Surface · ESP
Variable Speed Drive
The surface controller that feeds the ESP motor. It converts fixed line frequency into variable frequency, so the pump speed can be adjusted.
What it does
Matches pump output to what the well can deliver, starts the motor smoothly and protects it with underload, overload and imbalance trips. A fixed speed switchboard does the same job without speed control.
Basics
| Alternatives | Fixed frequency switchboard or soft starter |
| Sized by | Required surface voltage and motor current (kVA) |
| Typical protections | Underload, overload, phase imbalance, ground fault |
| Often reads | Downhole sensor data, can adjust speed automatically |
Common failures
- Nuisance underload trips from gas or low inflow
- Overheating of the cabinet in hot climates
- Harmonics that stress the cable and motor without an output filter
Troubleshooting
- Symptom
- Repeated underload trips
- Likely cause
- Gas interference or the pump outrunning the well
- What to check
- Intake pressure trend, lower the frequency, review gas handling
- Symptom
- Trips on phase imbalance
- Likely cause
- Cable or motor insulation fault, or supply problem
- What to check
- Insulation test of cable and motor from the junction box, check supply phases