Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions. The amperage rating for your transformer fuse may be labeled on the transformer, but will also be. Parameters of short circuit testthis is a big advantage of dpatt3bi that it can be usedfor transformer testing. This protects connected metering devices from overloading in the presence of fault level current flows. The ratio of an instrument transformer is the relationship of its primary rating to its secondary rating. Tech electrical, iii year, v semester k72 submitted to mr. Ct ratio is described as the ratio of primary current input to secondary current output at full load. Current transformer basics and the current transformer. Finish load test under kva below distribution transformer full current for single machine.
We perform one group on a routine basis known as preventative maintenance, and the second group on an adhoc basis i. Ct tap ratios can be verified by applying a voltage across the full ct winding a tap voltage ratio test. Arnolds method is used for getting very accurate results. Precautions should be taken when making this test on current transformers to prevent. Current transformers reduce high voltage currents to a much lower value and provide a convenient way of safely monitoring the. Test this by hooking up the secondary to its circuit and using your dmm to test the secondary lines. If the current transformer has primary to secondary current ratio of 100. Oct 12, 2012 parameters of short circuit testthis is a big advantage of dpatt3bi that it can be usedfor transformer testing.
So, primary current of ct assuming constant line current is constant irrespective of whether the secondary of. While primary winding carries a small current i 0 called noload current which is 2. Ppt transformer tests powerpoint presentation free to. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to. Iot based distribution transformer monitoring system ppt. Instrument transformer testing instrument transformers for metering purposes must have a high degree of accuracy up to class 0. The current transformer is solely assessed through its external behavior. It is a device used to measure large current by scaling large primary currents to a smaller, easy to measure, secondary currents. Making a wellinformed choice in equipment for transformer testing is an important step towards ultimately improving transformer life management decisions. Traditional current transformer testing follows a blackbox approach. 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.
Testing metering current transformers with ct analyzer youtube. This is a comparison current transformer testing involving null techniques. Power transformer testing procedures and schemes photo credit. The current flows first in one direc tion, stops, then reverses and flows in the other direc274 unit 74 transformers tion.
Testing potential transformers relay testing training. Testing metering current transformers with ct analyzer. Integrated system for the management of quality iso quality certifications. The value of full load current for transformers of different ratings is shown in the following table. Insulation tests on current transformers rated 600v or less are usually performed at vdc. Ct tap ratios can be verified by applying a voltage across the. Testing current transformers ratio vs applied burden cts installations can be fully verified in the field. Sometimes, the transferred voltage in the secondary and the. The errors of the transformer under test x are compared with those of standard transformer s.
Routine tests and type tests of transformers electrical4u. It buffers the meter from experiencing excessive torques that might be. Instrument transformer theory and testing steve hudson, pe engineering manager 10737 lexington drive knoxville, tn 37932 phone. The current transformer is solely assessed through its external behavior without. The international electrical testing association neta is an accredited standards developer for the american national standards institute ansi. Power transformers are the central hub in the field of energy distribution and transmission.
Current transformer testing on site presentation calmet. 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. Current transformers can be tested in their fieldmounted. It is a good idea to remove all as a safety precaution to prevent backfeeding dangerous voltages into the system during testing. Current transformer or ct is a type of instrument transformer that is used in power system for measurement, detection, and protection the system. Potential transformers pts or voltage transformers vts pts or vts are the most common device used. 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. Portable precision current transformer testing ct pt analyzer. This reduces the core saturation and also limits the charging current necessary in large power transformers. In transformer testing it is essential to record the waveforms of the applied voltage and current through the windings under test. Transformer on no load condition its phasor diagram. Gdbrp transformer power analyzertransformer power analyzer.
The electrical current flowing in a transformer is al ternating current. There are three basic styles used to transformer system voltages to control voltages. The insulation withstand strength can also be checked. These tests are done mainly in a prototype unit not in all manufactured units in a lot. A distinction has to be made between a metering class and a protection class current transformer. 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. Magnetization and primary injection test of current. William morse a free powerpoint ppt presentation displayed as a flash slide show on id.
Ct analyzer with one button click all test items, such as excitation, winding resistance, polarity, phase error, ratio, etc, can be performed automatically. Ensure the ct is connected to system properly in all respect primary and secondary. Calculate full load current from parameters available in transformer s name plate as described below. In order to isolate the measuring circuit from the secondaries of cts, a 55 current transformer t is used. Testing swp sp0507 current transformer testing sp0508 voltage transformer testing p53 operate the network enterprise process as2374. Some transformer tests are carried out for confirming the basic design expectation of that transformer. May 10, 20 transformer manufacturers perform two main types of transformer testing type test of transformer and routine test of transformer. In testing, if a voltage is applied across the secondary terminals the. We have two iot platforms are avilable to use for testing first is thingspeak and ubidot stem. Sometimes different types of impurities entered into the transformer oil. Cts for metering purposes must have a high degree of accuracy to ensure. Verify correct operation of transformer withdrawal mechanism and grounding operation. A free powerpoint ppt presentation displayed as a flash slide show on id. 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.
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. For example, the potential transformer mentioned above having a rating of 480. When current flow exceeds that rating, the metering core will become saturated, thereby limiting the amount of current level within the device. The voltage ratio shall be measured on each tapping and verified aginst manufacturer approved power transformer testing procedure. The current transformer function is different than that of a voltage transformer. A current transformer or ct is very essential equipment installed in an electrical substation for electrical measurement and protection purpose. Portable ct pt analyzertransformer testgfuve electronics. Transformers are tested for overvoltages by exciting the secondary of the transformer from a high frequency a. So far accurate measurement and smooth operation of an electrical power system, cts must be properly. Instrument transformer basic technical information and. Hence, it is essential to inspect and calibrate those instrument transformers at regular intervals.
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. To ensure that the product is fit for its intended use standards iec standards iec 60076 part 1 part 14 specification for transformers ieee. Neta defines the standards by which electrical equipment is deemed safe and reliable. Current transformer design guide an effective design of a ring type c. Ht voltage 11kv lt voltage 415v pp kva rating 200 kva full load current 10. 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. Why the secondary winding of current transformer is always.
Power transformer testing procedures and schemes eep. Morgan tm schaffer transformers the inside view transformer tests oil tests and online monitoring can increase transformer life expectancy by. Perform a polarity test of each current transformer page 12 4. If a current transformer does not perform properly, there may be a huge disturbance in the system due to malfunctioning of protection relays.
The importance of current transformer tests is often underestimated. In the protection subsystem, arduino controls the operation of a fan and protection relay to protect the transformer in a fault condition. The current state and measured parameters are sent to the remote iot server by using the data reception subsystem. 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. Testing of transformers impulse test of transformer. Presentation on current transformers submitted by roopal pancholi b. To confirm the physical condition and electrical characteristics of current transformer installed in the installation. The magnetic field around the winding is constantly in motion.
As such, their condition is critical for reliable, faultfree operation. If the reading is above the amperage rating for the transformer, the circuit is drawing too much power. Figure 144 shows the magnetic field during one cycle. Basics, maintenance, and diagnostics xi contents continued page 9. 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. Power transformer testing transformers may be tested using ac or dc voltage. 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. Oct 08, 2016 calculation of cts if the current transformer has primary to secondary current ratio of 100. 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 four typical types of current transformers. Nov 26, 2010 traditional current transformer testing follows a blackbox approach. When the pt is withdrawn ensure that there is no longer any connection with the primary electrical system. The test and assessment of transformers is a complicated task. Nov 17, 2019 a power transformer requires various routine maintenance tasks including measurement and testing of different parameters of the transformer.
The resulting overloads of grid sections can lead to farreaching supply and production failures. An alternating voltage v p applied to the primary creates an alternating current i p through the primary. The following tests are routinely conducted in the field on the transformer. There are two main types of maintenance of transformer. If the primary current changes, the secondary current output will change accordingly. 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. Scribd is the worlds largest social reading and publishing site.
A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. 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. To prove that the transformer meets customers specifications and design expectations, the transformer has to go through different testing procedures in manufacturer premises. Current transformer testing ppt video online download slideplayer. 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 current transformer is solely assessed through its external behavior without considering what is happening inside. Maintenance of transformers a detailed checklist electrical4u. Remove the neutral ground and isolate the ct from any associated burden. Our test systems provide highprecision, automatic testing and assessment of current transformers to iec 600441, iec 600446, iec 618692, ieee c57.
518 403 873 1224 240 238 686 307 1543 806 1022 491 918 1439 451 1279 183 1484 1020 584 633 937 266 786 996 1257 1140 293 8 901 1165 1088 903 1502 1585 1004 1466 1581 263 171 926 1452 482 1443 771 216 640 458