Asymmetry protection arrangement for series-connected capacitor units

Claim 2

An asymmetry protection arrangement for a plurality of serially connected capacitor units connectable across a voltage difference resulting in a voltage drop across each of the units, each of the units containing a plurality of fused capacitors connected in parallel with each other, the arrangement comprising a summation circuit for forming an electrical sum quantity proportional to the sum of the voltage drops across the capacitor units, a plurality of monitoring circuits corresponding to respective ones of the capacitor units for providing respective monitored quantities proportional to the voltage drops across the capacitor units, and a plurality of comparison circuits corresponding to respective ones of the capacitor units, each of said comparison circuits having a first input connected to said summation circuit for receiving said sum quantity and having a second input connected to a corresponding one of said monitoring circuits to receive the monitored quantity thereof, each of said comparison circuits comparing said sum quantity to the monitored quantity indicative of the voltage drop across the corresponding capacitor unit to provide an output in response to a failure of at least one of the fused capacitors in the corresponding capacitor unit.

Claim 3

The asymmetry protection arrangement of claim 1, each of said monitoring circuits comprising a voltage transformer having a primary winding connected in parallel with the corresponding capacitor unit and having a secondary winding, the respective secondary windings of the voltage transformers corresponding to the capacitor units being star-connected; and a plurality of auxiliary transformers having respective primary windings serially connected with corresponding ones of said secondary windings.

Claim 4

The asymmetry protection arrangement of claim 2,each of said auxiliary transformers having at least two secondary windings; said summation circuit comprising one secondary winding of the secondary windings of each of said auxiliary transformers, the one secondary windings being connected in a polygonal circuit; and the other secondary winding of the secondary windings of each of said auxiliary transformers providing the monitored output proportional to the voltage drop across the corresponding capacitor unit.

Claim 5

The asymmetry protection arrangement of claim 1 each of said comparison circuits comprising two rectifying circuits connected antiparallel with each other, said rectifying circuits having respective sets of ac terminals for receiving the monitored quantity of the corresponding monitoring circuit and said sum quantity of said summation circuit, each of said rectifying circuits having respective sets of dc terminals, and a measuring instrument connected with each of said sets of dc terminals for responding to a failure of at least one of the fused capacitors.

Claim 6

The asymmetry protection arrangement of claim 1 comprising a second plurality of said monitoring circuits likewise corresponding to respective ones of the capacitor units for providing respective second monitored quantities proportional to the voltage drops across the capacitor units, a second summation circuit for forming a second electrical sum quantity proportional to the sum of the voltage drops across the capacitor units, said first-mentioned summation circuit and said second summation circuit having respective proportionality factors selected so that for the same voltage drop on all capacitor units one of said sum quantities is the same amount over and the other one of said sum quantities is the same amount below the value of said monitored quantities of said monitoring circuits, each of said comparison circuits having first and second input pairs, each of said first-mentioned monitoring circuits being serially connected in difference fashion with said first-mentioned summation circuit to form a first plurality of dIfference circuits corresponding to the capacitor units respectively, each of said difference circuits being connected across said first input pair of a corresponding one of said comparison circuits, each monitoring circuit of said second plurality of monitoring circuits being serially connected in difference fashion with said second summation circuit to form a second plurality of difference circuits corresponding to the capacitor units respectively, each of said last-mentioned difference circuits being connected across the second input pair of a corresponding one of said comparison circuits.

Claim 7

The asymmetry protection arrangement of claim 5, each of said monitoring circuits comprising a voltage transformer having a primary winding connected in parallel with the corresponding capacitor unit and having a secondary winding, the respective secondary windings of the voltage transformers corresponding to the capacitor units being star-connected; and a plurality of auxiliary transformers having respective primary windings serially connected with corresponding ones of said secondary windings, each of said auxiliary transformers having four secondary windings, two of the secondary windings of the four secondary windings of each of said auxiliary transformers having the same number of turns for providing the monitored outputs proportional to the voltage drop across the corresponding capacitor unit, the first winding of the remaining two secondary windings of each of said auxiliary transformers having a first number of turns and the second winding of said remaining two secondary windings having a second number of turns different from said first number of turns, the first windings being connected in an open polygonal circuit to form the first-mentioned summation circuit and the second windings being likewise connected in an open polygonal circuit to form said second summation circuit.

Claim 8

The asymmetry protection arrangement of claim 6, said polygonal circuit made up of said first windings being a serial connection of said first windings, each of said difference circuits of said first plurality of difference circuits being made up of a serial connection of one of said first-mentioned two secondary windings corresponding to the capacitor unit and said last-mentioned polygonal circuit, said polygonal circuit made up of said second windings being a serial connection of said second windings, each of said difference circuits of said second plurality of difference circuits being made up of a serial connection of the other one of said first-mentioned two secondary windings corresponding to the capacitor unit and said last-mentioned polygonal circuit.

Claim 9

The asymmetry protection of claim 5 each of said comparison circuits comprising two rectifying circuIts connected antiparallel with each other, said rectifying circuits having respective sets of ac terminals, one of said sets receiving the monitored quantity of the corresponding first-mentioned monitoring circuit and said sum quantity of said first-mentioned summation circuit and the other one said sets receiving the monitored quantity of the corresponding second monitoring circuit and said sum quantity of said second summation circuit, said rectifying circuits having respective sets of dc terminals, and a measuring instrument connected with each of said sets of dc terminals for responding to a failure of at least one of the fused capacitors.