Inductor devices – With electric and/or magnetic shielding means
Reexamination Certificate
1995-06-28
2001-09-11
Mai, Anh (Department: 2832)
Inductor devices
With electric and/or magnetic shielding means
C336S08400R, C336S174000
Reexamination Certificate
active
06288625
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention proceeds from a current transformer for a metal-enclosed gas-insulated high-voltage installation accordance with the preamble of claim
1
or of claim
9
.
2. Discussion of Background
In this connection, the invention relates to a prior art as disclosed, for example, in the publication EP-A2-0 522 303.The combined instrument transformer described therein is intended for a metal-enclosed gas-insulated high-voltage installation. It has a current sensor and a voltage sensor and a signal processing system downstream of the current sensor and voltage sensor. The current sensor used is a pickup coil which is wound around an annular core composed of nonferromagnetic, predominantly isotropic material. Provided as voltage sensor is a hollow-cylindrically formed measuring electrode. After the current sensor and the voltage sensor have been installed in the metal enclosure, the coil and the measuring electrode concentrically surround a current conductor of the gas-insulated switching installation.
The pickup coil is embedded in an annular insulating body which is disposed in an annular space. The walls of the space are composed of electrically conducting material, preferably of an aluminum alloy. The insulating body is fixed in position in said space. On its circumferential surface adjacent to the current conductor, the space is bounded by an areal, annular screening electrode. One end face of this screening electrode is connected in an electrically conducting manner to the wall on one side of the annular space, while the end face situated opposite it is connected in an electrically insulating manner to the wall on the other side of the annular space. Provided here as insulating connection is a comparatively narrow gap completely filled with insulating material. The walls of the annular space form an electrically conducting screen with the screening electrode. Said screen protects the annular space against the influence of electrical interference fields. During measurement in the high-voltage installation under operating conditions, the pickup coil therefore delivers signals which are free of influences due to the electrical interference fields. The pickup coil provides signals which are proportional to the magnitude and the change with respect to time of the current flowing in the current conductor of the gas-insulated switching installation and which are virtually free of the effects of electrical extraneous fields because of the suitably disposed screen. For many practical applications, a current transformer constructed in this manner is probably completely satisfactory.
However, the gap filled with insulating material in the screen surrounding the pickup coil is the reason for rapid and very rapid transient electrical interferences, for example in a frequency range from more than 1 MHz to approximately several GHz, not being isolated from the pickup coil. Such interferences distort the measured signal and they may additionally be the reason for the overvoltage protection always present at the input of the signal processing system being overloaded.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention, as it is specified in the independent patent claims, is to provide a novel current transformer for metal-enclosed gas-insulated high-voltage installations which is also insensitive to extremely high-frequency electrical interferences, which is inexpensive to construct and which is notable for small dimensions and for a high measurement accuracy.
The current transformer according to the invention is notable for the fact that it is protected against high-frequency interferences. The current transformer has a toroidally formed current sensor enclosing a current path and a signal processing system downstream of said sensor. It furthermore has an annular cavity which surrounds the current sensor and is enclosed by an electrically conducting screen and which is filled with a compound. In addition, it is provided with at least one circumferential gap designed as an interruption in the screen. Said at least one interruption in the screen is designed so that it is fully effective during the normal operation of the current transformer and that it is shunted if high-frequency interferences occur. The high-frequency interference is accordingly rendered harmless, while the measured-value determination in the current transformer continues unaffected at the same time.
In a preferred embodiment of the current transformer, the gap is of labyrinth-type design. Conducting or semiconducting means are provided for shunting it.
In one embodiment, discrete ohmic resistors are provided as conducting means. However, suitably doped plastics materials which fill the gap or, alternatively, a suitably doped seal, preferably designed as a cord-packing ring, which seals the gap are also possible as conducting or semiconducting means.
In a further embodiment, the gap is shunted by means of an electrically conducting metal foil. However, the gap may also be shunted by means of an electrically conducting or semiconducting plastics foil.
In a further embodiment of the current transformer, in particular for metal-enclosed gas-insulated high-voltage installations which are subject to less intensive high-frequency interferences, the screen is formed as at least one electrically conducting or semiconducting foil having at least one layer. Said current transformer can be produced particularly favorably in terms of cost and, in addition, it is particularly easy to install in the installations.
The further developments of the invention are the subjects of the dependent claims.
REFERENCES:
patent: 1807996 (1970-05-01), None
patent: 2035553 (1979-04-01), None
patent: 3544508A1 (1987-06-01), None
patent: 4322944A1 (1994-05-01), None
patent: 0522303A2 (1993-01-01), None
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Mai Anh
LandOfFree
Current transformer for a metal-enclosed gas-insulated... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Current transformer for a metal-enclosed gas-insulated..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Current transformer for a metal-enclosed gas-insulated... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2473765