Siemens-Allis, Inc.

Allis-Chalmers Corporation

Siemens Energy & Automation, Inc.

Frederick A Stich

Conrad F Williams

John D Kleinecke

Thomas P Gilmore

Roger L Robertson

Glenn W Schwantes

John C Culligan

A brushless exciter is provided for controlling excitation of a synchronous motor. The brushless exciter uses a center tapped rotating transformer, a discharge resistor, a field winding which has one end coupled to the ends of the rotating transformer and the other end connected to the discharge resistor and center tap of the rotating transformer. Four power SCR's are used in the brushless exciter. The electronics for controllably firing the SCR's and applying and removing the field are arranged in modules. A field current regulator module is located externally of the rotating apparatus for external control and contains circuitry for field forcing. The circuitry controls the application of field current and the level of excitation. The circuitry monitors the presence, frequency and phase angle of the discharge current and determines the time for field application and removal.

Brushless exciter for controlling excitation of a synchronous machine

A voltage regulator using electronic control of two static switch circuits to permit tap changing without arcing at the switched electrical contacts, without interrupting the load current, and without inducing sizable circulating currents. As a mechanical drive connects a new tap to the auxiliary winding, current through the new winding is blocked by an auxiliary static switch. The drive next opens the main switch delivering current to the load. The opening of the main switch immediately allows the main static switch circuit to 'turn on' to prevent arcing and load interruption until the next current zero. The main static switch control senses no current passing through the main switch and ceases gating, and therefore conduction, of the main static switch. Since neither the main static switch nor the auxiliary static switch is conducting current from the auxiliary winding, the load voltage begins dropping and the voltage across the auxiliary static switch begins rising. When a threshold across the auxiliary static switch is sensed by the overvoltage circuit, the auxiliary static switch control gates the auxiliary static switch 'on' connecting the new tap voltage to the load without interruption. As the auxiliary static switch carries the load current, the main switch may be switched to the new tap connection arclessly. After the new tap is connected, the main switch closes. Any arcing of bouncing main contacts is prevented by a main static switch half cycle conduction shunting.

Gating of the thyristors in an arcless tap changing regulator

An overload relay is provided which monitors current flow in a circuit and triggers an electromagnetic interrupter to open the circuit upon detection of an overcurrent condition. A train of pulses is generated and received by the electromagnetic interrupter for maintaining the circuit closed. The pulse train is terminated upon detection of an overcurrent condition.

Digitally controlled overload relay

A system for controlling current flow to the actuating coil of a contactor or the like. A solid state switch is provided for gating current flow to the coil, and operated by an oscillator stage. A time delay causes the oscillator to operate at a high duty cycle when power is initially applied, allowing a relatively high current to flow to the contactor coil to operate the contacts. Subsequently the control causes the oscillator to operate at a low duty cycle, wherein the solid state switch passes a significantly lower current flow to the coil to maintain the contacts in position.

Time ratio control circuit for contactor or the like

An inexpensive power supply for an electconic control system or the like which is capable of converting a wide range of applied AC voltages into a regulated output voltage. A thyristor is coupled in series with an input terminal and a threshold device, such as a Zener diode, placed across the input terminals and paralleled by an RC circuit coupled to the thyrisor gate. Another capacitor is coupled to the thyristor cathode. A ramp-like voltage impressed on the thyristor gate effects triggering at a phase angle which varies in accordance with output voltage. The electronic control system outputs a uniform train of pulses which serve to disable a circuit interrupter. Termination or disruption of the pulse train causes the interrupter to open the protected circuit.

Power supply for electronic control system

A control is provided for an AC circuit protection system or the like which is capable of monitoring either single phase or polyphase current flow. The composite current is periodically sampled at a frequency f.sub.s which is not a harmonic frequency of circuit current. The current sample values are converted into digital form and processed, then stored in an accumulator stage. When an overcurrent condition occurs the accumulator stage overflows and trips a circuit interrupter.

Electronic control system for overload relay or the like

An improved system for sensing current flow in a single phase or polyphase circuit to be protected and deriving a single signal representing composite current flow. A ramp-like reference signal is applied to one input of a comparator at sampling intervals, and the outputs of a plurality of current amplifiers coupled to the other comparator input so that the duration of a change in signal output level of the comparator is an inverse function of composite current. An accumulator stage stores portions of incoming current signals less a predetermined fraction of previous accumulator contents. In the event of circuit interruption the accumulator is decremented in a manner which reflects the inferred thermal history of the system.

Signal processing system for overload relay or the like

A control for an AC circuit protection system which is capable of monitoring either single phase or polyphase current flow. The composite current envelope is periodically sampled and the sample values converted into digital form. Succeeding current signals are tested to determine whether they deviate from previous samples by a given amount. Non-deviant samples increment a first counter, while deviant samples increment a second counter. The ratio of the counts is used to recognize current imbalance and control system parameters are adjusted to compensate for the imbalance.

Solid state circuit protection system and method

A circuit interrupter of the type including an arc chute and separable contacts between which an arc may be drawn is provided with flash plates. The plates are disposed at either side of the region in which an arc forms and serve to protect the adjacent interrupter housing, while assisting in channeling the arc into the arc chute. The flash plates are formed of a ceramic material and are provided with a plurality of grooves running the direction generally transverse to the direction of the arc.

Circuit interrupter having flash plates with interrupted surfaces

A conduction limit protective arrangement for a power transistor switch regulated by a train of control pulses is disclosed which automatically changes the conduction limit as a function of the voltage, current, and temperature conditions to which the switch is subjected so that it is within its safe operating area limits at all times, thereby permitting the switch to carry maximum current while being fully protected at all times.

Conduction limit protection arrangement for power transistor switch

A tap changer voltage regulator permits a tap changer selector contact to engage an open circuited new tap without arcing and has a half-tap voltage auxiliary winding which permits halving the inter-tap voltage to thus double the number of steps, and an auxiliary switch with a pair of movable contacts. A first auxiliary contact initially connects a selector contact which has moved to a new tap through a circulating current limiting resistor to a load, preventing load current interruption. A second auxiliary contact is in series with a normally-closed switch through which load current and circulating current flow. A first set of inverse parallel SCR's is in series with the resistor, while the normally-closed switch is shunted by a second pair of inverse parallel thyristors. The first pair of thyristors is not gated until the first auxiliary contact has attained its new position, precluding initial arcing. The normally-closed switch is then opened to transfer the current to the thyristors, and gating current is subsequently removed from the second pair of thyristors so that load and circulating current are statically interrupted by the thyristors at current zero, thus completing the tap change by permitting the second auxiliary contact to arclessly interrupt the circuit to the selector contact on the previous tap.

Arcless tap changer for voltage regulator

A tap changer voltage regulator permits a tap changer switch selector contact to engage an open-circuited new tap without arcing and has a half-tap voltage auxiliary winding which permits halving the inter-tap voltage and doubling the number of steps, and also has an auxiliary switch system. An auxiliary static switch circuit initially connects a first tap selector in series with a circulating current limiting resistor and a load to prevent load circuit interruption. An auxiliary selector switch initially coupled to a second tap selector and is in series with a normally-closed switch through which the load current and circulative current flow. The normally-closed switch is shunted by a second static switch circuit. The first static switch is not gated until the first tap selector has attained its new position, precluding initial arcing. The normally-closed switch is then opened; subsequently gating current is removed from the second static switch so that load and circulating current are statically interrupted at current zero. The selector may then be arclessly disconnected from the second tap selector and moved to contact the first tap selector.

Arcless tap changer utilizing static switching

A power circuit arrangement for a power conditioning system adapted to supply variable frequency, variable magnitude voltage to an electromagnetic device such as an electric motor having a center-tapped winding includes first and second inverting thyristors connected to the respective winding ends and connected in series with a transistor chopper across a unidirectional source so that the inverting thyristors may be gated on alternately at a relatively low modulation frequency while the chopper is time ratio controlled at a higher carrier frequency to selectively vary the voltage applied to the winding; a capacitor in shunt to the chopper which is overcharged due to winding leakage reactance when the chopper is turned off to reverse bias and 'soft' commutate the thyristors when they are not conducting load current; a free-wheeling thyristor connected between the winding center tap and the chopper and poled to form a low-impedance free-wheeling path for winding current in series with the inverting thyristors when the chopper is turned off; and first and second energy recovery diodes connected across the serial arrangement of the chopper with the respective inverting thyristors to provide paths for out-of-phase currents and for current when the free-wheeling thyristor is turned off during commutation of the inverting thyristors.

Power circuit for variable frequency, variable magnitude power

An adjustable speed AC electric motor drive has a static inverter energized from a unidirectional power source through a semiconductor series chopper and eliminates a filter between chopper and inverter and controls the fundamental inverter output frequency as a function of an analog speed reference signal and also pulse width modulates the series chopper at a constant frequency as a function of the speed reference signal and synchronizes the series chopper to the fundamental inverter freqency to provide variable voltage and variable frequency power to the motor. The drive has a shunt chopper at the output of the series chopper and switches it to the opposite conductive state from the series chopper so that it coacts with the feedback diodes to form substantially continuous, low impedance, bidirectional free-wheeling paths for motor current and provides constant harmonic content current to the motor with reduced ripple.

Adjustable speed electric motor drive having constant harmonic content

A static inverter has a chopper transistor between a unidirectional source and the inverter load current carrying semiconductor switches, time ratio controlling means including a constant frequency oscillator for modulating the chopper at the constant oscillator frequency and for regulating the width of pulses conducted by the chopper as a function of the magnitude of an analog command signal, means for modulating the inverter semiconductor switches at a frequency which is a function of the analog command signal to establish the inverter output frequency, and means for synchronizing the switching of the chopper to the inverter output frequency so that the chopper is reset at the beginning of each half cycle of inverter output frequency.

Growing community of inventors

Milwaukee, WI, United States of America

Frederick A Stich