An instrument transformer, looking at the high voltage side with dot convention and h1 marking. Back to the basics current transformer ct testing as test equipment becomes more sophisticated with better features and accuracy, we risk turning our field personnel into test set operators instead of skilled field service technicians. In this article im only explain on how to test the linear transformer. Testing of three phase power transformer ijireeice.
To perform a polarity test, the primary and secondary windings are connected in series with each other, and a. During commissioning and operation it is essential that your power transformer is in good condition. An ideal transformer is a lossless entity categorized by a complex voltage ratioa,i. Singlephase transformers have polarity, and knowing their polarity is important when they are connected to form a threephase transformer bank. And polarity tests on current transformers using the voltage. Current transformer saturation, ratio and polarity test set description the megger mct1600 test set is a lightweight, robust, portable unit used to automatically or manually perform saturation, ratio, polarity, demagnetizing tests and insulation tests on current transformers.
Transformer theory quiz questions free online quiz test transformer theory and practice. Current transformers cts are instrument transformers that are used to supply a reduced value of current to me ters, protective relays, and other instruments. The test leads are connected as detailed in the section above. Voltage transformer polarity testing below is the test set up for testing a voltage transformer or potential transformer polarity testing. This article is about magnetically coupled transformer winding polarities. The turns ratio test, also known as a ttr transformer turns ratio is, like most tests, easier to perform now than it used to be. The way the connections are made affects angular displacement, phase rotation, and direction of rotation of connected motors. A test set operator connects the leads, pushes the buttons, and records the results.
The positive and negative terminals of the primary winding are a1, and a2, whereas the positive and negative terminals of the secondary winding are a1, and a2. After completing the sensitivity test by reversing the cts, all 3 phase ct connections to be normalized and again ref stability of the ct circuits to be confirmed before concluding the test. When the applied voltage reaches to the rated value of the lv winding, readings from all the three instrument. Otherwise, with incorrect polarity, it is not possible to connect them in parallel. Nov 17, 2019 in subtractive polarity, if v c v a v b, it is a stepdown transformer and if v c v b v a, it is a stepup transformer. What is polarity and why its important for transformers. Drytype transformer by trasfor company acquired by abb with power or distribution transformers, polarity is important only if the need arises to parallel transformers to gain additional capacity or to hook up three singlephase transformers to make a threephase bank. All transformers are subjected to the following routine tests. If the two transformers are connected in parallel, then the polarity should be known for the proper connection of the transformer. Insulation tests short ckt test power rating other tests 4.
This study focuses on the temperature of transformer winding, voltage ratio across hvlv, asymmetrical flux distribution in the core, insulation resistance of paper. Transformer polarity test addictive, subtractive and. The insulation tests on the complete transformer, however, constitute a check on the correct applicatlorr and installation of these components. The maximum temperature rise in a large transformer is determined by the full load test. Polarity test of transformer testing of transformer part. Diagnostic testing and monitoring of power transformers omicron. Transformer is the most important unit in an electrical distribution network. The winding terminals of a transformer possess polarities. Transformer polarity refers to the relative direction of the. What is backtoback test sumpners test on transformer.
When testing transformer windings with a very low impedance generally the low voltage side, it can be extremely difficult, if not impossible to achieve the iec. The low voltage side of the instrument transformer, with dot and x1 marking. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same. Current transformer saturation, ratio and polarity test. Testingall designs are tested at state of the art test labs, ul certified, and part of the test program. Insulation resistance test and polarization index test. We use additive polarity for smallscale distribution transformers and subtractive polarity for largescale transformers. Transformer theory quiz questions electrician practice tests. Transformer stability test procedure a media to get all.
Both insulation resistance test ir value test and polarization index test pi value test are conducted on hv machine to determine service condition of the insulation. Heres a summary of the current transformer testing paper. Similar scenario is for the secondary winding also. The naming convention popularly known as vector group of transformer was established by the international electrotechnical commission iec through iec 600761. To test polarity using dc voltage, a lantern battery and a voltmeter with an analog. Pdf easy method for testing transformer differential relays. Transformer polarity test it is unusual for a line crew to need to conduct a polarity test, since polarity is confirmed on nameplates. The following tests are routinely conducted in the field on the transformer. Polarity test of transformer circuit each terminal of the primary and secondary windings in a transformer are positive and negative as shown in the below circuit. This test is called, backtoback test, regenerative test or sumpners test. The primary and secondary of a transformer are not connected to. If you want to test for polarity, connect the transformer as shown in figure 14. A typical transformer differential protection scheme is applied. Why do you do polarity test of transformers answers.
Polarity testing of transformers is vital before connecting them in parallel. Free online quiz test transformer theory and practice. Verifying the polarity of a transformer can be accomplished with a simple voltage test using the following steps. Impulse generator is used to produce the specified voltage impulse wave of 1. Before attempting to connect test equipment to a transformer, one must make certain that it is fully isolated and grounded. Next, connect a volt meter between the h2 and x2 terminal. Testing of current transformers, voltage transformers or auxiliary transformers internal to the power transformer are not included in this swp.
Current transformer saturation, ratio and polarity test set. Magnetization and primary injection test of current transformer for protective relaying jacob tsado 8 current transformers. Magnetization and primary injection test of current. Polarity test of transformer its circuit diagram circuit. The rated voltage is applied to the primary and its two terminals are marked as a 1 and a 2, respectively, as. The connection of all the windings in a threephase transformer is indicated by a vector group symbol. Transformer stability test, ct in neutral electric power.
Field testing of a power transformer before putting into service 50mva. The test problem considered in the present study concerns the evaluation of the magnetizing current of the idealized singlephase shelltype transformer described in 4. The transformer turns ratio test is used to make sure that the ratio between the. The preference is that all large power transformers 1 mva be tested with ttr test set. After the stability test it is advised not to touch or disturb the ct circuits of both the sides to ensure proper operation of the differential scheme. Polarity test on a transformer 1 aim to determine polarities of transformer windings 2 theory a transformer is used to transform voltage and pass on electrical energy from primary to secondary circuit. Back to the basics current transformer testing ct as test equipment becomes more sophisticated with better features and accuracy, we risk turning our field personnel into test set operators instead of skilled field service technicians. The basics of current transformers nk technologies. A polarity test is normally performed from the highvoltage side of the transformer. This symbol indicates the winding connections and their relative phase displacement by means of a numerical index e. Constructional features of three phase transformers three phase. Testing transformer is very easy if you follow the procedure explained in this article.
Routine tests are carried out on every unit manufactured. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext. This was done in order to create a notation for threephase transformer winding configuration. Power transformer factory test using ieee standards. Now at any instant, one of its terminal is positive w. The h1 left hand primary bushing and the left hand secondary bushing are temporarily jumpered together and a test voltage is applied to the transformer primary. Universal testing method for power transformer differential protection. The high voltage winding of the transformer under test and the high voltage terminals of the ratio meter are connected to a low voltage single phase source.
For testing the diffrential schemewe apply a reduced voltage of 480v on the transformer primary. There are two types of polarity one is additive, and another is subtractive. The transformer test system is able to perform induced ac voltage tests, measurements of noload losses and noload currents, measurements of short circuit. Tests insulation resistance between windings and winding to earth. Polarity means the direction of the induced voltages in the primary and the secondary winding of the transformer. Feb 08, 2015 a routine test of transformer is mainly for confirming operational performance of individual unit in a production lot. Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions. Knowledge of polarity of transformer windings is essential when singlephase transformers are connected in parallel or threephase configurations.
Perform a polarity test on each transformer to verify the polarity marks or h1x1 relationship as applicable. The tap position of the transformer during test is determined according to test conditions. The polarity test can determine the relative polarity of the primary and secondary of a transformer at any instant. We describe the two polarity test methods available using the most basic equipment. Following is an approximate sequence for transformer testing. These relative polarities of primaries and secondaries. Polarity test of a singlephase transformer electrical. Square d brand ex low voltage distribution transformers. Various influences can impact the expected lifetime. The percent x and percent r values are desirable for calculation. Before proceding with transformer measurements the test engineer will become familiar with the safety rules of section 2. Using the cpc 100, electrical tests on various assets. In hv machines and winding are likely to be affected by moisture and contamination.
Polarity test of transformer electrical technology and. Polarity is very important for the operation of transformers and protection equipment. Polarity test of transformer pdf rise of the transformer is required, then test method is the most dependable one. First, jumper the h1 terminal to the x1 terminal of the transformer. The full load test on a small transformer is very convenient, but for large transformer, it is very difficult. Testing current transformers burden test only if we cannot get to the primary side of the ct we can. Note down the transformer ratings as well as the turn ration if accessible. You can easily test for transformer polarity by using a reduced voltage source to excite the primary winding. Polarity test of transformer transformer electrical. Transformer polarity is the relative direction of the induced voltages between the high voltage terminals and the low voltage terminals. If a voltage causes a current to flow throw the transformer windings, then. Powerfactor or dissipationfactor tipup exceeding 1.
Electrical machines for mechatronics laboratory 3 4 dc test introduction the internal resistance of each winding in a transformer is measured using a small dc current to avoid thermal and inductive effects. The resultant voltage is measured between the right hand. The objectives of this experiment are to find the approximate per phase equivalent circuit parameters of a 3. The best isolation is at the terminals bushings of the transformer and not at the end of a length of bus or cable. Apply a reduced voltage across h1 and h2, and record the voltage measured on the meter. A transformer is said to have additive polarity if, when adjacent high and lowvoltage terminals are connected and a voltmeter placed across the other high and lowvoltage terminals, the voltmeter reads the sum additive of the high and lowvoltage windings. Thus, it can be quite tricky to test a numerical transformer differential relay by secondary injection in order to verify that the relay is set properly to. Polarity test of transformer and lighting circuit elprocus. It is carried out with the rated voltage ur and the rated frequency fr. What is the procedure to polarity test a 3 phase transformer. A typical excitation current test data pattern for a threelegged core is two similar current. The clock method is used to produce the numerical index of. Transformer polarity copyright 2002 kilowatt classroom, llc.
There are four typical types of current transformers. If we would like to do transformer stability test on ynd11 transformer with one ct conected in neutral of the transformer wye hv side, and inject 400v on lv side of transformer and make 3ph short circuit to ground on hv side, is it neccesary to disconect neutral of the transformer during stability test. Figure 5 shows the result of the curve fitting for core 1, considering the y axis to be the current and x axis to be the voltage, the following expression give the standard. Therefore, for actual values, obtain nameplate impedance from owner or manufacturer. The only ttr available at one time was a singlephase unit that was cranked by hand to produce an output voltage of 8v. Generally there are two types of transformer in the market i. The primary winding can consist merely of the primary current conductor passing once through an aperture in the current transformer core window or bartype, or it may consist of two or more turns wound on the core together with the secondary winding wound type.
If available, take down the ratings of the transformer and the turn ratio. The measurement voltage is applied as close to ur as possible. The polarity test diagram of transformer circuit is shown above. Oct 03, 2016 lightening impulse test all the dielectric tests check the insulation level of the job. In this article, you will learn different types of transformer testing methods, test setup, and their acceptance criteria. The turns ratio test is used as both an acceptance test and a maintenance test, while the polarity test is primarily an acceptance test. Back to the basics current testing valence electrical. The mct provides a microprocessor controlled variable voltage output and. Open circuit test or no load test on a transformer is performed to determine no load loss core loss and no load current i0.
Transformers have been used at powerplants since the inception of. Polarity of transformer windings your electrical guide. The transformer turns ratio test is used to determine the number of turns in one winding of a transformer in relation to the number of turns in the other windings of the same phase of the transformer. C h g, cl g and c tg include capacitances of associated bushings.
Power transformer testing power transformer factory test using ieee standards waldemar ziomek cg power systems canada ieee training, houston, texas, oct. If the value equals the sum of the high and low windings, the transformer is said to have additive polarity. What is the advantage of noload test in a transformer. An electrical power transformer has to go through a number of transformer testing procedures for confirming its specifications and performances. Polarity test of transformer polarity means the direction of the induced voltages in the primary and the secondary winding of the transformer. All transformers are subjected to various tests at the manufacturer. Current transformer white paper the basics of current transformers ratio the ct ratio is the ratio of primary current input to secondary current output at full load. Tests the continuity of the winding healthy transformer must have continuity in all the phases but transformer with shorted windings can also have. Instrument transformer theory and testing steve hudson, pe.
Procedure of polarity test of transformer connect the circuit as shown above with a voltmeter v a across primary winding and another voltmeter v b across the secondary winding. Shorted turntoturn insulation, short circuited core laminations, loosening of the core clamping, or. By this way,the next impulse voltage waveform is applied. The rated voltage is applied to the primary and its two terminals are marked as a 1 and a 2, respectively, as shown in figures 1. The primary and secondary of a transformer are not connected to each other i. Polarity refers to the instantaneous direction of the primary current with respect to the secondary current and is determined by the way the transformer leads are brought out of the case. Vector group verification system for power transformers. A clear understanding of polarity is useful in understanding and analyzing of transformer connections and operation as well as.
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