the present invention has particular application to a line of equipment 114 involving the gas - insulated substations having gas - insulated components , and somewhat diagrammatically illustrated in fig1 and 2 of the drawings . fig2 is a one - line diagram of the equipment 114 illustrated in fig1 . it will be noted , from a consideration of fig1 and 2 , that the high - voltage equipment 114 is arranged so that both the space required , and the total length of the gas - insulated bus 2 is minimized . the power transformer 5 is located on an outside corner of the station , preferably , so that it can be easily removed . the gas - insulated bus 2 is attached directly to the transformer - bushing minimizing area and height required . the location of the cable pothead 17 is flexible . in the gas - insulated system 114 , as illustrated in fig1 and 2 , it is chosen to minimize the length of the sf 6 bus 2 . if a lightning arrester 36 is located at each pothead 17 , an arrester 36 is not required at the lower - transformer 5 it will be noted that the gas - insulated system 114 of fig1 can be connected to overhead lines . however , the air clearances , required by incoming power lines , will somewhat enlarge the total area required by the system 114 , and will require additional sf 6 bus 2 . the gas - insulated transmission system 114 , illustrated in fig1 and 2 is a line of equipment , which will significantly reduce the space required by the high - voltage side of substations rated 115 k . v . the space reduction is accomplished by replacing the open bus and air terminal - bushings , commonly used , with gas - insulated bus 2 filled with sulfur - hexafluoride ( sf 6 ) gas 8 , for example , at 45 psig ( at 70 ° f . ), and moving the component parts of the electrical equipment as close together as possible . the use of gas - insulated transmission systems 114 offers many advantages . the use of the system 114 offers several advantages to the utility user , some of these are : 1 . significant reduction in space requirements both in land area and overall height . 2 . added system reliability by eliminating the possibility of phase - to - phase faults , lightning strokes within the system 114 , or contamination of the environment . 3 . reduced maintenance because the closed system 114 is isolated from its environment . 4 . added personnel safety because all live parts are covered by grounded shields . 5 . the modular approach was chosen because it could provide the utility user with lower installation costs when compared with conventional or other gas - insulated systems . 6 . the system 114 can be overbuilt to permit multiple use of the land . generally , the equipment 114 includes a plurality of bus assemblies 2 determined by the length that can generally be shipped . the typical bus length 2 will be , for example , 40 feet , and may consist of two 20 feet lengths , with an epoxy spacer 2a ( fig3 ) in each length 2 . the ends of the bus 2 can be connected to additional lengths of bus 2 , or any functional member of the system 114 . expansion joints are located in each 20 foot bus - section 2 to absorb the maximum of 0 . 4 inches of expansion expected . as stated , sulfur - hexafluoride ( sf 6 ) gas 8 at 45 psig , for example , fills both the sheat 37 and the bus conductor 2 , and is free to move throughout the entire bus 2 . the 45 psig sf 6 gas pressure provides approximately the highest dielectric strength possible down to - 40 ° c . without liquefaction , eliminating the need for auxiliary heat . high - pressure sf 6 gas , however , does require a heat input at low ambient temperatures . with reference to fig3 of the drawings , it will be observed that there are provided two upstanding circuit - breaker assemblages 3 and 4 , each including an outer metallic grounded casing structure 15 , and an interiorly - disposed insulating high - pressure casing structure 10 . a conductor 38 , disposed within a horizontally - disposed grounded metallic gas - filled conduit 41 , electrically interconnects the two circuit - breaker assemblages 3 , 4 in electrical series relationship . the interiorly - disposed insulating casing structure 10 is positioned radially inwardly from the outer metallic grounded casing structure 15 and has an insulating gas 8 , such as sulfur - hexafluoride ( sf 6 ) gas , for examople there - between in the annular space 47 , at a pressure , say , for example , 45 psig . disposed interiorly of the inner insulating pressurized casing structure 10 is a circuit - interrupter module 51 , adaptable for relatively high ratings , and including two interrupting breaks 21 , 22 and , additionally , a resistance break 13 . the resistance break 13 is surrounded by a shunting closing resistance 14 , such as set forth in detail in u . s . patent application filed dec . 4 , 1973 ser . no . 421 , 574 , now u . s . pat . no . 3 , 863 , 041 , issued jan . 28 , 1975 , and assigned to the assignee of the instant patent application . disposed at the upper end of the circuit - breaker module 51 is a mechanism compartment 26 enclosing a control valve and an operating piston , not shown , which controls the opening and closing operations of a pair of movable interrupting contacts 20 and 23 , and also the operation of a lower - disposed movable resistance contact 11 . various details of the operating structure may be obtained from a reading of u . s . pat . no . 3 , 596 , 028 , and the patents therein referred to . however , for an understanding of the present invention , it is merely necessary to know that each upstanding column structure 3 , 4 contains two main arc - extinguishing units 6 and 7 together with a lower resistance unit 9 , which has the resistance contacts 11 , 12 thereof controlled in such a manner that during the closing operation of the interrupter 3 , the closing resistance 14 is inserted serially into the circuit to damp any high - voltage surges occurring on the line 16 ( fig3 ). however , as will be obvious , in the fully closed - circuit position of the interrupter 3 , it is desirable to shunt , or to take the resistance 14 out of the circuit , due to heating effects and energy losses , and the function of the separable closing contacts 11 , 12 is to achieve this end . during the opening operation , on the other hand , it is desirable to have the resistance 14 , which serves only a closing function , completely out of the circuit 16 during the opening operation . as a result , the closing resistance 14 is shunted out of the circuit 16 during the initial portion of the opening operation , where the task of interrupting the arcs 18 , 19 ( fig5 ) is imposed only on the main contact structures 31 , 22 , and not at the resistance - contact structure 11 , 12 . in the particular embodiment under discussion , and as illustrated in fig3 - 10 there are provided two main contact structures 21 , 22 and a lower serially - related resistance contact structure 11 , 12 , on each column structure 3 , 4 , such as illustrated in fig3 . reference may be made to the diagrammatic view of fig7 for an indication of the fact that there are provided six breaks through the entire transmission line circuit 16 from l 1 , through the two main contact structures 21 and 22 of the left - hand column 3 , through the lower resistance contact structure 11 , 12 of the left - hand column 3 , upper conductor 38 , and through the right - hand column structure 4 , in a similar manner , to the lower line terminal l . sub . 2 of the interrupter 4 . with further reference directed to fig3 of the drawings , it will be observed that there are provided two identical interrupting assemblages 3 and 4 spaced away from each other , as illustrated in fig3 and each of which contains two serially - related main contact assemblages 21 , 22 , together with a serially - related separable resistance contact assemblage 13 , which controls the insertion of the closing resistance 14 . disposed at the upper end of the columnar assemblage 3 of fig4 a is an operator , or driving mechanism 26 , more fully illustrated in u . s . pat . no . 3 , 590 , 189 , issued june 29 , 1971 to fischer et al , and assigned to the assignee of the instant application . to understand the present invention , however , it is only necessary to know that downward movement of the operator , generally designated by the reference numeral 26 in fig4 a , effects closing downward operation of the contact structures 13 , 21 and 22 . conversely , upward linear movement of the operator 26 , together with the main frame assembly 28 , comprising the operating rods 30 , 31 of fig5 a , will cause opening movement of the main contact structures 21 and 22 . it is an important feature of the present invention that there are two frame - assemblies 28 , 33 utilized . the upper frame - assembly 28 includes a generally h - shaped structure including transverse bridging members 39 , 40 together with a pair of downwardly - extending interconnecting movable operating rods 30 , 31 . the lower ends of the operating rods 30 , 31 are hollow , as indicated at 42 in fig6 c , and make separable abutment connection at 44 with a resilient bumper 46 , such as of rubber , affixed to and secured to a lower cross - member 48 attached to the lower frame - assembly 33 associated with the movable resistance contact 11 , as illustrated in fig5 c , 6c and 8 of the drawings . during the downward closing operation of the circuit - interrupter 1 , it will be observed that the light spring 50 , ( fig5 c ) maintains the two frame - members 28 and 33 in abutment , as at the separable connection 44 in fig6 c , so that the downward closing movement of the three contact structures 21 , 22 and 13 is simultaneous . the overlap distance of the two main movable contacts 20 , 23 , relevant to their associated stationary contacts 25 , 27 , is such that they make contacting closing engagement before the closing engagement of the movable resistance contact 11 with its stationary resistance contact 12 . this results in the closing resistance 14 being inserted into the circuit 16 prior to the subsequent closing of the resistance contacts 11 and 12 by roughly one - half cycle time duration . thus , in the closed - circuit position , all of the three pairs of contacts are closed , but due to the contact overlap distance at the stationary main contacts 25 , 27 , the main separable movable contacts 20 , 23 make contacting electrical engagement prior to the subsequent closing of the resistance contacts 11 , 12 due to the physical dimensions of the contact members utilized . in the closed - circuit position of the circuit - interrupter , as illustrated in fig6 a , 6b and 6c , the circuit 16 is closed through the two columnar assemblages 3 , 4 , and the resistance 14 is out of the circuit , as caused by the closing of the shunting resistor contacts 11 and 12 . the shunting of the closing resistance 14 is , of course , desirable as well appreciated by those skilled in the art , inasmuch as it would lead to heating and energy losses in the closed - circuit position of the interrupter 1 . its use during the closing operation is to avoid the occurrence of high - voltage surges occurring on the line 16 during a closing operation . the theory and functioning of a closing resistance of the proper value is , of course , set forth in the aforesaid van sickle u . s . pat . no . 3 , 291 , 947 , to which reference has been made and the subject matter of which is incorporated herein by reference . during the opening operation , it is , of course , desirable for the erosion and burning associated with the extinguishing of the arcs 18 , 19 to occur only at the main two contact assemblages 21 , 22 in the upper portion of each columnar arc - extinguishing assemblage 3 , 4 . the arrangement is such that the inertia of the lower resistance frame - assembly 33 is such that it &# 34 ; hangs &# 34 ; behind , or there is a lost - motion connection 52 fig8 between the two - frame assemblages 28 and 33 due to the inertia of the lower resistance frame - assemblage 33 and the relatively light biasing spring 50 of fig6 c . the net result is that the operator 26 has sufficient opening driving force to quickly and rapidly accelerate the upper frame - assembly 28 , together with its associated two moving main contacts 20 , 23 , upwardly to break the circuit 16 at these two points , whereas the resistance contacts 11 , 12 are yet closed , there - by shorting out the lower closing resistance 14 , and thus imposing all arcing 18 , 19 upon the upper two serially - related main arc - extinguishing structures 6 , 7 . by the time that the relatively light spring 50 of fig6 c raises the lower movable resistance frame assembly 33 to effect contact break at the resistance contacts 11 and 12 , at this time arcing 18 , 19 in the upper two serially - related units 6 , 7 has ceased , arcing is out and thus there is no arc erosion or burning occurring at the lower separable resistance contacts 11 and 12 . the closing resistance assemblage 14 is more clearly set forth in fig1 and 12 , where it will be observed that the carbon arcuate segments 54 are in compression , as caused by the compression springs 56 , and connections 58 between the carbon resistance segments cause the resistance assemblage 14 to be of the right ohmic value , as set forth in the aforesaid van sickle u . s . pat . no . 3 , 291 , 947 . with reference to the lower end of the columnar assemblage 3 , it will be observed that there is a lower contact portion 60 , which is connected to the line terminal l 1 . although the above description has been centered around one columnar assemblage 3 , it will be noted that the same description is appropriate for the other laterally spaced upstanding columnar arc - extinguishing assemblage 4 , which has a generally identical construction and function . as a result , there are four main separable contact structures in each pole - unit &# 34 ; a &# 34 ;, &# 34 ; b &# 34 ;, or &# 34 ; c &# 34 ;, as shown in fig1 . the function of these four main contact structures is to interrupt the electrical current flow through the pole - unit &# 34 ; a &# 34 ; during the opening operation , and the four separable main contact structures distribute the arcing 18 , 19 , and voltage division among the four series breaks is controlled by shunting capacitor branches paralleling the interrupting assemblages . these are designated by the reference numerals 62 and 63 of fig6 a and 4b . it is to be further noted that in each pole - unit &# 34 ; a &# 34 ;, &# 34 ; b &# 34 ;, or &# 34 ; c &# 34 ; there is provided the two closing resistances 14 together with their associated separable resistance contact assemblages 13 , which function , during the opening operation , to keep the resistances 14 out of the circuit 16 during the interruption process . during the closing operation of the interrupter 1 , on the other hand , the main contact structures 21 , 22 are closed , whereas the separable resistance contacts 11 , 12 are still open , so that the two resistances 14 are serially inserted into the circuit 16 during the closing operation to prevent high - voltage surges occurring on the line 16 . as set forth in fig3 a main operating mechanism 64 at ground potential , which is described in u . s . pat . no . 3 , 624 , 329 , which issued nov . 30 , 1971 to fischer et al , effects rightward movement of a connecting rod 68 , which effects counterclockwise rotation of two bell - crank levers 70 , 71 , each of which has an upstanding movable valve - rod 73 ( fig9 ) pivotally connected thereto at 75 . the two bell - crank levers 70 , 71 are pivotally mounted on stationary pivots 77 , 78 . pivotally connected at 86 to the right - hand bell - crank lever 71 is the upstanding valve - rod 73 associated with the right - hand column 4 of the pole unit &# 34 ; a &# 34 ;. clockwise pivotal rotation of the driving rod 68 effects upward movement of the two valve - rods 73 , which serve to pneumatically cause pressure to occur on the bottom side of an operating piston ( not shown ) constituting a part of the upper operator 26 illustrated in fig4 a of the drawings . the operator 26 is set forth and described in u . s . pat . no . 3 , 590 , 189 , and during the closing operation , as described hereinbefore , causes downward movement of the h - shaped frame 28 comprising the two operating rods 30 , 31 movable within stationary guide sleeves , or tubes 96 , 97 , and serving to simultaneously cause the downward closing movement of the two main movable contacts 20 , 23 in each assemblages 3 , 4 . as set forth in u . s . pat . no . 3 , 596 , 028 , a latching arrangement 100 ( fig6 a ) is associated with each main movable contact 20 or 23 , as disclosed more clearly in fig5 b of the drawings . it will be observed that there are provided a pair of pivotally - mounted latches 102 biased radially inwardly by a pair of compression springs 104 , only one latch assembly 102 being viewed in fig5 b of the drawings . the construction is such that during the closed position , as viewed in fig6 a , the latches set upon shoulder portions 106 associated with the secondary blast - valves 107 , which , when open , permits gas flow to occur out ports 108 associated with the rear side of the upper movable main contact 20 , as viewed in fig5 a . this gas - flow action is described in more detail in u . s . pat . no . 3 , 596 , 028 to which reference may be made , and the subject matter of which is incorporated herein by reference . following a predetermined opening motion of the movable contact structure 20 to 23 , a portion 103 of the movable contact structure bears on a cam portion 101 of the latches 102 , forcing the latches 102 outwardly to thereby release the blast - valves 107 , which move upwardly to the closed position , thereby halting any gas flow out of the interrupting chamber 88 ( fig5 a ) in the open position of the main contacts , as illustrated in fig5 a and 5b of the drawings . it will be noted that there exists at all times high - pressure gas within the region externally of the main contact structure , as designated by the reference numeral 99 in fig5 b of the drawings . this high - pressure gas is available immediately upon separation of the contacts to effect extinction of the arcs 18 , 19 , which are indicated in fig5 although the contact structure in illustrated in the fully - open position in fig5 a and 5b of the drawings . fig5 b and 6b show more clearly the mechanical interconnection of the movable main contact 23 of the lower - most main arc - extinguishing structure 7 . it will be observed that a cross - member 40 is mechanically interconnected between the two operating rods 30 , 31 , and serves somewhat the same function as the upper traverse member 39 of fig6 a and 7a . as mentioned hereinabove , the two main operating rods 30 , 31 have lower hollow extensions 42 which encompass movable projections 35 affixed to the lower movable traverse frame - member 48 of the resistance assemblage 33 , as indicated more clearly in fig6 c and 8 of the drawings . the lost - motion between the lower hollow tubular extensions 30a , 31a of the two main operating rods 30 , 31 and the resilient rubber bumpers 46 , affixed to the resistance traverse member , is designated by the reference numeral 52 in fig8 and the distance at this particular point of time is designated by the distance length &# 34 ; d &# 34 ; in fig8 of the drawings . consequently , fig8 illustrates a point in time during the opening operation of the interrupter 1 in which the main movable resistance contact 11 has lagged behind to short out the closing resistor 14 , while the upper two breaks 21 , 22 are causing the extinction of the arcs 18 , 19 within the interruptor 3 . also associated with each columnar assemblage 3 , 4 is an outer cylindrical insulating casing member 10 , which holds the high - pressure gas 8 within the regions 99 externally of the two main contact structures 21 , 22 . also , it will be noted that externally of the insulating casing member 10 is disposed an outer metallic grounded casing 15 utilized for its ground characteristics . the line connection l 1 is secured to a terminal structure 34 more clearly shown in fig3 which electrically connects the circuit 16 to the lower resistance contact 12 . as set forth in the aforesaid kane et al u . s . pat . no . 3 , 596 , 028 , the circuit 16 extends through both columnar assemblages 3 , 4 and terminates at the lower end 32 of the other assemblages 4 of fig3 . from the foregoing description it will be apparent that a novel arrangement has been provided , in connection with a closing resistance 14 and associated separable resistance contact structure 13 , controlling the insertion of the closing resistance 14 into the circuit 16 only during the closing operation of the breaker 1 . during the opening operation of the breaker , the closing resistance 14 is deliberately shorted out of the circuit 16 , so that the full burden of arc - extinction 18 , 19 is imposed only on the upper two main separable contact structures 21 , 22 , and no arcing occurs at the separable resistance contacts 11 , 12 . the inertia of the resistance frame 33 and the relatively light spring 50 are thus utilized to afford the desirable delaying , or lost - motion effect 52 for the lower resistance frame - member 33 . suitable mechanical support tubes 96 , 97 are provided to fixedly maintain the stationary contact structures 25 , 27 in the desired stationary location , and to provide mechanical integrity of the arc - extinguishing assemblage 3 as a whole . with reference to fig3 it will be observed that a low - pressure tank 29 is provided together with compressor equipment , as set forth in u . s . pat . no . 3 , 596 , 028 . the manner of arc - extinction and the operation of the various parts is also more clearly set forth in the aforesaid u . s . pat . no . 3 , 596 , 028 . this resistor contacts 11 , 12 are for use in a high voltage power circuit breaker rated at 362 kv . the breaker is capable of 40 ka interrupting ability and carrying 3000 amps continuously . the pre - insertion resistors 14 are available from 175 ohms to 300 ohms each . there are two of these per phase . they are electrically and thermally capable of closing into a full fault four times each hour . the movable contact 11 shorts out the resistor 14 from 6 to 9 milliseconds after it has been inserted into the circuit . the use of a closing resistor optimally sized for each system reduces the over - voltages caused by closing the circuit breaker into a transmission line with a trapped charge , and subsequently reduces the electrical stress imposed on the entire power system &# 39 ; s equipment . this stress is reduced to a maximum of 2 . 0 times the normal line to ground voltage whereas this maximum is 3 . 0 times the normal line to ground voltage when no closing resistor is used . for the lower - voltage and power ratings , where closing voltage surges are not a problem , a modified - type of circuit - breaker module 120 may be employed , such as set forth in fig1 - 15 or the drawings . the modified - type of circuit breaker module 120 includes only a single break 122 , having a double - flow through the moving contact structure 124 and also through the stationary contact structure 125 , as illustrated more clearly in fig1 of the drawings . the manner of operation is the same as set forth in the higher - rating circuit - breaker module 51 , hereinbefore discussed in connection with fig3 - 12 of the drawings . fig1 and 15 show the closed and fully - open circuit positions of the modified circuit - breaker module 120 , and it is , as mentioned , used for the lower ratings without a resistance 14 . fig1 and 17 show a modified - type of mounting construction 133 in which the position of the low - pressure reservoir tank 127 is removed to a side - lateral position , straddling the lower three frame - support members 129 - 131 for the three phases of the installation 132 . the other features of the circuit - breaker construction 132 of fig1 and 17 are the same as heretofore described . it will be observed that the improved construction of the present invention involves improved mounting support features , such as the pressurized tubes 49 ( fig3 ) not only supporting the circuit - breaker modules 51 , but , additionally , providing high - pressure gas - flow to the pressurized casing structure 10 disposed at the upper end of each of the two interconnected circuit - breaker assemblages 3 , 4 . additionally , the operating rods 73 for controlling the control - valves are passed through the exhaust tubes 74 , which carry the low - pressure gas , following an interrupting operation , down to the low - pressure reservoir tanks 29 . as will be obvious , a suitable gas compressor equipment , not shown , takes the gas at the lower pressure level , as supplied in low - pressure reservoir tank 29 , and compresses it to the high - pressure level , such as 240 psig , and provides it in through the conduit , or pipe 55 into the two pressurized insulating casings 49 , 10 . from the foregoing description , it will be apparent that there has been provided an improved circuit - breaker installation 1 , 120 adaptable for metal - clad switchgear , and accommodating a wide variety of ratings . for the very high - power ratings , with high - voltages , where the possibility of closing voltage surges may be encountered , the circuit - breaker module 51 , with a number of breaks and closing breaks , such as set forth in fig3 - 12 , may be utilized . however , for the lower - voltage ratings , where voltage surges are not a problem , then a more simplified - type of interrupter 120 having single or double - flow conditions , as desired , may be supplied , as set forth in fig1 - 15 . according to an alternate mounting arrangement 136 of the present invention , as set forth in fig1 of the drawings , a horizontally - arranged construction is provided . as shown in fig1 , it will be observed that instead of the circuit - interrupting assemblages 3 , 4 extending up in the air , the modified - type of construction 136 , as set forth in fig1 , the circuit - breaker assemblages 3 , 4 are mounted horizontally and close to the ground , with the gas - and - mechanism housing 139 provided longitudinally therealong also horizontally arranged . fig1 shows the gas - and - mechanism housing 139 in close horizontal proximity to one of the two circuit - interrupting assemblages 4 , as shown . the high - pressure supporting - tube construction 49 is the same as set forth hereinbefore , but , as set forth in fig1 , the terminal connections are somewhat modified , and extend vertically , as indicated by the reference numerals 140 , 141 in fig1 . the operation of the interrupter modules 6 , 7 is the same as herebefore described in connection with fig3 - 12 of the drawings . the high - pressure connection 150 extends between the two pressurized support tubes 49 to the mechanism housing 139 , where a suitable compressor equipment is provided . additionally , an operating mechanism is provided to effect reciprocal horizontal operation of the control - valves 73 , as heretofore described . the interconnecting linkage is somewhat diagrammatically illustrated by the reference numeral 150 of fig1 , but it will be obvious to those skilled in the art that suitable modifications may readily be made . although there have been illustrated and described specific structures , it is to be clearly understood that the same were merely for the purpose of illustration , and that changes and modifications may readily be made therein by those skilled in the art , without departing from the spirit and scope of the invention .