SU748528A1 - Null-sequence current transformer - Google Patents

Description

(54) CURRENT ZERO TRANSFORMER

I

The invention relates to the field of electrical engineering, and more specifically to current transformers and can be used in devices protected from current leaks in extensive electrical networks with voltage up to 1000 V s, an isolated or grounded neutral of the transformer, for example, in coal mines, coal preparation plants and quarries, as well as in domestic premises.

A zero-sequence current transformer is known, the primary winding of which is the wires of the three phases of the connectable connection. The principle of protection is that using a current-measuring organ is that, under normal conditions, the geometric sum of the phase currents must be equal to O and the current does not flow through the relay. With short circuits to ground or leakage of current to earth, this condition is violated and a zero sequence current arises, which causes the appearance of a magnetic flux in the TNTP and EMF magnetic circuit in the secondary circuit 1.

However, in reality, under normal conditions, with full equality of the primary sequence

current in the secondary circuit flows unbalance current, due to the asymmetrical arrangement of the phases of the primary circuit relative to the secondary winding of TTP. Due to the difference in mutual inductances of the phases

5, the primary circuit with the secondary winding of the TTPD, the sensitivity of the known means of protection to leakage currents does not exceed 3-5 A and varies slightly even with the use of special means to increase it. This sensitivity is sufficient for

10 are sewn from threads to. H. and unacceptable for protection against leakage currents, where it is necessary to safely set the operating current to 25 mA.

Known current transformer zero

J5 sequences in which, to reduce unbalance, the conductors of each phase of the primary winding of the TNCN are split up with at least two conductors and the divided conductors of each phase are diametrically opposite in the window

20 magnetic circuit 2.

This transformer has the disadvantage that the dissipation fluxes of each conductor are not equal to each other ;; -.

: "

Bridged and closed along a ferromagnetic core. Therefore, a prerequisite is: the presence of a closed toroidal magnetic circuit with a uniform secondary winding, which complicates the design. The use of a magnetic circuit, for example, with a rectangular window and a secondary winding made in the form of a separate coil, will not inevitably lead to a significant increase in unbalance; very precise installation of the split conductors with respect to the axis of the toroidal magnetic circuit and between them is necessary. With a large number of split conductors, this requirement is almost difficult to fulfill; An increase in the number of conductors drastically reduces their fill factor in the magnetic conductor window, which affects the performance of the TNCN and limits the effectiveness of unbalance reduction.

The closest in technical essence is a zero-sequence current transformer having a primary winding made in the form of cylinders arranged coaxially relative to each other. 3. In a known transformer, the mutual induction between different phases of the primary circuit and the secondary winding can be equal, and the current unbalance can be absent when perfect axial symmetry of conductors.

However, the fabrication of such perfectly symmetrical zero-sequence current transformers presents considerable difficulties, and even a small axial displacement of the cylinders will inevitably lead to an increase in unbalance current.

The purpose of the invention is to eliminate these drawbacks, namely, to simplify its implementation and reduce the unbalance current.

This goal is achieved by the fact that a zero-sequence current transformer containing a primary circuit made in the form of three coaxial surfaces alternating in phases, equipped with phase leads, separated by a dielectric and covered by a magnetic conductor, on which a secondary one is located, in the form of a multi-turn helix.

And besides, an option has been proposed in which the phase terminals are placed evenly along the turns of the primary circuit.

FIG. 1 shows a diagram of a current leakage protection device in which the proposed zero-sequence current transformer is used; in fig. 2 - conductor in expanded form; in fig. 3 - primary circuit of the zero sequence current transformer (end view).

The device consists of a zero-order current transformer, a TNT transformer, and an executive relay. TTPF has a magnetic core 1, a primary circuit 2, and a secondary

748528

Winding 3. Executive relay 4 is connected to the secondary winding. Each phase of the TTP primary circuit is made of sheet conductor 5, for example, from thin copper foil. Insulation 6, for example, made of thin capacitor paper, is placed between the conductors. The insulated sheet conductors are twisted into a roll and equipped with phase leads 7. Thus, the TTPD primary circuit is a multilayered roll of alternating in phases.

0 sheet conductors.

With full equality of the currents flowing through the primary circuit of the TNCN, there are no magnetic fluxes in the magnetic circuit 1, since there will be practically no external magnetic field. An increase in the number of phase leads 7 for each conductor makes it possible to increase the uniformity of current distribution over the entire surface of the conductor.

The resulting scatter flow in

The window of the TNTP magnetic circuit is determined by the sum of the dispersion flows of the conductors A, B, C.

Fe FA + FB + FS,

where Fd, Fz, Fs - scattering flows, due to the flow of current in the conductors.

Since the paths of magnetic fluxes in a coil are combined, then at 1d + Ig-b Ij, 0 the magnetic fluxes do not close in the magnetic circuit, the mutual induction of the individual conductors of the phases and the secondary winding will be the same, and the unbalance currents will be significantly reduced even in the case of a secondary windings, non-coaxially spaced conductors and magnetic circuit, arbitrary shape of the magnetic core and the presence of air gaps in it.

The use of this zero-sequence current transformer in current leakage protections will increase electrical safety and eliminate cases of electrical injury in extensive electrical networks by significantly reducing the error and simplifying the manufacturing of the zero-sequence current transformer.

Claims (3)

1. The current transformer zero sequence containing the primary circuit, made in the form of three coaxial surfaces, alternating in, provided with phase leads separated by a dielectric, and enclosed by a magnetic conductor on which a secondary circuit is located, characterized in that, in order to simplify it. making and reducing current unbalance, each of said surfaces is made with a guide in the form of a multi-turn helix. 2. The zero sequence current transformer according to claim 1, characterized in that the phase terminals are arranged evenly along the turns of the primary circuit. Sources of information taken into account in the examination 1. Mavritsyn-A. M. et al. Protection against single-phase earth closure in quarries. M., “Nedra, 1968: p. 31-33. 2. USSR author's certificate number 456335, cl. H 02 H 3/16, 1970. 3.J. “Electric stations, 1975, No. 7, p. 88-90. , 2i 3 T T / / / 7 And AT 6 / / / Y FIG. { ig.2 5 748528 Fb / gh