CAPACITOR BANK FOR AC NETWORKS

• US 3,703,680 A
• Filed: 02/08/1971
• Issued: 11/21/1972
• Est. Priority Date: 02/09/1970
• Status: Expired due to Term

• Current Assignee: Kjell Frank, Lennart Johansson
• Original Assignee: Kjell Frank, Lennart Johansson
• Inventors: Frank, Kjell, Johansson, Lennart
• Primary Examiner(s): Pellinen, A. D.
• Application Number:
  US05/113,316
• Time in Patent Office: 652 Days
• Field of Search: 307/99,103,135 323/22SC,93,101,105,24,106,128
• US Class Current: 323/210
• CPC Class Codes: G05F 1/573 with overcurrent detector
• CPC Class Codes: H02J 3/1828 with stepwise control, the possibility of switching in or out the entire compensating arrangement not being considered as stepwise control
• CPC Class Codes: H02J 3/1892 the arrangements being an integral part of the load, e.g. a motor, or of its control circuit
• CPC Class Codes: Y02E 40/30 Reactive power compensation

Abstract

A capacitor bank for alternating current networks has a number of parallel branches each of which is connected by antiparallelconnected thyristors to the network. There is a control device for each thyristor which, when the bank is fully loaded, connects the thyristors in one conducting direction or the other in synchronism with the maximum of the network voltage in such direction. Each branch of the bank can be recharged by the full load during each half-period of the network voltage. Upon the occurrence of reduced load on the bank, the control devices emit current pulses to connect the thyristor switches in one direction or the other of the maxima of the network voltage in such direction for recharging. These latter pulses are emitted at a frequency which is substantially less thaN the network frequency.

Claims

1. Capacitor bank for alternating current networks comprising a number of parallel branches (3, 4, 5), a thyristor switch (6, 7, 8) connecting each branch to the network (1, 2), each said thyristor switch (6, 7, 8) having thyristors (A, B) in both current directions, a control device (9, 10, 11) for each thyristor switch including means operative when the bank is fully loaded to connect the thyristors in one conducting direction or the other in synchronism with the maxima of the network voltage in such direction, for recharging each branch of the bank at full load during each half-period of the network voltage, at least some of said control devices including means responsive to a reduced load on the bank to emit control pulses to connect the thyristor switches in one direction or the other at the maxima of the network voltage in such direction for recharging the bank branch in question, said last means emitting pulses with a frequency which is substantially less than the network frequency.

2. Capacitor bank according to claim 1, including means operable during periods having lower connection frequency to furnish extra control pulses to the thyristors upon maximum voltage in the network having the same polarity as the respective capacitor voltage, said extra control pulses being phase-displaced 180* in relation to the original control pulses for the same branch, whereby to maintain the capacitor voltage.

3. Capacitor bank according to claim 1, in which a regulator means connects the network to the control devices (9, 10, 11) for the thyristor switches (6, 7, 8) to control the control devices in accordance with the reactive power of the network.

4. Capacitor bank according to claim 3, in which a permutating device (13, 40) is connected between said regulator (12) and control devices (9, 10, 11) for the thyristor switches, said permutating device including means operable when the capacitor bank is only partially loaded to switch the various branches in and out in a cyclic sequence.

5. Capacitor bank according to claim 4, in which the number of thyristor switChes (9, 10, 11) switched in during each half-period of the network voltage varies with the load.

6. Capacitor bank according to claim 5, in which said permutating device comprises a multiphase pulse generator (40), the phase number of which is equal to the number of parallel capacitor branches and having variable pulse length, each of said control devices (9 - 11) being connected to and activated from a separate output terminal (41 - 43) of said multiphase pulse generator, said regulator (12) including means to control the variable length of the pulses from said generator (40).

7. Capacitor bank according to claim 6, in which the number of parallel capacitor branches in 2 . n + 1, where n is an integer, the period of the pulse generator being (2 . n + 1) times half the period of the network (1, 2), whereas the pulse length is (2 . a + 1) times half the period of the network, where a is an integer which may be varied between O and no