Automatic fault protection system for power recovery control
First Claim
1. In a power recovery drive system for a wound-rotor motor driven from A.C. main lines, said power drive system providing automatic fault clearance of transient electrical distrubances, said motor including primary and secondary winding means, said primary winding means connected to the A.C. lines, rectifier bridge means connected to receive the output from said secondary winding means and provide a D.C. voltage, inductive reactor means serially connected to the output of said bridge means, a solid state inverter connected to receive said D.C. voltage from said rectifier means and provide an A.C. voltage output, means coupling the output of said inverter back to said A.C. lines, the improvement comprising, in combination, solid state switch means connected to said secondary winding means and to said rectifier bridge means for effectively shorting said secondary winding means when actuated;
- current level sensing means electrically coupled to the output of said inverter and sensing the increase of inverter current resulting such as from a fault and providing a signal representative of a current increase above a preselected level; and
control means responsive to said sensing means signal to actuate said solid state switch means to short across said rectifier bridge means and cause the D.C. voltage to drop, said reactor being effective to absorb and buffer at least one full cycle of A.C. voltage without saturating whereby the fault energy is dumped back into the A.C. main lines enabling the reactor current to drop to substantially zero and allowing the fault to clear.
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Abstract
An adjustable speed pumping system includes a plurality of pumps respectively driven by variable speed A.C. motors each having a power recovery circuit. Each power recovery circuit includes a series connected rectifier bridge, an inductive reactor and an inverter coupled to the secondary winding of the motor which has an A.C. source connected to the primary winding. A fault clearing mechanism is included in each circuit and includes solid state switches in the bridge actuated by a current level sensor coupled to the inverter output. The power recovery circuit also includes current foldback circuitry and secondary gating circuitry coupled to thyristors in the inverter. The power recovery circuits can be connected in parallel with a single motor and the system includes circuitry for sensing the highest amplitude current in the parallel circuits and controlling all circuits with this current. Each pump has a valve associated with the outlet and circuitry associated therewith to operate the pump at a low forward speed upon receipt of a stop command until the valve is closed to prevent significant reverse flow through the pump.
48 Citations
41 Claims
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1. In a power recovery drive system for a wound-rotor motor driven from A.C. main lines, said power drive system providing automatic fault clearance of transient electrical distrubances, said motor including primary and secondary winding means, said primary winding means connected to the A.C. lines, rectifier bridge means connected to receive the output from said secondary winding means and provide a D.C. voltage, inductive reactor means serially connected to the output of said bridge means, a solid state inverter connected to receive said D.C. voltage from said rectifier means and provide an A.C. voltage output, means coupling the output of said inverter back to said A.C. lines, the improvement comprising, in combination, solid state switch means connected to said secondary winding means and to said rectifier bridge means for effectively shorting said secondary winding means when actuated;
- current level sensing means electrically coupled to the output of said inverter and sensing the increase of inverter current resulting such as from a fault and providing a signal representative of a current increase above a preselected level; and
control means responsive to said sensing means signal to actuate said solid state switch means to short across said rectifier bridge means and cause the D.C. voltage to drop, said reactor being effective to absorb and buffer at least one full cycle of A.C. voltage without saturating whereby the fault energy is dumped back into the A.C. main lines enabling the reactor current to drop to substantially zero and allowing the fault to clear. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
- current level sensing means electrically coupled to the output of said inverter and sensing the increase of inverter current resulting such as from a fault and providing a signal representative of a current increase above a preselected level; and
- 20. In a drive system for a variable speed A.C. motor driven from a three-phase A.C. power source, said motor having primary and secondary windings and with source connected to said primary winding, solid state rectifier bridge means connected to an output of said secondary winding to produce a D.C. power, a solid state inverter connected to receive said D.C. power and including thyristors sequentially commutated to provide an A.C. power output which is fed back into the A.C. line connections with said power source, an inductive reactor connected intermediate said bridge means and said inverter, said inverter connected to couple power back to said power source, control means for sequentially commutating said thyristors, solid state switch means in said rectifier bridge means connected to said control means, and current level sensing means coupled to the output of said solid state inverter and said control means and producing an output when the current level reaches a predetermined value, said control means energizing said switch means to produce a low impedance current path in said rectifier bridge means and cause said D.C. voltage to drop to a substantially zero value, and thereby enable automatic clearing of said fault.
- 31. An adjustable speed pumping system comprising a plurality of adjustable speed pumps connected to a common supply and a common discharge with a valve between each pump and said discharge, a variable speed A.C. motor for each pump, each motor having a primary winding and a secondary winding, a three-phase A.C. power source connectible to the primary winding of each motor, a power circuit for each motor and coupled to said secondary winding with a resistor section in series therewith including a resistor for each line and a contactor in parallel therewith, voltage sensing means coupled to said secondary winding for opening and closing said contactor, each power recovery circuit including rectifier bridge means, inductive reactor means, and inverter means, with said bridge means converting said secondary voltage to a D.C. voltage and said inverter including a plurality of thyristors with control means for sequentially commutating said thyristors to convert said D.C. voltage to an A.C. voltage output, a secondary gating circuit for each thyristor and including voltage sensor means in series with a silicon unilateral switch (SUS) coupled to a gate electrode of a thyristor and actuable in response to sensing a peak point voltage to fire the thyristor, said control means including a current foldback circuit for each thyristor consisting of a transistor, a current sensing resistor connected in the current path of said transistor, a second silicon unilateral (SUS) connected in parallel with said current sensing resistor, said second SUS being responsive to the voltage developed by the current flow in said current sensing resistor and said SUS selectively controlling said transistor dependent on the amplitude of current flowing through current sensing resistor, solid state switch means in said bridge means and current level sensing means for sensing the current level of said A.C. voltage output from said inverter and actuating said solid state switch means when the current level exceeds a predetermined value to effectively isolate said bridge means from said inverter to cause the current in said inverter to drop, switch means between said secondary winding and said rectifier bridge means actuated in response to an associated motor approaching rated speed to effectively short said secondary winding, valve position sensing means coupled to each valve, and means connected to said sensing means and an associated motor for operating said motor at a low forward speed upon receipt of a stop command until said valve position sensing means senses a predetermined position for the valve.
- 33. A method of clearing faults in a power recovery circuit for a variable speed motor driven from an A.C. source wherein said motor has primary windings coupled to said source and secondary windings coupled to a rectifier bridge means to produce a D.C. voltage from said A.C. source to a serially connected inductive reactor means which is coupled to a solid state inverter providing an A.C. voltage output operatively coupled to said A.C. source, comprising the steps of sensing the current level of the output of said inverter and producing an output signal when the current level exceeds a predetermined value, feeding said output signal to an electronic controller and activating a switch means in said rectifier bridge means to effectively short said secondary winding thereby causing the D.C. voltage to drop to substantially zero while said reactor means effectively absorbs at least one full cycle of said A.C. voltage output without saturation enabling the reactor current to drop to substantially zero to clear said fault.
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40. A method of clearing faults in a power recovery drive circuit for a variable speed driven from an A.C. source wherein said motor has primary windings coupled to said source and secondary windings coupled to means to produce a D.C. voltage from said A.C. source to a serially connected inductive reactor means which is coupled to a solid state converter providing an A.C. voltage output operatively coupled back to said A.C. source, comprising the steps of:
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(a) sensing the change in current flow in the recovery circuit due to a fault in said converter; (b) turning off the current flow from the motor to the recovery circuit in response to a fault; and
,(c) providing a reactor which can absorb at least one full cycle of A.C. line voltage without saturating, whereby the fault may be allowed to automatically clear. - View Dependent Claims (41)
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Specification