Test · IEEE 95-2002
Hipot AC/DC Testing for Generator Insulation
Dielectric validation of stator and rotor insulation on synchronous generators and turbogenerators. The Hipot test (High Voltage Test) applies a stepped controlled voltage to verify the insulation withstands operating voltage with margin. It is the final acceptance test before commissioning or after rewind; the DC stepped test follows IEEE Std 95-2002 and the AC level is set in the agreed protocol.
High Voltage Test — stepped curve
IEEE 95-2002ISO 9001:2015Technical definition
What is the Hipot test
Hipot (High Voltage Test) is the final acceptance test for the dielectric insulation system. A controlled voltage is applied — in AC at the level and duration set in the agreed protocol, or in DC in steps or a ramp as described in IEEE Std 95-2002 — between the winding and ground. If the insulation withstands the voltage without breakdown, it is validated for service. The AC mode is more stringent (it includes capacitive effects); the DC mode is more controllable and less damaging for legacy machines. The stepped curve protects against false rejections by allowing the test to be halted if leakage current rises out of bounds.
- DC reference: IEEE Std 95-2002 (recommended practice, status inactive-reserved) for high direct-voltage insulation testing of AC machines rated 2300 V and above
- AC mode: sinusoidal voltage at 50/60 Hz — simulates real operating conditions
- DC mode: direct voltage, better for legacy or rebuilt machines
- Stepped curve: voltage rises in steps to detect progressive breakdown
- Leakage current measurement throughout the test
- Post-test analysis: polarization index (PI), dissipation factor (DF)
Operational opportunity
When the Hipot test is recommended
Hipot is the final acceptance test of the insulation system. It is applied at the following milestones:
- After stator or rotor rewind — pre-delivery validation
- Before commissioning a new or reinstalled generator
- After major maintenance with stator opening
- After magnetic core restacking
- Before re-energizing after a severe electrical event
- Periodically (every 4 to 6 years) as part of major maintenance
Client value
What the Hipot test detects
Weak or degraded insulation (high leakage current or breakdown)
Large voids that survive nominal voltage but fail at test voltage
Surface contamination (moisture, conductive dust, oil)
Post-rewind workmanship defects (loose wedges, weak connections)
General insulation aging from thermal degradation
Binary validation: insulation PASS / FAIL for service release
Deliverables
What we deliver at the end of the test
Each test is delivered with a signed documentation package and ISO 9001:2015 traceability. Full traceability by work-order number and signature of the responsible engineer.
- 1Signed test protocol with voltage and leakage-current curve (DC steps per IEEE Std 95-2002; AC level and duration as agreed in the protocol)
- 2Stepped diagram: voltage vs time, leakage current vs voltage
- 3Complementary test results: PI (polarization index), DF (dissipation factor)
- 4Binary diagnosis: insulation PASS or FAIL for release
- 5When applicable: identification of defect zone (phase, connection, ground)
- 6ISO 9001:2015 traceability with work-order number, responsible engineer and equipment used
Illustrative example
Not a published project record.
Pre-commissioning validation after synchronous generator rewind
IEEE 95-2002
Reference guide
Release with protocol
Option if criterion is met
Investigate the cause
Option if not met
After a stator rewind on an industrial synchronous generator, a stepped DC Hipot can be used as the final validation before shipment. Voltage is raised in steps up to the level agreed in the protocol, and the leakage current is checked for stability and absence of breakdown, together with the polarization index. If the result meets the criterion, the usual recommendation is to release with a signed protocol; if not, to investigate the cause before shipment.
FAQ
Frequently asked questions — Hipot AC/DC testing
Questions we often receive. Can't find yours? Email us at ventas@temisapowergen.mx.
When should I choose Hipot AC versus Hipot DC?
Hipot AC is more stringent because it simulates real service conditions, including the capacitive effects of the insulation. It is preferred for new generators or fully rewound machines. Hipot DC is less damaging and more controllable — preferred for legacy machines where AC could damage aged insulation without justifying the risk.
What voltage is applied during a Hipot test?
There is no single universal value. For the AC test, voltage and duration are set in the agreed written protocol, based on the manufacturer's data or the acceptance standard that applies to the machine (new, rewound or in service). For the DC test, IEEE Std 95-2002 describes the stepped and ramped procedures; the maximum DC level is also fixed in the protocol. For legacy or rehabilitated machines, a reduced level is agreed based on the initial insulation condition.
Can the Hipot test damage healthy insulation?
Not when it is applied correctly at the agreed level. In the DC stepped or ramped test (IEEE Std 95-2002), leakage current is monitored at each step and the test can be stopped if it rises abnormally. The test is destructive only when the insulation already has critical defects — those defects manifest as breakdown during the test, before commercial operation.
What happens if the generator does not pass the Hipot test?
We document the exact point of breakdown (voltage, phase, time) and propose an action plan: partial rewind, restacking, or major intervention depending on the detected failure mode. We never release a generator that has not passed Hipot — that is responsible delivery practice.
How long does a complete Hipot test take?
Between 4 and 8 hours onsite for setup, execution of the stepped curve, complementary tests (PI, DF) and disconnection. The signed protocol is delivered within 5 to 7 business days.
Can Hipot be performed onsite or only in a workshop?
Both. For new generators or post-commissioning, the test is performed onsite with calibrated portable equipment. For post-rewind, the test is performed in our own workshop before shipment. In both cases the same agreed written protocol is followed: DC steps per IEEE Std 95-2002, and AC level and duration as defined in the protocol.
Related testing
Combine Hipot acceptance with the full electrical testing suite
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ISO 9001:2015 · IEEE / IEC