Magnetic balance test of transformer

Some transformer tests are also carried out at the consumer site before commissioning and also periodically in regular and emergency basis throughout its service life. Type of Transformer Testing Tests done at factory • Type tests • Routine tests • Special tests Tests done at site • Pre-commissioning tests • Periodic/condition monitoring tests • Emergency tests To prove that the Type test of transformer confirms main and basic design criteria of a production lot. Routine Tests of Transformer Routine tests of transformer is mainly for confirming the operational performance of the individual unit in a production lot. Routine tests are carried out on every unit manufactured. Special Tests of Transformer Special tests of transformer is done as per customer requirement to obtain information useful to the user during operation or maintenance of the transformer. Pre Commissioning Test of Transformer In addition to these, the transformer also goes through some other tests, performed on it, before actual commissioning of the transformer at the site. The transformer testing performed before commissioning the transformer at the site is called the pre-commissioning test of transformer. These tests are done to assess the condition of transformer after installation and compare the test results of all the low Type tests of transformer include: • • • • Measurement of impedance voltage/short circuit impedance (principal tap) and load loss (Short circuit test) • Measurement of no-load loss ...

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magnetic core balance test is used to find out the flux distribution. It can conduct either in HV side or LV side. In HV side, applying voltage between 2 phases and measuring the voltage across other phase.(eg.applying b/w U&V, and voltage b/w V&W , W&U measuring.) In LV side, applying voltage b/w any phase....and measuring voltage across other phases. Result: sum of measured voltage will be equal to applied voltage. What is the purpose of 'Open Circuit Test' in Electrical Power Engineering? An open-circuit test is done on a transformer to isolate and measure those losses known as 'iron losses' that are due to eddy currents in the magnetic iron core of the transformer. Because the currents in the windings are very low the 'copper losses' are negligible. However the iron losses depend only on the applied voltage. Why is iron loss under the short circuit test considered as negligible? Because a short-circuit test is done at very low voltage to check the transformer windings on their maximum current. The low voltage ensures that the magnetic flux in the transformer's iron core is very low so that the eddy-current losses, usually known as iron losses, are negligible. Why is an open circuit test performed on the low voltage side of a single phase transformer? That's the wrong way round, it's the short-circuit test that is done with low voltage because that tests the resistive losses in the copper windings. The open-circuit test is done at high voltage to measure the iron losses...

Whenever a power or distribution transformer is isolated from the power system, it is probable that residual magnetism remains in the core due to the phase shift. However, residual magnetism also occurs when performing winding resistance tests. Since manufacturers use these measurements in their routine testing and these tests are typically performed for on-site condition assessment, transformers can be regularly influenced by the effect of residual magnetism. Residual magnetism leads to high inrush currents, which put a great and unnecessary load on the transformer. A large number of diagnostic measurements are also affected by residual magnetism. Therefore, it is difficult to get a reliable condition assessment of transformers. It is therefore recommended to demagnetize the transformer before re-energizing it or performing diagnostic measurements. Within the last few years, the first testing devices have been launched that allow practical demagnetization of transformers on-site. Influence of residual magnetism on inrush current When a transformer is re-energized, an inrush current occurs that can greatly exceed the nominal current. If the transformer core still contains residual magnetism, the first peak current can even reach the level of the short-circuit current. These high currents can cause undesirable effects, such as mechanical deformation of the windings, incorrect triggering of protection equipment, increased stress for the installation, and voltage dips in the ...

Healthiness of the transformer Once oil filling is completed, various pre‐commissioning checks and tests are performed to ensure the healthiness of the transformer (or reactor) prior to its energization. Various electrical tests must be performed and their significance and short description are given below. This test is performed to check the insulation between core and ground. Operational checks on: • Cooler bank (pumps and fans), • Breathers (silica gel or drycol), • Temperature gauges (temperature of transformer oil – OTI and the windings temperature – WTI), • Gas actuated relays (Buchholz, PRD, SPR etc.) and • Simulation test of protection system. Test reveals the condition of insulation (i.e. degree of dryness of paper insulation), presence of any foreign contaminants in oil and also any gross defect inside the transformer (e.g. Failure to remove the temporary transportation bracket on the live portion of tap‐changer part). Insulation resistance tests are performed to determine the insulation resistance from individual windings to earth or between individual windings. Knowledge of the insulation resistance is of value when evaluating the condition of the transformer insulation. Insulation resistance is commonly measured in megohms, (MΩ). It should be stated, that variations in insulation resistance can be caused by numerous factors including: design, temperature, dryness, and cleanliness of parts, especially of bushings. When insulation resistance falls below specifie...