You might wonder why it’s crucial to perform HiPot testing on a 25 MVA power transformer. In this instance, the transformer was hit by a lightning strike and has been producing gas since. Our client sought to determine if there was an imminent risk to the equipment.
To address this, Megavar’s technicians deployed our 300kV resonant HiPot unit for the task. We’re pleased to report that the transformer has passed the test and remains in service!
What is HiPot Testing?
“HiPot” (short for High Potential) testing, also known as high voltage testing or dielectric withstand testing, is a method used to verify the electrical insulation integrity of a device or component. For transformers, HiPot testing ensures that the insulation system can withstand high voltages without breaking down.
Why is HiPot Testing Important?
- Safety Assurance: Verifies that the transformer can safely operate at high voltages, preventing electrical shock or fire hazards.
- Risk Mitigation: Identifies potential insulation breakdowns or weaknesses that could lead to equipment failure or safety issues.
- Operational Reliability: Ensures the transformer remains reliable and efficient, minimizing the risk of unexpected outages or failures.
At Megavar, our commitment to thorough testing and safety helps ensure that your critical infrastructure operates smoothly and reliably.
Frequently Asked Questions
What is HiPot testing and how does it work?
HiPot (High Potential) testing, also known as dielectric withstand testing, applies a voltage higher than the equipment’s normal operating voltage to its insulation system. The test verifies that the insulation can withstand transient overvoltages (such as lightning strikes or switching surges) without breakdown. If the insulation holds without excessive leakage current, the equipment passes. Megavar performs HiPot testing using resonant test sets at voltages up to 500kV.
When should a power transformer undergo HiPot testing?
HiPot testing is recommended after any event that may have stressed the transformer insulation. This includes lightning strikes, through-faults, transportation, extended storage, significant oil leaks, or when dissolved gas analysis (DGA) indicates gas generation. It is also performed during factory acceptance testing (FAT) and before initial energisation of new or relocated transformers.
What equipment does Megavar use for transformer HiPot testing?
Megavar operates 300kV and 500kV AC frequency resonant HiPot test systems. These units use variable frequency resonant technology to achieve the required test voltages with significantly lower input power than conventional test sets. The resonant approach also provides inherent safety advantages, as the system cannot sustain a fault arc, protecting both the test equipment and the asset under test.
What is the difference between AC HiPot and DC HiPot testing?
AC HiPot testing applies an alternating voltage that stresses the insulation in a manner similar to normal service conditions. DC HiPot testing applies a direct voltage, which distributes stress differently through layered insulation systems. For oil-filled power transformers with cellulose insulation, AC testing is preferred because it more accurately represents real-world voltage distribution across the insulation. International standards including IEC 60076 and IEEE C57.12.00 specify AC withstand test voltages for power transformers.
Can HiPot testing damage a healthy transformer?
No. The test voltage for routine HiPot testing is set at or below the voltage the transformer was originally designed and factory-tested to withstand. If the insulation is in good condition, the test simply confirms that. The risk of damage only arises if the insulation has already degraded significantly, in which case the test is performing its intended function by identifying the weakness before it fails in service under less controlled conditions.
Can I hire Megavar’s HiPot test equipment?
Yes. Megavar’s 300kV and 500kV resonant HiPot test systems are available for hire as part of our specialist HV test equipment fleet. Equipment can be hired with or without a Megavar test technician, depending on your requirements. Contact rentals@megavar.com.au or call 1300 730 499 for availability and pricing.
