Patent Application
20200194200
This disclosure relates generally to a method for detecting a vacuum leak in a vacuum interrupter-based switching device.
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 turbine engines, nuclear reactors, coal-fired generators, hydro-electric dams, etc. The power plants generate a medium voltage that is stepped up to a high voltage AC signal for interconnection to 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 transformers, where the voltage is stepped down to a low voltage and is provided to a number of loads, such as homes, businesses, etc.
Power distribution networks of the type referred to above typically include a number of switching devices, circuit breakers, reclosers, interrupters, etc. that both help to control the flow of power throughout the network and interrupt high currents due to short circuit conditions created by faults. A vacuum interrupter is a switching component that has particular application for these types of devices. A vacuum interrupter employs opposing contacts, one fixed and one movable, positioned within an enclosure that maintains a vacuum. The enclosure is commonly referenced as the “bottle,” since it is typically constructed out of a ceramic insulating material. 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 due to the vacuum environment. A vapor shield is provided around the contacts to prevent any condensing products produced by the arcing across the contacts from causing a short circuit across the internal surface of the bottle. For certain applications, the vacuum interrupter is encapsulated in a solid insulation housing that either is exposed to the outside weather or may even have a grounded external surface.
Vacuum bottles employed in these types of vacuum interrupter switches typically have a very high dielectric withstand, i.e., a high arc breakdown discharge voltage across the contacts is required to create conduction when the switch is open, provided that the vacuum is maintained in the bottle. If there is a leak in the bottle for any reason and vacuum is reduced, the dielectric withstand voltage level decreases and the applied voltage may be sufficient to result in current conduction across the contacts when they are open, resulting in interrupter switch not operating properly. Should the interrupter switch not operate to according to specification, there can be significant consequences, for example, when the switch is open to clear a high-current fault or opened to keep a part of the circuit de-energized. Specifically, if a fault in the network is detected and a particular interrupter switch upstream of the fault is commanded to open to clear or remove the fault from the system, if that interrupter switch mis-operates, then a next upstream interrupter switch is commanded to open, which unnecessarily prevents power from being provided to some customers between interrupter devices. A longer time is required to clear a fault in this way due to time coordination between the devices.
Devices are known in the art to electrically monitor the level of vacuum in a vacuum interrupter switch. For example, it is known to provide a sensor including a pair of fiber optic cables and a control board, where a loss of vacuum blocks an optical signal propagating on the fiber cables being sent to the control board. However, these known devices typically require a connection through the bottle requiring a seal of the penetration through the bottle wall, thus providing an additional point of vacuum failure. Further, such devices provide additional cost and complexity to the interrupter vacuum switch and have limited reliability. It is desirable to provide a technique for reliably monitoring the status of the vacuum within a vacuum interrupter switch bottle without adding additional components to the switch.
The following discussion discloses and describes a method for detecting a vacuum leak in a vacuum interrupter-based switching device. The method includes monitoring for current conduction across contacts in the switching device when they are opened for any reason, where the monitoring starts after a predetermined time delay after opening the switching device. When current conduction is detected through the switching device when the contacts are mechanically opened, i.e., current flow across the open contacts, the method adds the time of current conduction to an accumulated current conduction timer if the magnitude of the detected current exceeds a predetermined current value. The method reduces the accumulated current conduction timer by a certain percentage of a predetermined reset value if the magnitude of the detected current does not exceed a predetermined current value, and sends a signal if the accumulated current conduction timer exceeds a predetermined current conduction time threshold.
In another embodiment for detecting a vacuum leak in a vacuum interrupter-based switching device, the method includes monitoring for current conduction across contacts in the switching device when they are opened for any reason and then measures current conduction across the contacts when they are open. The method also calculates a voltage across the contacts when the current conduction occurs and calculates a power value using the measured current and the calculated voltage. The method compares the power value to a threshold to determine if the power value indicates loss of vacuum in the switching device. Sensor inaccuracies can be compensated for by making the threshold large enough or making the threshold based on a maximum/minimum power ratio from a plurality of switching devices and including a timer in the logic. The voltage can be determined by calculating the voltage by subtracting a voltage measurement provided by a first voltage sensor at one side of the switching device from a voltage measurement provided by a second voltage sensor at an opposite side of the switching device.
In yet another embodiment for detecting a vacuum leak in a vacuum interrupter-based switching device, the method includes monitoring for current conduction across contacts in the switching device when they are opened for any reason and then measures current conduction across a gap between the contacts when they are open. The method also determines a voltage across the contacts when the current conduction occurs and calculates a resistance value using the measured current and the calculated voltage. The method compares the resistance value to a threshold to determine if the resistance value indicates loss of vacuum in the switching device. Sensor inaccuracies can be compensated for by making the threshold based on a maximum/minimum resistance ratio from a plurality of switching devices and including a timer in the logic. The voltage can be determined by calculating the voltage by subtracting a voltage measurement provided by a first voltage sensor at one side of the switching device from a voltage measurement provided by a second voltage sensor at an opposite side of the switching device.
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 detecting a vacuum leak in a vacuum interrupter-based switching device is merely exemplary in nature and is in no way intended to limit the invention or its applications or uses.
It is noted that although the discussion herein refers to the switching device 26 being part of a pole mounted recloser, it will be understood by those skilled in the art that the discussion below will be applicable for detecting leaks in other types of vacuum interrupter switches, such as, for example, vacuum interrupter switches employed in pad-mounted switchgear, underground switchgear, metal-enclosed switchgear, metal-clad switchgear, air insulated ring main units, wind turbine switchgear, etc.
If the vacuum has been significantly compromised in the vacuum bottle 28 of the switching device 26 there can be current conduction across the vacuum switch contacts when the switching device 26 is open, typically over a fraction or more than a few fundamental frequency AC current cycles depending on the remaining vacuum level in the bottle, the load connected to the circuit and the applied system voltage. The present disclosure describes a method for monitoring current conduction time across the contacts of an open vacuum interrupter to determine if the current conduction is significant enough to indicate that the vacuum bottle of the switching device 26 has lost vacuum. There is a possibility of conduction across the open contacts with a normal vacuum, however, such conduction is typically of very short duration. If a detected current conduction exceeds a certain RMS current magnitude, the time of the current conduction is accumulated with the previous current conduction times, and if the accumulated time reaches a predetermined value, the switching device 26 is identified as being compromised and needs to be replaced. In one non-limiting embodiment, the total time of current conduction occurrence is set at fourteen cycles and if no additional current conduction time is accumulated when the switch is in the open state, then the accumulated time is reduced over thirty days at a linear rate.
Once the accumulated current conduction time reaches a predetermined total threshold time, then the logic sends a signal indicating that the switching device 26 may have lost vacuum and the switching device 26 is compromised. For example, if the recloser 10 is on the utility pole 12, then the signal is transmitted to a control facility using, for example, the supervisory control and data acquisition (SCADA) protocol. In one specific embodiment, when the accumulation of time reaches 40% of the total time threshold an information signal is sent at box 62, when the accumulation of time reaches 80% of the total time threshold a warning signal is sent at box 64, and when the accumulation of time reaches 100% of the total time threshold an error signal is sent at box 66. In addition to providing the signal, in one embodiment a user selection can be provided that actuates closing of the switching mechanism.
If the switching device 26 is open, there still may be some current conduction through the switching device 26 above the threshold that occurs randomly even though the integrity of the vacuum bottle 28 has not been compromised. In this situation, the accumulator in the box 60 may accumulate time from brief current conduction when there is not a problem with the switching device 26. Therefore, the logic diagram 50 includes a reset box 68 that gradually reduces the accumulated time in the accumulation in the box 60 if the detected current conduction periods do not occur frequently enough or for enough of a time duration to indicate a failing switch. Specifically, the reset box 68 reduces the accumulation of time a certain amount if no current conduction is detected during a certain time period. In one example, the reset time could be thirty days so that for each day no current conduction is detected when the switching device 26 is open, the accumulation time is reduced about 3.3%.
The switching device 26 may be closed during normal operation while the leak detection accumulation timer has some accumulated time duration of current conduction but has not reached an information, alarm or error signal time threshold. When the switching device 26 is closed, then current will be detected if a load is connected to the circuit. Since it may be desirable to keep the accumulated time in this situation, so that a failing switch can be detected earlier, the logic diagram 50 stops updating the accumulated time value in the box 60 at box 70 if the switching device 26 is closed before the accumulation reaches the total time needed to set an information, alarm or error signal.
The present disclosure also proposes detecting loss of vacuum in the vacuum bottle 28 of the switching device 26 by observing the power dissipated in the pole units 14, 16 and 18 using the voltage and current measurements from the sensors 30, 32 and 34 when the switching device 26 is open. Particularly, when the switching device 26 in the pole units 14, 16 and 18 is closed, the power dissipated in each pole unit 14, 16 and 18 depends on the current flowing in the switching device 26 due to the downstream load and the total resistance of the switching device 26. When the switching device 26 in the pole units 14, 16 and 18 that has a proper vacuum is open no current should flow between the contacts and the power dissipated should be at or near zero. When the switching device 26 in the pole units 14, 16 and 18 that has lost vacuum is open periodic conduction across the switch contacts generates a substantial amount of power within the switching device 26. Therefore, monitoring the power over a time period in the switching devices 26 of the pole units 14, 16 and 18 when they are open can be used to determine current conduction across the open switch contacts due to loss of vacuum. For example, in order to assess power as a possible loss of vacuum detection mechanism in the switching devices 26, a power calculation can be made using measured voltage and current values from the sensors built into the switching device 26, or even from alternative sensors mounted in close proximity to the switching device 26.
An expected power loss across a vacuum interrupter-based switching device with appropriate contact pressure and rated current is approximately 10-15 watts. A practical switching device designed to meet industry requirements will have sensor errors that skew the conclusions of the condition of the pole units 14, 16 and 18, i.e., the pole units 14, 16 and 18 may have unexpected power levels due to the reported current in addition to voltage sensor tolerances. Current magnitude and phase angle reported by the pole units 14, 16 and 18 are also subject to errors in the derivation of RMS amperes in the control algorithm. In order to overcome measurement errors the process will also compare, at box 90, the calculated power values at a predetermined qualification time in each of the pole units 14, 16 and 18 to each other. In one example, a ratio of the maximum to the minimum measured values from the three poles in a switch, and to a predetermined threshold, with both measured values exceeding a threshold over a predetermined time interval, can be used to identify a failing switch, and a suitable warning can be given. Comparison of the results across the pole units 14, 16 and 18 over a time interval yields a better indication of interrupter switch leakage under the assumption that it is unlikely that all three of the switching device 26 would lose vacuum at the same time.
The present disclosure also proposes detecting loss of vacuum in the switching device 26 by observing the resistance of the switching devices 26 in each of the pole units 14, 16 and 18 using the voltage and current measured by the sensors 30, 32 and 34, where the resistance is determined by the difference in the voltage across the switching device 26 when it is open divided by the measured current.
A normally closed vacuum interrupter-based switching device should have a resistance between 30-50 μΩ. When the switching device 26 is open, the resistance should be infinite, i.e., zero amps in the denominator of the voltage/current calculation. However, the resistance values calculated in an opening device also includes the sensor accuracy issue referred to above in the calculations performed for an open vacuum interrupter-based switching device, and thus these values may not be known to a high enough confidence to conclude that the switching device 26 is in a failed state based on a single pole measurement using available measurements.
A technique can be implemented to remove the sensor inaccuracy in this embodiment for determining loss of vacuum in the switching device 26 by dividing the maximum resistance by the minimum resistance for the three pole units 14, 16 and 18 at each current conduction occurrence at box 110, and recording the value. For a normal switch load current with a properly operating vacuum interrupter-based switching device, a ratio of Max/Min resistance value should be a reasonably low multiple. For switches that have lost vacuum a suitable Max/Min threshold value could be 100. This would mean that any variance between the observed resistance between the maximum and the minimum of the three resistance values from the three-pole unit 14, 16 and 18 should be less than 100. The algorithm compares the calculated Max/Min resistance values to the threshold at box 112 to determine if the switching device 26 may have lost vacuum. A suitable warning can be given if the resistance value exceeds the threshold over some predetermined number of sample times and a predetermined time interval.
The embodiment discussed above uses the voltage and current measurements from the sensors 30, 32 and 34 to determine the resistance values that are then used to determine if a vacuum interrupter has lost vacuum in a pole unit. However, other embodiments may employ different techniques for determining the resistance of the pole units 14, 16 and 18 for this purpose. For example, a current supervised impedance/resistance relay element built as software operating in the controller 36 can be employed in the pole units 14, 16 and 18 to measure impedance from the current conducting conditions in the switching device 26, and those impedance values can be compared to known impedance values for a proper operating switch to determine loss of vacuum from observed current conduction when the switching device 26 is open.
In one of the herein disclosed embodiments, a method for detecting a vacuum leak in a vacuum interrupter-based switching device may include detecting current conduction when contacts of the switching device are open after a predetermined delay, adding a current conduction timer unit that accumulates current conduction time to an accumulated total current conduction time value if a magnitude of the detected current conduction exceeds a predetermined current conduction value; and sending a signal if the accumulated total current conduction time value exceeds a predetermined current conduction timer threshold.
The method may further include sending an information, alarm or error signal depending on the accumulated total current conduction time value. Alternatively, the method may include reducing the accumulated total current conduction time value a variable or fixed amount of a predetermined timer value over a settable reset time value if current conduction is not detected when the contacts are open. In a further alternative, the method may include stopping any timer update and preserving the accumulated total current conduction time value if the contacts are closed. In still a further alternative embodiment, the method may include sending information signal if the accumulated total current conduction time value reaches 40% of the predetermined current conduction timer threshold, sending a warning signal if the accumulated total current conduction time value reaches 80% of the predetermined current conduction timer threshold, and sending an error signal if the accumulated total current conduction time value reaches 100% of the predetermined current conduction timer threshold. In yet another embodiment,
In another of the herein described embodiments, a method for detecting a vacuum leak in a vacuum interrupter-based switching device may include monitoring for current conduction when contacts of the switching device are open after a predetermined delay; adding a current conduction timer unit that accumulates current conduction time to an accumulated total current conduction time value if a magnitude of the detected current conduction exceeds a predetermined current conduction value; reducing the accumulated total current conduction time value a certain percentage of a predetermined timer value over a settable reset time value if current conduction is not detected; and sending a signal if the accumulated total current conduction time value exceeds a predetermined current conduction timer threshold.
The method may further include sending the signal if the accumulated total current conduction time value exceeds fourteen fundamental frequency current cycles for a 60 Hz power system, and wherein the accumulated total current conduction time value may be reduced by a prorated equal percentage of 10 days or 30 days for each day current conduction is not detected when the contacts are open. The method may alternatively include storing and saving the accumulated total current conduction time value if the contacts are closed. In yet another embodiment, the method may further include sending an information signal if the accumulated total current conduction time value reaches 40% of the predetermined current conduction timer threshold, sending a warning signal if the accumulated total current conduction time value reaches 80% of the predetermined current conduction timer threshold, and sending an error signal if the accumulated total current conduction time value reaches 100% of the predetermined current conduction timer threshold. In still an further alternative embodiment, the predetermined current conduction value is 2 amperes root mean square (RMS) at fundamental frequency. In another embodiment the vacuum interrupter-based switching device may be part of a pole unit associated with a recloser.
In another of the herein described embodiments, a system for detecting a vacuum leak in a vacuum interrupter-based switching device may include means for monitoring for current conduction when contacts of the switching device are open after a predetermined delay; means for adding a current conduction timer unit that accumulates current conduction time to an accumulated total current conduction time value if a magnitude of the detected current conduction exceeds a predetermined current conduction value; means for reducing the accumulated total current conduction time value a certain percentage of a predetermined timer value over a settable reset time value if current conduction is not detected; and means for sending a signal if the accumulated total current conduction time value exceeds a predetermined current conduction timer threshold. The system may further include storing and saving the accumulated total current conduction time value if the contacts are closed. Alternatively, the means for sending a signal sends an information signal if the accumulated total current conduction time value reaches 40% of the predetermined current conduction timer threshold, may send a warning signal if the accumulated total current conduction time value reaches 80% of the predetermined current conduction timer threshold, and sends an error signal if the accumulated total current conduction time value reaches 100% of the predetermined current conduction timer threshold. Alternatively, the means for sending a signal may send an information, alarm or error signal depending on the accumulated total current conduction time value. In still further alternative the means for reducing the accumulated total current conduction time value reduces a variable or fixed amount of a predetermined timer value over a settable reset time value if current conduction is not detected when the contacts are open.
In yet another alternative embodiment, a method for detecting a vacuum leak in a vacuum interrupter-based switching device may include measuring current conduction across contacts of the switching device when they are open; determining a voltage across the switching device when the current conduction occurs; calculating a power value using the measured current and the calculated voltage; and comparing the power value to a power threshold to determine if the power value indicates loss of vacuum in the switching device. In this embodiment, measuring current conduction may include calculating a root mean square (RMS) current magnitude and phase angle value, which may include that the RMS current magnitude and phase angle value is calculated over the current conduction time. In another embodiment, determining a voltage may include calculating the voltage by subtracting a voltage measurement provided by a first voltage sensor at one side of the switching device from a voltage measurement provided by a second voltage sensor at an opposite side of the switching device. In still another embodiment, determining a voltage may include measuring the voltage. In yet an alternative embodiment, comparing the calculated power value to a threshold may include making the power threshold well above an expected power in the switching device so as to compensate for current and voltage sensor inaccuracies. In still another alternative embodiment, the method may include providing a warning signal if the power value exceeds the power threshold for a predetermined time interval. In a further alternative embodiment, comparing the power value may include comparing the power value to a calculated power value of at least one other vacuum interrupter-based switching device, wherein the number of vacuum interrupter-based switching devices is three and further wherein the vacuum interrupter-based switching devices are part of a pole unit associated with a pole mounted recloser.
In another of the herein described embodiment, a method for detecting a vacuum leak in a vacuum interrupter-based switching device that is in each of three pole units associated with a three-phase pole mounted recloser, may include measuring current conduction across contacts of the switching device when they are open; calculating a voltage across the switching devices when the current conduction occurs by subtracting a voltage measurement provided by a first voltage sensor at one side of the switching device from a voltage measurement provided by a second voltage sensor at an opposite side of the switching device; calculating a power value for each switching device using the measured current and the calculated voltage; and comparing the calculated power values to a power threshold and to each other for the three-phase pole units of the switching devices to determine if the power value indicates loss of vacuum in any one of the pole units. In an alternative embodiment measuring current conduction includes calculating a root mean square (RMS) current magnitude and phase angle value at fundamental frequency, and wherein further the RMS current magnitude and phase angle value is calculated over a current conduction time interval. In yet another alternative embodiment, comparing the power value to a threshold may include making the threshold well above an expected power in the switching device so as to compensate for current and voltage sensor inaccuracies. In still another alternative embodiment, the method may include providing a warning signal if the power value exceeds the power threshold for a predetermined number time interval.
In another of the herein described embodiments, a system for detecting a vacuum leak in a vacuum interrupter-based switching device, the system may include means for measuring current conduction across contacts of the switching device when they are open; means for determining a voltage across the switching device when the current conduction occurs; means for calculating a power value using the measured current conduction and the calculated voltage; and means for comparing the power value to a power threshold to determine if the power value indicates loss of vacuum in the switching device. In alternative embodiments, the means for measuring current conduction may calculate a root mean square (RMS) current magnitude and phase angle value, wherein the RMS current magnitude and phase angle value is calculated over the current conduction time. In still further alternative embodiments, the means for determining a voltage calculates the voltage by subtracting a voltage measurement provided by a first voltage sensor at one side of the switching device from a voltage measurement provided by a second voltage sensor at an opposite side of the switching device. In still a further embodiment, the means for determining a voltage measures the voltage.
In accordance with still additional herein described embodiments, method for detecting a vacuum leak in a vacuum interrupter-based switching device may include measuring current conduction across contacts of the switching device when they are open; determining a voltage across the switching device when the current conduction occurs; calculating a resistance value using the measured current and the calculated voltage; and comparing the resistance value to a threshold to determine if the resistance value indicates loss of vacuum in the switching device. In another embodiment, measuring a current conduction may include calculating a root mean square (RMS) current magnitude and phase angle value at fundamental frequency, and wherein the RMS current magnitude and phase angle value may be calculated over a current conduction time interval. In still another embodiment, a voltage may include calculating the voltage by subtracting a voltage measurement provided by a first voltage sensor at one side of the switching device from a voltage measurement provided by a second voltage sensor at an opposite side of the switching device, wherein determining a voltage includes measuring the voltage. In still another embodiment, the method may further include determining a resistance value of a plurality of vacuum interrupter-based switching devices using voltage and current during a current conduction time interval and determining a maximum/minimum resistance ratio value from the calculated resistances at certain sample points, wherein comparing the resistance value to a threshold includes using the resistance ratio value to determine the threshold so as to compensate for sensor inaccuracies, wherein the plurality of vacuum interrupter-based switching devices may be three vacuum interrupter-based switching devices and wherein the vacuum interrupter-based switching devices may be part of a pole unit associated with a pole mounted recloser. In another embodiment, the method may further comprise providing a warning signal concerning a vacuum interrupter leak if the resistance value exceeds the threshold for a predetermined time interval. In still another embodiment, the threshold may be 100.
In another of the herein described embodiments, a method for detecting a vacuum leak in a vacuum interrupter-based switching device may include detecting current conduction across contacts of the switching device when they are open; determining a resistance value of the switching device during the current conduction; and comparing the resistance value to a threshold to determine if the resistance value indicates loss of vacuum in the switching device. In another embodiment, determining a resistance value may include calculating the resistance value from a measured current through the switching device and a calculated voltage across the switching device, wherein determining a resistance value may include determining an impedance value and determining an impedance value may include using a supervised impedance/resistance relay element.
In still a further herein described embodiment, a method for detecting a vacuum leak in each vacuum interrupter-based switching device that is in each of three pole units associated with a pole mounted recloser may include: measuring current conduction across contacts of the switching device when they are open; calculating a voltage across the switching devices when the current conduction occurs by subtracting a voltage measurement provided by a first voltage sensor at one side of the switching device from a voltage measurement provided by a second voltage sensor at an opposite side of the switching device; calculating a resistance value for each switching device using an impedance element, the measured current and the calculated voltage; and comparing the calculated resistance values to a threshold to determine if the resistance value indicates loss of vacuum in any of the switching devices. In alternative embodiments, measuring a current conduction includes calculating a root mean square (RMS) current magnitude and phase angle value, wherein the RMS current magnitude and phase angle value may be calculated over a current conduction time interval. In an alternative embodiment, a maximum/minimum resistance ratio value is determined from the calculated resistances at certain sample points, and comparing the resistance value to a threshold may include using the resistance ratio to determine the threshold so as to compensate for sensor inaccuracies, wherein the threshold may be 100. In yet another embodiment, the method may include providing a warning signal concerning a vacuum interrupter leak if the resistance value exceeds the threshold for a predetermined time interval.
The foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. One skilled in the art will readily recognize from such discussion and from the accompanying drawings and claims that various changes, modifications and variations can be made therein without departing from the spirit and scope of the disclosure as defined in the following claims.
This application claims the benefit of priority from the U.S. Provisional Application No. 62/779,641, filed on Dec. 14, 2018, the disclosure of which is hereby expressly incorporated herein by reference for all purposes.
| Number | Date | Country | |
|---|---|---|---|
| 62779641 | Dec 2018 | US |
