Abstract:
A waveform correction filter is connected into an alternating current power line to absorb and remove various forms of power pollution, including high-frequency spikes, surges and other forms of high-frequency oscillations, such as those which result from switching inductive loads on and off. The waveform correction filter of the invention includes a fuse and a coaxial amorphous toroidal inductor connected between a power line and neutral with a low-pass filter connected in series with the fuse and coaxial amorphous toroidal inductor. The filter includes a capacitor, a varistor connected in parallel with said capacitor, and a magnetic core inductor connected in series with each other and in parallel with the capacitor and said varistor. A lamp may be connected in series with the resistor and the magnetic core inductor or across the resistor. Various arrangements are shown for connecting a plurality of the waveform correction filters into single phase or three-phase Wine or delta circuits.

Description:
BACKGROUND OF THE INVENTION 
     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. 
     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 causing 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. 
     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. 
     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 . 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. 
     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. 
     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. 
     It has been estimated that up to 60 percent of all electricity is now, or soon will be, passing through non-liner loads. It is such loads that are principal contributors to electric power pollution. 
     Considerable efficiency gain can be realized if means can be provided, which 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. 
     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. 
     It is another object of the present invention to provide a waveform correction filter in which all components are bi-directional, making the waveform correction filter bi-directional. 
     It is another object of the present invention to provide a waveform correction filter, which will substantially reduce maintenance costs for the associated equipment. 
     Other objects and advantages will appear from consideration of the following specification taken in connection with the drawings taken in connection with the drawings: 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     This invention may be more clearly understood with the following detailed description and by reference to the drawings in which: 
     FIG. 1 is a graph showing the distortion of a sinusoidal waveform resulting from a high-frequency transient voltage being imposed on it; 
     FIG. 2 is a schematic diagram of a basic waveform correction filter system; 
     FIG. 3 is a schematic diagram of a voltage divider showing characteristics of the transient voltage suppression system; 
     FIG. 4 is a graph showing a typical B-H curve having the characteristics of a magnetic core in applicant&#39;s system; 
     FIG. 5 is a graph showing flux density vs. pulse permeability of the magnetic material of the magnetic core in applicant&#39;s system; 
     FIG. 6 is a simplified equivalent RLC circuit showing the characteristics of the transient voltage suppression system; 
     FIG. 7 is a schematic diagram of the waveform correction filter system of the invention as connected to a single-phase motor; 
     FIG. 8 is a schematic diagram of the waveform correction filter systems as shown in FIG. 7 connected to a three-phase Wye circuit; and 
     FIG. 9 is a schematic diagram of the waveform correction filter system of the invention connected in a three-phase delta circuit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The waveform correction filter system of the invention performs in the following way. It is connected across the line (Line to Neutral, typically) as shown in FIG. 2, and acts only upon the disturbances that may exist. The unit performs three important functions: 
     1. It senses the rising transient voltage and clips and absorbs all energy in excess of 10% above the peak value of voltage. That is, for example, +/−190 volts, in the case of a 120 volt rms. line. 
     2. It shows down the rise time of the transient, so the rising transient “glides” into the level of clipping. This is done so the clipping will not represent another switching event, thereby causing further ringing. 
     3. It filters out and absorbs all high-ringing disturbances at a rate of 6 db per decade above 60 hertz. 
     These actions are depicted in the following illustration:                           
     FIG. 2 depicts a typical line to neutral connection of the waveform correction filter of the invention. 
     The component items in this schematic are described functionally as follows: 
       10  FUSE, protective line type 
       12  INDUCTOR, coaxial amorphous toroid of soft magnetic material 
       13  VARISTOR, metal oxide 
       14  CAPACITOR, polypropylene ac rated 
       15  MAGNETIC CORE, nanocrystalline toroidal 
       16  RESISTOR, carbon type limiting 
       17  LAMP, neon 
     The operation of the circuit proceeds as follows: 
     As the transient shown in FIG. 1 begins to rise, normally in an interval of 1 microsecond, its rise time is initially slowed or extended by a selectable predetermined amount by the INDUCTOR 12, and clamped by the VARISTOR  13  at approximately {square root over (2)} times the rms. line voltage. In the case of a 120 vrms line, this would be about 190 volts. This level depends upon the surge current and line impedance at the instant of the transient rise. Before the transient occurred, the VARISTOR  13  appeared as an infinitely high resistance in the circuit. But, at the instant of clipping, it becomes a very low impedance, and at the same time a current generator. Because the voltage across the CAPACITOR  14  cannot change instantaneously at the instant of the VARISTOR  13  switching, the CAPACITOR  14  becomes virtually a short circuit and provides a path for the high current to flow. Thus, the CAPACITOR  14  begins to charge. Now, connected across the CAPACITOR  14  are the elements depicted in FIG. 2 schematic: MAGNETIC CORE  15 , the RESISTOR  16 , and the LAMP  17 . The VARISTOR  13  switches back to a high impedance, and the CAPACITOR  14  transfers its energy into the components  15 ,  16 , and  17 . This energy is calculated to be: E (joules)=V (clamping voltage)×I (surge current)×time. Using a Siemens S20K130 varistor, for example, its maximum energy capacity is 44 joules and clamps between 185 and 225 volts. 
     The MAGNETIC CORE  15  is 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 RESISTOR  16  and the equivalent resistance of the LAMP  17 , where over a longer span of time such energy is collected and absorbed. 
     The network, in addition to absorbing the energy of the disturbance, also effectively functions as a low-pass filter. 
     Now it is important to consider the details of the low-pass filter network. 
     The voltage clamping device, which we have referred to as the VARISTOR  13  will be simply denoted “MOV”  13 . This MOV  13  is a component having a variable impedance depending upon the current flowing through the device or the voltage across its terminals. A nonlinear impedance characteristic is exhibited and Ohm&#39;s law applies, but the equation has a variable R. The variation of the impedance is monotonic and does not contain discontinuities. 
     As has been stated before, the circuit is essentially unaffected by the presence of the MOV  13  before and after the appearance of the over-voltage transient for any steady-state voltage below the clamping level. The voltage clamping action results from the increased current drawn through the device as the voltage tends to rise. If this current increase is greater than the voltage rise, the impedance is nonlinear. 
     The apparent “clamping” of the voltage results from the increased voltage drop (IR) in the source impedance due to the increased current. The device depends on the source impedance to provide the clamping. This action is depicted as a voltage divider, as shown in FIG.  3 . 
     The ratio of the divider is not constant, but changes. If the source impedance is very low, then the ratio is low. The MOV  13  cannot be effective with near zero source impedance and functions best when the voltage divider action can be implemented. 
     If the MOV were the only component serving in the role of removing over-voltage transients, it can be readily seen that because of its nonlinear switching process, further ringing transients would be generated. 
     The resulting ringing frequency components of the transient are several orders of magnitude above the power line frequency of an AC circuit and, of course, a DC circuit. 
     Therefore, an obvious solution is to incorporate a low-pass filter between the source of the transients and the sensitive load. 
     The simplest form of filter is a capacitor placed across the line. The reactive impedance of the capacitor forms a voltage divider with the source impedance, resulting in attenuation of the transient at high frequencies. 
     This simple approach can have undesirable side effects, such as: 
     1. Unwanted resonances with inductive components located elsewhere in the circuit, leading to high peak voltages. 
     2. High inrush currents during switching, or 
     3. Excessive reactive load in the power system voltage. 
     These undesirable effects can be reduced by adding a series resistor. However, the disadvantage of the added resistance is that less effective clamping results. 
     To achieve maximum success in clamping, attenuating, and absorbing the over-voltage transient energy, a highly permeable magnetic core is incorporated with the above-noted capacitor and damping resistor. 
     By second-order tuning, a critically damped RLC low pass filter can be created. Thus, the undesirable effects noted just above can be eliminated. However, not just any inductance will function satisfactorily. The specific requirements for this MAGNETIC CORE  15 , hereafter referred to as “L”, are as follows: 
     1) Because the capacitor response is nonlinear with frequency, but linear with current, the response of L with respect to current and frequency must be linear. This response requirement is depicted in the hysteresis graph FIG. 4 of Flux density B versus Magnetizing force H. 
     2) Also, since the impinging oscillatory wave statistically will not be balanced as a pure sinusoidal wave with no DC component, it is necessary that the core be reset for each cycle of the ringing frequency. This requirement is satisfied as shown in the above graph, where it is noted that the remanence Br is essentially near zero, as well as coercivity. 
     3) L must remain stable with respect to frequencies ranging up beyond 1 MHz, in order to function at its predetermined level throughout all components of the impinging ringing wave derived from that transient. This requirement is satisfied in the incorporation of the particular magnetic material utilized in the waveform correction filters of the invention. 
     4) The pulse permeability versus flux density variation of the magnetic core L must remain in a specified range as shown in the graph FIG.  5 . 
     The range in permeability noted above is important because under a rather random drive from the source, the inductance value must remain at its predetermined level. 
     The network essentially takes the form of a series RLC circuit, as shown in FIG.  6 . 
     The effective homogeneous equation for this system is given as:                   2        i            t   2         +       R   L               i          t         +     i   LC       =   0               s   2     +       R   L        s     +     ω   0   2       =   0                     t       =   s                          
     where d/dt=s The roots are          S   1     ,       S   2     =       -     R     2      L         ±           (     R     2      L       )     2     -     1   LC                                    
     The critical resistance is determined as:          R   cr     =     2          L   C                                
     And the corresponding damping ratio        ζ   =       R     R   cr       =       R   2            C   L                                  
     The natural frequency is given by          ω   n     =     1     LC                              
     and          R   L     =     2        ξω   n                              
     The characteristic equation now becomes: 
     
       
           S   2 +2ξω n   S+ξ   n   2   
       
     
     Implementing the special properties of the nanocrystalline core material, the two important parameters, ξ and ω n , in the above characteristic equation can and do govern the performance of the filter system. The performance centers on channeling current and tuning, both based on the cutoff frequency characteristic and proper damping. 
     The damping ratio ξ is chosen such that the impinging ringing transient is processed and absorbed by the dissipating R in the circuit (as indicated in FIG. 2) the final frequency ω n  is determined such that the roll-off at −40 dB per decade gives rise to sufficient attenuation at higher frequencies as required in a particular system. 
     The combination of core material and circuit configuration is the key to the operation of the filter as described above. 
     FIG. 7 is a schematic diagram showing two waveform correction filters of the invention connected in a single-phase line. In this example, a single-phase motor  18  is shown connected to an alternating current source through lines  19  and  20 . Connected between each of lines  19  and  20 , and a neutral line  21 , are two identical waveform correction filters  22 . A separate ground line  23  is connected between the motor housing and an earth ground. 
     Each such filter  22  includes a fuse  10 , a coaxial amorphous toroidal inductor  12  of soft magnetic material applied in series with the fuse, and a capacitor  14  connected between the coaxial inductor  12  and neutral line  21 . Connected in parallel with capacitor  14  are a MOV  26  and a winding with a magnetic core  28  and a resistor  16  connected in series with each other. A lamp  32  is connected in parallel with the resistor  30 . A ground line  23  is connected between the case of motor  18  and an earth ground or its equivalent. 
     FIG. 8 is a schematic diagram showing three of the waveform correction filters  22  connected in a three-phase Wye network to a three-phase motor  36  wherein each filter  22  is connected between one of the phase lines  40 ,  42  or  44 , and a neutral line  46 . As in FIG. 1, a separate ground line  48  is connected between the case of motor  36  and earth ground. Each of the filters  22  is identical to that of FIG. 7 except that values of components will vary according to the voltages applied, etc. 
     FIG. 9 is a schematic diagram showing three waveform correction filters connected in a three-phase delta network to a three-phase motor  50 . In this case, the waveform correction filters  52  are connected between phase lines  54 ,  56  and  58 . Each filter  52  is essentially like filters  22  except that the resistor  30 , lamp  32 , and magnetic core and winding  28  are all connected in series across capacitor  24 . This variation is a matter of design choice depending upon the effective resistance desired. A separate ground line  60  is connected between the case of motor  50  and earth ground. 
     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 including their equivalents.