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# Calculate size of transformer and voltage due to starting of large size motor

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## 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:

• 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

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1. fassil
Oct 26, 2022

how to size proper transformer for pump motor

2. Krishna rao
Jul 13, 2021

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

3. Brandon
Jun 28, 2021

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