Electricity: power supply or regulation systems – Including a transformer or an inductor – Polyphase or plural transformers
Reexamination Certificate
2000-01-27
2001-01-30
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Including a transformer or an inductor
Polyphase or plural transformers
C361S044000
Reexamination Certificate
active
06181125
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a power distribution equipment, and more particularly to a combination apparatus of a distribution transformer and switches.
BACKGROUND OF THE INVENTION
At present, in China, the majority of power distribution cabinet are provided with a &Dgr;/Y
0
connected three-phase three-leg distribution transformer, while high voltage load switches, tapping switches, high voltage fuses (or circuit breakers) etc. are installed outside the sealed enclosure of the distribution transformer. As a result, the power distribution cabinet used in China has a larger volume, occupies more land and needs more maintenance. In the United States, an integrated power distribution cabinet, in which a Y
0
/Y
0
connected three-phase five-leg distribution transformer is mounted, is popularly used, wherein the main bodies of high voltage load switches, tapping switches, and high voltage fuses are installed inside the sealed enclosure of the distribution transformer. Hence, the power distribution cabinet used in the United States has a smaller volume, occupies less land and needs less maintenance. However, the integrated power distribution cabinet has a disadvantage that it can not be used in a neutral non-grounded power system. Because in a neutral non-grounded power system, whether the transformer is connected in a Y
0
Y
0
connection mode or in a &Dgr;/Y
0
connection mode, interrupting of one phase of high voltage fuse will cause the other two phases to have supply voltages far higher or far lower than the rated voltages thereof. It not only impairs the quality of power supply, but also probably causes damages of the user's electric apparatus as operating under such a higher voltage or lower voltage. For the time being, in China, a solution is to trip simultaneously all three phases artificially when an one-phase fault occurs. Obviously it is not very reasonable.
SUMMARY OF THE INVENTION
The object of the invention is to provide a combination apparatus of a distribution transformer and switches, which can be utilized both in a neutral grounded power system and in a neutral non-grounded power system. When high voltage fuses are interrupted upon an occurrence of a phase-to-ground fault or a phase-to-phase fault, the fault-free phases can operate in an normal power supply state, only the faulty phases being in a completely open state so that the combination apparatus of a distribution transformer and switches according to the invention has three phases that are non-mutual interferential.
To this end, the combination apparatus of a distribution transformer and switches according to the invention comprises an enclosure provided with low voltage bushings and high voltage bushings, in which a three-phase five-leg distribution transformer is disposed. The low voltage windings of the three-phase five-leg distribution transformer are connected in Y
0
connection mode, and the output terminals thereof are led out of the enclosure through the low voltage bushings serving as the low voltage output terminals of the combination apparatus. The high voltage windings of the three-phase five-leg distribution transformer are connected in series with at least a set of high voltage fuses to form three phases of high voltage phase-arms, and the three phases of high voltage phase-arms are connected in &Dgr; connection mode. The high voltage output terminals of the combination apparatus are led out of the enclosure through the high voltage bushings from the connecting points of the three phases of high voltage phase-arms.
In order to improve the interruption capacity and the time-current characteristics of the high voltage fuses, two high voltage fuses having the same performances or different performances can be connected in serial in each high voltage phase-arm.
REFERENCES:
patent: 2198489 (1940-04-01), Snyder et al.
patent: 5341265 (1994-08-01), Westrom et al.
patent: 5886888 (1999-03-01), Akamatsu et al.
patent: 0024934 (1981-03-01), None
patent: 61-008645 (1986-03-01), None
International Search Report for PCT/CN98/00077 completed Aug. 20, 1998.
Li Shulin
Zhang Xujun
Han Jessica
Merchant and Gould P.C.
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