General Electric Company

Donald M Demarest

Dante E Piccone

Istvan Somos

Bernard D Leete

Edgar Frank Chandler

Angelo L DeCecco

A thermal protection system is provided for a solid state valve that includes at least one representative thyristor having a junction and a heat sink system. The protection system comprises a thermal analog model whose electrical network dynamic electrical operating characteristics are electrically analogous to the thermal characteristics of the solid state valve for any given value of instantaneous load current supplied through the valve, which thermal characteristics include the heat transfer to cooling fluid capability characteristics of said representative thyristor including its heat sink system. A first electrical signal is derived which is representative of the value of the D.C. load current through said valve. A D.C. current to watts generation simulation network responsive to the first electric signal is provided for deriving an output electrical signal representative of the instantaneous value of the watts being dissipated within the junction of said representative thyristor for a given value of load current flowing through said junction. The watts-being-generated signal is applied to said thermal analog model and an output electric signal is derived from said thermal analog model which is representative of the temperature of said thyristor junction. The thermal analog model comprises an RC ladder network having the signal from the simulation network applied to one of its terminals. To another terminal of the ladder network is applied an electric signal representative of the instantaneous temperature value of the cooling fluid flowing over said solid state valve means and said heat sink system.

Solid state valve thermal protection for HVDC power converters

An HVDC electric power delivery system having a floating current order current control subsystem is described. The system is comprised by power converters at each end of an HVDC power conductor link each of which includes a plurality of controllable electric valves connected between alternating current and the direct current electric power conductors together with means for cyclically firing the valves in a predetermined sequence and at firing angles measured with respect to the alternating voltage that can be varied to control the flow of power between the alternating current system and the direct current system. Each of the power converters further includes a regulator for comparing a plurality of input control signals which respectively represent different predetermined operating characteristics of the HVDC system during operation and for deriving an output error control signal that controls the firing angles of the valves. The present invention makes available a floating current order control subsystem which is coupled to the regulator of each power converter for supplying thereto as one of the input control signals a floating current order control signal representative of the magnitude of the direct current flowing in the direct current power conductors plus a predetermined current margin whose polarity is determined by the direction of power flow. The floating current order control subsystem further includes rate limiting means for limiting the rate of change of the floating current order control signal to some predetermined rate of change value either in an increasing or decreasing magnitude direction and maximum and minimum boundary setting limits for setting predetermined maximum and minimum magnitude value limits above and below which the floating current order control signal is not allowed to change the load current magnitude so that the load current magnitude is maintained within predetermined maximum and minimum load current values.

HVDC Floating current order system

A thyristor is shunted by a metal oxide varistor in series with switching means which switches abruptly from a normal high-resistance state to a low-resistance, current conducting state when the thyristor is subjected to a transient surge of reverse bias voltage the magnitude of which is higher than a predetermined repetitive peak magnitude and is nearly equal to the level at which the thyristor turns on in an avalanche breakdown mode. The voltage-current characteristic of the varistor is coordinated with the reverse breakdown characteristic of the thyristor so that surge current will divide therebetween in such proportions that the maximum reverse current flowing through the thyristor is lower than a predetermined critical magnitude which can damage the same, whereby the thyristor is able safely to participate in the surge-energy dissipating process.

Reverse voltage surge protection for high-voltage thyristors

An alternating current static switch comprising two branch circuits connected in inverse parallel circuit relation and having at least three semiconductor devices in series in each branch circuit has anode-to-cathode cross connections between oppositely poled devices at each voltage level. A single gate pulse transformer having secondary windings equal in number to the number of cross connections supplies positive gate current pulses to all semiconductor devices in both branch circuits once each half cycle of impressed circuit voltage. Each secondary winding has its negative terminal connected to one cross connection and its positive terminal connected to the gates of all devices having cathodes connected to the same cross connection.

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Wallingford, PA, United States of America

Donald M Demarest