RU2290653C2 - Mode of evaluation of parameters of the process of switching of fast-acting regulator of contactor's contacts under loading in a three-phase transformer without its opening and an arrangement for its fulfillment - Google Patents

Abstract

FIELD: the invention may be used in power engineering at complex inspection of power transformers, at balancing and commissioning, preventive, periodical tests for diagnostics of faultiness of regulators under loading.

SUBSTANCE: the mode of evaluation of parameters of the process of switching of the contactor's contacts of the fast-acting regulator (with active resistance) under loading of the power three-phase transformer according to a scheme including inductance of the winding of the power transformer without opening and discharging transformer oil. The mode of execution proposes measuring of the duration of the process switching, the duration of the so called "bridge" and also duration of presence of major contacts in the contactor's arms in closed and open position in accordance with the current curve. The arrangement for fulfillment of the mode has a three-channel source of constant voltage, a three-channel digital oscillograph, a connecting four-wire cable, a tested power three-phase transformer with regulators under loading.

EFFECT: development of the mode of all-season diagnostics of contactor's contacts of regulators under loading of a power three-phase transformer without its opening eliminates possibility of soiling of the environment , reduces man-hours a at its execution, allows to evaluate parameters of the process of switching contactor's contacts without discharging transformer oil and also creation of an arrangement for its execution allowing automatically synchronize launching of an oscillograph with the beginning of the process of switching of contactor's contacts, execute automatic processing of oscillograms and possibility of creating a data base of these oscillograms in an electronic form.

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Description

Technical field

The invention relates to methods for diagnosing power transformers in the electric power industry, namely, electrical measurements of the process parameters of switching contacts of a contactor (with active resistances) of a high-speed regulator under load (on-load tap-changer) without opening it and without draining the transformer oil.

It can be used in the energy sector for complex inspections of power transformers, during commissioning, preventive, periodic tests of on-load tap-changers, for the diagnosis of its malfunctions, for example, such as spontaneous disengagement of the contactor mechanism of PC devices.

For three-phase power transformers, a method for evaluating the process of switching contacts of a contactor of a high-speed controller under load without opening and draining transformer oil and a device for its implementation is proposed.

The method for evaluating the parameters of the dynamic process of switching the contacts of the on-load tap-changer involves the measurement of the current curve: duration of the switching process; the duration of the so-called “bridge”; durations of being in the closed and open positions of the main contacts in the arms of the contactor. The method also allows the current curves to determine the difference in switching contacts of the on-load tap-changer for three phases.

State of the art

A known method for evaluating the process of switching contactor contacts of a high-speed controller under load (with active resistances) on-load tap-changer of a three-phase power transformer, including oscillography of the contactor contact currents without taking into account the influence of the inductance of the winding of the power transformer with opening the on-load tap-changer and draining the transformer oil [Collection of methodological manuals for monitoring the state of electrical equipment . Section 2: Methods for monitoring the status of power transformers, autotransformers, shunt and arcing reactors. M., ORGRES, 1997, p.100].

However, this method requires opening the cover of the on-load tap-changer tank and draining the transformer oil to connect the oscilloscope inputs to the connection nodes of the voters, contacts of the contactor and branches with active resistance of the on-load tap-changer, since the contactor contacts are structurally located in the casing of the on-load tap-changer tank filled with transformer oil. This method requires the involvement of specially trained personnel to connect the oscilloscope to the conclusions of the contacts of the on-load tap-changer. In addition, the discharge of transformer oil is a time-consuming process and for its implementation it is necessary to have a specially prepared clean overall drained tank, oil pump, hose for pumping oil, etc., as well as additional personnel. When draining and subsequent pouring oil, its dielectric properties and environmental pollution may be degraded, as well as insulation resistance of the bakelite cylinder of the on-load tap-changer tank. In addition, at high humidity and in conditions of negative ambient temperatures, oscillography of the contacts of the contactor is practically impossible.

Therefore, the oscillography of high-speed on-load tap-changers with oil drain requires significant material resources and labor, and is only practicable in the warm season under favorable weather conditions.

Usually, multichannel oscilloscopes of the types H11, H13 and the like, or magnetoelectric oscilloscopes with ultraviolet recording on a photographic tape, are used as a device for oscillating the contacts of the on-load tap-changer of a power three-phase transformer. These devices have several disadvantages. These include the inconvenience of oscillography, which is the difficulty in synchronizing the start of the oscilloscope with the beginning of the contactor contact switching process, which entails unnecessary waste of photo paper or photo tape. Another disadvantage is the manifestation of waveform images on photo paper in a specially equipped laboratory. Among the disadvantages of these devices is the impossibility of creating a database in electronic form and the manual processing of waveforms.

SUMMARY OF THE INVENTION

The objective of the invention is the creation of a method of all-weather diagnosis of contacts of the on-load tap-changer contactor of a power transformer without opening it, eliminating the possibility of environmental pollution, reducing labor costs during its implementation, allowing to evaluate the parameters of the contactor switching process without draining transformer oil, and also creating a device for its implementation, allowing Automatically synchronize the start of the oscilloscope with the beginning of the contactor contact switching process, by Automatic processing of waveforms and the possibility of creating a database of waveforms in electronic form.

The problem is solved due to the fact that the method of oscillographing the currents of the contactors of the on-load tap-changer is performed without opening the on-load tap-changer tank and draining the transformer oil relative to the high-voltage winding of the power transformer, to which the on-load tap-changer is connected, followed by analysis of the waveforms, and the parameters of the switching processes of the contactors of the on-load tap-changer are evaluated by breaking the current waveform into five consecutive time intervals with increasing numbering, and I interval corresponds to the time before and the operation of the contacts of the contactor, the II interval is the time of the current passing through the active resistance of the first arm of the contactor, the III interval is the time of the parallel operation of the active resistances of the first and second arms of the contactor, the IV interval is the time of passing the current through the active resistance of the second arm of the contactor, V the interval is the time after switching contactor contacts. The boundary between I and II intervals is defined as the time at which the current begins to decline, the boundary between IV and V intervals is the time corresponding to the minimum current value, while the interface between II and III, as well as between III and IV intervals, is changing the time constant of the free transient component in the RL model of a three-phase transformer winding. To implement this method, it is proposed to use a device containing a three-channel digital oscilloscope with six opposite input terminals, of which three negative terminals are connected by connecting wires to the hardware terminals of the inputs of the three phases of the power transformer winding, and three positive terminals, respectively, with the positive terminals of the voltage channels of the DC voltage source whose common terminal is connected to the neutral terminal of the transformer, the negative input terminals of the current channels The digital oscilloscope and the common clamp of the DC voltage source are connected respectively to the hardware clamps of the inputs of the three phases and the neutral clamp of the winding of the power transformer with a four-wire cable, which has a different color marking of the wires. The three-channel digital oscilloscope is additionally equipped with a current sensor block, a digital registration trigger, a non-volatile memory block, a liquid crystal display, a communication port with a computer and a computing unit that automatically measures the average value of the phase currents of the windings by digital discrete values, and automatically synchronizes the registration start when switching on-load tap-changer . The three-channel DC voltage source additionally includes overvoltage-protective circuits, a unit for simultaneous regulation of the channel output voltages and channel-by-channel automatic protection against high currents.

Brief Description of the Figures

Figure 1 shows the structural diagram of an oscilloscope device for switching contacts of a contactor of a high-speed on-load tap-changer of a power transformer, combined with the connection diagram. The circuit contains a three-channel constant voltage source (1), a three-channel digital oscilloscope (2). four-wire connecting cable (3), tested three-phase power transformer with on-load tap-changer (4).

Figure 2 shows the structural diagram of a three-channel digital oscilloscope (2), including current sensors (2.1), analog-to-digital converter (2.2), non-volatile memory unit (2.3), computing unit (2.4), digital recording start unit (2.5), liquid crystal display (2.6), communication port with a computer (2.7).

Figure 3 shows a simplified equivalent circuit of the phase-neutral circuit of the power transformer (4) relative to high-voltage bushings with a connected DC source. The circuit contains a direct current source (1) with internal EMF E and current-limiting resistance R ₀ , an on-load tap-changer (4.1), depicted as a five-position switch SA and on-load tap-changers R ₁ and R ₂ , terminal clamps for phase-neutral AN inputs, a winding power transformer (4.2) with inductance L and resistance R _f .

Figure 4 shows an example of combined waveforms of currents in the contacts of the on-load tap-changer obtained by oscillography according to a simplified equivalent circuit for arbitrary parameters by the proposed method — curve f ₁ (t) and, in a circuit without inductance L, curve f ₂ (t).

Figure 5 shows examples of waveforms of phase currents of the transformer TDN-16000/110 with the factory number 13924, manufactured in 1983 at a transformer plant in Togliatti, with on-load tap-changer type RS-4. Oscillograms were obtained with the simultaneous three-phase switching of on-load tap-changer voters from an even to an odd position. They are shown combined for the existing and proposed method of oscillography, where ia, ib, ic are the currents of phases "A", "B", "C", changing with time t.

Disclosure of invention

To determine the parameters of the switching process of the contacts of the on-load tap-changer, the currents are oscillographed and the obtained oscillograms are analyzed.

Oscillography according to the circuit shown in figure 1, is as follows. The operator translates the on-load tap-changer with an electric drive, let's say to position 1. After turning on the three-channel DC voltage source 1 to the power supply network, the current passes through the current channels of the three-channel digital oscilloscope 2, the current channels of the three-channel digital oscilloscope 2 and the four-wire cable 3. In this case, the current rise time is about 10-15 minutes.

A three-phase digital oscilloscope (see figure 2) simultaneously measures currents with current sensors 2.1, converts analog values to digital using the analog-to-digital conversion unit 2.2. Next, the computing unit 2.4 calculates the constant components of the currents in each of the three phases by averaging them and provides the obtained values on the LCD 2.6. This cycle "measurement-calculation-visualization" is repeated with an interval of 1 second. Before the currents are established in the winding phases, the operator observes a smooth increase in current on the LCD. When currents are established in the phases of the transformer winding, the operator sends a start command using the digital recording start block 2.5. In this case, the computing unit determines three settings for the operation of three triggering organs for each of the current channels of the digital oscilloscope, taking them somewhat lower than the steady-state currents in the corresponding phases. Next, the digital oscilloscope enters a standby state.

After that, the operator with the help of an electric drive puts the on-load tap-changer into position 2. At the moment of switching the contacts of the contactor, phase-by-phase reduction of currents occurs. In this case, the triggering organs of the digital oscilloscope are triggered and it registers the phase currents of the transformer winding in the non-volatile memory unit - 2.3.

3 minutes after switching, when the currents in the phases are established, the digital oscilloscope performs the next measurement of phase currents and selects new settings for the triggering of trigger elements. Further, 5 minutes after the last switch, the operator transfers the on-load tap-changer with the help of an electric drive to the next position.

Such cycles "measuring currents - selecting the settings of the starting organs - switching on-load tap-changers with writing currents to non-volatile memory - waiting for the current to be established" are performed for several positions of the on-load tap-changers in the direction of increasing and decreasing the position of the selector.

The operations of the cycle "measuring currents - selecting the settings of the starting organs" perform automatic tuning to the changes in the steady-state current when switching on-load tap-changers, due to a change in the active resistance of the winding, namely the addition or exclusion of active resistance between the positions of the selector. This provides auto-triggering of a digital oscilloscope trigger.

To accelerate the establishment of current after turning on the constant voltage source, an increase in the output voltage of its channels by the operator can be used with the help of output voltage control circuits. At the same time, an increase in the steady-state current value also makes it possible to increase the measurement accuracy, since these measurements are made in that part of the measuring range where the measurement error is minimal.

After the end of the oscillography of the currents for several positions of the on-load tap-changer, the data from the non-volatile memory unit through the communication port - 2.7 is transferred to a personal computer, where the latter uses multifunctional capabilities.

When disconnecting a three-channel DC voltage source from the supply network, special protective circuits do not allow current interruption in the phases of the transformer winding, thereby eliminating switching overvoltages caused by disconnecting circuits with a large inductance of the transformer winding.

The wires of the four-wire cable have different color coding, which simplifies the process of assembling the connection scheme in the field at the substation.

In addition, the connection using a long cable allows you to place a workplace (where a three-channel digital oscilloscope and a three-channel constant voltage source are located) for making measurements at ground level in the immediate vicinity of the on-load tap-changer, that is, eliminates work at heights, resulting in increased safety works.

The analysis of the obtained waveforms having a piecewise analytical form is based on the use of the phase-zero model of the power transformer shown in Fig. 3, in which the high-voltage winding is modeled in series with the inductance L and the active resistance R, and the on-load tap-changer is modeled with a five-pole switch SA and active resistances R ₁ and R ₂ , alternately connected to it. One on-load tap-changer corresponds to a sequential translation of the switch positions into five positions: “a-b”; Bc; “Cd”; "De";"Ef" (see figure 3).

For the proposed RL-model, the instantaneous value of the oscillographic current — the current of the source with constant EMF — can be found by solving linear differential equations of the first order for each switch position.

Before the on-load tap-changer starts, when the switch is in the “a-b” position, the steady-state current will be equal to:

Transient current when switching from position “a-b” to position “b-c”:

(hereinafter, the time t - is counted from the moment the corresponding switching interval begins).

When switching from position “b-c” to position “c-d”:

where R ₃ is the resistance in the "bridge" position, and:

and A ₂ is the integration constant, which is found from the condition of continuity of the current in the inductance (all subsequent integration constants are found similarly).

Transient current when switching from the "cd" to the "de" position (taking into account the equality of the shunt resistances R ₁ and R ₂ ):

When switching from d-e to e-f:

As an example, figure 4 shows the waveform plotted for arbitrary model parameters and switching times, provided R ₁ = R ₂ and R ₃ = 0,5R ₂ .

The analysis of the waveform for determining the parameters of the switching process of the on-load tap-changer contacts is based on the obvious properties of the resulting curve: the curve is piecewise continuous, consisting of 5 intervals; the switching process of the on-load tap-changer contacts starts at the moment when the current curve decreases exponentially (concave), and ends at the minimum current value, after which the current curve exponentially increases (convex); the time constants of the oscillography curve before the “bridge” τ ₂ and after it τ ₄ during the switching process are equal, since the on-load tap-changer consists of symmetrical arms:

In the "bridge" position, the time constant τ _{3 is} calculated from the relation:

Obviously, τ _{3 is} greater than the time constants τ ₂ and τ ₄ . Therefore, at different intervals, the rate of change of current is different and the parameters of the switching process of the on-load tap-changer contacts are determined in the following order: there are four characteristic points (t ₁ , t ₂ , t ₃ , t ₄ ) waveforms: the interval between points (t ₁ ) and (t ₄ ) sets the switching time, and the interval between points (t ₂ ) and (t ₁ ) characterizes the duration of contactor contacts in the position of the so-called "bridge".

Finding the characteristic points of the waveform - the boundaries of the intervals of homogeneous sections of the transient current curve is carried out in the following sequence: t ₁ - is determined as the time at the end of the first interval of the largest current; t ₄ - as the moment of the smallest current value, which is the boundary value of the end of the fourth interval; finally t ₂ and t ₃ , are found similarly as moments where the time constants of the current curve of the switching contacts of the on-load tap-changer contactor change abruptly (abruptly). After that, the switching duration t _lane = t ₄ -t ₁ is calculated, the time of the duration of the "bridge" t _bridge = t ₃ -t _{2 is found} . Next, the switching time of the main contacts (t _pk ), on-load tap-changer contactor t _pk1 = t ₂ -t ₁ and t _pok2 = t ₄ -t _{3 is determined} . Note that in the branches with these contacts there is no active resistance (see figure 1).

The main advantages of the proposed method and device for its implementation are: reducing material costs and time for preparing the implementation of the oscillographic process, a simple measurement scheme, eliminating the likelihood of contamination of the dielectric fluid and the environment, the ability to determine the correct operation of the contactor contacts under any environmental conditions, the exception of specially trained personnel to connect the oscilloscope to the conclusions of the contacts of the on-load tap-changer, determination and evaluation of the main x contacts switching process parameters contactor RPN automatically synchronize the trigger on the start of the process of switching the contacts of the contactor, the ability to create a database in electronic form.

Execution example

To determine the parameters of the process of switching contacts of the on-load tap-changer contactor of a power three-phase transformer of the type ТДН-16000/110 (with the resistance of the high-voltage winding in the second position of the on-load tap-changer R _f = 2.67 Ohms) with a regulator under load of the type RS-4 (with active resistances R ₁ = R ₂ = 8 Ohms) on a sub-station. Zavolzhskaya of the Northern Electric Networks enterprise of Chuvashenergo OJSC uses a 4 × 2.5 PVA cable 12 meters long. The digital oscilloscope includes a high-speed microprocessor, non-volatile memory on an ATmel AT45DB161 chip, a PowerTip PG320240 graphic liquid crystal display, and an RS-232 serial port. The circuits that exclude the interruption of the current of a three-channel DC source when the power is disconnected from the mains consists of three high-speed Schottky diodes of type 1N5822, connected by anodes to a common terminal to a DC source and cathodes to its channels. The DC voltage source provides simultaneous regulation of the three channels of the output voltage in the range of 2-24 V and excludes currents of more than 3 A.

From the obtained oscillograms of Fig. 5, it was found: t ₁ = 5 ms, t ₂ = 25 ms, t ₃ = 30 ms, t ₄ = 45 ms, from which the switching parameters of the on-load tap-changer contactor contacts were calculated: total switching duration t ₄ -t ₁ = 45-5 = 40 ms, the duration of the “bridge” t of the _bridge = t ₃ -t ₂ = 30-25 = 5 ms, the duration of the switching of the main contacts in the arms of the contactor is t ₂ -t ₁ = 25-5 = 20 ms and t ₄ - t ₃ = 45-15 ms = 30 ms.

Claims (6)

1. A method for evaluating the parameters of the switching process of the contacts of the contactor of a high-speed (with active resistances) regulator under load (on-load tap-changer) of a power three-phase transformer, including oscillography of the contactor current, characterized in that the oscillation of the current of the contacts of the on-load tap-changer is performed without opening the on-load tap-changer and draining the transformer oil relative to the high-voltage windings of the power transformer to which the on-load tap-changer is connected, followed by analysis of the waveforms and parameter estimation, moreover, the evaluation of pairs The tap changer contactor contact switching process is measured by dividing the current waveform into five consecutive time intervals with increasing numbering, with I interval corresponding to the time before the contactor starts to work, II interval - current passage time along the active resistance of the first contactor arm, III interval - the time of parallel operation of the active resistances of the first and second arms of the contactor, the IV interval is the current passing time along the active resistance of the second arm to a tactor, the V interval is the time after switching the contacts of the contactor, and the boundary between I and II intervals is defined as the time at which the current begins to decline, the boundary between IV and V intervals is the time corresponding to the minimum current value, while the interface between II and III, as well as between the III and IV intervals, are found by the abrupt change in the time constant of the free component of the transient in the RL model of the winding of a three-phase transformer. 2. A device for evaluating the parameters of the contact switching process of a high-speed (with active resistance) contactor on-load tap-changer of a three-phase power transformer, containing a three-channel DC voltage source with positive clamps and common negative poles with a common clamp, the channels of which are connected through current-limiting resistances and shunts of the oscilloscope loops using connecting wires to the connection nodes of the voters, the first and second shoulder contacts of the contactor and the branches with the active the resistance of the on-load tap-changer of the corresponding phases of the three-phase transformer, and the common terminals of the contacts of the on-load tap-changer of each phase are connected to the common terminal of the three-channel DC voltage source, characterized in that the oscilloscope is made in the form of a three-channel digital oscilloscope, and the channels of the three-channel constant voltage source through three current channels of the digital oscilloscope with six opposite input terminals, of which three negative terminals are connected by wires to the hardware terminals of the inputs of three phases of coils of the power transformer, and three positive terminals are connected to the positive terminals of the voltage channels of the constant voltage source, whose common terminal is connected to the neutral terminal of the transformer. 3. The device according to claim 2, characterized in that the multichannel digital oscilloscope is additionally equipped with a current sensor unit, a digital recording start unit, a non-volatile memory unit, a liquid crystal display, a communication port with a computer and a computing unit that automatically calculates the average value of the windings phase currents by digital discrete values, to automatically synchronize the start of registration when switching on-load tap-changer, to determine the parameters of the process of switching contacts of the contactor P Mon on the built-in program. 4. The device according to claims 2 and 3, characterized in that the three-channel constant voltage source additionally includes overvoltage-protective protective circuits, a unit for simultaneously controlling the output voltages of the channels and the channel-by-channel automatic protection against high currents. 5. The device according to claims 3 and 4, characterized in that the negative input terminals of the current channels of the digital oscilloscope and the common terminal of the DC voltage source are connected respectively to the hardware terminals of the inputs of the three phases and the neutral terminal of the winding of the power transformer with a four-wire cable. 6. The device according to claim 5, characterized in that the four-wire cable has a different color marking of all wires.

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