Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electrical power distribution systems and devices
Reexamination Certificate
1999-11-05
2001-06-26
Tolin, G P (Department: 2835)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electrical power distribution systems and devices
C218S078000
Reexamination Certificate
active
06252763
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gas-insulated electrical apparatus, and especially to a gas-insulated electrical apparatus suitable for an electric power substation or a switching station, which is capable of reducing DC residual voltage and preventing an insulation breakdown.
A gas-insulated electrical apparatus is composed of bus-bars contained in tanks into which insulation gas is sealed, bus-bar disconnectors, circuit breakers, and line circuit breakers, and is connected to transmission-lines or transformers via bushings.
Each bus-bar circuit breaker and each line circuit breaker perform a charging-current interruption which interrupts power fed to a capacitive load by voltage-interruption between a fixed-contact and a moving-contact which are included each circuit breaker, which is carried out by parting the moving-contact from the fixed-contact, and perform a loop-current interruption in which a current-flowing route is switched by communicating the current-flowing route by means of arch-discharging. However, while the moving-contact is parted from the fixed-contact, the re-ignition of arc occurs, which causes a surge of voltage.
As an apparatus which is capable of reducing a surge voltage while parting a moving-contact from a fixed-contact by preventing the re-ignition phenomenon occurring during the charging-current interruption, Japanese Patent Application Laid-Open Hei 2-44620 discloses an apparatus in which an auxiliary moving-contact is provided in a main moving-contact, a pressing member which moves in accordance with motion of the main moving-contact presses a pressed member located in a drive member for driving the auxiliary moving-contact, and the pressed member further presses the drive member.
In the conventional gas-insulated electrical apparatus, when an opening operation is performed, at first, a moving-contact in a circuit breaker is parted from a fixed-contact to interrupt current. However, since the contact-parting speed is a high speed of the order of several m/s, the contact-parting operation (opening operation) is completed without the re-ignition between the fixed and moving-contacts. Next, a disconnector is opened, and the re-ignition of arc occurs during the opening operation of the disconnector, which causes surge-voltage. Further, DC voltage remains at high-voltage conductors in the circuit breaker and the disconnector. The level of this residual voltage depends on the structure of the disconnector and the contact-parting speed, and if the level of the residual voltage is high, the insulation between the contacts of the disconnector may break down. In the worst case, a reverse-polarity DC residual voltage remains between the contacts, and its value is about 2 pu, where 1 pu is a peak value in the ordinary AC voltage to the ground level, and it is required that this residual voltage be decreased.
The residual voltage remaining between the circuit breaker and each disconnector due to the opening operation of the disconnector depends on the structure of the disconnector and the contact-parting speed in the disconnector. Since it is usually necessary to interrupt a bus-bar loop current, an electromotive spring operation method is adopted in the contact-parting operation of the disconnector, and the contact-parting speed is set at about 1-3 m/s. At the speed in this range, the re-ignition of arc is repeated between the tops of the fixed-contact and the moving-contact, and the insulation recovery voltage increases while the distance between the contacts increase. Thus, a large residual voltage of maximally 1 pu to the ground level and of maximally 2 pu between the contacts in the disconnector remains as a residual DC voltage after the opening operation of the disconnector has terminated.
Generally, in the insulation recovery voltage, the value of the insulation recovery voltage increases with respect to the distance between the contacts, and a positive voltage value is larger than a negative voltage value. Accordingly, a positive insulation recovery voltage remains after the opening operation has terminated. However, at a high contact-parting speed of about 1-3 m/s, the residual voltage becomes either positive or negative depending on the phase at the start of the contact-parting operation. Therefore, the residual voltage in the disconnector is large, and its polarity becomes one of the positive or negative polarity in the same probability. Thus, the insulation between the contacts, or between the conductors and the tank, probably breaks down.
If a conductor between the circuit breaker and each disconnector possesses a positive potential, a metallic extraneous substance in the tank reciprocates between the conductor and the inside surface of the tank, and it is highly probable that the charged extraneous substance adheres to the coated inside surface of the tank.
However, if a negative voltage remains between the circuit breaker and each disconnector, and the conductor possesses a negative potential, a floatable extraneous substance floats up and reaches the central conductor. Further, the extraneous substance also possesses a negative potential, and moves down due to the electrostatic repulsive-force and the gravity force. Furthermore, electrons are emitted from the extraneous substance due to local discharge during moving-down of the extraneous substance, and the polarity of the extraneous substance becomes positive. Finally, the extraneous substance is attracted by and adhered to the conductor. If there is an extraneous substance near a conductor with a high voltage, and a high voltage due to a thunder surge, etc., is applied to the extraneous substance and the conductor, discharging is induced by the extraneous substance, and a grounding accident possibly occurs.
SUMMARY OF THE INVENTION
The present invention has been achieved in consideration of the above problems, and is aimed at providing a highly reliable gas-insulated electrical apparatus which is capable of reducing a residual voltage generating between a circuit breaker and a disconnector, due to a contact-parting operation of the disconnector, and in which a grounding accident scarcely occurs even if there is an extraneous substance in a tank containing the disconnector.
To attain the above object, the present invention provides a gas-insulated electrical apparatus comprising:
tanks into each of which insulation gas is sealed including bus-bars, bus-bar disconnectors connected to the bus-bars, circuit breakers connected to the bus-bar disconnectors, and line disconnectors connected to the circuit breakers, each line disconnector being further connected to a transmission or a transformer;
wherein a contact-parting speed in each line disconnector is lower than that in each bus-bar disconnector.
Further, in the above gas-insulated electrical apparatus, each bus-bar disconnector and each line disconnector include respective pairs of a fixed-contact and a moving-contact, the fixed-contact in the bus-bar disconnector is located at the side of a corresponding bus-bar connected to the bus-bar disconnector, the moving-contact in the bus-bar disconnector is located at the side of a corresponding circuit breaker connected to the bus-bar disconnector via a connection bus-bar, the fixed-contact in the line disconnector is located at the side of a transmission line or a transformer connected to the line disconnector, and the moving-contact in the line disconnector is located at the side of a corresponding circuit breaker connected to the line disconnector.
Furthermore, in the above gas-insulated electrical apparatus, a moving-contact parting speed in each line disconnector is in a range of about 0.1-0.3 m/s.
Moreover, the present invention provides a gas-insulated electrical apparatus comprising:
tanks into each of which insulation gas is sealed including bus-bars, bus-bar disconnectors connected to the bus-bars, circuit breakers connected to the bus-bar disconnectors, and line disconnectors connected to the circuit breakers, each line disconnector being further connected
Annou Kenji
Enokida Yoshikatsu
Shimokawa Masahiro
Takamoto Manabu
Yamagiwa Tokio
Hitachi , Ltd.
Mattingly Stanger & Malur, P.C.
Tolin G P
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