GB877440A - Improvements in or relating to electric control systems - Google Patents

Abstract

877,440. Automatic speed control systems. WESTINGHOUSE ELECTRIC CORPORATION. May 20, 1959 [May 26, 1958], No. 17137/59. Class 38 (4). In an automatic speed control system for a prime-mover driving an alternator, the throttle is controlled by an electromagnetic arrangement, the energization of which is derived through a magnetic amplifier controlled in dependence on the alternator frequency, throttle position and the rate of change of throttle position. As shown, a three-phase star-connected alternator G is driven by an engine E controlled by a throttle T. A frequency inverter FI, comprising transistors TR1, TR2 is fed from the alternator through a transformer T2 and a rectifier CR2. The alternating output of the inverter energizes a solenoid 14 through windings 13, 18 of a magnetic amplifier MA1 and a solenoid 16 through windings 15, 19 of a magnetic amplifier MA2. Variation in the energization of control windings of the magnetic amplifiers MA1, MA2 causes the solenoids 14, 16 to be differentially energized to vary the bleed from a double-acting piston valve C7 and displace a piston P mechanically coupled to the throttle T. A secondary of a transformer T1, energized from a phase 3P, feeds a resistor 19 through a frequency selective network L, C3, C4 and a rectifier CR3. The network is arranged so that the voltage across the resistor R19 is proportional to frequency for a range centred on the desired frequency. A resistor R7 and a rheostat R9 are fed from the phase BP through a resistor R10 and a rectifier R10 to derive a reference voltage opposing the frequency-dependent voltage across resistor R19. The difference voltage feeds control windings 41-44 of magnetic amplifiers MA1, MA2 so as to maintain the engine speed constant. The speed is adjusted by rheostat R7 and the control winding current by a rheostat R18. Bias windings 31, 32, 37, 38 are energized through a rectifier CR1 from the phase 3P. The current balance between the magnetic amplifiers MA1, MAS is adjusted by a rheostat R11 and the total current by a rheostat R12. A throttle operating lever LK is coupled to a throttle position feedback potentiometer R13 and the voltage difference between a slider 64 and a slider 57 of a reference potentiometer R14 energizes control windings 59-62 on the magnetic amplifiers MA1, MA2. A parallel combination of a rheostat R17 and a capacitor C9 in series with a rheostat R16 is arranged so that the current through the control windings 59-62 is also dependent on the rate-of-change of throttle position. The sensitivity is adjusted by the rheostat R16. Transient signals of large amplitude are by-passed by a rheostat R15 and semi-conductor diodes D1, D2. For parallel operation between similar alternators, windings 75-78 and windings 275-278 are energized by the difference between voltages representative of the positions of the throttles derived from potentiometers R28, R8.