Abstract:
A normally ungrounded power system for a oil well is provided which includes a power transformer above ground and a pump motor below ground. There is provided a signal system which includes a below ground sensor system and an above ground signal conditioning and monitoring unit where the sensor system utilizes the main power lines for carrying the sensor signals. A connectable high resistance grounding scheme is provided to the aforementioned floating system, so that in the event of a arcing ground fault or similar occurrence the system may be immediately grounded, thus compensating for the effects of the arcing ground fault and providing personnel safety and electrical equipment protection. When the high resistance grounding system is not utilized the aforementioned signals from the sensors are easily carried by the power conductors.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The subject matter of this invention relates generally to high resistance grounded systems and more particularly to high resistance grounding schemes for oil well electrical systems. 
     2. Description of the Prior Art 
     Through the years oil well pump installations have utilized an ungrounded high voltage power system. A system of this type allows for the connection of an instrumentation signal system located deep in the well between the neutral of the oil well pump motor and the electrically conducting casing of the well. This saves considerable wiring expense, which would otherwise be necessary to traverse the great distance between the down hole sensor system and the surface signal measurement system. This system has a disadvantage in that the common mode voltage of a three-phase electrical system is not controlled because it is ungrounded and can thus reach extreme levels. This is hazardous to personnel and possibly destructive of electrical insulation. In such a system there is no intentional connection to ground. It has been found, though, that occasionally these ungrounded systems have exhibited unexplained, sometimes very wide spread, insulation failures with catastrophic results. It has been found that the source of these unexplained insulation failures often turns out to be an arcing ground fault condition deep in the well case structure. Severe voltage escalation occurs in these situations and this is what causes the unexplained insulation failures. The solution to this is to unground the power system by connecting the neutral point, supposedly at zero voltage to ground, through a high resistance. High resistance grounding has proven to be the most reliable form of power system grounding. It limits the available fault current to only a few amperes under ground fault conditions and in the event a ground fault occurs, one can continue to operate the system without the need to close down the circuit. This is a desirable feature for continuous process facilities where failure would result in significant losses. The high resistance connection provides damping for the voltage escalation thereby preventing a transient overvoltage from building up and causing failure. At the same time the resistance limits the available fault current to a very low value. The traditional way in the past of applying the high resistance grounding was to connect the neural point of a Wye connected surface power supply system to ground through a resistance, the value of which is selected to allow less than 10 amperes maximum current to flow under the worst case condition. For a Delta system, the neutral point is derived through three grounding transformers or a zig-zag grounding transformer. In the oil field industry, electrically submersible pumps and motors have been traditionally run ungrounded for surface continuity considerations as well as the extremely high cost of pulling the pump and motor up when it has faulted. This provides a perfect application for high resistance grounding. The high resistances grounding will allow the electrically submersible pumps to operate for a longer period of time under ground fault conditions. However, a frequent requirement of the oil well industry is to know what the down hole temperatures, pressures, etc. are. Existing down signals to the surface via line-to-ground connections using the power conductors as part of the signal path. A small signal is superimposed on the power lines and is transmitted to the surface. In this manner extremely expensive control wires of up to 15,000 feet in length are not required. As long as the power system is ungrounded this method is cost effective. However, it does not provide the transient over voltage protection provided by a high resistance grounding system, as the high resistance grounding system will short out the signals on the power conductors. It would be advantageous therefore, if an electrical power system for a down-hole oil well pump could be found that had all the advantageous of high resistance grounding as described previously, but which would also allow for the utilization of the power wiring to carry sensor signals from deep in the well. In the recent past, a system has been found to accomplish both purposes. High resistance grounding is provided but left unconnected until it is needed, as would be the case if an arcing ground fault were detected. That means that signals from an electronic monitoring systems deep in the well can be carried on the power lines of the pump to the surface, utilizing the well casing as a ground conductor. However, if an arcing ground fault occurs, the presence of common mode voltage variation can be quickly sensed at the surface and the high resistance ground can then be quickly inserted into the circuit to limit current and voltage excursions. Once this happens the control system signals are swamped out, but that is an acceptable compromise. At this point in time the protection of the personnel and equipment becomes more important. In the past, this system has utilized a gas discharge switch or tube in series with the grounding resistance. The grounding resistance is interconnected, for example, between the neutral of the power supply transformer and the aforementioned gas discharge tube in turn is interconnected to ground. If the voltage of the neutral of the aforementioned power supply transformer is at zero, then no current flows through the gas discharge tube and it remains an open circuit. If an arcing ground fault begins to cause the common mode voltage at the neutral of the transformer to build up, the current through the high resistance grounding system and the serially connected gas discharge tube causes the gas discharge tube to flash over or conduct thus connecting the high resistance to ground, thus bringing the voltage on the neutral of the aforementioned power transformer back to ground potential. This prevents dangerous arcing ground faults and extreme levels of voltage excursion and also provides a current limiting function. This system has a disadvantage in that the break-over voltage and conduction characteristics of the gas discharge tube, once chosen are fixed for each value of gas discharge tube utilized. It would be advantageous if a high resistance grounding system could be utilized, which was controlled to be in the off state during a time period when it was not needed, but which would be controlled to be turned on by way of a highly reliable system when needed. In such a system, values of current, voltage, etc. could be programmed into the system to provide a wide range of application in a single system. It would be advantageous if such a system could be found which improved the safety of the overall system, which could be used on either Wye or Delta transformers and which provided continuous operation during all ground fault conditions and also provided an alarm to advise personnel of ground fault condition. 
     SUMMARY OF THE INVENTION 
     In the present invention, a pair of inverse, parallel connected silicon controlled rectifiers (SCRs) or gated devices are connected between the primary grounding transformer and ground in a signal blocker system (SBS). The SCRs are controlled by circuitry that senses the voltage between the neutral of the output transformer and ground. For Delta connected sources, alternate grounding transformer schemes are utilized. In normal operation the electronic system is interconnected with the neutral of the Wye connected transformer and senses when the neutral to ground voltage begins to deviate substantially from zero. When this happen an electronic sensor system is programmed to cause the inverse parallel gated SCRs to fire, thus connecting the series connected high resistance resistor to ground through the now conducting SBS. A timed out relay coil then closes a normally opened parallel relay contact to continue to provide a current path through the high resistance resistor device to ground, until the fault has been cleared or the system otherwise repaired and made operational again. 
     In particular, an electrical system of the kind that operates normally in the ungrounded state, but which occasionally is subject to a conductor thereof being grounded, that is, where an undesirable voltage may be generated between a first portion of the electrical system and ground is provided. A grounding impedance device is interconnected to a second portion of the electrical system for reducing the undesirable voltage by connecting it to ground. The control system is interconnected with the grounding impedance device and the electrical system for sensing the undesirable voltage and connecting the grounding impedance device to the second portion of the electrical system for reducing the undesirable voltage. The control device comprises a gated conduction device, such as an SCR system, connected with the impedance for interconnecting the second portion of the electrical system through the impedance. A control device is interconnected with the gated conduction device for causing the gated conduction device to operate in response to the presence of an undesirable voltage. In an embodiment of the invention, the impedance device is primarily resistive and the first and second portions are the same. Furthermore the undesirable voltage is reduced substantially to zero. The system may be Wye connected or Delta connected or a combination of both. In one mode of operation, the system is utilized in an oil well electrical system of the kind which operates normally in the ungrounded state, but which occasionally is subject to a down hole power conductor thereof being grounded, such as for example, through an arcing ground fault. There is a surface located power source and a down hole pump motor driven by the power source. The aforementioned conductor is electrically disposed therebetween and the undesirable voltage is generated between first portion of the surface located power system neutral and ground. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention reference may be had to the preferred embodiment thereof shown in the accompanying drawings in which; 
     FIG. 1 shows a schematic view, partially broken away, of an electric oil well down hole pump system being driven by a surface power source with down hole signal sensing system and the signal blocker system of the present invention; 
     FIG. 2 shows a signal blocking arrangement similar to that shown in FIG. 1 for a low voltage embodiment of the invention; 
     FIG. 3 shows a system similar to FIG. 1, disregarding the down hole portion of the power system, wherein the power system is Delta connected and the signal blocker and associated sensing system is modified accordingly; 
     FIG. 4 shows a down hole Delta connected pump motor system suitable for use with the surface Wye connected power supply of FIG. 1 or the Delta connected surface power system of FIG.  3 . 
     FIG. 5 shows a systems similar to that shown in FIG. 3, but for a low voltage arrangement; 
     FIG. 6 shows a surface connected Delta power supply system utilizing a zig-zag sensing transformer arrangement and medium voltage sensing arrangement; 
     FIG. 7 shows an arrangement similar to FIG. 6, but for a low voltage sensing and signal blocker system; and 
     FIG. 8A and B show a schematic diagram of the control system of FIG. 1 for controlling the signal blocker as a function of voltage and current in the power supply and pump system of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings and FIG. 1 in particular, FIG. 1 schematically shows an oil well system  10 , which includes an above ground power supply system  11  the heart of which is a Wye connected power transformer secondary winding  12  (transformer) which provides power to a down hole electrical oil well pump  14  having Wye connected oil well pump motor windings  15 . There is provided an electrically conductive well casing or inner production pipe  16  which traverses from the surface S above ground to the down hole region DH over a distance D. Interconnected with the windings  15  of the down hole electrical oil well pump  14  is a signal source  17 . The signal source provides electrical signals to the neutral N′ of the windings  15 , at one terminal thereof and is interconnected with the conductive oil well casing  16  at the other terminal thereof. Above the surface S is a signal receiver  18 . The windings  12  and the windings  15  each have phase lines A, B and C which are interconnected to terminals X, Y and Z and X′, Y′ and Z′ respectively, between which generally traverse the long lines  19  from the surface S to down hole region DH. Signals i a , i b  and i c  flow in lines A, B and C respectively between the signal source  17  and the signal receiver  18 . Return or ground current i g  flows between signal receiver  18  to signal source  17  through the casing  16  of the well. The signals i a , i b  and i c  may be direct current, pulsed DC or 200 kilohertz ac signals, for example. It is not unusual for the distance D to be approximately 8,000 feet or greater. The signal source  17  may provide information related to well pressure, temperature and vibration for example, from the down hole region DH to surface S by way of the signals i a , i b  and i c . The pump motor  14  represented by the windings  15  may be a 60 or 700 horsepower motor of the high voltage variety operating between, for example, 1100 volts and 4600 volts. The signals i a , i b  and i c  generally range from 4 to 20 milliamps. The power supply system  11  may supply power in the magnitude of 12 hundred to 5 kilovolts at a frequency of 40 to 90 hertz. Generally, the lines  19  may drop 600 volts between the surface S and the down hole region DH due to their excessive length. 
     The transformer  12  has a neutral N capable of having a common mode voltage V disposed therebetween and ground. In an ideal situation where the power loads are balanced, the voltage V is generally zero volts. The neutral N is interconnected by way of a line to point U of a high resistance grounding system HRG. High resistance grounding system HRG may comprise a step down transformer  20  having the primary P thereof connected at one terminal thereof to the point U and the other terminal thereof connected to the input terminal  23  of a signal blocker  24 . The other side or secondary S of the transformer  20  has connected thereacross a high resistance impedance or resistor R and parallel therewith a relay control device  22 . Between terminal  23  and ground G of the system signal blocker  24  are interconnected an electronic control system  26  (to be described in greater detail with respect to FIG. 8) for the system signal blocker, a normally opened relay  30  and pair of oppositely disposed or inverse connected silicon controlled rectifiers or gated control devices  28 A and  28 B. The control system  26  interconnects with the gated silicon controlled rectifier  28 B interconnected with the control system  26  by way of terminals F and H the voltage across which determine the firing status of silicon controlled rectifier  28 B. On the other hand the silicon controlled rectifier  28 A is controlled by the terminals J and K in the control system  26 , which also has a voltage impressed thereacross which controls the firing status of the silicon controlled rectifier  28 A. The series combination of the resistive element R 28  and capacitive element C 29  will operate with inductor LI to form an RLC circuit that limits the first derivative of system voltage with respect to time, that is the rate of rise of voltage across the silicon controlled rectifiers with respect to time. Said in another way, it is a high frequency filter for variable speed drives, in the event that variable speed drives are being utilized. In normal operation, when the voltage V is at approximately zero volts, the voltage on the primary P of the transformer  20  is essentially at zero and therefor the resistive value R is essentially out of the circuit, the normally opened relay contact  30  remains open and the oppositely disposed silicon controlled rectifiers  28 A and  28 B remain in a nonconductive state. Thus no electrical current flows between the neutral N of the transformer  12  and ground G, thus the resistive value R appears transparent or nonexistent to the voltage on the neutral N of the transformer  12 . However, if an arcing ground fault AF occurs in a first portion of the electrical system, such as is shown in the down hole region DH, between line C and the casing  16 , for example, it has a tendency to reduce the voltage between line C and ground and thus increase the voltage between line A and ground and line B and ground. The increased voltage on lines A and B has a tendency to escalate with the arcing ground fault condition, causing the voltage V on the neutral N of the transformer  12  in a second portion of the electrical system with respect to ground G to obtain some nonzero value. However, the primary P of the transformer  20  sees this voltage increase and reflects it through to the resistive value R. In addition, control system  26  senses the voltage between the point  23  and ground G and actuates the oppositely disposed silicon controlled rectifiers  28 A and  28 B to conduct. This places the resistance R in the circuit between the neutral N and ground G. This limits the current and damp the voltage V at the neutral N to a maximum of a line-to-neutral magnitude. At this point in time, the signals i a , i b  and i c  are damped out or shorted out by the presence of resistive value R, but this is of no great consequence, as it is more desirable to cure the effects of the arcing ground fault at this time to prevent damage to down hole components. The voltage across the primary P of the transformer  20 , which is reflected into the secondary S thereof actuates the relay control device  22 , which with an appropriate time delay, closes the normally opened contact  30 , thus eliminating the need for the control system to continue to control the silicon controlled rectifiers  28 A and  28 B to conduct and increasing the electronics&#39; life. 
     The natural effect of all this is to increase the serviceability of the entire system  10 , prevent the destruction of the down hole motor  14  and the sensors as indicated at  17 . In an embodiment of the invention, the net resistive value seen between the neutral N and the ground G may be 130 ohms. The time delay provided by the relay control  22  may be 1.5 seconds. The grounding resistor R may be approximately 6 to 7 ohms. The secondary of the transformer S may be connected to a warning system (not shown) which directly or remotely indicates to personnel that an arcing ground fault has occurred or is occurring. The control system  26  for the signal blocker  24  provides a significant portion of the present invention. Its construction and use will be described hereinafter with respect to FIG.  8 . 
     Referring now to FIG. 2 an alternate embodiment HRG′ of the high resistance grounding system is shown. In this case transformer  20  is not utilized. In this embodiment of the invention resistor R is directly connected between the neutral N of the transformer  12  (not shown) and ground G by way of a signal blocker  24 ′. Its counterpart shown to the right in FIG. 2 is relay  30 ′. Relay control  22  is interconnected to the terminal N and ground G to cause the normally open relay  30 ′ to close when an appropriate voltage is imposed between the neutral N and ground G as a result of a voltage excursion due to the presence of an arcing ground fault or the like as was described previously. Once the normally open contact  30 ′ closes, it remains that way, thus by-passing the signal blocker  24 ′. 
     Referring now to FIG. 3, another embodiment of the oil well system  10 ′ is shown in which an above ground power supply  11 ′ having a Delta connected transformer  12 ′ is utilized. For purposes of simplicity of illustration, the down hole or below surface portion of the embodiment is not depicted as it operates in similar fashion to that described previously with respect to FIG.  1 . In this embodiment of the invention, the transformer  12 ′ comprises windings interconnected at common junctions M, O and Q to form a Delta connection. Junctions Q, O and M respectively are carried forward to the high resistive grounding system HRG″ where they interconnect one terminal each with a terminal of primary windings P 1 , P 2  and P 3  of primary winding P of transformer  20 ′. The other sides of the windings P 1 , P 2  and P 3  are tied together and interconnected to the terminal  23  in the manner that was described previously. L 1 , L 2  and L 3  (or equivalent) relays can be used for determining when a phase voltage imbalance has occurred, thus triggering the remaining portion of the signal blocker  24 ′ to actuate in a manner that was described previously. The secondary windings S 1 , S 2  and S 3  of the secondary S of the transformer  20 ′ are tied together in broken delta and have connected there across the resistive element R and relay control device  22 . The resistive element R is reflected through the secondary winding to the primary winding of the transformer  20 ′ to act in a manner as described previously when the signal blocker  24 ′ is actuated by its control system in the presence of ground voltage unbalance a junctions Q, O or M. Once again the relay control device  22  causes the normally open contact not shown in the signal blocker  24 ′ to permanently short out the terminal  23  to ground G. 
     Referring now to FIG. 4, a Delta connected down hole pump  14 ′ is depicted. In this embodiment of the invention the down hole electrical oil well pump  14 ′ comprises Delta connected windings  15 ′, which interconnect with the signal source  17  in a manner to provide the signal currents i a , i b  and i c  to the lines A, B and C, to function in the manner that was described previously. As was the case previously, with respect to FIG. 1, the ground current i g  for the signal source  17  flows through the casing  16 . It is to be noted with respect to the embodiments of FIGS. 1,  3  and  4  that the above ground power supply arrangement and the down hole electrical oil pump arrangement may be mixed and matched in a convenient manner. That is to say, they both may be Delta connected, they both may be Wye connected, the upper one may be Wye connected and the lower one Delta connected or the upper one Delta connected, and the lower one Wye connected. 
     Referring now to FIG. 5 an arrangement similar to FIG. 3 but for a low voltage embodiment is depicted. In particular the junctions Q, O and M are shown interconnected with the primary windings P 1 , P 2  and P 3  of the primary P of the transformer  20 ″ of the high resistance grounding circuit HRG″′. The secondary windings S 1 , S 2  and S 3  are interconnected together in a closed delta circuit relationship. When the system voltage across the signal blocker  24  exceeds design value, the system blocker  24 ′ conducts, thus placing the resistance value R into the circuit in the manner that was described previously to basically achieve the results described previously. Once the resistor R conducts electrical current, the voltage thereacross is sensed by the relay control device  22  which in turn causes the relay  30  to close with a time delay as previously described, thus placing the resistor R into the circuit independent of the conduction characteristics of the silicon controlled rectifier within the system blocker  24 ′. 
     Referring now to FIGS. 6 and 7, two other embodiments of the invention are shown in which a Delta connected transformer secondary  12 ′ for an above ground power supply  11 ′ is interconnected by way of an zig-zag transformer  40  to a signal blocker system  24 . In the embodiment shown in FIG. 6, the high resistance grounding device HRGIV comprises the transformer  20  having the primary thereof interconnected between point  23  and the neutral N″ of zig-zag transformer  40 . The secondary S of the transformer  20  has connected thereacross the resistive value R and the relay control  22 . Once again the control system  26  (not shown) within the system blocker  24  senses the voltages at terminals Q, O and M and acts to reflect the resistive value R between the neutral N″ and the ground G as in the embodiment HRGV of FIG. 6, or directly interconnects the resistive element R between the neutral N′ and the ground G as in the embodiment of FIG.  7 . In the medium voltage embodiment of FIG. 6, the relay control  22  actuates the normally open contact (not shown) to provide a continuous insertion of the resistive element R as reflected though the transform  20  into the appropriate circuit. In the embodiment of FIG. 7, a relay control  22 , upon sensing the voltage drop across the blocker  24 , actuates the relay  30  to again dispose the resistor R into the circuit. 
     Referring now to FIG. 8 the construction and operation of control system  26 , as it interacts with the remaining elements of the signal blocker  24  will be described. There is shown a resistive element R 2  connected at one end with the junction point  23  as shown previously in FIG. 1, for example. The resistive element R 2  is connected at its other end to an anode of diode D 14 , the negative input terminal ( 2 ) of an operational amplifier U 6 ( 1 ), one side of a resistive element R 18 , one side of a capacitive element C 21  and the cathode of a diode D 13 . There is also shown a resistive element R 3  connected at one side to system ground and at the other side thereof to the cathode of diode D 14  and anode of diode D 13 , the positive terminal ( 3 ) of the operational amplifier U 6 ( 1 ), one side of a resistive element R 19  and one side of a capacitive element C 20 . The other side of a resistive element R 19  and the other side of a capacitive element C 20  are connected to system ground. The other side of capacitive element C 21  and the other side of resistive element R 18  are connected to the output terminal ( 1 ) of the operational amplifier U 6 ( 1 ) and to one side of resistive element R 16  forming a differential amplifier. The other side of resistive element R 16  is connected to the negative input terminal ( 6 ) of operational amplifier U 6 ( 2 ) and to one side each of a resistive element R 17  and a capacitive element C 17 . The other side of the resistive element R 17  is connected to the junction between a resistive element R 21 , one side of a rheostat or variable resistor RHEO and one side of a capacitive element C 19 . The other side of a resistive element RHEO is connected to one side of the resistive element R 20  and one side of a capacitive element C 18 , the other sides of which are grounded. The other side of capacitive element C 19  is grounded and the other side of the resistive element R 21  is connected to the positive 15 volt power supply. The output terminal ( 8 ) of the operational amplifier U 6 ( 2 ) is connected to the other side of capacitive element C 17  and to one side of a resistive element R 14 . The other side of the resistive element R 14  is connected to the anode of a diode D 15  the cathode of which is connected to the positive input terminal ( 7 ) of the operational amplifier U 6 ( 2 ) and to one side of a resistive element R 15 , the other side of which is grounded. The output terminal ( 8 ) of the operational amplifier U 6 ( 2 ) is connected to one side of a resistive element R 12 , the other side of which is connected to input terminals of NAND inverter U 5 , the output of which is connected to the B− input terminal ( 5 ) of a monostable multi-vibrator circuit U 3 . The CTC input terminal of U 3  is connected to the A+ input terminal ( 4 ) thereof and the system ground. The RCTC terminal of U 3  is connected to the junction between a resistive element R 11  and a capacitive element C 15 . The other side of resistive element R 11  is connected to the positive 15 volt power supply and the other side of the capacitive element C 15  connected to ground. The RST terminal of U 3  is connected to a junction between a resistive element R 10  and a capacitive element C 14 . The other side of resistive element R 10  is connected to the positive 15 volt power supply and the other side of the capacitive element C 14  is connected to ground. The output terminal ( 7 ) or Q-bar of U 3  is connected to an input terminal ( 1 ) of a NAND gate device U 4 ( 1 ), the second input terminal ( 2 ) of which is connected to the output terminal ( 4 ) of second NAND gate device U 4 ( 2 ). The output terminal  3  of the U 4 ( 1 ) gate is connected to the input terminal ( 5 ) of U 4 ( 2 ). The two NAND gates are connected together to form a set-reset flip-flop. The input terminal ( 6 ) thereof is connected to a series connected combination of input devices U 4 ( 3 ) and U 4 ( 4 ). The first of these, U 4 ( 3 ), has an input terminal ( 8 ), which is connected to the junction between resistive element R 13  and capacitive element C 16 . This combination forms a power up time delay for the flip-flop reset terminal ( 6 ) of U 4 ( 2 ). The second input ( 9 ) terminal thereof is also connected to the same junction, but through a resistive element R 1 . The other side of the resistive element R 13  is connected to the plus 15 volt power supply and the other side of capacitive element C 16  is connected to ground. The output ( 4 ) of the gate U 4 ( 2 ) is connected to the TB input terminal ( 2 ) of a current mode pulse width modulated circuit U 7  and to the junction between a resistive device Rx and a capacitive element C 24 . The other end of the resistive device Rx is connected to the reference terminal REF at ( 3 ). The resistive element Ry is connected to the RC terminal ( 4 ) of U 7  and to one side of a capacitive element C 22 . The other side of the resistive device Ry is connected to one side of a capacitive element C 23 . The CS terminal of U 7  is connected to one side of the capacitive element C 25 . The other side of the capacitive elements C 22 , C 23 , C 24 , C 25  and the GRND terminal of U 7  are connected to ground. The VCC power supply terminal of U 7  is connected to one side of a resistive element R 5  and one side of a capacitive element C 32 . The other side of capacitive element C 32  is connected to ground, and other side of resistive element R 5  is connected to the positive 24 volt power supply. The output terminal ( 8 ) out of U 7  is connected through resistive element  24  to the gate G of a field effects transistor Q 1 . The source S of the field effects transistor Q 1  is connected to a junction between resistive elements R 4  and R 25 . The other side of resistive element R 25  is connected to the CS terminal of U 7  and the other side of the resistive element R 4  is connected to ground. The drain D of the field effect transistor Q 1  is connected to the anode of a diode D 8 , the cathode of which is connected to one side each of resistive element R 26  and capacitive element C 27 . The other side of capacitive element C 27  is connected to ground and the other side of resistive element R 26  is connected to the 24 volt power supply. 
     Although not shown for purposes of simplicity of illustration, a power supply for the circuitry of FIG. 8 is provided, which includes ±15 volts and ±24 volts DC power derived in a convenient manner. 
     Operation of the Control System  26   
     The differential amplifier formed by utilizing the operational amplifier U 6 ( 1 ) is such that it creates a −0.01 voltage gain between the terminal U and the output terminal ( 1 ) of the operational amplifier U 6 ( 1 ). The voltage is supplied to the capacitor formed by the operational amplifier U 6 ( 2 ). A reference voltage formed across the capacitive element C 19  and controlled by the reostat RHEO cooperates with the voltage disposed at the bottom of the resistive element R 16 , such that if the voltage at pin ( 1 ) of the operational amplifier U 6 ( 1 ) is less than the reference voltage, then the voltage on the output terminal ( 8 ) of the operational amplifier U 6 ( 2 ) will be at a low. On the other hand, if the voltage at terminal ( 1 ) of the operational amplifier U 6 ( 1 ) is higher than the reference voltage, the output at the terminal ( 8 ) of the operational amplifier U 6 ( 2 ) will be at a high. The signal at terminal ( 8 ) of U 6 ( 2 ) is provided to NAND U 5 . As the output of U 6 ( 2 ) goes low to high the output of U 5  goes high to low. The monostable multi-vibrator U 3  is such that when the signal on its pin ( 5 ) undergoes a high to low transition, its Q-Bar output terminal ( 7 ) goes from high to low and then returns to high after a fixed period of time which amounts to the output pulse width PW. This pulse is then feed to the R-S flip-flop formed by the NAND gates U 4 ( 1 ) and U 4 ( 2 ). Thus when the neutral to earth ground voltage V of the secondary  12  of the transformer  11  of FIG. 1 exceeds the reference voltage established across capacitor C 19  the R-S flip-flop is set, that is pin ( 3 ) on U 4 ( 1 ) goes high and pin ( 4 ) on U 4 ( 2 ) goes low. This results in the silicon controlled rectifiers  28 A and  28 B being gated on, thus causing the resistive element R to be interconnected either by way of a reflecting transformer or otherwise between the neutral N and ground of the appropriate power transformer, such as for example, transformer winding  12  of the transformer  11 . In order that the silicon controlled rectifiers do not fire at power up, a low is forced on the flip-flop reset input, that is at pin ( 6 ) of U 4 ( 2 ) for a period of time determined by the time constant of the elements R 15  and C 16 . The current mode PWM integrated circuit is configured such that it forms an oscillator, whose output frequency, which is approximately 10 Khz, is determined by the external RC time constant derived by resistive element Ry and capacitive element C 24 . The pulse train starts when pin ( 2 ) of device U 7  goes low, that is the flip-flop U 4 ( 1 ) is set. When U 7  pin ( 8 ) goes high, the field effect transistor Q 1  is turned on resulting in current build up in the pulse transformer primary S of transformers L 1  and L 3 , which current flows through resistive element R 4 . When there is voltage across resistive element R 4 , that is, when the primary current reaches a certain level, the pin ( 8 ) of device U 7  will go low turning off the transistor Q 1 . The width of this pulse is approximately 2 microseconds. The pulse train continues until the 120 volt ac power, provided to the power supply is turned off. As a result of this, the pulse train is transformed to the secondary of the transformers L 1  and L 3  and the SCRs are continuously gated. The diodes D 9 ,  10 ,  11  and  12  and the resistive elements R 6  and R 7  are added to form gate input circuits. SCR  28 A is fed by outputs K-J and SCR  28 B is fed by outputs F-H. 
     It is to be understood with respect to the embodiments of the invention, that the resistive elements shown herein made of different values for different embodiments of the invention and the resistance symbol R is used simply for purpose of simplicity. The transformers  20  and  20 ′, for example, may be different transformer arrangements in different embodiments of the invention, as may be the relay control device  22  and actual system blocker  24  and  24 ′ for example. 
     The apparatus taught with respect to this invention has many advantages. One advantages lies in the fact that the system blocker may utilize the electronic circuitry on the control system  26  in such a manner as to provide one electronic circuit for utilization with many different kinds and configurations of oil well systems  10  without having to change the control system other than to change control parameters and settings thereon and therein.