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
0°	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