RU2714532C1 - Differential method of detecting coil short circuits in a three-phase transformer - Google Patents

Abstract

FIELD: electrical engineering.

SUBSTANCE: invention relates to electrical engineering, in particular to relay protection, and can be used for detection of turn-to-turn short circuits in windings of three-phase transformers. Summary: one winding of three-phase transformer is used as supply winding, to which AC voltage source with known characteristics is connected. Two other windings having one rated voltage value are used as measuring windings for detection of winding short circuits in data windings. Measuring windings of the three-phase transformer are connected so that magnetic fluxes in cores of measuring windings created by current in the supply winding are directed in one direction. Starts of measuring windings are connected together. Two ends of two measuring windings are connected to two inputs of alternating voltage or current sensor, respectively. Output of the alternating current sensor is connected to the connection point of two measuring windings. As per the readings of the sensor, compared to known values of voltage of the alternating voltage source, presence or absence of turn-to-turn closures in measuring windings is determined.

EFFECT: disclosed is a differential method of detecting coil short circuits in a three-phase transformer.

1 cl, 2 dwg

Description

The invention relates to electrical engineering, in particular to relay protection, and can be used to detect interturn short circuits in the windings of three-phase transformers.

Differential methods are based on the summation of two or more quantities, when as a result of the summation in the normal, not damaged mode, the sum of the quantities is equal to zero. When damage occurs, in total, a non-zero value occurs, which is associated with the severity of the damage.

Closest to the proposed technical solution is the transverse differential protection, which is used for relay protection of parallel lines having the same resistance, and is based on a comparison of the values and phases of the currents flowing along the lines. In normal mode, the currents are equal, and in the event of a short circuit on one of the lines, the equality is violated [Chernobrovov N.V., Semenov V.A. Relay protection of energy systems: Textbook. Manual for technical schools. - M .: Energoatomizdat, 1998. - 341 s]. If the currents are equal, if we subtract the current of one line from the current of another line, as a result we get a zero value. In the event of a short circuit on one of the lines, the equality of the currents of the two lines is violated, and the result of subtracting the current of one line from the current of the other line will not be zero, and will be equal to the short circuit current on one of the parallel lines.

The disadvantage of the prototype is that, although a three-phase transformer has three phase windings that have the same characteristics, the principle of operation of the transformer differs from the principle of operation of power lines, and the principle of transverse differential protection is not directly applicable to transformers.

The objective of the invention is to create a new method for detecting coil faults in the phases of three-phase transformers.

The technical result is the application of a differential method for the detection of coil faults in a three-phase transformer.

The technical result is achieved in that in the differential method for detecting windings in a three-phase transformer, according to the present invention, one winding of a three-phase transformer is used as a supply winding, to which an AC voltage source with known characteristics is connected, two other windings having one voltage rating, used as measuring windings, and used to detect the presence of coil faults in these windings, measuring windings a three-phase transformer is connected in such a way that the magnetic fluxes in the cores of the measuring windings generated by the current in the supply winding are directed in one direction, while the beginning of the measuring windings are connected together, the two ends of the two measuring windings are connected respectively to the two inputs of the AC voltage or current sensor, at this output of the AC sensor is connected to the connection point of the two measuring windings, and according to the sensor, compared with the known values of the source voltage alternating voltage, judge the presence or absence of coil circuits in the measuring windings.

In FIG. 1, 2 shows a connection diagram of the windings of a three-phase transformer, which illustrates the proposed differential method for detecting coil faults in a three-phase transformer. Moreover, in FIG. 1 is a diagram in which a voltage difference is measured; FIG. 2 is a diagram in which a current difference is measured. The numbers in FIG. 1, 2 are indicated:

1 is a measured three-phase transformer having three phase windings 2, 3, 4 on the high side, three phase windings 5, 6, 7 on the low side;

3-phase winding selected as the supply winding;

5, 7-phase windings selected as measuring windings;

8 - source of alternating voltage with known characteristics;

9 - AC voltage sensor;

10, 11 - two ends of two measuring windings 5, 7;

12,13 - two beginnings of two measuring windings 5, 7; 14 - connection point of two measuring windings 5, 7;

15 - sensor, alternating current.

For the proposed differential method for detecting coil faults in a three-phase transformer, one of the windings of the three-phase transformer is selected as the supply. At the same time, for two winding three-phase transformer there are six options for selecting the supply winding (Fig. 1): 2, 3, 4, 5, 6, 7. For three winding three-phase transformer there are nine options for choosing the supply winding, and the proposed differential method for detecting windings in a three-phase transformer it is applicable to three winding transformers. In FIG. 1, 2, winding 3 is selected as the supply winding. Two other windings, selected on one (high or low) side of a three-phase transformer, and having the same voltage rating, can be selected as measuring windings, since they will have identical characteristics, and are suitable for applying the differential method. In FIG. 1, windings 5 and 7 are selected as measuring windings.

The differential method for detecting coil faults in a three-phase transformer is as follows.

- A sinusoidal current or voltage of industrial frequency is supplied to the supply winding 3 of the measured three-phase transformer 1 from the AC voltage source 8. Thus, in all three phase cores of the measured three-phase transformer 1, an alternating magnetic flux is created.

- This magnetic flux creates an electromotive force (EMF) in the turns of all other windings of the measured three-phase transformer 1.

- In the absence of coil faults in the measuring windings 5, 7, which have the same voltage rating, due to the identical characteristics of the measuring windings 5, 7, the same EMF will be created.

- In the opposite connection of the measuring windings 5, 7, so that the magnetic fluxes in the cores of the measuring windings generated by the current in the supply winding are directed in one direction, the beginning of the measuring windings 12, 13 are connected together, the potential difference between the two ends 10, 11 of the measuring windings will be zero.

- To measure the potential difference between the ends 10, 11 of the measuring windings 5, 7, an alternating voltage sensor 9 is connected to them, which in the absence of windings in the measuring windings 5, 7 will show zero values.

- Thus, in the absence of coil faults in the measuring windings 5, 7, the readings of the AC voltage sensor 9 will be zero.

- If there is a short circuit in the measuring winding 5, the EMF of the measuring winding 5 will be less than the EMF of the measuring winding 7, since part of the turns in the measuring winding 5 will be closed by a short circuit, and the remaining part of the turns in the measuring winding 5 will be less than the number of turns in the measuring winding 7. Accordingly, the AC voltage sensor 9 will show the magnitude of the voltage that falls on the windings in the measuring winding 5. According to the magnitude of the measured voltage, relative to the magnitude of the voltage, supplied by the voltage source 8, it is possible to estimate the number of turns in the circuit, relative to the total number of turns in the measuring winding 5. According to the phase of the alternating voltage measured by the alternating voltage sensor 9, relative to the phase of the alternating voltage of the alternating voltage source 8, it is determined which of the two measuring windings 5 or 7 there are coil circuits.

- When using instead of an alternating voltage sensor an alternating current sensor 15 for measuring the difference in currents of the measuring windings 5, 7, the two inputs of the alternating current sensor 15 are connected to the ends 10, 11 of the measuring windings 5, 7, the output of the alternating current sensor 15 is connected to the connection point 14 of two began 12, 13 measuring windings 5, 7. In this case, both measuring windings 5, 7 are closed to the AC sensor 15, which measures the difference in currents flowing through the measuring windings 5, 7. In this case, the AC sensor 15 in obstacle interturn fault in the measuring windings 5, 7 show the zero values, since the windings 5, 7 have identical characteristics.

- If there is a short circuit in the measuring winding 5, the current of the measuring winding 5 will be distributed between the short circuit in the measuring winding 5 and the remaining turns of the measuring winding 5. Thus, the current generated by the remaining turns of the measuring winding 5 in the AC sensor 15 will be less current generated by the measuring winding 7. Accordingly, the alternating current sensor 15 will show the amount of current that falls on the windings in the measuring winding 4. According to the phase of the alternating current measured with an AC sensor 15, relative to the phase of the alternating voltage of the alternating voltage source 8, it is determined in which of the two measurement windings 5 or 7 there are coil faults.

Thus, non-zero readings of the AC voltage sensor 9 or the AC sensor 15 signal the presence of windings in the transformer. The magnitude of the measured current or voltage is judged on the properties of the circuit, the severity of damage to the transformer.

Measuring windings 5, 7 immediately after the manufacture of the transformer may have non-identical properties. Therefore, to increase the sensitivity of the proposed differential method for detecting coil faults in a three-phase transformer, it is necessary to take measurements using this method on the new transformer and write down the current and unbalance voltages that arise from the non-identical properties of the phase windings of the transformer in the passport of the new transformer. In the future, during the scheduled check of the transformer by the proposed method, it is necessary to take into account the certified values of currents and unbalance voltages during measurements.

Thus, the proposed differential method for detecting coil faults in a three-phase transformer allows to detect coil faults in the windings of a three-phase transformer, to assess the severity of damage to the transformer.

Claims (1)

A differential method for detecting coil faults in a three-phase transformer, namely, that one winding of a three-phase transformer is used as a supply winding, to which an AC voltage source with known characteristics is connected, two other windings having the same voltage rating are used as measuring windings, and used to detect the presence of coil faults in these windings, the measuring windings of a three-phase transformer are connected in such a way magnetic fluxes in the cores of the measuring windings generated by the current in the supply winding are directed in one direction, while the beginning of the measuring windings are connected together, the two ends of the two measuring windings are connected respectively to two inputs of the AC voltage or current sensor, while the output of the AC sensor is connected with the connection point of two measuring windings, and according to the readings of the sensor, in comparison with the known values of the voltage of the AC voltage source, the presence or absence final circuits in the measuring windings.

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