Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
1998-08-13
2001-02-06
Oda, Christine K. (Department: 2862)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
C324S127000
Reexamination Certificate
active
06184672
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to sensing power line current and, more particularly, to a current sensor responsive to magnetic fields.
BACKGROUND OF THE INVENTION
Power distribution systems include many electrical devices. Some of the electrical devices have current sensors for sensing current flow in a conductor. For example, power distribution systems generally include circuit breakers, electricity meters, and monitoring equipment. The accuracy of such current sensors is important, since inaccurate current sensing could lead to unnecessarily cutting-off power to a load and discrepancies and inaccuracies in power metering, which are undesirable. Although known sensors provide acceptable results, it would be desirable to even further improve the sensing accuracy of current sensors and to reduce costs.
In addition to high accuracy and low cost, the size of current sensors often is important. For example, if products must be redesigned in order to incorporate a new current sensor, the cost of adding the new current sensor to the product can be very expensive. Preferably, any new current sensor is sized so that the sensor can be easily installed into existing units, such as meters and circuit breakers. Further, since many power system components do not include batteries, the current sensor also should be extendible to provide self power. This generally means that any power required by the current sensing circuit and other electronic components in the breaker unit be provided by the power line being monitored rather than from an external battery.
It would be desirable to provide a current sensor assembly that is accurate and of small size. It would be further desirable to provide a semiconductor current sensor that is responsive to a magnetic field in the plane of a chip.
SUMMARY OF THE INVENTION
The foregoing benefits and advantages may be attained by a current sensor assembly including a sensor coil, an electrostatic shield coil, a core, a housing, and a magnetic shield. The sensing coil, electrostatic shield coil, core, housing, and magnetic shield are of toroidal symmetry and are arranged coaxially about a pair of primary current conductors. The conductors can be either asymmetrical or symmetrical with respect to the geometric center of the remaining sensor assembly. The core and a secondary winding make up a current sensor.
The core is toroidal in shape and is of non-magnetic material having a magnetic permeability substantially equal to that of air, and is therefore referred to as an air core. The secondary winding is wound over the cylindrical core to form a toroidally shaped winding. When assembled into the current sensor assembly, the core and windings are disposed around two single turn primary windings for the residential metering applications. AC currents to be measured flow in the primary windings, creating an alternating magnetic flux in the core. This flux induces a voltage in the secondary winding which is coupled to the input of an amplifier and an integrator. The amplifier and integrator are contained with in the electronic circuitry of the meter.
The current sensor assembly detects the value of current in a conductor by using either a toroidal winding or a semiconductor (or solid state) based sensor that is responsive to a magnetic field in the plane of the chip. The sensor assembly can be used in residential electronic meters, circuit breakers, and various monitoring equipment and electronics. Aside from the residential electronic meters, the other aforementioned sensor applications may employ different configurations of the primary conductors such as a single primary winding.
REFERENCES:
patent: 4413230 (1983-11-01), Miller
patent: 4491230 (1985-01-01), McColeman
patent: 4754218 (1988-06-01), Wagner et al.
patent: 4887029 (1989-12-01), Hemminger
patent: 5343143 (1994-08-01), Voisine et al.
patent: 5587652 (1996-12-01), Berkcan et al.
patent: 5642041 (1997-06-01), Berkean
General Electric Company
Oda Christine K.
Snyder Marvin
Stoner Douglas E.
Zaveri Subhash
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