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 under IEEE 95-2002.

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High Voltage Test — stepped curve

IEEE 95-2002CFE LAPEM W4200-12ISO 9001:2015

Technical definition

What is the Hipot test

Hipot (High Voltage Test) is the final acceptance test for the dielectric insulation system. A stepped voltage is applied — typically 2 × Vnom + 1 kV in AC, or its DC equivalent — 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.

Reference standard: IEEE 95-2002 (insulation testing of electric machinery)
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 under IEEE 95-2002 and ISO 9001:2015. Full traceability by work-order number and signature of the responsible engineer.

1Signed protocol under IEEE 95-2002 with voltage and current curve
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

Typical case

Pre-commissioning validation after synchronous generator rewind

IEEE 95-2002

Applicable standard

PI 4.2

Polarization index

Passed

Release status

Stator rewind on an industrial synchronous generator. A stepped DC Hipot was performed as the final validation before shipment. The curve was run from 0 to 2.5 × Vnom in 5-minute steps per level. Insulation was accepted: stable leakage current, no breakdown, polarization index of 4.2 (excellent). Documented release and shipment to the client with the signed IEEE 95-2002 protocol and ISO 9001:2015 traceability records.

FAQ

Frequently asked questions — Hipot AC/DC testing

Preguntas que recibimos con frecuencia. ¿No encuentras la tuya? Escríbenos a ventas@temisa.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?

Under IEEE 95-2002, the typical acceptance voltage is 2 × Vnom + 1 kV (AC). For Hipot DC, 1.6 to 2 times the equivalent AC voltage is applied. For legacy or rehabilitated machines, a reduced curve is applied based on the initial insulation condition.

Can the Hipot test damage healthy insulation?

No, when applied correctly under IEEE 95-2002. The stepped curve allows stopping if leakage current 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 IEEE 95-2002 protocol is followed without variation.

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