Field Testing / Commissioning Solution

Field testing is the stage where electrical equipment moves from an installed asset to an operating asset. Factory test reports can confirm that a transformer, switchgear panel, cable, circuit breaker, or protection relay met its factory requirements. They cannot confirm that the equipment arrived at site without damage, was installed correctly, was wired according to the drawings, and will operate correctly as part of the complete electrical system.

This is where field testing and commissioning become critical.

From the UHV perspective, field testing is not simply a matter of taking measurements on individual devices. The test plan has to follow the actual site sequence:

Installation → Inspection → Individual Equipment Testing → System Testing → Protection Testing → Energization → Functional Verification → Commissioning

UHV field testing solutions are applicable to:

Substations

Power Plants

Renewable Energy Plants

Industrial Facilities

Data Centers

Railway Power Systems

Oil & Gas Facilities

Mining Projects

Manufacturing Plants

Grid Connection Projects

Transformer Stations

MV/HV Cable Systems

GIS/AIS Switchgear Systems

The equipment scope can cover:

Transformer Testing · Cable Testing · GIS Testing · Circuit Breaker Testing · CT/PT Testing · Relay Protection Testing · Insulation Testing · Partial Discharge Testing · AC Withstand Testing · Battery Testing · Grounding Testing

1. Testing Background

A field commissioning project has one fundamental difference from laboratory testing: the test environment is the actual operating site.

The equipment may be located inside a substation, outdoors in a solar plant, inside an industrial facility, underground in a cable trench, or installed in a compact GIS room. Temperature, humidity, electromagnetic interference, access conditions, auxiliary power, grounding, and site safety all affect the test.

A typical commissioning project contains several layers.

Equipment Layer

Individual equipment is checked first:

• Transformer
• GIS
• Switchgear
• Circuit Breaker
• Cable
• CT/PT
• Motor
• Generator
• Battery

Protection Layer

The protection and control circuits are then checked:

• Protection Relay
• Trip Circuit
• Closing Circuit
• Alarm
• Interlocking
• Measurement
• Communication

System Layer

The complete electrical system is finally verified:

Transformer → Switchgear → Cable → Load

or:

Generation → Transformer → Substation → Grid

This sequence matters because a system can contain individually qualified components but still fail during commissioning because of an incorrect cable connection, CT polarity, phase sequence, relay setting, grounding connection, or trip circuit.

UHV's field testing approach therefore focuses on test sequence, equipment compatibility, field conditions, measurement reliability, and complete documentation.

2. Testing Objects

2.1 Power Transformers

Field transformer testing may include:

• Transformer Turns Ratio
• Winding Resistance
• Insulation Resistance
• Tan Delta
• Excitation Current
• Transformer Oil BDV
• Partial Discharge
• AC Withstand where required

The field results should be compared with factory test data and previous maintenance records where available.

2.2 GIS and AIS

GIS/AIS commissioning can involve:

• Insulation Resistance
• AC Withstand
• Partial Discharge
• Contact Resistance
• Circuit Breaker Timing
• SF6 Gas Quality
• Dew Point
• Gas Leakage
• Interlocking

For GIS, the quality of assembly and cleanliness can have a direct effect on insulation performance.

2.3 Circuit Breakers

Field testing evaluates both the electrical contacts and operating mechanism.

Typical measurements:

• Opening Time
• Closing Time
• Travel
• Speed
• Coil Current
• Contact Resistance
• Phase Synchronization
• Operating Sequence

2.4 MV/HV Cables

Cable commissioning is particularly important after installation and termination.

Typical tests include:

• Insulation Resistance
• Sheath Testing
• VLF Testing
• AC Hipot
• AC Resonance
• Partial Discharge
• Cable Fault Location

The test method should match the cable type, voltage level, insulation system, cable length, and project specification.

2.5 CT/PT

Field CT/PT testing verifies the actual installed measurement and protection circuits.

Typical tests include:

• Ratio
• Polarity
• Excitation
• Burden
• Accuracy
• Winding Resistance
• Insulation
• Knee Point for applicable CTs

2.6 Protection Relays

Commissioning tests may include:

• Overcurrent
• Earth Fault
• Differential
• Overvoltage
• Undervoltage
• Overfrequency
• Underfrequency
• Directional
• Distance where applicable
• Motor Protection
• Transformer Protection

The final test should verify the relay together with the trip circuit and circuit breaker.

2.7 Batteries and DC Systems

Substation batteries provide power for protection and control during abnormal conditions.

• Testing may cover:
• Battery Voltage
• Cell Voltage
• Internal Resistance
• Capacity
• Discharge
• Charger
• DC Insulation

2.8 Grounding Systems

• Field grounding tests can include:
• Ground Resistance
• Ground Grid
• Grounding Continuity
• Equipment Bonding
• Step Voltage
• Touch Voltage

Large substations and industrial facilities should be evaluated as complete grounding networks.

3. Testing Requirements

The field testing plan should be prepared before equipment arrives on site.

UHV recommends confirming the following information first:

Electrical Parameters

• System Voltage
• Rated Current
• Frequency
• Short-Circuit Level
• Transformer Capacity
• Cable Voltage
• Cable Length
• Cable Capacitance

Equipment Information

• Transformer Type
• GIS/AIS Type
• Circuit Breaker Type
• CT/PT Specifications
• Cable Type
• Motor/Generator Ratings
• Battery Voltage

Project Information

• Single-Line Diagram
• Equipment Layout
• Cable Schedule
• Protection Drawings
• Control Wiring
• Grounding Drawing
• Factory Test Reports
• Previous Test Records

Testing Requirements

• Required Test Items
• Test Voltage
• Test Duration
• Test Frequency
• Acceptance Criteria
• Applicable Standards
• Site Safety Requirements

This information determines whether a compact portable tester is sufficient or whether the project requires a larger high-voltage test system.

4. Testing Methods

4.1 Visual & Mechanical Inspection

Before electrical testing begins, the installation should be inspected.

Typical checks include:

• Equipment condition
• Nameplate data
• Terminal connections
• Cable terminations
• Grounding connections
• Mechanical assembly
• Oil level
• GIS gas condition
• Circuit breaker mechanism
• Control wiring

This stage can prevent incorrect energization and unnecessary test failures.

4.2 Insulation Resistance Testing

Insulation resistance testing is commonly used for:

• Transformers
• Cables
• Motors
• Generators
• Switchgear
• Auxiliary systems

The test provides an initial assessment of insulation condition before higher-voltage testing.

4.3 AC Withstand Testing

AC withstand testing verifies dielectric strength under specified test conditions.

Typical field applications include:

• GIS
• Switchgear
• Transformers
• Cables
• Motors
• Generators

When the test object has substantial capacitance, an AC Resonant Test System can be considered.

For system selection, UHV evaluates:

Required Test Voltage + Test Object Capacitance + Test Frequency + Test Duration

rather than selecting a system from voltage rating alone.

4.4 VLF Testing

VLF testing is widely used for specified medium-voltage cable field testing.

It is particularly useful where cable capacitance makes conventional power-frequency testing difficult to perform with a practical field setup.

Important parameters include:

• Cable Voltage
• Cable Length
• Cable Capacitance
• VLF Test Voltage
• Test Frequency
• Test Duration

4.5 AC Resonance Testing

AC Resonance is used when the test object presents a relatively high capacitive load.

Typical applications include:

• HV Cables
• GIS
• Large Electrical Equipment

The resonant circuit allows the test system to generate the required AC voltage without requiring the same apparent power as a conventional direct AC source.

4.6 Partial Discharge Testing

PD testing is used to identify localized insulation activity.

Potential defects include:

• Internal Voids
• Surface Defects
• Floating Particles
• Poor Insulation Interfaces
• Cable Accessory Defects
• Transformer Insulation Problems
• Field PD testing requires attention to:
• Background Noise
• Sensor Selection
• Grounding
• Shielding
• Test Connections
• Signal Separation

Industrial sites can contain strong interference from drives, motors, switching devices, communication equipment, and other electrical systems.

4.7 Transformer Testing

A typical field sequence is:

TTR

→ Winding Resistance

→ Insulation Resistance

→ Tan Delta

→ Excitation Current

→ Oil BDV

→ PD where required

The sequence can be adjusted according to equipment condition and project specifications.

4.8 Circuit Breaker Testing

Circuit breaker analyzers measure:

• Opening Time
• Closing Time
• Pole Synchronization
• Travel
• Speed
• Coil Current
• Contact Resistance

These measurements provide both electrical and mechanical information.

4.9 CT/PT Testing

CT/PT field testing confirms that the installed device and wiring correspond to the protection and metering design.

Typical sequence:

Ratio → Polarity → Excitation → Burden → Accuracy → Insulation

For protection CTs, knee-point and saturation characteristics may also need to be verified.

4.10 Relay Protection Testing

Secondary injection testing provides controlled current and voltage signals to the relay.

The commissioning sequence verifies:

Input → Pickup → Timing → Logic → Output → Trip

The final functional test should confirm that the actual circuit breaker responds correctly to the protection output.

4.11 Grounding Testing

Grounding testing may include:

• Earth Resistance
• Ground Grid Resistance
• Continuity
• Bonding
• Step Voltage
• Touch Voltage

The test method depends on the grounding system design and project requirements.

5. Recommended Equipment

For large EPC commissioning projects, UHV can combine multiple instruments into a field testing package rather than treating every test as a separate procurement item.

6. Testing Procedure

Step 1 - Site Preparation

Before testing:

• Confirm equipment isolation
• Confirm safety boundaries
• Check grounding
• Verify auxiliary power
• Review test points
• Confirm calibration status
• Prepare test cables
• Confirm communication with the site commissioning team

High-voltage testing should only proceed after the site safety and isolation conditions have been confirmed.

Step 2 - Documentation Check

Compare:

Nameplate → Drawing → Factory Report → Actual Installation

Any discrepancy should be resolved before electrical testing.

Step 3 - Individual Equipment Testing

Typical sequence:

Transformer

Ratio → Resistance → Insulation → Tan Delta → Excitation → Oil → PD

Cable

Insulation → Sheath → VLF / AC → PD

Circuit Breaker

Contact Resistance → Timing → Travel → Coil Current

CT/PT

Ratio → Polarity → Excitation → Burden → Accuracy

Step 4 - Secondary Circuit Testing

Verify:

• CT circuits
• PT circuits
• Relay wiring
• Trip circuits
• Closing circuits
• Alarm circuits
• Interlocking
• Remote signals

Step 5 - Protection Testing

Test each protection function individually, then verify the complete trip logic.

For example:

Fault Simulation → Relay Pickup → Trip Output → Circuit Breaker Opening → Alarm

Step 6 - System Testing

After individual equipment tests are completed, verify the electrical system as a whole.

Examples:

Transformer → MV Switchgear → Cable → Motor

or:

Generator → Transformer → GIS → Grid

Step 7 - Energization

Energization should follow the approved commissioning sequence.

Typical stages:

Auxiliary Power

→ Control Power

→ Protection

→ Main Equipment

→ Busbar

→ Transformer

→ Outgoing Feeders

→ Load

Step 8 - Functional Verification

After energization, confirm:

• Voltage
• Current
• Phase Sequence
• Protection
• Metering
• Alarms
• Interlocking
• Communication
• Remote Control
• Equipment Operating Status

Step 9 - Commissioning Documentation

The final field report should normally include:

• Equipment Identification
• Test Date
• Test Instrument
• Instrument Serial Number
• Calibration Information
• Test Conditions
• Test Parameters
• Test Results
• Acceptance Criteria
• Test Engineer
• Customer Witness
• Final Conclusion

7. Applicable Standards

Field testing and commissioning may reference different standards depending on the equipment and project.

Common standards include:

IEC 60076 - Power Transformers

IEC 62271 Series - High-Voltage Switchgear

IEC 60255 Series - Measuring Relays and Protection Equipment

IEC 60034 Series - Rotating Electrical Machines

IEC 60840 - High-Voltage Cables

IEC 62067 - Extra-High-Voltage Cables

IEC 61936 - Power Installations Exceeding 1 kV AC

Depending on the project, additional requirements may come from:

• IEEE Standards
• Local Electrical Codes
• Utility Specifications
• Grid Codes
• Equipment Manufacturer Instructions
• EPC Commissioning Specifications
• Owner's Testing Procedures

The acceptance criteria should always be established from the applicable project documents rather than applying a generic value to every installation.

8. Test Parameters

Field testing requires accurate information about the test object.

Most Important Data for Cable Testing

For UHV VLF or AC Resonance selection:

• Cable Rated Voltage
• Cable Length
• Cable Capacitance
• Required Test Voltage
• Required Test Frequency
• Test Duration

Most Important Data for AC Resonance

The required test system is primarily determined by:

Test Voltage + Capacitance + Frequency

For long cable systems, the cable capacitance is particularly important.

9. Common Testing Problems

Equipment Cannot Be Energized

Possible causes:

• Control wiring error
• Interlocking condition
• Protection lockout
• Incorrect auxiliary power
• Grounding problem

The commissioning team should trace the complete control path rather than repeatedly attempting energization.

Cable Test Failure

Potential causes include:

• Damaged insulation
• Poor termination
• Moisture
• Installation damage
• Incorrect test connection
• Incorrect test configuration

High PD Background

Common sources include:

• VFDs
• Motors
• Switching equipment
• Communication systems
• Poor grounding
• Nearby energized equipment

Field PD testing should begin with background measurement before interpreting the test object signal.

Abnormal Circuit Breaker Timing

Possible causes:

• Mechanism wear
• Coil problems
• Lubrication issues
• Control circuit problems
• Mechanical adjustment

CT Polarity Error

A polarity error can affect differential and directional protection.

The CT should therefore be verified before the relay functional test.

Protection Relay Does Not Trip the Breaker

The relay itself may be functioning correctly while the problem is located in:

Relay Output → Trip Circuit → Trip Coil → Breaker Mechanism

The commissioning test should therefore follow the complete path.

Inconsistent Test Results

Field conditions can change test results.

Possible causes:

• Temperature
• Humidity
• Grounding
• Test lead connection
• Electromagnetic interference
• Equipment temperature
• Previous test condition

Test conditions should be recorded with the measurement.

10. Equipment Selection Guide

Substation Commissioning

Recommended UHV package:

• Transformer Tester
• AC Resonant Test System
• PD Test System
• Circuit Breaker Analyzer
• CT/PT Analyzer
• Relay Protection Tester
• Ground Resistance Tester
• Battery Discharge Tester

Renewable Energy Commissioning

For solar and wind projects:

• Transformer Tester
• VLF Cable Tester
• AC Resonant Test System
• Cable PD System
• Circuit Breaker Analyzer
• CT/PT Analyzer
• Relay Protection Tester
• Grounding Tester

Industrial Plant Commissioning

Recommended scope:

• Transformer Testing
• Switchgear Testing
• Cable Testing
• Motor Testing
• Protection Testing
• Grounding Testing
• Battery Testing

GIS Commissioning

Typical equipment:

• AC Resonant Test System
• Partial Discharge Test System
• Circuit Breaker Analyzer
• Contact Resistance Tester
• SF6 Gas Analyzer
• SF6 Dew Point Meter

EPC Contractor

For EPC contractors, portability becomes important.

Consider:

• Equipment Weight
• Test Voltage
• Output Capacity
• Number of Test Modules
• Field Transportation
• Power Supply
• Environmental Rating
• Data Recording
• Software
• Calibration
• Local Service

UHV can configure the equipment according to the actual commissioning schedule and site conditions.

11. Case Studies

Case Study 1 - Substation Field Commissioning

A new substation is ready for energization.

UHV field testing equipment is used for:

Transformer

→ TTR
→ Winding Resistance
→ Insulation
→ Tan Delta

GIS

→ Contact Resistance
→ Circuit Breaker Timing
→ AC Withstand
→ PD

Protection

→ CT/PT
→ Relay
→ Trip Circuit

Grounding

→ Ground Resistance
→ Continuity

The final stage verifies the complete protection and energization sequence.

Case Study 2 - Renewable Energy Grid Connection

A large solar project needs to connect its collector system to the grid.

The commissioning scope includes:

• Transformer Testing
• MV Cable VLF Testing
• Cable PD Testing
• Switchgear Testing
• Circuit Breaker Timing
• CT/PT Testing
• Relay Protection Testing
• Grounding Testing

The equipment selection is based on the collector cable voltage, length, capacitance, transformer rating, and grid connection requirements.

Case Study 3 - Industrial Plant Commissioning

A new industrial plant contains multiple MV transformers, large motors, switchgear, and long cable circuits.

UHV's testing scope covers:

Transformer → Switchgear → Cable → Motor → Protection → Grounding

The field team verifies each stage before proceeding to the next energization stage.

Case Study 4 - Existing Substation Maintenance

An operating substation requires scheduled maintenance.

The testing program includes:

• Transformer Winding Resistance
• Tan Delta
• Circuit Breaker Timing
• Contact Resistance
• CT/PT Testing
• Relay Testing
• Battery Discharge

Ground Resistance

Historical data is used alongside current measurements to identify changes in equipment condition.

12. FAQ

13. Related Products

Transformer Testing

• Transformer Turns Ratio Tester
• Winding Resistance Tester
• Insulation Resistance Tester
• Tan Delta Tester
• Transformer Oil BDV Tester
• Transformer Comprehensive Tester

Cable Testing

• VLF Hipot Tester
• AC Hipot Tester
• AC Resonant Test System
• Cable Sheath Tester
• Cable Partial Discharge Tester
• Cable Fault Locator

GIS / Switchgear Testing

• AC Resonant Test System
• Partial Discharge Test System
• SF6 Gas Analyzer
• SF6 Dew Point Meter
• Contact Resistance Tester

Circuit Breaker Testing

• Circuit Breaker Analyzer
• Contact Resistance Tester
• Dynamic Resistance Tester

CT/PT Testing

• CT/PT Analyzer
• CT Analyzer
• PT Analyzer
• CT Excitation Tester

Protection Testing

• Relay Protection Test Set
• Three-Phase Relay Tester
• Secondary Injection Test System

Battery Testing

• Battery Discharge Tester
• Battery Capacity Tester
• Battery Internal Resistance Tester

Grounding Testing

• Ground Resistance Tester
• Ground Grid Tester
• Earth Resistance Tester
• Grounding Continuity Tester

14. Request a Quote

UHV Field Testing & Commissioning Solution

Field commissioning requires more than a collection of test instruments.

The equipment needs to match the project sequence, site environment, test object, electrical rating, and acceptance requirements.

UHV can configure a field testing package around:

• Transformer
• GIS / AIS
• Circuit Breaker
• Cable
• CT / PT
• Protection
• Motor / Generator
• Battery
• Grounding
• Grid Connection

Project Information to Send UHV

Project Type

→ Substation / Power Plant / Renewable Energy / Industrial / Railway / Data Center / Other

System Voltage

Installed Capacity

Transformer Rating

Cable Voltage

Cable Length

Cable Capacitance

GIS/AIS Type

Circuit Breaker Type

CT/PT Parameters

Protection Functions

Motor / Generator Ratings

Battery Voltage & Capacity

Grounding System

Required Test Items

Applicable Standards

Testing Location

Commissioning Schedule

UHV Field Testing Scope

Transformer Testing

Cable Testing

GIS Testing

Circuit Breaker Testing

CT/PT Testing

Relay Protection Testing

Insulation Testing

Partial Discharge Testing

AC Withstand Testing

VLF Testing

AC Resonant Testing

Battery Testing

Grounding Testing

Cable Fault Location

For a project-specific field commissioning package, UHV recommends sending the single-line diagram, equipment list, cable schedule, transformer data, GIS and breaker specifications, CT/PT information, protection configuration, grounding drawings, and required testing standards.

With these parameters, UHV can determine the appropriate test voltage, output capacity, test frequency, measurement range, portable configuration, and equipment combination for the actual field application.

Request a Field Testing / Commissioning Solution from UHV and let the test equipment configuration follow the electrical system-not the other way around.