This document describes a patent for a mechanical current converter (contact rectifier) with commutating reactors. The key aspects are that each reactor can be divided into two or more partial reactors that can be connected in series or parallel to vary the effective reactance. This allows the step current of the reactors to remain constant even if the supply voltage decreases. When the voltage decreases to half the original value, one of the reactors can be short-circuited to maintain the favorable step length.

1. * GB780016 (A)
Description: GB780016 (A) ? 1957-07-31
A mechanical current converter (contact rectifier) with commutating reactors
Description of GB780016 (A)
PATENT SPECIFICATION
Date of Application and filing Complete Specification: Oct. 27, 1954.
' y Application made in Germany on Nov. 3, 1953.
Complete Specification Published: July 31, 1957.
Index at acceptatice:-Class 38(2), Fl(AW:P:1).
International Classification:-H02n.
COMPLETE SPECIFICATION
A Mechanical Current Converter (Contact Rectifier) with Commutating
Reactors We, LICENTIA PATENT-VERWALTUNGSGMBH, a German Body Corporate,
of 31-32 Hohe Bleichen, Hamburg, Germany, do hereby declare the
invention for which we 5pray that a patent may be granted to us, and
the method by which it is to be performed to be particularly described
in and by the following statement: -
With mechanical current converters (contact converters) commutating
reactors are used in order to ensure a satisfactory operation of the
contacts. These reactors produce during the change of magnetisation a
low current step during which the contacts operate. If the alternating
voltage supplying such mechanical converters decreases below the
normal value, then it may happen that the low-current steps of the
commutating reactors become too long; moreover, the reactors' losses
and their inductance make themselves increasingly felt. It is possible
to reduce the length of the step by providing the reactors with a
winding which is provided with taps or with two or more windings which
can be switched-in in different ways. This possibility has the
disadvantage that, as a result of the change of the connection, the
magnitude of the step current (magnetising current) of the reactors
varies and that, therefore, also other auxiliary circuits of the
rectifier, such as contact by-pass circuits have to be changed. If the
number of turns is reduced it may happen that the magnetising current

2. increases to such an extent that the current converter does no longer
operate satisfactorily. Moreover, the change of the winding
connections of commutating reactors is difficult to perform.
Therefore, a multi-phase mechanical contact converter which is
connected to a multiphase transformer and has a reactor in series with
and at the alternating current side of each contact so as to produce a
low-current step each time the current wave passes through zero in
order to facilitate the current lPrice 3/6] commutation, is
characterised according to the invention in that each reactor is
divided into two or more partial commutating reactors which are
arranged in such a manner that the effective reactance can be varied
by 50 an alternative series or parallel connection of the individual
reactors, or by short-circuiting some or all but one of the reactors.
In order to secure that the step current of all the reactors in a
phase remains constant 55 or substantially constant, the individual
reactors may be so designed that they produce substantially the same
step current. A particularly simple arrangement can be obtained by
providing for each phase in series two 60 equal reactors.
The invention can be applied with particular advantage to an
arrangement with sixphase double-way connection of the rectifying
contacts in conjunction with an open 6 three-phase transformer
connection. Such an arrangement actually requires only three
commutating reactors in double-way connection. In view of the small
number of reactors which such an arrangement requires, a subdivision
of the reactors in each phase can be effected without increasing
unduly the first costs for the commutating reactors.
The above described rectifier connection is represented in the
accompanying drawing 75 as an example for an arrangement according to
the invention. As shown, the primary windings of the converter
transformer is delta-connected, and the secondary windings 1, 2, 3,
instead of being connected at their 80 centre points to form the
conventional sixphase diametric transformer connection, are completely
separated and form, what is called for the purpose of this
specification, an "open three-phase transformer connection". 85 Each
phase 1, 2, 3 is provided with two serially connected commutating
reactors 11, 12 and 21, 22 and 31, 32 respectively, one of each pair
of commutating reactors being adapted to be shunted by a disconnecting
90 7809016 No. 31001154.
780,016 switch 13, 23, 33 respectively. If the disconnecting switch is
in its position a (open position), then the shunt connection is
removed, whilst it is effective in the position b (closed position).
If one reactor is shortcircuited, the losses and the inductance of the
commutating reactance are reduced by one half, so that the efficiency
and the power factor of the converter are increased. Moreover, the

3. disadvantages of too long commutating reactor steps in connection with
commutating reactors used alternately for the positive and for the
negative current direction (double-way connection) as shown in the
drawing are overcome. With too long commutating reactor steps there is
a danger with arrangements of this kind that the reactors, after
termination of the contact period for current in one direction, have
not changed their saturation quickly enough at the start of the
current flow in the opposite direction.
As a result of the application of the invention it is possible to
dimension the serially connected commutating reactors in respect of
full supply voltage in such a manner that the length of the step is
comparatively large whereby the rectifier is safeguarded against
voltage or current disturbances. On the other hand, if the three-phase
supply voltage is reduced to a half of the original value, then one of
the reactors can be short-circuited so that again the same favourable
length of the step is obtained as without short-circuiting at full
supply voltage.
Apart from the commutating reactors, also the secondary winding of the
transformer may be switched over in order to avoid transformer losses
and leakage inductances during operation with partial voltage. For
this purpose the secondary winding of the transformer is provided, for
instance at its centre, with a tap b' to which at partial voltage the
one conductor feeding the contacts is switched over from contact a.
And if one of the reactors, e.g., 12, 22, 32, is arranged in the said
conductor adjacent to the transformer winding, it is then possible to
short-circuit this reactor and part of the transformer winding by a
single switching manipulation from ad to b'.
But it also possible to subdivide the secondary windings of the
transformer and to connect them alternatively in series or in parallel
as required.
The invention is of particular interest in its application to plants,
e.g., electrolytic plants, which work over long periods with a voltage
considerably lower than their nominal voltage and which require, for
economic reasons that the efficiency and the power 60 factor should be
as high as possible.
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