WO2011146028A1

WO2011146028A1 - Shielding method for reducing external magnetic effects in low-power current transformers

Info

Publication number: WO2011146028A1
Application number: PCT/TR2010/000153
Authority: WO
Inventors: Cemalettin Denizoglu
Original assignee: Cemalettin Denizoglu
Priority date: 2010-05-21
Filing date: 2010-07-22
Publication date: 2011-11-24
Also published as: TR201004047A2

Abstract

The present invention relates to a shielding method for reducing the effects of external magnetic fields on low-power transformers for the purpose of a shielding that will reduce the effect of external magnetic fields on transformers in low-power current transformers regardless of the direction and density of such external magnetic fields. The main principle of the invention is that conductive rings provided to cover the device generate a magnetic field opposite to the external magnetic fields, thereby reducing the external magnetic fields' effect on the device.

Description

PATENT SPECIFICATION

SHIELDING METHOD FOR REDUCING EXTERNAL MAGNETIC EFFECTS IN LOW-POWER CURRENT TRANSFORMERS

TECHNICAL FIELD

The present invention relates to a shielding method for reducing the effects of external magnetic fields on low-power transformers for the purpose of a shielding that will reduce the effect of external magnetic fields on transformers in low-power current transformers regardless of the direction and density of such external magnetic fields.

KNOWN STATUS OF TECHNIQUE

In the known status of technique, regardless of geometrical shape of the core, the magnetic or non-magnetic core is divided into two or more geometrically equal segments and each segment is wound with two or more coils in directions, the magnetic flux directions of which are mutually supportive. The two ends, which are formed by the parallel-coupling of the ends of coils wound in this manner, are taken out as transformer outputs. In this method, the magnetic field provided by the current passing along the axis creates the transformer's real magnetic field and the transformer carries out measurements over this field. Magnetic fields generated by external currents in directions and angles different from the axis, however, generate a magnetic field in the opposite direction of the external magnetic field with the circulation currents in the parallel-wound arms and thus eliminate each other. In this method, the fact that more than one coils are wound around the magnetic core gives rise to manufacture problems. Furthermore, the necessity to connect with parallel coils on the transformer complicates workmanship and increases the possibility of faults in workmanship. Since the same ampere-turn value is obtained with two or more coils, the amounts of material and labor hours used increase. In the known status of technique, independent of the geometrical shape of the core, part of the number of threads of the coil to be wound is wound as the main coil and in a manner that completes the full turn. The magnetic or non-magnetic core is geometrically divided into two or more segments and the amount of coil equal to the remaining number of threads is wound as two or more equivalent coils on each segment in a direction in which the magnetic flux directions support each other and are coupled in parallel. The main coil, which is the first segment of the coil to be wound, and the equivalent coils that are wound as two or more coils and are coupled in parallel are coupled to each other in series. The two ends that are formed are used as secondary coil ends. This method presents manufacturing difficulties since after winding part of the coil the remaining part is wound on the magnetic or non-magnetic core as parallel arms. The coil that is wound as a parallel arm causes an increase in the sizes of the secondary, which, in turn, causes an increase in the amounts of material and labor hours used. Furthermore, the connection made between the coils that are wound complicates workmanship and increases the possibility of faults in workmanship.

DESCRIPTION OF THE INVENTION The purpose of the present method is to eliminate, by using a different shielding technique, the effects on the coil caused by external magnetic fields, which are of external origin, which are in various directions different from the magnetic flux generated by the primary circuit, and which have an impact on the transformer's operation in low-power current transformers.

The main principle of the present invention is to pass, in three-dimensional space, external magnetic fields through a conductive ring in order to provide this conductive ring with a flux of a current that would generate a magnetic field opposite to the external magnetic effects, thus reducing the impact of external magnetic fields on the measurement circuit. Through this method the effect of external magnetic fields on the current transformer (1) is eliminated without the need for an additional coil, thereby circumventing possible workmanship flaws and an increase in cost. PARTS AND PIECES CONSTITUTING THE INVENTION

1. Current transformer, for which shielding is provided

2. Coils encircling the magnetic field

3. Magnetic field vectors

SHORT DESCRIPTION OF THE FIGURES

Fig. 1 shows a double-conductor ring shielding method over a single axis for reducing external magnetic fields' effects on the current transformer.

Fig. 2 shows a shielding method over two axes for reducing the effect that external magnetic fields of a different axis have on the current transformer.

Fig. 3 shows a shielding method over three axes for reducing the effect that external magnetic fields of a different axis have on the current transformer.

INVENTION DISCLOSURE

The shielding technique subject to the method involves the placing of the coils (2) encircling the external magnetic fields on the current transformers regardless of the features of the current transformer (1 ) to which shielding is applied.

The magnetic current transformers consist of materials with low or high magnetic conductivity. The magnetic core is manufactured in circular, oval, rectangular or polygonal shape and secondary coils are wound around this core. Disregarding the induction current, the sum of the primary currents passing through the magnetic core equals the total ampere-turn of the coils wound around the secondary.

In current transformers manufactured according to these principles, the secondary currents of the primary currents, while increasing from 1 Ampere to the kiloampere level, are generally at the level of 1-2-5-1 OA and their voltages are at Volt level. With the new current transformer technology, however, in "LPCTs," i.e. low-power current transformers, while the secondary currents are at the milliampere level the secondary voltages are at millivolt level.

In current transformers, the total flux passing through the magnetic core causes a voltage in the secondary coil and a current in the secondary circuit. However, with the return of the primary current passing through the core or with the magnetic field effect generated by the currents of other phases close to this core, the voltage generated by the primary current of the current transformer in the secondary is affected, which in turn deflects the current conversion ratio and the phase angle. This is a frequently-observed condition both in classic and in low- power current transformers and prevents the counters and relays from operating accurately. The method to diminish these external effects, however, is to provide a high-conductivity conductive ring in a direction orthogonal to the directions of the magnetic fluxes, thus allowing the generation of a current in this ring, thereby generating a flux in the opposite direction and enabling the diminishing of the external magnetic field in the vicinity of this ring.

As an alternative to known status of technique, the proposed system introduces a ring having a high current conductivity, thereby preventing the intensity of the magnetic flux within the ring in a manner similar to a shield effect. By placing two consecutive conductive rings at a distance from each other, the intensity of the external field vector (3) orthogonal to the ring is considerably reduced within the area remaining between the two rings. As an addition to this example presenting an aspect of the invention, in order to counter external magnetic effects that may come from the X, Y, Z directions in three-dimensional space the secondary voltage external magnetic field vectors (3) arising from the current transformer's own primary can be duly protected by placing rings orthogonal to the above flux directions. Thereby the healthy operation especially of low-power current transformers can be ensured.

Through this method, if the directions of the external magnetic fields on the X-Y-Z axes are known, the external magnetic field's effect on the transformer (1) for which shielding is provided can be considerably reduced through two conductive rings placed orthogonal to the external magnetic field from the X axis in the case of an external magnetic field only from this direction, and two conductive rings each placed orthogonal to the external magnetic fields X and Y in the case of external magnetic fields from these directions.

Claims

1. A shielding method to reduce external magnetic effects on low-power current transformers, characterized in that said shielding method comprises conductive rings, each of which is a conductive ring in three-dimensional space.

2. A shielding method according to claim 1 , characterized in that said shielding method ensures that external magnetic fields generate a current on the conductive shielding rings, which currents in turn generate magnetic fields opposite to the direction of each external magnetic field, thereby reducing the effect of the external magnetic field.

3. A coil system according to Claim 1 , characterized in that said coil system forms conductive rings encircling the device to be shielded in a manner that covers the device.