EP0504143B1

EP0504143B1 - Electrical control system for electrostatic precipitator

Info

Publication number: EP0504143B1
Application number: EP90911823A
Authority: EP
Inventors: David F. Johnston; Terry L. Farmer
Original assignee: BHA Group Inc
Current assignee: BHA Group Inc
Priority date: 1989-11-30
Filing date: 1990-06-29
Publication date: 1997-04-23
Anticipated expiration: 2010-06-29
Also published as: WO1991008052A1; WO1991008053A1; EP0504143A1; CA2069881C; DK0504143T3; EP0504143A4; DE69030583D1; DE69030583T2

Abstract

Form factor measurement and fault detection equipment to determine proper sizing of electrical components and efficiency of an electrostatic precipitator (22) by calculating a system form factor from either primary voltage or current. A power source (10) connects serially to an inverse parallel SCR 1 and SCR 2, to a current limiting reactor (16), and to a T/R set comprising a transformer (18) and rectifier (20) which supply power to precipitator (22). A current transformer (26) senses input current between the reactor (16) and T/R set (18, 20) to signal an input scaling and signal conditioner (28) connected to a current meter (34), a voltage meter (39) and a computer (40) having a display monitor (42). The computer (40) is also connected to an SCR control circuit (24) of SCR 1 and SCR 2. The appropriate electrical characteristic is converted to both its RMS value and average value and then sent to the computer (40). The computer (40) divides the RMS value by the average value and sends the resulting form factor value to the display (42). If system form factor value is not sufficiently close to the purely resistive circuit value of 1.11, then equipment resizing is needed to increase system efficiency. Additionally, secondary electrical characteristics are used to calculate fractional conduction. If the fractional conduction is not sufficiently close to a desired level, equipment adjustments are made to increase system efficiency.

Description

The invention relates to an apparatus for detecting and curing the performance of an electrical circuit generating electrical signals and operating at an efficiency level departed from a desired level of efficiency, the apparatus comprising:

sensing means for sensing the electrical signals;
comparing means connected to the sensing means for comparing the sensed electrical signals with predetermined signals to provide an indication of circuit operating efficiency; and
means for adjusting the circuit based on said comparison to alter the electrical signals if the circuit operating efficiency departs from a desired level, to maintain circuit operation at a desired efficiency.

More specifically, the invention relates to electrostatic precipitators for air pollution control and, still more specifically, concerns the electrical control of electrostatic precipitators.
An apparatus of the afore-mentioned kind has been known from document US-A-4 587 475.
Continuous emphasis on environmental quality has resulted in increasingly strenuous regulatory controls on industrial emisions. One technique which has proven highly effective in controlling air pollution has been the removal of undesirable particulate matter from a gas stream by electrostatic precipitation. An electrostatic precipitator is an air pollution control device designed to electrically charge and collect particulates generated from industrial processes such as those occurring in cement plants, pulp and paper mills and utilities. Particulate laden gas flows through the precipitator where the particulate is negatively charged. These negatively charged particles are attracted to, and collected by, positively charged metal plates. The cleaned process gas may then be further processed or safely discharged to the atmosphere.
To maximize the particulate collection, a precipitator should be operated at the highest practical energy level to increase both the particle charge and collection capabilities of the system. Concurrently, there is a level above which "sparking" (i.e., a temporary short which creates a conductive gas path) occurs in the system. Left uncontrolled, this sparking can damage the precipitator and control system. The key to maximizing the efficiency of an electrostatic precipitator is to operate at the highest energy level possible.
Ideally, the electrostatic precipitator should constantly operate at its point of greatest efficiency. Unfortunately, the conditions, such as temperature, combustion rate, and the chemical composition of the particulate being collected, under which an electrostatic precipitator operates are constantly changing. This complicates the calculation of parameters critical to a precipitator's operation. This is particularly true of the current limiting reactor (CLR) which controls and limits the current entering the precipitator and matches the precipitator load to the line to allow for maximum power transfer to the precipitator.
The CLR has two main functions. The first is to shape the voltage and current waveforms that appear in the precipitator for maximum collection efficiency. The second function of the CLR is to control and limit current.
Power control in a precipitator is achieved by silicon controlled rectifiers (SCRs). Two SCRs are connected in an inverse parallel arrangement in series between the power source and the precipitator high voltage transformer. The power source is an alternating current (AC) sinusoidal waveform whose value is zero at the beginning and end of every half cycle, and is a positive value during one half cycle and a negative value during the next half cycle. For a power source with a 60 Hz. frequency, this would occur every 8,33 milliseconds (10 milliseconds for a 50 Hz. power source).
Only one SCR conducts at a time on alternate half cycles. The automatic voltage control provides gating such that the appropriate SCR may be switched on at the same point during the half cycle to provide power control. The SCR remains switched on or in conduction until the current passing through the SCR falls below a specified value for the device. The cycle is then repeated for the next half cycle and the opposite SCR. The SCRs cannot be switched off by the automatic voltage control. If the precipitator spark level is reached with no control of current to the precipitator, equipment damage can occur. The CLR provides a means of controlling and limiting the current flow to the precipitator until the conducting SCR switches off at the end of the half cycle.
Because of its critical role in maximizing electrostatic precipitator performance, it is vital that the CLR be properly sized. In the prior art, the CLR is sized at 30 % - 50 % of the impedance of the transformer/rectifier (T/R) set. This calculation results in a rough estimate of the appropriate CLR size for a given application. The actual electrical efficiency is subjectively measured by viewing the shape and duration of the waveform of the secondary current with an oscilloscope and estimating the fractional conduction. The CLR is then adjusted by trial and error in an attempt to obtain the desired fractional conduction and, thereby, collection efficiency. Fractional conduction and other methods used to size CLRs in the prior art have been crude and inaccurate, allowing for operational inefficiency and equipment damage including blown fuses, equipment failure and inefficient performance from other components of the system.
The production output of many industries may be limited by the amount of pollution discharged. The government sets limits on the amount of pollution a facility may generate and discharge. In the event this limit is exceeded, a facility is subjects to fines and temporary or permanent shut-down. Therefore, in terms of profitability, it is imperative that the electrostatic precipitator operate at its highes efficiency, and in the event of a malfunction, minimizing down time is a high priority.
The prior art requires time consuming calculations to determine initial operation settings for precipitator controls. In the event of a malfunction or fault, determining the exact problem and repairing or replacing the faulty component is time consuming and often requires disassembling of much of the precipitator or its controls.
Document US-A-4 587 475 discloses a power supply for an electrostatic precipitator. Like many conventional power supplies, the device disclosed has, coupled in series combination, an AC power supply, an arrangement of anti-parallel thyristors, a transformer, and a rectifier. The output of the rectifier is coupled with the precipitators. The device disclosed generates a string of electrical pulses for use in powering the precipitator. This is accomplished by triggering the thyristors once during each half-cycle of operation. In developing the string of pulses for powering the precipitator, the device periodically generates a pulse of greater power than the power of the other pulses. As a result, the power in the precipitator is correspondingly periodically boosted.
Another power supply quite similar to that described before is disclosed in document US-A-4 290 003.
Document US-A-4 936 876 discloses a method and apparatus for detecting back corona in an electrostatic filter. The mean current in the precipitator section is increased over a preset limit at selected intervals until spark-over occurs. Back corona is detected by control equipment which compares the minimum value of the precipitator voltage before and after a spark-over, or a blocking of the precipitator current for a predetermined period if no spark-over has occurred, subject to accurately controlled escalation of the precipitator voltage after the spark-over. The precipitator voltage is increased to a level equal to the mean voltage before the spark-over within a maximum of three-half periods of the main supply frequency regardless of the load on the DC-voltage supply.
The above-described limitations of the prior art all lead to operation inefficiency, equipment damage, inadequate performance and increased pollution emissions.
A long felt need in the air pollution control industry remains for improvements in the electrical control of electrostativ precipitators to alleviate the many operational and performance difficulties which have been encountered in the past. The primary goal of this invention is to fulfil this need.
This goal is achieved with an apparatus as specified at the outset and being further characterized in that the sensing means are adapted to sense characteristic waveforms of the electrical signals and that the adjusting means includes means for altering the waveform that is being sensed to substantially a desired waveform.
Given the critical role the CLR plays in maximizing electrostatic precipitator performance, this invention provides an on-line means that accurately and dynamically measures fractional conduction for sizing the CLR, replacing the "trial and error" used in the prior art. Another accurate method of analysis is to measure the root mean square (RMS) value and the average value of the primary current, then divide RMS by average to obtain the form factor. The theoretical form factor in a purely resistive circuit i 1,11. It is well known in the art that at a low form factor of approximately 1,2, maximum power transfer and collection efficiency is achieved. Accordingly, a feature of this invention is to calculate the form factor to provide a verifiable basis on which to measure electrical efficiency of the CLR and other electrical components. Since a form factor can be calculated using primary voltage as well as primary current values, it is also an object of this invention to give the user the option of using either value.
The electrical efficiency of the precipitator is also dependent upon the secondary current waveforms. It is well known in the art that the length of time the secondary current waveform pulse is present during the half cycle is determined by the correct matching and proper design of the precipitator components. For example, the T/R set, CLR and the size of the precipitator field must be matched for the precipitator to have maximum attainable collection efficiency for the application. Prior art requires point by point measurement of secondary current waveforms using an oscilloscope or similar device. Fractional conduction is then calculated from the waveforms shown on the oscilloscope.
The duration of the pulse relative to the maximum duration possible (8,33 milliseconds for 60 Hz. applications and 10 milliseconds for 50 Hz. applications) is known as the fractional conduction. A fractional conduction of 1 would be considered ideal. That is, the secondary current pulse would be present for the entire half cycle of 8,33 milliseconds. Fractional conductions of 0,86 normally yield full rated average currents on the precipitator load. Fractional conductions less than 0,86 result in less than full rated average currents on the precipitator which decreases the collection efficiency. Therefore, it is a further feature of this invention to continuously measure the secondary current waveform and report the fractional conduction so that adjustments can be made, either manually or automatically, in system components to maintain maximum collection efficiency. This ability to automatically measure and report secondary current fractional conduction is not available under the prior art.
It is an advantage of this invention to give the user the option of using either the form factor or the secondary waveform fractional conduction as a means to size the CLR.
Another advantage of this invention is to provide these values in such a way as to facilitate manual or automatic adjustments to the CLR.
A further advantage is to reduce start-up time by allowing programmable operating instructions that can be calculated and down-loaded into the automatic voltage control. This will relieve the operator of initially having to calculate values and set the automatic voltage control, CLR, and other electrical components which will save time and reduce operator error.
Another feature of the invention is to provide a calculator from which the impedance of the CLR is calculated.
Another important advantage is to minimize repair and trouble-shooting time and expense by providing an automatic voltage control with the ability to diagnose fault conditions and suggest possible corrective measures.
Another advantage of this invention is to reduce repair time and costs by locating often damaged components in an easily accessible location. All over-voltage protection is positioned in a plug-in board. In the event that the automatic voltage control is damaged by over voltage, or modifications are needed for another application, this board can be removed an repaired without disassembling the entire automatic voltage control.
A further feature of this invention is to provide a portable, stand-alone form factor and fractional conduction meter for use separate from an automatic voltage control. This meter will calculate form factor or fractional conduction for any electrostatic precipitator or similar equipment and immediately inform the operator how efficiently the equipment is performing.
Another feature of this invention is to provide a novel method for calculating form factor and fractional conduction.
Other and further objects and advantages of the invention, together with the features of novelty appurtenant thereto, will appear in the course of the following description.
In the accompanying drawings which form a part of the specification and are to be read in conjunction therewith, and in which like reference numerals are used to indicate like parts in the various views:

Fig. 1 is a block diagram of an electrical sizing circuit constructed in accordance with a preferred embodiment of the invention for an automatic voltage control circuitry;
Fig. 2 is a block diagram illustrating in greater detail the input scaling and signal conditioning circuitry schematically shown in Fig. 1;
Fig. 3 is a block diagram illustrating in greater detail the components of the computer control schematically shown in Fig. 1; and
Fig. 4 is a block diagram of the form factor and fractional conduction meter of this invention illustrated as a stand-alone test instrument.

This invention specifically contemplates determining the form factor and fractional conduction of an electrostatic precipitator to accurately measure whether the electrical components are sized properly. A device to measure the form factor and fractional conduction is described both as part of an automatic voltage control system and as a stand-alone meter. The invention calculates form factor and fractional conduction utilizing electrical characteristics such as voltage and current.
Utilizing the form factor to properly size electrical components as part of an electrostatic precipitator's automatic voltage control is shown generally in Fig. 1 of the drawings. A power source 10, typically a 480-volt, single phase, AC power source, has two output terminals 12 and 14. Output terminal 12 connects serially to an inverse parallel SCR 1 and SCR 2, to a current limiting reactor 16, and to one side of the primary of a step-up transformer 18. Output terminal 14 connects to the other side of the primary of transformer 18. The secondary of transformer 18 is connected across a full-wave rectifier 20 which supplies power to precipitator 22. Transformer 18 and full-wave rectifier 20, in combination, is commonly referred to as the T/R set.
The positive output of rectifier 20 passes through a current meter 34 and resistor 32. The resistor 32 connects with an input scaling and signal conditioner 28. The negative output of rectifier 20 connects both to precipitator 22 as well as through a resistor 36 and a resistor 38 to ground. The voltage across resistor 38 is sensed by a voltage meter 39 and voltage meter 39 connects with input scaling and signal conditioner 28.
A current transformer 26 senses the input current and sends a signal to input scaling and signal conditioner 28. The primary of a potential transformer 30 is connected across the power input before transformer 18 and the secondary of transformer 30 is connected to the input scaling and signal conditioner 28.
The output of input scaling and signal conditioner 28 is connected to a computer 40 which is connected to an SCR control circuit 24. Computer 40 is also connected to a display 42 and bi-directionally connected to an input/output port 44. Display 42 may typically comprise an LM4457BG4C40LNY LCD display module such as manufactured by Densitron.
Input scaling and signal conditioner 28 is shown in detail in Fig. 2. Primary current is received from current transformer 26 and flows to two separate circuits, an averaging circuit 46 and an RMS circuit 48. The averaging circuit 46 has two operational amplifiers 50 and 51 and two diodes 52 and 53. The operational amplifiers 50 and 51 may typically comprise TL032CP chips as manufactured by Texas Instruments of Dallas, Texas; and diodes 52 and 53 may typically comprise IN4148 diodes as also manufactured by Texas Instruments of Dallas, Texas. The output of averaging circuit 46 connects with computer 40. The RMS circuit 48 has an operational amplifier 54, typically the above mentioned TL032CP chip, and an RMS converter 56, typically an AD536AJD chip as manufactured by Analog Devices of Norwood, Massachusetts. The output of RMS circuit 48 connects with computer 40.
Primary voltage is received from transformer 30 and flows to an RMS circuit 58. RMS circuit 58 is identical to RMS circuit 48 except that RMS circuit 58 receives primary voltage. The output of RMS circuit 58 connects with computer 40. The values of a resistor 60 and a resistor 62 control whether the averaging circuit 46 receives primary voltage or primary current.
Secondary voltage is received from voltage meter 39 and passes through two operational amplifiers 64 and 65 (both typically TL032CP chips as manufactured by Texas Instruments of Dallas, Texas) and enters computer 40. Secondary current present in precipitator 22 is received from current meter 34 and passes through external resistor 32. Resistor 32 converts the secondary current to a voltage which is directly proportional to secondary current. This voltage passes through resistor 37 and voltage comparator 41 on its route to computer 40. Voltage comparator 41 is a LM311N device as made by National Semiconductor Corporation of Santa Clara, California.
Computer 40 is detailed in Fig. 3. A multiplexer 66 of computer 40 receives data from input scaling and signal conditioner 28. Multiplexer 66 may typically comprise an ADG508AKN chip such as manufactured by Analog Devices of Norwood, Massachusetts. Multiplexer 66 is connected directly to a logic means 72 and connected in series with a buffer 68, an A/D converter 70 and logic means 72. The buffer 68 may typically be a Texas Instruments TL032CP operational amplifier chip and the A/D converter 70 may typically comprise an AD573JN chip such as manufactured by Analog Devices of Norwood, Massachusetts. Logic means 72 is connected to SCR control circuit 24 and display 42, and is bi-directionally connected to input/output port 44 and bi-directionally connected to a memory means 74.
Fig. 4 is a block diagram of a form factor and fractional conduction meter as would be used as a stand-alone device. External sensor 76, which senses both primary and secondary electrical characteristics, is connected to the input scaling and signal conditioner 28 which connects with computer 40, and computer 40 connects to display 42. A power source 78 will power input scaling and signal conditioner 28, computer 40 and display 42. Power source 78 may consist of circuitry allowing the meter to plug into an external power source, or a battery or similar power supply. Sensor 76 may typically be a clamp as found on many models of current meters. It should be understood that sensor 76 may comprise a plurality of sensors. Sensor 76 is shown in block form for illustrative purposes.
In operation, the primary embodiment of this invention is to work in cooperation with an electrostatic precipitator automatic voltage control device. A representative example of an electrostatic precipitator automatic voltage control is shown in my earlier patent U.S. Patent No. 4,605,424, issued August 12, 1986 and entitled "Method and Apparatus for Controlling Power to an Electronic Precipitator", which is incorporated by reference herein. It should be recognized that, while these two inventions may share hardware, the problems addressed by each are distinct. The '424 patent controls voltage or power to the precipitator while this invention addresses the inefficiency of improperly sized components of an electrostatic precipitator.
Upon start up, input/output port 44 is utilized to communicate information to logic means 72 within computer 40. Communication may be accomplished through a built-in keyboard, portable lap-top computer, remote computer connected to the input/output port 44 directly or by modem, or by a similar means. Equipment size and power levels are communicated which allows initial calculations by logic means 72 to determine the proper setting of CLR 16 and other settings for other equipment. CLR 16 and other equipment may be set automatically, or the appropriate values may be sent to display 42 and the equipment set manually according to the previously calculated settings. The impedance of CLR 16 is calculated using calculator screens programmed into computer 40. The impedance is expressed as a percentage of the T/R set.
In addition to equipment size and power levels, the desired spark rate, SCR firing angle, fault conditions and all other information required by the automatic voltage control to supply power to the precipitator is communicated through input/output port 44 to logic means 72. This relieves the operator from having to manually set the equipment and helps to eliminate operator error. Information and calculated values required for future reference are sent from logic means 72 to memory 74.
The desired power level is sent from logic means 72, within computer 40, to SCR control circuit 24 where the power level is converted into an SCR firing angle. Power is applied to precipitator 22 in terms of SCR firing angle degrees. The sinusoidal electrical cycle consists of 360 degrees, and consists of a positive half cycle and a negative half cycle with respect to polarity. Each SCR can be fired anywhere from 0 degrees to 180 degrees in the electrical cycle, 0 degrees being full power and 180 degrees being 0 power. When an SCR is fired at 45 degrees, for example, it will conduct from 45 degrees to 180 degrees. Therefore, a difference in firing angles can be represented as a distance along the abscissa of the sine wave. Due to polarity reversal, the SCR stops conducting when the current passing through the SCR falls below a specified value for the device.
The normal operating state of SCR 1 and SCR 2 is 180 degrees which allows 0 power from power source 10 to pass through to precipitator 22. After SCR firing circuit 24 translates the power level into the appropriate angle, this angle is sent to SCR 1 and SCR 2 which begins allowing the appropriate power to pass from power source 10 down line to step-up transformer 18 and full-wave rectifier 20, and eventually to precipitator 22.
SCR 1 and SCR 2 inherently produce sharp rises in power when their respective firing angles dictate each SCR to energize. Thus, a primary object of CLR 16 is to filter and shape the signal leaving SCR 1 and SCR 2. Ideally, the shape of the secondary current filtered wave will be a broad, rectified sinusoidal waveform since the average value produces work. Such a waveform yields the best precipitator collection efficiency. Ideally, the peak and average values of the signal entering precipitator 22 will be very close.
In addition, maximum power transfer is attained when load impedance matches line impedance. CLR 16 is set so that its inductance matches total circuit impedance including the precipitator load. This is attained by measuring the form factor and sizing the equipment within the circuit to attain a form factor approaching 1.11.
Full-wave rectifier 20 converts the AC signal which passes through SCR 1 and SCR 2 into a pulsating DC signal. The positive output of full-wave rectifier 20 passes through current meter 34 and resistor 32 to ground. The negative output of full-wave rectifier 20 connects directly to precipitator 22 as well as through voltage dividing resistors 36 and 38 to ground. Voltage meter 39 is in series with metering resistor 36. Current meter 34 and voltage meter 39 are utilized to sense operating conditions when sparking occurs in precipitator 22 and to sense fault conditions. The data obtained from voltage meter 39 and current meter 34 are sent to input scaling and signal conditioner 28 and eventually to computer 40.
Current transformer 26 measures the primary current and transformer 30 provides the primary voltage with respect to transformer 18. These values are sent to input scaling and signal conditioner 28 where they are converted to a state which allows the form factor to be calculated.
The circuitry that is principal to this invention can be found in Fig. 2. Primary current and voltage along with secondary current and voltage each enter input scaling and signal conditioner 28. Primary current from current transformer 26 is introduced and flows to averaging circuit 46 and RMS circuit 48.
The first half of averaging circuit 46 is a precision rectifier consisting of an operational amplifier 50 and two diodes 52 and 53. This precision rectifier provides a DC output that is not offset by the voltage drop of the diodes. A second operational amplifier 51 provides an averaging circuit such that the input of the total circuit 46 is AC and the output of the total circuit 46 is DC, proportional to the average value of the AC wave. The output of averaging circuit 46 is routed to computer 40.
The primary current also enters an RMS circuit 48. Operational amplifier 54 provides an input buffer and signal conditioning while RMS converter 56 changes the AC input to its RMS value and this value is routed to computer 40. Computer 40 now has primary current in two forms: average and RMS.
Transformer 30 provides primary voltage to input scaling and signal conditioner 28. The primary voltage enters RMS circuit 58 which changes the AC input to its RMS value, in the same manner as RMS circuit 48, and this value is routed to computer 40.
Two resistors 60 and 62 are provided. When resistor 60 is short and resistor 62 is open, the input scaling and signal conditioner 28 is configured to read the true RMS value and average value of the primary current for measuring form factor. By opening resistor 60 and shorting resistor 62, the true RMS value and average value of the primary voltage can be used to calculate form factor. At all times the true RMS of both primary voltage and primary current are provided. Resistors 60 and 62 allow the option of calculating either the average of the primary current or the average of the primary voltage so that the form factor can be calculated using either current or voltage.
Secondary current and voltage signals from circuitry associated with current meter 34 and voltage meter 39 both enter input scaling and signal conditioner 28. Secondary voltage passes through operational amplifiers 64 and 65 which provides isolation and scaling before it is routed to computer 40. The secondary current signal from resistor 32 is routed through resistor 37 to voltage comparator 41. Voltage comparator 41 compares the voltage proportional to the secondary current in precipitator 22 with a reference voltage. Ideally, the reference voltage would be zero volts. Preferably, since voltage comparator 41 is not an ideal device, and therefore, has some input offset voltage, the reference voltage is set slightly above zero volts.
The output of voltage comparator 41 will become positive when the secondary current present in precipitator 22 is greater than zero. The output of voltage comparator 41 will become zero volts when the secondary current present in precipitator 22 is zero. Therefore, the output of voltage comparator 41 is a pulse width that is proportional to the length of time that the secondary current pulse is present in precipitator 22. This pulse width is routed to computer 40.
Computer 40 is pre-programmed with the maximum duration of pulse width possible for various line frequencies, or, alternatively, computer 40 could calculate the maximum pulse width possible for a desired frequency. For example, 8.33 milliseconds for 60 Hz. and 10 milliseconds for 50 Hz. Computer 40 measures the duration of the pulse width received from voltage comparator 41 and divides the measured pulse width by the maximum duration of pulse width possible for selected line frequency to obtain fractional conduction. It should be understood that although division is preferred, the actual and theoretical values may be compared in another manner to obtain fractional conduction data.
Fractional conduction data is stored in memory 74 of computer 40 so that is can be subsequently retrieved. The data can be displayed locally on display 42. In addition, it can be transmitted to a remote computer or other display or control device. If the fractional conduction is not sufficiently close to a preferred level, corrective equipment adjustments are made to yield a more efficient output. Fractional conductions of .86 normally yield full rated average currents on a precipitator load.
Multiplexer 66 accepts each of the output signals of input scaling and signal conditioner 28. Upon a signal from logic means 72, multiplexer 66 allows one of the input signals from input scaling and signal conditioner 28 to pass. This signal passes through buffer 68, is converted to a digital signal at the A/D converter 70 and enters logic means 72. When logic means 72 receives both an RMS value and an average value for either primary current or primary voltage, the RMS value is divided by the average value to obtain the form factor. It should be understood that the RMS and average values could be compared in another manner to obtain form factor data. The form factor value is then transmitted to display 42. Display 42 can be a liquid crystal display or similar digital display, a CRT displaying the value graphically, a printed numerical or graphical representation or similar display. It is also understood that the form factor value can be transmitted to input/output port 44 and obtained remotely.
An operator evaluates whether this form factor value is sufficiently close to the 1.11 ideal value. If not, equipment sizing is manually adjusted. It is also understood that this can be a closed loop system where the CLR 16 is automatically adjusted upon the determination of a poor form factor.
To minimize repair and trouble shooting time in the event of unsatisfactory system performance, programmed help screens are employed. The programs diagnose fault conditions and display help screens on display 42. The help screens suggest possible corrective measures to the operator so that appropriate corrective adjustments may be made to increase system operating efficiency to a desired level.
All four inputs to multiplexer 66 are retrieved and analyzed by logic means 72 rapidly and continuously. When logic means 72 determines that current meter 34 experienced a sudden increase in current, a spark condition in precipitator 22 is analyzed. Upon determining a spark in precipitator 22, logic means 72 transmits information to SCR control circuit 24 to not energize again until the spark is extinguished. Since SCRs cannot shut off until the current passing through the SCR falls below a specified value for the device, up to an 8.33 millisecond delay, CLR 16 limits the current to precipitator 22 until the SCRs actually stop conducting. The time delay before re-energizing and the procedure for determining the appropriate firing angle with which to start energizing the SCRs is part of the automatic voltage control logic sequence and is detailed in the '424 patent.
The '424 patent also details how fault conditions are recognized and power shut down attained. But, in the '424 patent, determining what type of fault, the cause, specific location of the fault and potential solutions is left to the operator. The present invention incorporates diagnostic capabilities which greatly reduce down time. Therefore, computer 40 is fitted with non-volative memory 74, a device capable of retaining information when the power is removed. When the analog inputs to input scaling and signal conditioner 28 provide logic means 72 with a known fault condition, the information necessary to troubleshoot the precipitator 22, or its control circuits, and suggest corrective action can be retrieved from memory 74 and transmitted to display 42. For instance, if the primary and secondary current is found to be very high and the primary and secondary voltage found to be very low, this indicates a short condition. The memory device containing its pre-programmed information informs the computer 40 of a short condition. Computer 40 then analyzes the condition, retrieves the proper wording for a short and the corrective measures pre-programmed into memory 74, and routes them to display 42.
A major problem with the prior art has been that automatic voltage controls are connected to a precipitator that operates on a number of voltages. The line voltage is normally from 380-575 volts, 50-60 Hz. The secondary voltage is roughly 50,000 volts. The automatic voltage control runs on five (5) volts. The electrical supply is 120 volts. These diverse voltages create difficulties when isolating and protecting the circuitry from varying voltages.
For instance, a shorted primary to secondary transformer 18 can deliver damaging voltages. Therefore, a means must be available of protecting the automatic voltage control that can be easily and quickly repaired. This invention provides the automatic voltage control with a plug-in input circuit board where all the scaling and over-voltage protection is contained. When the automatic voltage control is wired into the system, it does not have to be removed to be repaired. This results in significant time and cost reductions.
The above mentioned form factor and fractional conduction measurement can be a part of the automatic voltage control that controls the SCRs or can be developed as a separate testing device to measure the efficiency and proper sizing of electrostatic precipitator components. Fig. 4 shows a form factor and fractional conduction meter as a stand-alone device. This device consists of sensor 76 which can typically be a clamp found on many present current transformers. Sensor 76 will sense the primary current of an electrostatic precipitator or similar device and provide this as an input to input scaling and signal conditioner 28. Input scaling and signal conditioner 28 will convert this current measurement to the average current and true RMS values. The true RMS value and average current value will be sent to computer 40 where the form factor calculations will be performed.
Additionally, sensor 76 detects the secondary current in the precipitator. Input scaling and signal conditioner 28 receives the secondary current signal and converts it to a pulse wave signal with a pulse width representing the duration of time secondary current is present in the precipitator. This converted signal is sent to computer 40 where the fractional conduction calculations are performed. Once the form factor and fractional conduction are determined, these values will be transmitted to display 42 for the operator to read and analyze the efficiency of the equipment being measured. Power source 78 will be available to drive each of these components. As a stand-alone portable device, this form factor and fractional conduction meter will be valuable to quickly and safely determine the present operating efficiency of electrostatic precipitators and similar equipment.
From the foregoing it will be seen that this invention is one well adapted to attain all end and objects hereinabove set forth together with the other advantages which are obvious and which are inherent to the structure.
It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of the claims.
Since many possible embodiments may be made of the invention without departing from the scope thereof, it is to be understood that all matter herein set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

Claims

An apparatus for detecting and curing the performance of an electrical circuit (10-14, 18, 20), generating electrical signals and operating at an efficiency level departed from a desired level of efficiency, the apparatus comprising:
- sensing means (26, 30, 34, 39) for sensing the electrical signals;

- comparing means (40) connected to the sensing means (26, 30, 34, 39) for comparing the sensed electrical signals with predetermined signals to provide an indication of a circuit operating efficiency; and

- means (16, 24) for adjusting the circuit based on said comparison to alter the electrical signals if the circuit operating efficiency departs from a desired level, to maintain circuit operation at a desired efficiency,
characterized in that the sensing means (26, 30, 34, 39) are adapted to sense characteristic waveforms of the electrical signals and that the adjusting means (16, 24) includes means for altering the waveform that is being sensed to substantially a desired waveform.
The apparatus of claim 1, characterized in that the adjusting means (16, 24) is comprised of a current limiting reactor (16), whereby adjustments are made to the current limiting reactor (16) if the electrical circuit operating efficiency departs from a desired level, thereby controlling power to the circuit (10-14, 18, 20) and altering the waveform that is being sensed to substantially a desired waveform to maintain electrical circuit operation at a desired level of efficiency.
The apparatus of claim 1 in cooperation with an electrostatic precipitator control system (18, 20, 22), characterized by means for calculating the form factor of the system, wherein the sensing means (26, 30, 34, 39) senses electrical characteristic waveforms selected from the group consisting of voltage and current, the apparatus further comprising:
- a conditioning circuit (28), connected to the sensing means (26, 30, 34, 39), for conditioning the electrical characteristic that has been sensed into values utilized in calculating the form factor, the conditioning circuit (28) including means (46) for changing the electrical characteristic that has been sensed into its average value and means (48, 58) for changing the electrical characteristic that has been sensed into its RMS value;

- the comparing means comprising a computer (40) with logic means (72) for calculating the form factor value, the computer (40) being connected to the conditioning circuit (28) and the adjusting means (16, 24), wherein the logic means (72) include means for retrieving the RMS value and means for retrieving the average value and comparing the RMS value with the average value to obtain the form factor value, whereby the adjustments made to the current limiting reactor (16), if the operating efficiency of the system (18, 20, 22) departs from a desired level, are based on the form factor value; and

- a source (78) of electrical power connected to the conditioning circuit (28) and the computer (40).
The apparatus of claim 3, characterized in that the control system (18, 20, 22) includes a transformer (18), the transformer (18) having a primary side and a secondary side with primary and secondary electrical characteristics associated therewith, wherein the sensing means (26, 30, 34, 39) sense the primary electrical characteristic waveforms selected from the group consisting of voltage and current for utilization in the calculation of the form factor value.
The apparatus of claim 1 in cooperation with an electrostatic precipitator control system (18, 20, 22), characterized by means for calculating the fractional conduction of the system, wherein the sensing means (26, 30, 34, 39) senses the secondary electrical characteristic waveforms in the precipitator (22), the apparatus further comprising:
- a conditioning circuit (28), connected to the sensing means (26, 30, 34, 39), for conditioning the electrical current waveform into a value indicative of the duration of time said electrical current is present in the precipitator (22);

- a computer (40) connected to the conditioning circuit (28) for calculating the fractional conduction, the computer (40) including logic means (72), the logic means (72) including means for retrieving the value indicative of the duration of time the electrical current is present in the precipitator (22) and comparing the value to a theoretical value at a preselected frequency to obtain the fractional conduction value, wherein adjustments are made to the current limiting reactor (16) to increase system operating efficiency if the fractional conduction value departs from a desired level; and

- a source (78) of electrical power connected to the conditioning circuit (28) and the computer (40).
The apparatus of claim 5, characterized in that the control system (18, 20, 22) includes a transformer (18), the transformer (18) having a primary side and a secondary side with primary and secondary electrical characteristics associated therewith, wherein a first sensing means (34) senses the secondary electrical current waveform and a second sensing means (39) senses the secondary electrical voltage for utilization in the calculation of the fractional conduction value.
The apparatus of claim 1 in cooperation with an electrostatic precipitator control system (18, 20, 22), characterized in that the control system (18, 20, 22) has a transformer (18), the transformer (18) having a primary side and a secondary side with primary and secondary electrical characteristics associated therewith, the apparatus including means for calculating the form factor and fractional conduction of the control system, the apparatus further comprising:
- primary sensing means (26, 30) for sensing the primary electrical characteristic waveforms of the control system (18, 20, 22);

- secondary detecting means (34, 39) for detecting the secondary electrical characteristic waveforms of the control system (18, 20, 22);

- a conditioning circuit (28), connected to the primary sensing means (26, 30) and the secondary detecting means (34, 39), for conditioning the sensed primary electrical characteristics into values utilized in calculating the form factor value and conditioning the detected secondary electrical characteristics into values utilized in calculating the fractional conduction value, the conditioning circuit (28) including means (46) for changing the sensed primary electrical characteristics to their average value, means (48, 58) for changing the sensed primary electrical characteristics into their RMS value, and means (41) for changing the detected secondary electrical characteristics to a value indicative of the duration of time a secondary current is present in the precipitator;

- a computer (40) connected to the conditioning circuit (28) for calculating the form factor and the fractional conduction, the computer (40) including logic means (72), the logic means (72) including means for retrieving the average value from the conditioning circuit (28) and means for retrieving the RMS value from the conditioning circuit (28), and means for comparing the RMS value with the average value to obtain the form factor value, and the logic means (72) further including means for retrieving the value indicative of the duration of time the secondary current is present in the precipitator (22) and comparing the time value to a theoretical time value at a preselected frequency to obtain the fractional conduction value, wherein the form factor value and the fractional conduction value indicate system operating efficiency; and

- a source (78) of electrical power connected to the conditioning circuit and the computer.
The apparatus of claim 7, characterized in that the primary sensing means (26, 30) further senses the primary electrical characteristic waveform selected from the group consisting of voltage and current; and
the secondary means (34, 39) further detects the secondary electrical characteristics selected from the group consisting of voltage and current, whereby the form factor value and the fractional conduction value provide a plurality of measurements, each individually indicating the system operating efficiency.
The apparatus of claim 1 in cooperation with an electrostatic precipitator control system (18, 20, 22), to recognize circuit fault conditions and to de-energize the electrostatic precipitator (22) upon the detection of a fault condition, characterized by:
- display means (42) connected to the computer (40);

- memory means (74) connected to the computer (40);

- means (44, 72) for storing predetermined fault conditions in the memory (74);

- means for storing potential causes and corrective measures to the fault conditions in the memory (74); and

- logic means (72) further including means for determining the fault conditions, and de-energizing the electrostatic precipitator (22) upon determination of a fault condition; the logic means (72) further including means to analyze the fault conditions, means to retrieve the corrective measures preprogrammed into the memory (74) or the appropriate fault, and means to route the corrective measures to the display (42).
The apparatus of claim 9, characterized by an input/output port (44) connected to the computer (40), and wherein the logic means (72) includes means to transmit the form factor value and other operating conditions to the input/output port (44), and means to receive from the input/output port (44) initial operating conditions, fault conditions, initial electrical equipment sizing and other information necessary for the start-up and operation of the electrostatic precipitator (22).