The ESP step-up transformer (SUT) matches the VSD output voltage with the ESP motor requirements using multiple manual voltage taps.
It is the critical link between the surface drive and the downhole motor: it converts the VSD's relatively low output into the high voltage needed for efficient power transmission over long cable runs.
Purpose and function
SUT means step-up transformer (it steps voltage up from the VSD toward the ESP motor nameplate voltage).
In CIS / GOST practice these pad transformers are typically oil-filled transformers for submersible (ESP) pumps - the same role as the familiar TMPN / TMPNG nameplate family. So: TMPN on the nameplate = the SUT sitting on the pad.
The main job is to step up the voltage from 380 V (or 480 V) to a range typically between 1000 V and 6000 V. This is essential to:
- Compensate for voltage drops in long power cables.
- Provide the specific nameplate voltage required by the ESP motor.
- Voltage taps: Unlike standard industrial transformers, the SUT has multiple output taps. Field engineers can manually adjust output voltage (e.g., in 50 V or 100 V increments) to compensate for cable length or motor specs.
- Oil-filled construction: The transformer is filled with dielectric oil for cooling and insulation, suitable for continuous outdoor operation in extreme environments.
- Expansion tank: Most units have an external expansion tank to manage oil volume changes with temperature.
The SUT is usually positioned between the variable speed drive (VSD) / ESP control panel and the wellhead. During commissioning, selecting the correct tap is vital:
- Undervoltage: Leads to insufficient torque and motor stalls.
- Overvoltage: Causes excessive motor heating and insulation breakdown.