Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Patent
1997-06-09
1999-11-16
Strecker, Gerard
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
324509, 324252, 340650, G01R 1900, G01R 3102, G01R 3309
Patent
active
059864443
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the detection of electrical currents and more particularly to a device for detecting low magnitude electrical currents.
2. The Prior Art
There are a number of situations where it is necessary to detect electrical currents so that they can be monitored, and there have been a number of different proposals put forward for achieving this. In the field of residual current devices, it is customary to detect an imbalance in current flow through live and neutral conductors by passing the conductors through a toroid of magnetic material and having a sensing winding around part of the toroid. This arrangement is such that if there is an earth leakage fault, there is an imbalance between the current flowing in the live conductor with respect of the current flowing in the neutral conductor, and this imbalance results in a current being induced into the sensing winding. This winding is then connected to suitable circuitry for indicating the presence of the fault condition.
Residual current devices have become more and more popular and there is consequently a continuing need to be able to manufacture such devices in as efficient and cost effective a manner as possible. Attention has therefore been directed to the need for a sensor coil to be wound on a toroid as this is a relatively expensive operation.
European Patent Application EP-A-0242560 describes an arrangement for non-contact measurement of the electric current in a conductor, and relates to a device having a magnetic core surrounding the conductor. In a gap in the magnetic core is a gap in which is positioned a magnetic field sensor. The aim of this prior invention is to increase the measuring sensitivity of the device, and this is achieved preferably by utilising a magnetic core whose cross-sectional area becomes greater with increasing distance from the gap.
It is known from the article "Stromsensor als Mikrosystem" (Elektronik, vol. 42 No. 5 October 1993. Munchen, DE; pages 42-44, XP 000396422; Ruhl et al) that different types of devices may be placed in the air gap of a toroidailly-shaped member in order to sense currents.
SUMMARY OF THE INVENTION
The present invention proposes to use a magneto resistive device to replace the sensor coil in an RCD device, for example. However, the use of a magneto resistive device is not without its problems, and consequently the present invention further provides a generally toroidially-shaped member which is arranged to saturate at a predetermined level of magnetic flux.
According to the present invention there is provided a device for detecting a low magnitude net electrical current comprising a generally toroidally-shaped member of magnetic material provided with an air-gap and a sensor disposed in the air-gap for sensing a magnetic flux indicative of the net current flowing in conductor means passing through the toroidally-shaped member, characterised in that cause saturation of the member at a predetermined level of magnetic flux.
In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawings in which
FIG. 1 is a diagrammatic perspective view showing the general arrangement according to the present invention;
FIG. 2 shows one form of a toroidially-shaped member for use with the present invention; and
FIG. 3 shows an alternative form of the toroidially-shaped member for use with the present invention.
Magneto resistive detectors are known and in particular magneto resistive bridge devices have been produced which will change their resistance as a function of applied magnetic field. A characteristic of existing devices is that they are only linear over a small proportion of their range and further it is necessary to bias each resistor of the bridge using a permanently magnetic coating. In the past, this has meant that magneto resistor devices have been restricted to uses where the amount of flux to be detected has been small
REFERENCES:
patent: 5103163 (1992-04-01), McLynn
patent: 5694103 (1997-12-01), Goodwin et al.
patent: 5734264 (1998-03-01), Berna et al.
Ruhl et al, "Stromsensor als Mikrosystem", Electronik, vol. 42, No. 5, Oct. 1993, Munchen, DE, pp. 42-44.
Power Breaker PLC
Strecker Gerard
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