Understanding the Compatibility of a 25 HP 3-Phase Motor with a 25 kVA Transformer

When considering the operation of a 25 HP 3-phase motor on a 25 kVA transformer, it's crucial to understand the interplay between motor and transformer specifications. This article delves into the calculations and considerations necessary to determine the feasibility of this setup.

Calculating Motor Current for a 25 HP 3-Phase Motor

The formula for calculating the current drawn by a 25 HP 3-phase motor is given by:

Power (P) √3 * V * I * cosΦ * efficiency

Where:

Power (P) is the power in watts (W), Voltage (V) is the voltage in volts (V), Current (I) is the current in amperes (A), Power factor (cosΦ) is the power factor, and Efficiency is the motor efficiency factor.

Substituting the given values:

Power (P) 18650 W, Voltage (V) 415 V, Power factor (cosΦ) 0.8, Efficiency 0.8

Note: 25 HP 18650 W (approximate value for 25 HP motor at nominal conditions)

The formula to find the motor current (I) is:

I P / (√3 * V * cosΦ * efficiency)

Plugging in the values, we get:

I 18650 / (1.732 * 415 * 0.8 * 0.8) 40 A (approximately)

Calculating Transformer Current Rating for a 25 kVA Transformer

The formula to calculate the rated current of a transformer is given by:

I S / (V * √3)

Where:

Number of kilovolt-amperes (kVA) (S) is the transformer capacity, Voltage (V) is the rated voltage.

Substituting the given values:

Transformer rating S 25 kVA, Voltage (V) 415 V, Efficiency 0.9863 (for 98.63%)

Since the efficiency is a factor that doesn't directly impact the current calculation, we can use the transformer's kVA value to determine its current rating:

I 25000 / (415 * 1.732 * 0.9863) 44.36 A (approximately)

Comparison of Motor and Transformer Currents

From the calculations:

Motor Current (I) 40 A Transformer Current Rating (I) 44.36 A

Since the motor current (40 A) is less than the transformer's rated current (44.36 A), it is feasible to operate a 25 HP 3-phase motor on a 25 kVA transformer.

Conclusion

Based on the calculations and considerations, a 25 HP 3-phase motor can indeed operate on a 25 kVA transformer. This is due to the current drawn by the motor (40 A) being within the safe and operational limits of the transformer's rated current (44.36 A).