Transformer Diagnostics

Presented By: Sanjeet Kumar Registration No.-1308143 Branch:-Electrical & Electronics Engineering

IntroductionTransformer is a device on which cost effective supply of electricity mostly depends.The life measurement of the transformer is made considering the following aspects:

a). Improvements over traditional time-based maintenance, e. g. condition based or reliability centered maintenance. b). Maintaining a transformer in service. c). Continuity of supply. d). Priority of in-field repair and on line processing. e). Minimizing the remedy actions and making the most effective remedial actions. f). Comprehensive life assessment and/or extension program.

Condition monitoring of power transformer

Transformer health it is essential to employ some form of monitoring to provide an idea of when to initiate the above process. In case of transformer monitoring, the following questions are to be answered.

a) Is it normal? b) Is there a fault? c) Is the fault serious? d) Is it fit for service? e) What is its reliability? The first two questions are answered effectively by i). Dissolved Gas Analyzer (DGA). ii). Power factor/ Tan delta testing

Transformer maintenance process

Causes of Failure

Transformer is the heart of any power system. Hence preventive maintenance is always cost effective and time saving. Any failure to the transformer can extremely affect the whole functioning of the organization.

Many failures occur due to aging phenomenon: •a). Shortened life due to accelerated deterioration of components particularly bushing and OLTCS.

•b). Overheating of the HV winding coils due to poor cooling excessive circulating current. •c). Change in the condition due to ingress of water, particle contamination, aging of oil, loosening of contacts and clamping forces, vibration, unusual stresses etc.

f). Three sources of excessive water may be developed in transformer insulation (i) Residual moisture in thick structural components not removed during dry out. (ii). Ingress from the atmosphere.(iii). Aging decomposition of cellulose and oil. g). Cellulose, fibers, iron, aluminum, copper and other particles resulting from the manufacturing process are normally present in the transformer oil. These form sludge particles slowly during normal and overload operating temperature. h). the present of bubbles may cause critical partial discharge (PD) to occur even at rated voltage. Bubble evaluation is a problem of a “hot transformer”

Dissolved Gas Analysis

Dissolved gas analysis is the most important test in determining the condition of a transformer. Insulating oils under abnormal electrical or thermal stresses break.

•The amount of gas detected in the sample is used to detect problems with the insulation structure in the transformer. Data from DGA can provide:•Advanced warning of developing faults.•Monitoring the rate of fault development.•Confirm the presence of faults for scheduling Repairs.•Monitoring of condition during overload 

Resistivity or Specific resistance

Resistivity is the most sensitive property of oil, it varies greatly with temperature. It is desirable to have resistivity of oil as high as possible. Resistivity of oil reduces considerably due to presence of moisture, acidity, solid contaminants etc.

Oil Analysis Techniques

The most common used insulating liquid is mineral oil. This is due to low cost and its ready availability. Insulating oil used in air breathing transformer has two important properties i.e. good insulator and used as coolant.

Frequency Response Analysis (FRA)

• Frequency Response Analysis (FRA) testing by swept frequency method makes a qualitative assessment of the mechanical condition of the transformer core and winding. The loss of mechanical integrity might occur due to:

• Large electromechanical forces due to fault Currents.• Winding shrinkage causing release of clamping pressure.• Transformer transportation and relocation.

Dielectric Dissipation Factor (DDF) or TanDelta

When an ac voltage is applied to insulation, the leakage current flows, and this leakage current have two components, resistive and capacitive.

A resistive component (IR) is in phase with voltage (V) and capacitive component (IC) is 900 out of phase with the voltage.

Presented By: Sanjeet Kumar

sanjeetkumar2101@gmail.co

+91-8968143473