Basics of high voltage test techniques abstract high voltage hv testing utilizes the phenomena in electrical insulations under the in. Cts for metering purposes must have a high degree of accuracy to ensure accurate billing while those used for protection must react quickly and correctly in the event of a fault. Transformers regulate the voltage in circuits, but in some cases these can go bad and cause a circuit to not. Testing power transformers highvoltage transformers are some of the most important and expensive pieces of equipment required for operating a power system.
Both symbols are found in the transformer literature. For primary side, apply voltage depending on rating of voltage rating of vt. The strength of primary insulation, minimum value of shortcircuit voltage and increasing transformer voltage ratio to level when value of secondary voltage high. The dielectric voltage withstand test is commonly known as the hipot test. T the history of electrical voltage trans formers can certainly be traced back as far as the. Potential transformers pts or voltage transformers vts pts or vts are the most common device used. Testing of power transformers seems like a similar experience. If no evidence of distress or insulation failure is observed by the. Low voltage winding to ground threephase transformer the following 5 tests and corresponding wiring diagrams will completely test a threephase transformer. Equipment required following equipment is necessary to perform testings. Select the megger range corresponding to the ratings of the equipment under test. High voltage transformers are some of the most important and expensive pieces of equipment required for operating a power system. Pdf design and testing of high voltage high frequency.
This type of supply ranges from 5 kv to about 30 kv. Basics, maintenance, and diagnostics xi contents continued page 9. In automotive engineering, high voltage is defined as voltage in range 30 to vac or 60 to 1500 vdc. A varying current in the first or primary winding creates a varying magnetic flux in the transformers core and thus a varying magnetic field through the secondary winding. Dc dielectric withstand test voltage shall not exceed 100 percent of the ac rms test voltage specified in ansi c57. Scribd is the worlds largest social reading and publishing site. Ensure that all equipment to be tested is properly grounded and treat all high voltage power equipment as energized until proven otherwise by using the proper lockouttagout procedures. These devices use standard transformer theory with 23 windings one primary with one or two secondary windings with a magnetic connection via an iron core. The transformer core is connected to the same potential as the tank body.
The amount of voltage induced in each turn of the secondary winding will be the same as the voltage across each turn of the primary winding. Cts current transformers pts potential transformers. The total amount of voltage induced will be equal to the sum of the voltages induced in each turn. Alok pandey assistant professor assistant professor department of electrical department of electrical engineering engineering a seminar on high voltage testing of electrical transformer presented by hari shankar singh. Transformer testing has developed considerably over the past years. Independent testing laboratory for high voltage equipment. Testing procedures for hv voltage transformers testing procedures for hv voltage transformers photo credit. High voltage winding to low voltage winding and ground b. For the purpose of this guide, medium voltage transformers are those having primary voltage ratings between 4. If a very high voltage is required, the transformer is usually build up in stages by cascading. Much of the actual winding area is taken up by voids between round wires, by wire insulation and any bobbin structure on which the wire turns are mounted as well as insulation between high voltage and low voltage windings. High voltage testing of transformer transformer capacitor scribd. Introduction a transformer is a static device that transfers electrical energy from one circuit to another. A resonant transformer for high voltage testing of generator stators article pdf available in australian journal of electrical and electronics engineering january 2003 with 2,326 reads.
High voltage testing 149 the high voltage is applied across the device under test by means of a transformer. It is typical the use of high voltage testing on transformers to confirm performance. The importance of current transformer tests is often underestimated. By means of cascading, the size of the transformer and the insulation bushing. High voltage testing of transformer seminar report pdf. The induced voltage on the low voltage side of the transformer is connected to the low voltage terminals of the ratio meter.
Performed by stressing the insulation of the product far beyond what it would encounter during normal use. Electrical routine testing of high voltage bushings. Pdf a resonant transformer for high voltage testing of. The accelerating voltage for a television cathode ray tube may be described as extra high voltage or extra high tension eht, compared to other voltage supplies within the equipment. It can be designed to step up or step down voltages and works on the magnetic induction principle. In case tertiary is also connected, ensure the isolation of. Ac dielectric withstand test voltage shall not exceed 65 percent of factory test voltage for oneminute duration. High voltage test transformers, construction, design and their. Test voltages used to determine highvoltage power transformer ratios are usually 1 of the windings rated voltage or less to reduce testing hazards. Threeormorewinding transformers will have winding designation h, x, y and z, where h is the highvoltage winding or, the highest kvarated winding in case windings have the same. Pdf the paper presents the results of the development of high voltage high frequency hvhf power transformer 0.
They can include features for electrical isolation, power distribution, and control and instrumentation applications. Because replacing a high voltage transformer requires planning for many reasons, including long manufacturing lead times that can exceed a full year, it is widely accepted that asset management, particularly of transformers, is a beneficial contribution to the operation of the grid. C electrical power from one voltage to another voltage keeping the frequency same by electromagnetic induction discover the worlds research 16. To withstand these impulse voltages, the insulation of these transformers must be carefully designed. The capacitors are connected between the system voltage and the polarity of a pt. As the pt secondary is normally grounded through an internal jumper, an external switch is often used to isolate the pt from ground during testing. In practice, only about 50% of the window area can actually carry active. Hipot test is the most common type of electrical safety test. Transformers are an electrical component that transmit electrical energy between at least two circuits. Instrument transformers convert signal levels from dangerous high voltage or inconvenient high current, or current at high voltage to levels appropriate for metering. A transformer is a static device that transfers electrical energy from one circuit to another through inductively coupled conductorsathe transformers coils. A potential transformer is a conventional transformer having primary and secondary windings. The ac hv test value should not surpass 75% of the factory test value.
High voltage testing low frequency constant dc high. To obtain values as close as possible to the manufacturers specifications the insulators must be very clean. Designed to verify that the insulation of a product is adequate enough to withstand high voltage. A transformer has no moving parts and is a completely. Apr 10, 2015 high vol tage testing of transformer by hari shankar singh 1. Greenlee is excited to expand the test and measurement portfolio with the hde high voltage line. As viewed from the highvoltage side, h 1 bushing terminal will be located on the right.
When ac hipot tests are used for routine maintenance, the power transformer can be examined at rated voltage for 3 min instead of testing at 65% of factory test voltage. High voltage transformer high voltage transformers convert voltages from one level or phase configuration to another, usually from higher to lower. Hde brings a rich history of innovation, reliability and customer focus and will allow greenlee to offer a more complete product solution to power utility and electrical professionals. The high side winding is constructed with more copper turns. Cvts are often used in high voltage 115kv and higher applications and use a series of capacitors as a voltage divider. The purchase, preparation, assembly, operation and maintenance of transformers represent a large expense to the power system. Tests can also be performed under rainy conditions for outdoor equipment. A transformer is an electrical apparatus designed to convert alternating current from one voltage to another.
In this book we have laid down important aspects on transformer. Insulation resistance tester, microohmmeter, high voltage test set, digital voltmeter, cvt test set, ratiometer or primary. Jan 29, 2019 high voltage transformers are normally used in high voltage labs for testing purpose. This transformer is subjected to transient voltages and surges during their normal operation when the insulation under test breaks down. For ul a transformer with at least 500va is enough to sustain the voltage during the test 8. 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. 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. Required output voltage tank type hv test transformer in this design, the oil insulated high voltage transformer is contained within a conducting vessel, typically a welded steel tank.
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