General Electric Company

General Electric Corporation Gmbh

Fred W Kelley, Jr

Charles H Titus

Georges R Lezan

Samuel A Thompson, Iii

James G Jewell

This line-commutated converter, in one form, has a pair of D.C. terminals for connection to a D.C. system and a pair of A.C. terminals for connection to an A.C. system. The converter comprises first, second, third, and fourth branches, each comprising the combination of a thyristor and a diode connected in inverse-parallel and an inductor connected in series with this combination. The first and fourth branches with a first node located therebetween are connected in series across the D.C. terminals; and the second and third branches with a second node located therebetween are also connected in series across the D.C. terminals. The nodes are effectively connected across the A.C. terminals. Controlled gating means simultaneously triggers the first and second branches into conduction at a controlled phase angle with respect to the A.C. system voltage and simultaneously triggers the third and fourth branches into conduction 180 degrees thereafter, repeating this sequence each cycle of the A.C. system voltage.

Line-commutated converter circuit

A regulating system for delivering a leading or lagging current to compensate for a load varying reactance is disclosed. The regulating system has an RMS composite controller for regulating the voltages at a critical area in a power system at which good voltage regulation is desired. In various embodiments the RMS composite controller has an arrangement to develop RMS quantities representative of the sequence components of the three phase power system. Each of the various RMS composite controllers provides an accurate control signal for the desired voltage regulation.

Regulating system employing an RMS composite controller

A thyristor-switched inductor circuit is connected across a portion of a power system at which good regulation is desired. The thyristor-switched circuit delivers a leading or lagging current to compensate for a load of varying reactance and provides proper regulation at the desired portion of the power system. The thyristor-switched circuit comprises two parallel circuit branches each comprising an inductor and a thyristor in series, the thyristors being oppositely poled. The thyristor-switched circuit is operated during both the normal and the transient overvoltage conditions of the power system. During normal conditions the thyristor-switched circuit is operated at a conduction angle of less than 180.degree. so that the forward and reverse currents, related to the thyristors, are not in an overlapped condition. Conversely, during transient overvoltage conditions the thyristor-switched circuit is operated at a conduction angle of greater than 180.degree. so that the forward and reverse currents, related to the thyristors, are in the overlapped condition. The overlapped condition increases the inductive compensation, which, in turn, provides an effect so as to smooth or regulate the transient conditions in the power system.

Thyristor switched inductor circuit for regulating voltage

In an alternating current electric power system of the type subject to rapid load voltage regulation as a result of variations in reactive load current, reactive load current compensation is provided by fixed capacitors and inductors in parallel with the load. The inductors are in series with static switches which are phase controlled to continuously maintain the net reactive compensating current substantially equal and opposite to the reactive components of load currents. Compensation control determines firing time of thyristor switches in accordance with the magnitude of reactive load current. In one embodiment, a signal representative of the condition of the reactive load current is provided with a positive phase shift correction to compensate for a negative phase shift which is provided by the thyristor switching technique.

Static var system with means for correcting for negative phase shift

A dc measuring circuit for power rectifiers is described wherein primary line current is utilized to measure direct current output. In the measuring circuit, line current transformers are connected to a multiphase instrument rectifier through a phase shifting current transformer which is adjustable to compensate for differences between the primary and secondary line current phase shift characteristics of the power transformer and any phase shift in the line current transformer. By such compensation, the average value of rectified primary line current in the measuring circuit is maintained independent of the commutating angle of the rectified power current. The dc measuring circuit includes means for providing unity current transformation through the phase shifting current transformer. The dc measuring circuit also includes means for handling the presence of zero sequence current without causing measurement error or circuit damage. The dc measuring circuit also includes means for indicating the blowing of a fuse associated with the power rectifier circuit. In one embodiment, the phase shifting current transformer comprises a double extended wye connected autotransformer. In another embodiment, the phase shifting current transformer comprises a truncated delta autotransformer.

Direct current measuring system for rectifiers

A voltage regulating system for an AC electrical power system includes a reactive converter having fixed capacitors and fixed inductors. Static switching devices are provided and include gating circuits for controlling the conduction angle of the switching devices so as to control the magnitude of the reactive current traversing the fixed inductors. RMS transducer circuitry is provided for generating an electrical signal representative of the RMS value of the voltage waveform at a critical point in the AC power system at which good voltage regulation is desired. Circuitry is provided for generating an electrical signal representative of a desired RMS value. Comparison components are provided for comparing these two electrical signals and generating an output signal for use in controlling the conduction angle of the switching devices so as to regulate the magnitude of the voltage waveform at the critical point in the AC power system. The RMS transducer circuitry employs a squaring function for generating a signal representative of the squared value of the voltage waveform. The RMS transducer circuitry also employs the positive and negative zero crossings of the waveform in combination with integrating components for operating on the squared value of the waveform for generating a signal representative of the squared RMS value of the waveform. Additional signal processing components provide an output signal therefrom which is representative of the RMS value of the voltage waveform over its last complete cycle. In one preferred embodiment, the value of the RMS over the last complete cycle of the voltage waveform is completely updated after each one half cycle. In this preferred embodiment, even and/or odd harmonics in the voltage waveform present no difficulties.

RMS Transducer and voltage regulating system employing the same

In an alternating current electric power system of the type subject to rapid load voltage regulation as a result of variations in reactive load current, reactive load current compensation is provided by fixed capacitors and inductors in parallel with the load, the inductors being in series with static switches which are phase controlled to continuously maintain the net reactive compensating current substantially equal and opposite to the reactive component of load current. Compensation control determines firing time of static switches in accordance with the magnitude of reactive load current. The compensation control includes means rapidly responsive to rapid current disturbances. In one embodiment, the compensation control includes devices for continuously sensing the phase and magnitude of the reactive load current. In another embodiment, the compensation control includes devices for sensing the phase and magnitude of the reactive load current 12 times per cycle of source frequency.

Apparatus for sensing the reactive or real components of current

In an alternating current electric power system of the type subject to rapid load voltage regulation as a result of variations in reactive load current, reactive load current compensation is provided by fixed capacitors and inductors in parallel with the load, the inductors being in series with static switches which are phase controlled to continuously maintain the net reactive compensating current substantially equal and opposite to the reactive component of load current. Compensation control determines firing time of the static switches in accordance with the magnitude of reactive load current. Regulating means additionally controls firing time to maintain line current and line to neutral voltage at a selected line location substantially in phase coincidence. The regulating means is provided with means for enhancing the stability of the system under no load or light load conditions. In a preferred embodiment, regulation stability is enhanced through the application of a small real or, in phase current signal whenever the real or in phase component of actual line current at the selected line location is less than a predetermined level which is desirable for stable regulation of the power system.

Gain compensation for power factor in line current regulating systems

In a multiphase alternating current electric power system subject to erratic and unbalanced reactive load current demand, reactive load current compensation is provided by a balanced multiphase reactive compensating impedance having equal but limited reactive current capability in all phases. To increase reactive current capability of any one selected phase of the reactive compensator in response to severe load unbalance a supplementary single phase compensating impedance is connected through a load current controlled switching bridge in parallel circuit relation with any one phase arm of the multiphase compensator. When any one such parallel connection is operative the switching bridge is prevented from connecting the supplementary impedance in any other phase arm of the multiphase compensator.

High speed control of reactive power for voltage stabilization in

A reactive current compensator for improving the power factor of a multiphase alternating current electric power circuit comprises a bank of fixed capacitors connected to multiphase line terminals in star circuit relation and two multiphase banks of fixed inductors connected to said terminals in parallel circuit relation, one inductor bank being star-connected and the other being ring connected, together with switching means responsive to a characteristic of power circuit current for controlling the magnitude of current in each phase of both inductor banks.

Reactive current compensating apparatus for electric power systems

In an alternating current electric power system subject to rapid load voltage regulation as a result of variations in reactive load current, reactive load current compensation is provided by fixed capacitors and inductors in parallel with the load, the inductors being in series with static switches which are phase controlled to continuously maintain the net reactive compensating current substantially equal and opposite to the reactive component of load current. Compensation control determines firing time of the static switches in accordance with the magnitude of reactive load current and regulating means additionally controls firing time to maintain line current and voltage at a selected line location substantially in phase coincidence. A reactive load current sensor and a current angle sensor each utilize a signal voltage representative in phase and magnitude of line-to-neutral voltage at a high voltage 'critical bus' location but derived from line-to-line voltage and line current at a remote low voltage system location.

Remote voltage sensor for power system regulation

Reactive current compensating apparatus for a multiphase electric power circuit comprises separately variable reactive impedance elements coupled to the power circuit in multiphase relation through phase shifting means such as a tertiary transformer winding. When phase voltage supplied to the compensating impedance leads or lags the line-to-neutral voltage of the power circuit the compensating effect in respect to negative phase sequence line current components is enhanced as compared to direct conductive connection of compensating impedance to the power circuit.

Reactive power compensator

A semiconductor valve type converter for supplying single phase load current at power frequency from an N phase polyphase power system without unbalance of polyphase current or voltage comprises a transformer having KN secondary phase voltages displaced by 180/KN electrical degress (where K is an integer) and a bridge type thyristor network for connecting each secondary phase voltage source alternately to positive and negative network buses. The network buses are connected through a centertapped reactor with the single phase load connected between the reactor tap and the secondary phase voltage sources. A commutating circuit effectively connected across the last thyristor to fire during each positive and negative half cycle of single phase output voltage may be provided if necessary to effect the network reversal of single phase current at each half cycle of power frequency.

Phase converter

A DC measuring circuit for power rectifiers is described wherein primary line current is utilized to measure direct current output. In the measuring circuit line current transformers are connected to a multiphase instrument rectifier through a phase shifting current transformer which is adjustable to compensate for difference between the primary to secondary line current phase shift characteristic of the power transformer and any phase shift in the line current transformers. By such compensation the average value of rectified primary line current in the measuring circuit is maintained independent of the commutating angle of the rectified power current.

To control the gating angles and hence the subsequent conduction angles of a complementary pair of alternately fired controllable electric valves, there is provided during intermittent intervals when neither valve is conducting a gating control signal which depends on the sum of a control signal indicative of a desired conduction angle, an on-time indicating signal indicative of the actual conduction angle of the last conducting valve, and an off-time indicating signal that varies with the duration of the non-conducting interval. Each time the gating control signal reaches a predetermined threshold level, the next to conduct valve is fired.

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Media, PA, United States of America

Fred W Kelley, Jr