Patent Description:
This disclosure relates generally to a method for separating welded contacts in a switch and, more particularly, to a method for separating welded contacts in a electro-magnetically actuated vacuum interrupter that includes providing multiple actuator hammer blows to the contacts.

An electrical power distribution network, often referred to as an electrical grid, typically includes a number of power generation plants each having a number of power generators, such as gas turbines, nuclear reactors, coal-fired generators, hydro-electric dams, etc. The power plants provide power at a variety of medium voltages that are then stepped up by transformers to a high voltage AC signal to be provided on high voltage transmission lines that deliver electrical power to a number of substations typically located within a community, where the voltage is stepped down to a medium voltage. The substations provide the medium voltage power to a number of three-phase feeder lines. The feeder lines are coupled to a number of lateral lines that provide the medium voltage to various distribution transformers, where the voltage is stepped down to a low voltage and is provided to a number of loads, such as homes, businesses, etc..

Periodically, faults occur in the distribution network as a result of various things, such as animals touching the lines, lightning strikes, tree branches falling on the lines, vehicle collisions with utility poles, etc. Faults may create a short-circuit that increases the load on the network, which may cause the current flow from the substation to significantly increase, for example, several times above the normal current, along the fault path. This amount of current causes the electrical lines to significantly heat up and possibly melt, and also could cause mechanical damage to various components in the substation and in the network.

Power distribution networks of the type referred to above typically include a number of switching devices, breakers, reclosers, interrupters, etc. that control the flow of power throughout the network. A vacuum interrupter is a switch that has particular application for these types of devices. A vacuum interrupter employs opposing contacts, one fixed and one movable, positioned within a vacuum enclosure. When the interrupter is opened by moving the movable contact away from the fixed contact the arc that is created between the contacts is quickly extinguished by the vacuum. A vapor shield is provided around the contacts to contain the arcing. For certain applications, the vacuum interrupter is encapsulated in a solid insulation.

These types of vacuum interrupters are sometimes employed in fault interrupter devices, such as single-phase self-powered electro-magnetically
actuated reclosers. These types of magnetically actuated reclosers generally include a solenoid type actuator having an armature that is moved by an electrical winding to open and close the vacuum interrupter contacts, where the armature and a stator provide a magnetic path for the flux produced by the winding. The winding is de-energized after the actuator is moved to the open or closed position, and permanent magnets are used to hold the armature against a latching surface in both the open and closed position. Reclosers of this type automatically open the vacuum interrupter contacts in response to the detection of fault current, and are often coordinated with other reclosers and breakers so that the first recloser upstream of the fault is the only one that opens to limit the number of loads that do not receive power. When the recloser opens in response to detecting a fault, it will close shortly thereafter to determine if the fault remains. If the fault current is detected again, then the recloser will automatically open again and remain open.

It is sometimes desirable to provide a manual actuation device in connection with a electro-magnetically actuated recloser of this type for manually closing and opening the vacuum interrupter contacts when no power is available to the recloser for electrically opening and closing the contacts. For example, when the recloser is first installed in a live circuit, such as on a utility pole, where the vacuum interrupter is in the open position, but power is not available because the contacts are open and unable to electrically close the vacuum interrupter, it is desirable for convenience purposes to be able to manually close the contacts. Further, the manual actuation device needs to be configured so that if a fault occurs in the circuit, or is present in the circuit when the vacuum interrupter is mechanically closed, the contacts will immediately open electrically as described above without the manual device interfering with the electrical operation of the actuator. Further, there may be occurrences where it is desirable to manually open the contacts when the vacuum interrupter is in operation without using the actuator.

There may be an occurrence where the contacts of a vacuum interrupter, breaker, recloser or other type of switch are welded closed because of high fault current. For example, an unknown fault may be on the line during the manual closing operation of a recloser of the type referred to above, where the vacuum interrupter is switched into the high fault current, which could cause the contacts to weld. If the weld cannot be removed by operating the actuator, then a farther upstream recloser will need to be opened to clear the fault.

<CIT> describes a circuit interrupting device having a circuit interrupter with a stationary contact and a moveable contact. The movable contact is controlled by a solenoid assembly. The movable contact is connected to a plunger of the solenoid assembly by a turnbuckle and weld break assembly. The turnbuckle and weld break assembly permits adjusting the contact wipe distance and generates a hammer force to break any welds between the contacts of the vacuum interrupter.

<CIT> describes a method for separating welded contacts in a switch assembly, the method comprising: initiating a manual closing operation of the contacts using a manual activation device; detecting a high fault current that occurs as a result of the closed contacts; commanding an actuator to open the contacts in response to detecting the high fault current, thereby providing a hammer blow to the contacts; detecting a continuity of the high fault current through the switch after the hammer blow is provided, the continuity of the high fault current indicating that the contacts are welded together. The document also discloses a recloser adapted to perform the above method.

The following discussion discloses and describes a method for separating welded contacts according to claim <NUM> and a single phase, self-powered electro-magnetically actuated fault interrupting switch assembly according to claim <NUM>.

Additional features of the disclosure will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.

The following discussion of the embodiments of the disclosure directed to a method for breaking welded contacts in a electro-magnetically actuated switch assembly including a vacuum interrupter that includes providing multiple actuator hammer blows to the contacts is merely exemplary in nature, and is in no way intended to limit the disclosure or its applications or uses. For example, the discussion herein refers to the method being applicable to a vacuum interrupter. However, as will be appreciated by those skilled in the art, the method will have application for other types of switches.

<FIG> is a side view of a electro-magnetic latching actuator operated switch assembly <NUM> including a vacuum interrupter <NUM>, a solenoid or magnetic actuator <NUM> that electrically opens and closes the vacuum interrupter <NUM>, and a manual actuation device <NUM> that manually opens and closes the vacuum interrupter <NUM>, where an outer insulation housing of the vacuum interrupter <NUM> and an outer protective housing of the actuator <NUM> and the device <NUM> have been removed. The switch assembly <NUM> has particular application as a single-phase self-powered electro-magnetically actuated fault recloser for use in medium voltage power distribution networks. The vacuum interrupter <NUM> includes an enclosure <NUM> defining a vacuum chamber <NUM>, a fixed upper terminal <NUM> extending through a top end and into the chamber <NUM> and including a contact <NUM> and a movable lower terminal <NUM> extending through a bottom end and into the vacuum chamber <NUM> and including a contact <NUM>, where a bellows <NUM> allows the movable terminal <NUM> to slide without affecting the vacuum in the chamber <NUM>. The vacuum interrupter <NUM> is shown in the closed position where the contacts <NUM> and <NUM> are in contact with each other.

The switch assembly <NUM> further includes a dielectric drive rod <NUM> extending through a spring <NUM>, where one end of the drive rod <NUM> is connected to the lower terminal <NUM> and an opposite end of the drive rod <NUM> is connected to an armature <NUM> in the actuator <NUM>. When the switch assembly <NUM> is in an open state and the actuator <NUM> is commanded to close the vacuum interrupter <NUM>, current flow is provided in one direction through a split winding <NUM> having an upper winding-half <NUM> and a lower winding-half <NUM> defining a space <NUM> therebetween, where a magnetic path is provided by the armature <NUM> and an E-shaped stator <NUM>. In response, the armature <NUM> is drawn upward, which also moves the rod <NUM> and the lower terminal <NUM> upward so that the contact <NUM> engages the contact <NUM>, where continued movement of the armature <NUM> to a closed latch position against a latch surface <NUM> compresses the spring <NUM> to increase the force of the contact <NUM> against the contact <NUM>.

When the armature <NUM> is latched closed the winding <NUM> is de-energized and a pair of permanent magnets <NUM> and <NUM> positioned in the space <NUM> on opposite sides of the armature <NUM> hold the armature <NUM> in the closed latch position and the spring <NUM> under compression, where the actuator <NUM> is shown in the closed position in <FIG>. When the switch assembly <NUM> is in the closed state and the actuator <NUM> is commanded to open the vacuum interrupter <NUM>, current flow is provided in the opposite direction through the split winding <NUM> and the armature <NUM> is drawn downward with help from the spring <NUM>. The rod <NUM> and the lower terminal <NUM> also move downward so that the contact <NUM> disengages the contact <NUM>, where continued movement of the armature <NUM> proceeds to an open latch position against latch surface <NUM>. The permanent magnets <NUM> and <NUM> also hold the armature <NUM> in the open latch position when the winding <NUM> is de-energized. No details of the device <NUM> are shown as it can be any mechanical device suitable for the purposes discussed herein.

<FIG> is a timing diagram <NUM> where time is on the horizontal axis and the position of the actuator <NUM>, specifically the armature <NUM>, is on the vertical axis, where graph line <NUM> shows the position of the actuator <NUM> between an open position and a closed position over time. At point <NUM>, the actuator <NUM> is in the open latch position and a manual closing operation of the actuator <NUM> is initiated by the manual actuation device <NUM> to close the vacuum interrupter <NUM>, for example, when the switch assembly <NUM> is first put into service or during subsequent maintenance, where the closing motion of the armature <NUM> occurs along line portion <NUM>. Unknown to the operator who is manually closing the vacuum interrupter <NUM>, the power line is faulted and high fault current is present. When the actuator <NUM> is in the closed latch position at point <NUM>, and thus the contacts <NUM> and <NUM> of the vacuum interrupter <NUM> are closed, the fault current is detected by the recloser, and an automatic open command is given to the actuator <NUM> at point <NUM> that energizes the winding <NUM> and the actuator <NUM> begins opening at point <NUM>, where the opening motion of the actuator <NUM> is performed along line portion <NUM>. However, the high fault current has welded the contacts <NUM> and <NUM> closed, so that actuation of the actuator <NUM> may not actually separate the contacts <NUM> and <NUM>. This attempted opening of the contacts <NUM> and <NUM> when they are welded shut is known in the industry as a hammer blow because the actuator <NUM> provides significant pressure to separate the contacts <NUM> and <NUM>. The armature <NUM> is able to move some distance without separation of the contacts <NUM> and <NUM> because of the spring <NUM>.

If the contacts <NUM> and <NUM> are welded shut and do not separate by the hammer blow, the actuator <NUM> is unable to continue to open at point <NUM> and remains at its current position as represented by line portion <NUM>. The high fault current is still occurring and thus the weld is detected from that current by the recloser at point <NUM>. When the weld is detected, the actuator <NUM> is automatically commanded closed at point <NUM> by energizing the winding <NUM>, where the actuator <NUM> begins closing at point <NUM> and the armature <NUM> moves upward and continues its closing operation along line portion <NUM> to its closed latch position at point <NUM>. By closing the actuator <NUM> it is reset for another hammer blow. Another open command is given to the actuator <NUM> at point <NUM> to initiate a second hammer blow by the actuator <NUM>, where the actuator <NUM> begins the opening motion at point <NUM> and opens along line portion <NUM> to the open latch position at point <NUM>. By providing multiple hammer blows to the contacts <NUM> and <NUM>, the likelihood that the weld will be broken between the contacts <NUM> and <NUM> is significantly increased.

In this illustration, the second hammer blow is successful, and the armature <NUM> moves to the open latch position along the line portion <NUM> to the point <NUM>, where the contacts <NUM> and <NUM> are separated and not welded. If the second hammer blow was not successful, then yet another closing and opening sequence of the actuator <NUM> can be initiated to try a third hammer blow to break the weld in the same manner as discussed above. As long as there is power available to open and close the actuator <NUM>, the recloser will continue to try and break the weld in this manner. If none of the hammer blows are successful, then eventually the upstream protection devices will take effect and the fault current will be removed.

Claim 1:
A method for separating welded contacts (<NUM>, <NUM>) in a switch assembly (<NUM>), the method comprising:
initiating a manual closing operation of the contacts (<NUM>, <NUM>) using a manual activation device (<NUM>);
detecting a high fault current that occurs as a result of the closed contacts (<NUM>, <NUM>);
commanding an actuator (<NUM>) to open the contacts (<NUM>, <NUM>) in response to detecting the high fault current, thereby providing a hammer blow to the contacts (<NUM>, <NUM>);
detecting a continuity of the high fault current through the switch (<NUM>) after the hammer blow is provided, the continuity of the high fault current indicating that the contacts (<NUM>,<NUM>) are welded together;
commanding the actuator (<NUM>) to close the contacts (<NUM>, <NUM>); and
commanding the actuator (<NUM>) to open the contacts (<NUM>, <NUM>), thereby providing a second hammer blow to the contacts (<NUM>, <NUM>).