Introduction to transformer turns ratio testing testguy. Tjc 4 transformer type code 6000v3100 v31003 v rated voltage ratio an terminal marking for measuring secondary winding dadn terminal marking for residual opendelta winding 0. Z l p p vi using transformer voltage and current relations in terms of turn ratio yields. Medium voltage products current and voltage instrument. Jun 26, 2016 transformer turns ratio test connections. The primary winding refers to the powered inductor, a circuit element that induces a. Testing of three phase power transformer ijireeice. If not available, input and output voltages can be measured. Performing a transformer turns ratio test with the vanguard atrt. The turns ratio test is an ac low voltage test which determines the ratio of the high voltage winding to all other windings at noload. There are two types of polarity one is additive, and another is subtractive. Vector group test of power transformer electrical4u.
As the primary current changes the secondary current will vary accordingly. The performance of a transformer largely depends upon perfection of specific turns or voltage ratio of transformer. Transformer ratio can change due to several factors, including. Increase the voltage slowly to the test voltage and let stand for one minute.
The recommended ratio for the test voltage steps is 1 to 5. All secondary winding terminals, core if there is a special earth terminal, frame, case if any should be earthed during this test. In this video we walk you through the simple steps for performing a transformer turns ratio test using the vanguard instruments atrt03 s2 threephase turns ratio tester. Measuring transformer ratio from one external terminal to another can. In power transformers the transformer turns ratio test is made through voltage injection, phase by phase and tap by tap, measuring the corresponding voltage ratio for the related windings, which is compared with the expected ratio of the nameplate. Testing of power transformers 9 a 6 appendix 92 a 6. The voltage detected on the low voltage winding is measured and the voltage ratio between high and low windings is determined. How to calculate transformer turns ratio sciencing. If no evidence of distress or insulation failure is observed by the end of the total time of voltage application during the dielectric withstand voltage test, the test specimen is. This tap voltage ratio test, however, should not be chosen as a substitute. Potential transformer pt definition the potential transformer may be defined as an instrument transformer used for the transformation of voltage from a higher value to the lower value. The noload voltage ratio between two windings of a transformer is called turn ratio.
Polarity test of transformer its circuit diagram circuit. What is the difference between current ratio and voltage. The test set outputs an excitation test voltage to the transformers primary windings and measures the voltage at the corresponding secondary winding. Transformer turns ratio test sets come in a variety of styles and test connections, however all turns ratio testers have at least two high leads and two low leads. Instrument transformer theory and testing steve hudson, pe. In this channel you find the topics related to technical field like. At each step, test voltage should be applied for the same length of time, usually 60 seconds. Transformers regulate the voltage in circuits, but in some cases these can go bad and cause a circuit to not. The voltage and current at the load are also defined as the secondary voltage and secondary current of the transformer.
Turn ratio test of transformer voltage ratio test of. What is a voltage transformer and a current transformer. The ratio determines the ct operating characteristics and is used as reference for. Turns ratio test voltage ratio test are done in transformer to find out open circuited turns, short circuited turns in transformer winding.
Voltage and turn ratio test of transformer electrical4u. The vector group of transformer is an essential property for successful parallel operation of transformers. Rated transformation ratios multiple secondary cores. Using this principle, the turns ratio is measured with the. Z l s s vi the apparent impedance of the on the primary side of the transformer is defined as. Performing a transformer turns ratio test with the. A transformer turns ratio is the division of the number of turns in the primary winding by the number of turns in the secondary winding by the equation t r n p n s. Ct ratios are expressed as a ratio of the rated primary current to the rated secondary current. Potential transformers pts or voltage transformers vts pts or vts are the most common device used. It employed in electrical energy power system for stepping down the voltage of the system to some protected value which is often provided to low rating meter. Power transformer turns ratio test is an ac low voltage test which determines the ratio of the high voltage winding to all other windings at.
Dec 08, 2017 hi guys, this channel is all about technical topics, thats why the name is etech bhoj. When testing a transformer for turns ratio, the connections are determined by matching parallel vectors. The transformer winding voltage ratio is directly proportional to the winding turns ratio. For all practical purposes, when the transformer is on open circuit, its voltage and turns ratios may be considered equal. Test voltages used to determine highvoltage power transformer ratios are usually 1 of the windings rated voltage or less to reduce testing hazards. The ratio test is conducted to prove that the ratio of the ct is as specified, and to verify the ratio is correct at different taps of a multi tap ct. Above rated primary and secondary voltage is standard type, and besides, can be manufacture the another voltage ratio products. Equipment required following equipment is necessary to perform testings. Transformer routine test measurement of voltage ratio.
Dc dielectric withstand test voltage shall not exceed 100 percent of the ac rms test voltage specified in ansi c57. Voltage transformer which is also called as a potential transformer. The transformer turns ratio tester ttr is device used to measure the turns ratio between the windings example shown below voltage is applied on the h marked leads and measured of the x marked lead by the test set ratio measurements are conducted on all tap positions and calculated by dividing the induced voltage reading into the applied voltage value. The ct ratio is the most important piece of information regarding the ct and must be recorded from the nameplate or the design criteria. Lvoc output volts measured with lowvoltage input measure range voltage range frequency range. C electrical power from one voltage to another voltage keeping the frequency same by electromagnetic induction discover the worlds research 16. On bushings, the voltage is applied to the main conductor while measuring the. The family of curves below describe the excitation characteristics for the 6005 multi ratio bushing current transformer shown on the previous sheet. Mar 10, 2020 transformer ratio test the performance of a transformer largely depends upon perfection of specific turns or voltage ratio of transformer.
First, the tap changer of transformer is kept in the lowest position and lv terminals are kept open. Hi guys, this channel is all about technical topics, thats why the name is etech bhoj. Instrument transformer basic technical information and. Basics, maintenance, and diagnostics vii contents continued page 4. Lvoc output volts measured with low voltage input measure range voltage range frequency range. The turns ratio is equivalent to the voltage ratio of potential transformers and can be expressed as follows. This is a simple test to perform, and voltage ratios will be directly proportional to the ct turns ratio between taps. The test set outputs an excitation test voltage to the transformers. Transformer routine test measurement of voltage ratio and. Confirming the noload voltage ratio given in the customer order specifications, determining the conditions of both the windings and the connections and examining the problems if any. Sep 23, 2016 in this video we walk you through the simple steps for performing a transformer turns ratio test using the vanguard instruments atrt03 s2 threephase turns ratio tester. The application of increased voltage creates electrical stresses on internal insulation cracks. Transformer ratio test the performance of a transformer largely depends upon perfection of specific turns or voltage ratio of transformer.
Trl ratio of turns calculated from inductance measure range voltage range frequency range. If no evidence of distress or insulation failure is observed by the. Transformers are subject to several stresses and changes in their operational life, and so utilities and service companies schedule different transformer testing programs to assess their condition throughout the life of the transformer. Transformers are used in a wide array of electrical or electronic applications, providing functions that range from isolation and stepping up or stepping down voltage and current to noise rejection, signal measurement, regulation and a host of functions particular to specific applications.
Actually the no load voltage ratio of transformer is equal to the turn ratio. In this video we walk you through the simple steps for performing a transformer turns ratio test using the vanguard instruments atrt03 s2. A transformer turns ratio test set such as the threephase automatic ttr can directly measure the ratio of most types of transformers. C electrical power from one voltage to another voltage keeping the frequency same by electromagnetic induction discover. The typical excitation current test data pattern for a. It can be designed to step up or step down voltages and works on the magnetic induction principle. Voltage ratio is proportionally equal to turns ratio. If the two transformers are connected in parallel, then the polarity should be known for the proper connection of the transformer. The pt ratio is the most important piece of information and must be recorded. A potential transformer is a conventional transformer having primary and secondary windings. The circuit diagram of the capacitor potential transformer is shown in the figure below. The voltage should be applied only in the high voltage winding in order to avoid unsafe voltage.
So transformer ration test is an essential type test of transformer. The behavior of a 3phase transformer bank is analyzed in the same way as for a singlephase unit assume that both the primary and secondary windings are connected in wye configuration consider only one transformer the primary voltage is the linetoneutral voltage, vh1, n the secondary voltage is the linetoneutral voltage. Performing a transformer turns ratio test with the vanguard. How to perform a power transformer turns ratio test eep.
Turnsratio test results should not deviate more than onehalf percent from either the adjacent coils or the calculated ratio. Transformer turns ratio transformer turns ratio is the ratio of the number of turns in the high voltage winding to that in the low voltage winding. The presence of true threephase test voltage allows trt63 to test any type of transformer, even those with irregular vector groups, including phaseshifting transformers. True threephase transformer turns ratio tester trt63. Polarity test of transformer polarity means the direction of the induced voltages in the primary and the secondary winding of the transformer. The voltage detected on the lowvoltage winding is measured and the voltage ratio between high and low windings is determined. Ratio test of transformer and check of phase displacement. Capacitor potential transformer is a combination of capacitor potential divider and a magnetic potential transformer of relatively small ratio. The windings are shorted and the test voltage is applied to one winding while the current through the insulation is measured on the opposite winding or the tank. Connecting trt63 to a phaseshifting transformer current transformer trt63 can also be used for verifying turns ratio and polarity of current transformers cts. Their primary voltages being equal, voltage ratio of transformer under test is equal to voltage ratio of ratio meter. Transformer voltage ratio and turns ratio test youtube. Ac dielectric withstand test voltage shall not exceed 65 percent of factory test voltage for oneminute duration. The secondary windings often have 2 taps with a nominal voltage of 11567v, 12069v, or 120208v.
The terms current ratio and voltage ratio are usually used when we speak of instrument transformers. The voltage ratio is displayed and compared with the expected target ratio. This style of pt is the most accurate style in use. The turns ratio test is performed on all taps of every winding. A vt shall withstand a powerfrequency test voltage applied for 1 minute between all primary terminals connected together and earth. Transformers are an electrical component that transmit electrical energy between at least two circuits. This ratio should also equal the voltage of the primary winding divided by the voltage of the secondary winding, as given by v p v s.
A transformer has no moving parts and is a completely. Transformers objectives after studying this unit, the student will be able to state the purpose of a transformer. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another. This transformer step down the voltage to a safe limit value which can be easily measured by the ordinary low voltage instrument like a voltmeter, wattmeter and watthour meters, etc. The test equipment used is ordinarily a turns ratio tester designed for the purpose. Testing procedures for hv voltage transformers testing procedures for hv voltage transformers photo credit. The voltage ratio of a transformer is the ratio of the rms terminal voltage of a higher voltage winding to the rms terminal voltage of a lower voltage winding under specified conditions of load. Conventional wound type transformer is very expensive because of the requirement of the insulations. In the case of an electronic ttr test set, a voltage usually 80 v ac is applied to the tested transformer hv winding. Step voltage test method in this test, the operator applies two or more test voltages in steps.
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