SU108148A1 - Method for detecting defects in transformers - Google Patents

Description

The described method is intended to identify such defects in transformers as inter-turn closures in the windings of the closures in the magnetic cores, equivalent to a short circuit; parallel connections of the windings or parts thereof; accidental closure of adjusting winding taps; erroneous connections of windings, taps in switches, etc., and can be applied in factory conditions of transformer testing at different stages of production; under operating conditions - after repairs, after installation, before being put into operation, etc.

The proposed method is based on a method for measuring losses in idle mode at low voltage in the order of several percent. The main drawbacks of the methods used are the possibility of self-clearing of the closures (burr burnt), even with excitations of the order of 5-10% of the nominal, and the need to reduce the obtained loss values to the nominal voltage, which complicates the control process.

In accordance with the proposed method, losses are measured at energization in the order of 1-2% of nominal, which practically excludes the possibility of self-elimination or excessive development of a possible defect, the presence of which is determined by comparing the losses of this transformer with the values of its own losses measured earlier ( or) with losses of other known-good transformers that are completely identical with the subject.

When testing the proposed method of three-phase transformers, measurements are made in three steps-with single-phase power supply on the phase or line terminals of the transformer (depending on the connection circuit of the excited winding), with the remaining windings of all phases open, and the presence of a defect is determined by the relative increase in one of the values measured phase loss, violating their normal ratio.

FIG. Figures 1 and 2 show two variants of the loss measurement circuit for single-phase transformers; in fig. 3-5 circuits for the inclusion of obmo№ 108148

and various “counter-joints”, which consists in measuring losses in idling mode with a voltage of several percent of the nominal voltage, characterized in that, in order to avoid self-elimination or excessive development of a possible defect and to simplify the monitoring process achieved by eliminating the recalculation loss values to the nominal voltage, the losses are measured at excitation of about 1-2 V o from the nominal voltage, and the presence of a defect is determined by comparing the losses of this transformer with that of the transformer. azom previously measured values of his own losses and (or) a lossy other known good transformers, completely identical with the test.

2. A method according to claim 1, characterized in that when testing three-phase transformers, measurements are made in three steps, with a single-phase power supply at the phase or linear outputs of the transformer (depending on the circuit of the excited winding), with the other windings of all phases open, and the presence of a defect is determined by the relative increase in one of the values of the measured " phase loss, which violates their normal ratio.

tani this transformer. The conclusion of a defect that has arisen (and sometimes, on the contrary, disappeared) after the first test, can be given by the proposed method in the most usual order.

When determining defects in single-phase transformers under operating conditions (prior to first commissioning), the initially measured losses for all identical transformers are compared with each other.

When comparing, it is taken into account that the same value of no-load losses at nominal voltage (determined during factory tests and specified in the corresponding technical documentation) must correspond to practically the same values of the originally measured losses according to the proposed method. The clearly overestimated value of losses in the tested transformer compared to the “normal value indicates its defectiveness.

When testing three-phase transformers, the detection of defects is made by conducting a double comparison.

The first practically minor comparison does not differ from that described for single-phase transformers, i.e. a comparison is made with the data of the same transformers tested under the same conditions as the tested transformer. In this comparison, it is recommended to focus attention not only on the equivalence of the absolute values of the corresponding phase loss (which may differ a little), but also on the same arithmetic difference between the value of the loss upon excitation of the extreme phases and the middle phase.

The second, almost basic, comparison does not require the presence of such a transformer: it uses a certain regularity in the ratio of the “phase loss of a given transformer, the so-called“ normal ratio ”of phase loss.

Depending on the connection circuit of the excited winding, the "normal ratios" of phase losses (i.e. the ratio in the absence of a defect) are the following ratios of the phase losses:

in connection diagrams shown in fig. 3 and 5, the losses on the excitation of each of the extreme phases are almost the same between themselves (usually within 5Vo) and, as a rule, not less than 25% more, cpl losses on excitation of the middle phase;

with the coupling scheme shown in fig. 4, the excitation losses of each pair of phases from the extreme and middle phases should be almost the same (usually within 5%), and the losses upon excitation of a pair of two extreme phases should, as a rule, be no less than 25% greater than the losses measured with the excitation of each pair of middle and extreme phases; The last relation (only for a star connection without an available neutral) is usually close to the known relation determined by the geometrical data of the magnetic circuit.

A clear violation of these “normal ratios indicates a defect.

Defect monitoring in terms of phase loss ratio is practically a sufficiently sufficient method for monitoring defects even without using a comparison technique with a similar transformer; The combined application of the principle of double comparison for three-phase transformers makes the method extremely reliable.

Subject invention

1. The method of determining defects in transformers (winding closures in windings, contour short circuits in magnetic circuits equivalent to them, erroneous parallel connections of different numbers of windings. Inventions and Discoveries Committee of the Council of Ministers of the USSR Editor E. G. GoncharGr. 94

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