US2217481A - Precipitator indicating system - Google Patents

Description

Patented Oct. 8, 14940 UNITED STATES PRECIPITATOR INDICATING SYSTEM Ralph L. Hildebrand and Irvine A. Yost, Lakewood, Ohio, assignors to Westinghouse Electric & Manufacturing Oompany, East Pittsburgh, Pa., a corporation of Pennsylvania Application September 20, 1939, Serial No. 295,7 36

6- Claims.

Our invention relates to a reliable indicating and alarm system for use in connection with electrostatic gas-cleaning devices.

While our invention is generally applicable to electrostatic gas-cleaning devices of any type, it has been more specifically adapted as an improvement over the invention which constitutes the subject matter of Gaylord W. Penneys Patent No. 2,129,783, granted September 13, 1938, relating to a gas-purifying precipitator in which the gas is blown rst through an ionizing chamber, and then through a separate precipitating chamber, a significant feature of the precipitator being that the ionizing wire is of such small diameter that practically utilizable ionization of suspended particles in the gas may be obtained at a wire-charging voltage which is below the critical corona voltage, so that the wire-charging voltage may be below this critical value, thereby limiting the ionizing current input and also limiting the ozone-generation when the precipitator is used for cleaning air.

Such a precipitator utilizes an ionizing wire of less than 32 mils thickness, which is a somewhat roughly critical value of the wire-diameter, somewhere near the knee of the curve expressing the relatio-n between the critical corona voltage and the wire-diameter. In ordinary practice, the wire is much finer than this upper limit, and is frequently a tungsten wire 5 mils in diameter, or even very much less in diameter. As the result of the use of such fine wire, the currentinput into the ionizing chamber is kept down to very small values, of an order similar to the current-input into the precipitating chamber, so that it becomes possible to energize both chambers by means of a high-voltage rectifying -poWer-unit having an extremely small currentrating, as distinguished from the very much larger currents which were fed into previous precipitating systems utilizing much heavier ionizing wires.

In the aforesaid Penney patent, a special power-unit of limited energy-output was shown,

(Cl. 18S- 7) transformer, because an electrostatic precipitator has th'e habit of producing a momentary spark or iiash, at infrequent intervals, as a result of a piece of lint or other dirt which might momentarily short-circuit the equipment, so that it was necessary to limit the energy which would be withdrawn through the small rectifier-tubes during such ashes. As theequipment gets dirtier and dirtier, from the accumulation of foreign particles withdrawn from the gas being treated, these flashovers become more numerous and more severe. The equipment should be taken out of service long enough to flush it out with a water hose, or to otherwise clean it, before these flashover conditions get too severe, or lead even to failure or an inoperative condition, but it' has been deemed necessary to provide some sort of means for indicating a failure or inoperative condition of the equipment, either because of a permanent short-circuit, or because of breakage of the fine wire, or because of a failure of one of the rectifier-tubes or other parts of the apparatus.

It is the particular object of our invention to provide an inexpensive and reliable indicating and alarm system for either showing the existence of any sort of failure of the apparatus, or, if desired, ior shutting down the entire apparatus or any part of the entire apparatus. i

In an application of R. L. Hildebrand, Serial No. 202,232, lecl April 15, 1938, (Patent No. 2,200,085, dated' May 7, 1940) a tertiary winding was supplied, on the secondary leg of the transformer, to operate an undervoltage relay for responding to short-circuits and an overvoltage relay for responding to tube-failures and opencircuits. Experience has-shown, however, that the overvoltage relay would not satisfactorily respondunless it was so sensitive as to be too expensive, in most cases. Experience further showed that an .undercurrent relay connected in the grounded return-circuit of the high-voltage direct-current circuit, for the purpose of realternating-current step-up transformer would protect the coil of the primary-circuit under-current relay against insulation-failure as a result of the high-voltage surges which are produced in the secondary circuit whenever the secondary-circuit capacitors are suddenly short-circuited as a resultof a momentary precipitator-fiashover such as might be caused by apiece of lint.

With the foregoing objects in view, and others which will become apparent as the description proceeds, our invention consists in the systems, methods, apparatus and combinations hereinafter described and claimed, and illustrated in the accompanying drawing, the single figure of which is a diagrammatic view of circuits'and i apparatus illustrating our invention in a preferred form.

In the illustrated embodiment of our invention, which is only one of many forms which the invention can take, air to be treated is drawn in through the bottom of a precipitator-cabinet I., as by means of a fan or blower 2. The air passes upwardly, first through an ionizing chamber 3, and then through a precipitating chamber 4, from the top of which the air-is discharged from the apparatus.

The ionizing chamber usually comprises a plurality of ionizing unitsdisposed transversely with respect to the direction of air iiow, but for simplicity of illustration, only one of these ionizing units is illustrated in the drawing, and that illustration is somewhat schematic. In this ionizing unit, the air passes upwardly between two spaced horizontal tubular electrodes 5 which are grounded on the metal cabinet I. Between these two tubular electrodes there is suspended a. fine ionizing wire 6 of the type which has already bee'n discussed.

The precipitating chamber usually comprises a relatively large number of alternately insulated and noninsulated plates 'I and 8, these plates standing vertically, or parallel to the direction of air-flow. The insulated plates 'I are supported on notched bars 9 which are carried by insulators I0, while the non-insulated plates 8 are carried by notched bars I2 which are grounded on the metal cabinet I.

Electrical energy is supplied to this precipitator-apparatus by means of a. power-unit which derives its energy from a 11G-volt alternatingcurrent line I4, or any other suitable source of supply. The power-unit comprises a specially designed step-up transformer I5 having a magnetizable circuit including a primary portion I6, a secondary portion I1, andv a magnetic-leakage path I8 therebetween, the magnetic-leakage path preferably including an air-gap I9 or its equivalent. On the primary portion I6 of the magnetizable circuit, this transformer carries a low-voltage primary winding 2| and two separately insulated filament-circuit auxiliary windings 22 and 23 which are usually of considerably lower voltage. On the secondary portionII of the magnetizable circuit, this transformer carries a high-voltage secondary winding 24 which, in the illustrated embodiment of the invention, is provided with an intermediate tap 25 near one end. This secondary portion I of the magnetizable circuit also carries a low-voltage tertiary winding 26.

Energy is derived from the secondary winding 24 and applied to the ionizing Wire 6 and to the insulated precipitator-structure 9 in any convenient manner, the illustrated embodiment bem8 the same as that which is shown in the Penney patent, and involving two rectifier-tubes 3I and 32 having lamentary cathodes which are energized from the auxiliary transformerwindings 22 and 23, respectively. The rectifier tubes 3| and 32 are of a special design, capable of withstanding a high inverse peak-voltage of 20,000 volts, and capable of carrying a continuous load of 20 milliamperes of rectified direct current.

These rectier-tubes 3I and 32 are utilized to cumulatively charge two serially connected capacitors 33 and 34, the charges on which are indicated by plus and minus signs. The capacitors should be large enough not only to avoid resonance withthe transformer-secondary reactance, but also to reduce the ripple of the pulsating rectied current to a value no larger than 15 percent of the mean direct-current value. The capacitors 33 and 34 may be shunted by discharging-resistors 35, which are capable of reducing the voltage to zero in 5 seconds after the power is turned oi.

The negative terminal of the capacitor 34 is grounded 'on the cabinet I. 'Ihe positive terminal of this capacitor is connected, at 36, to the insulated precipitating structure 1-9. The negative terminal of the capacitor 33 is connected to the same point 36, while the positive terminal of this capacitor 33 is connected, at 31, to the ionizing wire or wires 6. As a result of the foregoing construction, it is possible to apply a voltage of the order of from 5,000 to 6,000 volts to the oppositely charged precipitating electrodes 'I and 8, and a voltage of the order of from 12,000 to 13,000 volts to the ionizing wire 6, this voltage being variable by means of primary taps 38, so as to accommodate several different sizes of precipitators, as well as different operating-conditions.

Our protective equipment is two-fold. To respond to overload conditions or short-circuits, we utilize the tertiary winding 26 to energize an undervoltage relay 4I. To respond to underload conditions indicative of a tube-failure or an open circuit, we utilize an undercurrent relay 42 havinga winding which is connected in series with the primary winding 2| of the transformer. The undervoltage tertiary relay 4I has a make-contact 43 which is utilized to energize a green light G when normal voltage-conditions prevail on the secondary winding 24 (and hence on the tertiary winding 26). The undervoltage tertiary relay 4I also has a back-contact 44 which is utilized to energize a red light R when the secondary voltage drops as a result of a short-circuit. The undercurrent primary relay 42 has a back-contact 45 which is utilized to energize the red light R.

The indicating-system relays 4I and 42 are so adjusted that, under normal operating conditions, the green light vG is on, and the red light R is off, because sufficient voltage is applied to the undervoltage tertiary relay 4I to hold its front-contacts 43 closed and its back-contacts 44 open, while normal load-conditions prevail on the transformer I5, so that sufficient primary current flows through the undercurrent primary relay 42 to hold its back-contacts 45 open.

In operation, it will be observed that the voltage of the tertiary winding 26 will always be proportional to the voltage of the secondary winding 24, because both windings are interlinked with the same portion I1 of the magnetizable circuit of the transformer I5, with relatively little leakage between the two windings. A separately insulated tertiary winding 26 is utilized, rather than taps on the secondary winding, because this secondary winding, as a whole, may rise to 8,000 to 14,000 volts above ground, particularly in .transformer a poor voltage-regulation, the secondary voltage varies strongly with slight changes in the secondary load, and, of course, the tertiary voltage of the relaying winding 26 follows the secondary voltage, as already explained. If one of the rectifying tubes 3|` and 32 should fail, or if one of the ne ionizing wires 6 should break, the usual result is to decrease the load on the transformer l5, so that the primary current reduces, and the undercurrent primary relay 42 drops out, closing its back-contact 45 and lighting thered light R. At the same time, the decreased load on the secondary winding 24 increases the relaying voltage supplied by the tertiary winding 26 to the undervoltagetertiary relay 4I so that the latter remains energized and holds its front-contact 43 closed and keeps the green light G on. A tube-failure or an opencircuit is thus indicated by a showing of both lights G and R.

Foreign material on or between theprecipitating plates 'I and 8, causing short-circuits, and short-circuits produced from any other cause, will usually increase the secondary load, thereby decreasing the relaying voltage applied to the undervoltage tertiary relay 4|, causing the same to respond by dropping out, opening its frontcontact 43 and closing its back-contact 44, thus turning oil the green light G, and turning on the red light R. This drop in the tertiary relaying voltage is really a very positive indication of a short-circuit in the equipment, because of the very poor voltage-regulation of the transformerv l5, causing the voltage of the tertiary winding 26 to respond to changes in the secondary load. At the same time, the heavy oscillatory dischargecurrents of the capacitors 33 and 34, because of short-circuits in the precipitator equipment, do

not produce correspondingly heavy current-surges in the primary winding 2| of the transformer, because of the high magnetic leakage which is introduced in the transformer by the leakagepath l8-I9, thus protecting the turn-insulation on the coil of the primary undercurrent relay 42 against failure as a result of these high-frequency surges or oscillatory capacitor-discharges.

In the foregoing description and'in the appended claims, when we refer to the critical corona voltage of the ionizing wire, we refer to the lowest voltage which produces a .corona-discharge of the sort which is visible in sunlight, which is the kind of corona. which was obtained in electrostatic precipitating equipments prior to Mr. Penneys introduction of the critically fine ionizing wire. With the hereinabove described fine ionizing wire, the ionizing voltage which it is necessary to utilize, in order to obtain a substantially utilizable degree of ionization of the suspended particles in the gas being treated, is very much below this criticalv corona voltage, so that there is 'no corona-discharge which is visible in sunlight. In a dark room, however, there will be a corona-glow which is distinctly visible, surrounding the ionizing Iwire 8 as a result of the very slight discharge therefrom.

'While we have described our invention in a preferredform of embodiment, and have suggested certain limitations in accordance with our best understanding of the same at the present time, we desire it to be distinctly understood that we are not altogether limited to these limitations or understandings, or to the particular form of embodiment shown in the drawing. We desire,

therefore, that the appended claims shall be accorded the broadest constructions consistent with their language and the prior art.

We claim as our invention:

1. A gas-purifying precipitator-assembly comprising electrostatic gas-cleaning means for ionizing foreign particles in the gas and -for electrostatically attracting said ionized particles; voltage-conversion, relatively high-voltage means comprising a step-up transformer, rectifyingmeans, and capacitor,voltage-smoothing means for supplying a rectified voltage or voltages to .said gas-cleaning means; and a current-responsive .device in series with the primary circuit of 'the transformer for making a predetermined recharged, spaced precipitating electrodes substantially parallel to the direction of gas-flow; voltage-conversion, relatively high-voltage means comprising a step-up transformer, rectifyingmeans, and capacitor voltage-smoothing means for supplying a rectified voltage or'voltages to both said ionizing Wires and said oppositely charged precipitating electrodes; said ionizing wire or wires being of less than 32 mils diameter and being of such neness that substantially utilizable ionization of suspended particles in the gas-is obtained at a low ionizing current with a wire-charging voltage below the critical corona voltage, the unidirectional wire-charging voltage being below said critical corona voltage; and a current-responsive device in series with the primary circuit of the transformer for making a predetermined response to a predetermined change in the primary current, whereby said current-responsive device is protected, by the intervening transformer, from high-voltage surges appearing on the secondary side of the transformer.

3; A gas-purifying precipitator-assembly comprising electrostatic gas-cleaning means for ionizing foreign particles in the gas and for electrostatically attracting said ionized particles; limited-energy, voltage-conversion, relatively high voltage means'comprisng a step-up transformer, rectifying-means, and capacitor voltage-smoothing means for supplying a rectified voltage or voltages to said gas-cleaning means; said stepup transformer having a magnetizabie circuit including a primary portion, a secondary por-` tion, and a'magnetic-leakage path therebetween, said step-up transformer having a high-voltage secondary winding and a low-voltage tertiaryl winding both disposed on the secondary portion of the magnetizable circuit, and a low-voltage primary winding disposed on the primary portion of the magnetizable circuit; means energized from said tertiary winding for obtaining a predetermined response or responses to a departure of the voltage from a predetermined voltagerange; and a current-responsive device in series with the primary circuit of the transformer for making a predetermined response to a predetermined change in the primary current, whereby said current-responsive device is protected, by the intervening transformer, from high-voltage surges appearing on the secondary side of the transformer.

4. A gas-purifying precipitator-assembly comprising an ionizing chamber, a separate precipitating chamber, and means for causing a gasfiow successively through rst said ionizing chamber and thensaid precipitating chamber, said ionizing chamber comprising one or more insulatedly supported fine wires spaced between substantially uninsulated large electrodes; said precipitating chamber comprising oppositely charged, spaced precipitating electrodes substantially parallel to the direction of gas-now; limited-energy, .voltage-conversion, relatively highvoltage means comprising a step-up transformer,

rectifying-means, and capacitor voltage-smoothing means for supplying a rectified voltage or voltages to both said ionizing wires and said oppositely charged precipitating electrodes; said step-up transformer having a magnetizable circuit including a primary portion, a secondary portion, and a magnetic leakage path therebetween, said step-up transformer having a highvoltage secondary winding and a low-voltage tertiary winding both disposed on the secondary portion of the magnetizable circuit, and a lowvoltage primary winding disposed on the primary portion of the magnetizable circuit; said ionizing wire or wires being of less than 32 mils diameter and being of such fineness that substantially utilizable ionization of suspended-particles in the gas is obtained at a low ionizing current with a wire-charging voltage below thel critical corona voltage, the uni-directional wire-charging voltage being below said critical corona voltage; means energized from said tertiary winding for obtaining a predetermined response or responses laarzgcm to a departure of the voltage from a predetermined voltage'range; and a current-responsive device in series with the primary circuit of the transformer for making a predetermined response to a predetermined change in the primary current, whereby said current-responsive device is protected, by the intervening transformer, from high-voltage surges appearing on the secondary side of the transformer.

5. In combination, voltage-conversion, relative- 1y high-voltage means comprising a step-up transformer, rectifying-means, and capacitor voltage-smoothing means for supplying a rectied voltage or voltages to one or more loadcircuits; and a current-responsive device in series with the primary circuit of the transformer for making a predetermined response-to a predetermined change in the primary current, whereby said current-responsive device is protected, by the intervening transformer, from high-voltage surges appearing on the secondary side of the transformer.

6. In combination, limited-energy, voltage-conversion, relatively high-voltage means comprising a step-up transformer, rectifying-means, and capacitor voltage-smoothing means for supplying a rectified voltage or voltages to one or more load-circuits; said step-up transformer having a magnetizable circuit including a primary portion, a secondary portion, and a magnetic-leakage path therebetween, said step-up transformer having a high-voltage secondary winding and a low-voltage tertiary Winding both disposed on the secondary portion of the magnetizable circuit, and a low-voltage primary winding disposed on the primary portion of the magnetizable circuit; means energized from said tertiary winding for obtaining a predetermined response or responses to a departure of the voltage from a predetermined voltage-range; and a current-responsive device in series with the primary circuit of the transformer for making a predetermined response to a predetermined change in the primary current, whereby said current-responsive device is protected, by the intervening transformer, from high-voltage surges appearing on the secondary side of the' transformer.

RALPH L. HILDEBRAND. IRVINE A. YOST.

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