The current transformer is solely assessed through its external behavior. Ct ratio is described as the ratio of primary current input to secondary current output at full load. Maintenance of transformers a detailed checklist electrical4u. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the. Finish load test under kva below distribution transformer full current for single machine. As such, their condition is critical for reliable, faultfree operation. Transformers are tested for overvoltages by exciting the secondary of the transformer from a high frequency a. This new ctpt testing set are based on low frequency and variable frequency methods which lead to the great reduction in weight and high knee point test range. The importance of current transformer tests is often underestimated. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to. 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. May 10, 20 transformer manufacturers perform two main types of transformer testing type test of transformer and routine test of transformer. Verify correct operation of transformer withdrawal mechanism and grounding operation. Testing swp sp0507 current transformer testing sp0508 voltage transformer testing p53 operate the network enterprise process as2374.
Magnetization and primary injection test of current. If the current transformer has primary to secondary current ratio of 100. Scribd is the worlds largest social reading and publishing site. The ratio of an instrument transformer is the relationship of its primary rating to its secondary rating. To prove that the transformer meets customers specifications and design expectations, the transformer has to go through different testing procedures in manufacturer premises. We have two iot platforms are avilable to use for testing first is thingspeak and ubidot stem. William morse a free powerpoint ppt presentation displayed as a flash slide show on id. The electrical current flowing in a transformer is al ternating current. The magnetic field around the winding is constantly in motion. The voltage ratio shall be measured on each tapping and verified aginst manufacturer approved power transformer testing procedure. Current transformer testing on site presentation calmet. Our test systems provide highprecision, automatic testing and assessment of current transformers to iec 600441, iec 600446, iec 618692, ieee c57. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load.
Measurement shall be carried out with direct current dc by the voltage drop method or the bridge method as specified in the manufacturer approved power transformer testing procedure. The test and assessment of transformers is a complicated task. To ensure that the product is fit for its intended use standards iec standards iec 60076 part 1 part 14 specification for transformers ieee. A distinction has to be made between a metering class and a protection class current transformer. 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 errors of the transformer under test x are compared with those of standard transformer s. The current state and measured parameters are sent to the remote iot server by using the data reception subsystem. Routine tests and type tests of transformers electrical4u. Presentation on current transformers submitted by roopal pancholi b.
A free powerpoint ppt presentation displayed as a flash slide show on id. Testing current transformers ratio vs applied burden cts installations can be fully verified in the field. Ensure the ct is connected to system properly in all respect primary and secondary. Iot based distribution transformer monitoring system ppt. The objective of testing is to ensure quality to ensure that the products manufactured have met the requirements of customer specificationstandard to prevent accidents which may occur if a failed product is put into service. Making a wellinformed choice in equipment for transformer testing is an important step towards ultimately improving transformer life management decisions. Oct 12, 2012 parameters of short circuit testthis is a big advantage of dpatt3bi that it can be usedfor transformer testing.
An alternating voltage v p applied to the primary creates an alternating current i p through the primary. Portable ct pt analyzertransformer testgfuve electronics. Some transformer tests are also carried out at the consumer site before commissioning and also periodically in regular and emergency basis throughout its service life. Insulation tests on current transformers rated 600v or less are usually performed at vdc. 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. Oct 08, 2016 calculation of cts if the current transformer has primary to secondary current ratio of 100. We know that, in a ct the primary current is dependent on the load current or line current as ct is connected in series with the line. So, primary current of ct assuming constant line current is constant irrespective of whether the secondary of. Portable precision current transformer testing ct pt analyzer. The resulting overloads of grid sections can lead to farreaching supply and production failures. We perform one group on a routine basis known as preventative maintenance, and the second group on an adhoc basis i.
Occasionally it is not possible to perform a current ratio test. Why the secondary winding of current transformer is always. Testing metering current transformers with ct analyzer. The international electrical testing association neta is an accredited standards developer for the american national standards institute ansi. A current transformer or ct is very essential equipment installed in an electrical substation for electrical measurement and protection purpose. The following tests are routinely conducted in the field on the transformer. Ct tap ratios can be verified by applying a voltage across the. Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions.
In the protection subsystem, arduino controls the operation of a fan and protection relay to protect the transformer in a fault condition. Nov 17, 2019 a power transformer requires various routine maintenance tasks including measurement and testing of different parameters of the transformer. This is a comparison current transformer testing involving null techniques. Current transformer or ct is a type of instrument transformer that is used in power system for measurement, detection, and protection the system. Current transformer basics and the current transformer. In testing, if a voltage is applied across the secondary terminals the. Test this by hooking up the secondary to its circuit and using your dmm to test the secondary lines. Parameters of short circuit testthis is a big advantage of dpatt3bi that it can be usedfor transformer testing.
These tests are done mainly in a prototype unit not in all manufactured units in a lot. Gdbrp transformer power analyzertransformer power analyzer. Ct tap ratios can be verified by applying a voltage across the full ct winding a tap voltage ratio test. Ht voltage 11kv lt voltage 415v pp kva rating 200 kva full load current 10. Potential transformers pts or voltage transformers vts pts or vts are the most common device used. Figure 144 shows the magnetic field during one cycle. While primary winding carries a small current i 0 called noload current which is 2 to 10% of the rated current. Arnolds method is used for getting very accurate results. Power transformers are the central hub in the field of energy distribution and transmission. On pressing button 3 of the keypad of dpatt3bi, wpf page appears on the lcd display showing copper losses. Ppt transformer tests powerpoint presentation free to. This protects connected metering devices from overloading in the presence of fault level current flows. In order to isolate the measuring circuit from the secondaries of cts, a 55 current transformer t is used.
The value of full load current for transformers of different ratings is shown in the following table. If the reading is above the amperage rating for the transformer, the circuit is drawing too much power. The amperage rating for your transformer fuse may be labeled on the transformer, but will also be. The current transformer function is different than that of a voltage transformer. Tech electrical, iii year, v semester k72 submitted to mr. It is a device used to measure large current by scaling large primary currents to a smaller, easy to measure, secondary currents. Cts for metering purposes must have a high degree of accuracy to ensure.
Precautions should be taken when making this test on current transformers to prevent. The current flows first in one direc tion, stops, then reverses and flows in the other direc274 unit 74 transformers tion. While primary winding carries a small current i 0 called noload current which is 2. 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. Instrument transformer basic technical information and. Perform a polarity test of each current transformer page 12 4.
Morgan tm schaffer transformers the inside view transformer tests oil tests and online monitoring can increase transformer life expectancy by. It is a good idea to remove all as a safety precaution to prevent backfeeding dangerous voltages into the system during testing. Variac, stepup transformer 02kv primary current injection set. When the transformer is operating at no load, the secondary winding is opencircuited, which means there is no load on the secondary side of the transformer and, therefore, current in the secondary will be zero. Transformer on no load condition its phasor diagram. Sometimes different types of impurities entered into the transformer oil.
The current transformer is solely assessed through its external behavior without considering what is happening inside. Remove the neutral ground and isolate the ct from any associated burden. It buffers the meter from experiencing excessive torques that might be. Current transformer design guide an effective design of a ring type c. Considering it is in operation 7 days a week, incorrect billing due to an inaccuracy of just one current transformer circuit in a single feeder may lead to significant financial consequences. Hence, it is essential to inspect and calibrate those instrument transformers at regular intervals. Current transformer testing ppt video online download slideplayer. Calculate full load current from parameters available in transformer s name plate as described below. If the primary current changes, the secondary current output will change accordingly. Some transformer tests are carried out for confirming the basic design expectation of that transformer.
Prior to testing, short the primary winding of the ct under test by connecting h1 and h2, then short the secondary winding of the ct under test by connecting x1 and x2x5. Outline current transformer ct test setup tap, ratio and polarity test megger test excitation test testing cts in a circuit breaker testing cts in a three. There are three basic styles used to transformer system voltages to control voltages. The current transformer is solely assessed through its external behavior without.
Power transformer testing procedures and schemes eep. Power transformer testing transformers may be tested using ac or dc voltage. For example, the potential transformer mentioned above having a rating of 480. So far accurate measurement and smooth operation of an electrical power system, cts must be properly. Testing potential transformers relay testing training. Testing of transformers impulse test of transformer. Integrated system for the management of quality iso quality certifications. There are two main types of maintenance of transformer.
When the pt is withdrawn ensure that there is no longer any connection with the primary electrical system. Sometimes, the transferred voltage in the secondary and the. 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. This reduces the core saturation and also limits the charging current necessary in large power transformers. Power transformer testing procedures and schemes photo credit. Ct analyzer with one button click all test items, such as excitation, winding resistance, polarity, phase error, ratio, etc, can be performed automatically. Current transformers can be tested in their fieldmounted. Feb 24, 2011 considering it is in operation 7 days a week, incorrect billing due to an inaccuracy of just one current transformer circuit in a single feeder may lead to significant financial consequences.
If a current transformer does not perform properly, there may be a huge disturbance in the system due to malfunctioning of protection relays. Testing metering current transformers with ct analyzer youtube. Basics, maintenance, and diagnostics xi contents continued page 9. The insulation withstand strength can also be checked. Instrument transformer testing instrument transformers for metering purposes must have a high degree of accuracy up to class 0. There are four typical types of current transformers. Traditional current transformer testing follows a blackbox approach. Neta defines the standards by which electrical equipment is deemed safe and reliable. When making three phase transformer noload, load test, the instrument will judge if the wiring is correct automatically, and shows three phase voltage, current vector diagram. In transformer testing it is essential to record the waveforms of the applied voltage and current through the windings under test. To confirm the physical condition and electrical characteristics of current transformer installed in the installation. Nov 26, 2010 traditional current transformer testing follows a blackbox approach. The schematic diagram for impulse testing of transformer is shown in figure ii and the wave shapes of the full and chopped waves are shown in figure iii.
384 611 1296 601 651 1457 974 1442 326 420 56 779 1232 886 391 433 130 766 1162 225 152 1044 666 117 263 1365 338 768 1289 1260 60 1421