LCDI power cord circuit having a power cord fault circuit for monitoring a neutral wire shield and a line wire shield integrity

A LCDI power cord circuit is provided. The circuit includes energizing shielded wires and monitoring the energized shields for surges, e.g., arcing, and/or voltage drops, e.g., shield breaks detected by a Power Cord Fault Circuit (PCFC). The PCFC includes one dual purpose amplifying/switch transistor and the LCDI power cord circuit does not include any discrete capacitive components.

BACKGROUND

1. Field of Use

This invention relates to leakage current detection and interruption (LCDI) power cord circuits for detecting a leakage current and open or faulty shields in a power cord.

2. Description of Prior Art (Background)

With the wide use of household electrical appliances, such as air conditioners, washing machines, refrigerators, etc., more attention is being paid to the safety of using such appliances. An appliance typically has a power cord of one meter or longer.

Power cords may age due to long-term use, or become damaged when the appliance is moved, which may cause a current leakage between the phase line and the neutral or ground lines in the cord. Such leakage current may cause sparks, which may cause fire and property damages. To quickly and accurately detect leakage current in the power cord, an additional conductor is often provided and electrically connected to a metal sheath surrounding the phase line and the neutral line. Leakage current can be detected by detecting a voltage on the metal sheath. The metal sheaths are conventionally made by weaving thin copper wires.

Further, the metal sheath can fail due to failure in structural integrity or corrosion. Failure of the metal sheath to provide continuity between the power cord source and the power cord load may allow leakage current to not be detected by an ordinary LCDI circuit.

Prior art solutions often provide a circuit for detecting an open metal, i.e., failed structural integrity and a separate circuit for detecting leakage current. Multiple circuits require more components, increased footprint, and longer production cycles. Therefore, a need exists for a single circuit for detecting leakage current, metal sheath structural integrity, and metal sheath corrosion that could interfere with leakage current detection.

BRIEF SUMMARY

Accordingly, the present invention provides a power cord circuit useful for appliances such as air conditioners, washing machines, refrigerators, etc.

In accordance with one embodiment of the present invention a Leakage Current Detection Interrupter (LCDI) circuit for interrupting AC power from an AC source connected to a load via an insulated neutral wire surrounded by a neutral wire shield (NWS) and an insulated line wire surrounded by a line wire shield (LWS) is provided. The LCDI circuit includes a power supply circuit for supplying a rectified voltage waveform and a floating load connected to the power supply circuit. The floating load includes a power cord fault circuit (PCFC) for monitoring the NWS and LWS integrity and leakage current. The LCDI does not include any discrete capacitors as in other prior art solutions, thereby reducing cost, footprint, and production times.

The invention is also directed towards an A Leakage Current Detection Interrupter (LCDI) circuit for interrupting AC power from an AC source connected to a load via an insulated neutral wire and an insulated line wire, wherein the insulated neutral wire and an insulated line wire are surrounded by a conductive shield (CS). The LCDI circuit includes a power supply circuit for supplying a rectified voltage waveform and a floating load connected to the power supply circuit. The floating load includes a power cord fault circuit (PCFC) for monitoring the CS integrity and detecting leakage current. The PCFC includes a solid-state amplifier (SSA) connectable to the CS; a bi-stable latching device having on/off states. The SSA connected to the bi-stable latching device being selectively turned on and off based upon sufficient application of a portion of the rectified signal positive pulse to a base of the SSA. The LCDI does not include any discrete capacitors as in other prior art solutions, thereby reducing cost, footprint, and production times.

In accordance with another embodiment of the present invention a power cord circuit comprising a floating load is presented. The floating load includes a power cord fault circuit (PCFC) for monitoring power cord integrity and detecting leakage current. The PCFC includes a solid-state amplifier (SSA) connectable to a conductive shield (CS). The bi-stable latching device having on/off states and wherein the SSA connected to the bi-stable latching device being selectively turned on or off based upon application of a portion of a rectified signal positive pulse to a base of the SSA. The PCFC does not include any discrete capacitors as in other prior art solutions, thereby reducing cost, footprint, and production times.

DETAILED DESCRIPTION

Referring toFIG.1there is shown a circuit block diagram of a LCDI POWER CORD CIRCUIT10(LCDI). LCDI circuit10includes Line Wire Shield (LWS)24A and Neutral Wire Shield (NWS)24B, switch18, power supply circuit100, power cord fault circuit (PCFC)110, relay16; and, manually engaged ganged switches12A,12B, hereinafter referred to as the manual reset switch. As shown herein the PCFC comprises a floating load with respect to the power supply100.

As is described herein, when manual reset switches12,12A are set line voltage is connected to LOAD and to power supply circuit10via relay16. Power supply circuit100supplies bias voltages to PCFC110, and shields24A and24B. Shields24A and24B are connected in series at the Load end, are connected in series between power supply100and PCFC110. As is discussed and shown in more detail herein, the PCFC110allows a small amount of relay current to flow through relay16but less than the energizing current needed to energize relay16to disengage manual reset switches12A,12B. It is appreciated that not starting from zero energizing current allows solenoid519to energize faster when a fault is detected.

Referring also toFIG.1Athere is shown a detailed circuit10A of the block diagram10shown inFIG.2. LCDI circuit10A includes Line Wire Shield (LWS)24A and Neutral Wire Shield (NWS)24B, switch18, power supply circuit100A, and PCFC110A. Line Wire Shield (LWS)24A and Neutral Wire Shield (NWS)24B may be any suitable conductive shield surrounding the line and neutral wires as discussed in more detail herein. As is described in more detail herein, when manual reset switches12,12A are set line voltage is connected to LOAD and to power supply circuit100A via relay16. Power supply circuit100A supplies bias voltages to PCFC110A, and shields24A and24B. As is discussed and shown in more detail herein, the PCFC110allows a small amount of relay current to flow through relay16but less than the energizing current needed to energize relay16to disengage manual reset switches12,12A. It is appreciated that not starting from zero energizing current allows relay519to energize faster when a fault is detected.

Referring now toFIG.1AandFIG.2. When switches12,12A are mechanically (manually) engaged AC line voltage is connect to LOAD. 60 Hz AC line voltage is also connected to power supply circuit110A via relay16. Power supply circuit110A, comprising bridge rectifier (diodes D1-D4) outputs a rectified unsmoothed DC signal at BRIDGEOUT. The rectified unsmoothed DC signal at BRIDGEOUT is routed through R1 to Q1 base via shields24A,24B. The rectified unsmoothed DC signal at BRIDGEOUT is also routed through R2 to Q1 collector and SCR1 gate.

Still referring toFIG.1AandFIG.2, the rectified unsmoothed DC signal at BRIDGEOUT is routed to the base of npn transistor Q1, R1 and R3 biasing Q1 into an on condition during the positive cycle of the rectified unsmoothed DC, dropping the rectified voltage across R2. When Q1(B) voltage drops below VBEQ1 turns off and the voltage at Q1(C) is near 0v due to the unsmoothed DC signal at BRIDGEOUT dropping to near 0v in the cycle. When the unsmoothed DC signal at BRIDGEOUT swings positive, Q1 is again biased on, dropping the unsmoothed DC signal at BRIDGEOUT across R2, keeping SCR1 in an off condition during normal operation.

Still referring toFIG.1A, it is understood that under normal conditions the rectified unsmoothed DC signal at BRIDGEOUT is dropped across resistor R2 and that R2 is sized to allow an amount of AC current less than the relay16energizing current to flow through R2 through Q1 back to neutral when Q1 is conducting. During Q1's off state, or non-conducting state, relay16inductively opposes the change in current until Q1 again turns on, thus maintaining, or nearly maintaining the current flow through relay16. It is understood and appreciated that the small amount of relay current flowing through relay16is less than the energizing current needed to energize relay16to disengage manual reset switches12,12A. It is further appreciated that not starting from zero energizing current allows relay16to energize faster when a fault is detected.

Still referring toFIG.1Aand nowFIG.4, when either of the shields24A or24B integrity is compromised, such as, for example, a break in either shield, or a voltage drop across areas of corrosion within the power cable, the bias-on voltage VBEat the base of Q1 is insufficient to keep Q1 in its full conductive state. The voltage at the Q1 collector (V(SCRGATE)) begins to rise on the first positive rectified input cycle to trigger SCR1 into an on condition, sufficiently increasing current flow through relay16to energize relay16to disengage manual reset switches12,12A. Thus, interrupting power from the AC line source to the load. It is understood and appreciated that the full wave bridge rectifier100A enables the PCFC110A to detect and disconnect the AC line source from the load when a fault is detected during the positive or negative cycle of an input AC waveform (not shown). In other words, the PCFC110A detects and interrupts power between the AC line source and load within approximately 1 ms or less for a 60 Hz AC source.

Still referring toFIG.1AandFIG.4, when either of the shields24A or24B integrity is compromised, such as, for example, a leakage current, the bias-on voltage VBEat the base of Q1 is insufficient to keep Q1 in its full conductive state. The voltage at the Q1 collector (V(SCRGATE)) begins to rise on the second positive rectified input cycle to trigger SCR1 into an on condition, sufficiently increasing current flow through relay16to energize relay16to disengage manual reset switches12,12A. Thus, interrupting power from the AC line source to the load. It is understood and appreciated that the full wave bridge rectifier100A enables the PCFC110A to detect leakage current and disconnect the AC line source from the load when a fault is detected during the negative cycle of an input AC waveform (not shown). In other words, the PCFC110A detects and interrupts power between the AC line source and load within approximately 17 ms. or less for a 60 Hz AC source.

Referring now toFIG.5there is shown a diagram of Power Cord50including Line Wire Shield (LWS)24A and Neutral Wire Shield (NWS)24B shown inFIG.1andFIG.1A. Power Cord50includes neutral wire53, line wire54, and ground wire55. Neutral wire53, line wire54, and ground wire55are each surrounded by an insulator52. The LWS24A includes a conductive foil54B, a conductive braid54A surrounding the conductive foil54B, and an electrical insulating film56surrounding the conductive foil54B and the conductive braid54A. The electrical insulating film56may be any suitable insulating film such as a polyester film made from stretched polyethylene terephthalate (PET). The NWS24B includes a conductive foil53B, a conductive braid53A surrounding the conductive foil53B, and an electrical insulating film56surrounding the conductive foil53B and the conductive braid53A. The electrical insulating film56may be any suitable insulating film such as a polyester film made from stretched polyethylene terephthalate (PET).

Referring now toFIG.6there is shown an alternate embodiment60of the Power Cord50including Line Wire Shield (LWS)24A and Neutral Wire Shield (NWS)24B shown inFIG.1A. Power Cord60includes neutral wire53, line wire54, and ground wire55. Neutral wire53, line wire54, and ground wire55are each surrounded by an insulator52. The LWS24A includes a conductive foil54B, a conductive braid54A surrounding the conductive foil54B, and an electrical insulating film56surrounding the conductive foil54B and the conductive braid54A. The electrical insulating film56may be any suitable insulating film such as a polyester film made from stretched polyethylene terephthalate (PET). The NWS24B includes a conductive foil53B, a conductive braid53A surrounding the conductive foil53B, and an electrical insulating film56surrounding the conductive foil53B and the conductive braid53A. The electrical insulating film56may be any suitable insulating film such as a polyester film made from stretched polyethylene terephthalate (PET). Power cord60also includes accessory wire61surrounded by insulation62.

Referring now toFIG.7there is shown an alternate embodiment70of the Power Cord50including Line Wire Shield (LWS)24A and Neutral Wire Shield (NWS)24B shown inFIG.1A. Power Cord70includes neutral wire53, line wire54, and ground wire55. Neutral wire53, line wire54, and ground wire55are each surrounded by an insulator52. The LWS24A includes wire54, an insulator52surrounding wire54, conductive foil74, a conductive braid54A sandwiched between the conductive foil74and insulator52. The conductive foil74further includes a conductive side and a non-conductive side. The conductive side of conductive foil74faces outward and is in electrical contact with the conductive braid54A. The NWS24B includes wire53, an insulator52surrounding wire53, conductive foil73, a conductive braid53A sandwiched between the conductive foil73and insulator52. The conductive foil73further includes a conductive side and a non-conductive side. The conductive side of conductive foil73faces outward and is in electrical contact with the conductive braid53A. Each of the LWS and NWS are surrounded by a conductive foil75. The conductive foil75further includes a conductive side and a non-conductive side. The conductive side of conductive foil75A and75B faces inward and is in electrical contact with the conductive braids53A and54A, respectively.

Referring now toFIG.8there is shown an alternate embodiment80of the Power Cord50including Line Wire Shield (LWS)24A and Neutral Wire Shield (NWS)24B shown inFIG.1A. Power Cord80includes neutral wire53, line wire54, and ground wire55. Neutral wire53, line wire54, and ground wire55are each surrounded by an insulator52. The LWS24A includes a conductive foil54B surrounding the insulated line wire54, at least one copper strand wire84in electrical contact with the conductive foil54B, and an electrical insulating film56surrounding the conductive foil54B and the least one copper strand wire84. The electrical insulating film56may be any suitable insulating film such as a polyester film made from stretched polyethylene terephthalate (PET). The NWS24B includes a conductive foil53B surrounding the insulated neutral wire53, at least one copper strand wire83in electrical contact with the conductive foil53B, and an electrical insulating film56surrounding the conductive foil53B and the least one copper strand wire83. The electrical insulating film56may be any suitable insulating film such as a polyester film made from stretched polyethylene terephthalate (PET).

Referring now toFIG.9there is shown an alternate embodiment90of the Power Cord50including Line Wire Shield (LWS)24A and Neutral Wire Shield (NWS)24B shown inFIG.1A. Power Cord90includes neutral wire53, line wire54, and ground wire55. Neutral wire53, line wire54, and ground wire55are each surrounded by an insulator52. The LWS24A includes a conductive foil54B surrounding the insulated line wire54, at least one copper strand wire84in electrical contact with the conductive foil54B, and a conductive foil91A surrounding the conductive foil54B and the least one copper strand wire84. Each of the conductive foils54A and91A include a conductive side and a non-conductive side, The at least one copper strand wire84is sandwiched between the conductive sides of conductive foils54A and91A. The NWS24B includes a conductive foil53B surrounding the insulated neutral wire53, at least one copper strand wire83in electrical contact with the conductive foil53B, and a conductive foil91B surrounding the conductive foil54B and the least one copper strand wire83. Each of the conductive foils53B and91B include a conductive side and a non-conductive side, The at least one copper strand wire83is sandwiched between the conductive sides of conductive foils3B and91B.

It should be understood that the foregoing descriptions are only illustrative of the invention. It will be appreciated that the PCFC accomplishes leakage current detection and open shield detection. It will also be appreciated the PCFC does not include any discrete capacitors; thus, reducing the number of components and associated product production cycles. Thus, various alternatives and modifications can be devised by those skilled in the art without departing from the invention. For example, solid state devices SCR1 or Q1 can be any suitable solid-state device. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances that fall within the scope of the appended claims.