Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H83/00—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current
  • H01H83/14—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by imbalance of two or more currents or voltages, e.g. for differential protection
  • H01H83/144—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by imbalance of two or more currents or voltages, e.g. for differential protection with differential transformer
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H83/00—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current
  • H01H83/14—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by imbalance of two or more currents or voltages, e.g. for differential protection
  • H01H83/144—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by imbalance of two or more currents or voltages, e.g. for differential protection with differential transformer
  • H01H2083/146—Provisions for avoiding disadvantages of having asymetrical primaries, e.g. induction of a magnetic field even by zero difference current
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H83/00—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current
  • H01H83/14—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by imbalance of two or more currents or voltages, e.g. for differential protection
  • H01H83/144—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by imbalance of two or more currents or voltages, e.g. for differential protection with differential transformer
  • H01H2083/148—Protective switches, e.g. circuit-breaking switches, or protective relays operated by abnormal electrical conditions otherwise than solely by excess current operated by imbalance of two or more currents or voltages, e.g. for differential protection with differential transformer with primary windings formed of rigid copper conductors

Definitions

• the present invention relates to a current imbalance sensor suitable for use in. for example, a residual current operated circuit breaker.
• Sensors for use in such applications are known, and often comprise a ferromagnetic core through which the two lines to be monitored pass, and around which there is wrapped an output winding.
• the two lines to be monitored constitute primary windings of a transformer a secondary winding of which is the output winding wrapped around the ferromagnetic core.
• the lines passing through the core are arranged to extend such that their current flows are in opposite directions and the intention is that if the current in both lines is the same then there will be no current generated in the output winding.
• the two lines passing through the core are individually insulated electrical leads and it is difficult, if not impossible, to ensure that the leads are so arranged within the core that the flux generated by the same current flow in one of the leads completely negates the flux generated by the same current flow in the other lead, with the result that even though the current in both leads may be the same there will still be an output current generated in the output winding.
• Any detection circuit associated with the output winding will thus need to incorporate threshold comparison, so that output current generated by the same current flowing in both of the leads being monitored does not result in a current imbalance warning or action initiated by the detector.
• a current imbalance sensor comprising a toroidal core and output winding assembly and a first conductor in the form of a tubular element formed from an electrically conductive and non-magnetic material extending co- axially through said toroidal assembly and arranged, at its ends, to be connected in one of the two lines to be monitored, whereby in use a lead constituting the other line to be monitored can extend co-axially through said tubular element.
• the tubular element and the wire or lead extending therethrough constitute primary windings of a transformer the secondary winding of which is the toroidal output winding.
• the flux generated by the current flowing in the tubular element is negated by the flux flowing in the lead passing through the tubular element and no current is induced in the output winding.
• the tubular element receives an electrically insulating tubular liner for guiding the lead co-axially through the tubular element in use.
• said tubular element is provided, at its end, with terminal means to facilitate its connection in said one line.
• a moulded synthetic resin housing encloses the toroidal core and output winding assembly.
• said housing includes an integral terminal block carrying terminals accessible at the exterior of the block and electrically connected to the output winding.
• said housing is assembled around said toroidal assembly prior to securing said terminal means to the ends of said tubular elements.
• Figure 1 is an exploded perspective view of a current imbalance sensor in accordance with one example of the present invention
• Figure 2 is a side elevational view of the sensor of Figure 1 assembled with certain items omitted for clarity, and
• Figure 3 is a view in the direction of arrow A in Figure 2.
• the senor comprises a toroidal core and output winding assembly 11 consisting of a toroidal ferromagnetic core upon which is wound a toroidal output winding consisting of a large number of turns of relatively fine copper wire, the resultant assembly being arranged to be of cylindrical form.
• first and second flux concentrators defined by ferromagnetic washers 12 of internal and external diameter substantially equal to the external and internal diameters of the toroidal core and winding assembly.
• the assembly 1 1 and flux concentrators 12 are received within a moulded synthetic resin housing 13 formed in two axially separate parts 13a,13b respectively.
• the housing parts 13a, 13b are interengaged as a snap-fit by means of resilient legs on the part 13a engaging corresponding recesses in the wall of the part 13b.
• the housing parts 13a, 13b include axially aligned and abutting tubular components 14 which extend within the core and winding assembly 1 1 as a relatively close fit to support the assembly 1 1 against movement within the housing.
• Integral with the housing parts 13a, 13b are respective interengagable parts 15a, 15b of a terminal block 15 supporting terminals 15c electrically connected to the output winding, and providing a means of connecting the output winding to external circuitry.
• a copper tube 16 of circular cross-section Extending through the tube defined by the abutting tubular components 14 of the housing, as a relatively close fit therein, is a copper tube 16 of circular cross-section.
• the tube 16 projects at its opposite axial ends from the housing 13 and the projecting end regions are of reduced wall thickness to define external shoulders (not shown).
• first and second apertured terminal members 1 7, 18 stamped from copper strip Seated on the end regions of the tube 16 and abutting the respective shoulders thereof are first and second apertured terminal members 1 7, 18 stamped from copper strip.
• the regions of the tube 16 which are seated in the apertures of the terminal elements 17, 18 are electrically and physically connected to the terminal elements 17, 18 by hot air soldering using a solder paste. It will be recognised that the temperature achieved during the hot air soldering operation is not sufficient to damage the moulded synthetic resin housing 13 of the core and winding assembly 11.
• the terminal elements 17, 18 could take a wide variety of different forms dependent upon the application of the sensor.
• the element 17 is a plane L-shaped component one limb of which is apertured to receive the tube 16 and the other limb of which has the core of an electrically insulated lead 19 electrically and physically secured thereto, so that the lead 19 is electrically connected through the terminal 17 and the tube 16 to the terminal element 18.
• the terminal element 18 is again of L-shaped form one limb being apertured to receive the end of the tube 16.
• the other limb of the terminal element 18 receives a clamp housing 21 and a clamp screw 22 of known form whereby the bared core of a further electrical lead can be clamped onto the terminal element 18 so as to be electrically connected through the element 18, the tube 16, and the terminal element 17 to the lead 19.
• a tubular, moulded synthetic resin liner 23 Slidably received within the tube 16 is a tubular, moulded synthetic resin liner 23 having an enlarged diameter inlet region 24 at one end thereof.
• the sensor illustrated in the accompanying drawings is intended for use in a residual current operated circuit breaker and monitors the flow of current in a live supply lead and the corresponding neutral return lead.
• the sensor may be positioned on, or in, the housing of the circuit breaker and the live supply lead or wire from the circuit breaker to the circuit being controlled (usually known as the "contractors wire") is introduced through the inlet end 24 of the liner 23 so as to pass completely through the sensor.
• the lead is connected to a terminal of the circuit breaker, and at the other end the lead extends to, for example, a domestic ring main.
• the corresponding neutral return wire from the circuit is terminated at the clamp terminal 21 and the end of the lead 19 remote from the terminal element 17 is electrically connected to, for example, the neutral rail within the domestic consumer unit or electrical distribution board supporting the circuit breaker.
• the neutral return wire is electrically connected through the tube 16, and the tube 16 becomes part of the neutral return path.
• the internal diameter of the liner 23 is preferably chosen to suit the external diameter of the insulated live lead which passes therethrough, such that the lead is positioned co-axially within the tube 16. In such a situation the tube 16 and the lead extending therethrough, which together constitute primary windings of a transformer the secondary winding of which is the output winding of the assembly 1 1 , are co-axial with one another and co-axial with the toroidal core and winding assembly.
• Such an arrangement increases the sensitivity of the sensor by avoiding an imbalance in the flux fields generated by the live and neutral primaries so that provided that the current flow in the live primary is equal to, and opposite the current flow in the neutral primary, their flux fields will cancel one another and no current will be generated in the output winding. It will be recognised that where the live and neutral primaries are not co-axial (as in known arrangements) then even though their current flows may be equal and opposite the fields generated may not cancel one another and thus an unwanted current may be generated in the output winding of the transformer. It will be recognised that with minor modifications the sensing arrangement can be used as an integral part of a wide variety of different circuit breaker designs, or alternatively the sensor can be incorporated in a module for attachment to a circuit breaker. Moreover, the sensor could, if desired, be a stand-alone component positioned remote from a circuit breaker, or indeed for use in non-circuit breaker environments.
• a current flowing in the output winding of the toroidal assembly 11 is utilised is not of significance to the present invention, and it is sufficient to recognise that the generation of a current in the output winding can be used either to trigger a switching arrangement for example in a circuit breaker, and/or to trigger a warning device.
• the threshold at which a valid warning is given, or switching action occurs can be lower than with conventional arrangements and thus the sensor can operate with a higher degree of sensitivity.
• the sensor can readily make use of the existing contractors wiring as one of its primary windings.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Transformers For Measuring Instruments (AREA)

Priority Applications (1)

Applications Claiming Priority (2)

Publications (1)

Family

ID=10758774

Family Applications (1)

Country Status (5)

Cited By (3)

Citations (4)

• 1994
  • 1994-07-23 GB GB9414873A patent/GB9414873D0/en active Pending
• 1995
  • 1995-07-18 WO PCT/GB1995/001691 patent/WO1996003760A1/en active Application Filing
  • 1995-07-18 AU AU29342/95A patent/AU2934295A/en not_active Abandoned
  • 1995-07-21 ZA ZA956113A patent/ZA956113B/xx unknown
  • 1995-07-22 TW TW084107614A patent/TW276345B/zh active

Patent Citations (4)

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