Solid state voltage control system for electrostatic precipitators

Claim 2

In a voltage control system for electrostatic precipitators comprising: power input means for providiNg power to the system from power lines; a transformer; a primary of the transformer connected to the input means for developing an AC signal thereacross; solid state gating means connected between the input means and the transformer primary for controlling power delivery to the primary; first current sensing means coupled to the primary for developing a signal corresponding to current flow through the primary; first switching means connected at the input thereof to the output of the sensing means for switching to a conductive state when a preselected threshold of the sensing means signal is exceeded indicating excessive current in the primary; gate drive means connected at inputs thereof to the power input means and said first switching means, the output of the drive means connected to the gate means for triggering the gating means into conduction when said first switching means is in a non-conductive state; the secondary of the transformer transforming the AC signal to a rectifier for rectification of the AC signal; means connecting the rectifier to the precipitators for developing electrostatic charges thereon which attract particulate matter passing across the precipitators; and resistor means connected to said rectifier for developing voltage pulses thereacross when arcing occurs between said precipitators; logic means connected to receive said voltage pulses from said resistor means and for producing first and second control voltages in response thereto; and soft start analog circuit means including second switching means responsive to said first and second control voltages for momentarily disabling said gate drive means and subsequently causing gradual increased power delivery from the power lines to the gating means.

Claim 3

The subject matter as defined in claim 1 wherein the gating means comprises at least one pair of reverse positioned parallel connected SCRs, the anode and cathode of each SCR conducting line current therethrough in response to trigger signals applied to gate terminals of the SCRs by the drive means.

Claim 4

The subject matter set forth in claim 1 together with an inductor connected in series with the transformer primary for inhibiting momentary increases in primary current.

Claim 5

A voltage control system for electrostatic precipitators comprising: power input means for providing power to the system from power lines; a transformer; the primary of the transformer connected to the input means for developing an AC signal thereacross; an inductor connected in series with the transformer primary for inhibiting momentary increases in primary current; solid state gating means connected between the input means and the transformer primary for controlling power delivery to the primary, the gating means including a pair of parallel connected, reverse positioned SCRs, the anode and cathode of each SCR conducting line current therethrough in response to trigger signals applied to the gate terminals of the SCRs; first current sensing means coupled to the primary for developing a signal corresponding to current flow through the primary; switching means including a transformer/rectifier set connected at the input thereof to the output of said first current sensing means, said switching means including means connected to the output of said transformer/rectifier set for establishing a threshold reference voltage and a first switching device responsive to the output of said establishing means for switching to a conductive state when a preselected threshold of the sensing means signal is exceeded, indicating excessive current in the primary; gate drive means connected at inputs thereof to the power input means and the switching means, the output of the drive means connected to the gate terminals of the SCRs for generating the trigger signals when the switching means is in a non-conductive state; the secondary of the transformer transforming the AC sIgnal to a rectifier for rectification of the AC signal; means connecting the rectifier to the precipitators for developing electrostatic charges thereon which attract particulate matter passing across the precipitators; second current sensing means coupled to the primary for developing a signal corresponding to current flow through the primary; circuit means connected to the output of the second sensing means for generating a pulse voltage signal from the second sensing means output in response to arcing at the precipitator; means connecting the circuit means to logic means for detecting the occurrence of the pulse voltage signal; and soft start means connected between the logic means and the gate drive means, the soft start means being responsive when the logic means detects the pulse voltage for momentarily disabling the gate drive means and subsequently causing gradual increased power delivery from the power lines to the gating means; the logic means comprising first and second circuit paths; the first path including a one-shot for generating disabling pulses of predetermined duration in response to said pulse voltage signal; a second switching device connected at its input to the one-shot output, the second switching device changing state for the duration of each disabling pulse, and means connecting the output of the switching means to the soft start means which momentarily disables the gate drive means in response to the change of state of the second switching means; the second current path including a second one-shot having its input connected to the input of the first one-shot; the second one-shot generating a squarewave pulse train, the pulses of the train being of constant width and amplitude but having a repetition rate equal to that of the pulses from the pulse voltage signal; the output from the second one-shot connected to an operational amplifier for integrating the pulse train and forming a DC level therefrom, the DC level being an input to the soft start means for achieving the gradual increase of power delivered from the power lines to the gating means after the momentary disabling of the gate drive means.

Claim 6

A voltage control system for electrostatic precipitators comprising: power input means for providing power to the system from power lines; a transformer; the primary of the transformer connected to the input means for developing an AC signal thereacross; an inductor connected in series with the transformer primary for inhibiting momentary increases in primary current; solid state gating means connected between the input means and the transformer primary for controlling power delivery to the primary, the gating means including a pair of parallel connected, reverse positioned SCRs, the anode and cathode of each SCR conducting line current therethrough in response to trigger signals applied to the gate terminals of the SCRs; first current sensing means coupled to the primary for developing a signal corresponding to current flow through the primary; switching means including a transformer/rectifier set connected at the input thereof to the output of said first current sensing means, said switching means including means connected to the output of said transformer/rectifier set for establishing a threshold reference voltage and a first switching device responsive to the output of said establishing means for switching to a conductive state when a preselected threshold of the sensing means signal is exceeded, indicating excessive current in the primary; gate drive means connected at inputs thereof to the power input means and the switching means, the output of the drive means connected to the gate terminals of the SCRs for generating the trigger signals when the switching means is in a non-conductive state; the secondary of the transformer transforming the AC sIgnal to a rectifier for rectification of the AC signal; means connecting the rectifier to the precipitators for developing electrostatic charges thereon which attract particulate matter passing across the precipitators; second current sensing means coupled to the primary for developing a signal corresponding to current flow through the primary; circuit means connected to the output of the second sensing means for generating a pulse voltage signal from the second sensing means output in response to arcing at the precipitator; means connecting the circuit means to logic means for detecting the occurrence of the pulse voltage signal; and soft start means connected between the logic means and the gate drive means, the soft start means being responsive when the logic means detects the pulse voltage for momentarily disabling the gate drive means and subsequently causing gradual increased power delivery from the power lines to the gating means; the logic means comprising first and second circuit paths; the first path including a one-shot for generating disabling pulses of predetermined duration in response to said pulse voltage signal; a second switching device connected at its input to the one-shot output, the second switching device changing state for the duration of each disabling pulse, and means connecting the output of the switching means to the soft start means which momentarily disables the gate drive means in response to the change of state of the second switching means; the second current path including a second one-shot having its input connected to the input of the first one-shot; the second one-shot generating a squarewave pulse train, the pulses of the train being of constant width and amplitude but having a repetition rate equal to that of the pulses from the pulse voltage signal; the output from the second one-shot connected to an operational amplifier for integrating the pulse train and forming a DC level therefrom, the DC level being an input to the soft start means for achieving the gradual increase of power delivered from the power lines to the gating means after the momentary disabling of the gate drive means.

Claim 7

The subject matter as described in claim 4 wherein the soft start means comprises: a transformer having a primary and secondary; means connecting the primary to the power input means for impressing an AC signal thereacross; means connecting the secondary to a rectifier for rectifying the AC signal; means connected to the output of the rectifier for filtering the rectified signal; a charging circuit connected to the output of the filtering means for charging at a predetermined relatively slow rate when power is restored after an initial power interruption; diode means connected to the charging circuit for effecting rapid discharge thereof in the event of power interruption; and a buffer transistor connected at its base to the charging circuit for disabling the gate drive means via the transistor emitter, in response to power interruption, the gate drive means subsequently achieving gradual increase of power delivered from the power lines to the gating means after disabling of the gate drive means; the collector of the transistor connected to the output of the operational amplifier for conducting the DC level therefrom, through the transistor to the gate drive means; the base of the buffer transistor being connected to the switching device of the logic means for causing momentary disabling of the gate drive means in response to arcing at the precipitators, the charging circuit achieving gradual increase of power delivered from the power lines to the gating means after the momentary disabling.

Claim 8

The subject matter defined in claim 5 wherein the current sensing means comprises a current transformer.

Claim 9

The subject matter of claim 6 wherein the first and second switching devices are transistors.