Electrical transmission or interconnection systems – Plural supply circuits or sources – Plural transformers
Reexamination Certificate
1998-09-25
2001-02-27
Fleming, Fritz (Department: 2836)
Electrical transmission or interconnection systems
Plural supply circuits or sources
Plural transformers
Reexamination Certificate
active
06194795
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention:
The invention relates to a transformer configuration for feeding additional voltage to transmission lines. More specifially, to a transformer configuration having an auxiliary transformer connected in series with a transmission line and supplied with energy by an exciter transformer.
To control the energy flow on an electrical energy transmission line, such as a high-voltage line, so-called diagonal or auxiliary transformer configurations are used as needed. In them, longitudinal and/or transverse voltages or currents of arbitrary phase relationship are coupled into the transmission line.
Such a configuration as a rule includes an auxiliary transformer, connected by at least one of its windings into the transmission line and supplied with energy via an exciter transformer. The two transformers, typically also called a transformer unit, can be connected to one another via a control member, such as a converter or a converter set. Such a configuration is known for instance from Published, Non-Prosecuted German Patent Application DE 43 43 992 A. Such configurations are also known in the literature as UPFCs (unified power flow controllers).
In the configurations known in the prior art, the throughput rating of the total configuration, which is definitive for the dimensions, is the product of the maximum network current multiplied by the maximum additional voltage. In the limit case, in which the current on a parallel, uncontrolled transmission line is equal to zero and the total current flows via the controlled transmission line, the full throughput rating must be brought to bear by the auxiliary transformer.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a transformer configuration which overcomes the above-mentioned disadvantages of the prior art devices of this general type, in which a transformer configuration for controlling energy flow in at least two interconnected transmission lines is provided and control the of both transmission lines is achieved at little effort or expense. With the foregoing and other objects in view there is provided, in accordance with the invention, in combination with transmission lines including a first transmission line and a second transmission line, a transformer configuration for feeding an additional voltage into the transmission lines, including: auxiliary transformer having a winding with a center tap being a network node, the center tap dividing the winding into a first partial winding and a second partial winding, the first partial winding connected in series with the first transmission line and the second partial winding connected in series with the second transmission line; and an exciter transformer supplying energy to the auxiliary transformer.
According to the invention, the object is attained with a transformer configuration feeding an additional voltage into a first transmission line for electrical energy. The configuration has an auxiliary transformer that can be connected in series by at least one of its windings with the first transmission line and supplied with energy via an exciter transformer. The configuration has a winding with a center tap that divides the winding into two partial windings, and in which, to connect the first transmission line to a second transmission line, one partial winding can be connected in series with the first transmission line and the other partial winding can be connected in series with the second transmission line, in such a way that the center tap forms a network node.
In this simple way, the energy flow over both transmission lines can be controlled simultaneously, with the controllability for both transmission lines being coupled. No additional devices are needed. For limit cases in which only one of the partial windings has a maximum current Ig flowing through it at a time, the definitive throughput rating P for the transformer configuration is in accordance with the equation
P=
0.5
×Ig×Uz,
where Uz designates the additional voltage. In any other current allocation, a power transfer of the in-phase current components takes place between the partial windings that are not loading the exciter transformer. When there is the same current on both transmission lines, the transformer configuration is in the idling mode, regardless of the requisite additional voltage. The center tap, for carrying energy onward, can be connected to a network or to a transmission line leading onward.
A third and fourth transmission line may also be provided, which are likewise connected to one another via respective partial windings of a second auxiliary transformer. The center tap of both auxiliary transformers can be connected to one another and form a network node. This forms a kind of controlled network node, and a power flow between arbitrary pairs of lines can be adjusted.
Advantageously, both auxiliary transformers can be supplied with energy via the same exciter transformer. This keeps the expense and effort involved in the exciter circuit low. Alternatively, the auxiliary transformers can be supplied with energy via separate exciter transformers. Once again, this allows a favorable setup and completely independent control.
The center tap or taps can be connected to the high-voltage side of the exciter transformer. The exciter transformer can thus be operated independently of the voltage on the transmission lines. This is especially favorable in the event of a failure.
It is advantageous if the exciter transformer acts as a machine transformer and if a generator can be connected to its winding on the low-voltage side. The exciter transformer thus performs a dual function. Depending on the construction of the transformer configuration, it is thus possible to dispense with one transformer.
It is favorable if a control member can be connected between each auxiliary transformer and its associated exciter transformer. This enables especially good adjustment of the energy flow.
The control member advantageously acts as a converter configuration here. This makes good control performance attainable. Semiconductor valves, such as thyristors, in the form of current inverters are preferably employed.
The converter configurations may have an equal-energy intermediate circuit, in particular a direct-current or direct-voltage intermediate circuit. As a result, the energy source and the actual exciter circuit are decoupled from one another.
The transformer configuration preferably has a number of phases equal to the number of phases of the transmission lines. The preferred application is for rotary current networks, especially three-conductor rotary current networks.
The center tap(s) may have a pickup at approximately 50% of the total number of windings, or some other value. In this way, either symmetrical or asymmetrical partial windings are formed depending on the demands of the network.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a transformer configuration, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
REFERENCES:
patent: 4626697 (1986-12-01), Nelson
patent: 4777380 (1988-10-01), Wathelet
patent: 4906859 (1990-03-01), Kobayashi et al.
patent: 1 941 047 (1970-03-01), None
patent: 43 43 929 A1 (1995-06-01), None
patent: 0 152 002 A1 (1985-08-01), None
patent: WO97/37419 (1997-10-01), None
International Application WO 94/27351 (Pelletier et al.), dated Nov. 24, 1994.
R.J. Nelson: “Transmission Power Flow Control: Electronic vs
Fleming Fritz
Greenberg Laurence A.
Lerner Herbert L.
Siemens Aktiengesellschaft
Stemer Werner H.
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