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Electrical Thumb Rules

  12:41 AM Blogger   No comments   Edit

Current rating of Transformer / Generator (I)  

 KVA  X  1.4

 

Impedence of  Transformer  (Z) 

5 %

 

Short circuit rating of Transformer   

Current Rating / % Impedence  =  I / Z

 

No Load Current of Transformer

< 2 % of rated current of Transformer

 

Impedence of Generator

15 %

 

Short circuit rating of Generator

Current Rating / % Impedence  =  I / Z

 

Full load current ( FLC ) of 3 Phase Motor  

HP  X  1.5

  

No load current of 3 Phase Motor

30%  of FLC 

 

Full load current of Single Phase Motor 

HP  X  6

 

KW  rating of Motor 

HP  X   0.75

 

OLR  selection

 DOL  STARTER :-   FLC  X  1

STAR & DELTA  STARTER  :-   FLC  X  0.6

 

Fuse Rating for  Motor  protection

 DOL    :-  FLC  X  2

 STAR & DELTA   :-   FLC  X  1.5

 SLIP RING MOTOR  :-    FLC  X   1.25

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