Electrical Assessment

ROTATING EQUIPMENT TEST & MEASUREMENT

Reducing the risk of failure in rotating machines
Rotating machine such as motor and generator are highly important components in power generation and Industrial application, therefore machine reability and availableity are in high demand. premature failur may lead to significant economical losses, due to unexpected outages and posible damage to asset itself to plan maintenance effectifelyit is essential to have accurate condition information about when commponents need repairing or replacing.

A variety of electrical test can be performed over the complete life cycle of your machine to incrase their reliability prevent premature failure and to extend reliable service life. off-line diagnostic test provide you with a snapshoo t of curent condition and detected posible defect temporary and permanently on-line monitoring enable continous condition assesment under normal operating condition.

ROTATING EQUIPMENT TEST & MEASUREMENT

Detecting faults to prevent failure
Electrical static tests are part of a series of activities performed during overhaul. Electrical static test aims to determine the condition of the generator that can not be captured by visual check. The series of tests is refers to the international standards and also the standard of manufacturer, in this case the Alstom generator.

ROTATING EQUIPMENT TEST & MEASUREMENT

TRANSFORMER TEST & MEASUREMENT

Survey done by a CIGRE working group on failures in large power transformer found that about 41 percent failures were due to on-load-tap changers/OLTC and about 19 percent were due to windings. The failure origin were 53 percent mechanical and 31 percent dielectric. On transformer without on-load-tap changers/OLTC, 27 percent of failure were due to the windings, 6 percent were due to magnetic circuit, 33 percent were due to terminals, 17 percent were due to the tank and dielectric fluid, 12 percent were due to other accessories, and 5 percent were due to the tap changer.

Looking into the failures type and percentage the transformer assessment were concentration in the causes of aging transformer with the following breakdown of causes:

Dielectric Causes, electrical stress particularly in areas with high electrical field strengths
· Dielectric losses produce of heat
· Decomposition of solid and liquid insulation by partial discharge
· Generation of gases
· Generation of acids and sludge
Electromagnetic Causes, high current (ea. due to short circuits nearby the transformer) produce high
mechanical forces
· Deformation of the winding
· Damage to paper insulation (cracks), particularly on aged parts
· Initiation of partial discharge
· Initiation of partial breakdowns
Chemical Causes, organic acids are produced as a result of ageing
· In particular, they affect the paper insulation -> accelerated ageing
· Metals like copper, iron, aluminum and zinc are behaving like catalyst. -> accelerated ageing
Thermal Causes, High currents (ea. due to short circuits nearby the transformer) produce high mechanical forces
· Hysteresis losses in the magnetic core
· Shorted laminates
· Ohmic losses in the windings due the voltage drop
· Dielectric losses in the insulation
· Load changes will cause warming up and cooling down negative influences on the lifetime of the insulation.
· The ageing of the insulation is accelerated if the temperature increase.

Detecting faults to prevent failure with oil analysis
Gas detection periodically in the oil-filled transformers in service can be used as the first indication of a problem in the transformer that may eventually lead to failure if not corrected. Electrical discharges or thermal stresses in the oil or solid insulation, for example, paper pressboard etc, of an oil-filled transformer cause degradation of these materials with the formation of gases of various types.

The Failure of transformer can be a devasting and costly experiance. However, it is an unfortunate fact that despite even the most rigorous preventive maintenance program, failures can and will occur. The foregoing classification of failures is admittedly general in nature, but usually sufficient for our claims process. However, in order to prepare an accurate failure scenario, and develop proper recommendations to prevent a recurrence, a more in-depth analysis of the failure is necessary.

Detecting faults to prevent failure with electrical static test
Electrical static tests are part of a series of activities performed during overhaul. Electrical static test aims to determine the condition of transformer that can not be captured by visual check. The series of tests is refers to the international standards and also the standard of manufacturer