POWER TRANSFORMER MAINTENANCE

POWER TRANSFORMER MAINTENANCE

Power transformers are stationary electrical machines used for transforming power from one circuit to another without changing frequency. This is a very basic definition of transformer. Since, there is no rotating or moving part, so a transformer is a static device. Transformer operates on an A/C supply. A transformer works on the principle of mutual induction.

Power transformers are electrical devices used to step up or step down the voltage level of its supply source. The process of stepping up or down depends upon the number of turns of primary and secondary winding. Transformers have primary winding and the secondary winding. The primary winding is the coil that draws power from the source. The secondary winding is the coil that delivers the energy at the transformed or changed voltage to the load.

Generally, a power transformer is used in stepping up the voltage of the supply to decrease the transmission losses, and then stepping down is done for the distribution purpose at the load centers. Power transformers are larger size devices that transfer the energy to substations or public electricity supply.

MAINTENANCE OF POWER TRANSFORMER

GZ Industrial Supplies, in adherence to IS 10028-3: Code of practice for selection, installation and maintenance of transformers advocates proper transformer maintenance. The efficiency of transformers is dependent on proper installation, loading, and maintenance, as well as on proper design and manufacture. Neglecting certain fundamental requirements may lead to serious troubles, if not to the loss of the equipment. The types of transformer maintenance can be described as follows:

Unscheduled Maintenance: 

This type of maintenance is based on reactionary mode of operation. That is to say, maintain the equipment when it breaks down, otherwise leave it alone.

Ordinary Maintenance: 

This type of maintenance takes irregular visual inspection and making repairs, adjustments, and replacements as necessary.

Routine Basis (Preventative Maintenance): This maintenance consists of performing preventive maintenance, predictive maintenance, and corrective maintenance. The preventive maintenance involves schedule maintenance and testing on a regular basis. Predictive maintenance involves additional monitoring and testing, whereas corrective maintenance involves repairing and restoring transformer integrity to its original condition when exacerbate conditions are discovered.

This maintenance can be summarized by the following:

  • Maintain transformer protective coating
  • Test and maintain transformer insulation systems
  • Inspect and maintain transformer auxiliary devices
  • Control transformer heat
  • Maintain transformer bushing insulation

There are different preventative maintenance actions we perform on a power transformer, they can be on a daily, monthly, quarterly, half-yearly, or yearly interval.

Daily Interval Transformer Maintenance: 

Testing and Checking

  • Always maintain to keep oil filled up to the desired level in Magnetic Oil Gauge (MOG)
  • Change the silica gel if its color changes to pink.
  • Seal any leakage detected.

Monthly Interval Transformer Maintenance

  • The oil level in the oil cap must be checked on a monthly interval.
  • Breathing holes in silica gel breather should also be checked and properly cleaned for proper breathing action.
  • If your electrical transformer has oil filling bushing, make sure that the oil is filled up to the correct level.

Maintenance of Transformer on Half Yearly Interval

The transformer oil must be checked on a half yearly interval, for dielectric strength, water content, acidity, sludge content, flash point, and resistivity for transformer oil.

Yearly Transformer Maintenance

  • Oil pumps, air fans, along with other items that are used to cool down a transformer and control circuit must be inspected annually.
  • Ensure to clean all the bushings of your electrical transformer with only soft cotton.
  • Oil conditions should be carefully examined on a yearly basis.
  • Ensure to clean out the inside of all of the marshalling boxes yearly.
  • Check proper functioning of the space and illumination heaters.
  • Terminal connections of control and relay wiring should be tightened at least once a year.
  • Control Panel has to be cleaned with a proper cleaning agent.
  • Ensure to measure the resistive value of the earth connection
  • Mechanical inspection of Buchholz relays should be carried out on a yearly basis.

FAULTS AND ITS CAUSES IN POWER TRANSFORMERS

The causes of faults and failures in power transformers can be classified into: electrical, mechanical, and thermal. The failures can be further classified into external or internal components.

Winding Failure: There are different causes of breakdown of winding which are listed below.

Dielectric faults: This happens in the winding because of the turn-to-turn insulation breakdown. These are the insulation between the turns of the winding. Insulation breakdown occurs because of the high current and voltage which are high above the rated values. The breakdown of the insulation upshots in the spark of the winding turns and causes a short circuit.

Windings are made of copper: Because of the copper line resistance, thermal losses do occur. This makes hot areas in the winding due to poor or lack of maintenance. This with time causes wear and tear and reduction of the physical strength up to the point of breaking of the winding.

Mechanical faults: This includes deformation, loosening or supplanting of the windings. The outcome is the deformation in the efficiency of the transformer and the tearing of the turn-to-turn ratio. The major causes of this fault include poor maintenance, improper repair, corrosion, manufacturing deficiencies, and vibrations in the transformer.

Deterioration of oil: This occurs due to the effect of lengthened overloading of the transformer. High oil temperature produces the formation of sludge, water, and acids. Water entering the oil as a result of the breathing action reduces its dielectric strength.

Bushing: Bushing are insulating devices that allow a high voltage electrical conductor to pass through an earth conductor. In the transformer, it provides a current path through the tank wall. In the transformer paper, insulators are used which are surrounded by oil that provides further insulation. Bushings may fail due to incomplete discharge. This is sometimes due to the slow and progressive degradation of the insulation over many years of service. Seal breaking of bushes happens due to entrance of water, aging or excessive dielectric losses. Because of this fault, core failure of the transformer may happen.

BENEFITS OF POWER TRANSFORMER MAINTENANCE

  • Increased safety
  • Problems are detected before they are a hazard
  • Increased equipment efficiency,
  • Reduced expenses
  • Repair work can be properly scheduled.
  • MAINTENANCE PROCESS

    This encompasses maintenance activities such as: overhauls, breakdowns prevention and removing, changeover management and production of tools and special equipment. The structure also includes maintenance resources: tools and equipment, spare parts, procedures and documentation, maintenance works, etc.

    The Maintenance Process can be summarized in four stages: Planning, Organization, Execution and Recording with a feedback stage providing for Optimization.

    RECORDING OF DISTURBANCES

    Power transformer maintenance must include historical test data. A properly documented and readily accessible testing data is required to assure an effective analysis during the power transformer maintenance.

    • Date and time of the occurrence.
    • Data for installed over-voltage protection.
    • Network data, were connections or other relevant things made when the disturbance took place.
    • Weather data
    • Is the gas relay filled with gas?
    • Is oil sooty?
    • Thermometer readings.
    • Were coolers or tanks damaged?
    • Are there visible marks of arcing on the bushings, cover or conservator?

    WHY TRANSFORMER MAINTENANCE IS IMPORTANT

    The main purpose of maintenance of the transformer is to ensure the internal and external parts of the transformer and accessories are in good condition, efficient and able to operate safely. Another essential purpose is to maintain a historical record of the condition of the transformer.

    For further information on procurement, installation and maintenance of power transformers, kindly contact us at GZ Industrial Supplies.

    23rd Dec 2020 Ernest Orhuebor

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