Current transformer testing swp check this is the latest process zone version before use. Use the oden at kit to inject high current for example. Traditional current transformer testing follows a blackbox approach. Instrument transformer theory and testing steve hudson, pe. Not all ct probes work for both direct current dc and alternating current ac. 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.
Transformer, operation, testing and maintenance 33kv and below 9. In addition some other tests are also carried out by the consumer at site before commissioning and also periodically. On theother hand, when j is large, then theuse of a detector of highimpedance may shift theload from transformer of higher. Of the two factors which might combine to introduce an error when the. Shortcircuit may be a preset or b post set duration of each test being 0.
The typical excitation current test data pattern for a threelegged core transformer is two similar current readings and one lower current reading. Current transformer, temperature rise test, type test, optimization, protection. If a ct test switch is used, the switch must have a makebeforebreak contact pattern to. The following tests are routinely conducted in the field on the transformer. Check that all parts of the transformer are properly assembled and tight. Clampon cts are commonly used for one time measurements, rather than long term. The current transformer will operate into either a short circuit or a resistive load until the voltage induced is enough to. The current transformer function is different than that of a voltage transformer. All oil valves are in correct position closed or opened as required. Ac voltage is preferable to dc voltage for transformer testing because ac voltage simulates the internal stress that the transformers face during operating conditions. As the temperature may vary widely, it must be measured so that temperature correction can be applied to the results. Polarity refers to the instantaneous direction of the primary current with respect to the secondary current and is determined by the way the transformer leads are brought out of the case. General inspection mechanical checks general visual inspection and compliance with the drawings and manuals.
Ieee guide for field testing of relaying current transformers. A test set operator connects the leads, pushes the buttons, and records the. Transformer testing commissioning, routine, diagnostic. Check nameplate ratings and hv, lv terminal markings.
A fault leading to an open secondary could cause the primary current to overwhelm the insulation, causing the winding to short circuit. Hence, it is essential to inspect and calibrate those instrument transformers at regular intervals. Ensure the ct is connected to system properly in all respect primary and secondary. Partial discharges in transformers are typically measured by applying a prespecified voltage to the transformer windings and measuring induced charges via a coupling device e. In this book we have laid down important aspects on transformer. Testing current transformers burden test only if we cannot get to the primary side of the ct we can. Testing of oil in the field is typically limited to testing at whatever temperature prevails at the test site. The current transformer is solely assessed through its external behavior without. Testing will commence only after the equipment is completely installed as per approved method statement for the installation of the transformer and released for testing commissioning. Turnsratio test results should not deviate more than onehalf percent from either the adjacent coils or the calculated ratio.
To confirm the physical condition and electrical characteristics of current transformer installed in the installation. The transformer has been built to standard damage has not been sustained during transit or installation. Page 2 of 9 standard work practice sp0507 ver 5 ergon energy corporation limited abn 50 087 646 062. Pdf electronic voltage and current transformers testing device. 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. Nonobservance can result in death, personal injury or substantial. The working procedure on how transformers work types. General block diagram of electronic current transformers. Inductive current and voltage transformers ct and vt and capacitive voltage transformers cvt can. On subtractive polarity transformers the h1 primary lead and the x1 secondary lead will be on the same.
It is carried out as a type test as well as routine test. Measure the secondary current in all loop up to the end of this loop. Dfr technology is an established test procedure in laboratories that in an innovative effort by megger has been adapted for field use in the idax range of instruments. After the current transformers have been subjected to the dielectric type tests 3, 4 and 5 they shall be subjected to all the routine. Occasionally it is not possible to perform a current ratio test. Procedure for current transformer factory and site. Electrical testing methods on instrument transformers.
Back to the basics current testing valence electrical. This amounts to a rigorous examination of the transformer intended to. Back to the basics current transformer testing ct 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. The digital output is a data stream coming from the merging unit. Experimental testing of a standalone merging unit is also performed with the. Magnetization and primary injection test of current transformer for protective relaying jacob tsado 8 current transformers. Clampon current transformer ct probes allow noncontact current measurements using a digital multimeter dmm or other instrument without interrupting the circuit under test. Electronic voltage and current transformers testing device mdpi. The standards which apply to nonconventional instrument transformers and digital. It is also done at site to ensure healthiness of a transformer that is to check loose connections, broken strands of conductor, high contact resistance in tap changers, high. There are various test required on transformer to conform performance of transformer. A primary part of commissioning a transformer involves testing it after its installation in the field. Supply is made on and closed after specified duration of short circuit.
Our distribution transformer test system dtts has been designed with these requirements in mind, as a multifunctional tool for testing distribution transformers. Before attempting to connect test equipment to a transformer, one must make. All materials and relevant documentation to this testing works shall be checked by the responsible personnel prior to the commencement of testing activities. The testing times have been greatly reduced using modern microprocessor based test equipment. Model cter91 is designed for a maximum continuous output of 2. Current transformer design guide an effective design of a ring type c. Procedure for current transformer factory and site acceptance tests note. Safety information dangerous voltages can occur on the connectors, even though the auxiliary voltage has been disconnected. A more accurate calculation can be made if the test reports for the transformer are.
Mainly two types of transformer are done by manufacturer before dispatching the transformer mainly 1 type test of transformer and 2 routine test. Application of optical current transformers in digital. The basics of current transformers nk technologies. Magnetization and primary injection test of current. The equipment and test procedure developed at the bureau of standards for measuring the ratio and phase angle of current transformers up to currents of. A current transformer operates with a set primary current and will try to output a constant current to the load, independent of the load. Additional checks during commissioning of power transformer. There should not be any mechanical distortion, fire to the transformer during this test. Current transformers play an important role in the monitoring and protection of electrical power systems. In short, dfr is the measurement of capacitance and losses dissipation factor tan. Instrument transformers application guide abb group. Heres a summary of the current transformer testing paper.
Figure 5 shows the result of the curve fitting for core 1, considering the y axis to be the current and x axis to be the voltage, the following expression give the standard. It is possible to combine the use of abb cvts as voltage transformers with using. It evolved from the simple gonogo verdict into a sophisticated segment within transformer manufacturing. Ac equivalent and combine both sets of data into one excitation. 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.
In this article, you will learn different types of transformer testing methods, test setup, and their acceptance criteria. Itts stationary and mobile instrument transformer test systems 9. Equuipment for testing current transformers nvlpubsnistgov. Power transformer testing transformers may be tested using ac or dc voltage. A stepdown transformer is used for reducing the voltage. A method for testing electronic instrument transformers is. Current transformer working current transformer testing. Instrument transformer testing instrument transformers for metering purposes must have a high degree of accuracy up to class 0.
Current transformer requirements for cts according to other standards. Procedure for current transformer factory and site acceptance tests 2 the choice between lists 1 and 2 should be made by considering the degree of exposure to lightning and switching over voltages, the type of system neutral earthing and the kind of the overvoltage protection. When the regulation began, the current was essentially constant in spite of the inductance of the windings and fluctuation of the battery voltage or lead resistance. Cts are instrument transformers used for converting primary current into a reduced secondary current for use with meters, relays, control equipment and other instruments the importance of instrument transformer tests is often underestimated. Transformer winding resistance measurement is carried out to calculate the i 2 r losses and to calculate winding temperature at the end of a temperature rise test. The need for a comprehensive current transformer testing regime is evident when the alternative is considered. The magnetizing current can be measured by feeding 400 v, three phase 50 hz supply from hv side keeping the lv side open circuited and the value in different phases could be compared. Temperature rise testing of current transformers semantic scholar. Pdf a method for testing electronic instrument transformers is described, including electronic voltage and current transformers evts, ects. Most power supplies use a stepdown transformer to reduce the dangerously high voltage to a safer low voltage. Tm 5686 power transformer maintenance and acceptance. Testing of power transformers seems like a similar experience. 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.