AC dielectric testing is essential for verifying that high voltage electrical equipment can withstand the electrical stresses it may encounter during operation. Whether testing transformers, switchgear, bushings, motors, or other electrical components, manufacturers and test facilities need a reliable way to verify that insulation can withstand the electrical stresses it encounters in service.
This is where AC dielectric testing comes in.
An AC dielectric test applies a controlled high voltage AC source to a test object to evaluate the integrity of its insulation. Depending on the application and applicable standards, the test may be used for type testing, quality assurance testing, or as part of a more comprehensive machinery insulation maintenance program.
The HAEFELY ACS AC Test Sets provide a flexible solution for AC High Voltage testing, with options to add additional diagnostic testing capabilities.
What Is AC Dielectric Testing?
AC dielectric testing evaluates whether an electrical insulation system can withstand a specified AC voltage for a defined period without breakdown
These tests may be performed on a variety of high voltage equipment, including:
☑️Transformers
☑️ Instrument transformers
☑️ Switchgear
☑️ Bushings
☑️ Motors and Generators
☑️ Cables
☑️ Other high voltage electrical components
The required test voltage, duration, and acceptance criteria depend on the type of equipment being tested and the applicable industry standards.
Why Use an AC High Voltage Test System?
A properly designed AC test system provides controlled high voltage output for dielectric testing while supporting accurate measurement, repeatable testing, and safe operation.
The HAEFELY ACS AC Test Sets are available in configurations ranging from wide range of ratings, allowing the system to be matched to different test objects and applications.
Key features include:
➡️ AC output ranging from 25 to 100 kV
➡️ Power output ranging from 20 to 100 kVA
➡️ HVC 300 AC control unit with HAEFELY CaMS control and measurement software
➡️ Optional fiber optic communication
➡️ Electronic flash detection
➡️ Optional PD-free configuration
➡️ Expandability for partial discharge testing
➡️ Expandability for tan delta/power factor testing
➡️ SIL 3 safety certification
Why Does Waveform Quality Matter?
During AC High Voltage testing, insulation is subjected to electrical stress based on the applied voltage waveform.
For this reason, waveform quality is an important consideration when performing dielectric withstand testing. A non-distorted waveform helps ensure the test object is subjected to the intended electrical stress and supports accurate, repeatable test results.
When selecting an AC High Voltage test system, voltage measurement accuracy and waveform performance should be considered alongside voltage and power ratings.
Can an AC Test System Also Perform Partial Discharge Testing?
Yes, depending on the system configuration.
A dielectric withstand test determines whether insulation can withstand a specified voltage. Partial discharge testing, however, can provide additional information about localized insulation defects that may result in long term failure.
Partial discharge can occur in areas such as insulation voids, interfaces, or other locations where electrical stress is concentrated.
The ACS AC Test Sets can be configured for partial discharge measurement, including a PD-free option for applications where minimizing background electrical noise is important.
For manufacturers and laboratories evaluating insulation quality, the ability to combine AC dielectric testing and partial discharge measurement can provide a more complete picture of insulation performance.
What About Tan Delta / Power Factor Testing?
Tan delta, also known as the dissipation factor or power factor testing, can provide additional information about the condition and quality of an insulation system.
While a dielectric withstand test answers whether the insulation can withstand a specified voltage, tan delta and power factor measurements evaluate dielectric losses of the whole insulation system.
These measurements are very useful when evaluating insulation condition and identifying changes associated with factors such as aging, contamination, or moisture content.
The ACS system can be expanded to support tan delta and power factor measurement, allowing additional insulation testing capabilities to be integrated into the overall test setup.
What Should You Consider When Choosing an AC Test System?
Selecting the right AC high voltage test system involves more than simply choosing a voltage rating.
Important considerations include:
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- The Type of Equipment Being Tested
Different test objects have different electrical characteristics and testing requirements. The system should be appropriately sized for the intended application.
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- Required Voltage and Power
The test system must provide sufficient voltage and power for the equipment being tested and the applicable test requirements. The vast majority of test objects are highly capacitive, so a test system must be capable of supplying sufficient current to charge the test object while maintaining the required test voltage
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- Current and Future Testing Requirements
If partial discharge, tan delta, or power factor testing may be required in the future, selecting an expandable system can help avoid the need to replace the entire test setup later.
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- Control and Measurement Capabilities
Modern control and measurement systems can improve test repeatability and simplify operation and documentation.
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- Safety Requirements
High voltage testing requires a properly designed safety system that includes appropriate interlocks, grounding, emergency stop functions, controlled access, and operating procedures.
A Flexible Solution for AC High Voltage Testing
High Voltage testing requirements can change as testing programs, equipment, and industry requirements evolve. Selecting a system that meets today’s requirements while providing options for future expansion can offer significant long-term value.
The HAEFELY ACS AC Test Sets provide configurable AC High Voltage testing solutions for a range of dielectric testing applications. With a wide range of ratings, integrated control and measurement capabilities, and options for partial discharge and tan delta/power factor testing, the ACS range can be adapted to a variety of laboratory and production testing requirements.
When selecting an AC test system, factors such as voltage, power, waveform quality, measurement capabilities, safety, and future expandability should all be considered.
Frequently Asked Questions
What is an AC dielectric test?
An AC dielectric test applies a specified alternating voltage to electrical equipment or an insulation system to verify its ability to withstand electrical stress without breakdown or unacceptable failure.
What is the difference between an AC hipot test and a dielectric withstand test?
There is no difference AC hipot is just the old terminology.
Why is partial discharge testing important?
Partial discharge testing can help identify localized insulation defects that may not cause immediate dielectric breakdown but could indicate potential insulation weaknesses.
Can one system perform AC withstand, partial discharge, and tan delta testing?
Depending on the configuration, a single system can support multiple insulation testing functions. The HAEFELY ACS AC Test Sets can be configured and expanded to support partial discharge and tan delta/power factor measurement.
What are the input power/mains requirements?
ACS system may be designed for a wide variety of input voltages; the most common voltages are 208/240 or 480V.
Is onsite commissioning and training available?
Most systems include a complete start-up and training package. So, the system will be ready to use from day one, and operators are made familiar with the safety features of the equipment.
How often does the ACS system need to be calibrated?
The initial recommended calibration interval is 24 months from factory calibration. After a record of performance is established, the calibration interval may be increased.