1. Monitoring Electrical Health of ESPs: What Are Your Measurement Options?
By Anthony Thornberry
Presented at the Mid-Continent Digital Oilfield Conference.
Tulsa, OK
January 26, 2017

2. Overview How’s your health?
Components of an ESP (Electrical Submersible Pump) system
Megger Testing
Critical downhole measurements
4 Critical electrical downhole measurements
Motor Temperature
Motor Fluid Conductivity
Line Current (Leakage Current)
Wye Voltage
ESP Motor Lab Test Data
Summary

3. How’s Your Health? Monitoring your system Blood pressure Temperature
Pulse rate
Strength
Speed
Flow lines – arteries, veins
Valves
Electrical signals

4. Components of an ESP System
Surface Choke
Surface Readout Unit (SRO)
Variable Speed Drive (VSD)
Wellhead
3-Phase Power Line
Discharge Sub
Discharge Sub
ESP Pump
Motor Oil Seal
ESP Motor
Motor Wye Point
ESP Sensor

5. Electrical Components and Measurements
Megger
Testing
Choke
High Voltage Protection
SRO
Power
Voltage
Data
Surface Readout Data
Wellhead
Ground
VSD
Powers the motor, Drive frequency
3-Phase Power Line
Discharge Sub
Discharge Pressure
Line Current (Leakage Current)
Motor Seal – Conductivity Measurement
Motor Temperature
Motor Wye Point Voltage
System sensors (P, T, Vib. Etc.)

6. Megger Testing
The Megger test is the most important electrical test of an ESP system.
It is an IR (Insulation Resistance) test.
A high DC Voltage (-5KVDC typical) is applied to the downhole cable, motor, and gauge to verify High Voltage insulation rating of the system.
An insulation breakdown results in a dangerous shock hazard.
Measured Parameter
Observation
Possible Causes
Megger Voltage test at wellhead
Apply -5KVDC typical Measure Resistance
Phase to Phase high resistance (> 100 ohms)
Motor cable damaged, high resistance connection, motor winding damaged
Phase to Ground low resistance (< 100K ohms)
Motor cable has low resistance to ground, cable short to ground, gauge internal short
Megger Breakdown test failure (< 1M ohms)
Motor Cable or winding insulation breakdown failure, eventual motor failure
Common Megger Questions:
What is the standard Megger Voltage? 5KVDC is typical but some systems allow 10KVDC
What is the polarity for the Megger Test? Typical measurements are REVERSE meaning + to Ground
Will the Megger damage the Gauge? Most gauges contain a Megger Diode that protects and isolates the gauge during the Megger test.
Is the Megger Test dangerous? The Megger uses High Voltage and Low Current to prevent instrument damage, however High Voltage is always dangerous. Use with caution. High Voltage and High Current is extremely dangerous.

7. Critical Downhole Measurements
Downhole gauge measures critical system parameters
Intake Pressure
Intake Temperature
Discharge Sub Pressure
Vibration (Vx, Vy, Vz)
Line Voltage
Motor Temperature
Motor Fluid Conductivity
Line Current (Leakage Current)
Wye Point Voltage
Measurements shown in RED are indicators of the Electrical Health of the ESP System.

8. ESP Motor Temperature
Monitoring motor temperature is the most important parameter for long motor life.
RTD (Resistive temperature Detector) or thermocouple near the motor windings
Set a baseline motor temperature.
Compare motor temperature with pump intake temperature to establish true motor temperature reference point.

9. ESP Motor Temperature Trending
Operating the motor at high temperatures reduces the useful life of your motor.
Typical motor temperatures are between 125°C to 200°C depending upon the downhole applications.
High motor temperatures can indicate:
Motor bearing wear
Motor winding stress
Breakdown of wiring insulation and polymer fillers in windings
Higher than expected motor torque
Perform slow shutdown of motor to allow well fluid to cool motor since cooling is accomplished by the pump.
Avoid sudden temperature changes or spikes to your motor to increase motor operating life.

10. Motor Fluid Conductivity
Measures the electrical insulation properties of the motor fluid.
It is the electrical resistance between an internal pin and the gauge housing in the presence of motor oil.
The reading is usually in Ohms.
Good, clean motor oil is important.
Well fluids contaminate motor oil.

11. Motor Fluid Conductivity Trending
Data Ranges can vary depending upon the measurement scheme.
Typical range is 0 to 20 Meg Ohm with 1Kohm resolution steps.
A decreasing resistance (increasing conductivity) indicates there are intrusive fluids in the motor oil.
High conductivity can lead to motor failure caused by:
Motor seal leak
Motor oil contamination
Bladder or capillary failure
Poor motor oil quality, burned motor oil

12. Line Current (Current Leakage)
Measures the lost electrical current between the surface equipment and the downhole motor.
Calculated by subtracting the downhole gauge current from the current supplied by the Surface Gauge Power Supply.
It is valid with and without the motor running since it is supplied external to the VSD three phase power.
Choke
High Voltage Protection
SRO
Power
Voltage
Data
Wellhead
Ground
VSD
Powers the motor, Drive frequency
Discharge Sub
Discharge Pressure
Current Leakage on Cable
Seal – Conductivity Measurement
Motor Temperature
Motor Wye Point Voltage
System sensors (P, T, Vib., etc.)

13. Line Current (Current Leakage) Trending
It is important to “Zero” the Leakage Current setting during the initial installation.
After zeroing, trending data can be collected and monitored.
Trending the data helps predict the electrical quality of the 3- phase motor power cable and connections.
Increasing Line Current can indicate cable and connection failures can be caused by:
Faulty or unsealed “Pot Head” connections to the motor
Motor cable splices
Cracking in the cable insulation
Motor winding insulation breakdown failure

14. Motor Wye Point Voltage
Measures the AC voltage between the motor WYE point and motor casing or ground.
It is located between the downhole gauge and ESP motor.
The WYE point voltage is the sum of all 3 phases of the downhole motor cable.
If there is no imbalance between the phases, it measures 0V.
System losses and mismatches in an ESP system can generate an imbalance voltage.
Wye Point voltage changes can be an indication of pre-mature downhole motor failure.
Wye Point Voltage V1 V3 V2

15. Motor Wye Point Voltage Trending
Acceptable limits of imbalance voltage are 3-5% of the voltage seen at the ESP motor.
For example, an acceptable imbalance voltage for a 3000V motor is between 90 – 150V (RMS).
Higher voltages will shorten the motor life and can result in loss of data to the SRO.
A higher imbalance voltage can indicate:
Insufficient VSD line filtering
Motor winding mismatch
Poor motor electrical connection
3-phase motor cable mismatch or dropped phase
Arcing, harmonic distortion of the sine wave signal from the VSD
3rd harmonic line ripple due to motor winding losses
Choice of type of VSD drive (direct, 6/12 step, PWM, etc.)
PWM carrier noise – high frequency noise

16. ESP Motor Test Lab Motor Test Lab simulates downhole conditions
A single downhole induction motor rated to 1500V
2000 ft of 3-phase power cable
Dynamic torque resistance load (dyno)
Sensors are tested at temperatures up to 230ºC

17. Wye Point Imbalance with Temperature
The WYE Voltage can be difficult to measure over a wide temperature, voltage, and frequency range.
An example of uncompensated raw data collection is shown below with increasing motor imbalance.
Digital Signal Conditioning is used to compensate readings over a wide temperature range (25ºC to 150ºC).

18. Data Communication Integrity at Low Drive Frequencies
ESP Gauge Data Protocols
Digital PW Data - data is communicated in the form of pulse widths in time which are proportional to the sensor reading. PW data uses a single sample per measurement.
Digital Lossless Data - sending the actual measurement encoded into a digital numeric coding format. Oversampling data reduces errors in the data stream for low frequency noise.
The illustration below is a plot of sensor data vs motor speed for a Digital Data PWM ESP gauge (competitor gauge) operating over a range of motor drive frequencies. Gauges are tested from 5Hz to 75Hz for operation while collecting sensor data. Sercel-GRC gauges utilize Digital Lossless Data format.
Motor Drive Frequency (Hz)

19. Summary – 4 Critical Electrical Measurements
Measured Parameter
Observation
Possible Causes
Motor Temperature
Increasing
Motor bearing wear
Motor winding stress
Breakdown of wiring insulation and polymer fillers in windings
High motor torque
Motor Fluid Conductivity
Motor Seal Leak
Bladder or capillary failure
Leakage Current
Cable insulation breakdown, cable splice failure, damaged or pinched cable
Motor Wye Point Voltage
Decreased pump efficiency; motor temperature increase; motor and/or cable failure due to imbalance, capacitive cable coupling, CMC Common Mode Current, Reflected Wave Voltage from HV pulses (PWM or Reflection)
* Megger testing should be performed as a requirement before initial operation of any ESP system.