Inductive current and voltage transformers ct and vt and capacitive voltage transformers cvt can develop ratio and phase deviations. This test determines the current required to maintain the magnetic excitation of the core. Basics, maintenance, and diagnostics vii contents continued page 4. The iron core inside the transformer is magnetized. Transformers are an electrical component that transmit electrical energy between at least two circuits. The power transformer is used to convert voltage using the number of windings in the two coils as ratio, while the current transformer is just an inductor placed around a wire to sense the magnetic field caused by the changing current. It buffers the meter from experiencing excessive torques that might be. Abb field engineering services instrument transformer. In this book we have laid down important aspects on transformer. 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. A test set operator connects the leads, pushes the buttons, and records the.
Current transformer testing swp check this is the latest process zone version before use. Connection on cpc100 will be same as the shown figure. A bartype current transformer which has 1 turn on its primary and 160 turns on its secondary is to be used with a standard range of ammeters that have an internal resistance of 0. The block diagrams of testing evts and ects are shown in figures 1 and and2, 2, respectively. Making a wellinformed choice in equipment for transformer testing is an important step towards ultimately improving transformer life management decisions. Page 1 of 9 standard work practice sp0507 ver 5 ergon energy corporation limited abn 50 087 646 062. Instrument transformer theory and testing steve hudson, pe.
Excitation current is measured at 100% of rated voltage. 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. Testing of power transformers seems like a similar experience. Transformers regulate the voltage in circuits, but in some cases these can go bad and cause a circuit to not. It is expressed in per unit or percent of the rated transformer winding current. Voltage transformer testing swp page 3 of 19 standard work practice sp0508 ver 7 ergon energy corporation limited abn 50 087 646 062 if any risks cannot be managed or reduced to an acceptable level. Contact with high voltage at ct primary connections. These tests are done to assess the condition of transformer after installation and compare the test results of all the low voltage tests with the factory test reports. Current transformer insulation resistance measurement. Power transformer testing transformers may be tested using ac or dc voltage.
A routine series of diagnostics and testing for your current transformer should include ct saturation testing to identify the knee point against ieee or iec standards, ct ratio tests to identify that the voltage ratio is within expected parameters and current transformer resistance testing for both the transformer windings and ct insulation. The tap voltage method cannot establish true orientation. The meter measures only the voltage and current reaching the meter terminals. Replaces 7200pd9206, 031992 medium voltage transformer testing. Voltage transformer or potential transformer theory. Aug 20, 20 build your own current limiter for protection when repairing and testing electronic equipment duration. Figure 1 represents the essential elements for a transformer a magnetic core, with a primary and secondary coil wound on the limbs of the magnetic core. The testing device consists of a precision voltage transformer pvt, precision current transformer pct, data acquisition boards daq1 and daq2, synchronous sampling pulse circuit spc and computer pc. The battery negative terminal is connected to current transformer terminal h2 and the positive side is left hanging for. The connection arrangement for a kick test for a current transformer is presented in figure 3. Equuipment for testing current transformers nist page. If the secondary circuit is closed, a current will flow through the secondary circuit in proportion to the ct ratio.
For example, if 150 amps flow through a 300 amp rated primary the secondary current output will be 2. The test and assessment of transformers is a complicated task. The magnetized iron core induces a voltage in the secondary coils. When the circuit burden gets too large, the ct secondary voltage becomes distorted. Secondary terminal voltage which the ct must maintain within the c rating which is 200v in this example. May 10, 20 the transformer testing performed before commissioning the transformer at the site is called the precommissioning test of transformer. Mainly two types of transformer are done by manufacturer before dispatching the transformer mainly 1 type test of transformer and 2 routine test.
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. Power transformer testing procedures and schemes photo credit. Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions. Bartype current transformer this type of current transformer uses the actual cable or busbar of the main circuit as the primary winding, which is equivalent to a single turn.
Ct is essentially tested as a voltage transformer by applying voltage to the ct. It evolved from the simple gonogo verdict into a sophisticated segment within transformer manufacturing. Unlike the voltage or power transformer, the current transformer consists of only one or very few turns as its primary winding. Repeat the test for the other phases and the other secondary cores. Instrument transformer basic technical information and. At 5% rated current through 100%, the current transformer must maintain 0. Power transformer testing procedures and schemes eep. When current flow exceeds that rating, the metering core will become saturated, thereby limiting the amount of current level within the device. This primary winding can be of either a single flat turn, a coil of heavy duty wire wrapped around the core or just a conductor or bus bar placed through a central hole.
Basics, maintenance, and diagnostics xi contents continued page 9. Morgan lacey in 1925, based on a series of pamphlets entitled transformer abstracts that were. Huayi professional current transformer, voltage transformer, capacitor voltage transformer, transformer, surge arrester manufacturers and suppliers in china, providing the best quality transformer made in china with competitive price. Field testing swp sp0506, particular safety risks applicable to. Routine tests and type tests of transformers electrical4u. C electrical power from one voltage to another voltage keeping the frequency same by electromagnetic induction discover the worlds research 16. I am je of nagbhir sub station of 225 kv newly electrified section and testing started of current transformer when test ct ratio by injecting current in primary bushing of old ct which was 20 years old ct installed in circuit,after testing values not found according to ratio,100 amps inject and found in secondary terminal 3.
They are fully insulated from the high operating voltage of the system and are usually bolted to the current carrying device. A voltage transformer theory or potential transformer theory is just like a theory of general purpose step down transformer. The transformation from primary to secondary current requires a small amount of energy to. Routine, design, and other tests routine tests design tests other tests. China current transformer, voltage transformer, surge. Testing and protection of current transformer practical experiences. Transformer testing serves for the accuracy test including polarity check and demagnetisation for current and voltage transformers in low voltage, middle voltage and high voltage grids according to iec standard 600441, 600442. The following tests are routinely conducted in the field on the transformer. Force is proportional to square of current transformer consulting services inc. Stationary and mobile transformer transformer testing.
The raptor system meet all the previous commented key features. There are various test required on transformer to conform performance of transformer. Portable ct pt analyzertransformer testgfuve electronics. Determines the regulation voltage drop across transformer under load conditions. Transformer book is still in demand is a tribute to the publishers and to the authors who have carried the torch to light our way for 75 years. Use caution when conducting a ct ratio test and do not apply a voltage high enough that would cause the transformer to saturate. The difference is not in the phisical principle, just in the usage. Nov 26, 2010 traditional current transformer testing follows a blackbox approach. Dec 30, 2018 voltage transformer or potential transformer theory.
An alternating voltage v p applied to the primary creates an alternating current i p through the primary. Primary of this transformer is connected across the phase and ground. This protects connected metering devices from overloading in the presence of fault level current flows. Transformer testing has developed considerably over the past years. The basics of current transformers nk technologies. Electronic voltage and current transformers testing device. Current transformer basics and the current transformer. The current transformer is solely assessed through its external behavior without considering what is happening inside.
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