RU2284536C1 - Device for determining transformation ratio of three-phase transformers - Google Patents

Abstract

FIELD: arrangements for measuring or indicating electric quantities.

SUBSTANCE: device comprises additional first and second commutating members, two four-wire cables, and unit for data input made of analogue-digital unit, unit of power-independent memory, computing unit, liquid crystal display, and interface for connection to the computer.

EFFECT: expanded functional capabilities.

3 cl, 2 dwg

Description

Technical field

The invention relates to electrical measurements, in particular to measurements of the transformation coefficient (K _m ) of three-phase transformers, in order to verify the correct ratio of the number of turns of the transformer, as well as to detect interturn short circuits in it. The invention can be used in the energy sector for testing power transformers during commissioning and maintenance work, as well as for their comprehensive examination. In addition, the definition of K _m three-phase transformers prescribed by regulatory documents after exposure to a short circuit current of the transformer windings.

It can be successfully used for measuring K _{m of} three-phase transformers at the factory and in repair organizations.

The preferred field of application of the device is the measurement of the transformation coefficient of power transformers of 6 kV and higher.

State of the art

A device is known for determining K _{m of} three-phase transformers that do not have a zero-output high-voltage (HV) winding, comprising a three-phase variable voltage source supplying the HV winding and four voltmeters, the first voltmeter being connected between any terminals of the HV winding, and the other three between linear the findings of the low voltage winding (LV) [Section 2. Methods for monitoring the status of power transformers, autotransformers, shunt and arc suppression reactors. Moscow, ORGRES, 1997, S.100]. In this case, the linear voltage on the high-voltage VH winding is measured (the sinusoidality and symmetry of the voltage are checked previously) and the linear voltages U _ab , U _bc , U _ac on the LV low-voltage winding are measured. Instrument readings should be carried out simultaneously.

However, to determine K _m using this device, it is necessary to have a three-phase control autotransformer, several voltmeters, a symmetrical three-phase network voltage without higher harmonics and to be able to simultaneously visualize all voltmeters.

To determine K _{m of the} transformer using this device, it is necessary to divide the value of the linear voltage of the HV winding by the linear voltage of the HV winding, i.e. it does not allow to automatically determine K _m , and also it cannot be used to automatically calculate the percentage deviation of K _m phases at different positions of the regulator under load (on-load tap-changer) and record the measurement results on paper. In this case, the measurement error is affected by the components of multiple frequencies of the fundamental harmonic, in addition, for the simultaneous fixing of the voltage values at all voltmeters, it is necessary to have several operators.

Another disadvantage of the device is the inability to transfer measurement data to a personal computer to use the multifunctionality of the latter.

Closest to the proposed device is a device for determining K _{m of} three-phase transformers, containing a variable voltage source and a first voltmeter, which are connected by combined terminals to the terminals of each phase and neutral of the HV transformer winding, and a second voltmeter, also connected alternately to the corresponding linear outputs av, sun, ac LV voltage winding using connecting wires [Section 2. Methods for monitoring the status of power transformers, autotransformers I bypass them and arc suppression coils. Moscow, ORGRES, 1997, P.100], moreover, to find K _m, the voltmeter reading at the HV winding phase is divided by the voltmeter reading of the corresponding LV winding phase.

However, the determination of K _{m of the} transformer windings using this device is also laborious: considerable time is spent, since K _{m of} each phase is measured separately at all on-load tap-changer positions. Another disadvantage of this device is the need to assemble a separate circuit to determine K _m each pair of phases. For this purpose, each time the operator must climb the power transformer to disconnect and connect the device wires with the leads of the high-voltage bushings, using protective equipment and devices, i.e. the safety of work using this device is also low. In addition, the device does not automatically detect K _m ; to determine it, it is necessary to know the circuit and the connection group of the transformer. For example, when determining the transformer connection group with the Yn / Yn / Δ-0-11-K connection scheme, _m is defined as follows:

The accuracy of the determination of K _m decreases due to the components of the harmonics of the mains voltage.

The determination of K _{m of the} transformer using this device is carried out first on one phase at all positions of the on-load tap-changer, then on the second and third phases, which requires additional time to switch the on-load tap-changer from the first to the extreme position. In addition, at the end of the measurements, when a deviation of K _m from the passport data is detected in one of the tap-changer branches, a control measurement is performed on this branch, which increases the amount of work and the loss of time for making the measurement.

This device, like the previous one, does not allow transferring measurement data to a personal computer for creating a database and archiving.

SUMMARY OF THE INVENTION

The objective of the invention is the creation of a device that allows you to automate the mode and reduce the measurement time, increase the safety of measurements and the accuracy of the determination of K _m three-phase power transformer, as well as having the ability to quickly save electronically the measurement data in non-volatile memory and subsequent data transfer to a personal computer so that take advantage of the numerous capabilities of the latter, in particular for creating a database and archiving.

The problem is solved due to the fact that the first and second switching elements, two four-wire cables with phase color and neutral color marking, a transformation coefficient meter, which has a control output, are additionally introduced into the device, which contains an adjustable AC voltage source and connecting wires, connected to the control inputs of a variable voltage source, the first, second switching body, and three voltage channels with a common "ground"; the first channel and the common ground are simultaneously connected to the terminals of the adjustable AC voltage source and to the two inputs of the first switching organ, whose four outputs are connected to the terminals of the high-voltage winding and neutral of the transformer using the first four-wire cable, and the three terminals and neutral of the low-voltage winding of the transformer are connected to using a second four-wire cable with four output terminals of the second switching body, the inputs of which are connected to the second and third voltage channels of Tell transformation coefficient. Moreover, the transformation coefficient meter is additionally equipped with a data input unit that allows you to select the circuit and connection group of the tested transformer, voltage sensors with galvanic isolation and protective circuits against switching overvoltages, an analog-to-digital converter, non-volatile memory, a liquid crystal display, a port for interfacing with a personal computer, and a computing unit allowing to calculate the rMS value of the first harmonic voltage, and to calculate K _m for the phase windings different groups of compounds of transformers, and in adjustable AC voltage source further includes precluding overvoltage protective circuit.

Brief Description of the Figures

Figure 1 shows the structural electrical diagram of the proposed device, combined with a circuit of electrical connections.

The device contains a source of adjustable AC voltage 1 with an additional control input, a transformation coefficient meter 2 having three voltage channels with a common "ground" and control output D, switching bodies 3 and 4, each having one control input 25 and 26, respectively, two four-wire cables 5 and 6, test transformer 7.

Figure 2 shows the structural diagram of the transformation coefficient meter 2, which includes three voltage channels (9, 11, 12) with a common "ground" 10 and a control output D analog-to-digital Converter 2.2, non-volatile memory unit 2.3, computing unit 2.4, input unit data 2.5, liquid crystal display (LCD) 2.6, communication port with a computer 2.7.

Table 1 shows K _m transformers, determined by single-phase power supply of VN (SN) windings, for various schemes and groups of connection of transformer windings.

Table 2, 3, 4 as examples shows the positions of the switches P ₁ ÷ P ₄ and K ₁ ÷ K ₄ when determining K _m , determined with single-phase power supply of the BH (CH) windings with the circuit and group of transformers Yн / Δ-11, Y / Δ-11, Y / Yn-0.

Disclosure of invention

The device is designed to determine K _m transformers. It allows you to simplify the assembly process of the circuit, reduce the measurement time, automatically measure with high accuracy the voltage applied to the corresponding phases of the high-voltage winding of the transformer and the voltage removed from the low-voltage winding at the same time. Due to the automatic switching of the circuits, the proposed device provides increased safety of work. In addition, the device allows you to transfer measured and calculated values to a personal computer for archiving and creating a database.

Consider an example of measuring K _{m of a} power transformer with a circuit and a connection group Yн / Δ-11 of a three-phase power transformer ТДН-10000-110 / 10, having an on-load tap-changer of the RS-4 type.

The measurement begins with the fact that the operator transfers the on-load tap-changer to position 1 and turns on the variable voltage source 1 in the power supply network (see Fig. 1). Then the operator, using the data input unit 2.5 of the digital oscilloscope 2, selects the mode corresponding to the circuit and connection group of the tested transformer 7, in our example, the circuit and connection group Yн / Δ-11. After that, the transformation coefficient meter 2 at the control output D sets a signal that is supplied to the control inputs of the first 3, second 4 switching bodies and a source of adjustable alternating voltage 7.

After that, the first switching body 3 connects its inputs 13 and 14 using the switch P ₁ and P ₂ to its outputs 15 and 18, respectively, and the second switching body 4 using the switch P ₃ and P ₄ connects the inputs 19 and 20 respectively to its outputs 21, 23. Thus, the variable AC voltage source 1 is connected to the inputs of the high-voltage winding AN and the line voltage “ac” to the transformation coefficient meter 2. Thus, the circuit for measuring the voltage on phase “A” relative to the zero “N” output of the transformer is switched and the HV winding and the line voltage "ac" of the HV winding with a transformation coefficient meter 2 (see Fig. 1 and Table 2).

After that, the voltage of the regulated source of alternating voltage 1 automatically starts to smoothly increase to a certain value, while the signals from the inputs of the voltage channels 9, 11, 12 of the transformation coefficient meter 2 enter the analog-to-digital converter 2.2., Where they are converted from analog values to digital (see Fig. 2). Next, the computing unit 2.4 performs the Fourier transform on the input signals: i.e. filters the components of the harmonics of the multiple frequencies of the fundamental and determines the effective value and phase of these signals at the first harmonic. After that, the line voltage “ac” is calculated. Next, K _{m is} calculated by dividing the effective value of the sinusoidal voltage of phase “A” of the HV winding by the effective value of the linear voltage “ac” of the HV transformer winding.

After the calculation is completed, the obtained values of K _m are displayed on the LCD 2.6 and simultaneously recorded in the non-volatile memory unit 2.3.

Next, the transformation coefficient meter 2, using the control output D, supplies a disconnect signal to the source of adjustable AC voltage 1 and the voltage of the latter smoothly drops to zero.

After this, a scheme is prepared for measuring K _{m of the} next phase “B”: the transformation coefficient meter 2 gives a signal, according to which the first and second switching organs connect inputs 13, 14 to outputs 16, 18 and inputs 19 and 20 to outputs 27, 22. The meter transformation coefficient 2 processes the input signals in the same manner as previously described.

Next, a circuit is prepared for measuring K _{m of the} next phase “C”: the transformation coefficient meter 2 gives a control signal, by which the first and second switching organs connect inputs 13, 14 to outputs 17, 18 and inputs 19 and 20 to outputs 22, 23. The meter transformation coefficient 2 processes the input signals in the same manner as previously described and turns off the source of adjustable AC voltage.

After writing K _m phase "C" in non-volatile memory 2.3 on the liquid crystal display 2.6, the computing unit 2.4 calculates the percentage deviation of the phase transformation coefficient, which is recorded in non-volatile memory 2.3 and is displayed on the LCD 2.6.

Then the operator performs similar measurements for all on-load tap-changer positions.

Thus, the transformer K _{m is} automatically detected at all on-load tap-changer positions and its percentage deviation in phases.

For all circuits and groups of transformer connections, the measurement process is similar, except for transformers with a circuit and connection group Y / Yn-0 and Y / Δ-11, according to which an alternating, regulated voltage is supplied by the first switching element not between the phase and neutral of the transformer, but to the linear output of the VN winding. Moreover, for the circuit and group of connecting transformers Y / Yn-0, the phase voltages are removed from the LV winding, i.e., the voltage between the phases and the neutral of the transformer. The first and second switching bodies according to this circuit switch the switches and contacts according to table 3, and for the circuit and group of connecting transformers Y / Δ-11, the line voltages are removed from the LV winding, but contacts K ₁ ÷ K _{2 are} additionally included in the operation, the sequence of operations is shown in table 4.

The use of four-wire cables with color coding makes it possible to simplify the assembly process of the circuit, which is also an important factor in the performance of work in the field.

In addition, the use of the cable allows you to place the workplace at ground level, which eliminates work at heights, thereby increasing the safety of work.

The device can also be successfully used to determine the coefficient of transformation of single-phase transformers and autotransformers.

Claims (4)

1. A device for determining the coefficient of transformation of three-phase transformers, containing a source of adjustable AC voltage and connecting wires, characterized in that the device circuit is additionally introduced the first and second switching organs, two four-wire cables and a coefficient of transformation coefficient, which has a control output connected to the control the inputs of a source of controlled alternating voltage, the first, second switching body and three voltage channels with a common "ground", the first channel and the common ground are simultaneously connected to the terminals of the adjustable AC voltage source and to the two inputs of the first switching body, whose four outputs are connected to the terminals of the high-voltage winding and the neutral of the transformer with the first four-wire cable, and the three terminals and neutral of the low-voltage winding of the transformer are connected to using a second four-wire cable with four output terminals of the second switching body, the inputs of which are connected to the second and third voltage channels of Tell transformation coefficient. 2. The device according to claim 1, characterized in that the transformation coefficient meter is additionally equipped with a data input unit that allows you to select a circuit and a group of transformers, voltage sensors with galvanic isolation, protective circuits against switching overvoltages, analog-to-digital converter, non-volatile memory, liquid crystal display, interface port with a personal computer and a computing unit that allows you to calculate the effective voltage value of the first harmonic, as well as subtract casting transformation ratio of windings of phases for different groups of compounds transformers. 3. The device according to claim 1, characterized in that the protective circuit excluding overvoltage is additionally included in the adjustable AC voltage source. 4. The device according to claim 1, characterized in that the four-wire cables at their terminals have terminals with color-coded phases and neutrals.

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