Generator Testing

Doble provides engineering solutions for electrical apparatus condition assessment of HV substation and generator plants. Electrical measurement condition monitoring and chemical analytical methods provide data that is analyzed by apparatus experts. Doble provides the answer of ‘use – or remove from service' for your apparatus.

Generator Tests Performed:

Electromagnetic Interference (EMI) Diagnosticssm

Doble Engineering, world leader in diagnostic instruments and knowledge services for the electric power industry, is proud to offer an innovative approach to test generators, motors, exciters, isophase bus, switchgear, transformers, and power cables – Electromagnetic Interference (EMI) Diagnosticssm. This newest addition to Doble’s consulting services is a non-invasive on-line surveillance technique that can detect and identify defects in a motor or generator and associated electrical systems while each power system remains in service.  For more information on EMI Testing, email

EMI analysis techniques can provide critical information useful for developing targeted maintenance strategies for power systems, and can also identify equipment that does not need attention or repair. This is a passive, totally non-invasive measurement technique, with no applied signal. Data is collected without affecting operations, and the process is inherently safe. EMI Diagnosticssm can provide valuable maintenance recommendations on the very first test. The testing equipment is very sensitive and measurement accuracy is traceable to NIST standards. EMI presents an opportunity for companies to dramatically improve their condition assessment and maintenance programs. EMI Diagnosticssm can save money and time by identifying specific areas that require maintenance, repair, or replacement allowing strategic, proactive, planned decisions to be made well in advance of an upcoming scheduled outage. 
To find out more information about EMI Diagnosticssm  please see the above link to the brochure.
On-line Stator Winding Partial discharge
Doble can visit on-site to down load data, or make spot measurements using our instrumentation. An assessment of data will be provided on an annual basis.

On-line Rotor winding integrity diagnostic using Air gap search coils
An inter-turn fault is detected in current carrying air gap search coils. In this case we can monitor the condition and analyze results with the generators on load.

On-line Generator condition monitor
Many generators have a detector to identify particulate products of overheating. Doble will visit on a 3-monthly schedule to check functionality.

Minor or major outage test for DC Insulation resistance (IR) and polarization index(PI)
The IR test is useful as a check that the stator will not to be at risk from AC testing at the lower gas pressure following degassing. At the end of the outage it is a simple indicator of adequate dryness and absence of foreign bodies.

Minor or major outage test for AC Power factor and capacitance
After satisfactorily completing the DC test a main diagnostic set of tests can be performed. The next step of testing is performing AC tests at high voltage and involving the measurement of power factor (or loss tangent), capacitance and partial discharge. These tests provide a measure of contamination, moisture de-bonding and void growth within the insulation and detect contamination on the end-winding.

Minor or major outage test for AC Partial discharges
The PD characteristic can be used to identify the type of defect, and so adds an additional diagnostic tool to the power factor tip up. If end covers are removed and end-winding discharge is indicated, these areas can be scanned when the winding is energized using ultra-Sonics and a daylight camera to locate the sites.

Minor or major outage test for Rotor winding integrity a diagnostic using RSO
Rotor winding insulation inter-turn and earth faults are detected using the recurrent surge oscillograph (RSO) method. The test is very sensitive and will give an indication of the early stages of an inter-turn fault.

Minor or major outage test for AVR testing
AVRs are inspected off load plus a test sequence involving three- phase injection, with DC sequence and operating load tests during recommissioning of the unit.

Minor or major outage test for Instrumentation
Thermocouples, RTDs, and Insulated bearings are checked with a low voltage DC test for continuity and resistance to earth.

Major outage test for ELCID and Ring Flux test
The major additional test in a major outage checking for core damage causing overheating.

Visual Inspection
A visual inspection is one of the most valuable processes and should only be performed by an experienced engineer. The inspection is done by performing a minor outage confined to the endwinding areas. Removing the rotor and exposing the slot wedges and core teeth will allow for a more extensive visual inspection. The wedge tightness can also be checked.

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