Therefore, transformer under test may be demagnetized before commencement of magnetizing current test. Before any Item of equipment is accepted for testing a visual inspection will be carried out on that equipment. Winding resistance serves a number of important functions like: There are basically two different methods for resistance measurement: The measurement is carried out using DC current. Larger transformers have to be dispatched with bushings, a conservator and cooling equipment and all minor accessories have to be disassembled. In case of drop in pressure, dew point of N2 has to be measured to check the dryness of the transformer/ reactor. During measurement of insulation resistance, the transformer must not be connected with any external lines or lightning arrestor etc. for use of this form see tm 5-694; the proponent agency is coe. The ratio should match with the specified value. Test reveals the condition of insulation (i.e. I need it. cond* notes check point. This test is used to detect winding movement that usually occurs due to heavy fault current or mechanical damage during transportation or installation since dispatch from the factory. Transformers while experiencing severity of short circuit current looses its mechanical property by way of deformation of the winding or core. Oil is at correct level in the bushing, conservator tank, diverter switch tank etc. Measure phase to phase voltage between the IV terminals and current on each of the IV terminals. Tell us what you're thinking... we care about your opinion! Where defective equipment is found it will be reported to Consultant for further action. It Rating plate show nominal voltage, current of primary and secondary voltage at various of the tap changer, connection symbols ( vector group), % impedance weight of oil etc. Thermovision scanning of transformer to be done at least after 24 hours of loading and repeated after one week. To check for any abnormalities due to loose connections, broken strands and high contact resistance in tap changers. The ratio check has to be carried out as indicated in Figure 5 below. Representing as vectors, the HV winding is represented as 12 (0) hour and the other windings of the connection group are represented by other numbers of the clock in reference to the real or virtual point. Measurement of power‐factor values in the factory is useful for comparison with field power‐factor measurements and assessing the probable condition of the insulation. A sampling technique proven to produce repeatable results when testing the Dissolved Gas content or Moisture (Water) Content in the oil is by sampling with a Glass Syringe. The measurements are repeated in all phases and at all tap positions, sequentially. The polarization index (PI) is defined as the ratio of IR values measured at the intervals of 600 and 60 seconds respectively. Once erection is completed, various pre-commissioning checks and tests are performed to ensure the healthiness of the switchyard equipment prior to their energization. Electrical4U is dedicated to the teaching and sharing of all things related to electrical and electronics engineering. For many tests, this will be almost essential to diagnose problems effectively in the future. • Read thoroughly and understand the TRANSFORMER INSTALLATION & COMMISSIONING MANUAL, before starting the erection work. As I remember – Knee point has Imag increase of not more than 50% for 10% increase in exciting voltage . Insulation resistance shall be measured after the intervals of 15 sec, 60 sec and 600 sec. Test leads should not touch any live part. Ambient temperature and weather conditions are to be recorded. POWER TRANSFORMER - STANDARDISATION MANUAL 183 Chapter - 5 Transportation, Erection, Testing and Commissioning Working Group Members Mr. S. K. Negi - GETCO Mr. Gautam Mazumdar - CGL Mr. Umapathi - Voltech Mr. Y. V. Joshi - GETCO Mr. D. C. Patel - J. H. Parabia Mr. N. G. Patel - GETCO Ms. Asha Agravatt - GETCO. To assess the mechanical integrity of the transformer. 3) establish a baseline with which to compare results of future tests. The low oil level alarm of the magnetic oil gauge should be checked. The insulation power‐factor test, similar to the insulation resistance test, allows certain conclusions to be drawn concerning the condition of the transformer insulation. In case the impact recorder indicates some serious shocks during shipment, further course of action for internal inspection, if necessary shall be taken jointly. can you explain the actual method adopted to identify the vector group of the transformers. Arcing horn of the bushing is set correctly. Full disclaimer here. Knee point is normally considered for class PS or equivalent class X(or PX) . Carry out the measurement as per standard procedure given by the kit supplier. Alternatively, ratio test is to be conducted as per the following method as shown in Figure 6. After testing with high voltage, test terminals must be grounded before being touched by any personnel. The IR values obtained should be comparable with those indicated in the manufacturer’s test reports. Later, they will be explained in details. The test is conducted with the help of mega‐ohmmeter. This test is used to determine the phase relationship and polarity of transformers. However, when the center phase is excited then the voltage induced in the outer phases is generally 30 to 70% of the applied voltage. For oil filled units depending upon the level up to which the oil is drained decides the exposure time. IR measurement should be carried out preferably in dry and sunny weather. There is a certain procedure and criteria for evaluation for vector group identification.. e.g. Changes in the normal insulation resistance (IR) value of CT indicate abnormal conditions such as presence of moisture, dirt, dust, crack in insulator of CT and degradation of insulation. 40450 Shah Alam, Selangor, Malaysia. If all the above tests/checks are found satisfactory, a settling time of at least 24 hours, should be allowed for the oil and air released from all points at six hourly intervals, before commissioning the transformer. All oil valves are in correct position closed or opened as required. After the testing work is completed the supervisor checks all the testing equipment and returns to the storage cabin. All packings should be kept above ground by suitable supports so as to allow free air flow underneath. We can offer a packaged solution including disassembly in preparation for transportation, packaging of sensitive components, transportation of the unit, reassembly at site, complete installation and commissioning of the unit. We are a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for us to earn fees by linking to Amazon.com and affiliated sites. Insulation resistance tests are performed, The significance of the power factor figure is still a matter of opinion. All the utilities introduced said test as precommissioning test. During erection, the exposure of active part of transformers should be minimized. Ensure only trained persons shall operate the power tools. Pls I need the video for this program, I love it, Any other causes on this topic? The ratio test between the HV and LV at all tap positions should also be performed. A primary part of commissioning a transformer involves testing it after its installation in the field. Magnetizing current readings may be effected by residual magnetism in the core. N2 pressure to be monitored on daily basis so that chances of exposure of active part atmosphere are avoided. The resistance is calculated from the readings in accordance with Ohm’s Law. Make connections as per diagram shown below (Figure 3). Depending on the type of the transformer, the input and output windings of a multi‐phase transformer are connected either as star (Y) or delta(D) or zigzag(Z). – If the tap changer is Off load type, switch of the power supply and rise one step and apply the Three phase 415 V AC across the Secondary termination and measure the voltage at both Secondary and Primary side. If the circuit breaker is tripped on differential, Buchholz or any other devices, the cause must be investigated before re-energizing the transformer. Test results should be comparable to factory values. The electrical field tests available to diagnose a transformer include: Copyright © 2020 Megger, all rights reserved. degree of dryness of paper insulation), presence of any foreign contaminants in oil and also any gross defect inside the transformer (e.g. Whether you are installing a new, repaired or refurbished unit or if it is a reallocation of an existing unit, Hitachi ABB Power Grids offers a secure and efficient solution to meet your needs. Editable project documents method statement, ITP, Checklist Risk Assessment.
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