Selection of Variable Frequency Drives – Examples

The equations for calculating the power requirement for VFD has been discussed in Selection of Variable Frequency Drives.

Using the equation below, we will provide some examples on selecting a VFD for a specific motor.
Note:These motors are used for electric submersible pumps hence the voltages are different from the usual motor ratings.

$P_IN = {sqrt{3}*V_motor*I_motor*PF_motor}/{{eta_VFD}*{eta_motor}}$

1. For the 150HP motor data:
η_vfd = 95%, VFD Efficiency
η_motor = 85%, Motor Efficiency
V_motor = = 2100 V, Motor terminal voltage
I_motor = 46.6 A, Motor current
PF_motor = 0.95, Motor power factor

${P_IN} = {sqrt{3}*{2100/1000}*46.6*0.95}/{{0.95}*{0.85}}=199kW (267HP)$

2. For the 300HP motor data:
η_vfd = 95%, VFD Efficiency
η_motor = 85%, Motor Efficiency
V_motor = = 2940 V, Motor terminal voltage
I_motor = 78.9 A, Motor current
PF_motor = 0.95, Motor power factor

${P_IN} = {sqrt{3}*{2940/1000}*78.9*0.95}/{{0.95}*{0.85}}=400kW (537HP)$

Selection of VFD

1. Based on Toshiba VFD catalogue:

The VFD ratings for each of the motors above will be:
1. For 150 HP Motor - Toshiba T300MV2, Model 400 HP, 50A, 4160V.
2. For 300 HP Motor - Toshiba T300MV2, Model 700 HP, 87A, 4160V.

2. Based on ABB VFD catalogue:

The VFD ratings for each of the motors above will be:
1. For 150 HP Motor - ABB ACS1000-033-A01A-J4-010, 70A, 3300V.
2. For 300 HP Motor - ABB ACS1000-033-A01C-J4-010, 87A, 3300V.

3. Based on WEG VFD catalogue:

The VFD ratings for each of the motors above will be:
1. For 150 HP Motor - WEG Model MVW01-C096-T3300-EH30G2Z, 85A, 3300V.
2. For 300 HP Motor - WEG Model MVW01-C096-T3300-EH30G2Z, 85A, 3300V.

Final Note

The size selection of a variable frequency drive (VFD) should be based on motor voltage and current and not on the torque or power rating.