Abstract:
A hydraulic time delay device couples to a fault-sensing element in a circuit recloser. The time delay device includes a piston that has an external connection and is operable to move through a housing in the device to cause hydraulic fluid in the housing to flow out of the housing and into a passageway. The time delay of the time delay device corresponds to a time required to move the piston. A first adjustable orifice is formed the passageway to define an adjustable first fluid flow path through the passageway. An adjustable valve is positioned to provide an adjustable second fluid flow path through the passageway. A second adjustable orifice is formed in the passageway to provide further adjustment of the second fluid flow path. Adjustment of the first orifice, the valve, and the second orifice affect the time required to move the piston.

Description:
TECHNOLOGY FIELD 
     This invention relates to a time delay device for a circuit recloser. 
     BACKGROUND 
     On high voltage lines, many problems, such as lightning striking the line, tree branches or wires blowing in a wind gust, or animals on the lines, are only temporary. However, even these temporary problems can cause permanent damage to electrical equipment if power is not shut off for their duration. A device such as a recloser may be used in high voltage lines to deal with such problems. 
     A recloser is an automatic, high-voltage electric switch that shuts off electric power in an electric distribution line when a problem, such as a short circuit, occurs. After shutting off power, and waiting for expiration of a time delay, the recloser automatically restores power and tests the distribution line to determine whether the problem has been removed. If the problem is still present, the recloser shuts off power again. The recloser may repeat the shut-off-wait-restore process several times. If the fault is permanent, the recloser may shut off the power permanently after a certain number of repetitions (for example, three or four). 
     SUMMARY 
     The invention provides a hydraulic time delay device for coupling to a fault-sensing element in a circuit recloser. To this end, the time delay device includes a piston having an external connection and operable to move through a housing in the device to cause hydraulic fluid in the housing to flow out of the housing and into a passageway. A time delay of the time delay device corresponds to a time required to move the piston. 
     In one general aspect, the time delay device includes a first adjustable orifice formed in the passageway to define an adjustable first fluid flow path through the passageway, and an adjustable valve positioned to provide an adjustable second fluid flow path through the passageway. A second adjustable orifice formed in the passageway provides further adjustment of the second fluid flow path. Adjustment of the first orifice, the valve, and the second orifice affect the time required to move the piston. 
     Embodiments may include one or more of the following features. The time delay device may further include a piston spring inside the housing. The piston moves through the housing in a first direction in response to a force on the external connection, and the piston spring asserts a force on the piston in an opposite direction. The piston may include an aperture that closes when the piston moves in the first direction to push the hydraulic fluid into the passageway, and opens when the piston moves in the opposite direction to permit the hydraulic fluid to flow through the aperture. 
     Adjustments to the orifices may be made by adjusting their sizes. Adjustments to the valve may be made by adjusting the position of the valve. 
     The time delay device may further include an adjustable screw that applies a force to the valve through a valve spring which couples the valve to the screw. The force applied to the valve may modify the second fluid flow path. A set screw positioned inside the adjustable screw may be used to adjust the second orifice. 
     The circuit recloser may be used to open contacts in the circuit after the time delay. The fault sensing element may be linked to the external connection of the piston. 
    
    
     Other features and advantages will be apparent from the following description, including the drawings, and from the claims. 
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an electric distribution system that uses a circuit recloser. 
     FIG.  2 . is a block diagram of operation of a circuit recloser of the system of FIG.  1 . 
     FIG. 3 is a side view of a time delay device used in the circuit recloser of FIG.  2 . 
     FIG. 4 is a front view of the time delay device of FIG.  3 . 
     FIG. 5 is a sectional view through the time delay device of FIG. 4 along section  5 — 5 . 
     FIG. 6 is a sectional view through the time delay device of FIG. 4 along section  6 — 6  and showing a previous design of a high pressure adjustment mechanism. 
     FIG. 7 is a cross sectional view of a high pressure screw used in the time delay device of FIG.  6 . 
     FIG. 8 is a top view of the high pressure screw of FIG.  7 . 
     FIG. 9 is a sectional view through the time delay device of FIG. 4 along section  6 — 6  and showing a design of a new high pressure adjustment mechanism. 
     FIG. 10 is a cross sectional view of a pressure adjustment screw used in the time delay device of FIG.  9 . 
     FIG. 11 is a top view of the pressure adjustment screw of FIG.  10 . 
     FIG. 12 is a generalized graph of a time-current characteristic curve for the time delay device. 
    
    
     DETAILED DESCRIPTION 
     Referring to FIG. 1, a recloser  100  is used in an electric distribution system  105  in conjunction with other protective devices  110 , such as fuses or other reclosers, to supply power to at least one load  115  in a feeder line  120  that emanates from a main power line  125 . The recloser  100  is connected in series with the main power line  125 , which is connected to a high-voltage source  130 . Upon occurrence of a fault, the recloser  100  executes a series of circuit opening and closing operations. These operations continue until the fault clears or the recloser  100  determines that the fault is permanent and leaves the circuit in an open state. 
     It is desirable to vary timing of the open/close operations. For example, when the fault first occurs, the recloser  100  will open and close the power line rapidly to avoid unnecessary damage to protective devices  110  in the circuit. If, however, the fault does not clear after the series of rapid operations, the fault may be considered permanent. Thus, it may be necessary to isolate certain feeder lines  120 , or even the main power line  125 , depending on the location of the fault. Therefore, following the rapid open/close operations, the recloser  100  will open and close the main power line  125  at a slower rate to permit protective devices  110  to carry excessive current for a time sufficient to open one or more of the protective devices  110  and isolate the corresponding feeder lines  120 . If a fault exists in one of the feeder lines  120 , it is then isolated, and the recloser  100  remains closed at the end of the open/close operation to keep the main power line  125  energized. On the other hand, if the fault exists in the main power line  125 , the recloser  100  may open again after a time delay and remain open until manually reset. 
     Referring also to FIG. 2, time delay for recloser operations is accomplished using a mechanical time delay device  200 , which has predetermined time/current characteristics for different timing operations. Because timing operations affect other protective devices  110  associated with the electric distribution line  105 , such as fuses or other reclosers, the time delay device  200  used in the recloser  100  coordinates with these other protective devices  110 . 
     The time delay has been difficult to adjust to meet timing limits set by protective devices  110  and loads  115  in the lines  120 ,  125 . This is due to the fact that only two adjustments (a low pressure orifice and a high pressure spring adjustment) are typically provided to adjust the timing of three different current ranges. The new design for the time delay device  200  adds a high pressure orifice adjustment to permit independent timing adjustment of all three different current ranges. 
     A linkage  205 , which selectively couples an electric current sensing solenoid  210  to the time delay device  200 , is used to determine a speed of the open/close operation sequence. Movement of a magnetic plunger  217  in the solenoid  210  causes contacts  215  in the main power line  125  to open or close. A lockout and sequence control system  225  in the recloser  100  initiates the opening and closing of the contacts  215  based on operation of the plunger  217 . Opening of the contacts  215  (that is, circuit tripping) may be delayed by the time delay device  200  if the linkage  205  engages a pin  300  on a delay arm  305  of the time delay device  200 . Movement of the delay arm  305  is slowed by hydraulic resistance to movement of a shaft  325  that extends out of the device  200 . Alternately, opening of the contacts  215  may be instantaneous if the linkage  205  does not engage the time delay device  200  through the pin  300 . When the contacts  215  are opened, the solenoid  210  is de-energized and the plunger  217  may be retracted by a spring  220 . The lockout and sequence control system  225  counts a number of times the recloser  100  operates and initiates lockout (that is, it permanently opens the contacts  215 ) after a preset number of open/close operations. The contacts  215  remain open until they are manually reset by a human controller. 
     Referring also to FIGS. 3 and 4, the time delay device  200  is activated when the linkage  205  engages the pin  300  extending transversely through the time delay arm  305  which is connected to a housing  310  of the time delay device  200 . A force exerted by the solenoid on the arm  305  varies with the current on the line. 
     A minimum trip spring  315  is adjusted using a screw  320  to set a minimum fault current at which the recloser will trip open. On delayed opening operations, sequencing of the lockout and sequence control system  225  causes the linkage  205  to engage the pin  300  and activate the time delay device  200 . Once the pin  300  is engaged, the delay arm  305  pushes down on the shaft  325  which extends into the housing  310 . Movement of the delay arm  305  is slowed by hydraulic resistance to movement of the shaft  325  from within the housing  310 . This resistance is transmitted to the time delay arm  305 , and, in turn, to the linkage  205 . 
     The time required for the interrupter contacts  215  to open is governed by the rate of movement of the magnetic plunger  217 . The rate of movement is governed by the current level. Once the current level reaches a predetermined value, there is enough force to activate the plunger  217 . Because the maximum uniform pull of the solenoid  210  is a function of current in the solenoid  210 , an opening time of the interrupter contacts  215  is a function of fault current. 
     FIGS. 5 and 6 are cross sectional views taken along sections  5 — 5  and  6 — 6 , of FIG.  4 . In general, the components shown in FIGS. 5 and 6 are consistent with prior art designs, and are illustrated to aid in understanding of operation of the time delay device  200 . 
     Referring to FIGS. 5 and 6, the housing  310  of the time delay device  200  contains a sealed chamber  500  which is filled with hydraulic fluid  505 . The shaft  325  pushes down a pump piston  510  in response to movement of the time delay arm  305 . An upper surface of the pump piston  510  faces the chamber  500  while a lower surface of the pump piston  510  faces a cylinder  515  which receives the pump piston  510 . A flapper valve  520  attached to the pump piston&#39;s lower surface seals the pump piston  510  to allow pumping on the downstroke by blocking an aperture  525  through which fluid  505  can flow. The flapper valve  520  opens to allow fluid  505  to freely flow from above the piston  510  to below through the aperture  525  on the upstroke. A force needed to return the piston  510  on the upstroke is provided by a spring  530  in the cylinder  515 . 
     The fluid  505  pumped by the piston  510  on the downstroke flows into two passageways  535  and  540 . The flow rate of the fluid  505  through the passageways  535 ,  540  is controlled by the setting of two sealed, self-locking adjustment screws  545  and  550  positioned inside the passageways  535  and  540 , respectively. The passageway  535  provides a low pressure path while the passageway  540  provides a high pressure path. 
     At relatively low fault currents, the solenoid  210  does not exert a force sufficient to drive fluid  505  through the high pressure path. Accordingly, the rate of descent of the pump piston  510  at low values of fault current is governed by the sealed self-locking adjustment screw  545  and the passageway  535 . With higher currents, and correspondingly higher forces, fluid  505  flows through both passageways such that the rate of descent of the pump piston  510  at medium and high fault currents is governed by the screw  545  and the screw  550 . 
     The low pressure adjustment screw  545  has a slot  555  at its bottom end. As the screw  545  is adjusted, an orifice size defined by the slot  555  and the passageway  535  is varied by how much of the slot  555  is exposed above a small bore  560  connecting a lower passageway  565  to an entrance  570  into the chamber  500 . Once the screw  545  is adjusted, the orifice size remains constant regardless of how much force is applied to the pump piston  510 . The screw  545  is sealed in the passageway  535  and is locked in place by an O-ring  575  placed around an outer smooth surface of the screw  545 . Adjustment is made by manipulating a head  580  of the screw  545 , which is exposed at an outer surface of the housing  310 . 
     Referring to FIG. 6, the medium/high pressure adjustment uses a valve  600  which varies an orifice size defined by a location of the valve  600  relative to a small bore  605  connecting a lower passageway  610  to an entrance  615  of the chamber  500 . The valve  600  is sealed at the small bore  605  with a valve O-ring  620 . Adjustment of the valve  600  is controlled by adjustment of the screw  550 , which alters compression of a valve spring  625  that contacts the valve  600 . Compression of the spring  625  determines an activation force at which the valve  600  opens through the small bore  605  and how far it opens when a particular force is applied to the pump piston  510 . Once the valve  600  opens through the small bore  605 , fluid  505  flows around the valve O-ring  620  and valve  600 , up along an outside surface of the adjusting screw  550  and through the entrance  615  to the chamber  500 . 
     Referring also to FIGS. 7 and 8, a hole  630  may be formed in the adjusting screw  550  to permit unimpeded flow of the hydraulic fluid  505  through the passageway  540 . Furthermore, a valve stem  635  attached to the valve  600  may protrude into the adjusting screw  550  for alignment. Threads  645  are formed on an outer surface of the screw  550 . These threads match with threads formed on an inner surface of the passageway  540  to permit adjustment of the screw  550 . As with the low pressure adjustment, an O-ring  650  is used to seal the adjustment screw  550  and lock it in place. Adjustment is performed at a head  655  of the screw  550  which is exposed at an outer surface of the housing  310 . 
     Upon descent of the pump piston  510 , the hydraulic fluid  505  from cylinder  515  can either exhaust through passageway  535 , slot  555 , and entrance  570 , or through passageway  540 , past valve  600 , and through entrance  615 . If the force on the piston  510  is sufficiently small, passageway  535  will accommodate all of the fluid  505  displaced from cylinder  515 . As a result, the pressure below valve  600  will be insufficient to overcome the biasing force of valve spring  625 , valve  600  will remain in its closed position, and all of the fluid will exhaust through slot  555  and entrance  570 . 
     By contrast, if a large fault current causes a large force on pump piston  510  and a rapid descent, the passageway  535  will be unable to accommodate all of the fluid, and pressure will build up until the pressure is sufficient to open valve  600  and permit fluid to exit through passageway  540 . 
     Because a single valve adjustment is used to achieve two current level settings, operation of the time delay device  200  at high and medium currents is interdependent and desired settings are difficult to achieve. 
     FIGS. 9-11 show a modification of the previous time delay device. The modification provides a third self-locking adjustment screw  900  formed inside another self-locking adjustment screw  905  that corresponds to the self-locking adjustment screw  550 . The adjustment screw  900  provides a third adjustment that allows adjustment of a high pressure orifice size in addition to adjustment of the spring force which controls movement of the valve  600 . 
     The adjustment screw  905  has a second set of threads  910  formed on a lower surface of the screw  905  that match with threads in the passageway  540  and align with threads  645  on an upper surface of the screw  905 . The seal between the threads  910  and the passageway  540  restricts the free flow of fluid  505  around an outer surface  915  of the adjustment screw  905 . The seal between the threads  910  and the passageway  545  eliminates the need for special machining of the small bore  605  in the lower passageway  610  and the outside surface of the screw  905  if the O-ring  620  is used. The resulting restriction forces the fluid  505  to flow through a lower cross hole  920  in the adjustment screw  905 , up an internal passageway  925 , and out through an upper cross hole  930  to bypass the restriction. The internal passageway  925  is threaded to allow insertion of the adjustment screw  900  down a center of the adjustment screw  905  to partially close off the upper cross hole  930  to provide an adjustment of the orifice size. The orifice size is defined by the location of the adjustment screw  900  relative to the upper cross hole  930 . In this way an adjustment of the internal adjustment screw  900  provides an adjustment of the orifice size that is completely independent of the valve spring force setting provided by the adjustment of the adjustment screw  905 . 
     The adjustment screw  900  may be a set screw to allow independent adjustment at a head  935  of the screw  905  using a top  940  of the set screw. A set of threads  945  are formed on an outer surface of the adjustment screw  900  to move the screw  900  through the internal passageway  925  of the screw  905 . The threads  945  are coated with a nylon sealer to provide the sealing and locking function required for the adjustment screw  900 , while the adjustment screw  905  uses the O-ring  650  for sealing and locking within the passageway  340 . 
     Because hydraulic fluid  505  is substantially incompressible, the rate of discharge through the passageways  535  and  540  governs the rate at which pump piston  510  can descend and, hence, the time delay characteristics of the time delay device  200 . This rate of discharge is governed by the biasing force of spring  625 , the position of slot  555 , and the position of adjustment screw  900 . As a result, the time delay characteristics of the time delay device  200  may be varied by modifying the flow restricting effect of these elements. 
     FIG. 12 is a graph  1200  of a set of time-current characteristics which may be desired for a fault-sensing system on a high-voltage line. The curves designated by letter A  1205  represent a rapid opening operation which may be used to test the high-voltage line  125 . The other curves (given by letters B, C, D, and E) represent time-current characteristics which are desired when a fault does not clear after the rapid opening operations have been performed by the recloser. The time-current curves B, C, D, and E may therefore be used to test devices  110  along the feeder lines  120 . The time-current characteristics B and C are given by curves  1210  and  1215  of the graph  1200 . The time-current characteristics D and E are given by curves  1220  and  1225  of the graph  1200 . 
     In the previous time delay device, timing adjustment at both middle and high fault currents required reaming of orifices in the time delay housing  310 , cutting or stretching the valve spring  625 , filing the high pressure valve  600 , or replacing parts or the whole time delay device. In the time delay device  200 , replacement or alteration of parts such as the valve spring  625  or valve  600  is unnecessary since there are three adjustment screws  545 ,  905 , and  900  which may be adjusted to better meet the curves B, C, D, and E desired for a time delay device  200  used with various solenoid sizes. 
     The time delay device  200  enables easier timing adjustment to within timing limits and provides a more stable adjustment. A saving in adjustment time should be realized. Additionally, the time delay device  200  can be adjusted to provide four separate delay timing curves (that is, B, C, D, and E) without changing parts as in the previous time delay device. Furthermore, since the self-locking adjustment screw ( 550  and  905 ) is the only part modified in the time delay device  200 , it is possible to retain the exterior shape of the previous time delay device to allow new time delays to be installed on existing reclosers presently in service. Because of these advantages, the manufacturer and members of the power industry will notice a significant cost savings. 
     Other embodiments are within the scope of the claims.