Electricity: electrical systems and devices – Safety and protection of systems and devices – Feeder protection in distribution networks
Patent
1994-08-03
1997-07-08
Gaffin, Jeffrey A.
Electricity: electrical systems and devices
Safety and protection of systems and devices
Feeder protection in distribution networks
361 82, H02H 300
Patent
active
056468113
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a reverse-charge prevention apparatus including a 1st breaker for connecting or disconnecting an electric power system to or from a distributed electric power apparatus, in which reverse-charge from the distributed electric power apparatus to the electric power system is prevented by switching off the 1st breaker when the distributed electric power apparatus is disconnected from the electric power system by switching off a 2nd breaker disposed in the electric power system.
2. Description of the Prior Art
In recent years, in order to harness natural energy or improve the efficiency of energy use, there has been developed an inverter type of distributed electric power apparatus in which direct-current electric power output by a solar battery or a fuel battery is transformed into alternating-current electric power by means of an inverter or a so-called "cogeneration" type of distributed electric power apparatus in which alternating-current electric power is generated by linking an engine to a generator. By connecting such a distributed electric power apparatus to the electric power system (constituted of power stations, transmission lines, substations, distribution lines, etc.), an electricity shortage can be filled up by the electric power of the electric power system to constantly supply electric power when an accident occurs to the distributed electric power apparatus or electric power generated by only the distributed electric power apparatus cannot sufficiently meet electric power demand.
However, the following problem might occur in a case in which the distributed power apparatus and the electric power system are connected to each other.
That is, there is a case in which, before construction work or repairs are carried out for the electric power system, breakers are switched off to stop supplying electric power. If the distributed electric power apparatus is connected to a distribution line, a voltage of the distributed electric power apparatus is applied to the distribution line so that a state of reverse-charge is made even if the electric power system is intercepted (in other words, even if a breaker of the distribution line is switched off to stop supplying electricity). For this reason, a worker carrying out the construction work or the like on the distribution line has a lot of danger of receiving an electric shock due to the reverse-charge.
Accordingly, a method is conventionally adopted in which the distributed electric power apparatus is provided with an over-under voltage relay (about .+-.10% with respect to a reference voltage), an abnormal frequency relay (about .+-.1 Hz) with respect to a reference frequency), or the like and is disconnected from the electric power system on the assumption that the circuit of the electric power system is opened (broken) if an allowable value is exceeded by a difference between the reference voltage and a voltage generated when the circuit of the electric power system is opened or a difference between the reference frequency and a frequency generated when the same is opened.
However, in the above method, if the electric power from the distributed electric power apparatus and a load needed by consumers are balanced with each other, there occurs a problem that the openness of the circuit of the electric power system cannot be certainly detected since variations in voltage and frequency are too small to be detected by the above relays.
To solve the problem, in view of the fact that the inverter type of distributed electric power apparatus has a variation different from a periodic variation peculiar to the electric power system in a period of an outputted alternating-current voltage, a reverse-charge prevention apparatus is proposed in which, by judging that a supply of power is cut off from the electric power system when a variation in the period of the alternating-current voltage is observed on the side of the distributed electric power apparatus, the distributed electric power ap
Higasa Hiromasa
Ishikawa Fumihiko
Gaffin Jeffrey A.
Kabushiki Kaisha Shikoku Sogo Kenkyujo
Leja Ronald W.
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