Abstract:
An actuator, such as a motor of a power distribution switching device, may be operated by measuring at least one temperature parameter associated with an energy storage device (e.g., a battery) of the actuator, and establishing a recovery period and a reference voltage based on a measured temperature parameter. The reference voltage represents a sufficient terminal voltage of the energy storage device in the operational condition. During testing, a load is applied to the energy storage device for a predetermined time period, and the terminal voltage for the energy storage device is measured during the predetermined time period and compared with the reference voltage as a measure of the capability of the energy storage device to deliver an operational load. Following testing, actuator operation is inhibited for the established recovery period to allow the energy storage device to recover the capability to deliver the operational load. Actuator operation is allowed after the expiration of the actuator recovery period if the measured terminal voltage exceeds the reference voltage at that time.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims priority to U.S. Provisional Application No. 60/646,533, which was filed on Jan. 25, 2005, and is incorporated by reference. 

   TECHNICAL FIELD 
   This document relates to testing batteries and other energy storage devices, and more particularly to measuring the capability of a rechargeable battery or other energy storage device to operate a power distribution switching device. 
   BACKGROUND 
   Battery tests for high-power, rechargeable batteries are inherently complicated. In many situations, especially where the batteries are used to power heavy-duty motors, it is often not sufficient to determine whether a battery is fully charged, because the battery may exhibit correct voltage at the terminals or even deliver its rated load for a short time, and yet fail to power the motor over a longer period. The problem of correctly evaluating battery capability is particularly relevant for batteries powering motor-operated power distribution switches. Power distribution switches are often located in remote areas and are difficult to service. Therefore, it is important to prevent battery failures before they cause full-blown power switch failures. However, because motor batteries powering the switches remain idle for long periods of time and have to operate during extreme temperatures, the traditional load tests for these batteries may produce inaccurate results. As a result, the motor battery may pass the traditional load test, yet fail to supply enough energy to open or close a power distribution switch during actual operation. 
   SUMMARY 
   Operation of an actuator may include measuring at least one temperature parameter associated with an energy storage device of the actuator, and establishing a recovery period and a reference voltage based on the measured temperature parameter. For example, the actuator may be a motor of a power distribution switching device, and the energy storage device may be a battery that powers the motor. The reference voltage represents a sufficient terminal voltage of the energy storage device in the operational condition. During testing, a load is applied to the energy storage device for a predetermined time period, and the terminal voltage for the energy storage device is measured during the predetermined time period and compared with the reference voltage as a measure of the capability of the energy storage device to deliver an operational load. Following testing, actuator operation is inhibited for the established recovery period to allow the energy storage device to recover the capability to deliver the operational load. Actuator operation is allowed after the expiration of the actuator recovery period if the measured terminal voltage exceeds the reference voltage at that time. 
   In one general aspect, temperature-compensated operation of an actuator includes measuring at least one temperature parameter associated with an energy storage device of the actuator, computing at least one temperature-dependent variable based on at least one of the measured temperature parameters, and restricting one or more actuator operations based on at least one of the temperature-dependent variables. 
   Implementations may include one or more of the following features. For example, the actuator may comprise a motor, and the energy storage device may comprise, for example, a battery or a capacitor. 
   The temperature-dependent variable comprises an energy storage device recovery period, and restricting one or more actuator operations may include inhibiting actuator operation for the computed recovery period to allow the energy storage device to recover the capability to deliver its operational load. A user may be notified that actuator operation has been inhibited. 
   A reference voltage that represents a sufficient terminal voltage of the energy storage device to operate the actuator may be computed based on at least one of the measured temperature parameters. A load test may be performed on the energy storage device by applying a load to the energy storage device for a predetermined time period, measuring a terminal voltage for the energy storage device during the predetermined time period, and comparing the terminal voltage with the reference voltage as a measure of the capability of the energy storage device to operate the actuator. The load may include the actuator and/or a predetermined resistive load. Actuator operation may be allowed after the expiration of the recovery period if the measured terminal voltage exceeds the reference voltage, or inhibited after the expiration of recovery period if the measured terminal voltage does not exceed the reference voltage. 
   The temperature-dependent variable also may include the number of actuator operations without an external power source, or an allowable time for actuator operations without the external power source. Actuator operation may be inhibited after exceeding the allowable number of actuator operations or the allowable actuator operation time without the external power source. The external power source may be an AC power source or a DC power source. 
   The temperature parameter may include an ambient temperature within a housing of the actuator or a surface temperature of the energy storage device. 
   In another general aspect, operating an actuator includes applying a load to an energy storage device of the actuator for a predetermined time period, measuring a terminal voltage for the energy storage device during the predetermined time period, and comparing the terminal voltage with a reference voltage that represents a sufficient terminal voltage of the energy storage device to operate the actuator. When the comparison indicates that the energy storage device is unable to operate the actuator, actuator operation is inhibited for an energy storage device recovery period associated with the energy storage device to allow the energy storage device to recover the capability to deliver its operational load. 
   Implementations may include one or more of the features discussed above. For example, as noted above, the load may be the actuator or a motor of the actuator, and the energy storage device comprises a battery. 
   The details of one or more implementations are set forth in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims. 

   
     DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram of a switch. 
       FIG. 2  is a flowchart illustrating a battery test. 
       FIG. 3  is a flowchart illustrating a temperature-compensated motor battery test. 
       FIG. 4  is a flowchart of a battery recovery procedure following the motor battery test. 
       FIG. 5  is a flowchart of a recovery procedure following the loss of AC power to a device including a battery. 
   

   Like reference symbols in the various drawings indicate like elements. 
   DETAILED DESCRIPTION 
   A switch allows a switch operator to perform two distinct battery tests. First, a quick control battery test allows the operator to test the capability of a battery through a traditional load test of a predetermined resistive load. However, in some cases, the battery may pass the load test and still fail to operate the motor. Therefore, an additional motor battery test is provided to assure that the battery has sufficient energy to power the motor. 
     FIG. 1  shows a switch system  100  for controlling and monitoring the operation of contacts  105  that may be used to selectively make or break a connection between power lines  110  and  115 . For example, the switch system  100  may control the contacts  105  to break the connection so as to provide fault protection between the power lines  110  and  115  and/or to isolate problem areas based on trouble that may be sensed by a remotely-located protective relay or by the switch system  100 . The switch system  100  may include assemblies of switching or interrupting devices, along with control, metering, protective, and regulating devices. For example, the system  100  may act as a recloser, a switch, or a breaker. In one implementation, the switch system may provide switching and/or tying operations between connections of the electrical power lines  110  and  115 . 
   The switch system  100  includes a switch controller  120  connected to a motor  125 , a battery  130 , a temperature sensor  135 , and a testing load  140 . The controller  120  includes an interface and other electronic circuitry through which a user can monitor and control the operation of the switch. For example, the controller  120  may be operated through a communication interface  145 , a front panel  150 , or a datagram interface  155 . In one implementation, the front panel  150  may include various LEDs or other indicators to visually communicate with a user, such as a “Battery Test in Prog” LED  160  and a “Low Battery Voltage” LED  165 . Under control of the controller  120 , the motor  125  operates the contacts  105  to provide switching operations between power lines  110  and  115 . In one implementation, the switch may connect or disconnect power lines  110  and  115  by making or breaking a power circuit connection between the contacts  105  and the power lines. 
   The controller  120  and the motor  125  share a common connection to the battery  130 . The controller  120  is also connected to an AC power source  170  that provides power to the controller  120  as well as power for charging the battery  130 . In addition, the controller  120  is able to gather various performance and operational statistics from the battery  130  and the temperature sensor  135 . For example, the controller  120  may measure the terminal voltage of the battery  130  by applying the testing load  140  to the battery  130 , and the temperature sensor  135  may measure the temperature of the CPU of the controller. Based on the collected statistics or in response to a user request, the controller  120  may run or schedule various battery tests. For example, the controller  120  may schedule motor battery tests every 24 hours at user-defined times, may perform the battery test in response to user input from one of the interfaces  145 - 155  of the controller, or may perform the test during AC-power loss scenarios. 
     FIG. 2  shows a method  200  of load testing motor batteries that may be employed by the controller  120 . The controller  120  connects the testing load  140  to the battery  130  for a predetermined time period and then measures the terminal voltage of the battery. If the terminal voltage remains above a certain predetermined threshold for a given period, the battery  130  is considered operational. In the beginning of the test, the controller illuminates the “Battery Test in Prog” LED  160  ( 205 ). Next, the controller connects the 5-ohm resistive load  140  to the battery  130  for 5 seconds ( 210 ). During the 5 seconds, the controller measures the terminal voltage of the battery  130  ( 215 ). If the measured voltage drops below 22.8 volts for at least one second, the battery  130  is considered drained. In such a situation, the controller  120  illuminates the “Low Battery Voltage” LED  165  ( 220 ) and generates an additional sequence of safety operations, such as inhibiting the motor  125  ( 225 ). In certain implementations, the LED  165  may only be deactivated, and the safety operations may only be reversed, when the battery passes a subsequent test. If the terminal voltage does not drop below 22.8 volts for at least 1 second, then the battery  130  is considered operational and the controller takes no responsive action ( 230 ). 
     FIG. 3  illustrates a motor battery test  300  that accurately determines whether the battery  130  is capable of powering the motor  125  under varying temperature conditions. The motor battery test may be administered separately or in conjunction with the control battery test  200 . For example, the test  300  may be initiated as a further check after the test  200  determines that the battery  115  is operational. 
   The motor battery test may be triggered ( 305 ) by, for example, manipulation of a front panel key, receipt of a test request through a communication interface, actuation of application datagram push buttons, as a daily automatic test, or by the controller as part of a loss of AC motor battery test such as is described below. Initially, the controller  120  illuminates the “Battery Test in Prog” LED  160  ( 310 ). Next, the controller  120  energizes electromechanical brakes of the motor  125  to operate without any external load ( 315 ). If the switch is in the “Open” position, the controller  120  energizes only the opening contactors ( 320 ). On the other hand, if the switch is in the “Closed” position, the controller  120  energizes only the closing contactors ( 325 ). After enabling the motor  125  and releasing the brakes, the controller  120  operates the motor  125  ( 330 ), simulating an actual open or close operation. In one implementation, the motor is operated for 0.5 seconds. Since the clutch is not engaged, the position of the switch does not change. While operating the motor  125 , the controller  120  measures and determines the minimum terminal voltage of the battery  130  and compares it to a Minimum Operate Threshold Voltage (MOTV). MOTV is temperature dependent. In general, as battery temperature rises, electrochemical activity in a battery increases. Conversely, electrochemical activity in a battery decreases as temperature falls. Therefore, the battery will tend to generate higher terminal voltages at higher temperatures, and the MOTV increases with temperature. The computation of MOTV is described below. 
   First, the controller  120  measures the (control) temperature of the CPU of the controller ( 335 ). Due to the internal self-heating, there is a temperature difference between the ambient temperature (e.g., the ambient temperature within a housing that contains the controller) and the temperature measured by the temperature sensor  135 . As a result, the control temperature is usually higher than the ambient temperature. The two temperatures may be related according to the equations below:
 
 T   difference =−0.127( T   control )+12.58
 
 T   ambient   =T   control   −T   difference  
 
   The controller  120  next checks the measured control temperature for validity. The valid measurements must remain between −45 C and +90 C. The controller  120  considers measurements falling outside of this range to be invalid and, when faced with such measurements, assigns a default value to MOTV ( 342 ). If, on the other hand, T control  is valid ( 340 ), the controller  120  computes the value of MOTV based on Table 1 ( 345 ). 
   
     
       
             
             
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Tcontrol 
               −15 &lt;= T 
               −15 &lt;= T &lt;= 15C. 
               &gt;=15C. 
               Invalid Value 
             
             
                 
             
           
           
             
               MOTV 
               19.7 V 
               20.5 V 
               20.5 V 
               20.5 V 
             
             
                 
             
           
        
       
     
   
   In the final stages of the test, the controller  120  compares the measured battery voltage to MOTV ( 350 ). If the measured voltage is less than MOTV, the controller  120  decides that the battery  130  does not have sufficient stored energy to safely open or close the power switch. In such a situation, the controller  120  illuminates the “Low Battery Voltage” LED  165  ( 355 ) and generates an additional sequence of safety operations, such as inhibiting the motor  125  ( 360 ). On the other hand, if the measured voltage exceeds or is equal to MOTV, then the controller  120  proceeds to the battery recovery mode illustrated in  FIG. 4  ( 365 ). 
     FIG. 4  shows a block diagram of a battery recovery process  400  that may be implemented after the motor battery test or after open/close operations. To begin the process, the controller  120  illuminates the “Battery Recovery Mode LED ( 405 ). Due to a large current drain caused by operation of the motor  125 , the battery  130  requires time to recover before the next operation in order to replenish its stored energy and insure reliable operation of the switch. The recovery time varies according to the control temperature as shown in Table 2. Since Electrochemical activity in a battery normally decreases as temperature falls, the battery  130  generally requires more time to recover at lower temperatures. The controller  120  may measure the value of T control  after the motor battery test or after the open/close motor operation ( 410 ). Alternatively, the controller  120  may reuse the value computed in the first stage of the motor battery test. 
                                   TABLE 2               Tcontrol   −15 &lt;= T   −15 &lt;= T &lt;= 15C.   &gt;=15C.   Invalid Value                   Recovery   15   5 seconds   15   15 seconds       Time   seconds       seconds                    
Once the recovery time is determined, the controller  120  inhibits all motor operations for a computed recovery time in order to ensure that the battery  130  is not used and has a sufficient time to recover the lost energy ( 420 ). After expiration of the recovery period, the controller  120  releases the motor inhibit  125  and turns off the “Battery Recovery Mode” LED  160  ( 425 ). At that point, the battery  130  should recover sufficient energy to perform the subsequent switch operations.
 
     FIG. 5  illustrates a recovery procedure  500  that may be implemented following the loss of AC power to the switch. When AC power is not present, the battery is unable to be recharged. However, since the switch and control are powered by the battery, both remain operational until the battery&#39;s health has been determined to be poor. Whenever AC power is lost, the controller  120  may impose a limit on the number of times the motor  125  can be operated to ensure reliable operation of the switch ( 505 ). In addition, to ensure reliable operation, the controller  120  may disallow the switch operation without AC power after expiration of a certain time limit. Both the operation count limit and the time limit are temperature-dependent. If AC power is lost for more than 60 seconds ( 510 ), the controller  120  measures the control temperature of the battery  130  (T control ) ( 515 ). Next, the controller  120  computes operation and time limits based on Table 3 ( 520 ). 
   
     
       
             
             
             
             
             
           
         
             
               TABLE 3 
             
             
                 
             
             
                 
                 
                 
                 
               Invalid 
             
             
               Tcontrol 
               t T &lt; −15C. 
               −15 &lt;= T &lt; 15C. 
               T &gt;= 15C. 
               Value 
             
             
                 
             
           
           
             
               Number of 
               6 
               12 
               20 
               6 
             
             
               Operations 
             
             
               Operation Time 
               6 
               12 
               24 
               6 
             
             
               (hours) 
             
             
                 
             
           
        
       
     
   
   If the time limit is exceeded ( 525 ) the controller  120  performs the motor battery test, as has been previously discussed with respect to  FIG. 3  ( 530 ). Additionally or alternatively, the controller  120  also may perform the motor battery test once the limit on the allowed number of operations has been exceeded ( 535 ). In this case, the controller  120  inhibits motor operation for a period (e.g., 60 seconds) sufficient to allow for battery recovery ( 540 ) before performing the battery test ( 530 ). 
   If the battery  130  fails the test, the controller  120  inhibits further motor operations, illuminates the “Low Battery Voltage” LED  165  and generates an additional sequence of safety operations, such as inhibiting the motor  125  ( 545 ). 
   If the battery  130  passes the test, the controller  120  determines that the battery  130  has enough stored energy to operate for another six hours or, alternatively, for three full open or close operations ( 550 ). The controller  120  then repeats the above battery testing process every three operations or every six hours until the battery  130  fails the motor battery test when the number of operations is exceeded ( 555 ) or when the time limit is exceeded ( 560 ). Once the battery  130  fails the test, the controller proceeds as noted above ( 545 ). 
   If AC power is returned after the controller  120  inhibits the motor  125  due to failed battery test, another motor battery test is performed at a later time to ensure that the battery  130  has a sufficient amount of stored energy to properly operate the switch. 
   A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made. For example, the methods described above are applicable to other systems using batteries to power electric motors in outdoor conditions. Such systems may include alarm systems, communication equipment, emergency lightning systems, electric powered bicycles and wheelchairs, fire and security systems, geophysical equipment, marine equipment, solar powered systems, and telecommunication systems. Accordingly, other implementations are within the scope of the following claims.