Abstract: A power conversion apparatus comprises an inverter for converting a voltage of a DC power source into AC power having a frequency higher than the commercial frequency, a transformer, fed by the inverter, for outputting AC power, which is adjusted at a desired voltage, a frequency converter, formed by two pairs of two gate turn-off thyristors (GTOs) connected in reverse-parallel, for converting the frequency of the AC power supplied from the transformer into the commercial frequency, and an energy regenerating device having capacitors for absorbing the energy of a spike voltage occurring due to a circuit inductance upon interruption of a current of each GTO of the frequency converter and a bridge circuit, formed by GTOs and diodes connected in reverse-paralel therewith, for switching over the direction of connecting the capacitors with a secondary winding of the transformer in accordance with the polarity of a voltage of the secondary winding in such a manner that the energy stored in the capacitors is regener

Abstract: For maintaining the current-blocking switching state of a thyristor that can be turned off, a low-resistance shunt is added between the gate and cathode terminal of the thyristor in the event of a fault, i.e., in case of a failure of the blocking negative gate- cathode voltage. The shunt preferably is a self-conducting field-effect transistor which is kept in the cut-off state, at least with the thyristor turned off by the negative thyristor gate-cathode voltage itself or indirectly by a supply voltage causing this voltage. The drain-source path of the transistor is connected in series with a diode having a low forward voltage in order to prevent undesirable inverse operation of the transistor.

Abstract: This invention relates to an enclosed D.C. converting station having enclosed 3-arm integral type bulbs constructed integrally with bulbs for three arms of the same polarity side of bulb arms for forming a 3-phase bridge circuit.

Abstract: An automatic overvoltage protection circuit is provided for an electrical power supply of the type comprising a variable speed three phase alternator (50) having a permanent magnet rotor and three stator output windings (51, 52 and 53), a gated three phase rectifier bridge (60) connected to the three stator output windings and producing a d.c. output voltage, and a control circuit (120) for supplying gating signals at controlled firing angles to the gated three phase rectifier bridge. The control circuit includes first, second and third reference circuits (73, 74 and 75) each including a resonant LRC circuit and connected to a respective one of the three stator output windings, a gating logic circuit (135) connected to the first, second and third reference circuits and providing six outputs, feedback means (122) connected to receive the d.c.

Abstract: The invention relates to an AC voltage supplied rectifier circuit with a downstream smoothing capacitor. A prior art problem with this type of circuit was that the inductive impedance of the supply voltage caused a practically umdamped oscillation between the inductive supply impedance and the smoothing capacitor during start-up which caused the voltage to rise to about twice the stationary value. A rectifier circuit is provided which substantially prevents the over-oscillation having at least one controllable rectifier which brings the rectifier to a conductive state during the charging period of the smoothing capacitor over such a time that the output direct voltage of the rectifier circuit exceeds the momentary capacitor voltage by no more than a predetermined limited value.

Abstract: A static converter circuit has a voltage summing transformer (Tr-Tr13) with several part transformers (Tr1-Tr13) the static-converter-side winding of which are connected via one four-quadrant actuator each to a direct-voltage link circuit. The four-quadrant actuators are single-phase bridge circuits with one GTO thyristor each and a diode, which is antiparallel thereto, per bridge branch. The static-converter-side windings of the part transformers can be short circuited in each case by means of an alternating-current circuit breaker with antiparallel-connected thyristors. Each part transformer has a separate core. The power-system-side windings of the power transformers are connected in series and are connected at their ends to a railroad power system with 162/3-Hz. The direct-voltage link circuit is connected via power-system-commutated static converters and a static converter transformer to a national power system with 50 Hz.

Abstract: A method of controlling a six pulse bridge phase controlled rectifier using a microprocessor is provided by the invention herein. The method involves synchronizing an oscillator to the frequency of an ac power source and driving first and second counters with the oscillator. The first counter is used in conjunction with a phase locked loop to monitor and adjust the oscillator frequency. The count of the second counter generates an .alpha. value used in a firing angle match routine. The match routine compares the desired output voltage to the cosine of .alpha. minus an inductance factor. The match routine takes less than 20 microseconds to run allowing a new .alpha. value to be checked every 0.5 degrees for a 60 hertz power source. When a match is found, the thyristors are fired and a reload value projecting a subsequent firing in 60.degree. is calculated for the second counter.

Abstract: A triggering method for a thyristor switch which has at least two thyristors wired in series and a thyristor wired in antiparallel to each of these thyristors. The thyristor switch is triggered or cut off as a function of a specifiable on-off signal. At least a single triggering of a thyristor to be switched-on takes place at the earliest if a positive anode-cathode voltage is applied to it which exceeds a specifiable switch-on voltage limiting value. The method comprises generating a trigger standby signal if the on-off signal is in the switch-on condition and, with a specifiable minimum number of thyristors to be triggered wired in series, their anode-cathode voltage is greater than the specifiable switch-on voltage limiting value. At least a single triggering of each thyristor to be switched on takes place by means of a short-duration trigger pulse only during the duration of the trigger standby signal.

Abstract: A protection circuit is provided which digitally detects the presence/absence of individual forward voltages across all thyristors at a level low enough compared to the allowable voltage, judges a partial turn-off in accordance with the number of detection signals indicative of the presence/absence, and determines simultaneous firing protection of all the thyristors in accordance with the result of the judgement.

Abstract: A power supply apparatus, in which the three phases of an alternating-current main are connected each through rectifier elements connected in antiparallel to the primary winding of a three-phase transformer. The secondary windings of this transformer are connected through rectifiers to a load device, such as an electron beam gun or other such device which produces short-circuits while in operation. Measuring sensors are provided on the primary AC side which, in the presence of an excess current on the primary AC side, block controlled rectifier elements. The blocking takes place very rapidly because GTO thyristors are used as rectifier elements. The decay of the magnetic energy in the transformer is achieved by the fact that the primary side of this transformer is connected in delta.

Abstract: In a gate pulse generator for a thyristor converter of the type in which in order to fire thyristors of the thyristor converter in which each arm is comprised of a plurality of series-connected thyristors, the gate pulses are generated in response to the gate command signal and the thyristor forward voltage signal and are converted into the light signals which in turn are transmitted to the thyristor converter, whether or not the forward voltage signal exists when the gate command signal is generated is detected and when the forward voltage signal is generated prior to the generation of the gate command signal, the pulse duration is narrowed to a minimum required for firing the thyristor.

Abstract: An apparatus and method relative to the operating of a control turn-off semiconductor device provide for determining the actual control electrode to cathode voltage upon the application of a turn-off control signal by adjusting the apparent value of that voltage by a value representing the voltage drop due to inductance in lead lines. The thusly adjusted value is employed to develop an output signal which indicates that the device has been turned off. In a further embodiment, the output signal may also be employed to reduce the value of the control signal from a first, relatively high value to a second, relatively low value.

Abstract: In a current-source GTO converter, protection against a DC fault or a commutation fault condition is provided by immediately interrupting the conduction of a GTO device which is ON and by turning ON another GTO device to allow fault current to bypass the bridge or safely pass through the bridge. As a result, protective action is immediate and an early recovery is made possible. Bypassing of the bridge is done by freewheeling, with an auxiliary GTO switch or with one of the main GTO switches. Diversionary action is done through the bridge by changing the mode of operation of the bridge from rectifier to inversion, or conversely.

Abstract: In a current-type converter system in which a DC current is fed to a load through a pulsating current suppressing DC reactor from a current-type converter constituted by self-extinction elements connected in a bridge circuit, a converter protection apparatus is arranged such that when a fact that a terminal voltage of the DC reactor becomes an overvoltage is detected, the self-extinction elements are turned on so as to form a closed circuit including the DC reactor, the load, and the converter so that the overvoltage can be suppressed and continuous operation of the converter can be carried out.

Abstract: A high efficiency integrated power converter adapted for direct connection to line voltage and having on chip protection from overcurrent may be implemented utilizing a GTO-SCR as the switch element in a switching power converter such that the converter requires no external transformer or inductor based voltage reducing circuitry. The input voltage may vary over a wide dynamic range without deterioration in circuit performance due to the extremely high anode to cathode breakdown voltage of the switching element and further due to the on chip protection from excess current flow through the switching element.

Abstract: The invention relates to a high-voltage thyristor conversion/inversion apparatus wherein alternating current supplied from A.C. buses (R), (S), (T) is converted into direct current through bridge-connected valves (U)-(Z), and direct current supplied from D.C. buses (P), (N) is inverted into alternating current. To the end of eliminating problems in reducing the area of the site of an A.C.-D.C. converting/inverting station still more, among the valves constituting a bridge, those (U), (V), (W) or (X), (Y), (Z) of each portion of three arms to be connected to the D.C. bus (P) or (N) of identical sign and lightning arresters (LA1), (LA2), (LA3) or (LA4), (LA5), (LA6) connected in parallel with the respective valves are received in a single sealed tank (TA), thereby to scale down the whole conversion/inversion apparatus. The apparatus is used in the A.C.-D.C. converting/inverting station.

Abstract: A fault detector apparatus for a power converter in which a plurality of GTOs, functioning at a predetermined potential, are used. The apparatus includes a first fault-detecting circuit, coupled to the gate-cathode path of one of the GTOs, for generating a first fault signal when this GTO malfunctions, a second fault-detecting circuit, coupled to the gate-cathode path of another one of the GTOs, for generating a second fault signal when this GTO malfunctions, a photocoupler for transmitting a DC-isolated optical signal corresponding to the first fault signal, and one optical fiber system for transmitting a DC-isolated output signal, corresponding to the logical sum of the optical signal transmitted by the photocoupler and the second fault signal, to external circuits set at a potential different from the potential at which the GTOs are arranged. The fault-detecting circuits are provided in the same number as the GTOs. The fault-detecting circuits are coupled by the optical signals.

Abstract: In a semiconductor arrangement including at least one semiconductor element composed of a semiconductor material which generates recombination radiation when current flows through the semiconductor element, and a control element disposed for monitoring the operation of the semiconductor element, the control element has an internal photoelectric effect and is disposed for receiving the recombination radiation generated in the semiconductor material for producing an output parameter representative of the intensity of such radiation.

Abstract: A circuit for detecting current flow in a triac, wherein the circuit operates with only one operating voltage with one pole of this operating voltage being connected to a current terminal of the triac and simultaneously being the voltage reference point for the triac. The triac gate voltage fluctuating around the voltage reference point is used to detect the triac current flow, the gate voltage of the triac is transformed, if necessary, into the voltage range of the operating voltage of the detector circuit, and digital information is generated as a function of the gate voltage to indicate whether a load current is flowing in the triac or not.

Abstract: A power converter having an ac side connected through a reactor to an ac power source and a dc side connected to a smoothing capacitor and a load, the converter being capable of converting and inverting electric power in accordance with the pulse width modulation control, characterized by comprising: a voltage detection circuit for detecting a voltage on the side of the ac power source when viewed from the reactor; a first judgement section for detecting that the amplitude of a voltage component on the ac side of the power converter, which is included in the ac power source voltage, is above a predetermined value on the basis of an output signal from the voltage detection circuit to produce a signal indicative of the judgement result; a second judgement section for detecting that the amplitude of the ac power source voltage is below the predetermined value to produce a signal indicative of the judgement result; and a gate circuit for performing logical sum of the outputs from the first and second judgement se

Abstract: An apparatus of the invention includes an AC power source for providing AC electric power, a thyristor converter, being formed of self-extinctive switching elements, for converting the AC electric power to a DC excitation current, a coil for storing magnetic energy corresponding to the excitation current, and a bypass circuit coupled in parallel to the coil. The above appartus uses a method having the steps of: (a) circulating the excitation current between the thyristor converter and the coil when the excitation current reaches a reference value, and (b) commutating the circulated excitation current from the thyristor converter to the bypass circuit after a given elapsed period of time from when the excitation current reaches the reference value, so that the coil generates a high voltage or induces a large current corresponding to the magnitude of the stored magnetic energy.

Abstract: The field windings of large generators of hydroelectric power stations which are continuously connected to a three-phase system and are designed to produce large capacitive powers, are fed from a "positive" main static converter, designed for 8 kA, via a field circuit. An anti-parallel "negative" auxiliary static converter designed for 600 A maintains a link current (i.sub.Z) of 200 A in a direct-current link with a link choke. To prevent overcurrents, which can be harmful for the link choke and the auxiliary static converter, in the direct-current link due to disturbances such as, for example, a short-circuit in the three-phase system or connection or disconnection of capacitor banks, a free-wheeling residual current is initiated in the direct-current link when the link current (i.sub.Z) exceeds a predeterminable first current limit value (i.sub.G1), corresponding to 120% of the nominal link current, during a minimum period of time of 0.5 ms.

Abstract: An excitation control apparatus for a rotary electric machine according to this invention is such that principal portions of an automatic voltage regulator are dualized by effectively combining circuits preferring decrease of a field current and circuits preferring increase of the field current, thereby to enhance the reliability of the apparatus. The circuits preferring the decrease of the field current when the ignition phase of a thyristor circuit advances precede the circuits preferring the increase of the field current, so that an excitation system is normally operated even in cases of the damages or abnormalities of any internal component, etc.

Abstract: For suppressing an abnormal rise in the anode-cathode voltage of a gate turnoff thyristor (GTO), a main snubber circuit and a number of sub snubber circuits are disposed across the anode and cathode of the GTO, and selected ones of the sub snubber circuits are selectively activated by a control circuit in accordance with the magnitude of a main current flowing through the GTO in order to minimize the power loss of the entire snubber circuit. The main snubber circuit includes a capacitor of comparatively small capacity corresponding to a comparatively small and steady main current. The control circuit includes a current detector detecting the main current. For a small steady load, only the main snubber circuit is operated, but at higher loads the control circuit selectively activates an increasing number of the sub snubber circuits.

Abstract: A device for failure detection in series-connected semiconductor rectifiers (1) comprises transformers (2) whose number is equal to that of the rectifiers (1) and which comprise input windings (3), supply windings (6), and additional parallel-connected windings (9), RC-circuits whose number is equal to that of the rectifiers (1), having resistors (4) and capacitors (5), and also a pulse generator (7), and a measuring element (8).The input winding (3) of each transformer (2) has one lead-out thereof connected to a cathode of the respective rectifier (1), and another lead-out to the capacitor (5) of the respective RC-circuit. The resistors (4) of each RC-circuit are connected to the anodes of each rectifier (1). The supply windings (6) of the transformers (2) are connected to one another in series and connected by one terminal to the first lead-out of the pulse generator (7).

Abstract: An improved switching arrangement for a direct coupled switching power supply is provided by utilizing a gate turn off SCR as the primary switching element and a second SCR as the turn-off control such that upon detection of any of a fully charged storage element, an excessive current through the gate turn off SCR, or an insufficient input voltage, the switch is turned off.

Abstract: For recognizing the blocked state of a thyristor which can be switched off (GTO thyristor), especially also if it is alloyed through or the driver addressing the thyristor is defective, a state signal indicating the actual advent of the blocked state is generated after the occurrence of a turn-off signal, if the derivative in time of the gate current has exceeded a positive upper limit, which indicates that the thyristor has been turned off successfully. The maxima of the derivative in time of the gate current are almost independent of the actual anode-cathode current to be extinguished. The derivitive in time of the gate current is advantageously determined via a coupling inductance. Preferably, the method and apparatus are used with a mutual adaptive turn-on interlock of GTO thyristors in converter equipment and can be urged to release protective measures in time if permanent conduction (short circuiting) of a thyristor occurs.

Abstract: A current-source power converting apparatus having a three phase AC-DC converter composed of self-extinction devices for converting an AC power furnished from an three phase AC power source into a DC power and a DC-AC inverter connected with the AC-DC converter through a DC reactor for re-converting the DC power into a three phase AC power to supply the re-converted power for a load. When the failure of the AC power source is detect according to one embodiment, the AC power source is detached from the AC-DC converter and a battery is connected between arbitrary two phases at the input end of the AC-DC converter. After that, the DC power of the battery is supplied for the DC-AC inverter intermittently by switching the corresponding self-extinction devices of the AC-DC converter and controlled by varying the duty ratio of the switching operation.

Abstract: A way of placing chokes with air core, such as thyristor commutating chokes, in a three-phase alternating current rectifier. With a view to eliminating the drawbacks of air-core chokes especially in three-phase rectifying applications, the three chokes of three phases, wound in the same winding direction, are placed on one and the same plane at the corner points of an imagined triangle which brings the chokes as close together as possible.

Abstract: A protection circuit for use with a thyristor having several break over diode, BOD, elements is connected between the anode and the gate of a thyristor providing static and dynamic overvoltage protection. With the exception of the BOD element connected to the gate, all the BOD elements have RC circuits connected in parallel, whose respective resistance and capacitance values are essentially identical. The BOD element connected to the gate and the cathode-gate portion of the thyristor has an additional RC circuit connected in parallel, whose resistance value is smaller or the same and whose capacitance value is smaller than the respective resistance and capacity values of the other RC circuits. Preferably, in this last RC circuit the resistance value is very small in contrast to the resistance values of the other RC circuits, and the capacitance value is negligible.

Abstract: Fault-protection is added to static AC-to-AC converter to protect the GTO devices bilaterally by adding at least two line bridges of diodes having an inductor thereacross. Fault-protection is extended to a UFC system by incorporating such inductor in the diode bridges of the GTO devices forming the bilateral switches of the UFC system. The dissipating energy is minimized by combining such fault-protection bridges. The inductors may be coupled controlled demagnetization of the inductors is provided.

Abstract: A static VAR generator for providing reactive power compensation to an n-phase AC network subject to transient surge currents utilizing mechanically switched shunt circuits in parallel with the thyristor arrays.

Abstract: A dv/dt protection circuit device for an AC-DC converter apparatus including control board switching arrangement having a current cut-off function which conducts an interrupts current from a power source to a load and refluxes the load current while the current is uninterrupted by a full-wave bridge rectifier circuit having a plurality of arms. Each arm of the bridge rectifier circuit connects a reactor for suppressing a rate of change of a power source line voltage of the bridge rectifier circuit at the switching time of the switching arrangement and a condenser is provided for absorbing an overvoltage generated at an inductance on the side of the power source, the condenser being connected on the side of the power source connected to the bridge rectifier circuit.

Abstract: An automated SCR cell test exercises each of the twelve SCRs in a dual, 3 phase, full wave SCR rectifier bridge singly to detect shorted SCRs and in pairs to detect open SCRs or faulty gate circuits.

Abstract: An applied voltage detecting device for an electric power convertor is disclosed which detects a forward voltage and a backward voltage applied to a power convertor consisting of a semiconductor power control rectification element.The forward and backward voltages are detected by a detecting circuit while a relative potential difference is being provided to these voltages. The voltages detected by the detecting circuit are converted to optical signals and are picked up by a single optical transmission circuit. The optical signal is again converted to the electric signal by a discrimination circuit, which discriminates whether the signal is the forward detection voltage or the backward detection voltage from the potential difference between them.The present invention can simplify the detecting device because both forward and backward voltages can be detected by the single optical transmission circuit.

Abstract: An apparatus for controlling a thyristor converter includes a plurality of voltage detectors provided for individual series-connected thyristors respectively for detecting the presence or absence of voltage applied to the thyristors, and elements for generating a thyristor triggering pulse signal representative of the logical sum of the voltage presence-absence signals from the voltage detectors and a triggering command signal commanding the desired triggering phase and on-period of the thyristor converter. The apparatus comprises a plurality of differentiation circuits differentiating the output signals of the plural voltage detectors respectively, and a signal synthesis circuit synthesizing the output signals of the differentiation circuits to generate an output signal indicative of the voltage presence or absence. By virtue of the above construction, the thyristor converter can continuously operate without being shut down even when any one of the thyristor voltage detection signals is disabled.

Abstract: The invention is a method and a circuit for the emergency firing of individual thyristors in a thyristor valve that have a protection circuit for providing an emergency gate control signal for firing the thyristor when the voltage applied thereto equals or exceeds a predetermined initial emergency voltage triggering level. In operation a thyristor is initially fired using the emergency gate control signal produced by the protection circuit when the voltage applied thereto equals or exceeds the emergency voltage triggering level. The emergency voltage triggering level is then reduced. The subsequent firing of the thyristor by the protection circuit occurs when the applied voltage equals or exceeds the reduced emergency voltage triggering level. This allows both economy of operating conditions and protection of the individual thyristor and its associated snubber circuit during prolonged emergency firing conditions.

Abstract: A gate-turn-off thyristor failure detecting circuit includes a detector which detects an off-gate signal for a gate-turn-off thyristor and a current level detector which compares the signal with a predetermined value and produces an output signal indicative of the failure of the gate-turn-off thyristor.

Abstract: Each of the three phase power source voltages coupled to a three phase (3.0.) thyristor power converter are respectively half-wave rectified to provide both positive and negative voltages. Signals representing the largest positive rectified voltage and the smallest positive rectified voltage are developed as are signals representing the largest negative rectified voltage and the smallest negative rectified voltage. Using signals from both the positive and negative rectified voltages, at least one comparison is made to determine a difference which, when in excess of a predetermined limit, effects a logic signal to provide an indication that an asymmetrical fault exists either phase to neutral or phase to phase across the power converter and the power lines connecting the converter to a polyphase alternating current (AC) source.

Abstract: An AC-to-DC power conversion by connecting GTO elements to the positive arms of a three-phase full wave bridge circuit and by repeating the mode of supplying power to a load from an AC power supply by controlling the GTO elements, and the mode of making the current flowing to the load flow back at the time of interruption of the power supply mode, when the power supply mode and the flow-back mode are switched over, overvoltage at the time of the switching is suppressed by simultaneously causing the power supply and flow-back currents to flow.

Abstract: A device is taught for controlling the residual charge on a thyristor switched capacitor. A capacitor is in series circuit relationship with at least two bidirectional back-to-back thyristor switches which are then connected across an AC network. Each back-to-back thyristor combination is shunted by a non-linear clamping device which exhibits a very high resistance below a specified voltage level and a very low resistance above that voltage level. A pulse stretcher and a sequential firing circuit arrangement is used to prolong the conduction of one of the thyristor switches at a time to allow the shunting of its associated clamping device. During an overvoltage condition in the AC network, the residual charge on the capacitor will be limited to the breakdown voltage of the conducting clamping device. A plurality of capacitor, thyristor switch, non-linear clamping device combinations may be utilized in parallel with the AC network.

Abstract: A phase detecting apparatus comprises a first PLL and a second PLL having a response time shorter than the response time of the first PLL. An AC voltage signal produced by the first PLL which is in phase with the detected AC voltage except until the expiration of the response time of the first PLL after an abrupt change in the phase of the detected AC voltage is normally applied to the second PLL. Until expiration of the response time of the first PLL after rising of the detected AC voltage to a certain level, the detected AC voltage is applied, in place of the AC voltage signal produced by the first PLL, to the second PLL. The second PLL provides a digital signal indicative of the phase of the detected AC voltage.

Abstract: A circuit for the arcless de-energization of a direct current load receiving direct current from a rectified alternating current source. The circuit includes a means for rectifying alternating current from an alternating current source to provide direct current to the direct current load. The means for rectifying has a current flow controller, such as a silicon controlled rectifier, connected with each phase of the alternating current source. The circuit also has means for de-energizing the then conducting current flow controller in said means for rectifying, the means for de-energizing having a current flow controller, such as a silicon controlled rectifier. The circuit further includes a voltage detection device for detecting a predetermined voltage drop in the circuit; and a time delay device for regulating the activation of the means for de-energizing.

Abstract: A thyristor apparatus employing light-triggered thyristors comprises forward voltage detecting circuits (15) and a thyristor number detecting circuit (17). The forward voltage detecting circuits (15) detect forward voltages applied to light-triggered thyristors (13) to provide detected signals. The thyristor number detecting circuit (17) is responsive to the detected signals to cause light-triggered thyristors in a thyristor arm (U) to be turned on simultaneously in the case where the number of the light-triggered thyristors being supplied with forward voltages is one or more but not more than a predetermined number. Accordingly, if and when an overvoltage is applied to the thyristor arm (U), overvoltage suppressing elements (14) are prevented from being damaged even if partial commutation failure occurs in the light-triggered thyristors.

Abstract: A thyristor converter control system comprising a voltage detector for detecting the thyristor voltage and a detector output suppressing circuit provided at the output of the voltage detector. The detector output suppressing circuit operates to detect an erroneous output of the voltage detector that it provides a voltage-presence signal while it must provide a voltage-absence signal, and cuts off the output of the voltage detector upon detecting the erroneous output from the voltage detector.

Abstract: A power converter adapted for use in a high-voltage circuit and equipped with a plurality of arms each comprising a plurality of thyristor elements connected in series, wherein an overvoltage limiter having an overvoltage limiting element and means for short-circuiting the ends of the overvoltage limiting element in response to flow of a load current therein are connected between the anode and the cathode of each thyristor element. The short-circuiting means has a gap between the two electrodes connected respectively to the anode and the cathode of each thyristor element, and also a metal layer of a low melting point which is molten by heat generated due to the flow of a load current in the overvoltage limiting element to fill the gap.

Abstract: A method and apparatus for use in conjunction with a power conversion system employing a plurality of switching elements for controlling the electrical power supplied to a load from a source includes the sensing of the instantaneous voltage furnished to the load and providing a signal representing the time derivative of the sensed voltage. The derivative signal thus developed is compared with predetermined reference values to develop output signals which are logically combined to provide a final signal representative of the instant in time at which one of the switching elements is commutated (turned off).

Abstract: An optical gate signal generating apparatus for firing a plurality of thyristors in a thyristor converter apparatus, including a circuit for generating an electrical gate signal, a plurality of first light emitting elements, each being connected to receive the electrical gate signal for generating a first optical signal.

Abstract: A voltage limit circuit for phase controlled rectifiers avoids shoot-through and limit cycling conditions by limiting the d.c. output voltage of the rectifier bridge. The circuitry follows a voltage reference signal as long as the reference signal is less than an input derived from the a.c. voltage applied to the bridge, reduced by the volt-seconds required for commutation. Should the reference signal exceed the a.c. derived input, the a.c. derived input limits the maximum available d.c. voltage. To this end, a voltage reference signal provides an output signal corresponding to the desired output voltage of the bridge. A slew limit circuit limits the rate by which the output signal may be changed. A magnitude limit circuit is coupled to the output of the slew limit circuit and provides a reference signal for the firing circuit of the rectifier bridge. The magnitude limit circuit receives the a.c.

Abstract: A protective circuit for a plurality of series connected thyristors where each thyristor has in parallel with it a resistance, capacitance type snubber circuit and a metal oxide varistor. The arrangement of the series connected thyristors, snubber circuits and their metal oxide varistors has in parallel with it a main metal oxide varistor. The main varistor is responsive to external transient surges so as to conduct large currents. The outer varistors are selected to have values so as to conduct a much smaller or minimal current relative to the current conducted by the main varistor. In a preferred arrangement, a tuning inductor is in series with the thyristors, snubber circuits and parallel arranged varistors. Also, the main varistor is arranged in parallel with the series connection of thyristor, snubber, varistor combination and inductor, and in series with a bank of capacitors.