Electric power conversion systems – Current conversion – Having plural converters for single conversion
Reexamination Certificate
1999-09-22
2001-08-14
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Having plural converters for single conversion
C363S068000
Reexamination Certificate
active
06275396
ABSTRACT:
BACKGROUND OF THE INVENTION
Power feed equipment is required to provide electrical power to the cables of submarine communications systems. An example of a conventional power feed is shown schematically in FIG.
1
. The power feed
1
is constructed using a stack of four identical power converters
2
1
to
2
4
connected in series which together convert a 50V DC supply at the input terminals of the power feed to provide a 10 kV DC power feed voltage across the output terminals. The first power converter
2
1
in the stack provides a 2.5 kV DC output, but it is elevated from earth by an additional 7.5 kV DC due to the effect of the adjacent power converters
2
2
to
2
4
in the stack. The centre-tapped transformer secondary winding
3
of the transformer
4
in the first power converter
2
1
must therefore be insulated to 10 kV DC from earth to prevent Corona discharge and ultimately flash-over. Accordingly, blocking capacitors
5
and
6
are provided in this circuit which are designed to block the high DC voltage relative to earth and thereby insulate the secondary winding. Due to the magnitude of the DC voltage, the required blocking capacitors are large, bulky and expensive, and are not available as off-the-shelf components. Indeed, each capacitor typically has a capacitance of 0.5 &mgr;F and a DC voltage breakdown greater than 15 kV. The use of such components is clearly undesirable.
Furthermore, although typically a nominal 2.5 kV DC output is produced by each power converter the corresponding AC pulse voltage from the high voltage secondary winding
3
is about 4 kV to allow for pulse width voltage control. Accordingly, rectifying and smoothing circuits
7
associated with each power converter must be designed and built using electrical components which can withstand these high AC voltages. Again, as with the DC blocking capacitors, such components are expensive and not generally available off-the-shelf.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a power feed for a submarine communications system comprises a plurality of power converters connected together in series to convert a low voltage received at an input to the power feed to a high voltage at an output of the power feed, in which each power converter has at least two step-up transformer stages, and wherein at least one of the windings of the or each transformer in at least one of the transformer stages of at least one of the plurality of power converters is wound using a high voltage insulating wire to insulate against a DC voltage appearing at an output of an adjacent power converter.
According to a second aspect of the present invention, a power converter for a power feed for a submarine communications system comprises at least two step-up transformer stages, wherein at least one of the windings of the or each transformer in at least one of the transformer stages is wound using a high voltage insulating wire.
In the present invention, high voltage insulating wire is used to insulate against a DC voltage associated with the stacking and series connection of power converters. High voltage insulating wire has a relatively large diameter and so there is a restriction on the number of turns which can fit into the available space of the conventional transformer design described above without increasing the size of the transformer core, which is undesirable. As the output voltage of a transformer depends directly on the ratio of number of turns of wire on the primary and secondary windings, the limited availability of space on the secondary makes it impossible to achieve the required voltage step-up with a single transformer stage. To overcome this, in the present invention one or more additional transformer stages are included, thereby reducing the turns ratio required for each individual transformer. Accordingly, there is no need for any components to block the DC potential associated with adjacent power converters in the stack since the high voltage insulating wire used, for example, to provide the secondary winding of the transformer in the first transformer stage, provides this function.
Preferably, the step-up transformer stages are connected sequentially in series. Each of the transformers may be connected in series. However, preferably, the transformers are cascaded together to form a tree structure with the outputs of end branches of the tree structure connected in series to provide a combined voltage output at the terminals of the power converter. More preferably, each end branch of the tree structure comprises an AC rectifying circuit to provide a DC electrical output. In this manner, each end branch of the tree structure provides a proportion of the total output of the power converter and the output of each end branch is processed separately by a respective rectifying and smoothing circuit. As such, the AC voltages processed by each end branch are correspondingly smaller and so custom built components are not required in the individual rectifying and smoothing circuits.
Preferably, the power converter comprises a first transformer stage having a transformer in which the secondary winding of the transformer is wound from high voltage insulating wire. More preferably, the power converter further comprises a printed circuit board supporting a second and any subsequent transformner stages. Most preferably, the or each transformer on the printed circuit board comprises a planar ferrite core.
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patent: 4039924 (1977-08-01), Scales et al.
patent: 4222099 (1980-09-01), Hill
patent: 4967333 (1990-10-01), Callier et al.
patent: 5272612 (1993-12-01), Harada et al.
patent: 5465010 (1995-11-01), Rimmer
patent: 997706 (1965-07-01), None
patent: 1036565 (1966-07-01), None
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patent: 1 510 084 (1978-05-01), None
patent: 1 543 153 (1979-03-01), None
patent: 2 217 931 A (1989-11-01), None
patent: 2-202324A (1990-10-01), None
Alcatel
Han Jessica
Sughrue Mion Zinn Macpeak & Seas, PLLC
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