Continued from first part: Electrical Thumb Rules You MUST Follow (Part 1)

## Useful Electrical 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 (I**) = 0.637 x Im (Im = Max.Value)_{av}**RMS Value of Sinusoidal Current (I**0.707 x Im (Im = Max.Value)_{rms}) =**A.C Current =**D.C Current/0.636.**Phase Difference between Phase =**360/ No of Phase (1 Phase=230/1=360°, 2 Phase=360/2=180°)**Short Circuit Level of Cable in KA (I**0.094 x Cable Dia in Sq.mm) /√ Short Circuit Time (Sec)_{sc}) =

(**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 Al = 105, K for steel = 58 , K for GI = 80**Most Economical Voltage at given Distance =**5.5 x √ ((km/1.6) + (kw/100))**Cable Voltage Drop (%) =**1.732 x current x (RcosǾ+jsinǾ) x 1.732 x Length (km) x 100) / (Volt(L-L) x Cable Run.

(**Spacing of Conductor in Transmission Line (mm) =**500 + 18 x (P – P Volt) + (2 x (Span in Length)/50).**Protection radius of Lighnting****Arrestor**= √h x (2D-h) + (2D+L).

Where h= height of L.A, D-distance of equipment (20, 40, 60 Meter), L=V x t (V=1m/ms, t=Discharge Time).**Size of Lightning Arrestor =**1.5x Phase to Earth Voltage or 1.5 x (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) x 100)/Average Voltage

**Ex:**462V, 463V, 455V, Voltage Variation= ((460 – 455) x 100)/455 =**1.1%**.**Current Variation (10%) =**((Average Current – Min Current) x 100)/Average Current

**Ex:****Fault Level at TC Secondary**= TC (VA) x 100 / Transformer Secondary (V) x Impedance (%)

**Motor Full Load Current =**Kw /1.732 x KV x P.F x Efficiency

Hasmukh Patel

Really very good knowledge, that helps to know even very difficult to find solution.

deshmukh V.

thanks for ‘useful’ information.

Rajan.K

The thumb rules are really great. thanks a lot for providing such information in a capsule

NITIN

Size of Lightning Arrestor = 1.5x Phase to Earth Voltage or 1.5 x (System Voltage/1.732)

MEANS WHAT SIZE OF THAT ARRESTER ???

PARAG NIKUMBH

will reply once sure

aakifnouman

A.C Current = D.C Current/0.636

what is 0.636??

sumitfloyd

A.C Current = D.C Current/0.636.

Please clarify this relation on how do you get it?