Testing medium-voltage and high-voltage rotating machines

highvolt-lab-tall-375px__1_Design and manufacturing problems can cause premature equipment failure. To minimize that risk, Doble’s high-voltage laboratory offers a wide range of qualification and acceptance tests for medium-voltage and high-voltage rotating machines up to AC 3000 kV, DC 400 kV and Impulse 1200 kV.

Doble’s team has more than 100 years combined experience with testing and evaluating generator and motor insulation systems, including large rotating machine stator bars and coils. Serving satisfied customers for over 80 years, our laboratories can perform over 200 laboratory tests on both solid and liquid insulation.

In addition to laboratory testing, Doble specialists have extensive field testing experience in power factor, partial discharge, electromagnetic signature analysis, EL CID and AC/DC Hi-Pot testing as well as visual inspection, condition assessment and failure investigation of generators, motors, transformers, cables and other power apparatus.

Qualification & Quality Control of Manufactured Coils

  • Voltage endurance test as per IEEE-1043 & IEEE-1553
  • Dissipation factor and tip-up test
  • Partial discharge test
  • Turn-to-turn insulation test
  • AC Hi-Pot test for groundwall insulation integrity
  • Dissection & microscopic examination of coils
  • Customer technical specification preparation
  • Independent factory inspections, material verification & quality conformance

Voltage Endurance Tests

highvolt-lab-square-295px__1_The voltage endurance test is performed according to IEEE-1043 and IEEE-1553. An AC high voltage is applied to the coils for 400 hours. The heaters are set to 90°C – 120°C and thermocouples are placed in the heater plates to monitor temperature. Several diagnostic tests, such as polarization index, Hi-Pot, partial discharge, dissipation factor and tip-up, are carried out.

To pass the test, the coils should not fail in less than 400 hours (time length depending on voltage). Failing the voltage endurance test can indicate a manufacturing quality issue even if similar coils have previously passed the voltage endurance test.

Diagnostic tests

  • Visual inspection of coils to check for any defects, impressions or damages
  • Tap test to check for any delaminations
  • Surface partial discharge test (lights-out test)
  • Surface resistivity measurement
  • Insulation resistance and polarization index test as per IEEE 43-2000
  • Dissipation factor and tip-up test
  • Partial discharge test

Turn-to-Turn Insulation Tests

An impulse test can be performed per IEEE 522-2004 to evaluate turn-to-turn insulation in multi-turn coils.

AC Breakdown Tests

Doble can perform insulation breakdown tests on stator coils and bars. The failure site can be dissected.

Coil Dissections

Dissection locations are chosen by an experienced generator insulation specialist to discover the weakest insulation spots. If a coil fails voltage endurance testing, a dissection is required at the failure location. A Doble specialist will determine the cause of failure based on knowledge and experience of the generator insulation system. Microscopic examination on dissected samples can be conducted to check any manufacturing quality issues.

Doble Engineering Company

Doble Engineering Company