US 4,390,831 AGranted

Electrostatic precipitator control

AssigneeResearch-Cottrell, Inc.

InventorsWilliam Byrd, Stephen J. Kohke

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Abstract

Voltage and current supplied to the primary winding of the transformer-rectifier (T-R) set of an electrostatic precipitator via silicon-controlled rectifiers and a reactor are automatically controlled by sensing spit and spark discharges within the precipitator and the phase shift which occurs between line voltage and line current (usually referred to herein as primary current) when precipitator voltage drops to a low value, as caused by a heavy spark or arc. Signals are developed therefrom which are used to control precipitator voltage through phase control of the SCR's. An arc is extinguished at the end of the current one-half cycle in which it starts. An inhibit circuit is provided for preventing detectable transients caused by SCR turn on from falsely triggering the automatic control system thereby permitting increased sensitivity in the spit sensing circuit. Automatic soft-start brings precipitator voltage to the operating level both at start-up and after a process change, as evidenced by the absence of sensed spits, sparks, or arcs over a set interval of time which signifies the need for prompt upward adjustment of precipitator voltage. Precipitator current and voltage are limited and the power supply is disconnected when an undervoltage condition is detected. This is accomplished independently of the automatic control in response to spits, sparks and arcs.

Claims25

Dependent claims

Electronic apparatus providing means for controlling AC voltage and current supplied from a source to the primary of a transformer/rectifier set (T/R set) feeding a load circuit comprising an electrostatic precipitator which is subject to spitting, sparking, arcing or shorting, said control means comprising:

a. inductive series impedance in the circuit of said transformer sufficient to limit transient primary currents to an acceptable maximum value in the event of said spitting, sparking, arcing or shorting in said load circuit;
b. a pair of silicon controlled rectifiers (SCR's) in inverse-parallel connection in circuit with said primary of said transformer of said T/R set;
c. gate current supply means connected to the gates of said SCR's for controlling the condition thereof;
d. phase control means for providing output signals which are phase controlled with respect to line voltage;
e. means for supplying voltage representative of AC line voltage to said phase control means;
f. means for developing an AC current signal whose instantaneous values and polarities represent the instantaneous values of current drawn from the source of AC voltage;
g. means for developing an AC voltage pulse during a set time interval following each zero crossing of the AC voltage supply, the polarity of said voltage pulse being the same as the polarity of said AC voltage supply during said set interval;
h. AC sensing means developed by said AC current signals and said AC voltage pulses for producing an output signal only when said current signal exceeds a set minimum value during a voltage pulse and has reverse polarity with respect to the polarity of said voltage pulse;
i. direct current sensing means for developing output signals in response to sudden changes of current in the load circuit of said T/R set resulting from said spitting and sparking;
j. an automatic control system;
k. means for applying said output signals developed by either or both of said sensing means to said automatic control system;
l. means for applying output signals from said automatic control system to said phase control means;
m. means for applying output signals from said phase control means to said gate current supply means for controlling the conduction of said SCR's.

10 more elements

Electronic apparatus providing means for controlling AC voltage and current supplied from a voltage source to a load circuit including the primary of a transformer/rectifier set (T/R set) feeding an electrostatic precipitator which is subject to spitting, sparking, arcing or shorting, said control means including:

a. inductive series impedance in the circuit of said transformer sufficient to limit transient primary currents to an acceptable maximum value in the event of said spitting, sparking, arcing or shorting in said load circuit;
b. a pair of silicon controlled rectifiers (SCR's) in inverse parallel connection in circuit with said primary of said transformer of said T/R set;
c. gate current supply means connected to the gates of said SCR's for controlling the conduction thereof;
d. phase control means for providing output signals which are phased controlled with respect to said voltage source;
e. means of supplying voltage representative of said AC voltage source to said phase control;
f. means for providing an AC control current whose instantaneous values represent the instantaneous values of said AC current supplied to said load circuit;
g. means for developing a current output signal when said AC control current equals or exceeds a predetermined value and only after a momentary dead interval starting with each turn-on of said SCR's;
h. spark sensing means for developing output signals in response to sudden changes of current in the load circuit of said T/R set resulting from said spitting and sparking, said spark sensing means being held passive except when rendered operational by said current output signal;
i. an automatic control system;
j. means for applying said output signals from said spark sensing means to said automatic control system;
k. means for applying output signals from said automatic control system to said phase control means;
l. means for applying output signals from said phase control means to said gate current supply means for controlling the conduction of said SCR's.

9 more elements

Control means to phase-control voltage and current obtained from an AC line and applied to the primary winding of a transformer/rectifier set (T/R set) which supplies voltage to an electrostatic precipitator wherein spark discharges of varying intensity, arcs and short circuits occur, said control means including:

a. silicon controlled rectifiers (SCR's) in said primary circuit;
b. a current transformer in said primary circuit and means for developing therefrom a current output signal only when said current in said primary circuit equals or exceeds a predetermined value, and only after a momentary dead interval starting with each turn-on of said SCR's;
c. sensing means for sensing said spark discharges and for developing output signals therefrom;
d. gate current supply means connected to the gate circuits of said SCR's;
e. phase control means for providing output signals to said gate current supply means which are phase controlled with respect to said AC line voltage;
f. an automatic control system for controlling said voltage applied to said primary winding of said T/R set through control of said phase control means, said automatic control system being responsive to said output signals obtained from said sensing means;
and
g. means for applying said output signals from said sensing means to said automatic control system which includes inhibit means for rendering said sensing means inoperative whenever said current output signal obtained from said current transformer is not present, thereby preventing faulty responses to transients caused by turn-on of said SCR's.

5 more elements

Dependencies are inferred from the claim text.

Facts

Application: 06/264,577Filed 18 May 1981 · continuation
Priority: 17 Sep 1979
Granted: 28 Jun 1983
Term ends: Not estimatedThe source records don’t support an estimate.

Classification7 codes

H02M 3/3155
Using semiconductor devices only: with automatic control of the output voltage or current
B03C 3/68
Applications of electricity supply techniques: control systems therefor
H02M 7/155
Using devices of a thyratron or thyristor type requiring extinguishing means: using semiconductor devices only
Y10S 323/903
Electricity: power supply or regulation systems: precipitators