RU2533530C2 - Method to measure current losses and excitation current of power transformers in field conditions and device for its implementation - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: suggested method to measure current losses and excitation current of power transformers in field conditions and device for its implementation are referred to electric engineering and may be used for calculation and justification of standards for process power losses during its transmission through electric mains. The device comprises a controlled power source to change voltage at one winding of the transformer when the second winding is open. In order to reach the claimed result a free-running asynchronous generator with excitation capacitors is used as the controlled power source. Output voltage of the generator is controlled stepwise within the limits of 70-110% of rated voltage by reswitching of adjustment capacitors at transition of commutation voltage through zero value. Reswitching is made by three-phase contactless electronic keys controlled through optically coupled inputs by a decoder and a multiposition switch.

EFFECT: improved accuracy for real excitation losses of the power transformer.

2 cl, 3 dwg, 1 tbl

Description

The invention relates to energy and can be used to calculate and justify the standards of technological losses of electricity during transmission through electric networks.

A known method for measuring losses and idling current of power transformers and determining the equivalent circuit of a transformer (see pages 291-293: Fig. 14-10. Voldek AI Electric machines / Textbook. L .: Energy, 1978. - 832 s., ill.).

This method involves changing the voltage on the primary winding of the transformer with an open secondary winding. In this case, primary voltages, current, and idle loss power are measured.

The disadvantage of this method is that the measurements are performed under stationary conditions in the presence of an adjustable source of sinusoidal voltage.

A known method for measuring losses and open circuit current of power transformers (GOST 3484.1-88. Power transformers. Methods of electromagnetic tests. Measurement of losses and open circuit current).

According to this GOST, during an idle test, one of the windings (usually a low voltage) with the remaining windings open, the rated voltage (with an acceptable deviation within ± 0.5%) of the rated frequency (with an acceptable deviation within ± 1%) is practically applied sinusoidal shape, and when testing three-phase power transformers, in addition, it is almost symmetrical.

Moreover, the system of linear stresses should be considered almost symmetric if each of the linear stresses differs by no more than 3% from the arithmetic average of three linear stresses of the system. The voltage curve can be considered almost sinusoidal if the ratio of the effective voltage to the average value differs from 1.11 by no more than ± 2%. If the ratio of the effective voltage to the average in the experiment differs from 1.11 by more than ± 2%, then a correction is made for the non-sinusoidal shape of the curve.

Measurement of losses and idling current during acceptance tests of transformers should be carried out at at least five points in the voltage range from 80 to 110% of the nominal, including at the rated voltage of the supplied transformer winding.

The disadvantage of this method is that in the field requires an autonomous powerful adjustable power source with high quality output voltage.

GOST 3484.1-88 also provides a method for determining losses and idling current of power transformers at a low excitation voltage, which is carried out in the form of the following three single-phase experiments.

The first experiment - they carry out a short circuit of the phase A winding, excite the phases B and C of the transformer and measure the losses.

The second experiment - they perform a short circuit of the phase B winding, excite the phases A and C of the transformer and measure the losses.

The third experiment - they carry out a short circuit of the phase C winding, excite the phases A and B of the transformer and measure the losses.

A short circuit of the winding of any phase is carried out at the corresponding terminals of any of the transformer windings (higher medium or low voltage).

Losses and open circuit current at low voltage are measured in order to compare them with the results of similar measurements during operation; this method has large errors in the calculation of technological losses, due to large errors in the conversion of these losses to the real voltage of the network.

On the other hand, in such tests it is necessary to carry out a large number of switching windings, which increases the measurement time.

Thus, to measure the real losses and open circuit current of power transformers, an autonomous regulated source of alternating voltage is required.

Under stationary conditions, when measuring losses XX, voltage regulation at the input of the tested power transformer is performed by an induction voltage regulator.

Known induction voltage regulators, which are designed for smooth regulation of voltage at a load over a wide range with a constant voltage of the supply network (see pages 584-585: Fig. 29.2. Voldek AI Electric machines / Textbook. L .: Energy, 1978 . - 832 p., Ill.).

These regulators are used in many industries, including for testing power transformers. They are asynchronous machines with a locked phase rotor, in which using the rotary device you can change the position of the rotor relative to the stator. In induction controllers, the summation of the primary and secondary voltages occurs, while the change in the phase of the emf of the secondary winding, which occurs when the rotor is turned, causes a change in voltage on the regulator load.

The disadvantage of induction regulators is that for their operation in the field, an autonomous source of electrical energy is required.

A device is known for measuring current and idling losses of power transformers at a low excitation voltage, comprising a source of controlled alternating voltage, with which phases of the low-voltage winding of the power transformer "a-b", "b-s", "a-s" are alternately excited measuring instruments connected to it using connecting wires (see US Pat. RU 2282862 G01R 31/06. Device for measuring current and idle losses of power transformers at low voltage. Declaration. 02.21.2005. Publish. 08.27.2006. Bull. No. 24).

The listed methods and devices for measuring current and idle losses of power transformers provide for the presence of a stationary network, an autotransformer or an induction regulator for voltage regulation, which is not acceptable for use in the field.

On the other hand, when testing the windings of power transformers at a low voltage, and when recalculating the results obtained to the rated voltage, large errors occur.

The technical result is to increase the accuracy of measuring real idle losses of power transformers for calculating and substantiating the standards of technological losses of electricity during transmission through electric networks.

The technical result is achieved by the fact that in the inventive method for measuring losses and open circuit current of power transformers in the field, providing for a voltage change on the low voltage winding of the transformer with an open high voltage winding, according to the invention, an autonomous asynchronous generator with excitation capacitors is used as an adjustable voltage source, the output voltage which is stepwise regulated within 70 ÷ 110% of the rated voltage by switching cond nsatorov regulation during the transition through the switching voltage "zero", carried out three-phase contact-free electronic switches controlled through optocoupler input decoder and a multiposition switch.

The method is implemented using a device containing a controlled voltage source, connecting wires, a measuring device, according to the invention, a self-contained asynchronous generator is used as a controlled voltage source, the phases of which are connected with excitation capacitors, output contacts, three-phase contactless electronic switches in the form of optoelectronic three-phase AC relays with phase control of the switched voltage through "zero" connected by outputs to the regulation capacitors, and about Tron inputs to the DC source via the decoder and selector switch, and the test power transformer by means of connecting wires multifunction measuring device is connected to the output terminals of the asynchronous generator.

The novelty of the proposed proposal is due to the fact that in the inventive method for measuring losses and open circuit current of power transformers in the field, an autonomous asynchronous generator with field capacitors is used as the source of controlled voltage, the output voltage of which is stepwise regulated within 70-110% of the nominal voltage by switching capacitors regulation when switching switched voltage through "zero", carried out by a three-phase contactless electronic and keys controlled via optocoupler inputs with a decoder and a multi-position switch.

According to the scientific, technical and patent literature, the authors are not aware of the claimed combination of features aimed at achieving the task, and this solution does not follow clearly from the prior art, which allows us to conclude that the solution corresponds to the level of the invention.

The proposed technical solution is industrially applicable, since it is workable, and its use in industry is proposed.

To test the method for measuring losses and idling current of power transformers in the field, a special stand was made in the laboratory of the Department of Electric Machines and Electric Drives of KubSAU to test the operation of the regulated voltage source, which consists of a special design asynchronous generator (AG) and a drive motor. The AG was made on the basis of an induction motor of type 4A112M2UZ (P _n = 7.5 kW, n ₀ = 3000 rpm). DC drive motor (DCT) of type 2PN132MUHL4 (P _n = 10.5 kW, U _n = 220 V, U _n = 2500 ÷ 3500 rpm) and AG connected the “shaft” to the “shaft” through an elastic coupling and secured to the base of the stand. The rotation speed of the drive DCB is regulated by changing the voltage at the armature of the DCB with a DC source of the required power.

Checking the method of measuring losses and open circuit power transformers in the field is performed according to the scheme (Fig. 1 and 2). According to the calculation results, the excitation capacitance is 2-56 μF, regulation capacitors: 9-10 μF, 10-20 μF, 11-30 μF. Solid-state relays with a rated current of 25 A and a permissible voltage of 440 V were used as three-phase contactless electronic relays. In tests, the asynchronous generator was rotated by a drive motor at a speed of 3010 min ^-1 . After excitation of the generator by the switch 16, control capacitors 9-11 were connected in series. The test results are shown in table 1 and in the graph of FIG. 3.

Table 1. Test results of a regulated voltage source Switch position 16 17 eighteen 19 twenty 21 22 23 24 The connected capacity, microfarad 56 +10 +20 +30 +40 +50 +60 +70 Generator voltage, V 270 310 340 376 398 410 412 418

Analyzing the data of table 1 and the graph in FIG. 3, we can conclude that the adjustable voltage source meets the specified parameters: the voltage is regulated stepwise within 70 ÷ 110% of the nominal voltage (380 V). Therefore, such a source can be used to measure the losses and idle current of power transformers in the field, using an internal combustion engine as a diesel generator.

The essence of the invention, which implements a method for measuring losses and open circuit current of power transformers in the field, is explained in the diagrams in FIG. 1 and 2.

A device for measuring losses and open circuit current of power transformers in the field (Fig. 1) contains an autonomous asynchronous generator (AAG) 1, the phases of which are connected to excitation capacitors 2, output contacts 3 (A, B, C), a multifunction measuring device 4 connected to the studied power transformer 5, three-phase electronic switches 6, 7, 8, connected by outputs to regulation capacitors 9, 10, 11, and optocoupler inputs 12, 13, 14 with a decoder 15 and a multi-position switch 16 having contacts 17-24.

As three-phase switches 6–8, three-phase electronic alternating current relays (solid state relays) are used with phase-controlled switching voltage through “zero”, for example 5P36.30TM1, or similar (see http://www.proton-impyls.ru).

As a multifunctional measuring device 4, electric power quality meters Pecypc-UF2M, ERIS-KE.02 of Russian manufacture or imported electric power quality analyzers such as AR.5L, Fluke-1760 and the like are used.

A device for implementing the method of measuring losses and open circuit power transformers in the field works as follows. A power transformer 5 with a low voltage winding (with an open high voltage winding) is connected through a multifunction measuring device 4 to the output contacts 3 (A, B, C). The multi-position switch is installed in position 17. At the same time, the current does not pass through the diodes VD1 -VD12 of the decoder 15 and the optocoupler inputs 12, 13, 14 of the three-phase electronic switches 6, 7, 8, the electronic switches 6, 7, 8 are closed and the regulation capacitors 9, 10 11 are not connected to AAG 1.

After starting the drive motor (not shown in the diagram), the AAG self-excites itself from the excitation capacitors 2. The capacitance of these capacitors is selected so that at idle the AAG has a minimum voltage value. This voltage through a multifunctional measuring device 4 is supplied to the studied power transformer (CT) 5 and will be the first point of the idling characteristic CT. The multi-position switch 16 is installed in position 18. In this position, current passes through the optocoupler input 12, the three-phase electronic switch 6 is turned on, and connects the regulation capacitors 9 to the AAG stator. Its voltage increases (point 18 in Fig. 3). The multifunctional measuring device 4 records the voltage in three phases, the consumed current, power and other parameters of which are stored in the device memory or on an external storage device.

By changing the number of the closed contact of switch 16, control capacitors 6–11 with a total capacity of 70 μF are connected to the stator of the asynchronous generator, which causes a change in the voltage at the generator output. Thus, the idle characteristic of the power transformer 5 is obtained.

The advantages of the proposed method for measuring losses and idling current of power transformers in the field and devices for its implementation are as follows.

1. Switching of capacitors is performed at the moment the sinusoid passes through zero. Therefore, there are no current surges, which is typical for turning on capacitors under voltage, there are no switching overvoltages that can damage the source itself and the high-voltage winding of the tested power transformer.

2. Asynchronous generator due to the symmetrical short-circuited rotor winding generates a sinusoidal voltage symmetrical in three phases with a low level of harmonic distortion.

Claims (2)

1. A method for measuring losses and idling current of power transformers in the field, providing for a voltage change at the transformer primary winding with an open secondary winding, characterized in that a self-contained asynchronous generator with field capacitors is used as a source of controlled voltage, the output voltage of which is stepwise regulated in limits 70 ÷ 110% of the rated voltage by switching the regulation capacitors when switching the switching voltage through "zero", carried out by three-phase contactless electronic keys controlled through optocoupler inputs by a decoder and a multi-position switch. 2. The device for implementing the method according to claim 1, containing an adjustable voltage source, connecting wires, a measuring device, characterized in that an autonomous asynchronous generator is used as an adjustable voltage source, the phases of which are connected with excitation capacitors, output contacts, three-phase contactless electronic keys in the form of optoelectronic three-phase AC relays with phase control of the switched voltage through "zero" connected by outputs to the regulation capacitors, and optocoupler inputs with a direct current source through a decoder and multi-position switch, and the tested power transformer is connected to the output contacts of an asynchronous generator through connecting wires through a multifunctional measuring device.

Images