Step by Step Guide: How to Check and Test a Power Transformer

Testing of power transformers is continuous monitoring of faults in all units of such equipment and their timely removal after detection. All this is achieved with one objective continuation of the continuous activity of a significant node in the power supply system of many energy consumers.

A variety of tests are used to determine the reliability, economic performance, safety and technical soundness of the power generation unit. In order to get acquainted with a variety of electrical installation exercises, their thorough consideration of particular examples helps. For example, a comprehensive explanation of the instructions on how to check a 250 kVa power transformer in this article is the most effective option for acquaintances of this type.

Why test of power transformers is important?

A power transformer is an important transmission unit as part of a powerful and complex power system that supplies power to a large number of industrial and domestic energy consumers. Such a unit must be reliable and serviceable for a long time to ensure that there is no deficiency in the valuable work of industrial consumers.

That’s why oil and dry power converters are continuously experiencing:

• Numerous checks and performance tests are carried out at manufacturing plants-to ensure that a complex technological system for transferring voltage from one class to another is understood after output.

• When installing a supply system as a whole, checking on the basis of a special form of acceptance tests-in order to understand that, at the time of transport and subsequent installation of the power equipment, no faults or installation failures have occurred or have not been made that would not be capable of delivering a proper, secure power supply.

• Periodically during the operation of electrical systems and assemblies, as a result of which there might also be certain faults or deficiencies of complex transmission equipment-preventing pre-emergency or emergency modes.

Such monitoring, the monitoring of the output of the power transmission equipment, ensures the optimum quality of the power systems as a whole, which means that the optimum quantity and quality of electricity in industry and in the domestic sector is ensured, which has a beneficial impact on their production.

Method of acceptance tests for power transformers

Acceptance tests of power transformers on new power systems or at the time of scheduled preventive maintenance of already working power plants include up to 20 types of different checks and control tests, depending on the type of transformer, on the difference in the class of voltage in its cooling systems and on the other complexity of other power supply systems.

Power transformers are subject to monitoring and testing in order to detect potential faults during the commissioning of the equipment or to assess the degree of reliability of the electrical units operating in compliance with a strict frequency schedule and after a certain amount of testing:

• Mandatory preliminary determination of the conditions for the connection of the transformer without drying shall be made.
• The DC resistance of the windings of the transformer is measured.
• Measurements of resistance, experiments with increased voltage of industrial frequency of winding insulation, insulation of structural elements are carried out.
• Transformer oil is being tested for this.
• Tank testing for tightness.

Methods of Measurement

The following methods of measuring nodes and mechanisms are carried out at the time of testing of power transformers, driven by the above-mentioned documentation:

• Measurement of the insulation resistance of the winding transformers-this process is carried out by means of a megohmmeter with a rated operating voltage of 2500 volts. All transformer windings must be grounded before and between measurements.

• The measurement of the tangent angle of dielectric loss is provided by the AC bridge. If the transformers under test are oil-filled during this time, the calculation shall be carried out at a supply voltage reduced from a nominal rated voltage equal to 2/3 of that voltage.

• Measurement of the capability of the windings is referred to as electrical tests of the transformer, which provide data on the moisture content of the windings of the transformer. This method of calculation is possible when monitoring the coefficient of absorption of the transformer.

Conditions of Use

The method of testing and testing such a complex technological instrument requires the selection of certain climatic conditions for the conduct of preparatory, organizational and technological preliminary work. They shall have the conditions:

• Any calculation methods for transformer voltage systems shall be carried out only in dry weather conditions.
• The power unit itself must be pre-built before the tests, all positions of the planned measurements must be free of dust and have free access to the staff tested.
• All the requisite test instruments must contain the actual dates of verification, and must be absolutely in good condition.
• Tests to test the resistance of windings to direct current are carried out by laboratory means-an ohmmeter with corresponding ratings. In the process, the value of constant frequency current must be set at 20% of the value of the winding current. The wire resistance in the measurement circuit does not exceed 0.5 per cent of the voltmeter resistance value.

Author Bio: Kiran Daware is the junior electrical engineer at Nicore India Pvt. Ltd. He works with the development team of silicon steel magnetic core. He is also a technical writer at Nicore India where he owns blog at electricaleasy