Elec Calcu

2009

Electrical Formula

M ALI WAQAR KHAN (Sr, Service Engineer)

GUIDE TO STANDARD UNIT Kilo volts Amps

Legend

= KVA

R = Resistance, in ohms

Kilo Watts (1000w x =1Kw) = KW

P = Power, in watts

Amps (volts Amp or current) =

V = Voltage, in volts

I

Volts

=

Power Factor

= PE

Percent Efficiency

= % EFF

I = Current, in amps

E

HP = Horsepower L = Length Eff = Efficiency e.g. 85% = 0.85

Horse Power

= HP

pF = Power Factor Output kW = Net effective mechanical power of a motor

Ohms Law Power =

V2 R

or

R x I2

or

Voltage =

P I

or

R x I

or

V I

or

V2 P

or

P V

or

V R

or

Resistance =

Current =

V x I

P I2

Three Phase, Single Phase & DC Formula Three Phase

Single Phase

Direct Current

kW =

I x V x 1.732 x pF

I x V x pF kW =

1000

kW =

KVA x pF

I x V kW =

1000

kW =

1000

KVA x pF

HP x 746 kW = 1000 x Eff

Output kW =

I x V x 1.732 x pF x Eff

Output kW =

1000

Output kW =

1000

I x V x 1.732 kVA =

I x V x pF x Eff

I x V x Eff 1000

I x V kVA =

1000

1000

kW kVA = pF

kW x 1000 I =

V x 1.732 x pF x Eff

kW x 1000 I =

kVA X 1000 V

HP x 746

HP =

V x Eff

I = V x 1.732

I =

I = V x pF x Eff

kVA X 1000 I =

kW x 1000

V x 1.732 x pF x Eff

I x V x 1.732 x pF x Eff 746

HP x 746 I =

HP x 746 I =

V x pF x Eff

HP =

I x V x pF x Eff 746

V x Eff

HP =

I x V x Eff 746

kW x Eff x 1000 HP = 746

HP =

kVA x Eff x 1000 x pF 746

kW x 1000 pF =

kW x 1000 pF =

I x V x 1.732

I x V

HP x 746

HP x 746

Eff =

Eff = I x V x 1.732 x pF

HP x 746 Eff =

I x V x pF

I x V

Voltage Drop

1000 x Vd Vc =

or

Vd =

L x I

Vc x L x I 1000

where:

Vc = mV/Am L = Length I = Current Vd = Voltage Drop

Australian Standards specify a maximum of 5% voltage drop across the entire circuit (including mains, sub mains and final sub circuit).

Maximum Circuit Length Calculation

where:

Lmax = Tha x Uo x Sph x Spe Ia x Resistivity x (Sph+Spe)

Tha = System Impedance Factor Uo = Phase Voltage Sph = Cable CSA Spe = Cable Earth CSA Resistivity = Resistivity for Copper Ia = Magnetic release operating current, or fuse interupting

capacity