Power Transformers Testing

Testing of transformer is done to decide their electrical, warm and mechanical reasonableness for the framework where they will be applied or utilized. test bank The greater part of the tests performed on force transformers are characterized in public principles made by IEEE, NEMA and ANSI, whose design is to characterize a uniform arrangement of tests perceived by both the producer and the client.

Transformer Test Details:

Field Testing. Field testing can be isolated into three classifications

Acknowledgment tests

Occasional tests

Tests after disappointment

Acknowledgment tests ought to be performed following the item shows up at the objective. A couple of tests can be completed which are expressed underneath:

Turns proportion

Protection resistance(Winding and center)

Force factor

Opposition (winding)

Extremity and stage connection

Oil tests (DGA, dampness, dielectrics, and so forth)

Visual investigation

Occasional tests are done after the item is introduced in its lasting area. The fundamental reason for this test is to screen the state of the unit with the goal that any potential difficulty might be spotted ahead of schedule before a disappointment happens. A portion of these are recorded beneath:

Turns proportion

Protection opposition

Force factor

Opposition (winding)

Oil tests (DGA, dampness, dielectrics, and so forth)

Excitation current test

Visual review

An unscheduled blackout and the capability of out and out disappointment can be forestalled by following an occasional test plan.

Disappointment tests led on electric transformers are:

Turns proportion

Protection obstruction

Force factor


Oil tests

Excitation current test

Flammable gas/gas-in-oil examination

Visual assessment (interior)

At the point when a transformer falls flat, the hour of disappointment tests will choose whether the unit can be fixed at the site or whether it should be gotten back to the maker, or a particular place for fix. By contrasting the consequences of the tests and the set up standards, a ‘past filled with’ the transformer can be assembled, and the explanations behind disappointment can be diagnosed.Here is a snappy review of the previously mentioned tests:

Transformer Turns Ratio Test (Common to all categories)The Transformer Turns Ratio test (TTR) is utilized to ensure that the Turns Ratio between the windings of the transformer is right. This proportion chooses what the yield voltage of the transformer will be as for the info voltage. The proportion is determined under no-heap conditions, with proportions determined at the tap positions for each twisting and for the twisting in general. A voltage is applied to one winding and the voltmeters associated with both low voltage and high voltage windings are perused all the while. The transformer proportion is the proportion of the HV voltmeter and the LV voltmeter readings. At the point when proportion tests are being made on three-stage transformers, the proportion is taken on each stage in turn, and the deliberate proportion ought to be contrasted and the proportion determined utilizing nameplate voltages. Any variety ought to be inside .5%.

Transformer Insulation Resistance Test (Common to all categories)The winding protection obstruction test (otherwise called the Meggar test) is a proportion of nature of protection inside the transformer. It can differ because of dampness substance, neatness and the temperature of the protection parts. All estimations are rectified to 20’C for examination purposes. It is suggested that tank and center are constantly grounded when this test is performed. Each winding ought to be shortcircuited at the bushing terminals. Protections are then estimated between each winding and any remaining windings and ground (for 2 winding transformer – H-LG, L-HG and HL-G and three winding transformer H-LTG, L-HTG, T-HLG, HL-TG, HT-LG, LT-HG and HLT-G ).

vPower Factor (Common to all categories)This test is made to screen the dryness of transformer protection. Force factor is characterized as the proportion of the force dispersed isolated by the info volt-ampere increased by 100. The estimation of intensity factor is made with a capacitance connect and the associations are equivalent to for the protection obstruction tests.

Transformer Resistance (Common to all categories)The obstruction of a transformer winding can be estimated after current has not gone through the transformer for a few hours, permitting it to arrive at similar temperature as its environmental factors. Winding opposition is determined by estimating the voltage and current all the while, with the current as near the appraised current as could reasonably be expected. Ascertaining the winding obstruction can be useful as it allows you to figure and make up for I2R misfortunes, a significant segment of burden misfortunes in general. Winding opposition estimations can be made to decide whether any progressions have happened in the current conveying way. The winding opposition estimations ought to be made with a Wheatstone connect, Kelvin connect or comparable scaffold fit for estimating partial ohms precisely. For Wye associated values, estimations ought to be made between each pair of bushings, at that point added and increased by three-parts to get the correlation esteem.

Transformer Oil Test (Common to all categories)A test of protecting oil from a transformer in assistance can uncover a lot of data about the thing is occurring inside the transformer. There are three fundamental foes to protecting oil – oxidation, tainting and over the top temperature. The accompanying tests should be possible:

Corrosive number

Dielectric breakdown

Force factor

Dampness content

Interfacial pressure

In the wake of playing out the tests the oil can named reusable; reusable with minor reconditioning; or dispensable.

Transformer Polarity (Acceptance test)The extremity of a transformer is either added substance or subtractive. To discover the extremity of a transformer, a voltage is applied between the essential bushings. On the off chance that the resultant voltage between the optional bushings is more noteworthy than the applied voltage that implies that the transformer has added substance extremity. In the event that it is lower, the transformer has subtractive extremity. Extremity isn’t significant for a solitary associated conveyance transformer, yet it is a fundamental concern if transformers are to be resembled or bank associated. Three stage transformers are additionally checked for extremity by similar methods.

Transformer Phase Relation (Acceptance test)A eliminate connection test is conveyed for polyphase (for example, three-stage) transformers to ensure that they have been associated so that their stage relationship is right. A stage connection test computes the precise dislodging and relative stage grouping of the transformer, and can be done related to proportion and extremity tests. The voltages of the period of essential and auxiliary can be recorded and examinations made to get the stage connection.

Visual Inspection (Periodic and Failure tests)This may uncover either present or potential issues that may not be gotten by symptomatic testing. For instance, decaying gaskets, low oil level or chipped bushing skirts. A standard rundown of check focuses ought to be set up for every unit and afterward a record of every review kept up.

Gas/Gas-in-Oil Test (Failure test):A investigation of gases either broke up in the oil or from the gas over the oil can likewise show strange conditions inside the transformers, for example, nascent issues. Three contemplations are significant:

The complete level of ignitable gas

The level of each gas segment

The pace of progress in flammable gas content

On the off chance that the level of ignitable gases is above 5%, at that point prompt activity is required