

 Standard Meter Room Size (As per GERC):

Meter Box Height Upper level does not beyond 1.7 meter and Lower level should not below 1.2 meter from ground.
Facing of Meter Box Meter Box should be at front area of Building at Ground Floor.
Meter Room / Closed Shade 4 meter square Size

 Approximate Load as per Sq.ft Area (As per DHBVN):

Sq.ft Area Required Load (Connected)
< 900 Sq.ft 8 KW
901 Sq.ft to 1600 Sq.ft 16 KW
1601 Sq.ft to 2500 Sq.ft 20 KW
> 2500 Sq.ft 24 KW
For Flats :100 Sq.ft / 1 KW
For Flats USS /TC: 100 Sq.ft / 23 KVA

 Contracted Load in case of High-rise Building:

For Domestic Load 500 watt per 100 Sq. foot of the constructed area.
For Commercial 1500 watt per 100 Sq. foot of the constructed area
Other Common Load For lift, water lifting pump, streetlight if any, corridor/campus lighting and other common facilities, actual load shall be calculated
Staircase Light 11KW/Flat Ex: 200Flat=200×11=2.2KW

Sanctioned Load for Building

Up to 50 kW The L.T. existing mains shall be strengthened.
50 kW to 450 kW (500 kVA) 11 kV existing feeders shall be extended if spare capacity is available otherwise, new 11 kV feeders shall be constructed.
450 kW to 2550 kW (3000 kVA) 11 kV feeder shall be constructed from the nearest 33 kV or 110 kV substation
2550 kW to 8500 kW (10,000 kVA) 33kV feeder from 33 kV or 110 kV sub station
8500 kW (10,000 kVA) 110 kV feeder from nearest 110 kV or 220 kV sub-station

Sub Station Capacity & Short Circuit Current Capacity:

As per GERC

Voltage Sub Station Capacity Short Circuit Current
400 KV Up to 1000 MVA 40 KA  (1 to 3 Sec)
220 KV Up to 320 MVA 40 KA  (1 to 3 Sec)
132 KV Up to 150 MVA 32 KA  (1 to 3 Sec)
66 KV Up to 80 MVA 25 KA  (1 to 3 Sec)
33 KV 1.5 MVA to 5 MVA 35 KA (Urban) (1 to 3 Sec)
11 KV 150 KVA to 1.5 MVA 25 KA (Rural) (1 to 3 Sec)
415 V 6  KVA to 150 KVA 10 KA  (1 to 3 Sec)
220 V Up to 6 KVA 6 KA  (1 to 3 Sec)

 Sub Station Capacity & Short Circuit Current Capacity:

As per Central Electricity Authority

Voltage Sub Station Capacity Short Circuit Current
765 KV

4500 MVA

31.5 KA for 1 Sec
400 KV

1500 MVA

31.5 KA for 1 Sec
220 KV

500 MVA

40 KA for 1 Sec
110/132 KV

150 MVA

40 KA or 50 KA for 1 Sec
66 KV

75 MVA

40 KA or 50 KA for 1 Sec

 Minimum Ground Clearance and Fault Clearing Time:

Voltage Min. Ground Clearance Fault Clear Time
400 KV 8.8 Meter 100 mille second
220 KV 8.0 Meter 120 mille second
132 KV 6.1 Meter 160 mille second
66 KV 5.1 Meter 300 mille second
33 KV 3.7 Meter
11 KV 2.7 Meter

 Bus bar Ampere Rating:

For Phase Bus bar Aluminium 130 Amp / Sq.cm or 800Amp / Sq.inch.
For Phase Bus bar Copper 160 Amp / Sq.cm or 1000Amp / Sq.inch
For Neutral Bus bar Same as Phase Bus bar up to 200 Amp than Size of Neutral Bus bar is at least half of Phase Bus bar.

 Bus bar Spacing:

Between Phase and Earth 26mm (Min)
Between Phase and Phase 32mm (Min)
Bus bar Support between Two Insulator 250mm.

 Sound Level of Diesel Generator (ANSI 89.2&NEMA 51.20):

KVA

Max. Sound Level

<9 KVA 40 DB
10 KVA to 50 KVA 45 DB
51 KVA to 150 KVA 50 DB
151 KVA to 300 KVA 55 DB
301 KVA to 500 KVA 60 DB

IR Value of Transformer:

IR Value of Transformer

Voltage

30°C

40°C

50°C

>66KV

600MΩ

300MΩ

150MΩ

22KV to 33KV

500MΩ

250MΩ

125MΩ

6.6KV to 11KV

400MΩ

200MΩ

100MΩ

<6.6KV

200MΩ

100MΩ

50MΩ

415V

100MΩ

50MΩ

20MΩ

Standard Size of MCB/MCCB/ELCB/RCCB/SFU/Fuse:

MCB Up to 63 Amp (80Amp and 100 Amp a    per Request)
MCCB Up to 1600 Amp (2000 Amp as per Request)
ACB Above 1000 Amp
MCB Rating 6A,10A,16A,20A,32A,40A,50A,63A
MCCB Rating 0.5A,1A,2A,4A,6A,10A,16A,20A,32A,40A,50A,63A,80A,100A (Domestic Max 6A)
RCCB/ELCB 6A,10A,16A,20A,32A,40A,50A,63A,80A,100A
Sen. of ELCB 30ma (Domestic),100ma (Industrial),300ma
DPIC (Double Pole Iron Clad) main switch 5A,15A,30 A for 250V
TPIC (Triple Pole Iron Clad) main switch 30A, 60A, 100A, 200 A For 500 V
DPMCB 5A, 10A, 16A, 32A and 63 A for 250V
TPMCCB 100A,200A, 300Aand 500 A For 660 V
TPN main switch 30A, 60A, 100A, 200A, 300 A For 500 V
TPNMCB 16A, 32A,63A For 500 V, beyond this TPNMCCB: 100A, 200A, 300A, 500 A For 660 V
TPN Fuse Unit (Rewirable) 16A,32A,63A,100A,200A
Change over switch (Off Load) 32A,63A,100A,200A,300A,400A,630A,800A
SFU (Switch Fuse Unit) 32A,63A,100A,125A,160A,200A,250A,315A,400A,630A
HRC Fuse TPN (Bakelite) 125A,160A,200A,250A,400A.630A
HRC Fuse DPN (Bakelite) 16A,32A,63A

MCB/MCCB/ELCB Termination Wire / Cable

Up to 20A MCB Max. 25 Sq.mm
20A to 63A MCB Max. 35 Sq.mm
MCCB Max. 25 Sq.mm
6A to 45A ELCB 16 Sq.mm
24A to 63A ELCB 35 Sq.mm
80A to 100A ELCB 50 Sq.mm

Transformer Earthing Wire / Strip Size:

Size of T.C or DG

Body Earthing

Neutral Earthing

<315 KVA 25×3 mm Cu / 40×6 mm GI Strip 25×3 mm Cu Strip
315 KVA to 500 KVA 25×3 mm Cu / 40×6 mm GI Strip 25×3 mm Cu Strip
500 KVA to 750 KVA 25×3 mm Cu / 40×6 mm GI Strip 40×3 mm Cu Strip
750 KVA to 1000 KVA 25×3 mm Cu / 40×6 mm GI Strip 50×3 mm Cu Strip

 Motor Earthing Wire / Strip Size:

Size of Motor

Body Earthing

< 5.5 KW

85 SWG GI Wire

5.5 KW to 22 KW

25×6 mm GI Strip

22 KW to 55 KW

40×6 mm GI Strip

>55 KW

50×6 mm GI Strip

 Panel Earthing Wire / Strip Size:

Type of Panel

Body Earthing

Lighting & Local Panel

25×6 mm GI Strip

Control & Relay Panel

25×6 mm GI Strip

D.G & Exciter Panel

50×6 mm GI Strip

D.G & T/C Neutral

50×6 mm Cu Strip

 Electrical Equipment Earthing:

Equipment

Body Earthing

LA (5KA,9KA)

25×3 mm Cu Strip

HT Switchgear

50×6 mm GI Strip

Structure

50×6 mm GI Strip

Cable Tray

50×6 mm GI Strip

Fence / Rail Gate

50×6 mm GI Strip

 Earthing Wire (As per BS 7671)

Cross Section Area of Phase, Neutral Conductor(S) mm2

Minimum Cross Section area of Earthing Conductor (mm2)

S<=16

S (Not less than 2.5 mm2)

16<S<=35

16

S>35

S/2

 Area for Transformer Room: (As per NBC-2005):

Transformer Size Min. Transformer Room Area (M2) Min. Total Sub Station Area( Incoming HV,LV Panel, T.C Roof) (M2) Min. Space Width (Meter)
1X160

14

90

9

2X160

28

118

13.5

1X250

15

91

9

2X250

30

121

13.5

1X400

16.5

93

9

2X400

33

125

13.5

3X400

49.5

167

18

2X500

36

130

14.5

3X500

54

172

19

2X630

36

132

14.5

3X630

54

176

19

2X800

39

135

14.5

3X800

58

181

14

2X1000

39

149

14.5

3X1000

58

197

19

  •  The Capacitor Bank should be automatic Switched type for Sub Station of 5MVA and Higher.
  • Transformer up to 25KVA can be mounted direct on Pole.
  • Transformer from 25KVA to 250KVA can be mounted either on “H” Frame of Plinth.
  • Transformer above 250KVA can be mounted Plinth only.
  • Transformer above 100MVA shall be protected by Drop out Fuse or Circuit Breaker.

 Span of Transmission Line (Central Electricity Authority):

Voltage

Normal Span

765 KV

400 to 450 Meter

400 KV

400 Meter

220 KV

335,350,375 Meter

132 KV

315,325,335 Meter

66 KV

240,250,275 Meter

 Max. Lock Rotor Amp for 1 Phase 230 V Motor (NEMA)

HP

Amp

1 HP

45 Amp

1.5 HP

50 Amp

2 HP

65 Amp

3 HP

90 Amp

5 HP

135 Amp

7.5 HP

200 Amp

10 HP

260 Amp

 Three Phase Motor Code (NEMA)

HP

Code

<1 HP

L

1.5 to 2.0 HP

L,M

3 HP

K

5 HP

J

7 to 10 HPPHPHPHHHHH

H

>15 HP

G

 Service Factor of Motor:

HP

Synchronous Speed (RPM)

3600 RPM

1800 RPM

1200 RPM

900 RPM

720 RPM

600 RPM

514 RPM

1 HP

1.25

1.15

1.15

1.15

1

1

1

1.5 to 1.25  HP

1.15

1.15

1.15

1.15

1.15

1.15

1.15

150 HP

1.15

1.15

1.15

1.15

1.15

1.15

1

200 HP

1.15

1.15

1.15

1.15

1.15

1

1

> 200 HP

1

1.15

1

1

1

1

1

 Type of Contactor:

Type

Application

AC1

Non Inductive Load or Slightly Inductive Load

AC2

Slip Ring Motor, Starting, Switching OFF

AC3

Squirrel Cage Motor

AC4,AC5,AC5a, AC5b,AC6a

Rapid Start & Rapid Stop

AC 5a

Auxiliary Control circuit

AC 5b

Electrical discharge Lamp

AC 6a

Electrical Incandescent Lamp

AC 6b

Transformer Switching

AC 7a

Switching of Capacitor Bank

AC 7b

Slightly Inductive Load in Household

AC 5a

Motor Load in Household

AC 8a

Hermetic refrigerant compressor motor with Manual Reset O/L  Relay

AC 8b

Hermetic refrigerant compressor motor with Automatic Reset O/L  Relay

AC 12

Control of Resistive Load & Solid State Load

AC 13

Control of Resistive Load & Solid State Load with Transformer Isolation

AC 14

Control of small Electro Magnetic Load (<72 VA)

AC 15

Control of Electro Magnetic Load (>72 VA)

 Contactor Coil:

Coil Voltage

Suffix

24 Volt

T

48 Volt

W

110 to 127 Volt

A

220 to 240 Volt

B

277 Volt

H

380 to 415 Volt

L

Overhead Conductor /Cable Size:

Voltage

Overhead Conductor

Cable Size

33 KV ACSR-Panther/Wolf/Dog , AAAC 150,185,300,400,240 mm2 Cable
11 KV ACSR-Dog/Recon/Rabbit , AAAC 120, 150,185,300 mm2 Cable
LT ACSR-Dog/Recon/Rabbit , AAC,AAAC 95,120, 150,185,300 mm2 Cable

 Transmission / Distribution Line:

Span

Height of Tower

400KV=400 Meter

400KV=30Meter (Base 8.8 Meter)

220KV=350 Meter

220KV=23Meter (Base 5.2 Meter)

132KV=335 Meter

220KV Double Circuit=28 Meter

66KV=210 Meter

66KV=13Meter

Conductor Ampere

Voltage wise Conductor

Dog=300Amp

400KV=Moose ACSR=500MVA Load

Panther=514Amp

220KV=Zebra ACSR=200MVA Load

Zebra=720Amp

132KV=Panther ACSR=75MVA Load

Rabbit=208Amp

66KV=Dog ACSR=50MVA Load

Moose=218Amp

 Type of Tower:

Type

Used

Angle/Deviation

A

Suspension Tower Up to 2°

B

Small Angle Tower 2° to 15°

C

Medium Angle Tower 15° to 30°

D

Large Angle / Dead End Tower 30° to 60° & Dead End

 Tower Swing Angle Clearance (Metal Part to Live Part):

Swing Angle

Live Part to Metal Part Clearance (mm)

66KV

132KV

220KV

400KV

915mm

1530mm

2130mm

3050mm

15°

915mm

1530mm

2130mm

22°

3050mm

30°

760mm

1370mm

1830mm

44°

1860mm

44°

610mm

1220mm

1675mm

 Cable Coding (IS 1554) ???? A2XFY / FRLS / FRPVC / FRLA / PILC)

A

Aluminium

2X

XLPE

F

Flat Armoured

W

Wire Armoured

Y

Outer PVC Insulation Sheath

W

Steel Round Wire

WW

Steel double round wire Armoured

YY

Steel double Strip Armoured

FR

Fire Retardation

LS

Low Smoke

LA

Low Acid Gas Emission

WA

Non Magnetic round wire Armoured

FA

Non Magnetic Flat wire Armoured

FF

Double Steel Round Wire Armoured

 Corona Ring Size:

Voltage

Size

<170 KV 160mm Ring put at HV end
>170 KV 350mm Ring put at HV end
>275 KV 450mm Ring put at HV end & 350 mm Ring put at Earth end

 Load as per Sq.Ft:

Type of Load

Load/Sq.Ft

Diversity Factor

Industrial

1000 Watt/Sq.Ft

0.5

Commercial

30 Watt/Sq.Ft

0.8

Domestic

15 Watt/Sq.Ft

0.4

Lighting

15 Watt/Sq.Ft

0.8

  Size of Ventilation Shaft:

Height of Building in meter Size of ventilation shaft in sq meter Minimum size of shaft in meter

9.0

1.5

1.0

12.5

3.0

1.2

15 and above

4.0

1.5

 

Accuracy Class of Metering CT:

Metering Class CT

Class Applications
0.1 To 0.2 Precision measurements
0.5 High grade kilowatt hour meters for commercial grade kilowatt hour meters
3 General industrial measurements
3 OR 5 Approximate measurements

 Accuracy Class Letter of CT:

Metering Class CT

Accuracy Class Applications

B

Metering Purpose

Protection Class CT

C

CT has low leakage flux.

T

 CT can have significant leakage flux.

H

 CT accuracy is applicable within the entire range of secondary currents from 5 to 20 times the nominal CT rating. (Typically wound CTs.)

L

 CT accuracy applies at the maximum rated secondary burden at 20 time rated only. The ratio accuracy can be up to four times greater than the listed value, depending on connected burden and fault current. (Typically window, busing, or bar-type CTs.)

 Accuracy Class of Protection CT:

Class Applications
10P5 Instantaneous over current relays & trip coils: 2.5VA
10P10 Thermal inverse time relays: 7.5VA
10P10 Low consumption Relay: 2.5VA
10P10/5 Inverse definite min. time relays (IDMT) over current
10P10 IDMT Earth fault relays with approximate time grading:15VA
5P10 IDMT Earth fault relays with phase fault stability or accurate time grading: 15VA

Electrical Useful Equations

  • For Sinusoidal Current : Form Factor = RMS Value/Average Value=1.11
  • For Sinusoidal Current : Peak Factor = Max Value/RMS Value =1.414
  • Average Value of Sinusoidal Current(Iav)=0.637xIm (Im= Max.Value)
  • RMS Value of Sinusoidal Current(Irms)=0.707xIm (Im= Max.Value)
  • A.C Current=D.C Current/0.636.
  • Phase Difference between Phase= 360/ No of Phase (1 Phase=230/1=360°,2Phase=360/2=180°)
  • Short Circuit Level of Cable in KA (Isc)=(0.094xCable Dia in Sq.mm)/√ Short Circuit Time (Sec)
  • Max.Cross Section Area of Earthing Strip(mm2) =√(Fault Current x Fault Current x Operating Time of Disconnected Device ) / K
  • K=Material Factor, K for Cu=159, K for Alu=105, K for steel=58 , K for GI=80
  • Most Economical Voltage at given Distance=5.5x√ ((km/1.6)+(kw/100))
  • Cable Voltage Drop(%)=(1.732xcurrentx(RcosǾ+jsinǾ)x1.732xLength (km)x100)/(Volt(L-L)x Cable Run.
  • Spacing of Conductor in Transmission Line (mm) = 500 + 18x (P-P Volt) + (2x (Span in Length)/50).
  • Protection radius of Lighting Arrestor = √hx (2D-h) + (2D+L). Where h= height of L.A, D-distance of equipment (20, 40, 60 Meter), L=Vxt (V=1m/ms, t=Discharge Time).
  • Size of Lighting Arrestor= 1.5x Phase to Earth Voltage or 1.5x (System Voltage/1.732).
  • Maximum Voltage of the System= 1.1xRated Voltage (Ex. 66KV=1.1×66=72.6KV)
  • Load Factor=Average Power/Peak Power
  • If Load Factor is 1 or 100% = This is best situation for System and Consumer both.
  • If Load Factor is Low (0 or 25%) =you are paying maximum amount of KWH consumption. Load Factor may be increased by switching or use of your Electrical Application.
  • Demand Factor= Maximum Demand / Total Connected Load (Demand Factor <1)
  • Demand factor should be applied for Group Load
  • Diversity Factor= Sum of Maximum Power Demand / Maximum Demand (Demand Factor >1)
  • Diversity factor should be consider for individual Load
  • Plant Factor(Plant Capacity)= Average Load / Capacity of Plant
  • Fusing Factor=Minimum Fusing Current / Current Rating (Fusing Factor>1).
  • Voltage Variation(1 to 1.5%)= ((Average Voltage-Min Voltage)x100)/Average Voltage
  • Ex: 462V, 463V, 455V, Voltage Variation= ((460-455) x100)/455=1.1%.
  • Current Variation(10%)= ((Average Current-Min Current)x100)/Average Current
  • Ex:30A,35A,30A, Current Variation=((35-31.7)x100)/31.7=10.4%
  • Fault Level at TC Secondary=TC (VA) x100 / Transformer Secondary (V) x Impedance (%)
  • Motor Full Load Current= Kw /1.732xKVxP.FxEfficiency
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