Improvements in and relating to automatic means for controlling the capacitance in a load circuit connected to a frequency converter.

摘要

1,151,733. Automatic power control systems. AJAX MAGNETHERMIC CORP. May 18, 1966, No.22164/66. Heading G3R. The power supplied to a load L, e.g. a furnace, from a frequency converter 10 is maintained constant by a circuit 40 controlling the operation of a reversible motor 57 which can be actuated to add or subtract capacitors C to the load circuit. The circuit 40 includes a wattmeter relay 42 which receives a voltage signal derived from the supply 10 by way of a transformer 11 and an adjustable transformer 41, and a load current signal derived from a current transformer 60, this latter signal being applied to the circuit 40 over a further control circuit 50. If the power supplied to the load should vary from a value determined by the setting of transformer 41, contact 45 or contact 46 of relay 42 will energize relay 54 or relay 47 respectively to cause the motor 57 to run in one direction or the other to add or subtract the capacitors C to the load circuit in a manner to keep the power supplied constant. If the capacitance added to the load circuit goes beyond that required for maximum tuning of the circuit, the control circuit 50 operates to de-energize relay 54 and thus prevents the further addition of capacitors. If the value of the load is such that excessive voltage would be required to achieve the desired power level, the operation of control circuit 40 is over-ridden by a voltmeter switch 25 the contacts 26 of which close on over-voltage to de-energize relay 54 and to energize relay 47 so that the motor 57 operates to subtract capacitance from the load circuit until the voltage falls below a safe level. A further embodiment including a modification of the circuit 50 is described with reference to Fig. 2 (not shown).