Testing of transformer is completed to find out their electrical, thermal and mechanical suitability for the system the place they are going to be utilized or used. Many of the checks carried out on power transformers are outlined in nationwide requirements created by IEEE, NEMA and ANSI, whose objective is to outline a uniform set of checks acknowledged by each the producer and the consumer.

Transformer Take a look at Particulars:

Subject Testing. Subject testing might be divided into three classes

1. Acceptance checks
2. Periodic checks
3. Checks after failure

Acceptance checks ought to be carried out instantly after the product arrives on the vacation spot. Just a few checks might be carried out that are acknowledged under IQ 테스트: 

• Turns ratio
• Insulation resistance(Winding and core)
• Power issue
• Resistance (winding)
• Polarity and section relation
• Oil checks (DGA, moisture, dielectrics, and many others.)
• Visible inspection

Periodic checks are achieved after the product is put in in its everlasting location. The principle objective of this take a look at is to watch the situation of the unit in order that any potential bother could also be noticed early earlier than a failure happens. A few of these are listed under: 

• Turns ratio
• Insulation resistance
• Power issue
• Resistance (winding)
• Oil checks (DGA, moisture, dielectrics, and many others.)
• Excitation present take a look at
• Visible inspection

An unscheduled outage and the potential of outright failure might be prevented by following a periodic take a look at schedule. 

Failure checks performed on electrical transformers are:

• Turns ratio
• Insulation  resistance
• Power issue
• Resistance
• Oil checks
• Excitation present take a look at
• Flamable fuel/ gas-in-oil evaluation
• Visible inspection (inner)

When a transformer fails, the time of failure checks will determine whether or not the unit might be repaired on the website or whether or not it must be returned to the producer, or a specialised middle for restore. By evaluating the outcomes of the checks with the established norms, a ‘historical past’ of the transformer might be compiled, and the explanations for failure might be identified.Here’s a fast overview of the above talked about checks: 

• • Transformer Turns Ratio Take a look at (Frequent to all classes)The Transformer Turns Ratio take a look at (TTR) is used to ensure that the Turns Ratio between the windings of the transformer is right. This ratio decides what the output voltage of the transformer will likely be with respect to the enter voltage. The ratio is calculated below no-load situations, with ratios calculated on the faucet positions for every winding and for the winding as a complete. A voltage is utilized to at least one winding and the voltmeters related to each low voltage and excessive voltage windings are learn concurrently. The transformer ratio is the ratio of the HV voltmeter and the LV voltmeter readings. When ratio checks are being made on three-phase transformers, the ratio is taken on one section at a time, and the measured ratio ought to be in contrast with the ratio calculated utilizing nameplate voltages. Any variation ought to be inside  .5%.
  • Transformer Insulation Resistance Take a look at (Frequent to all classes)The winding insulation resistance take a look at (often known as the Meggar take a look at) is a measure of high quality of insulation throughout the transformer. It will probably fluctuate attributable to moisture content material, cleanliness and the temperature of the insulation components. All measurements are corrected to twenty’C for comparability functions. It is strongly recommended that tank and core are at all times grounded when this take a look at is carried out. Every winding ought to be short-circuited on the bushing terminals. Resistances  are then measured between every winding and all different windings and floor (for two 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 Issue (Frequent to all classes)This take a look at is made to watch the dryness of transformer insulation. Power issue is outlined because the ratio of the power dissipated divided by the enter volt-ampere multiplied by 100. The measurement of power issue is made with a capacitance bridge and the connections are the identical as for the insulation resistance checks.
  • Transformer Resistance (Frequent to all classes)The resistance of a transformer winding might be measured after present has not handed via the transformer for a number of hours, permitting it to achieve the identical temperature as its environment. Winding resistance is calculated by measuring the voltage and present concurrently, with the present as near the rated present as attainable. Calculating the winding resistance might be useful because it allows you to calculate and compensate for I2R losses, a significant part of load losses as a complete.  Winding resistance measurements might be made to find out if any modifications have occurred within the present carrying path. The winding resistance measurements ought to be made with a Wheatstone bridge, Kelvin bridge or comparable bridge able to measuring fractional ohms precisely.  For Wye related values, measurements ought to be made between every pair of bushings, then summed and multiplied by three-halves to get the comparability worth.
  • Transformer Oil Take a look at (Frequent to all classes)A pattern of insulating oil from a transformer in service can reveal a lot details about what’s happening contained in the transformer. There are three primary enemies to insulating oil – oxidation, contamination and extreme temperature. The next checks might be achieved:
    • Acid quantity
    • Dielectric breakdown
    • Power issue
    • Moisture content material
    • Interfacial rigidity

After performing the checks the oil can labeled as reusable; reusable with minor reconditioning; or disposable. 

• • Transformer Polarity (Acceptance take a look at)The polarity of a transformer is both additive or subtractive. As a way to discover out the polarity of a transformer, a voltage is utilized between the first bushings.  If the resultant voltage between the secondary bushings is bigger than the utilized voltage that signifies that the transformer has additive polarity.  Whether it is decrease, the transformer has subtractive polarity. Polarity is just not essential for a single related distribution transformer, however it’s a important concern if transformers are to be paralleled or financial institution related. Three section transformers are additionally checked for polarity by the identical means.
  • Transformer Section Relation (Acceptance take a look at)A section relation take a look at is carried out for polyphase (as an example, three-phase) transformers to ensure that they’ve been related in such a approach that their section relationship is right.  A section relation take a look at calculates the angular displacement and relative section sequence of the transformer, and might be carried out along side ratio and polarity checks.  The voltages of the section of main and secondary might be recorded and comparisons made to get the section relation.
  • Visible Inspection (Periodic and Failure checks)This will reveal both current or potential issues that will not be picked up by diagnostic testing. For instance, deteriorating gaskets, low oil stage or chipped bushing skirts. An ordinary record of test factors ought to be established for every unit after which a document of every inspection maintained.
  • Gasoline/ Gasoline-in-Oil Take a look at (Failure take a look at):A examine of gases both dissolved within the oil or from the fuel above the oil can even present irregular situations throughout the transformers, equivalent to incipient faults. Three concerns are crucial:
    • The overall share of flamable fuel
    • The share of every fuel part
    • The speed of change in flamable fuel content material
    • If the share of flamable gases is above 5%, then quick motion is required

• • Excitation Present Take a look at (Periodic and Failure checks)The excitation present is the minimal quantity of present wanted to take care of the core in a state of magnetic excitation. It’s measured on the rated voltage, and often given as a share of the rated present.The take a look at is carried out with a single section supply with, ideally, a voltage rated at roughly 10% of the section voltage of the winding to which the supply is to be related, though decrease voltages can be utilized.

There are 2 strategies that can be utilized: the primary is to attach a single-phase supply to any obtainable winding with an ammeter within the circuit to watch the thrilling present.  Three such single-phase checks are vital for a three-phase transformer. The connection between the one section readings is essential; it ought to be as follows: 

• The readings taken on section A and C ought to be inside 5% of one another.
• The studying on section B ought to be between 65 and 90% of the readings on section A and C.

Readings that fall exterior of the relationships given above could also be indicators of a winding fault. Within the different methodology, the identical voltage stage and ammeter necessities apply besides the next connections ought to be made:

• Quick one winding on section C and apply voltage and browse the thrilling present on section A.
• Quick one winding on section A and apply voltage and browse the thrilling present on section C.
• Quick one winding on section B and apply voltage and browse the thrilling present on section A or section C.

Different Transformer Checks: 

Different checks which might be carried out are:

• Core Loss Take a look at Below no-load situations, a transformer will proceed to empty sources {of electrical} vitality. The chief supply of this drain is core loss, which happens within the magnetic core via a mixture of hysteresis and eddy present loss, amongst others.  Core-loss is calculated by making use of the rated voltage and frequency to a transformer below no-load situations.  The resultant present is then measured, from which the lack of vitality might be extrapolated.
• Load Loss Take a look at Load loss is a mixture of I2R losses, stray losses and eddy losses, all of which contribute to the lack of electrical vitality that’s seen as present transferred from one winding to a different. Load loss modifications with the magnitude of the load: that’s to say, increased hundreds see increased charges of loss.  The load loss is subsequently typically calculated for the rated load, whereas the transformer is below full-load situations. It may be measured by making use of a voltage to at least one winding whereas the opposite winding is short-circuited. The voltage is adjusted till the present flowing via the circuit is similar because the rated present. The power loss measured at the moment is the load loss.
• Impedance Take a look at Impedance is a measure of the resistance that results in the lack of electrical vitality in a transformer at full load, inflicting the ratio of the enter and output voltages to vary from the Turns Ratio. It may be measured concurrently load loss. Impedance is discovered by measuring the voltage required to cross the rated present via one winding of the transformer, whereas the opposite winding is short-circuited. This voltage known as the impedance voltage.
• Utilized Potential Take a look at The utilized potential take a look at is used to see how effectively the transformer’s insulation offers with voltages increased than the rated voltage, for given durations of time. The utilized potential take a look at checks the insulation between particular person windings; and between windings and floor by making use of voltages to every of those areas.
• Induced Potential Take a look at The induced potential take a look at is used to check the standard of the transformer’s insulation, as with the utilized potential take a look at above. It checks the insulation of the person windings of the transformer by making use of voltages between turns, between layers and between traces.
• High quality management impulse take a look at High quality management impulse checks are made on transformers in an effort to simulate lightning; to see how effectively they stand up to such excessive bursts of voltage.  The electrical impulses utilized right here can embody decreased  full-wave checks, chopped-wave checks and front-of-wave checks, to simulate a variety of maximum voltage conditions.
• Stress Leak Take a look at A transformer might be checked for stress leaks by pressurizing the tank after which leaving it alone for a number of hours. If the stress drops in the course of the interim, or if there are indicators of liquid leakage, than a leak is current.  In any other case, the transformer is leakage free.

Whereas studying about and overseeing the usual testing procedures of your transformer is usually a laborious activity, it positively helps higher your understanding of the transformer’s operation, minimizes hazard to life and property, reduces downtime, minimizes the prospect of sudden failure and thus permits optimum use of the transformer.