Thermal & Voltage Endurance Testing

How do Original Equipment Manufacturers (OEMs) and operating companies know the insulation system being proposed by a particular vendor will meet the operational requirements for longevity and endurance required under current operating regimes?

Kinectrics offers a dedicated laboratory for the assessment of HV stator winding systems (bars & coils) associated with high voltage machines to assess insulation systems to accepted international standards. This advanced facility is used extensively by OEMs, consultants and utilities to independently assess and establish the condition of:

• New Insulation – Assessment of insulation systems to IEEE standards to ensure that the system being proposed, or being applied to bars or coils, meets acceptable standards.
• Aged Insulation - Full assessment of the insulation condition of HV stator insulation in hydro and turbo generator stators to provide a prognosis for insulation condition, and the potential need for replacement of stator windings after a given number of years in operation.

  Kinectrics’ assessment techniques include:

Voltage Endurance Tests to IEEE 1043

This is an accelerated aging test, wherein the bars or coils are subjected to a voltage higher than that in normal service, typically 30 kV over a period of 400 hours, in order to determine the adequacy of the insulation systems from the design, materials and processing perspectives.

These tests are preceded by and then followed up with electrical diagnostic tests such as Loss Tangent, Partial Discharge, TVA probe and mechanical tests such as Tap Testing, visual inspection and dimensional analysis.

Thermal Cycling to IEEE 1310

Winding insulation failures are often attributed to Partial Discharge activity occurring in the main wall insulation, as a result of the de-bonding of insulation due to operational load cycling of the machine.

This test is carried out by passing a high current through the bars to apply temperatures up to 150 C and cycling this over a long period of time, typically weeks, in order to establish the effects of thermal aging and load cycling on the insulation system on motors or generators.

Turn Insulation (Surge) Testing to IEEE 522

This test consists of applying high voltage fast rise-time (100 ns) pulses to the stator coil. Typically for 13.8 kV stator windings the turn insulation is rated at 50 to 100 V between turns. The test establishes the capability of the interturn insulation and if it is adequate to meet the machine design and operating requirements.

Dissection of coils and bars

Following all tests and in order to establish the true insulation condition, the insulation is dissected and the layers removed one at a time to establish bonding between insulation layers, and if there are any defects in the system.

Particular attention is paid to any areas that were subject to distress during the testing stage, thereby aiding in establishing insulation quality, voltage stress and potential areas for failure and further investigation / design improvements.

For more information

rotating.machines@kinectrics.com