Abstract:
A high power disintegrator system comprising a master disintegrator unit and a power booster disintegrator unit, the units being connectable in parallel to a common electrode, each unit including a cutting transformer and an adjustable auto transformer arranged to supply an adjustable voltage to its cutting transformer, an electrical control circuit responsive to voltage detected in the power booster unit that prevents operation of the booster unit when the auto transformers are set to produce different voltages at their respective cutting transformer.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to devices that use an electric arc struck between a metal object and an electrode to disintegrate the metal object. 
       PRIOR ART 
       [0002]    Electric arc disintegrators are useful in the removal of broken tools, broken and/or corrosion locked bolts and removal of spent or physically obstructing metal components. The rate of metal removal and the cross-sectional area of the material being removed is limited by the power capacity of the disintegrator. As technology progresses, there is a need for increased power capacity over that developed by commercially available units. One obstacle in simply increasing the size of existing designs is that a large I 2 R heating loss occurs in the cutting transformer. Dissipation of this heat already can tax the materials and construction of existing transformer arrangements to their practical limits. 
         [0003]    Simply connecting two disintegrators in parallel for operation of a single, common electrode is problematic because different settings on their respective auto transformers and/or connections to different phases of a power supply can cause back feed into a disintegrator unit that results in damage or destruction of a unit. 
         [0004]    The electrical power required for a particular job is related to the cross-sectional area of the electrode and the part being disintegrated. These factors will, of course, vary considerably in the applications in which the disintegrator equipment is used. To account for this variation, a disintegrator unit, as is conventional, uses a multi-tapped auto transformer to drive a water cooled cutting transformer. Where, as contemplated by the invention, two disintegrator units are to be used in parallel, it is imperative that the tap settings, and therefore the output voltages be the same so that one unit does not back feed destructive current or voltage levels to the other unit. For the same reasons, each unit must be supplied by the same phase of a three phase supply. 
       SUMMARY OF THE INVENTION 
       [0005]    The invention provides a system in which two separate disintegrator units can be safely connected in parallel to energize a common electrode. The disclosed system comprises a master disintegrator unit and a booster disintegrator unit incorporating special safety circuitry. The circuitry automatically checks that the settings of the auto transformer of each unit is the same and that the connections made to each unit from an electrical power source is on the same phase. 
         [0006]    The ability to reliably use two disintegrator units in parallel offers many benefits as compared, for example, to a single larger unit. The total heat loss in the cutting transformer and related componentry is cut in half. Identical componentry can be used in both units thereby simplifying inventory, production, and diagnostics. Some of the components, including the cooling water circulating pump, heat exchanger, and control power supply, can be shared between the units. The units can be individually moved through passageways and into confined spaces separately where a single larger unit could not fit. Where a job has a low power requirement, only one disintegrator unit need be transported to and used at the worksite. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a diagrammatic representation of a master disintegrator unit, a power booster disintegrator unit, and an electrode positioner; and 
           [0008]      FIGS. 2A and 2B , combined, show an electrical circuit diagram of the booster unit. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0009]    Referring now to  FIG. 1 , a master or host disintegrator unit  10  and a power booster disintegrator unit  11  are shown. The units  10 ,  11  comprise separate metal cabinets in each of which are mounted electrical and electronic components (hereafter each referred to as electrical components). Electrical components discussed below in the units  10 ,  11  that are identical are identified by the same numerals. Multi-tap auto-transformers  12  are each manually set by rotating a knob  13  on the front of the respective unit  10 ,  11 . The auto-transformers  12  drive their respective cutting transformers  14  such that a cutting transformer will develop, for example, 3 to 30 volts in 8 steps or settings of an auto-transformer. Secondary windings  16  of the cutting transformers  14  as well as lines  17 ,  18  connecting the winding to output and ground terminals or sockets  21 ,  22  can comprise double wall copper tubing for supply and return of water coolant. 
         [0010]    An electrically operated pump  26 , located in the master unit  10  forces coolant water through the cutting transformer secondary windings  16  and lines  17 ,  18  through supply and return lines  27 ,  28  within the master unit  10  and through hoses  31 ,  32  connected between the units  10 ,  11  at their rear faces. Water circulated through the cutting transformers  14  by the pump  26  passes through a heat exchanger  33  that transfers heat to utility water passing through the heat exchanger. 
         [0011]      FIG. 2  shows the electrical connections between the auto-transformer  12  and the cutting transformer  14 . The secondary coil of the auto-transformer  12  is connected across the cutting transformer primary coil. Relay contacts 1CR, discussed below, in the lines connecting these transformers  12 ,  14  in the power booster unit  11  are not present in the wiring between the corresponding auto-transformer and cutting transformer in the master unit  10 . The output socket  21  and ground socket  22  are located on the front of respective master and power booster cabinets. 
         [0012]    The master unit  10  and power booster unit  11  are used together such as when a job requires a high power consuming electrode and/or when a fast cut is desired. In such a high power mode, the high side terminals  21  of both units are connected together, i.e. operate in parallel, through cables  36 . Similarly, the ground terminals  22  are connected together. The cables from the high side sockets or terminals  21  are connected together at a common connector  38  at an electrode  39 . Typically, the electrode  39  is carried on an electrode positioner  41  ( FIG. 1 ) generally known in the art. Grounding cables  37  from the ground terminals  22  are connected together at a grounding connector  42  on a base of the positioner  41  or otherwise disposed to ground a workpiece. A line  17  between the master unit cutting transformer and its high output socket  21  can have a sensing transformer (not shown) to monitor current through the cutting transformer. A reactor 4RT in the line  17  between the power booster cutting transformer  14  and the output socket  21  serves to match the impedance of the current sensing transformer in the line  17  between the master unit cutting transformer  14  and the output socket  21 . The wiring between the auto-transformer  12  and the cutting transformer  14  in the master unit  10  is essentially the same as that in the power booster unit  11  shown in  FIG. 2  with the exception that, as previously mentioned, there are no relay contacts equivalent to the contacts 1CR. 
         [0013]    The control circuit shown in  FIG. 2  serves to verify that the auto-transformer settings on the main and power booster units  10  and  11  are the same and that both of these units are connected to the same phase of power supplied by a utility or local generator before the power booster unit cutting transformer is energized through the contacts 1CR. If these settings and phase connections are not identical, there is a risk that when the two disintegrator units are used in parallel that one can develop a destructive voltage in the other. Initially, the open contacts 1CR of a control relay 1CR disconnect the power booster auto-transformer  12  from the associated cutting transformer  14 . 
         [0014]    When the master unit  10  is first turned on, its cutting transformer will back feed its voltage through its cables  36 M,  37 M, and the power booster unit cables  36 B,  37 B to the power booster unit cutting transformer  14 . This master unit voltage will be multiplied by transformer action in the primary winding of the power booster unit cutting transformer. During this start up time, the lines out of each auto transformer will carry a voltage corresponding to the settings selected by the machine operator at the knob  13 . Since the auto transformer  12  and cutting transformer  14  of the master and power booster units are functionally and preferably physically the same, the voltage induced by the master unit in the primary of the power booster cutting transformer  14  will be the same and of the same phase as that existing in the secondary of the booster auto transformer  12  provided that the auto transformer settings of the units are the same and the supply power to each of these units is connected to the same phase. In the context of the circuit of  FIG. 2 , the voltage on both sides of both of the open contacts of 1CR (interrupting the lines between the auto and cutting transformers of the power booster) will be the same if the auto transformer settings and phase connections at both units are correct, i.e. the same. 
         [0015]    During start up of the power booster unit  11 , the voltage across the lines from the power booster auto transformer  12  on the proximal side of the contacts 1CR and the voltage in these lines on the distal side of the contacts being back fed from the master unit and multiplied by the power booster cutting transformer  14  is monitored by a protection circuit  50 . The protection circuit  50  has two sides  51 ,  52 , one sensing the power booster auto transformer voltage, the other sensitive to the back fed voltage. Each circuit side  51 ,  52  has a transformer  3 T,  4 T that proportionately reduces the AC voltage to a range between 6 and 40 volts. The reduced voltage is rectified in a bridge 2BR, 3BR. The rectified voltage is applied to a solid state relay 2SSR, 3SSR. A failure of either or both of the protection circuit relays 2SSR, 3SSR to be excited indicates a malfunction in the respective circuit side and through relay logic embodied in the circuit of  FIG. 2  causes the master and power booster units  10  and  11  to shut down. 
         [0016]    A differential circuit  54  includes a bridge rectifier 1BR having each of its input terminals individually connected to the secondary of one of the protection circuit transformers  3 T,  4 T. The output of the rectifier 1BR is applied to a solid state relay 1SSR. Contacts 1SSR of this relay 1SSR are shown in the top rung of a ladder control circuit  56 . The control circuit  56  receives 120 volt AC power through lines  34  and  32  shown at the bottom of  FIG. 2A . This 120 volt control voltage on the lines  134 ,  132  is provided by a power supply indicated at  57  in  FIG. 1  through an external cable  59  connected to the power supply through a control circuit  58  in the master unit  10 . A third line  136  in the cable  59  is connected to a part of the master unit control circuit  58  such that if the continuity of this line is interrupted in the power booster ladder control circuit  56 , the master unit  10  is shut off. 
         [0017]    Control relays 1R, 2R in the ladder control circuit  56  and 3R associated with a ground fault interrupter 1GFI monitoring for leakage current in the power supply lines to the power booster unit  11  have contacts in a serial line that is inserted in between parts of the line  136  when an on-off switch 1SS of the power booster  10  is switched on. Relay 1R latches on to shut off the master unit  10  when the differential circuit  54  detects a voltage difference between what the power booster auto-transformer  12  is delivering to the lines to the cutting transformer  14  on one side of the contacts 1CR and what is produced on these lines on the other side of the contacts from the back fed signal from the master unit  10 . Relay 2R (initially temporarily energized by 2TR) de-energizes if either or both relays 2SSR, 3SSR in the protection circuit  50  fail to remain energized thus signaling a failure of its or their respective side  51 ,  52  of the protection circuit  50 . In this event, relay contacts 2R open and shut off the master unit  10  by interrupting continuity in the line  136 . 
         [0018]    The relay 3R associated with the GFI monitors incoming power at the power booster unit and trips off when a fault is detected, opening its normally open contacts 3R, thereby interrupting the continuity of line  136  and shutting down the master unit  10 . 
         [0019]    A supplemental explanation of the function of certain electrical or electronic components of the power booster unit electrical circuit is given below. 
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 1GFI 
                 Deenergizes 3R which deenergizes 1CR, 
               
               
                   
                   
                 if a leakage currently exceeds more 
               
               
                   
                   
                 than 7 ma from either L1 or L2 through 
               
               
                   
                   
                 ground reference resistor 4RES. Can be 
               
               
                   
                   
                 tested and reset with buttons at 1GFI 
               
               
                   
                 1R 
                 Latches up during a differential fault. 
               
               
                   
                   
                 This shuts the master power unit off 
               
               
                   
                   
                 and keeps it off until control circuit 
               
               
                   
                   
                 is reset. 1 LT lights under this 
               
               
                   
                   
                 condition. 
               
               
                   
                 2R 
                 Energizes when 3T and 4T along with 2BR 
               
               
                   
                   
                 and 3BR are supplying DC voltage to 
               
               
                   
                   
                 2SSR and 3SSR. After 1 second 2TR will 
               
               
                   
                   
                 open. If there is a fault in either DC 
               
               
                   
                   
                 supply, 2R will deenergize opening 
               
               
                   
                   
                 control circuit of master power unit. 
               
               
                   
                   
                 2 LT will flash. This circuit is 
               
               
                   
                   
                 provided to not let the master power 
               
               
                   
                   
                 unit run if the protection circuit in 
               
               
                   
                   
                 the slave unit is not functioning 
               
               
                   
                   
                 properly. 
               
               
                   
                 3R 
                 Pilot relay opens when 1GFI senses a 
               
               
                   
                   
                 ground fault on incoming service line 
               
               
                   
                   
                 to machine, opens control circuit and 
               
               
                   
                   
                 energizes 3 LT. 
               
               
                   
                 1TR 
                 Set at 300 milliseconds. It delays the 
               
               
                   
                   
                 start up of 1CR to check fault 
               
               
                   
                   
                 circuitry. 
               
               
                   
                 2TR 
                 Set at 2 seconds. Energizes 2R for 1 
               
               
                   
                   
                 second by bypassing 2SSR and 3SSR, 
               
               
                   
                   
                 which verifies DC sources from 3T and 
               
               
                   
                   
                 4T are functioning 
               
               
                   
                 3TR 
                 Set at a minimum of 100 milliseconds. 
               
               
                   
                   
                 Energizes through 1SSR, if a voltage 
               
               
                   
                   
                 difference is sensed between 3T and 4T. 
               
               
                   
                   
                 3TR compensates for time lag in all the 
               
               
                   
                   
                 relays. Keeps 1R from latching up when 
               
               
                   
                   
                 the stop button is pushed. 
               
               
                   
                 4TR 
                 Set at a minimum of 100 milliseconds. 
               
               
                   
                   
                 It applies DC voltage from differential 
               
               
                   
                   
                 circuit to 1SSR when master power unit 
               
               
                   
                   
                 is energized. It also keeps 1 cap from 
               
               
                   
                   
                 discharging through 1SSR when master 
               
               
                   
                   
                 power unit is on, and differential 
               
               
                   
                   
                 voltage is zero. This circuit is 
               
               
                   
                   
                 necessary to allow a faster start up 
               
               
                   
                   
                 time through 1TR, especially on higher 
               
               
                   
                   
                 tap settings. When 4TR deenergizes, 1 
               
               
                   
                   
                 cap discharges through 2RES. 
               
               
                   
                 1CR 
                 Energizes 250 milliseconds after master 
               
               
                   
                   
                 power unit is energized. If no 
               
               
                   
                   
                 differential faults are sensed and 3TR 
               
               
                   
                   
                 remains closed 1CR and 6LT will 
               
               
                   
                   
                 energize from 1CR circuit on master 
               
               
                   
                   
                 power unit and 2LT cutting transformer 
               
               
                   
                   
                 will be energized. 
               
               
                   
                   
               
             
          
         
       
     
         [0020]    It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited. It is envisioned, for example, that verifying electrical circuitry ascertaining that the auto-transformer setting of two self-contained master disintegrator units are at the same setting and that the same phase of electrical power source is being supplied to both units before they are enabled to operate in parallel can be provided in accordance with the present invention.