Power cord LCDI and hotspot detector circuit

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). In addition to shield breaks the PCFC also monitors the energized shields for shield degradation due to, for example, galvanic corrosion.

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 detector 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 age due to long-term use, or may become damaged when the appliance is moved, which may cause a high current leakage between the phase line and the neutral or ground lines in the power cord. In addition to personal safety concerns, leakage current may cause sparks, which may cause fire and property damage. Leakage current can be detected by monitoring a small test voltage or current on conductive metal sheaths surrounding a conductive jacket surrounding the insulated phase and neutral lines. The metal sheaths are conventionally made by weaving thin copper wires surrounding, typically, an aluminum conductive jacket.

The conductive metal sheaths can fail due to failure in structural integrity (e.g., open) or corrosion due to galvanic action between dissimilar metals (e.g., copper braid and aluminum jacket). Failure of the metal sheaths may let dangerous leakage current go undetected by an ordinary LCDI circuit. Conventional LCDI circuits that test the continuity of the metal sheaths only test if the metal sheath is conductive or open. However, not tested by conventional LCDI circuits is galvanic corrosion between the dissimilar metals that may result in hot spots in the power cord, indicative of pending failure of the conductive metal sheaths.

Also, prior art solutions often provide a circuit for detecting an open shield, i.e., failed structural integrity, and a separate circuit for detecting leakage current. However, multiple circuits require more parts, 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

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 and an insulated line wire is provided. The LCDI circuit includes the insulated neutral wire surrounded by a neutral wire shield (NWS); the insulated line wire surrounded by a line wire shield (LWS) connected to the NWS. The LCDI circuit also includes a power cord fault circuit (PCFC) for monitoring the NWS and LWS integrity and leakage current. The PCFC includes a non-linear device (NLD) and a bi-stable latching device for interrupting the AC power from the AC source via a relay. The LCDI circuit also includes a power supply circuit for supplying a rectified voltage waveform to the PCFC and the LWS.

In another aspect, the present invention provides a Power Cord Shield Monitoring (PCSM) 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), wherein the NWS and LWS are connected via a shield connector. The PCSM circuit includes a non-linear NPN transistor connectable to the NWS. The non-linear NPN transistor includes a saturation mode; a cut-off mode; and an active mode. The PCSM also includes a base biasing circuit for biasing the base of the NPN transistor. The base biasing circuit includes one or more base biasing resistors, the NWS; the LWS; the shield connector; and at least one collector biasing resistor connectable to the collector and the bi-stable latching device. The NPN transistor, the base biasing circuit and the at least one collector biasing resistor determine the NPN transistor mode. Also included: a mechanically latched double pole switch disposed between the AC source and the load; a relay for delatching the double pole switch; and a bi-stable latching device connected to the NLD and the relay for interrupting the AC power from the AC source based on the NLD mode. At least one capacitor connectable to the NLD and the bi-stable latching device and a power supply circuit for biasing the NLD and the bi-stable latching device are also provided.

The invention is also directed towards a Power Cord Shield Monitoring (PCSM) 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), wherein the NWS and LWS are connected via a shield connector. The PCSM circuit includes a non-linear device (NLD) connectable to the NWS. The NLD may be any suitable NLD such as a transistor having a collector, an emitter, and a base. The NLD has several operation modes: a saturation mode where the NLD acts as a short circuit, a cut-off mode where the NLD acts like an open circuit, and an active mode where current through the NLD is proportional to the bias current on the NLD's control port such as the base of an NPN transistor configured as a common emitter as described herein. The PCSM circuit also includes a bi-stable latching device connected to the NLD for interrupting the AC power from the AC source based on the NLD operating mode.

Various other features and advantages will appear from the description to follow. In the description, reference is made to the drawings which form a part thereof, and in which is shown by way of illustration, specific embodiments for practicing the invention. These embodiments will be described in enough detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be used and that structural changes may be made without departing from the scope of the invention. That means the following detailed description is, not to be taken in a limiting sense.

DETAILED DESCRIPTION

The term “comprising” means including but not limited to, and should be interpreted in the way it is typically used in the patent context;

The phrases “in one embodiment,” “according to one embodiment,” generally mean that the particular feature, structure, or characteristic following the phrase may be included in at least one embodiment of the present invention, and may be included in more than one embodiment of the present invention (such phrases do not necessarily refer to the same embodiment);

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, TEST switch18, power supply circuit100, power cord fault circuit (PCFC)110, relay16; and, manually engaged ganged switches12A,12B, the manual reset switch. LCDI circuit10also includes R4and LED for indicating normal operation. Also included are metal oxide varistors MOV1and MOV2for circuit overload protection.

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. As discussed and shown in more detail herein, the PCFC110lets a small amount of relay current 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 lets solenoid16energize faster when a fault is detected.

Referring also toFIG.1Athere is shown a detailed circuit10A of the block diagram10inFIG.1. LCDI circuit10A includes Line Wire Shield (LWS)24A, Neutral Wire Shield (NWS)24B, SHIELD CONNECTOR24C, TEST switch18, power supply circuit100A, and PCFC110A. PCFC110A includes transistor Q1, capacitor C1, and silicon-controlled rectifier SCR. It will be understood that Q1may be any suitable non-linear device having a saturation mode, a cut-off mode, and an active mode. SCR may be any suitable bi-stable latching device. 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. 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 discussed and shown in more detail herein, the PCFC110lets a small amount of relay current 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 lets relay16energize 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 manually engaged 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 Q1base via shields24A,24B and resistors R1and R3. The rectified unsmoothed DC signal at BRIDGEOUT is also routed through R2and R2A to Q1collector and SCR1gate.

Still referring toFIG.1AandFIG.2, the rectified unsmoothed DC signal at BRIDGEOUT is routed to the base of NPN transistor Q1, R1and R3biasing Q1into an on condition during the positive cycle of the rectified unsmoothed DC, dropping the rectified voltage across R2and R2A. When Q1(B) voltage drops below Q1's VBEsaturation voltage Q1turns off. The voltage at Q1(C) and SCR1gate are near 0 v due to the unsmoothed DC signal at BRIDGEOUT dropping to near 0 v in the cycle. When the unsmoothed DC signal at BRIDGEOUT swings positive, Q1is again biased on, dropping the unsmoothed DC signal at BRIDGEOUT across R2and R2A, keeping SCR1in 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 R2and R2A and that R2and R2A are sized to allow an amount of AC current less than the relay16energizing current to flow through R2and R2A through Q1back to neutral when Q1is conducting. During Q1's off state, or non-conducting state, relay16inductively opposes the change in current until Q1again 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 lets relay16energize faster when a fault is detected.

Still referring toFIG.1Aand nowFIG.4, when either shield24A or24B integrity is compromised, e.g., open, the bias-on voltage VBEat the base of Q1is not enough to keep Q1in its full conductive state. The voltage at the Q1collector (V(SCRGATE)) rises on the first positive rectified input cycle to trigger SCR1into 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).

Referring also toFIG.5there is shown a waveform diagram for the shield degraded condition of the Power Cord Circuit inFIGS.1,1A. It will be appreciated that R1, Shield24A, Shield24B, connector24C and R3form the base biasing circuit for Q1. As shield resistance goes up, e.g., due to galvanic corrosion due to dissimilar metals in the power cord shields, Q1VBEwill begin to fall below Q1's VBEsaturation voltage thus decreasing ICE. As ICE decreases C1begins to charge. When the charge on C1reaches SCR1gate trigger voltage, the SCR triggers into an on condition, which increases current flow through relay16to energize relay16to disengage manual reset switches12,12A. Thus, interrupting power from the AC line source to the load.

Referring also toFIG.6there 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.7there 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 also toFIG.8there 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.9there 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.10there 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 will be appreciated that the present invention detects degraded shields and open shields. Further, it should be understood that the foregoing descriptions are only illustrative of the invention. Thus, various alternatives and changes can be devised by those skilled in the art without departing from the invention. For example, solid state devices SCR1or Q1can be any suitable solid-state device. For example, Q1may be any suitable non-linear device or transistor configuration, such as a common base configuration. The present invention is intended to embrace all such alternatives, changes and variances that fall within the scope of the appended claims.