Electricity: electrical systems and devices – Safety and protection of systems and devices – Ground fault protection
Reexamination Certificate
2002-11-07
2003-07-15
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Ground fault protection
C361S062000
Reexamination Certificate
active
06594127
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power generation system, and more particularly, to a power generation system which can prevent an unnecessary operation due to an accident of external grounding.
2. Description of the Related Art
A description will now be provided of a solar power generation system connected to an ordinary low-voltage distribution system with reference to FIG.
9
.
FIG. 9
is a schematic diagram illustrating conventional connection between a solar power generation system and a low-voltage distribution system. In
FIG. 9
, A represents a consumer having a solar power generation system, which includes a solar-cell array
1
, a system interconnection inverter
2
, and a receiving-end earth leakage breaker
3
. The solar-cell array
1
, serving as a DC power supply, includes solar-cell modules interconnected in series and/or in parallel so as to provide desired voltage and current. The solar-cell array
1
is connected to the system interconnection inverter
2
, which is connected to a low-voltage distribution system
4
via the receiving-end earth leakage breaker
3
. A load
5
is connected between the system interconnection inverter
2
and the receiving-end earth leakage breaker
3
. DC electric power from the solar-cell array
1
is input to the system interconnection inverter
2
in order to be converted into an AC electric power, which is output to the load
5
or the low-voltage distribution system
4
. Wiring within the consumer A is provided from the receiving-end earth leakage breaker
3
to the system interconnection inverter
2
and to the load
5
. The receiving-end earth leakage breaker
3
detects an accident of grounding by detecting a ground current, and disconnects connection between the inside and the outside of the consumer A so that the accident of grounding does not influence the low-voltage distribution system
4
at the outside of the consumer A.
Other consumers B
1
and B
2
which do not have power generation facilities are connected to the low-voltage distribution system
4
via respective receiving-end earth leakage breakers
3
.
Since the solar-cell array
1
has a large area, an earth floating capacitance
6
is present. Recently, solar-cell modules integrated with a building material, or thin solar-cell modules have been developed as solar-cell modules constituting the solar-cell array
1
. Sometimes, a conductive member (a metal plate or the like) is used as a reinforcing material or a substrate material for such a solar-cell module. In such a case, a solar-cell array sometimes faces a metal plate with a short distance and a large area, thereby increasing the earth floating capacitance
6
. Particularly when the metal plate is grounded, the solar-cell array has a stable earth floating capacitance. Furthermore, if, for example, water from rain adheres to the surface of the solar-cell array, the earth floating capacitance
6
is sometimes generated via the water.
In accordance with recent tendency toward a higher efficiency, a smaller size, a lighter weight and a lower cost and the like, the system interconnection inverter
2
mostly adopts a transformerless system in which an insulating transformer is not provided.
We found that, if an accident of grounding occurs at another consumer B
1
or B
2
when the earth floating capacitance
6
is large and the system interconnection inverter
2
adopts the transformerless system, a ground current Ig
2
penetrates into the system via the earth floating capacitance
6
of the solar-cell array
1
, passes through the system interconnection inverter
2
, and is detected by the reception-end earth leakage breaker
3
, thereby causing an unnecessary operation. If such an unnecessary operation is generated, the inside of the consumer A having the solar power generation system is disconnected from the low-voltage distribution system
4
and power supply to the inside of the consumer A is failed, although no accident occurs within the consumer A.
The above-described problems are not limited to the solar power generation system. For example, in a wind power generation system or in a power generation system using fuel cells or the like, the same problems also arise if the earth floating capacitance is large. Hence, there is the possibility that the reception-end earth leakage breaker unnecessarily operates due to an accident of external grounding and electric power supply fails within a consumer.
SUMMARY OF THE INVENTION
It is an object of the present invention to solve the above-described problems.
It is another object of the present invention to provide a power generation system which can prevent an unnecessary operation of a receiving-end earth leakage breaker due to an accident of external grounding.
According to one aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system to which a plurality of consumers, each having an earth leakage breaker, are connected and one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. An operational time limit of the receiving-end earth leakage breaker of the power generation system is set to a value larger than an operational time limit of the earth leakage breakers provided in the consumers.
According to another aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. The system also includes ground-direction determination means for determining whether a grounded position is inside or outside the power generation system.
According to still another aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. The receiving-end earth leakage breaker includes voltage-to-ground detection means, a zero-phase current transformer, zero-phase-current detection means connected to the zero-phase current transformer, phase comparison means connected to the voltage-to-ground detection means and the zero-phase-current detection means, a time-limit selector, connected to the phase comparison means, for selecting a different time limit in accordance with a signal output from the phase comparison means, zero-phase-current-level determination means connected to the zero-phase-current detection means, and contact driving means, connected to the zero-phase-current-level determination means and the time-limit selector, for driving a contact in accordance with an output of each of the zero-phase-current-level determination means and the time-limit selector.
According to yet another aspect, the present invention which achieves these objectives relates to a power generation system including a DC power supply connected to a low-voltage distribution system one wire of which is grounded, via a receiving-end earth leakage breaker, and including at least a transformerless inverter and an earth floating capacitance. The receiving-end earth leakage breaker includes voltage-to-ground detection means, voltage-to-ground-level determination means connected to the voltage-to-ground detection means, a zero-phase current transformer, zero-phase-current detection means connected to the zero-phase current transformer, zero-phase-current level determination means connected to the zero-phase-current detection means, and contact driving means, connected to the zero-phase-current-level determination means and the voltage-to-ground-level determination means, for driving a contact in accordance with
Manabe Naoki
Takehara Nobuyoshi
Benenson Boris
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Sircus Brian
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