RU2060568C1 - Current transformer of zero sequence - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: invention can be used to monitor leakage currents while insulation of electric installation is damaged or as part of devices of protective disconnection employed in industry and agriculture. Current transformer has toroidal core 1 with uniformly wound secondary winding 2 and primary phase winding 3. Each phase is manufactured in the form of n sections. Each section is composed of two identical conductors connected in parallel uniformly placed in window of core and alternating within order of phase sequence so that angle between conductor of one section amounts to 180 deg/n and angle between two adjacent conductors is 60 deg/n. Screen of magnetically soft material is placed between primary 3 and secondary 2 windings. EFFECT: expanded application field. 4 cl, 3 dwg

Description

 The invention relates to electrical engineering and can be used to control leakage currents during destruction of insulation of electrical installations, as well as as part of residual current circuit breakers used in industry and agriculture.

 Currently, zero-sequence current transformers are used in electrical engineering, most of which are characterized by the presence of an unbalance signal, which cannot be fully compensated even with a zero-sequence current equal to zero.

 Thus, a zero-sequence current transformer is known in which each phase conductor of the primary winding having the shape of a helix is equally adjacent to the turns of the secondary winding [1]. Such a transformer contains a toroidal soft magnetic core with a uniform secondary winding and a primary winding located in the window of the transformer core, consisting of from phase conductors uniformly adjacent to the turns of the secondary winding and attached to it with a holder.

 Such a design of the transformer in some cases can reduce the unbalance signal, but does not make it possible to get rid of it, since depending on the asymmetry of the load, currents of different magnitude can flow in each phase of the primary winding. Therefore, the magnetic coupling between the conductors of the primary winding and the conductors of the secondary winding is not equal to zero, and an unbalance signal is induced in the secondary winding, which in some cases may decrease when leakage currents appear. In addition, with a change in consumer power, the unbalance signal changes, that is, the sensitivity to leakage currents changes.

The closest in technical essence to the present invention is a zero sequence current transformer containing a toroidal core of soft magnetic material with a uniformly wound secondary winding, a primary three-phase winding located in the core window, and a screen of soft magnetic material installed between the primary and secondary windings [2]
As in the above-described current transformers in the known structural embodiment, the unbalance signal cannot be fully compensated. The screen used closes the scattering flows of the primary winding, reducing the flux linkage with the secondary winding, and hence the unbalance signal in it. However, the transformer is unstable when the consumer power changes, which leads to a decrease in sensitivity to leakage currents.

 In addition, the screen design used does not protect the transformer from external magnetic and electric fields, which also reduces the sensitivity to leakage currents.

 The aim of the invention is the creation of a zero sequence current transformer with such a design of the primary winding, in which the sum of the currents of the scattering flux generated by the primary winding conductors would be practically zero when the zero sequence current is zero, which would increase the sensitivity of the transformer to leakage currents.

This is solved by the fact that in a zero-sequence current transformer containing a toroidal core of soft magnetic material with a uniformly wound secondary winding, a primary three-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 made in the form of n sections, each of which consists of two identical parallel-connected conductors uniformly spaced around the circle and alternating I with each other in phase sequence order, so that the angle between the conductors of one section is ¹⁸⁰ / n, and the angle between adjacent conductors is 60 ^o / n.

 It is advisable that the screen was made of two parts, together covering the core with the secondary winding, while the parts of the screen on the inner side of the core are overlapped and with the possibility of changing the distance between the edges of the parts of the screen in the axial direction.

 Technologically, the parts of the screen are fastened together by means of a threaded connection and spring-loaded to the ends of the core.

 Structurally, it is advisable that the transformer contains a holder of conductors of sections of the primary winding of electrical insulation material located in the window of the core.

 The proposed zero-sequence current transformer, due to the use of sectional execution of the primary winding phases in it, allows one to compensate for the scattering flux created by the primary winding conductors, regardless of the load asymmetry and technological errors in the manufacture of the transformer, which increases the sensitivity to leakage currents.

 Using the proposed structural design of the screen made of soft magnetic material allows, on the one hand, to change the electromagnetic coupling between the primary and secondary windings when the load power changes to normalize the unbalance signal, and on the other hand to reduce the interference from external magnetic and electric fields.

 In addition, with the same dimensions of the transformer due to the sectional execution of the primary winding, it is possible to protect more powerful electrical receivers, since this increases the permissible current through the sections of the primary winding.

 The invention is illustrated by a description of specific embodiments thereof and the accompanying drawings, where in FIG. 1 shows a zero sequence current transformer with a primary winding, in which each phase consists of one section (with a partial breakout); in FIG. 2 is a section along AA in FIG. 1; in FIG. 3 is a schematic illustration of a primary winding in which each phase consists of two sections.

 The zero sequence current transformer contains a toroidal core 1 (Fig. 1) of soft magnetic material with a secondary winding 2 evenly wound. In the core window 1 there is a primary three-phase winding 3, each phase A, B, which is made up of n sections A'-A '', B'-B '', C'-C '' (in the described embodiment, n 1).

Each section of the primary winding 3 consists of two identical parallel-connected conductors 4, evenly spaced around the circle and alternating between themselves in the order of phases A, B, C. Moreover, the angle between the conductors 4 of one section (phase) A'-A '', B'-B '', C'-C '' in the general case is 180 ^o / n (in the described embodiment 180 ^o ), and the angle between adjacent conductors 4 is 60 ^o / n (60 ^o ). When n 1 sections of the phase conductors A, B, C are located at an angle of 120 ^about , and in each section A 'A', B 'B'',C' C '' the conductors 4 are diametrically opposite.

 To reduce the influence of external magnetic and electric fields and to reduce the scattering fluxes, the transformer is provided with a screen 5 of soft magnetic material that completely covers the core 1 with the secondary winding 2. Moreover, to change the electromagnetic coupling between the primary and secondary windings 3 and 2 when changing the load power for normalization unbalance signal screen 5 is made detachable, in two parts. Parts of the screen 5 on the inner side of the core 1 are overlapped and with the possibility of changing the distance between the edges of the parts of the screen 5 in the axial direction. In the described embodiment, for this purpose, a thread 6 is made on the adjacent parts of the screen 5, and the parts of the screen 5 themselves are held by springs 7 on the core 1.

 In FIG. 2 shows a zero-sequence current transformer in longitudinal section. The phase section of the primary winding 3 has the shape of a frame, in other embodiments, it can be in the form of a helix, as well as be rigid or flexible.

 To give the entire structure of the transformer stiffness current and for a uniform arrangement of conductors 4 sections of the primary winding 3 there is a holder 8 of electrical insulation material installed in the window of the core 1.

 In FIG. 3 conventionally presents the location of the conductors 4 of the primary winding 3 with the number of sections equal to two. Moreover, an even greater degree is achieved by reducing the unbalance signal.

 The principle of operation of the proposed current transformer is similar to the principle of operation of known feed-through current transformers. However, in it each system of phase conductors A ', B', C 'and A' ', B' ', C' '(Fig. 1) creates scattering fluxes, which at each moment are vectorly opposite to each other and mutually compensated regardless of the load asymmetry and technological errors in the manufacture of transformers.

 Experimental studies have shown that in this way the unbalance signal can be reduced by more than an order of magnitude. This allows, on the one hand, to increase the sensitivity of the protection devices against leakage currents, and on the other hand, to simplify these devices. In addition, with the same dimensions of the current transformer due to the splitting of the phase conductors, it is possible to protect more powerful electrical receivers, since the permissible current through the sections of the phase conductors increases.

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. В этом случае нулевые проводники для уменьшения сигнала небаланса располагают в пространстве между фазными проводниками одинаково прилегающими к внутренней поверхности вторичной обмотки.When the fourth zero current conductor passes through the zero-sequence current transformer, it becomes a transformer that responds not to the zero-sequence current, but to the leakage current, since

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. In this case, the zero conductors to reduce the unbalance signal are located in the space between the phase conductors equally adjacent to the inner surface of the secondary winding.

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.In three-wire three-phase networks, the zero sequence current transformer is identical to the leakage current transformer, since

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 The leakage current transformer can be used in two-phase networks with zero wire and single-phase networks, connecting their windings accordingly. In the first case, two sections of the transformer are included in the gap of the phase conductors, and the third section in the gap of the neutral wire, in the second case, the phase conductor is included in the gap of one section, and the neutral conductor in the gap of the second section, one section is not connected. However, for better compensation of the unbalance signal in the second case, you need to leave only two sections, placing them perpendicular to each other.

Claims (4)

1. A zero-sequence current transformer comprising a toroidal core of soft magnetic material with a uniformly wound secondary winding, a primary three-phase winding located in the core window, and a screen of soft magnetic material installed between the primary and secondary windings, characterized in that each phase of the transformer primary winding made in the form of n sections, each of which consists of two identical parallel-connected conductors uniformly spaced around the circle and alternating I am interconnected in the sequence of phases so that the angle between the conductors of one section is 180 ^o / n, and the angle between adjacent conductors is 60 ^o / n.  2. The transformer according to claim 1, characterized in that the screen is made of two parts, in total covering the core with a secondary winding, while parts of the screen on the inner side of the core are overlapped and with the possibility of changing the distance between the edges of the parts of the screen in the axial direction.  3. The transformer according to claim 2, characterized in that the parts of the screen are fastened together by means of a threaded connection and are spring-loaded to the ends of the core.  4. Current transformer according to any one of paragraphs. 1 to 3, characterized in that it contains a holder of conductors of the sections of the primary winding of insulating material located in the window of the core.

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