Virtual Instrument for Lightning Impulse Tests
TL;DR: In this paper, an objective formulation of the impulse analysis problem from a signal analysis viewpoint is proposed, where the winding response is quintessentially that of a deterministic network to a finite energy signal, with breakdown and partial discharge being inherently nonlinear events.
Abstract: We propose an objective formulation of the impulse analysis problem from a signal analysis viewpoint. The winding response is quintessentially that of a deterministic network to a finite energy signal, with breakdown and partial discharge being inherently nonlinear events. A significant improvement to the acquisition of waveforms is demonstrated by a virtual instrument approach. It retains the advantages of the time- and frequency-domain methods. The drawbacks of the transfer function method are highlighted and a new piecewise linear approach is proposed for analysis. Experiments on a discrete lumped parameter model of the winding are used to validate the PXI based instrument.
Citations
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TL;DR: In this article, the limitation of time domain correlation method in locating partial discharge (PD) in transformer windings is found out, and frequency domain correlation with Gram Schmidt orthogonalization is proposed.
Abstract: Partial discharge (PD) is one of the sources of insulation failures in Power transformers. Knowledge of the PD source locations are important for transformer maintenance and repair. Due to the complex structure of the transformer, it is very difficult to locate the PD accurately in transformer winding. Correlation methods are applied to locate the PD source across the winding. The PD across parts of the winding are simulated by applying voltage pulse across the sections. The winding response for a reference PD impulse across transformer sections are taken as base for correlation and correlated with winding response of PD impulse across any section with different PD pulse widths. In this paper the limitation of time domain correlation method in locating PD in transformer windings is found out. To overcome the limitation of time domain correlation method, frequency domain correlation with Gram Schmidt orthogonalization is proposed. Simulation and experiments are performed on layer, continuous disc and interleaved windings to prove the feasibility of the proposed method.
39 citations
Cites background from "Virtual Instrument for Lightning Im..."
...From the extensive literature survey on the PD pulse width, it is found that the PD pulse width ranges between 1ns to few μs [15, 16]....
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TL;DR: In this article, the authors propose new techniques for fault detection based on continual assessment during the test. They include voltage comparison, current comparison, and real/reactive power measurements, which are validated on a number of models including a voltage transformer and a distribution transformer winding.
Abstract: The ability of a transformer to withstand the dynamic effects of a short circuit test is conventionally evaluated by a measurement of short circuit reactance before and after the test. We propose new techniques for fault detection based on continual assessment during the test. The methods are based on the comparative null method for accuracy measurement in instrument transformers. They include voltage comparison, current comparison and real/reactive power measurements. High resolution sampling based acquisition systems are used to compute changes on a cycle-to-cycle basis. The proposed methods are validated on a number of models including a voltage transformer and a distribution transformer winding. They would be useful for designers in assessing events leading to failure in a more transparent manner.
37 citations
Cites background from "Virtual Instrument for Lightning Im..."
...A full description of the virtual instrument is available in [20]....
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TL;DR: In this paper, a tapped transformer is designed and test platforms are built to compare winding diagnoses using the impulse wave and sweep frequency response analysis methods by recording voltage responses on both the high and low-voltage sides and calculating the respective transfer functions.
Abstract: Monitoring of winding faults is the most important item used to determine the maintenance status of a transformer. Commonly used methods for winding-fault diagnosis require the transformer to exit operation before testing and an external exciting signal, whether the transformer is malfunctioning or not. However, if an overvoltage signal can be regarded as a broadband excitation source for fault diagnosis, then the interference caused by signal injection can be eliminated without the need for additional pulse or impulse signals. In this paper, a tapped transformer is designed and test platforms are built to compare winding diagnoses using the impulse wave and sweep frequency response analysis methods by recording voltage responses on both the high- and low-voltage sides and calculating the respective transfer functions. Based on comparison of statistical indicators, it is found that the sensitivities of both methods are similar for detecting conditions of winding-ground and winding-interlayer short circuits. It is concluded that it is feasible to use a transient overvoltage monitoring system for winding-fault diagnosis.
24 citations
TL;DR: A technique based on an Archimedean copula is proposed to find the location of a Partial Discharge source in a transformer winding and demonstrates that the proposed approach is capable of achieving an accurate prediction of the locations of the PD source.
Abstract: Precise localization of a Partial Discharge (PD) source inside a winding is one of the important tasks for early detection and prevention of catastrophic failure of a transformer. However, due to the highly complex structures of the windings and statistical nature of PD, the exact location of a PD source is quite difficult to discover. In this paper, a technique based on an Archimedean copula is proposed to find the location of a PD source in a transformer winding. The winding responses to the PD signals of known pulse-widths applied at all the sections are taken as reference data. Further, the winding responses, obtained from the PD pulses of random shapes and magnitudes applied across various sections of the winding, are taken as test data. To predict the location of the test signals, the best-fit copula and its parameters are established using the reference and test data. The maximum value of log-likelihood between the reference data and the test signal indicates the location of the PD source. Firstly, simulation case-studies are conducted to demonstrate how the proposed approach can be implemented to locate the PD source. The results of the proposed method are then compared with the time-domain and frequency-domain based correlation techniques. Finally, the proposed method is tested with experimental data acquired from a laboratory scale model of the transformer winding. The simulation and experimental results demonstrate that the proposed approach is capable of achieving an accurate prediction of the location of the PD source.
19 citations
Cites background from "Virtual Instrument for Lightning Im..."
...In general, pulse-widths of PD signals lie between 1 ns to a few μs [30-31]....
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TL;DR: In this article, statistical techniques are used to locate the partial discharge in transformer windings, and the experimental studies are performed on a 22-kV prototype interleaved winding to prove the feasibility of the methods.
Abstract: To locate the partial discharge in transformer windings, statistical techniques are proposed. The experimental studies are performed on a 22-kV prototype interleaved winding to prove the feasibility of the methods.
17 citations
Cites background from "Virtual Instrument for Lightning Im..."
...Generally, PDs are very short pulses of durations from tens of nanoseconds to 5 s [2]....
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References
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TL;DR: In this article, the time dependence of discharge processes in dielectric bounded voids of 40 mm have been studied under power frequency voltage and fast oscilloscopic techniques were used to observe the pulse shape of single discharges or clusters of discharges.
Abstract: The time dependence of the discharge processes in dielectric bounded voids of 40 mm have been studied under power frequency voltage. Fast oscilloscopic techniques were used to observe the pulse shape of single discharges or clusters of discharges. Synchronous optical registration of discharge images was performed using a highly sensitive video system. At least two distinct discharge types were registered as a function of time. A 'streamerlike' discharge regime is gradually replaced by a more diffuse 'Townsendlike' discharge regime. This transition could be recognized in the shape of the discharge pulses and in the pattern of the optical image. A key parameter governing the transition is the surface resistance of the void-dielectric interfaces. This surface resistance was seen to decrease gradually due to discharge by-products. In its turn, a low surface resistance strongly favours the transition from 'streamerlike' to 'Townsendlike' discharges.
88 citations
"Virtual Instrument for Lightning Im..." refers background in this paper
...From an analysis of the PD events in literature [12], [13] and [14] it is known that PD events can occur from 1 ns to a few microseconds ( )....
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TL;DR: In this paper, it is shown how streamers and tree-like structures develop; how, on the surface of these primary streamers, instabilities initiate fast growing secondary streamers; and how these events lead to the establishment of a conducting channel.
Abstract: The phenomenon of electrical breakdown in condensed matter has been the subject of many studies. While the ultimate result is relatively easy to observe and study, attempts to uncover its initial phases that lead to the short circuit as evidenced by light and acoustical emissions defied discovery. In the past decades some of the initial phases of the breakdown process have been elucidated with the help of sophisticated devices that permit registration on photographic film and/or on transient digitizing instruments. The progress made in this field is summarized and an attempt is made to establish the significance of these observations. Starting with the events occurring at the metal surface, it is shown how streamers and tree-like structures develop; how, on the surface of these primary streamers, instabilities initiate fast growing secondary streamers; and how these events lead to the establishment of a conducting channel. These stages are examined in the light of published information. The implications of these findings in terms of the performance of actual systems are also considered.
66 citations
"Virtual Instrument for Lightning Im..." refers background in this paper
...From an analysis of the PD events in literature [12], [13] and [14] it is known that PD events can occur from 1 ns to a few microseconds ( )....
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TL;DR: In this paper, the relation between the motion of charges in an electrode gap and the current induced in the external circuit is described on the basis of energy considerations and based on the Ramo-Shockley theory.
Abstract: The relation between the motion of charges in an electrode gap and the current induced in the external circuit is described on the basis of energy considerations and on the basis of the Ramo-Shockley theory. It is shown that both approaches are applicable, and mutually consistent, not only for gas-filled gaps but, if applied properly, also when the gap is partially filled with a solid dielectric. Energy considerations are especially useful for two-electrode gaps. If more than two electrodes are involved, the Ramo-Shockley theory has to be invoked. Based on the theoretical description, fast measuring systems with a subdivided measuring electrode can be constructed (typically 400 MHz bandwidth, 1 ns risetime). Fundamental and electrotechnical bandwidth limitations are discussed. The derived techniques and insights are applied to perform and interpret time-resolved measurements of currents induced by avalanches in homogeneous fields corona discharges in inhomogeneous fields and partial discharges in voids. >
51 citations
30 Jan 2004
TL;DR: In this article, an objective classification of faults that can occur during impulse tests on power transformers is proposed, including nonlinear elements, breakdown, and partial discharge events, and an analysis of a layer winding, in the time and frequency domains, with these faults shows that current assessment methods must be used with caution.
Abstract: An objective classification of faults that can occur during impulse tests on power transformers is proposed. It includes nonlinear elements, breakdown, and partial discharge events. An analysis of a layer winding, in the time and frequency domains, with these faults shows that current assessment methods must be used with caution. A model reference approach is proposed to distinctly improve recognition in such cases. The method is immune to changes of wave shape and the instant of fault is available by observation.
35 citations
TL;DR: It is proved that the transfer functions of a sequence of impulse tests with the same test circuit can be compared with each other and the differences found are mostly due to hardware and software which is not suitable for the determination of the transfer function.
Abstract: A new diagnostic tool available with digitally recorded waveforms for lightning impulse tests on a transformer is the so called transfer function. For the calculation of the transfer function, two waveforms are recorded. The first waveform is the impulse voltage and the second waveform is the impulse current. Both waveforms recorded in the time-domain are transformed to the frequency-domain and the transfer function is calculated. This paper proves that the transfer functions of a sequence of impulse tests with the same test circuit can be compared with each other. In the author's opinion, the differences found between transfer functions are mostly due to hardware and software which is not suitable for the determination of the transfer function. A statement about reliability is only possible if the technology used for determination of the transfer function is beyond any doubt. This paper compares the transfer functions of the full impulse waveform and the chopped impulse waveform on the same terminal of the transformer and test circuit, which is the worst case condition for the comparison, to prove that comparison of transfer functions is possible. >
23 citations
"Virtual Instrument for Lightning Im..." refers methods in this paper
...Digital techniques [2], [3] have been increasingly used for recording waveforms during impulse testing....
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