RU2067330C1 - Current-to-voltage converter - Google Patents

Abstract

FIELD: devices for relay protection and automatic control of electric systems. SUBSTANCE: device has current transformer with short-circuited by-pass winding 3 and measuring winding 4 and second short-circuited winding. Measuring winding is located between short-circuited windings 5. Greatest effect is detected when short-circuited windings are designed as current-conducting container, first of which embraces magnetic circuit 1, while second embraces measuring winding 4, which is located over first container 3. EFFECT: compensation of dissipation flows. 2 cl, 3 dwg

Description

 The invention relates to techniques for relay protection and automation of electrical systems and can be used to control and measure current.

 A known converter based on a current transformer (VE Kazansky. Measuring current transducers in relay protection. M. Energoatomizdat, 1988. Fig. 1.1, p. 11), containing a measuring winding placed on the magnetic circuit that covers the primary current.

 The disadvantage of such a converter is the limited conversion range resulting from the influence of the transformer winding inductance, and the large dimensions.

 These disadvantages are eliminated in the converter, which additionally contains a short-circuited winding, which is made in the form of a continuous layer of conductive material covering the magnetic circuit (ed. St. 1347025, class G 01 R 19/00, BI N 39, 1987). However, this device has a limited frequency conversion range, which narrows the scope of its application. The limitation of the frequency range from above is due to the influence of the finite thickness of the short-circuited winding (Electrical Engineering, 1989. N 2, p. 38 43), in the space of which the own flow (or the so-called scattering flux) of this winding closes.

 The purpose of the invention is the expansion of the range of operating frequencies and, as a consequence, the expansion of the scope.

 For this purpose, a current-to-voltage converter comprising a magnetic circuit, a single-turn short-circuited winding placed on top of the magnetic circuit in the form of a continuous layer of conductive material, and a multi-turn measuring winding, additionally introduces a second short-circuited winding located on top of the measuring one in the form of a continuous layer of conductive material.

 In the second embodiment, both short-circuited windings are structurally made in the form of two conductive containers placed first inside the second, and the magnetic core is placed inside the first container, and the measuring winding is on top of it.

 The introduction of a second short-circuited winding causes the distribution of power current in two parallel-connected short-circuited windings. In this case, the measuring winding is located between two currents flowing in the same direction of the currents of the power windings. This arrangement leads to the fact that the action of magnetic fluxes of scattering created by the first and second short-circuited windings is mutually compensated in the space of the measuring winding. As a result, the EMF of this winding will be determined only by the flux, which closes in the magnetic circuit and is created by the power current.

 The most noticeable compensation for the effect of scattering fluxes is achieved with a uniform distribution of current over the surface of short-circuited windings covering the entire magnetic circuit. This effect can be achieved with the constructive implementation of the aforementioned short-circuited windings in the form of continuous conductive containers with rigidly maintained dimensions and their corresponding placement: the first (internal) covering the magnetic circuit, and the second (external) measuring winding located on top of the first container.

 Since almost the entire power current is closed in conductive containers, the measuring winding can be made with an extremely thin wire. As a result, the splitting of one power winding into two (i.e., execution in the form of two conductive layers or two containers) does not lead to a noticeable increase in the size of the device compared to the prototype. The location of the measuring winding between these short-circuited windings has the positive effect of expanding the operating frequency range towards the higher ones by compensating for the action of the dissipation flows of the power windings.

 An additional effect of this solution is to improve the thermal regime. In the prototype, the short-circuited power winding, which determines the thermal regime, is slightly cooled due to the presence of a measuring winding on top of it. And in the proposed device, on the contrary, one of the power windings is located on top of the measuring one and is well accessible for cooling. Temperature equalization occurs due to the automatic redistribution of current in them, since both short-circuited windings turn out to be connected in parallel. In addition, the internal short-circuited winding (first conductive container) simultaneously performs the function of a casing protecting the magnetic circuit from mechanical influences when using high-permeability alloys, and the external (second conductive container) function of the casing, which also provides shielding from electrical noise, which significantly increases noise immunity and reliability total converter.

 Thus, the converter, in which the power winding is made in the form of two continuous conductive layers or containers, creating the effect of parallel switching on of two short-circuited windings and dividing the power current in them so that the action of the scattering fluxes in the space of the measuring winding is compensated, according to the applicant, appears new previously unknown.

 The appearance, in addition to the main positive effect, namely, a decrease in the influence of scattering inductance, and the following new qualities, an improvement in the thermal regime of the converter, shielding of the measuring winding from electrical and mechanical influences significantly distinguishes the proposed device from the prototype and expands its scope.

 It is known to use volumetric short-circuited turns covering magnetic circuits with windings (A. Gorsky et al. Calculation of electromagnetic elements of secondary power sources. M. Radio and communications, 1988. S. 9, Fig. 1-6), which provides electrical shielding, reduces parasitic winding capacity and at the same time is the casing of the transformer. However, this design is designed to connect two transformers. The proposed technical solution is characterized in that a system of two short-circuited windings is used, in which the windings themselves act as measuring resistors, and their relative position relative to the measuring winding gives the effect of compensating for the effects of scattering fluxes. Moreover, this effect cannot be achieved in the above-mentioned transformer with a three-dimensional communication loop.

 In FIG. 1 shows a conditional image of the proposed Converter, figure 2 its equivalent circuit. A cross section of a device with a container embodiment of the windings is presented in Fig.3.

 The transducer (Fig. 1) contains a magnetic circuit 1, covering a winding with a primary current 2, a first short-circuited winding 3, covering a magnetic circuit 1 in a continuous layer, a measuring winding 4 located on top of a winding 3, and a second short-circuited winding 5, covering windings 3, 4 and the magnetic circuit 1 continuous layer.

 In figure 2, the ohmic resistance of the windings 3 and 5 are represented by equivalent resistors 6 and 7.

где W число витков измерительной обмотки 4;
Ф_м магнитный поток в магнитопроводе 1;
Ψ_s3 и Ψ_s5 потокосцепления измерительной обмотки 4, обусловленные магнитными потоками рассеяния короткозамкнутых обмоток 3 и 5 соответственно.The converter operates as follows. As the primary winding 2, a conductor with a controlled current i _{1 is used} , which is passed to the magnetic circuit window 1. Under the action of the current i ₁ , a magnetic flux is created in the magnetic circuit, creating a current i ₂ in both short-circuited windings 3 and 5. In this case, in the measuring winding 4, appearing between the currents of windings 3 and 5 flowing in the same direction, a voltage U _ism equal to

where W is the number of turns of the measuring winding 4;
F _m magnetic flux in the magnetic circuit 1;
Ψ _s3 and Ψ _{s5 of the} flux linkage of the measuring winding 4, due to magnetic fluxes of scattering of the short-circuited windings 3 and 5, respectively.

,

,
где i₂ i₃ + i₅ i₁ i_м ≈ i₁.Active resistance R ₃ and R ₅ shorted windings 3 and 5 accordingly remain much smaller than the resistance branch magnetization converter in a wide range of controlled current i _{1, and} therefore the magnetizing current i _m is much smaller than the current i ₂ of two parallel-connected short-circuited windings 3 and 5. Since as the resistances of short-circuited windings can be unequal, the currents in them will be distributed as follows

,

,
where i ₂ i ₃ + i ₅ i ₁ i _m ≈ i ₁ .

.The voltage at the measuring winding 4 is equal to
U _ISM WR _EQ ,
Where

.

 In this device, compared with the prototype, the influence of the scattering fluxes, and hence the scattering inductances, on the voltage value of the measuring winding is significantly reduced.

 Thus, the proposed Converter has a wider range of operating frequencies, which makes it possible to use it in high-frequency devices for measuring power currents.

 The experimental model of the converter for high-frequency welding electrical equipment has the following parameters: a magnetic circuit made of 82K3XSR alloy with a core size of K34X29X4 is placed in a special copper container 1 mm thick, over which a measuring winding with the number of turns W 1000 is laid with a PEV-1-0.06 wire. The second container is formed by a winding of bare wire d 1.0 mm, superimposed on top of the measuring winding. The upper cutoff frequency for this converter is 25 kHz. The converter is without an external conductive layer (prototype) has a cutoff frequency of 4 kHz.

 Experiments conducted on a welding machine with an operating frequency of 5-8 kHz showed that for the prototype the effect of the influence of scattering inductance is manifested clearly. And the option based on the proposed solution yielded results comparable to ethanol with a non-inductive shunt.

 Thus, the practical implementation confirms the effectiveness of the proposed technical solution and indicates the possibility of widespread use of the converter in high frequency installations. YYY2

Claims (2)

 1. A current to voltage converter containing a magnetic circuit on which the first short-circuited and measuring windings are located, characterized in that a second short-circuited winding is inserted into it, located on top of the measuring winding and made in the form of a continuous layer of conductive material.  2. The Converter according to claim 1, characterized in that both short-circuited windings are made in the form of two conductive containers placed first inside the second, and the magnetic circuit is located inside, and the measuring winding is on top of the first container.

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