Circuits for controlling the power supplied to an electrical precipitator

Claim 2

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the transformer primary winding, means for generating signals representative of precipitator current, means coupled to said signal generating means for suppressing the leading and trailing edges of said current signals to thereby prevent overlap between the edges of said signals and said reference pulses during normal operation of said precipitator, gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide in time with said precipitator current signals as a result of sparking or arcing in the precipitator, and means responsive to the gate output signals for reducing the power supplied to the precipitator.

Claim 3

A system as defined in claim 1, wherein said power reducing means includes means for double integrating the gate output signals.

Claim 4

A system as defined in claim 1, in which means are provided for increasing the power supplied to the precipitator following said power reduction.

Claim 5

A system as defined in claim 3, in which said power increasing means restores power to the precipitator rapidly during an initial period immediately subsequent to the sparking that resulted in the reduction of power and then more slowly following said initial period.

Claim 6

A system as defined in claim 4, in which said power increasing means includes a capacitor, and means for charging said capacitor in response to the gate output signals.

Claim 7

A system as defined in claim 5, in which said means for charging the capacitor comprises a one shot multivibrator responsive to the gate output signals.

Claim 8

A system as defined in claim 1, in which is provided a high sensitivity spark detector means for generating output signals responsive to the precipitator current signals when there is lighter sparking in the precipitator than would cause said zero excursions of the primary voltage, and said power reducing means is responsive to said spark detector output signals independently of said gate output signals, for reducing the power supplied to said precipitator.

Claim 9

A system as defined in claim 7, in which means are provided for increasing the power supplied to the precipitator following operation of said power reducing means.

Claim 10

A system as defined in claim 8, in which said power increasing means includes a capacitor, and a one shot multivibrator responsive to the spark detector output signals for providing a pulse for charging the capacitor.

Claim 11

A system as defined in claim 1 wherein said power reduCing means includes a saturable reactor interposed before the primary winding of the high voltage transformer to receive the gate output signals to reduce the power supplied to the precipitator.

Claim 12

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: thyristors for supplying power to the transformer, a trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator, means for supplying control current to the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator means for supplying control current to the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator, means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the high voltage transformer primary winding, means for generating signals representative of precipitator current, means coupled to said signal generating means for suppressing the leading and trailing edges of said current signals to thereby prevent overlap between the edges of said signals and said reference pulses during normal operation of said precipitator, gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide with said precipitator current signals as a result of sparking or arcing in the precipitator, and means responsive to the gate output signals for changing the control current, the trigger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator.

Claim 13

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: thyristors for supplying power to the transformer, a trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator, means for supplying control current to the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator means for supplying control current to the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator, means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the high voltage transformer primary winding, means for generating signals representative of precipitator current, means coupled to said signal generating means for suppressing the leading and trailing edges of said current signals to thereby prevent overlap between the edges of said signals and said reference pulses during normal operation of said precipitator, gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide with said precipitator current signals as a result of sparking or arcing in the precipitator, and means responsive to the gate output signals for changing the control current, the trigger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator.

Claim 14

A system as defined in claim 11, wherein said control current changing means includes means for double integrating the gate output signals.

Claim 15

A system as defined in claim 11, in which means are provided for changing the control current supplied to the trigger unit to advance the phase angles at which the thyristors are fired to increase the power supplied to the precipitator following said power reduction.

Claim 16

A system as defined in claim 13, in which said control current changing means advances the phase angles rapidly during an initial period immediately subsequent to the sparking that resulted in the reduction of power and then more slowly following said initial period.

Claim 17

A system as defined in claim 14, in which said control current changing means includes a capacitor, and means for charging said capacitor in response to the gate output signals.

Claim 18

A system as defined in claim 15, in which said means for charging the capacitor comprises a one shot multivibrator responsive to the gate output signals.

Claim 19

A system as defined in claim 11, in which is provided a high sensitivity spark detector means for generating output signals responsive to the precipitator current signals when there is lighter sparking in the precipitator than would cause said zero excursions of the primary voltage, and said control current changing means responsive to said spark detector output signals independently of gate output signals for retarding the the firing phase angles of the thyristors to reduce the power supplied to the precipitator.

Claim 20

A system as defined in claim 17, in which means are provided for changing the control current supplied to the trigger unit to advance the phase angles at which the thyristors are fired to increase the power supplied to the precipitator following said power reduction.

Claim 21

A system as defined in claim 18, in which said control current changing means includes a capacitor, and a one shot multivibrator responsive to the spark detector output signals for providing pulses for charging the capacitor.

Claim 22

A system as defined in claim 11, which incLudes voltage monitoring circuit means providing an output when the level of voltage supplied to the primary winding of the high voltage transformer drops below a selected value, current monitoring circuit means providing an output when the level of precipitator current rises above a selected value, and means responsive to the outputs of said voltage circuit means and said current circuit means to interrupt the power supply to the transformer upon occurrence of a short circuit resulting in trans-former voltage below said selected value and precipitator current above said selected value.

Claim 23

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: voltage monitoring circuit means providing an output when the level of voltage supplied to the primary winding of the high voltage transformer drops below a selected value, current monitoring circuit means providing an output when the level of precipitator current rises above a selected value, means for simulating a precipitator current level above said selected value when a short circuit occurs in the precipitator at a relatively low power level, and means responsive to the outputs of said voltage circuit means, said current circuit means and said simulating current means to interrupt the power supply to the transformer upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 24

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: voltage monitoring circuit means providing an output when the level of voltage supplied to the primary winding of the high voltage transformer drops below a selected value, current monitoring circuit means providing an output when the level of precipitator current rises above a selected value, means for simulating a precipitator current level above said selected value when a short circuit occurs in the precipitator at a relatively low power level, and means responsive to the outputs of said voltage circuit means, said current circuit means and said simulating current means to interrupt the power supply to the transformer upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 25

A system as defined in claim 21, wherein the precipitator current simulating means includes means for generating pulses in response to short circuit conditions in the precipitator that cause the precipitator current to lag the voltage across the high voltage transformer by 90*, and circuit means responding to said pulses to provide output signals simulating precipitator current.

Claim 26

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: voltage monitoring circuit means providing an output when the level of voltage supplied to the primary winding of the high voltage transformer drops below a selected value, current monitoring circuit means providing an output when the level of precipitator current rises above a selected value, means for simulating a precipitator current level above said selected value when a short circuit occurs in the precipitator at a relatively low power level, and means responsive to the outputs of said voltage circuit means, said current circuit means and said simulating current means to operate an alarm circuit upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 27

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: voltage monitoring circuit means providing an output when the level of voltage supplied to the primary winding of the high voltage transformer drops below a selected value, current monitoring circuit means providing an output when the level of precipitator current rises above a selected value, means for simulating a precipitator current level above said selected value when a short circuit occurs in the precipitator at a relatively low power level, and means responsive to the outputs of said voltage circuit means, said current circuit means and said simulating current means to operate an alarm circuit upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 28

A system as defined in claim 23, wherein the precipitator current simulating means includes means for generating pulses in response to short circuit conditions in the precipitator that cause the precipitator current to lag the voltage across the high voltage transformer by 90*, and circuit means responding to said pulses to provide output signals simulating precipitator current.

Claim 29

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: thyristors for supplying power to the transformer, a magnetic amplifier trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator, means for supplying control current to a first winding on the magnetic amplifier in the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator, means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the primary winding of the high voltage transforMer, means for generating signals representative of precipitator current, means coupled to said signal generating means for suppressing the leading and trailing edges of said current signals to thereby prevent overlap between the edges of said signals and said reference pulses during normal operation of said precipitator, gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide with said precipitator current signals as a result of sparking or arcing in the precipitator, and means responsive to the gate output signals for changing the control current, the trigger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator.

Claim 30

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: thyristors for supplying power to the transformer, a magnetic amplifier trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator, means for supplying control current to a first winding on the magnetic amplifier in the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator, means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the primary winding of the high voltage transforMer, means for generating signals representative of precipitator current, means coupled to said signal generating means for suppressing the leading and trailing edges of said current signals to thereby prevent overlap between the edges of said signals and said reference pulses during normal operation of said precipitator, gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide with said precipitator current signals as a result of sparking or arcing in the precipitator, and means responsive to the gate output signals for changing the control current, the trigger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator.

Claim 31

A system as defined in claim 25, in which is provided a second control winding on the magnetic amplifier, a circuit responsive to gate output for temporarily supplying high level currents to said second winding on the magnetic amplifier to rapidly overdrive the amplifier and retard the firing phase angles of the thyristors.

Claim 32

A system as defined in claim 26, wherein said control current changing means includes means for double integrating the gate output signals.

Claim 33

A system as defined in claim 26, in which means are provided for changing the control current supplied to the first control winding to advance the firing phase angles to increase the power supplied to the precipitator following said power reduction.

Claim 34

A system as defined in claim 26, in which said control current changing means advances the phase angles rapidly during an initial period immediately subsequent to the sparking that resulted in the reduction of power and then more slowly following said initial period.

Claim 35

A system as defined in claim 29, in which said control current changing means includes a capacitor, and means for charging said capacitor in response to the gate output signals.

Claim 36

A system as defined in claim 30, in which said means for charging the capacitor comprises a one shot multivibrator responsive to the gate output signals.

Claim 37

A system as defined in claim 26, in which is provided a high sensitivity spark detector response to the precipitator current signals representative of sparking for generating output signals, and said control current changing means responsive to said spark detector output signals for retarding the firing phase angles of the thyristors to reduce the power supplied to said precipitator.

Claim 38

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: A. a. thyristors for supplying power to the transformer; b. a trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator; c. means for supplying control current to the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator; d. means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the primary winding of the high voltage transformer; e. means for generating signals representative of precipitator current; f. gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide in time with said precipitator current signals as a result of sparking or arcing in the precipitator; g. means responsive to the gate output signals for changing the control current, the trigger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator; and B. a. voltage monitoring circuit means providing an Output when the level of voltage supplied to the high voltage transformer drops below a selected value; b. current monitoring circuit means providing an output when the level of precipitator current rises above a selected value; c. precipitator current simulating means for generating pulses in response to short circuit conditions in the precipitator that cause the precipitator current to lag the voltage across the high voltage transformer by 90*; d. circuit means responding to said pulses to provide output signals simulating precipitator current; and e. means responsive to the outputs of said voltage circuit means, said current circuit means and said current simulating means to interrupt the power supply to the trans-former upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 39

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: A. a. thyristors for supplying power to the transformer; b. a trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator; c. means for supplying control current to the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator; d. means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the primary winding of the high voltage transformer; e. means for generating signals representative of precipitator current; f. gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide in time with said precipitator current signals as a result of sparking or arcing in the precipitator; g. means responsive to the gate output signals for changing the control current, the trigger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator; and B. a. voltage monitoring circuit means providing an Output when the level of voltage supplied to the high voltage transformer drops below a selected value; b. current monitoring circuit means providing an output when the level of precipitator current rises above a selected value; c. precipitator current simulating means for generating pulses in response to short circuit conditions in the precipitator that cause the precipitator current to lag the voltage across the high voltage transformer by 90*; d. circuit means responding to said pulses to provide output signals simulating precipitator current; and e. means responsive to the outputs of said voltage circuit means, said current circuit means and said current simulating means to interrupt the power supply to the trans-former upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 40

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: A. a. thyristors for supplying power to the transformer; b. a magnetic amplifier trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator; c. means for supplying control current to a first winding on the magnetic amplifier in the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator; d. means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the primary winding of the high voltage transformer; e. means for generating signals representative of precipitator current; f. gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide with said precipitator current signals as a result of sparking or arcing in the precipitator; and g. means responsive to the gate output signals for changing the control current, the trig-ger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator; and B. a. voltage monitoring circuit means providing an output when the level of voltage supplied to the high voltage transformer drops below a selected value; b. current monitoring circuit means providing an output when the level of precipitator current rises above a selected value; c. means for simulating a precipitator current level above said selected value when a short circuit occurs in the precipitator at a relatively low power level; and d. means responsive to the outputs of said voltage circuit means, said current circuit means and said simulating current means to interrupt the power supply to the transformer upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 41

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: A. a. thyristors for supplying power to the transformer; b. a magnetic amplifier trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator; c. means for supplying control current to a first winding on the magnetic amplifier in the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator; d. means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the primary winding of the high voltage transformer; e. means for generating signals representative of precipitator current; f. gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide with said precipitator current signals as a result of sparking or arcing in the precipitator; and g. means responsive to the gate output signals for changing the control current, the trig-ger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator; and B. a. voltage monitoring circuit means providing an output when the level of voltage supplied to the high voltage transformer drops below a selected value; b. current monitoring circuit means providing an output when the level of precipitator current rises above a selected value; c. means for simulating a precipitator current level above said selected value when a short circuit occurs in the precipitator at a relatively low power level; and d. means responsive to the outputs of said voltage circuit means, said current circuit means and said simulating current means to interrupt the power supply to the transformer upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 42

A system as defined in claim 34, wherein the precipitator current simulating means includes means for generating pulses in response to short circuit conditions in the precipitator that cause the precipitator current to lag the voltage across the high voltage transformer by 90*, and circuit means responding to said pulses to provide output signals simulating precipitator current.

Claim 43

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: A. a. thyristors for supplying power to the transformer; b. a magnetic amplifier trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator; c. means for supplying control current to a first winding on the magnetic amplifier in the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator; d. means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the primary winding of the high voltage transformer; e. means for generating signals representative of precipitator current; f. gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide with said precipitator current signals as a result of sparking or arcing in the precipitator; and g. means responsive to the gate output signals for changing the control current, the trigger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator; and B. a. voltage monitoring circuit means providing an output when the level of voltage supplied to the high voltage transformer drops below a selected value; b. current monitoring circuit means providing an output when the level of precipitator current rises above a selected value; c. means for simulating a precipitator current level above said selected value when a short circuit occurs in the precipitator at a relatively low power level; and d. means responsive to the outputs of said voltage circuit means, said current circuit means and said simulating current means to operate an alarm circuit upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 44

In a system for controlling AC power supplied to a high voltage transformer energizing an electrical precipitator through rectifier means: A. a. thyristors for supplying power to the transformer; b. a magnetic amplifier trigger unit for firing the thyristors at selected phase angles to control the power supplied to the precipitator; c. means for supplying control current to a first winding on the magnetic amplifier in the trigger unit to advance and retard the phase angles at which the thyristors are fired to increase and decrease the power supplied to the precipitator; d. means for generating reference pulses in response to instantaneous zero excursions of voltage supplied to the primary winding of the high voltage transformer; e. means for generating signals representative of precipitator current; f. gate means receiving said reference pulses and said precipitator current signals, said gate means providing output signals representative of said precipitator current signals when said reference pulses coincide with said precipitator current signals as a result of sparking or arcing in the precipitator; and g. means responsive to the gate output signals for changing the control current, the trigger unit responding to the changed control current for retarding the firing phase angles of the thyristors to reduce the power supplied to the precipitator; and B. a. voltage monitoring circuit means providing an output when the level of voltage supplied to the high voltage transformer drops below a selected value; b. current monitoring circuit means providing an output when the level of precipitator current rises above a selected value; c. means for simulating a precipitator current level above said selected value when a short circuit occurs in the precipitator at a relatively low power level; and d. means responsive to the outputs of said voltage circuit means, said current circuit means and said simulating current means to operate an alarm circuit upon occurrence of a short circuit resulting in transformer voltage below said selected value and at least one of the precipitator current and the simulated precipitator current above said selected value.

Claim 45

A system as defined in claim 36, wherein the precipitator current simulating means includes: A. a. means for generating pulses in response to short circuit conditions in the precipitator that cause the precipitator current to lag the voltage across the high voltage transformer by 90*; and b. circuit means responding to said pulses to provide output signals simulating precipitator current.