High Rise Rate Research Articles

The Rating and Application of SCRs Designed for Power Switching at High Frequencies

Inverter, chopper, and other pulse applications, operating at repetition rates up to 25 000 pps (pulses per second), are very demanding for the silicon controlled rectifier because of the high rates of rise of anode current (di/dt) which are imposed. The di/dt rating of the SCR is important since high di/dt of anode current produces excessive heating in the device and, if this is not controlled, device destruction will result. This necessitates an SCR specifically designed for such applications and, also, a family of performance curves to enable the circuit designer to determine its capability reliably in his particular application. These performance curves consider the combined effect of the important SCR dynamic parameters, di/dt, dv/dt, and turn-off time. As a result, the high-frequency SCR is adaptable to many applications which previously imposed dynamic conditions too severe for SCRs to withstand because of excessive switching losses. The use of these curves is demonstrated through actual circuit application examples. The rating methods used for high-frequency SCRs are discussed and compared to methods normally used for conventional SCRs which do not include the effects of switching losses and high di/dt.

MAGNETIC COMPRESSION OF TOROIDAL PLASMA PART (I)

The possibility of confining the plasma in a toroidal shape by means of axial magnetic field of high rate of rise has been examined in our laboratory. The plasma column was pre-heated with the induced axial current by' ohmic heating' before it is adiabatically compressed. The glass torus of 600 m/m, major and 120 mm minor diameters was used. The plasma machine was most carefully designed to provide high degree of uniformity of the electromagnetic field in the torus. The plasma of air and He was constricted to about 1/3 of the torus inner diameter, around the center axis for 10 to 20 μS, and after that the drift of the column due to the charge separation was observed to drive it toward the wall. The temperature was estimated from the plasma conductivity to attain as high as 100, 000 to 200, 000oK. Magnetic probe and spectroscopic disgnostics have also been applied. In part I, Discussions on the designing considerations about the plasma machine and the results of electrical measurements with streak photographs of the plasma appearance are given. The results of magnetic probe measurements and the spectroscopic investigations are now being prepared for publication and will be reported in part II.

Time-controlled unit-function, constant-voltage generator

A time-controlled, unit-function, constant-voltage generator has been developed having a variable output amplitude from 40 to 1000 V with a rise time of 1 μs and constant for 150 μs. The output voltage is independent of current from 0 to 12 A and can be applied with an accuracy of ±1 μs. The generator consists of a source of high-capacity capacitors connected in parallel with non-inductive capacitors which supply the initial energy at a high rate. A mercury thyratron (type BT61A) with a special triggering circuit gives the necessary time control. By keeping the thyratron at a constant temperature, its appropriate volt-ampere characteristic shows that the voltage amplitude is maintained constant independent of variation in current output. A high rate of rise of the unit function is achieved by connecting a high-voltage auxiliary circuit between anode and cathode. Detailed circuit diagrams of the generator, etc., are given. The effects of temperature, accentuation of field due to additional space charge and oscillations on the voltage waveform are also discussed.

Circuit cushioning of gas-filled grid-controlled rectifiers

In certain common rectifier and inverter circuits, gas-filled rectifier tubes supplying highly inductive loads with firing delayed by grid control, are subjected to the application of high rates of rise of initial inverse voltage. This phenomenon results in short tube life because of the sputtering of anode material by the impact of residual ions attracted at high velocity to the negatively charged anode with consequent gas cleanup. The paper describes a method of slowing down or cushioning this rate of rise of initial inverse voltage. A small resistance and capacitance circuit connected between cathode and anode of each tube delays the voltage rise the few microseconds necessary to eliminate gas cleanup. Life test data and practical applications are cited.

Circuit Cushioning of Gas-Filled Grid-Controlled Rectfiers

In certain common rectifier and inverter circuits, gas-filled rectifier tubes supplying highly inductive loads with firing delayed by grid control, are subjected to the application of high rates of rise of initial inverse voltage. This phenomenon results in short tube life because of the sputtering of anode material by the impact of residual ions attracted at high velocity to the negatively charged anode with consequent gas cleanup. The paper describes a method of slowing down or cushioning this rate of rise of initial inverse voltage. A small resistance and capacitance circuit connected between cathode and anode of each tube delays the voltage rise the few microseconds necessary to eliminate gas cleanup. Life test data and practical applications are cited.

Design and Construction of High-Capacity Air-Blast Circuit Breakers

THE air-blast principle of circuit interruption is a recent introduction to the United States, although interrupting devices utilizing compressed air have been available in Europe for a number of years. The service performance of European breakers has been satisfactory, but inherent limitations prevented adoption in this country where large values of fault current and high rates of rise of recovery voltage are the rule rather than the exception. Exhaustive tests on forms of available air breakers heretofore available have shown that approximately 40,000 amperes represents the maximum current that can be safely interrupted at generator voltage, and then only under conditions of moderate rate of rise of recovery voltage. This fact alone made it essential, if air breakers were to be utilized, to develop an entirely different type, since applications in this country have commonly required oil breakers with interrupting ratings up to 60,000 amperes at 15 kv. Even this value of current does not represent the maximum requirement, since an increasingly strong demand exists for ratings at least up to 100,000 amperes at 15 kv or 2,500,000 kva.

Design and construction of high-capacity air-blast circuit breakers

THE air-blast principle of circuit interruption is a recent introduction to the United States, although interrupting devices utilizing compressed air have been available in Europe for a number of years. The service performance of European breakers has been satisfactory, but inherent limitations prevented adoption in this country where large values of fault current and high rates of rise of recovery voltage are the rule rather than the exception. Exhaustive tests on forms of available air breakers heretofore available have shown that approximately 40,000 amperes represents the maximum current that can be safely interrupted at generator voltage, and then only under conditions of moderate rate of rise of recovery voltage. This fact alone made it essential, if air breakers were to be utilized, to develop an entirely different type, since applications in this country have commonly required oil breakers with interrupting ratings up to 60,000 amperes at 15 kv. Even this value of current does not represent the maximum requirement, since an increasingly strong demand exists for ratings at least up to 100,000 amperes at 15 kv or 2,500,000 kva.