ESP Power Overview

Training Guide

Why This Matters

Most ESP electrical configurations are set once at installation and rarely revisited. The transformer tap is picked from a nameplate, the VSD base frequency is left at 60 Hz by default, and the system runs until something fails or production drops.

The problem is that wells change. Operating frequency shifts. Wells develop gas constraints. Reservoir pressure declines. The electrical configuration that made sense at installation may be quietly stressing equipment and wasting energy every single day.

Enerview's VSD tap calculation workflow answers one question with physics: given what this well is actually doing right now, is the electrical system configured correctly?

Part 1: The Power Chain (The Big Picture)

Before anything else, understand the path electricity takes to reach the ESP motor.

Grid → VSD → Step-Up Transformer → Power Cable → Motor

Each component in that chain has a job:

The VSD (Variable Speed Drive) controls motor speed by changing the frequency it delivers. It takes grid power (typically 480 V, 3-phase) and outputs the same voltage at a variable frequency. Think of it as a dimmer switch. At its set base frequency it delivers full voltage. Below that it scales down proportionally.

The Step-Up Transformer takes the VSD's 480 V output and boosts it to the high voltage the downhole motor needs, typically 1,500 to 3,500 V. The "tap" is the voltage setting on this transformer. It determines the turns ratio, which determines how much the voltage gets boosted.
The Power Cable runs thousands of feet downhole. Current flowing through it loses voltage along the way. The longer or smaller the cable, the greater the loss.

The Motor receives whatever voltage arrives at its terminals after traveling through the transformer and down the cable. If that voltage is wrong, the motor underperforms, overheats, or draws excessive current.

Part 2: The VSD Is a Dimmer Switch

This is the most important concept to internalize.
The VSD does not output a fixed voltage. It scales voltage linearly with frequency.
If base frequency is set to 60 Hz and the VSD outputs 480 V at 60 Hz, then at 50 Hz it only outputs 480 × (50/60) = 400 V. At 45 Hz it outputs 360 V.
This means the transformer does not always see 480 V on its primary side. It sees whatever the VSD delivers at the actual operating frequency.
This is why you cannot simply set the tap equal to the motor's nameplate voltage.

Part 3: The Tap Formula

The tap must be sized for what the transformer sees at base frequency, so that the V/Hz scaling naturally delivers the correct voltage at the actual operating point.

Tap = (Base Frequency / Operating Frequency) × Motor Terminal Voltage Required

Example: Well operating at 52 Hz. Motor needs 1,000 V at its terminals.

Tap = (60 / 52) × 1,000 = 1,153 V

Verification:

VSD output at 52 Hz: 480 × (52/60) = 416 V
Turns ratio: 1,153 / 480 = 2.40
Motor receives: 416 × 2.40 = 1,000 V exactly

If someone had simply set the tap to 1,000 V, the motor would only receive 867 V at 52 Hz. It would be undervoltaged, draw higher current to compensate, run hot, and degrade faster.

Part 4: The Full 8-Step Workflow

The workflow starts downhole with physics and works up to the grid. Here is what each step calculates and why.

Step 1: Pump BHP

Calculate the brake horsepower the pump requires at its maximum recommended operating frequency. This is the mechanical load the motor must deliver. It comes from the pump performance curves scaled to the operating frequency and flow conditions.

Step 2: Motor

Using the pump BHP from step 1 and motor performance coefficients, calculate what the motor needs electrically at that load: terminal voltage, current draw, power factor, and efficiency. Terminal voltage is the voltage the motor needs at its own input leads, downhole, at the operating frequency.

Step 3: Cable Voltage Loss

Calculate the voltage the power cable consumes running from the transformer down to the motor. This depends on cable length, conductor size, and the current the motor draws. The longer and smaller the cable, the bigger this loss.

Step 4: Required Tap

Add what the motor needs at its terminals plus what the cable consumes:
V_TAP,required = Terminal Voltage + Cable Voltage Loss
This is the true voltage the transformer must deliver at surface to ensure the motor receives exactly what it needs downhole.

Step 5: Configured Tap

Transformer taps come in fixed increments. Select the next available tap above the required value. This becomes the actual field setting.

Step 6: VSD Model

With the configured tap known, model the VSD: its efficiency, input conditions, and power factor. This determines what the drive must pull from the grid primary side.

Step 7: Surface Power

Calculate the total surface electrical load:
Input kW: real power, what the energy bill charges for
Input kVA: apparent power, what sizes the equipment
Input Amps: what flows through the surface conductors

Step 8: Compare and Save

Compare the optimized configuration against the current field configuration. Quantify the delta in kW, kWh, and cost.

Part 5: Base Frequency Optimization

Most engineers set VSD base frequency to 60 Hz by default and never change it. This is a significant hidden cost on wells that cannot operate near 60 Hz.

Here is what happens on a well capped at 51.3 Hz:

With base frequency at 60 Hz, the VSD only delivers 393.6 V at 51.3 Hz (86% of capacity). To still get the required 2,203 V at the motor, the transformer tap must be set to 2,576 V. Higher tap means higher turns ratio. Higher turns ratio means more reactive current through every component.

Change one setting: set base frequency to 51.3 Hz.

Now the VSD delivers full 460 V right at the operating point. The required tap drops to 2,203 V. Lower ratio, less reactive current, better power factor.
Same well. Same production. Same motor voltage. About 29 kVA less at the controller input.

That 29 kVA difference does not show up dramatically on the energy bill. It shows up as less heat in the VSD's power electronics, less stress on the transformer windings, and less reactive current through every connection between the grid and the motor. Over months and years, that is equipment life.

Part 6: Reading the Dashboard (Real Well Example)

When Enerview runs this workflow on a real well, the dashboard shows the output of every step.

Motor panel shows the physics-calculated values versus what sensors actually measure. If calculated load is 66% but measured load is 99%, the gap is a diagnostic signal. Either the motor is experiencing an issue the physics model does not explain, or there is a configuration mismatch driving excess current.

Re-Tap row shows the direct output of step 4 and 5: the current configured tap versus the recommended tap at the actual operating frequency. For example: From 2,664 V at 60 Hz → To 2,524 V at 53.8 Hz. That is not a small adjustment. It cascades through every component in the chain.
VSD panel shows the surface power chain: transformer input and output, VSD input and output, kW, kVA, and amps at each node. This is step 7 made visible.

Re-Size kVA compares installed VSD capacity against what the model says is actually needed. An installed 390 kVA unit on a well that only needs 256 kVA is a 34% oversized drive. It carries reactive burden, costs more to maintain, and may be replaced with a right-sized unit at the next intervention.

Motor load chart visualizes the supply-demand relationship across all frequencies. The blue line is what the motor can deliver. The purple curve is what the pump demands. The green dot is where the well is operating today. The red vertical line is the ceiling. Everything above that line overloads the motor.

Key Takeaways

kW costs you money. kVA costs you equipment life.

The tap is not the motor's nameplate voltage. It is the voltage the transformer must be rated at so the V/Hz scaling delivers exactly what the motor needs at the actual operating frequency.

Base frequency is not a set-and-forget parameter. On wells with frequency ceilings, defaulting to 60 Hz forces every component in the system to work harder than necessary for zero production benefit.
The workflow runs from physics downhole up to the grid. Every number on the dashboard traces back to a physical calculation, not a correlation or a guess.

Notes:

Real vs. Reactive, vs Apparent Power

Imagine you are pulling a heavy cart down a straight road. If you pull directly forward, every bit of your effort moves the cart. That is real power (kW), doing actual useful work.

Now imagine you pull the cart at a diagonal. Some of your force moves the cart forward (useful), but some pulls it sideways into the wall (wasted effort). Your muscles still had to generate all of that force. The total force your body exerted is apparent power (kVA). The sideways wasted portion is reactive power (kVAR).

The three types of power

Real Power (kW) is the actual work being done. Spinning the motor. Lifting fluid. This is what the energy bill charges for.
Reactive Power (kVAR) is power that shuttles back and forth between the source and the load without doing useful work. It is consumed by magnetic fields in motors and transformers. It does not appear on the energy bill directly, but it still flows through every wire and component, generating heat and stress.

Apparent Power (kVA) is the total power the system must carry. It includes both real and reactive. This is what sizes the hardware: the VSD, transformer, cable, and switchgear all must be physically large enough to handle kVA, not just kW.

The relationship between them:

kVA² = kW² + kVAR²

Or expressed as the power factor:

Power Factor = kW / kVA

A power factor of 0.80 means 80% of the power being carried does real work. The other 20% is reactive, carried for free by the system but doing nothing productive.

Why it matters for ESP systems

Every component between the grid and the motor is sized for kVA. If reactive power is high, the VSD needs to be larger, the transformer needs a higher rating, and more current flows through the cable even though none of that extra current is lifting fluid.

This is exactly why the base frequency optimization matters. When the tap is set incorrectly at a wrong base frequency, the turns ratio goes up, reactive current increases, kVAR rises, and the entire system carries more apparent power (kVA) for the same production output. The documents show a real case where correcting base frequency reduced controller kVA by 29 kVA on a single well. Across a fleet, that compounds into meaningful equipment life and capital savings. (VSD_Base_Frequency_Optimization.docx)

What a transformer does

A transformer takes voltage in on one side (primary) and delivers a different voltage out on the other side (secondary). It does this using two coils of wire wrapped around an iron core. The ratio of how many times each coil is wound determines how much the voltage gets stepped up or down.
That ratio is the turns ratio.

The simple math

If the primary coil has 100 turns of wire and the secondary coil has 500 turns:

Turns Ratio = 500 / 100 = 5

That means whatever voltage goes in gets multiplied by 5 on the way out.
480 V in × 5 = 2,400 V out.

In ESP terms

The VSD outputs 480 V. The motor needs 2,400 V downhole. The step-up transformer bridges that gap. The turns ratio tells you exactly how much the transformer multiplies the voltage.

Turns Ratio = Tap Voltage / VSD Primary Voltage

Using the example from the documents (VSD_Tap_Calculation_Technical_Reference.docx):

Tap set to 1,153 V
VSD outputs 480 V at base frequency
Turns Ratio = 1,153 / 480 = 2.40

So at 52 Hz when the VSD delivers 416 V, the transformer multiplies it: 416 × 2.40 = 1,000 V at the motor. Exactly right.

Why turns ratio matters beyond just voltage

Here is the part most people miss. When voltage goes up through the transformer, current goes down proportionally. A turns ratio of 2.40 means voltage doubles and current is cut roughly in half on the secondary side.

But if the turns ratio is unnecessarily high because the tap was set incorrectly or base frequency was left at 60 Hz on a well capped at 51 Hz, the transformer has to work harder. More magnetic flux, more reactive current drawn from the primary side, more heat in the windings.

The documents show this directly (VSD_Base_Frequency_Optimization.docx): correcting base frequency from 60 Hz to 51.3 Hz dropped the turns ratio, which dropped reactive current, which dropped controller kVA by 29 kVA on a single well. Same production. Less stress on every component.

ESP Power Overview

Why This Matters

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