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Home / Download Center / Electrical Software Reviews / Calculate size of transformer and voltage due to starting of large size motor
Calculate size of transformer and voltage due to starting of large size motor (MS Excel Spreadsheet)
Calculate size of transformer and voltage due to starting of large size motor (MS Excel Spreadsheet)

Easy way to calculate transformer and motor details

Transformer details:

  1. Transformer size
  2. Transformer secondary voltage (v2)
  3. % Impedance (z)
  4. Allowable voltage drop in system

Motor details for one and more motors:

  1. Motor full load current (ILM)
  2. Locked rotor current multiplier (Min)
  3. Locked rotor current multiplier (Max)
  4. Locked rotor current (L1) (Min)
  5. Locked rotor current (L2) (Max)
  6. Motor inrush KVA at starting (IrsM)
  7. How many times motor starts per hour

and Calculations:

  1. Full load current of transformer (ILX)
  2. Short circuit current at transformer secondary (Isc)
  3. Maximum KVA of transformer at Isc (Q1)
  4. Motor inrush KVA At starting (IrsM)
  5. Voltage drop at transformer secondary due to motor inrush (Vd)
  6. Transformer secondary voltage

Results you get:

  • Motor Full Load Current
  • Voltage Drop at Transformer Secondary Due to Motor inRush
  • Transformer Size:(20% Added due to motor starts more than once/Hour)

Calculation formulas used:

  • ILX = KVA / (1.732 x v2)
  • ILM = (Kw x 1000) / (1.732 x Vm x P.F)
  • Isc = ILx / z
  • Q1 = (v2 x ISC x ILM x 1.732) / 1000
  • IrsM = (Vm x L2 x 1.732) / 1000
  • Vd = IrsM / Q1
Software:Calculate size of transformer and voltage due to starting of large size motor
Version:10.6.13
Developer:Jignesh Parmar
Size:40 KB
Price:Free
Download:Right here | Video Courses | Membership | Download Updates
Code Letter (KVA per HP) -Locked Rotor Current
Code Letter (KVA per HP) -Locked Rotor Current

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23 Comments


  1. Krishna rao
    Jul 13, 2021

    Whether this calculation holds good for heavy starts as for ballmills.


  2. Brandon
    Jun 28, 2021

    Rule of thumb large motors should be ___ of the KVA of XFMR?

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