Patent Application
20180108461
The present invention is directed to electric power systems and, more particularly, to an electric power arrester containing a temperature sensor, wireless transmitter and visual indication of arrester status.
A voltage surge arrester is a device used on electric power systems to protect the insulation and conductors of the system from the damaging effects of switching and other transient voltage surges. An arrester is typically located in the supply side of a protected load, such as piece of equipment or distribution segment, to protect the load from voltage surges. The arrester includes an internal voltage-variable resistor known as a “varister” that conducts an electric current when the voltage across the arrester reaches a certain voltage to effectively limit the voltage experienced by the protected load to that voltage. A failed arrester behaves Ike an open circuit exposing the protected load to transient voltage surges without the protective voltage limiting effect of the arrester.
Arrester failures are among the most common causes of power outages in electric transmission and distribution systems. Although arrester failure may result from a number of causes, an increase in the internal temperature of the arrester often provides an early warning of impending failures. This is because increasing leakage current through the arrester creates heat that tends to build up until complete failure occurs. Arrester failure can cause local voltage overloads resulting in faults on the system that must be isolated and cleared. Most commonly, arrester failure results in local power outages and lost service to customers as well as expensive field service crews to replace the arrester to return the network to full service.
Conventional maintenance practices involve periodic arrester monitoring with heat detecting infrared (IR) cameras. This is time consuming, difficult because a temperature difference of only a few degrees difference can be an early indication of impending arrester failure. This is problematic because this level of temperature difference is so low that solar heating and other ambient conditions can mask real problems and trigger “false alarm” arrester replacement. This problem is acerbated by the fact that the vast majority of arrester failures result from moisture getting into the arrester housing, which shorts out several varister blocks causing sustained overvoltage on the other blocks. It is difficult, of course, to conduct arrester monitoring during severe when the electric distribution system experiences the highest level of lightning strikes and weather related outages. Even aggressive monitoring during fair weather therefore fails to detect the most common causes of arrester failure. Arresters therefore continue to be a major cause of unplanned outages and transient voltage related power quality events requiring repair activities at any time of day or night. There is, therefore, a need for a more effective approach for electric power arrester monitoring and replacement.
The present invention may be embodied in an instrumented electric power arrester including a temperature sensor, wireless transmitter, and a visual over-temperature indicator. There are several illustrative examples of the temperature sensor/transmitter including a disk shaped module configured to be placed between varister blocks inside the arrester housing, a replacement varister block containing the sensor/transmitter, and a strap-on module configured to be attached to the outside of the arrester housing. The sensor/transmitter may utilize a harvesting power supply that draws electric power for the electronics from the power line protected by the arrester. The sensor/transmitter may also utilize an ambient temperature sensor to enhance accuracy of its temperature measurements.
The temperature sensor/transmitter typically sends arrester monitoring data wirelessly to an RTU or handheld unit located outside the arrester, which relays the monitoring data to an operations control center that scheduled replacement of the arrester based on the monitoring data. The sensor/transmitter may also implement a dynamic data transmission cycle that automatically adjusts to the time required to harvest transmission power.
The instrumented electric power arrester or an associated device may also include a surge counter configured to count a number of temperature surges experienced by the arrester. The surge counter may also count a number of equipment related temperature surges and a number of lightening related temperature surges experienced by the arrester.
It will be understood that specific embodiments may include a variety of features in different combinations, as desired by different users. In view of the foregoing, it will be appreciated that the present invention provides a cost effective high voltage capacitor monitoring system. The specific techniques and structures for implementing particular embodiments of the invention and accomplishing the associated advantages will become apparent from the following detailed description of the embodiments and the appended drawings and claims.
The numerous advantages of the invention may be better understood with reference to the accompanying figures in which:
Embodiments of the invention include an instrumented arrester including a temperature sensor and wireless transmitter (sensor/transmitter) that provides a cost effective solution for continuously monitoring arrester temperature to detect an elevated risk of arrester failure. Autonomous continual monitoring helps to eliminate unexpected arrester failure and unnecessary replacements. Arresters are typically made of housings with a series of internal Zinc Oxide varister blocks in series from line voltage to ground. These varister blocks are the active elements that limit voltage surges on power systems. In various embodiment, a temperature sensor is added as a replacement block into the varister stack, a disk-shaped sensor positioned between varister blocks, or strapped to the arrester housing adjacent to the varister stack. The sensor includes a harvesting power supply that draws electricity to power the electronics from the power line and a wireless transmitter that communicates the arrester monitoring data to an external device, such as remote transmission unit (RTU) or handheld interrogator. The RTU or handheld interrogator typically relays the arrester monitoring data on to an operations control center, which schedules replacement of the arrester as indicated by the arrester monitoring data. The arrester monitor may also utilize and ambient temperature monitor to help distinguish temperature variations due to leakage current from ambient temperature changes. A surge counter keeps track of the number of equipment and lightening related temperature surges experienced by the arrester.
It will be appreciated that a wireless transmissions emanating from inside the central canister formed by the arrester housing are not blocked by the arrester housing (bells) because the housing is constructed from a non-conducting insulator material. Temperature sensors located inside the arrester housing may more precisely measure the actual temperature of the arrester blocks, while an external sensor may be more easily installed without taking the arrester out of service. Measuring ambient temperature helps to improve the accuracy of the external strap-on sensor.
The sensor block may be installed near the center of the arrester as the ends are frequently cooler because of the cooling that comes from the attachments for mechanically supporting the arrester assembly. The sensors typically harvest power for the electronics from voltage pickups located in the high voltage electric field produced by the power line. Other types of harvesting power supplies may be used, such those induce electricity from an external RF energy beam or the magnetic field produced by the power line. Another option includes harvesting the trickle of current that normally passes through the internal varister stack of the arrester. Energy may also be harvested from the electrostatic field between the sensor to ground by virtue of capacitive coupling between a capacitive foil insulated from the sensor, which would could be housed in a cylindrical puck.
The present invention may be embodied in an instrumented electric power arrester including a temperature sensor, wireless transmitter, and a visual over-temperature indicator. There are several illustrative examples of the temperature sensor/transmitter including a disk shaped module configured to be placed between varister blocks inside the arrester housing, a replacement varister block containing the sensor/transmitter, and a strap-on module configured to be attached to the outside of the arrester housing. The sensor/transmitter may utilize a harvesting power supply that draws electric power for the electronics from the power line protected by the arrester. The sensor/transmitter may also utilize an ambient temperature sensor to enhance accuracy of its temperature measurements.
The temperature sensor/transmitter typically sends arrester monitoring data wirelessly to an RTU or handheld unit located outside the arrester, which relays the monitoring data to an operations control center that scheduled replacement of the arrester based on the monitoring data. The sensor/transmitter may also implement a dynamic data transmission cycle that automatically adjusts to the time required to harvest transmission power.
The visual indicator may resemble a bracelet placed around the arrester housing between the “weather sheds.” This type of visual indicator can be easily installed over an existing arrester insulator. This bracelet may carry one or more patch antenna suitable for bidirectional RF communications and receiving power for the LED indicator lights. These patches can also be used to harvest energy from the electrostatic electrical field. While a bracelet placed on the arrester insulator without other connections will be electrically “floating.” Since the top of the arrester is at line voltage and the bottom is at ground, the bracelet will be closely coupled to the power line voltage gradient with an intermediate voltage related to the point on the arrester where the bracelet is placed. This will cause capacitive currents through the housing insulation predominated by the voltage of the arrester at the point where the arrester is located. The stray capacitance to ground will cause a slight shift in this voltage but since this is not a voltage monitor, it will not cause any undesirable issue. Alternatively, energy can be scavenged by having two partially circumferential rings under the edges of this bracelet and using the voltage difference between them to provide sensor power. This uses the voltage gradient along the internal arrester blocks to provide a differential voltage between these rings. These rings will be capacitive coupled to the arrester at the local voltage where the sensor in mounted. This has the advantage of being in close proximity to the arrester, it is easier to obtain the needed energy. With this approach, the bracelet can be placed near the bottom of the arrester where the LED's or other visible indicator allowing technicians in the field to easily see which arrester is indicating a problem.
The arrester monitoring data from these sensors is collected periodically to measure temperature differences, trends and rapidly changing conditions. From this information, an arrangement of measurements and other data can be utilized to schedule maintenance and provide alarms and indications of impending equipment failures. This information is collected by the multiple arresters to uniquely identify specific arresters for careful monitoring and replacement at a time when they can be replaced with minimal disruption to customer service. This allows scheduled arrester replacement based on continual temperature monitoring rather than emergency replacement driven by arrester failure.
The temperature sensor may be a resistance temperature detector (RTD), surface acoustic wave (SAW), thermocouple, or any other suitable type of temperature sensor. RTD sensors are accurate and inexpensive, while SAW sensors are passive devices having the advantage of requiring no power to sense temperature. A SAW sensor can is typically read when illuminated by a signal from a reader, which receives and interprets energy reflected from the sensor. The antenna/sensors may have a unique identity code built into the sensor for identification of the sensor and associated arrester. Powered arrangements can harvest energy to run active transmitters and use thermocouples, RTD or other approaches to sense the temperature.
The sensor/transmitter 12 continually supplies the control center 17 with arrester monitoring data allowing the control center to detect impending arrester failure presaged by a detected increase the temperature of the arrester. This allows arrester replacement to be planned and scheduled, typically during an off-peak, night time or weekend period when the protected load is inactive, without waiting for the arrester to fail unexpectedly. In addition to providing continual autonomous temperature monitoring, the temperature sensor/transmitter 12 that is physically connected to the arrester 11 provides improved accuracy over conventional infrared (IR) readers used to occasionally measure the arrester temperature from a distance. This reduces the occurrence of “false alarm” replacement of properly functioning arresters. False alarms are a persistent problem with conventional arrester maintenance because a relatively low temperature change caused by leakage current through the arrester, in the range of three degrees Celsius, typically indicates an increased risk of failure. This relatively small temperature difference can be easily triggered or masked by solar heating, rain, wind or other ambient conditions.
The arrester 11 includes a hollow cavity filled with a stack of varister blocks separated insulator spacers electrically connected between the protected power line and ground. Many arresters can be opened to remove and replace the varister blocks, which are typically stacked on a central tube and compressed together with a spring. The disk-type temperature sensor/transmitter 12 in this embodiment, with a size that is similar to a spacer, is configured to be positioned within the varister stack either instead of or in addition to a spacer. This configuration allows the disk-type temperature sensor/transmitter 12 to be built into an arrester as original equipment, or as a retrofit component added to a pre-existing arrester. In addition, the arrester may contain multiple disk-type temperature sensor/transmitters, for example between every other varister block such that at least one sensor/transmitter is positioned adjacent to each varister block. This may be an advantageous configuration because each varister block can fail independently of the other blocks.
There are a number of electric power harvesting techniques available to power the electronics of the sensor/transmitter because the arrester is located in the high voltage electro-magnetic field of the power line with a large voltage gradient across the arrester from line potential at the top of the arrester to ground at the bottom of the arrester. For example, the voltage pickup 13 may include two electrodes spaced apart radially (horizontal on
The visual over-temperature indicator 14 can communicate with the sensor/transmitter 12 through a wired or wireless link, either directly or indirectly (e.g., through the RTU 16). As a result, the visual indicator may be positioned in any suitable position on or off the arrester 11. While the bottom of the arrester is a convenient and intuitive location for technicians visually inspecting the arrester, the visual indicator could be located on a control panel, transmitted to a remote unit, or any other suitable location. While any type of visible, audible or other indicator may be used, LEDs are durable, low power, inexpensive well suited for this purpose. The indicator may be attached to the arrester in any suitable way. For example, one option is a resilient band that can be twisted or stretched to fit onto the arrester. Another option is a two-piece bracelet style with a hinge and hasp. Another option is a half-circle rigid band with eyelets on either end fastened to the arrester with a heavy duty cable tie, Velcro strap or band clamp. Another option is two half-circle rigid bands that snap fit into each other. The indicator could also be configured on a stainless steel similar to the strap 91 for the sensor/transmitter shown in
The ambient temperature sensor 15 or 19 may be located in any suitable location that reliably represents the ambient temperature at the arrester 11. The sensor/transmitter 12 or other device that determines over-temperature alarm conditions may use the temperature measured by the sensor/transmitter independently, with respect to the detected temperature, or both. The temperature sensor/transmitter 12 shown in
Distribution and transmission substations typically have preexisting RTUs as part of the Supervisory Control and Data Acquisition (SCADA) used by most electric utilities. The RTU 16 and the Operation and Control Center 17 may therefore be part of a preexisting SCADA system. As all of these components are functionally connected, the software that determines over-temperature alarms from the measured parameters may therefore be located in the sensor/transmitter 12, the visual indicator 14, the RTU 16, the Operation and Control Center 17, the portable unit 18, or any other suitable location. These components may be connected to each other through wired or wireless links, as desired. The portable unit 18 allows data collection from arresters outside of substations, such as locations along power lines, at tap points, transformers capacitors, voltage regulators, customer service points, and so forth.
If the transmit capacitor has been charged up to a minimum transmission threshold, the “Yes” branch is followed from step 122 to step 124, in which the sensor/transmitter records a temperature measurement. Step 124 is followed by step 125, in which the sensor/transmitter determines whether the temperature change since the previous temperature measurement is above a preset threshold, such as two degrees Celsius (2° C.). If the temperature change since the previous temperature measurement is above the preset threshold, the “Yes” branch is followed to step 126, in which the sensor/transmitter transmits the measured temperature. If the temperature change since the previous temperature measurement is not above the preset threshold, the “No” branch is followed to step 127, in which the sensor/transmitter waits for a sleep cycle. Step 127 is followed by step 121, in which the sensor/transmitter wakes up for another transmit cycle.
Is should be noted that the temperature change in step 125 may be a independent measurement of the sensor/transmitter or a relative measurement of the sensor/transmitter with respect to the ambient temperature measurement. For example, sensor/transmitters located inside the arrester may use an independent temperature measurement, while sensor/transmitters located outside the arrester may use a relative temperature measurement. A weighted sum of the sensor/transmitter temperature measurement and the ambient temperature measurement, a temperature dependent scale of weighting factors, or another determined combination may be used based on calibration of the sensor/transmitter.
In step 131, the instrumented arrester detects an over-temperature condition. Step 131 is followed by step 132, in which the instrumented arrester transmits an over-temperature indication along with the arrester model number and location to the RTU.Step 132 is followed by step 133, in which the RTU sends an alert to the operations control center including the arrester model number and location. Step 133 is followed by step 134, in which the operations control center checks the inventory for a replacement arrester and orders a replacement arrester if necessary. If a replacement arrester has to be ordered, step 134 is followed by step 135, in which the operations control center waits for a notice of arrival of the replacement arrester. Steps 134 and 135 are followed by step 136, in which the operations control center creates a work order for replacement of the arrester. Step 136 is followed by step 137, in which a repair crew is dispatched the replace the arrester at a convenient time, such as an off-peak, night or weekend period. Step 136 is followed by step 137, in which the operations control center adjusts the inventory and orders a replacement arrester if appropriate.
Conventional lightening counters utilize current measurements, which requires relatively expensive current sensors (known as current transformers or CTs) to be installed at each monitored arrester. The temperature transmitter/sensor 141 provides a lower cost equivalent because arrester temperature surges are invariably caused by current surges surge counter 144. In addition to counting the total number of surge events, the surge counter 144 can discriminate between equipment related current surges, such as switching and line shorts that cause arrester currents on the scale of hundreds of Amperes, versus lightening related surges that cause arrester currents on the scale of hundreds of Amperes. To do so, a surge detection system utilizes a surge detection temperature change threshold TS (e.g., TS=10° C.) and a lightening detection temperature change threshold TL (e.g., TL=100° C.). The total surge count is the number of surge detection events in which the detected temperature change is greater than TS (e.g., temp. change >10° C.). The equipment related surge count is the number of surge detection events in which the detected temperature change is greater than TS (e.g., temp. change >10° C.) and less than the TL (e.g., temp. change <100° C.). And lightening related surge count is the number of surge detection events in which the detected temperature change is greater than TL (e.g., temp. change >100° C.). The illustrated threshold temperature thresholds are merely illustrative and may vary based on the ambient conditions, the type of arrester, the type of sensor/transmitter, the operating voltage, and so forth.
In view of the foregoing, it will be appreciated that present invention provides significant improvements in monitoring and response systems for high voltage capacitors. The foregoing relates only to the exemplary embodiments of the present invention, and that numerous changes may be made therein without departing from the spirit and scope of the invention as defined by the following claims.
This application claims priority to commonly owned U.S. Provisional Application Ser. No. 62/410,262 entitled “Arrester Temperature Monitor Using RF Communication with Integral Mounted Sensor” filed on Oct. 19, 2016, which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62410262 | Oct 2016 | US |
