Abstract:
Insulating oil in electric power transmission devices such as a transformer is filtered for removal of accumulated water and carbon particles. The filter and circulation pump are usually located in a separate cabinet external to the transformer with circulation conduits connecting the filter, the pump and the transformer. To prevent environmental contamination by leaks or ruptures in the oil circulation conduits, secondary or sleeving conduits surround and protect the circulation conduits and additionally provide an independent leak flow conduit back to the filter cabinet dry sump. An accumulation of oil in the dry sump actuates a fluid sensor to transmit an alarm signal.

Description:
RELATED APPLICATION 
     The present invention is a continuation of presently copending application Ser. No. 08/400,985 filed Mar. 8, 1996, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to electric power transmission devices. More particularly, the invention relates to apparatus and methods for preventing environmental contamination by dielectric insulation oil. 
     Electric power transmission devices such as transformers and switch gear are often immersed in a specially compounded oil with dielectric properties for purposes of insulation, isolation and cooling. On occasion, these devices generate extremely high operating temperatures. Although the oil will not burn in the absence of atmosphere or oxygen, small portions will directly decompose under the intense heat of electrical arcing into elemental carbon, which remains in the oil body as suspended graphite particles. 
     Additionally, the chemical nature of the oil is hydrophilic. Any atmospherically carried water coming into surface contact with the oil is adsorbed and entrained. 
     Both, water droplets and graphite particles are intolerable contaminants of the oil and must be removed, either periodically or continuously. Fortunately, both contaminants are effectively removed by relatively simpler depth wound unsized paper reel filters. A traditional installation often will connect a transformer oil cavity by external plumbing conduits to adjacently housed pump and filter units. Circulation around the conduit loop is driven by the pump motor which is controlled by cycle timers and filter pressure differential monitoring switches. Circulation may be continuous or intermittent, depending on the type of transformer or the service to which it is applied. 
     An adverse consequence of such dielectric oil is the environmentally hazardous nature of its chemical composition. Consequently, these oils are heavily regulated and monitored. Affected site clean-ups due to leaks and spills are extremely expensive and subject to the responsible manager to fines and other penalties. Accordingly, great care is exercised in handling these fluids and every reasonable precaution is taken to prevent leaks from the external filter circulation system. Nevertheless, leaks can and do occur. 
     It is, therefore, an object of the present invention to protect the local environment from leaks and other losses of insulating oil from transformer and other electrical power transmission devices. 
     Another object of the present invention is the provision of an alarm system to alert responsible management of a defective transformer oil circulation system. 
     A further object of the present invention is provision of a secondary conduit system enclosing the primary insulation oil circulation system for an electric power device. 
     SUMMARY OF THE INVENTION 
     These and other objects of the invention are provided by an independent insulating oil circulation system having a motor driven pump connected in fluid circuit with a filter unit. The pump, motor and filter assembly are preferably secured within an independent cabinet enclosure above a normally dry reservoir volume. 
     The cabinet reservoir volume is guarded by a fluid sensor such as a level switch to indicate the presence of oil within the normally dry reservoir. 
     Primary circulation conduits connect the filter and pump, respectively, with the oil filled cavity of an associated electric power transmission device such as a transformer, load tap changer, breaker, closure, reclosure, switch or switching bank. A full circulation loop at least includes a conduit from the transmission device oil cavity to the pump, a flow connection between the pump and the filter, a conduit between the filter and the transmission device oil cavity and an internal flow connection within the transmission device oil cavity between the pump conduit connection and the filter conduit connection. 
     Fluid-tight housings are secured to the external surface of the transmission device casement around respective circulation conduit connectors to or through the casement whereby the point of casement penetration by the connector is enclosed by a secondary containment volume. These housings are of such dimension and volume as to permit hand-tool accessibility through resealable port covers to the circulation conduit connectors. 
     The circulation conduits enter the secondary containment housing and the isolation cabinet through sealed bulkhead connectors. The bulkhead connectors are continuously interconnected by large conduits for a continuous enclosure therebetween. Accordingly, a sealed and continuous secondary fluid flow channel is established around the primary circulation system with the pump/filter cabinet reservoir, preferably at the elevationally lowest point in the system. Oil escaping from the primary circulation circuit at any point outside of the transmission device case will gravity drain to the cabinet sump volume. Depending on the type of fluid detection system used, when sufficient oil accumulates in the sump, an alarm signal is transmitted to the filter circulation and central control systems to stop the pump drive and seal off the primary circulation circuit from the oil cavity of the transmission device. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which: 
     FIG. 1 is a fluid circulation schematic of the present invention; 
     FIG. 2 is an electrical control schematic of the invention; 
     FIG. 3 is a partially sectioned detail of an upper surface connector housing: and, 
     FIG. 4 is a partially sectioned detail of a lower surface connector housing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Relative to the drawings wherein like reference characters designate like or similar elements throughout the several figures of the drawings, FIG. 1 schematically shows a fluid circuit of the invention supporting the load tap changer  12  of an electric power transformer  10 . Typically, such a power transformer stands about 10 to 14 ft. high with a nominal diameter or rectangular side dimension of 3 to 6 feet across. The transformer  10  and load tap changer  12  of FIG. 1 are merely representative of many types of electric power transmission devices that further include breakers, closures, reclosures and switches. 
     Each transformer casement is usually externally finned for heat dissipation and sealed to prevent loss and leakage of internal fluids which immerse a plurality of core and winding assemblies. The internal fluid is an oil substance, not necessarily petroleum based, but moderately viscous and highly dielectric to insulate the several winding sets from arcing between themselves and the transformer case. Localized heating of the oil stimulates internal convective circulation which transfers the heat generated by electrical transform losses to the outer case for conduction therethrough to the exterior dissipation fins. Pumps and radiators may also be used to cool the insulating oil. 
     The load tap changer is a mechanical switching array by which the transformer output is regulated for line demand. The electrical arcing usually incident to the closure and opening of charged electrical contacts is a momentary point source of extreme heat if not vacuum isolated. Such extreme heat on the presence of the insulating oil generates particulate graphite from a dissociation of the oil. Such particulate graphite becomes a contaminant in the oil body and contributes to a reduction of the dielectric property of the oil. For reasons which amount to a greater propensity for contaminant generation, a load tap changer oil cavity of 300 to 800 gallons capacity is frequently isolated from the oil cavity respective to the transformer winding case. Breakers, closures, reclosures and switch boxes may encase 50 gal. to 200 gal. of dielectric insulating oil. 
     Typically, the transformer or load tap changer insulating oil is circulated by a pump  20  through a filtration unit  22 . Section conduit  24  provides a fluid flow channel between the bottom of the load tap changer oil cavity (FIG. 4) and the pump  20  suction connection. Pump discharge conduit  26  connects to the inlet of filter  22 . Return conduit  28  carries the oil circulation flow loop back to load tap changer (FIG. 3)  12 . 
     The pump  20  and its associated electric motor  21  (FIG.  2 ), the filter  22  and the related electric control panel  36  are housed within a cabinet enclosure  30  which is generally located closely adjacent to the transfer load changer  12  and elevationally below the conduit  24  and  28  connection points with the load tap changer. 
     Also within the enclosure  30 , preferably at an elevational point below the enclosure penetration points  31  and  33 , is a normally dry oil sump reservoir  32 . A perforated cabinet floor  35  preferably, but not necessarily, separates the upper volume of the cabinet enclosure from the lower reservoir volume  32 . Fluid presence within the reservoir  32  is monitored by a level sensor  34  shown to be a float switch. It should be understood that no particular volume of oil is required in reservoir  32  for effecting a signal from the sensor  34 . Accordingly, any of numerous sensor types may be used equivalently in this application. For example, a dielectric sensor which measures the dielectric strength of a fluid covering the sensor surface would signal not only the presence of the insulation oil when air over the sensor surface is displaced but also the dielectric condition of the oil contacting the sensor surface. Other sensor types that may be used are ultrasonic sensors that respond to volumetric changes within the reservoir and special sensors that respond to the light color reflected from the reservoir floor. 
     At each of the load tap changer case penetration points for the primary circulation conduits  24  and  28 , connector housings  40  and  50  are provided. Each of housings  40  and  50  are of different style suited for a particular installation circumstance. Depending on the mix of these installation circumstances, either housing type could be used at both locations or other, functionally equivalent, secondary containment housings may be used. 
     In the example of the penetration housing  40  for the suction conduit  24  shown best by FIG. 4, the housing body is a flanged cylinder that is secured tightly against the load tap changer case  12  by the clamping pressure of machine screws  49  compressing a gasket  48  into the opposite faces of the load tap changer case and the flange  47 . At the other or bottom end of the flanged cylinder, the open cylinder bore is closed by the flange  45  of a threaded plug  44  compressing a ring gasket  46 . 
     An aperture  43  in the cylinder  40  wall receives a flanged bulkhead nipple  60  which is drawn by a compression nut  62  against a gasket  64 , The exterior threaded end of the bulkhead nipple is provided with half of a pipe union  66 . The other half of the pipe union  66  is threaded upon a pipe sleeve  68  that completely encloses the pump suction conduit continuously to the cabinet enclosure  30 . 
     Threaded plug  44  provides resealable tool access to the interior of housing  40  while in sealed position against the load tap changer case  12 . Within the housing  40 , oil flow from the load tap changer through the pipe stub  70  is controlled by an electric solenoid valve  72  energized by winding  74  and conductors  76 . A 90° elbow sub  78  connects the valve  72  to the conduit  24  with a tubing union  79 . 
     Penetration housing  50  of FIG. 3 may have a cylindrical or rectangular sectional form that is secured by machine screws  59  through an integral flange  58  sealed against a gasket  57 . Access to the interior of the housing  50  is provided through an end port  56 . A cover  53  secured by machine screws  52  against a gasket  54  and an internal flange  55  provides resealable tool access to the interior of the housing  50 . 
     Through one aperture in the wall of housing  50  is a threaded bushing  80  screwed into a 90° ell  82  to compress a gasket or O-ring  83  against the exterior face of housing  50 . A nipple  84  connects the 90° ell to half of a pipe union  85 . The other half of the union  85  is threaded upon a stub  86  welded into an aperture  87  in the load tap chamber casing. A compression nut  90  threaded into the face of bushing  80  seals and secures a subsection of tubing  91  within the 90° ell  82 . An extended tail of the subsection  91  extends through the stub nipple  86  into the load tap changer oil cavity. Within the interior of the housing  50 , the subsection  91  is flow connected by union  92  to a terminal end of return conduit  28 . 
     A second aperture through the wall of housing  50  is sealed by a flanged bulkhead nipple  100  compressed against a gasket  102  by a nut  104 . The threaded outer end of the nipple  100  receives halt of a union  106 . The other half of the union  106  is threaded upon a pipe sleeve  108  that encloses a fluid drain channel around the return conduit  28  between the connector housing  50  and the cabinet  30 . 
     The pump motor and alarm control shown schematically by FIG. 2 includes a fused, 240 VAC power circuit  110  to energize the pump motor  21  and a voltage reduction transformer  111 . on the low voltage side of the transformer  111 , is a motor starting control relay C 1  which operates to close the power circuit switches C 1  and the 120 V circuit switch C 1 . An operation cycle control timer T 2  operates to close the normally open subcircuit switch T 2  to energize other control functions in coordination with the load tap changer operation. Load element  112  is a power meter for system management and lamp  115  provides a remote indication of normal motor  21  operation. 
     Switch  114  is a pressure differential control switch responsive to the pressure drop of pumped insulating oil across the filter unit  22 . The control elements of this switch are adjusted to monitor a pressure differential range above a lower threshold and below an upper threshold. When pressure falls below the lower threshold, as in the case of circuit conduit rupture or pump malfunction, the pump motor is disconnected from its energy source. Similarly, when the filter unit  22  is sufficiently loaded to cause the pressure differential across the unit to exceed the upper threshold limit, the pump motor power is disconnected. 
     An alternative embodiment of the invention may provide an electric clutch connection between the pump  20  and motor  21  whereby the motor runs continuously to drive other units or equipment and a mechanical drive connection between the motor and pump is disengaged. 
     In the event of leakage from the primary circulation circuit, whether by conduit rupture or faulty connector seal, fluid lost from the primary circuit will flow into the secondary containment volume within the housing  40  and  50 , the cabinet  30  and the sleeve conduits  68  and  108 , The pump and filter cabinet  30  is positioned elevationally below the load tap changer and the related connector housings  40  and  50 . Consequently, significant fluid leakage from the primary circuit will eventually flow by gravity drive into the cabinet sump reservoir  32  thereby activating a signal from the fluid sensor switch  34 . 
     When the fluid sensor  34  in the cabinet reservoir  32  detects the presence of oil in the reservoir due to leakage in the primary circulation circuit, switch  34  will close, energize the relay coil R 3  and illuminate the associated lamp  116 . With the energization of relay winding R 3 , switch R 3  closes to energize the closure of solenoid valve  72  thereby preventing the drainage of fluid in the primary circuit from the load tap changer cavity. Relay winding R 3  might also be employed to actuate external alarms or other systems as a consequence of the fluid sensor  34  signal. 
     When the valve  72  in the pump suction conduit  24  closes, a continued attempt of the motor  21  to operate pump  20  effects an operation of the pressure differential switch  114  and the general emergency shut down circuitry of relays R 1 , R 2  and the alarm represented by lamp  118 . All operating elements of the unit thereafter shut down and a general alarm is transmitted to the remote control center. To start the pump  20  again, a reset protocol must be followed. 
     Although a preferred embodiment of the invention elevationally positions the sump volume  32  and fluid sensor  34  below the load tap changer connection housings, those of ordinary skill may reverse this alignment and position the pump higher than either of the connector housings. Such may be the case for circulation of insulation oil from the transformer  10  case cavity and the desirability of placing the pump suction housing  40  near the transformer case bottom. Such an elevational reversal of the invention components may be readily accommodated by positioning the fluid sensor  34  within the lowest connector housing or wherever the lowest gravity flow position is in the circulation system. 
     It also should be noted that more than one fluid sensor  34  may be employed by the invention. For example, parallel connected fluid sensors may also be positioned in both of the connector housings  40  and  50 . 
     Having fully disclosed the preferred embodiments of our invention, those of ordinary skill in the aft may devise obvious equivalencies and alternatives. As our invention, however,