Oscillating Switching Impulse Voltage Research Articles

Fault diagnosis technologies for power transformers during the on‐site inductive oscillating switching impulse voltage withstand test

Although oscillating switching impulse (OSI) voltage is recommended for the transformer field test, the lack of corresponding fault diagnosis technologies limits its application in the field. In this study, the inductive OSI test technology and diagnostic methods are investigated. The front time and the oscillation frequency of the OSI are altered by changing the additional inductance, whereas the tail time is affected by both the front and tail resistance. The OSI voltage withstand test is carried out on a 110 kV three-phase double-winding transformer on site. Furthermore, transfer function (TF) analysis is used for the diagnosis of transformer insulation with high sensitivity during the OSI test. The fault winding is distinguished by comparing the change in the voltage TF and current TF at different voltage levels. The partial discharge (PD) detection method has the highest sensitivity, which realizes the early diagnosis of insulation faults. The insulation status of the windings is ascertained based on the number and amplitude of PDs. The test results prove that the inductive OSI voltage withstand test is easy to perform on site and can successfully diagnose the insulation faults of the transformer in more detail compared with other routine insulation tests.

A New Switching Impulse Generator Based on Transformer Boosting and Insulated Gate Bipolar Transistor Trigger Control

To make the switching impulse (SI) generator more compact, portable and feasible in field tests, a new approach based on transformer boosting was developed. To address problems such as triggering synchronization and electromagnetic interference involved with the traditional spark gap, an insulated gate bipolar transistor (IGBT) module with drive circuit was employed as the impulse trigger. An optimization design for the component parameters of the primary winding side of the transformer was realized by numerical calculation and error correction. Experiment showed that the waveform parameters of SI and oscillating switching impulse (OSI) voltages generated by the new generator were consistent with the numerical calculation and the error correction. The generator was finally built on a removable high voltage transformer with small size. Thus the volume of the generator is significantly reduced. Experiments showed that the waveform parameters of SI and OSI voltages generated by the new generator were basically consistent with the numerical calculation and the error correction.

Partial Discharge Measurement under an Oscillating Switching Impulse: A Potential Supplement to the Conventional Insulation Examination in the Field

Partial discharge (PD) detection under oscillating switching impulse (OSI) voltage was performed on three types of insulation defects, including a protrusion on a conductor, a particle on an insulator surface, and a void in an insulator, which are three kinds of the common potential insulation hazards in gas insulated power apparatus. Experiment indicated that the PD sequences under OSI were composed of various combinations of the single pulse, the multiple pulses, and the reverse polarity pulse. The difference between the PD inception voltage (PDIV) and the breakdown voltage (BDV) under OSI voltage was greater than that under alternating current (AC) voltage in some cases, which can provide a more sufficient margin below the BDV for PD diagnosis. The OSI voltage also showed a better performance for exciting PDs with detectable magnitudes from small-scale defects, of which the AC voltage was incapable under our test conditions. The different PD activities with different interfaces under an impulse and a slowly varying voltage were speculated to be associated with the gradient of the background electric field and the space-charge mobility.

Influence of voltage waveforms on partial discharge characteristics of protrusion defect in GIS

The CIGRE WG D1.03 has indicated the breakdown voltage of GIS with protrusion defect under standard lightning impulse (LI) voltage is significantly smaller than that under standard switching impulse (SI) or AC voltage, and LI withstand test is more efficient to find protrusion defect. The question is that whether the partial discharge (PD) inception voltage of protrusion defect under LI is also lower than that under standard switching impulse or AC voltage. In order to understand the relations between voltage waveforms and protrusion defect, three kinds of protrusion with different curvature radius are designed, namely, 0.025 mm curvature radius, 0.25 mm curvature radius, and 0.5 mm curvature radius, and the PD characteristics of protrusion defects are measured under four types of voltage waveforms (standard lightning impulse, standard switching impulse, oscillating switching impulse (OSI), AC voltage), and the influence of voltage waveforms on PD characteristics of protrusion is analyzed. The results indicate that, for protrusion with 0.025 mm curvature radius, the steeper the impulse voltage front is, the lower PD inception voltage of protrusion defect is, and PD under LI has higher detection sensitivity to protrusion compared with AC voltage and SI. While for protrusions with 0.25 mm curvature radius and 0.5 mm curvature radius, the steeper the impulse voltage front, the higher the PD inception voltage of protrusion defect is, and PD under LI has lower detection sensitivity of protrusion with 0.25 mm and 0.5 mm curvature radius compared to AC voltage. As PD exacerbated, the shape changes occur in the q−φ scatter plot, N−φ histogram under oscillating switching impulse voltage, and q−1 scatter plot and N−1 histogram under non-oscillating impulse voltage, which can be used as important criterion in assessing the severity levels of the partial discharge triggered by protrusion under impulse voltage waveforms.

Study on Oscillating Switching Impulse Voltage Generation for Power Transformer Onsite Test

In this paper, the authors describe an oscillating switching impulse voltage generation method using a power transformer induction principle through which the power transformer itself can produce the oscillating switching impulse voltage in accordance with the requirements of the IEC60060-3 standard. The circuit of the oscillating switching impulse voltage generator is proposed. Estimation for the circuit parameters is also pointed out in this paper. An oscillating switching impulse voltage generator is set up to verify the proposed method. Two power transformers are utilized to generate the oscillating switching impulse voltage. The simulating and experimental results verify that the proposed oscillating switching impulse voltage generation method can generate the oscillating switching impulse voltage accorded with the requirements of the IEC60060-3 standard. The steps and consideration for the oscillating switching impulse generation are suggested in this paper. The power transformer onsite oscillating switching impulse test can be easily carried out by the steps and consideration.

The Simulation Study of Transformer Inductive Oscillating Switching Impulse Voltage Generation

According to IEC60060-1, IEC60060-2 requirements, the large transformer should take impulse voltage test in site. However, this test is not performed in the field for the impulse voltage generator huge and difficult to operate. To solve this problem, IEC60060-3 propose using oscillating impulse voltage for equipment on-site impulse withstand voltage test. Oscillating impulse voltage has higher generation efficiency and close to the actual voltage waveform that electrical equipment bear. For the transformer, the oscillating impulse voltage can generated through inductive method. In order to study the generation of oscillating impulse voltage through inductive method for transformer, the simulation circuit is established using ATP soft and the oscillating switching impulse voltage characteristics is studied in this paper. The result show that the oscillating switching impulse voltage waveform that accordance with IEC requirements can be generated through inductive method for transformer.

Generation Oscillating Switching Impulse Using Power Transformer

According to IEC60060-1, IEC60060-2 requirements, on-site tests for the high voltage apparatus can not be achieved due to many external factors such as the huge impulse voltage source and external electrical and magnetic fields, weather condition, etc. Therefore, IEC60060-3 points out the impulse waveforms for the high voltage apparatus during on-site tests, one of the impulse waveforms is the oscillating switching impulse, but the oscillating switching impulse source with high amplitude is a bulky test equipment which is not suitable for the on-site test, consequently the demands for portable oscillating switching impulse source is urgent. This paper presents that the high oscillating switching impulse voltage can be generated by a low oscillating switching impulse voltage with the power transformer which is the test object, the simulation and experiment results show this method can be used for the power transformer during oscillating switching impulse on-site test.

420 kV SF6-insulated tubular bus for the Wehr pumped-storage plant electric tests

Two 420 kV SF 6 -insulated tubular bus systems, 600m and 700m long, have been completed in the spring of 1975. The three-phase systems consist of isolated-phase transmission lines and form the power link for the Wehr pumped-storage plant. After a brief description of the electrical data specified and of the mechanical design, the authors describe the large number of electrical tests carried out. These included laboratory tests, which were concluded by type-testing of the tubular bus and metalclad surge diverter, and routine tests on insulators and diverters. Special attention was also paid to the performance of the equipment under various fictitious fault conditions, and several test series were carried out for this purpose. For the test at the site, an oscillating switching impulse voltage was applied.