RU2244972C1 - Differential current transformer - Google Patents

Abstract

FIELD: electrical engineering; protection against electric shock, current leakage, overload and short-circuit currents.

SUBSTANCE: proposed differential current transformer that may be found useful in off-operation protective gear has toroidal core of magnetically soft material that carries secondary winding. Its primary winding in the form of two line conductors is disposed in core port in diametric opposition. Secondary winding has two sections, two equally wound coils of one of them being differentially connected; each of these coils has n turns with primary winding conductors tightly abutting against them. Two equally wound coils of other section having m turns per coil are connected in series and disposed at 90 deg. to primary winding conductors.

EFFECT: provision for electrical isolation of differential current signal proportional to leakage current and unbalance signal proportional to load.

1 cl, 4 dwg

Description

The present invention relates to electrical engineering and can be used to protect a person from electric shock, fire protection against thermal manifestation of leakage currents, as well as overload and short circuit currents in automated control systems and protective shutdown devices that respond to differential (differential) current and load currents.

Currently, differential current transformers are used in electrical engineering (Recommendations for the design, installation and operation of electrical installations of buildings when using residual current circuit breakers. M .: MEI Publishing House, 2002, pp. 19-27, 66-67), which are characterized by the presence of a signal unbalance (interference) in the useful signal, proportional to the leakage current or the differential current. Such transformers contain a toroidal soft magnetic core with a uniform or concentrated secondary winding and a primary winding randomly located in the window of the transformer core, consisting of conductors of the supply network.

In this design of the transformer, the magnetic coupling of the primary winding conductors with the secondary winding conductors is random, therefore, the sum of their flux linkages with the secondary winding conductors is also random, and an unbalance signal is induced in the secondary winding, which can differ not only in magnitude but also in phase . Therefore, when a leakage current appears, the signal at the output of the secondary winding of the differential current transformer can increase in some cases, and decrease in others. This limits the minimum threshold for tripping devices and restricts their use in electrical installations with peak or inrush currents, since the unbalance signal is proportional to the load current, and this leads to false, unauthorized tripping of devices of protective tripping. The trigger element (threshold element) in the residual current circuit breakers is usually performed on sensitive direct-acting magnetic-electric relays or electronic components, and the actuator includes a power contact group with a drive mechanism.

The unbalance signal is reduced in a differential current transformer (Shchipunov N.V. “Protective shutdown”, M .: Energia, 1968, pp. 81-85), containing a toroidal core made of soft magnetic material with a uniformly wound secondary winding, a primary winding consisting of from phase conductors of the supply network located in the core window, and a screen of magnetic material mounted between the primary and secondary windings.

As in the differential current transformers described above, in this structural embodiment of the transformer, the unbalance signal cannot be fully compensated. The screen closes the scattering fluxes of the primary winding, reducing their adhesion to the secondary winding, and hence the unbalance signal. However, this leads to a decrease in sensitivity and leakage currents, it also works unstably in the presence of peak and inrush currents, which limits the protection of powerful power consumers.

The closest differential current transformer in technical essence to the present invention is a differential current transformer (RF patent No. 2060568, class H 01 F 38/28, 05/20/1996), containing a toroidal core made of soft magnetic material with a uniformly wound secondary winding, primary n -phase winding located in the core window, and a screen of soft magnetic material, installed between the primary and secondary windings. Each phase of the primary winding of the transformer is made in the form of sections, each of which consists of two identical, parallel-connected conductors, evenly spaced around the circle and alternating between themselves in the order of the phases, so that the angle between the phase conductors of the adjacent sections is 180 ° / n. The location of the windings and the screen is fixed by the holder of electrical insulation material. The screen is designed so that it allows you to change the electromagnetic coupling between the primary and secondary windings when the load power changes to normalize the unbalance signal.

The principle of operation of this transformer is similar to the principle of operation of known feed-through transformers. However, in it, due to the splitting of the phase conductors, scattering fluxes are created, which at each moment of time are vectorly opposite to each other and mutually compensated regardless of the load asymmetry. This allows reducing the unbalance signal by more than an order of magnitude, increasing the sensitivity of residual current circuit breakers, and protecting more powerful electrical receivers with inrush and peak currents.

However, such differential current transformers exhibit a change in the unbalance signal with changes in the load asymmetry, since this changes the orientation of the elliptical rotating magnetic scattering field relative to the asymmetric secondary winding, which occurs due to technological and structural errors and the entire magnetic system of the differential current transformer as a whole .

In addition, the considered differential transformers do not provide information about the currents of the load, overload and short circuit.

The basis of the present invention is the creation of a differential current transformer that provides galvanic separation of the differential current signals proportional to the leakage current and the unbalance signal proportional to the load due to the structural design of the primary and secondary windings, in which the primary winding creates the main stream proportional to the leakage current, and scattering fluxes proportional to the load currents.

The problem is solved in that in a differential current transformer containing a toroidal core of soft magnetic material with a secondary winding wound on it, a primary n-phase winding in the form of phase conductors located in the core window, and a conductor holder, according to the invention, the primary winding is made of two network conductors located diametrically opposite, and the secondary winding consists of two sections, two equally wound windings of one of which are connected in the opposite direction, and each winding Single has n windings, which seal tightly the primary winding conductors, wherein two identically wound with m-winding turns in each winding of the other sections are connected in series and are arranged at an angle of 90 ° with respect to the conductors of the primary winding.

The problem is also solved by the fact that in another embodiment of the proposed differential current transformer, the primary winding is made of three conductors of a three-phase network located at an angle of 120 ° relative to each other, the secondary winding consists of sections, while three p equally wound windings of the first section are connected in series through 120 ° / r and each winding has n turns, to which the conductors of the primary winding are tightly adjacent, and six equally wound windings with m turns in each pair They are diametrically opposite and are combined into three sections, in each of which the windings are connected counterclockwise, one of the windings in each section tightly adjoining the corresponding conductor of the primary winding. In this case, either one neutral conductor or three neutral conductors of the same cross section, located in the middle between the phase conductors and tightly adjacent to the core, can be passed through the holder.

The sections of the secondary windings are connected in such a way that a signal proportional only to the leakage current is induced in some sections of the secondary winding, and signals proportional to the phase currents of the load are induced in other sections of the secondary winding. These signals are galvanically separated and independent of each other. This will make it possible to create protective disconnecting devices with greater sensitivity to leakage currents, selective, that is, multi-level, without false trips, and to expand their functionality, namely: to respond to overload currents and short circuit currents.

In the future, the invention is illustrated by specific examples of its implementation and the accompanying drawings, in which:

figure 1 depicts a diagram of the inclusion of a differential current transformer in a single-phase or two-phase network without a neutral conductor;

figure 2 is a diagram of the inclusion of a differential current transformer in a three-phase network without a neutral conductor at p = 1;

figure 3 is a diagram of the inclusion of a differential current transformer in a three-phase network with one neutral conductor located in the center of the core at p = 1;

figure 4 - the same as in figure 2, but with three neutral conductors located in the middle between the conductors of the primary winding and equally adjacent to the core.

The differential current transformer according to the invention comprises a toroidal core 1 (Fig. 1) of soft magnetic material with a secondary winding wound on it, consisting of two sections. Two identical, evenly wound windings 2 of one section are connected in the opposite direction and each winding 2 has n turns to which two primary conductors 3 of the primary winding are located horizontally. Two other identical windings 4 of another section of the secondary winding, each of which has m turns, are uniformly wound perpendicular to the horizontal axis on the core 1. The windings 4 are connected in series and are located at an angle of 90 ° with respect to the conductors 3. All windings 2 and 4 have the same direction of winding the turns. To impart rigidity to the design of the transformer, a holder 5 made of an insulating material is installed in the window of the core 1.

Figure 2 presents a diagram of the inclusion of a differential current transformer in a three-phase network without a neutral conductor, which allows to separate a leakage signal proportional to the leakage current and unbalance signals (interference) proportional to the load currents in phases.

The differential current transformer contains a toroidal core 6, a primary winding of three conductors 7 of a three-phase network, located in a holder 8 of electrical insulation material at an angle of 120 ° relative to each other on the inner surface of the core 6. A secondary winding consisting of sections is wound on the core 6. Three identical, evenly wound windings 9 of the first section are connected in series and each winding has n turns, to which the phase conductors 7 of the primary winding tightly fit. Six equally wound windings 10 and 11 with m turns in each pair (winding 10 and winding 11) are diametrically opposed and are combined into three sections, in each of which windings 10 and 11 are connected counterclockwise, and winding 10 in each section is tightly adjacent to the corresponding phase conductor 7.

Figure 3 presents a diagram of the inclusion of a differential current transformer in a three-phase network with a neutral conductor, which performs the same functions as the differential current transformer in figure 2. It additionally contains a neutral conductor 12, passed through the center of the holder 8.

Figure 4 presents a diagram of a differential current transformer, similar to the circuit shown in figure 2, characterized in that it further comprises three identical neutral conductors 13, passed through a holder 8, located in the middle between the phase conductors 7 of the primary winding and equally adjacent to the core 1 .

The principle of operation of the proposed differential current transformer is as follows.

In the absence of a leakage current, the main magnetic flux in the transformer magnetic circuit is zero, since the phase currents are equal. But since the current flows through the conductors 3 (Fig. 1) of the primary winding, magnetic fluxes Фσ _{1 of the} scattering pulsate around them, the directions of which are shown in Fig. 1 and which induce the same emf interference e _n or imbalance proportional to the load current in the windings 2 The direction e _n is associated with the direction of the flows by the rule of the gimlet and in FIG. 1 are directed upward. If the windings 2 are connected in the opposite direction, then the signal 2e _{n is} obtained at the output, which is proportional to the load current.

When a leakage current appears, a flux _{m m is created} , which closes along the transformer’s magnetic circuit and, according to the direction adopted in Fig. 1, induces signals e _m proportional to the leakage current. In windings 2, they are mutually compensated, therefore, they do not affect the signal 2e _n in these windings. The windings 4 are connected in series and a signal 2e _m is generated at their output, proportional to the leakage current. The number of turns in each of the windings can be the same, it all depends on the ratio of the load current and leakage current. Since the magnetic resistance along the path in the air is much greater than the magnetic resistance along the path in the core 1, and the current in the conductors 3 is much greater than the leakage current, by varying the number of turns of the windings 2 and 4, an approximate equality of the signals e _n and e _m can be achieved. Thus, such a transformer makes it possible to separate a leakage signal proportional to the leakage current and an unbalance signal (interference) proportional to the load current.

This makes it possible, on the basis of such differential current transformers, to develop new protective disconnecting devices with advanced functionality that allow them to be configured for different load currents, protecting against overload and short circuit currents, change the sensitivity to leakage currents, observe selectivity conditions and not respond to starting and peak load currents. They can be performed on sensitive direct-acting magnetic-electric relays or electronic components.

These provisions of the galvanic separation of the signal can be used to protect electrical receivers in three-phase networks with symmetric and asymmetric loads.

Figure 2 presents a diagram of the inclusion of a differential current transformer in a three-phase network without a neutral conductor. In the absence of leakage current, the main magnetic flux in the transformer magnetic circuit is zero, since the sum of the currents in a three-wire network without a neutral wire is zero. But since phase currents flow through the conductors 7 of the primary winding, primary scattering fluxes Фσ ₁ pulsate around them with a network frequency, the directions of which are shown in FIG. 2 for the moment, primary scattering fluxes Фσ ₁ , the directions of which are shown in FIG. 2 for the time moment ωt = π / 6, which induces interference in the windings 9 of the EMF or e _n proportional to the load current in any operating mode - symmetric or asymmetric. If these windings 9 are connected in series, then the sum of the signals e _n from the flows Фσ ₃ will be equal to zero for any moment of time.

When a leakage current appears, a flux Φ _{m is created} , which closes along the transformer magnetic circuit, and, according to the direction adopted in Fig. 2, induces a signal e _m proportional to the leakage current in each of the windings 9, 10 and 11. They are summed up in the windings 9 and at the output of the series-connected windings 9 there is a signal 3 e _m , which does not depend on the values of the currents in the conductors 7 of the network, that is, on the load.

Он вращается с угловой скоростью ωt, замыкаясь по воздуху и магнитопроводу дифференциального трансформатора тока, сцепляясь с обмотками 10 и 11. На фиг.2 показано направление потока Фσ₂ для момента времени ωt=π/6 и направления е_n и e_m в каждой обмотке 10 и 11 от действия Ф_m и Фσ₂. Если теперь соединить каждую пару обмоток 10 и 11, находящихся на одной оси, так чтобы скомпенсировались e_m, то есть встречно, то на выходе обмоток 10 и 11 каждой секции будут иметь место двойные сигналы небаланса 2e_na, 2e_nв, 2е_nc, пропорциональные токам нагрузки соответствующих фаз. Их удобно соединить в звезду и каждый фазный сигнал небаланса так же, как сигнал утечки, подавать на исполнительные органы, выполняющие функции, аналогичные для двухпроводного дифференциального трансформатора тока. Такой дифференциальный трансформатор тока работает и при несимметричном режиме, включая неполнофазный режим, так как любую несимметричную трехфазную систему токов без нулевого провода можно представить в виде суммы двух трехфазных, симметричных систем: прямой и обратной последовательности.It is known that in a symmetric three-phase network, which is the primary winding of a differential current transformer, when the currents in the phase wires 7 are equal, the fluxes Фσ ₁ create a resultant magnetic flux Фσ ₂ , the vector of the resulting magnetic induction of which is equal to

It rotates with an angular velocity ωt, closing through the air and the magnetic circuit of the differential current transformer, interlocking with the windings 10 and 11. Figure 2 shows the flow direction Фσ ₂ for the time moment ωt = π / 6 and the directions е _n and e _m in each winding 10 and 11 from the action of Ф _m and Фσ ₂ . If now we connect each pair of windings 10 and 11 located on the same axis so that they compensate e _m , that is, counter, then at the output of windings 10 and 11 of each section there will be double unbalance signals 2e _na , 2e _nв , _{2е nc} , proportional load currents of the corresponding phases. It is convenient to connect them to a star and each phase unbalance signal in the same way as a leak signal, to apply to executive bodies that perform functions similar to a two-wire differential current transformer. Such a differential current transformer also works in single-ended mode, including single-phase mode, since any asymmetric three-phase current system without a neutral wire can be represented as the sum of two three-phase, symmetric systems: direct and reverse sequence.

The principle of operation of the differential current transformer in figure 3 and 4 is similar to the principle of operation of the differential current transformer in figure 2.

The difference lies in the fact that with an asymmetric load and the presence of a neutral wire 12 (Fig. 3), any asymmetric three-phase current system can be represented as the sum of three symmetric components of the currents: zero, forward and reverse sequence.

Direct and reverse sequence currents create their own rotating fields and induce signals proportional to the load current in the windings 10 and 11 of the differential current transformer.

Zero-sequence currents do not create a rotating magnetic field, since the flows created by the zero-sequence currents simultaneously in all three phase conductors 7 in FIGS. 3 and 4 are forced to pulsate, closing along the transformer’s magnetic circuit and induce a signal proportional to triple in windings 10 and 11 zero sequence current, but since the neutral conductors 12 and 13 in FIGS. 3 and 4 are passed through a differential current transformer and only the triple zero component of the asymmetric system t flows through them of the reverse direction, compensation of the zero sequence signal occurs in the windings 10 and 11.

When a leakage current appears in the windings 10 and 11, the signal e _m is induced, but since the windings 10 and 11 are connected in FIGS. 3 and 4 in the same way as in FIG. 2, the signals 3e will be output from the corresponding systems of the windings 10 and 11 _na , 3e _nv , 3e _nc .

Thus, the differential current transformer, presented in figure 3, and figure 4, allows you to galvanically separate the signals of the differential current and load, which allows you to create multifunctional devices based on all the proposed options for the differential current transformer with protection not only against leakage currents, but also from overload and short circuit. Such devices are also promising because there is no need to install thermal and electromagnetic relays in their current circuits, limiting their own resistances to load and short circuit currents. They are not reliable and not durable.

Claims (1)

A differential current transformer containing a toroidal core of soft magnetic material with a secondary winding wound on it, a primary n-phase winding in the form of phase conductors located in the core window, and a conductor holder, characterized in that the primary winding is made of two network conductors arranged diametrically on the contrary, and the secondary winding consists of two sections, two equally wound windings of one of which are connected counterclockwise and each winding has n turns, to which it is snug conductors of the primary winding, while two equally wound windings with m turns in each winding of the other section are connected in series and are located at an angle of 90 ° with respect to the conductors of the primary winding.

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