Low Voltage Impulse Test Research Articles

MTL-Based Analysis to Distinguish High-Frequency Behavior of Interleaved Windings in Power Transformers

An elaborate method to analyze the high-frequency behavior of transformer windings by means of the multiconductor transmission line (MTL) method is presented. A procedure for the evaluation of per-unit length parameters for transformer windings (TWs) is enumerated, which is not available in existing literature on the subject. A full-length detailed solution of the MTL method for TW is also demonstrated. A comparison of this method with the conventional circuit approach is illustrated wherever necessary. The analysis of two types of commonly used interleaved windings is performed in this paper. It is also inferred from experimental results that a conventional low-voltage impulse test is insufficient to make a distinction between the two windings. As far as interwinding oscillations at high-frequency excitations are concerned, it also proved by the MTL analysis that one type is better than the other.

Novel technique to improve the fault detection sensitivity in transformer maintenance test

AbstractEarly detection of incipient faults in transformer windings is important, so that required corrective measures can be taken to help prevent interruption during operation. Low voltage impulse (LVI) and sweep frequency response analysis (SFRA) tests have been widely adopted within the industry to determine a transformer winding's deformation. However, these tests have drawbacks, including limited frequency ranges for the LVI test and time‐consuming measurements for the SFRA test. To obtain better signature analysis in the transformer maintenance test, especially detection of minor faults, this paper suggests a new input signal using a pulse sequence (PS) in the transfer function (TF) analysis. The results of the PS test are compared against the LVI and SFRA tests to complete the assessments, which are derived from experimental works on the 25 kVA distribution transformer. It is concluded that the PS method improves fault detection sensitivity significantly. Copyright © 2009 John Wiley & Sons, Ltd.

Bonneville Power Administration Transformer Short Circuit Test Results - Comparison of Winding Inspection With Diagnostic Methods

This paper summarizes Bonneville Power Administration's transformer short circuit test experience of three-phase units rated 115-kv Delta to 12.47-kv Wye; reviews BPA's diagnostic and low voltage impulse test results, and correlates them with factory inspection of damaged units. Special emphasis is on the low voltage impulse method of evaluating transformer damage.

Surge-transference characteristics of generator-transformer installations

Progressive increases in generator outputs and in transmission voltages necessitate a re-examination of the relevance of surge transference to the security of the insulation of generators. Simple equivalent circuits representing inductive and capacitive transference are taken as a basis for the analysis of oscillograms of transferred voltages recorded in low-voltage impulse tests on three generator installations. Reasons are found for substantial differences between the measured peak voltages and values calculated from consideration of inductive transference alone. The analysis accounts for the observed asymmetric distributions of voltage between the three phases, and supports the use of a simple lumped-parameter circuit to represent the generator impedance in calculations. From the experimental results, the highest overvoltages to which the three generators could be exposed by surge transference are calculated.