US 5,856,902 A · Earth leakage breaker

Abstract

The earth leakage breaker of the invention includes a first comparator; a second comparator connected to the first comparator; a third comparator having a threshold higher than the threshold of the first comparator for distinguishing a leakage current from the grounding current caused by a lightning surge or by the heavy ground fault; a monostable multivibrator triggered by the output of the third comparator for forming a time gate of a predetermined period; a counter for detecting a pulse outputted from the first comparator to distinguish whether the grounding current is caused by the lightning surge or by the heavy ground fault; and a trip signal generator circuit for outputting a trip signal in the case of leakage and heavy ground fault. The earth leakage breaker facilitates avoiding unnecessary breaking of the impulsive grounding current caused by the lightning surge.

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Claims9

Dependent claims

An earth leakage breaker having main circuit conductors comprising:

a zero-phase current transformer through which the main circuit conductors are inserted;
first detecting means for detecting a leakage current and a grounding current including heavy ground fault and lightning surge, said first detecting means comprising a first comparator connected to the zero-phase current transformer for detecting if a secondary output of the zero-phase current transformer exceeds a first detection level;
an integrator connected to the first comparator for integrating an output of the first comparator;
and a second comparator connected to the integrator, said second comparator detecting an output of the integrator exceeding a second detection level and out putting a first signal;
second detecting means connected parallel to the first detecting means and having a third detection level higher than said first detection level, said second detecting means detecting if said secondary output of said zero-phase current transformer repeatedly exceeds said third detection level to thereby output a second signal indicative of one of said leakage current and said grounding current caused by heavy ground fault, said second detecting means including a third comparator connected to the zero-phase current transformer for detecting if said secondary output of said zero-phase current transformer is higher than said third detection level;
a monostable multivibrator connected to the third comparator to be triggered by an output of the third comparator for a predetermined operating period;
a counter connected to the monostable multivibrator and the first comparator, said counter counting pulses outputted from said first comparator for said predetermined operating period of said monostable multivibrator and outputting a counting signal indicating that said counter has counted a predetermined number of pulses;
and an OR gate connected to the counter and the monostable multivibrator, said OR gate receiving-said-counting signal and an inverted output from said monostable multivibrator and outputting the second signal;
a first AND gate connected to the first and second detecting means, said first AND gate receiving said second signal from said second detecting means and said first signal from said second comparator and outputting an AND output;
and
a trip signal generator connected to the first and second detecting means through the first AND gate, said trip signal generator outputting a trip signal to a trip coil in response to said first signal and said second signal.

8 more elements

An earth leakage breaker having main circuit conductors comprising:

a zero-phase current transformer through which the main circuit conductors are inserted;
first detecting means for detecting a leakage current and a grounding current including heavy ground fault and lightning surge, said first detecting means comprising a first comparator connected to the zero-phase current transformer for detecting if a secondary output of the zero-phase current transformer exceeds a first detection level;
an integrator connected to the first comparator for integrating an output of the first comparator;
and a second comparator connected to the integrator, said second comparator detecting an output of the integrator exceeding a second detection level and outputting a first signal;
second detecting means arranged parallel to said integrator and said second comparator of said first detecting means, said second detecting means detecting a predetermined number of pulses outputted from said first comparator in a period based on said first signal from said second comparator, and outputting a second signal indicative of one of said leakage current and said grounding current caused by heavy ground fault;
and
a trip signal generator connected to the first and second detecting means, said trip signal generator outputting a trip signal to a trip coil in response to said first signal and said second signal.

4 more elements

An earth leakage breaker having main circuit conductors comprising:

a zero-phase current transformer through which the main circuit conductors are inserted;
first detecting means for detecting a leakage current and a grounding current including heavy ground fault and lightning surge, said first detecting means comprising a first comparator connected to the zero-phase current transformer for detecting if a secondary output of the zero-phase current transformer exceeds a first detection level;
an integrator connected to the first comparator for integrating an output of the first comparator;
and a second comparator connected to the integrator, said second comparator detecting an output of the integrator exceeding a second detection level and outputting a first signal;
second detecting means connected parallel to the first detecting means and having a third detection level higher than said first detection level, said second detecting means detecting if said secondary output of said zero-phase current transformer repeatedly exceeds said third detection level to thereby output a second signal indicative of one of said leakage current and said grounding current caused by heavy ground fault, said second detecting means including a third comparator connected to the zero-phase current transformer for detecting if the secondary output of said zero-phase current transformer is higher than said third detection level;
a monostable multivibrator connected to the third comparator to be triggered by an output of the third comparator for a predetermined operating period;
a counter connected to the monostable multivibrator and the first comparator, said counter counting pulses outputted from said first comparator for said predetermined operating period of said monostable multivibrator and outputting a counting signal indicating that said counter has counted a predetermined number of pulses;
and an RS flip-flop having a reset terminal for receiving an OR output by said counting signal and an inverted output of said first signal from said second comparator, and a set terminal for receiving an AND output by an output from said monostable multivibrator and said first signal from said second comparator, an inverted output of said RS flip-flop being said second signal;
a first AND gate connected to the first and second detecting means, said first AND gate receiving said second signal from said second detecting means and said first signal from said second comparator and outputting an AND output;
and
a trip signal generator connected to the first and second detecting means through the first AND gate, said trip signal generator outputting a trip signal to a trip coil in response to said first signal and said second signal.

8 more elements

An earth leakage breaker having main circuit conductors comprising:

a zero-phase current transformer through which the main circuit conductors are inserted;
first detecting means for detecting a leakage current and a grounding current including heavy ground fault and lightning surge, said first detecting means comprising a first comparator connected to the zero-phase current transformer for detecting if a secondary output of the zero-phase current transformer exceeds a first detection level;
an integrator connected to the first comparator for integrating an output of the first comparator;
and a second comparator connected to the integrator, said second comparator detecting an output of the integrator exceeding a second detection level and outputting a first signal;
second detecting means connected parallel to the first comparator of the first detecting means and having a third detection level higher than said first detection level, said second detecting means detecting if said secondary output of said zero-phase current transformer repeatedly exceeds said third detection level to thereby output a second signal indicative of one of said leakage current and said grounding current caused by heavy ground fault, said second detecting means including a third comparator connected to the zero-phase current transformer for detecting if the secondary output of said zero-phase current transformer is higher than said third detection level;
a monostable multivibrator connected to the third comparator to be triggered by an output of the third comparator for a predetermined operating period;
and a charge-up condition change-over circuit connected to the monostable multivibrator for changing over a charge-up condition of said integrator to thereby prolong an integration period of the integrator for said predetermined operating period of said monostable multivibrator;
and
a trip signal generator connected to the second comparator of the first detecting means, said trip signal generator outputting a trip signal to a trip coil in response to said first signal and said second signal.

6 more elements

Dependencies are inferred from the claim text.

Description6,020 words

Summary2,378 words

#The present invention relates to an earth leakage breaker. More specifically, the present invention relates to an earth leakage breaker that facilitates avoiding unnecessary break caused by lightning surge.

#FIG. 16 is a block diagram of a conventional earth leakage breaker. FIG. 17 is a time chart of the outputs from the constituent devices of the conventional earth leakage breaker of FIG. 16. Referring now to FIGS. 16 and 17, a secondary current is generated in a secondary winding of a zero-phase current transformer 3 (hereinafter referred to as a "ZCT") wound around main circuit conductors 2 of an earth leakage breaker 1 when a leakage current or a grounding current caused by lightning surge flows in the main circuit conductors 2. The secondary current is converted to a voltage signal by a resistor 4. The voltage signal is amplified by an amplifier 6 after impulsive noise or high frequency leakage current components on the secondary side of an inverter are removed from the voltage signal by a low-pass filter 5. The output of the amplifier 6 is resolved to positive and negative pulses by the threshold of a first comparator 7. The positive and negative pulses are synthesized in an OR circuit (OR1). The output of the first comparator 7 through the OR circuit (OR1) is integrated in an integrator circuit 8. When the output of the integrator circuit 8 exceeds the threshold of a second comparator 9, a trip-signal generator circuit 10 feeds a trip signal .gamma. to a trip coil 11 based on the output .alpha. of the second comparator 9 to trip the earth leakage breaker 1.

#The breaking period of the high-speed earth leakage breaker is specified to be within 40 ms by the IEC specification for protecting the human body. Since it usually takes about 23 ms at the maximum for the earth leakage breaker to operate mechanically, 40-23=17 ms is left for the judging period until feeding the trip signal to the trip coil. If the period during which the output of the amplifier 6 exceeds the threshold of the first comparator 7 described in FIG. 17, i.e. the pulse width of the output of the first comparator 7, is set at 7 ms and the pulse interval at 3 ms, the total pulse width necessary to output the trip signal .gamma. within the foregoing 17 sec., i.e. the integration period of the integrator circuit 8, will be 17-3=14 ms.

Brief description of the drawings17 figures

#FIG. 1 is a block diagram of a first embodiment of an earth leakage breaker according to the invention;

#FIG. 2 is a time chart of the outputs from the constituent devices of the earth leakage breaker of FIG. 1;

#FIG. 3 is another time chart of the outputs from the constituent devices of the earth leakage breaker of FIG. 1;

Detailed description3,304 words

#Now the present invention will be explained hereinafter with reference to the accompanied drawings which illustrate the preferred embodiments of the invention. In the following drawings, constituent devices similar to those of the conventional earth leakage breaker are designated by the same reference numerals.

#FIG. 1 is a block diagram of a first embodiment of an earth leakage breaker according to the invention. FIG. 2 is a time chart of the outputs from the constituent devices of the earth leakage breaker of FIG. 1. FIG. 3 is another time chart of the outputs from the constituent devices of the earth leakage breaker of FIG. 1.

#Referring now to FIGS. 1 and 2, a secondary current is generated in a secondary winding of a ZCT 3 wound around main conductors 2 when a leakage current of, e.g., 15 mA, flows in the main conductors 2. The secondary current is converted to a voltage signal by a resistor 4. The voltage signal is amplified by an amplifier 6 after the voltage signal passes a low-pass filter 5. The output of the amplifier 6 is resolved, e.g. at the commercial frequency of 50 Hz, to the positive and negative pulses of 7 ms in the pulse width and 3 ms in the pulse interval by the threshold of the first comparator 7 (1st detection level) set for converting the voltage signal corresponding to the foregoing 15 mA to the pulse signal. The positive and negative pulses are synthesized in an OR circuit (OR1). An integrator circuit 8 is charged up with the output of the OR circuit (OR1), wherein the charge-up time constant of the integrator circuit 8 is set such that the total pulse width of, e.g., 14 ms or more, will exceed the threshold of the second comparator 9 (2nd detection level), and the output .alpha. of the second comparator 9 is set to be "H".

Earth leakage breaker

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Earth leakage breaker

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Abstract

Drawings

Drawings

Claims9

Description6,020 words

Drawings

Classification3 codes

Life of this patent

Description6,020 words