Abstract:
A number of wave correction filters are disclosed which respond to power surges or spikes outside the intended frequency and/or voltage for a load device. The circuits respond to such undesired frequencies and voltage levels by sensing and separating them from the desired voltage and frequencies and connecting the energy from such undesired voltages and/or frequencies to resistors where it is dissipated as heat. In this way, the resulting energy is prevented from distorting the input voltage to the load device. It is also retained in the filter and prevented from traveling through a ground connection to pollute other related circuits.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     For many years, those who are responsible for monitoring usage of significant amounts of alternating current power have been concerned with the quality of such power. Much of the newer equipment now in use is sensitive to transient voltages, such as spikes, power surges, and random radio frequency (r.f.) noise; but at the same time, such equipment may be creating its own transient voltages which it injects back into the power line. When switches turn off and on, reverberating impulses are created on the line. Motors that start and stop cause power impulses known as surges.  
         [0002]     Besides random r.f., pollution, electrical machinery of various kinds may generate harmonic frequencies. All of these kinds of power pollution detract from the efficiency of, inter alia, electric motors, generators, and transformers. The waveform of the power supplied to such equipment becomes distorted, resulting in the creation of eddy currents in the ferrous metal parts of such equipment, such as transformer cores and motor stators and rotors. The result is that eddy currents in a motor, for example, dissipate power as heat causes it to consume more power to perform the same tasks. The motor may become damaged, either from the effect of excessive heat or from damage to insulation, causing it to break down long before its expected life.  
         [0003]     While much has been done to improve that quality of the power being supplied to various consumers, there has been little recognition of the power pollution produced within a single facility as a result of the operation of significant numbers of electric motors, switches, computers, and other power-consuming devices.  
         [0004]     Fundamentally, any time an inductive load is switched off, a very high voltage reverberation rising many times higher than the normal peak value of the applied voltage flows back into the power line. A typical transient voltage is shown superimposed on a sine wave in  FIG. 1 . It will be recognized that the result of the transient voltage is to cause peak voltages at a much higher value and frequency to distort the normal sine wave voltage. The average industrial or commercial circuit receives many daily transients in excess of 1000 volts. These transients reverberate and trigger other oscillations within the network. These reverberations bounce back and forth until they are absorbed or have done damage within the system.  
         [0005]     Other disturbances occur when loads are unbalanced in three-phase lines, causing undesirable phase differences between voltage and current. High harmonic neutral currents flow, reacting with transient and surge activity on the line.  
         [0006]     From the foregoing, it will be appreciated that the internal power pollution within a network frequently may be a much more serious factor in efficiency of motors, etc., than irregularities in the power supplied from outside the facility.  
         [0007]     It has been estimated that up to 60 percent of all electricity is now, or soon will be, passing through non-linear loads. It is such loads that are principal contributors to electric power pollution.  
         [0008]     Considerable efficiency gain can be realized if means can be provided that is connected to the individual power lines to such power-consuming units, which can absorb or otherwise remove such transient voltages, thereby preventing them from being injected back into the power line.  
         [0009]     Further, in a digital logic control system, where binary bit patterns are used to implement control signals, random impulsive noise can knock out bits or put in bits where they should not exist. Thus, the control signal is altered and the desired action is lost. For this reason, it is important to inhibit the impulsive noise by clamping, filtering, and absorbing such noise before reaching the circuitry that will try to correlate the oncoming binary signal.  
         [0010]     The present application constitutes a refinement and an extension of the teaching of U.S. Pat. No. 6,486,570 (common assignee) and describes different waveform correction filters useful with different applications.  
         [0011]     It is, therefore, an object of the present invention to provide a waveform correction filter that removes and absorbs random r.f. noise, spikes, surges, and harmonics from the alternating current power supplied to the above-described power-consuming units.  
         [0012]     It is another object of the present invention to provide a group of waveform correction filters that will substantially reduce maintenance costs for the associated equipment.  
         [0013]     Other objects and advantages will appear from consideration of the following specification taken in connection with the drawings.  
       BRIEF SUMMARY OF THE INVENTION  
       [0014]     The several waveform correction circuits described herein utilize some particular components in what may appear to be conventional filter circuits to provide ways of filtering and absorbing energy from the various transients referred to above rather than permitting it to be reflected back into the associated network. In each case, one or more reactance devices are used, in combination with one or more resistors, to detect alternating voltages outside of a described pass band and to supply the resulting current to resistors where they are absorbed as heat.  
         [0015]     In some of the circuits described herein, the waveform correction filter is connected in parallel with an alternating current source and a load device. In these circuits, unless the filter detects voltage outside its pass band, the correction filter has no effect. In one such circuit, when a transient voltage, such as from the surges or spikes referred to above appear across the line, its rise time is initially slowed or extended by an inductor and clamped by a varistor or MOV (Metal Oxide Varistor) at approximately √2 times the line voltage. In the case of a 120-volt rms line, this would be about 190 volts. At the instant of clipping, the MOV becomes a very low impedance, and at the same time, a current generator. Because the voltage across the capacitor cannot change at the instant the MOV is switching, the capacitor becomes virtually a short circuit and provides a path for high current to flow.  
         [0016]     Connected across the capacitor are a toroidal magnetic core inductor, one or more resistors and a lamp, which may be an LED. The inductor has a highly permeable magnetic core with effectively zero remanence and zero coercivity. The response L of the inductor, with respect to current and frequency, must be linear and must be stable with respect to frequencies ranging up beyond 1 MHz in order to function at its predetermined level through all components of the impinging ringing wave derived from the transient. This requirement is satisfied in the incorporation of the particular magnetic material described.  
         [0017]     Another circuit in which the waveform correction filter is connected in parallel with the load utilizes a circuit breaker, an inductor, a capacitor, and a transformer primary winding connected in series with each other. Alternating current disturbances above the desired pass band, which is a selected harmonic of the intended a.c. source, cause the circuit breaker to close, diverting the energy at the harmonic frequency into the waveform correction circuit where it is filtered, stepped up in voltage and dissipated in a resistor connected to the transformer secondary winding.  
         [0018]     Another circuit connected in parallel with a load device constitutes a low pass filter having a capacitor connected in parallel with a resistor with frequencies above a desired frequency absorbed in the resistor and dissipated as heat, rather than flowing back into the lines connected to the load or to the ground where such higher frequencies would constitute a disturbance in the overall system.  
         [0019]     For loads such a telephones or televisions connected to cable or satellite transmission having two leads, the waveform correction circuits are connected in series/parallel fashion. In the embodiments described herein, the circuits discriminate against frequencies above the normal telephone pass band or above the frequencies of cable or satellite television, for example. In one embodiment, ferrite bead inductors in the leads cooperate with a capacitor and a bi-directional TVSS connected between the leads to provide a low pass filter with the higher frequencies being absorbed in series resistors.  
         [0020]     Another circuit utilizes resistors in the leads with diodes and unidirectional TVSS diodes connected with opposite polarity between the leads. The inherent capacitance of the diodes and TVSS diodes comprise low pass filter circuits which separate the higher frequency disturbances that are dissipated at heat in the resistors.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]     This invention may be more clearly understood with the following detailed description and by reference to the drawings in which:  
         [0022]      FIG. 1  is a graph showing the distortion of a sinusoidal waveform resulting from a high frequency transient voltage being imposed on it;  
         [0023]      FIG. 2  is a schematic drawing showing a waveform correction filter designed for high current situations according to the invention;  
         [0024]      FIG. 3  is a schematic drawing of a waveform correction filter operating in series/parallel between two telephone or DSL communication lines;  
         [0025]      FIG. 4  is a schematic drawing of a waveform correction filter that is connected in parallel between two cable lines or satellite input lines and which is isolated from a system ground;  
         [0026]      FIG. 5  is a schematic drawing of a waveform correction filter of a parallel line connected device operating as a passive low order harmonic filter and absorber;  
         [0027]      FIG. 6  is a schematic drawing of a waveform correction filter that functions as a high-frequency filter to attenuate and absorb energy within a specified frequency range.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0028]      FIG. 1 , referred to in the “Background of the Invention” above, is a graph showing the distortion of a sinusoidal waveform resulting from a high frequency transient voltage being imposed on it.  
         [0029]      FIG. 2  shows a first embodiment of my invention, which would normally be a three-phase system but which, for simplicity, is shown with a single phase. In this embodiment, as well as others described hereafter, the circuits for the remaining phases are identical to the one shown. This embodiment includes a source, such as an electrical generator  11  connected across a load  12  through lines  9  and  10 . Connected in parallel with load  12 , between lines  9  and  10 , is a filtering circuit  16 A.  
         [0030]     The component items in this schematic are described functionally as follows: 
         2  FUSE, protective line type      1  INDUCTOR, ferrite bead      3  VARISTOR, metal oxide      4  CAPACITOR, polypropylene ac rated      5 A &amp;  5 B MAGNETIC CORES, nanocrystalline toroidal      6  &amp;  7  RESISTOR, carbon type limiting      8  LAMP, neon        
 
         [0038]     Circuit  16 A includes a ferrite bead inductor  1 , a fuse  2 , and a MOV or varistor  3 . A capacitor  4  is connected in parallel with varistor  3 , as are inductors  5 A and  5 B, in series with a resistor  6 . A second resistor  7 , in series with an LED lamp  8 , is connected in parallel with resistor  6 . Also connected in parallel with varistor  3  are a gas tube voltage clamp  13  and a thermistor  14 . The gas tube voltage clamp  13  and the thermistor  14  assist varistor  3  in high-current situations. Gas tube voltage clamp  13  is slower in reactance time than varistor  3  but can handle higher energy, as in lightning strikes.  
         [0039]     When a surge voltage across lines  9  and  10  exceeds the clamping level of varistor  3 , then, because varistor  3  has clamped to a very low resistance, a high current is generated and also accelerated through capacitor  4 . Because the voltage across capacitor  4  cannot change instantaneously at the instant of the varistor  3  switching, capacitor  4  becomes virtually a short circuit and provides a path for high current to flow. The rapidly rising current will pass through inductors  5 A and  5 B, is spread out in time and passed into resistors  6  and  7  and LED  8  where the energy is absorbed in heat.  
         [0040]     The MAGNETIC CORES  5 A and  5 B each include a soft magnetic element having relatively very high initial permeability (μ=30,000), extremely low losses, and high saturation flux density (Bsat=1.2 tesla). This means that the core is very easily magnetized and maintains this condition throughout a wide flux penetration. Thus, the energy that was impressed into the capacitor is now transferred to the “reservoir” of the highly magnetic core. This energy is then processed into the RESISTORS  6  and  7  and the equivalent resistance of the LAMP  8 , where over a longer span of time such energy is collected and absorbed.  
         [0041]     Ferrite bead  1  will act in a similar manner in spreading the otherwise fast-changing current. The advantage of the above-described system is that it captures the rebounding current of varistor  3  and dissipates the energy in resistors  6  and  7 . Details regarding these special resistors appear on pages  11  and  12  below. Otherwise, the surge current would proceed back into lines  9  and  10  and further affect the overall distribution system.  
         [0042]     The embodiment of  FIG. 3  would normally have two lines but will be described with one line for purposes of simplicity. This embodiment operates in series/parallel between leads  19  and  20 , which may be connected to a telephone or to another data system. Ferrite bead inductors  22 ,  23 ,  24 , and  25  act in conjunction with bi-directional TVSS diode  17 , with capacitor  18 , and with resistors  15  and  16  to function as a low-pass filter attenuating frequencies higher than that of the telephone voice spectrum. Resistors  15  and  16  are also carbon type as described above. Other resistors described below are all the same carbon type as described in connection with  FIG. 2 .  
         [0043]     Higher frequency disturbance is absorbed and dissipated in resistors  15  and  16 . Frequencies higher than the set breakpoint frequency are attenuated as normally expected in a second order filter at 40 dB per decade. Resistors  15  and  16  are placed in series with lines  19  and  20  to absorb and dissipate as much of the over-voltage anomaly as possible. The bi-directional TVSS diode  17  is a fast-acting clamp serving to protect the telephone  21  by shunting the high current into the resistors  15  and  16  at the specified voltage level. Since there is no connection to ground  10 A, all of the absorption is contained in the  FIG. 3  circuit and not allowed to enter into the facility ground  10 A. This also protects telephone  21  from anomalies that arise through spurious ground loops. The filter characteristics of the embodiment of  FIG. 3  can be designed to pass higher frequencies to allow DSL communication on the telephone line.  
         [0044]     The embodiment of  FIG. 4 , which would normally be a three-phase system, is described as a single phase for simplicity and includes two lines  32  and  33  connected to a load device  34 , which may be communication equipment. Versions of this embodiment differ in the clamping level between lines due to the difference between cable and satellite transmission. This embodiment of wave correction circuit operates in series/parallel between cable lines  32  and  33 .  
         [0045]     Resistors  26  and  27  act in conjunction with unidirectional TVSS diodes  28  and  31  and diodes  29  and  30  to act as a low-pass filter attenuating frequencies higher than that of the cable information spectrum. Higher frequency disturbance is absorbed and dissipated in resistors  26  and  27 . Frequencies higher than the spectrum used for cable or satellite transmission are attenuated at a rate of 20 dB per decade. The inherent capacitance of the combination of diodes  29  and  30  and unidirectional TVSS diodes  28  and  31  is used in conjunction with resistors  26  and  27  to provide the low-pass filtering in the embodiment of  FIG. 4 . Resistors  26  and  27  are placed in series with lines  32  and  33  to absorb and dissipate as much of the over-voltage anomaly as possible. The unidirectional TVSS diodes  28  and  31  are a fast-acting clamp serving to protect the equipment  34  by shunting the high current into the resistors  26  and  27  of the specified voltage level of the unit. Since there is no connection to system ground  10 A, all of the absorption is contained in the circuit of  FIG. 4  and not allowed to enter into the facility ground  10 A.  
         [0046]     Various versions of  FIG. 4  may be modified for a breakpoint frequency and clamping voltage to match that of the communication equipment being protected.  
         [0047]     The embodiment of  FIG. 5  would normally be a three-phase system but will be described herein with a single phase for purposes of simplicity. Alternating current is supplied from a source  11  to equipment  12 , which may be data processing equipment.  
         [0048]     The waveform correction circuit of  FIG. 5  consists of circuit breaker  35 , inductor  36 , capacitor  37 , transformer  38 , and resistor  39  connected across lines  9  and  10 . Transformer  38  includes a magnetic core of very low remanence.  
         [0049]     The system of  FIG. 5  functions as a parallel line connected device and operates as a passive low order harmonic filter and absorber. As a harmonic voltage appears (such as 3rd, 5th, 7th, etc.) between lines  9  and  10 , the circuit of  FIG. 5  will provide a very low impedance path for the resulting current associated with a given harmonic. The current will be driven by the voltage and will be processed through the resonant combination of inductor  36  and capacitor  37 , and further transferred through step-up transformer  38  to be dissipated in resistor  39 . Transformer  38  serves to step up the voltage derived from the resonant current input on the primary winding and the harmonic voltage is stepped up sufficiently to pass the energy of the harmonic into resistor  39 , where it is dissipated. All other frequencies outside of the band pass of the series resonant circuit composed of inductor  36  and capacitor  37  will be attenuated so that only the targeted harmonic will be allowed to pass through to transformer  38 .  
         [0050]     Due to the parallel nature of this filter, circuit breaker  35  will actuate upon a fault current and control the let-through of the circuit of  FIG. 5 . The energy of the harmonic is all absorbed in resistor  39 , and no current is delivered to system ground  10 A. Because the  FIG. 5  embodiment is not a series device, it is system load  12  independent, which affords its use in any system configuration.  
         [0051]     As in the case of  FIG. 5 , the embodiment of  FIG. 6  would normally be a three-phase system but is described as a single phase for purposes of simplicity. The circuit of  FIG. 6  includes a fuse  42 , a special carbon resistor  40  and a capacitor  41  (15 mfd) and functions as a high-frequency filter designed to attenuate signals at 20 dB per decade (120 k Hz-2 MHz). The  FIG. 6  circuit is designed to absorb the energy within a specified frequency range in resistor  40  and this energy is totally contained within the circuit of  FIG. 6  and not allowed to re-enter lines  9  and  10  through system ground  10 A.  
         [0052]     While the circuit of  FIG. 6  operates as a filter, to perform as described, resistor  40  and capacitor  41  are somewhat special components. Characteristics of resistor  40  are: 
        Resistance range: 0.010 to 1 Megohm     Power rating: to 50 watts     Nominal voltage: 300 v rms     Temperature range: −55° C. to +155° C.     Thermal resistance: 2 degrees C. per watt     Inductance: &lt;0.1 microhenry     Dielectric strength: 2000 v        
 
         [0060]     Capacitor  41  must have a voltage of rating of 600 WVDC and operate in the same temperature environment as does resistor  40 . This is a special metallized polypropylene film capacitor whose essential quality is low inductance and low equivalent series resistance up to 100K H z . Another very important requirement is the ΔV/ΔT transfer: 10 volts per microsecond maximum.  
         [0061]     The above-described embodiments of the present invention are merely descriptive of its principles and are not to be considered limiting. The scope of the present invention instead shall be determined from the scope of the following claims.