On-site testing and commissioning of transducers


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Power Transformer Commissioning Since I started operation 30 years ago, transformer commissioning has consisted of more tests, but nowadays, the number of tests has been reduced due to costs and time savings. This article will give you the full on-site testing that must be done during the operation of the transformer Power transformer testing and commissioning on site Table of Contents: Testing and commissioning of power transformers on site. Power transformer tests: winding insulation resistance measurement, winding resistance test, voltage ratio test, polarity test, no load loss test, load loss test (short circuit), vector group test capacitance and tan testδOil breakdown test, temperature rise test, Frequency Response Analysis (FRA Test) Transformer Partial Discharge Test General Transformer Tests Transformer Primary Tests Secondary Tests Transformer Load Tests Transformer Load Tests 1. Power Transformer Tests These tests include winding insulation resistance test, winding resistance test, vector array test, tan delta test, No load or iron loss test, load or copper loss test, overheating test, partial discharge test, frequency response analysis test and transformer oil cracking test, these tests are detailed as follows: 1.1 Measurement of insulation winding resistance The purpose of this test is to determine the insulation resistance for insulation. high voltage winding to earth, low voltage winding to gron d, high voltage winding to low voltage winding, also to evaluate the amount of moisture in transformer insulation, this test is done with a DC Meger, 5000 V by applying this voltage -5000-volts DC for one 30 seconds and if there is no insulation malfunction, we extend the test to 1 minute. If the reading is unstable, we must extend the test to 5 minutes, and this test should be carried out between the coils as follows: High voltage winding to ground as shown in the figure below. Wind the low voltage to ground like HV-Earth but the connection will be between LV-Earth. High voltage windings to low voltage windings as shown in the figure below Figure 1 – Insulation resistance test: HV-Earth and HV-LV Figure 1 – Insulation resistance test: HV – Earth and HV – LV We take the reading after 15 seconds and after 60 seconds , the result will give the polarization index of the transformer insulation, which indicates the insulation state of the transformer. Polarization index (PI) = R60 / R15 should be as follows: more than 1.3 for a transformer with a voltage of up to 35 kV between 1.5 to 1.7 for a transformer with a voltage of 66 kV up to 500 kV If the PI reading is more than 3.1 then this It means that the insulation of the transformer is in good condition. As a practical reading guide: LV-Earth 1 G-Ohm. HV-Earth 2.5 G-ohms. LV to HV 2.5 G-Ohm. Conclusion: Do not choose the megger test voltage as the 5000V standard as some transformer manufacture has low insulation for large neutral points, for example, 500MVA, 500kV transformers and if you apply 5000 DC voltage in the winding you will lose the transformer windings so please refer to DC voltage Specified for testing transformer windings according to the manufacturing manual’s instructions. After the test, do not energize the transformer before grounding the windings to ensure that the windings are discharged, if you find that the insulation resistance is not satisfied the transformer should be further investigated before energizing. For a Megger, discharge the current to avoid shock. Turn off the power supply when the circuit is connected to avoid sparking. Refer to Table of Contents ↑ 1.2 Winding resistance test The purpose of this test is to measure the DC resistance of transformer windings, this test can be done by voltmeter and ammeter method. For low reading values, we connect the voltmeter after the ammeter, but for high resistance values, we connect the voltmeter before the ammeter. A sensitive voltmeter and ammeter with 100 DC amps will be used. This test will give accurate results as shown below: Figure 2 – DC winding resistance test (current voltage method) Figure 2 – DC winding resistance test (current voltage method) This test can be performed when the transformer is hot or cold, but the temperature must be recorded Coil and oil during testing. If the transformer is for example delta/star windings, check the resistance as follows: Winding resistance HV between phase R and phase S HV A winding resistance between phase S and phase T HV A winding resistance between phase T and phase R LV A winding resistance between phase R and a winding resistance N neutral at Tap 9 LV between S phase and N neutral at tap 9 LV winding resistance between T phase and N neutral in Tap 9 Premium Membership Required This article/technical manual requires a premium membership. You can choose a Plus, Pro, or Enterprise membership plan on an annual basis. Subscribe and enjoy the study of specialized technical articles, online video courses, electrical engineering guides and research. With the EEP Premium Membership, you get an additional core that enhances your knowledge and expertise in the low, medium and high voltage engineering fields. Check the benefits of each plan and choose the membership plan that best suits you or your organization. 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