Electrical Contactor Health Monitoring

Abstract

A method for monitoring contactor health of an electrical contactor of an electrical device, the electrical contactor being switchable in a switching event between an open state and a closed state or between a closed state and an open state, in response to a switching event command, the method includes determining a current value indicative of a current flowing in the closed electrical contactor at a time proximate the switching event, attributing a percentage of a total contactor life estimate to the switching event based on the current value, determining an updated percentage remaining contactor life estimate by subtracting the percentage of the total contactor life estimate from an initial percentage remaining contactor life estimate, and outputting the updated percentage remaining contactor life estimate.

Description

[Technical field]

[0001] The present disclosure relates to the field of electrical equipment at work sites. [Background technology]

[0002] Electrical contactors are known to have a finite lifespan and are typically capable of a finite number of actuations. The lifespan of a contactor is current dependent and is generally shorter if the contactor is opened when the current draw is higher.

[0003] As an example, the battery of an electric work vehicle includes at least one contactor that is used to open or complete a circuit, making it possible to charge, discharge or isolate the battery. These contactors operate electrically and are typically high-voltage contactors with software-controlled switches. Contactors used in the battery of an electric work vehicle are often supplied with data that gives the expected life of the contactor (in terms of the total number of operations before failure occurs) if the contactor is opened each time at the same given current and voltage. In reality, the contactors in the battery are opened at different currents over their life, so that the life deviates from the supplied data.

[0004] Contactors, which have a finite life that is dependent on current and voltage, may also be found in other electrical equipment on the work site, such as other electric work machines, chargers, generator sets, or other equipment. Summary of the Invention

[0005] Against this background, a method is provided for monitoring contactor health of an electrical contactor of an electrical device, the electrical contactor being switchable between an open state and a closed state or between a closed state and an open state with a switching event. In response to a switching event command, the method includes determining a current value indicative of a current flowing in the closed electrical contactor at a time proximate the switching event. The method further includes attributing a percentage of a total contactor life estimate to the switching event based on the current value, the total contactor life estimate being an estimate of the total life of the contactor. The method further includes determining an updated percentage remaining contactor life estimate by subtracting the percentage of the total contactor life estimate from an initial percentage remaining contactor life estimate, the updated percentage remaining contactor life estimate including an estimate of the contactor life after the switching event, and the initial percentage remaining contactor life estimate including an estimate of the contactor life before the switching event. The method further includes outputting the updated percentage remaining contactor life estimate.

[0006] An apparatus is also provided for monitoring contactor health of an electrical contactor of an electrical device, the electrical contactor being switchable in a switching event between an open state and a closed state or between a closed state and an open state. In response to a switching event command, the apparatus is configured to determine a current value indicative of a current flowing in the closed electrical contactor at a time proximate the switching event. The apparatus is further configured to attribute a percentage of a total contactor life estimate to the switching event based on the current value, the total contactor life estimate being an estimate of the total life of the contactor. The device is further configured to determine an updated percentage remaining contactor life estimate by subtracting the percentage of the total contactor life estimate from the initial percentage remaining contactor life estimate, the updated percentage remaining contactor life estimate comprising a contactor life estimate after the switching event and the initial percentage remaining contactor life estimate comprising a contactor life estimate before the switching event. The apparatus is further configured to output the updated percentage remaining contactor life estimate.

[0007] In this way, the remaining life of the contactor can be monitored by using the current value at which the switching event occurred to impute the percentage of the total contactor life estimate that is estimated to have been used during the switching event. Because contactor life varies with current, this allows for accurate prediction of the contactor's remaining life even though the current may vary between switching events. [Brief description of the drawings]

[0008] Particular embodiments of the present disclosure will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0009] [Figure 1] FIG. 1 illustrates a flow chart illustrating a method for monitoring the health of a contactor according to one embodiment of the present disclosure. [Diagram 2] FIG. 2 illustrates a flow chart illustrating a method for monitoring the health of a contactor according to one embodiment of the present disclosure. [Diagram 3] FIG. 3 shows a schematic histogram of the number of switching events versus current with two distributions (shown in FIGS. 3A and 3B). [Figure 4] FIG. 4 shows a schematic graph of the relationship between the percentage of total contactor life that is reduced during a switching event and the current at which the switching event occurs. [Diagram 5] FIG. 5 shows a schematic graph of the relationship between the total life of a contactor and the current at which a switching event occurs. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] An electrical contactor of an electrical device can be switched in a switching event between an open state and a closed state or between a closed state and an open state. Referring to FIG. 1, a method of monitoring the health of a contactor in response to a switching event command 110 includes determining (at step 120) a current value indicative of a current flowing through the closed electrical contactor at a time proximate to the switching event. The current value may be indicative of a current flowing through the electrical contactor before the contactor switches from a closed state to an open state or after the contactor switches from an open state to a closed state. The current value may include a maximum current in a period including the switching event command. The maximum current may be an actual peak of the current in a period of time or may be close to the peak (e.g., the peak may be between measured current samples, in which case the highest measured current may be selected as the maximum current).

[0011] At step 130, the method further includes attributing a percentage of the total contactor life estimate to the switching event based on the current value, where the total contactor life estimate is an estimate of the total life of the contactor. The percentage of the total contactor life estimate is a percentage estimate of the total contactor life where the contactor life is reduced during the switching event. The percentage of the total contactor life estimate may be further based on a voltage value indicative of the system voltage or the voltage across the open electrical contactor at a time proximate to the switching event. The voltage value may include a nominal voltage value or a measured voltage value. In one embodiment, the voltage value may be known to be the same for all switching events, in which case the percentage of the total contactor life estimate may be based only on the current value. At step 140, an updated percentage remaining contactor life estimate 151 is determined by subtracting the percentage of the total contactor life estimate from the initial percentage remaining contactor life estimate 141. The updated percentage remaining contactor life estimate 151 comprises a contactor life estimate after the switching event. The initial percentage remaining contactor life estimate 141 comprises a contactor life estimate before the switching event. The method further includes outputting the updated percentage remaining contactor life estimate 151 at step 150.

[0012] The updated percentage remaining contactor life estimate 151 may then be used as the initial percentage remaining contactor life estimate 141 for the next switching event. Referring to FIG. 2, a first switching command 110 is made for a first switching event. At step 120, a first current value indicative of a current flowing in a closed electrical contactor at a time proximate to the first switching event. At step 130, the method further includes attributing a first percentage of a total contactor life estimate to the first switching event based on the first current value, the total contactor life estimate being an estimate of a total life of the contactor. At step 140, the first updated percentage remaining contactor life estimate 151 is determined by subtracting the first percentage of the total contactor life estimate from the initial percentage remaining contactor life estimate 141. The first updated percentage remaining contactor life estimate 151 is output at step 150. A second switching command 210 is then made at a later time relative to a second switching event (the next switching event after the first switching event). At step 220, a second current value indicative of a current flowing in the closed electrical contactor at a time proximate to the second switching event. At step 230, the method further includes attributing a second percentage of the total contactor life estimate to the second switching event based on the second current value, the total contactor life estimate being an estimate of the total life of the contactor. At step 240, a second updated percentage remaining contactor life estimate 251 is determined by subtracting the second percentage of the total contactor life estimate from the first updated percentage remaining contactor life estimate 151 (used as the initial percentage remaining contactor life). The second updated percentage remaining contactor life estimate 251 is output at step 250. The second updated percentage remaining contactor life estimate 251 may be used as the initial percentage remaining contactor life of the method in response to a next switching event, and so on.

[0013] This can be further explained via an equation: The updated remaining percentage contactor life after a switching event is given by the following formula: L Re =L R(e-1) -ΔL Re It can be calculated from:

[0014] During the ceremony, L Re is the updated percentage remaining contactor life estimate after a switching event e (with reference to the example shown in FIG. 2, this is the second updated percentage remaining contactor life estimate after a second switching event e), L R(e-1) is the initial percentage remaining contactor life estimate before a switching event and corresponds to the percentage remaining contactor life estimate after a previous event e-1 (with reference to the example shown in FIG. 2 , this is the first updated percentage remaining contactor life estimate after a second switching event e-1), ΔL Re is the percentage of the total contactor life estimate, i.e., an estimate of the percentage reduction in contactor life due to switching event e (referring to the example shown in FIG. 2, this is the second percentage of the total contactor life estimate for the second switching event e).

[0015] Percentage of total contactor life estimate, ΔL Re is the following formula: ΔL Re =100 / N cycles can be calculated from the maximum number of cycles that the contactor is expected to perform at a current value (eg, as specified by the contactor manufacturer).

[0016] N cycles is the expected number of cycles for a particular contactor type at a given current value. N cycles is generally the maximum current value, I MAX , and a function of both the system voltage, V,, i.e., N cycles= f(V,IMAX ). MAX may be determined by taking the maximum current over a period of time that includes the switching event command.

[0017] The method may further include recording the current value (the current value may include a maximum current in a period including a switching event command). The switching current may be recorded by incrementing one of a number of bins. Each bin may correspond to a current range, such that the incremented bin corresponds to a current range that includes the current value. The recorded current value may be communicated to a controller. The bins may be communicated to the controller or operator in the form of a histogram, as a numerical value, or by other means. The bins may correspond to a current range that exceeds a threshold current value. The total number of switching events recorded in each bin may be summed. The total number of switching events recorded in all bins may be summed. In the schematic diagram shown in FIG. 3, two examples of bin distributions are shown for the same set of bins corresponding to the same current range. The number of switching events is plotted against the current. FIG. 3A shows a distribution where most switching events occur in the lower two bins. FIG. 3B shows a distribution where more switching events occur at higher currents than the distribution in FIG. 3A. This may be used in a predictive setting by using the current at which a contactor was previously switched to predict the current at which it may be switched in the future, and thus the number of switching events that the percentage remaining contactor life estimate may correspond to. For example, if a particular contactor is known to normally switch at lower currents (as shown in FIG. 3A), then the percentage remaining contactor life estimate may correspond to a higher number of switching events than if the contactor is normally switched at higher currents (as in FIG. 3B). The number of bins and distributions shown are purely illustrative and may vary considerably. The bins are shown with equal widths for simplicity. The current ranges for each bin may be equal in size or may differ in size.

[0018] Recording the current value of each switching event in this manner may allow an operator or controller to analyze how the contactor was used. It may then be possible to use historical data to provide context to the remaining percentage contactor life estimate. In one embodiment, a user may be notified of switching data based on recorded current data from previous switching events. For example, it may be possible to convert the remaining percentage contactor life estimate to a predicted number of remaining switching events based on previous current values ​​at which switching events occurred. In one example, the predicted number of remaining switching events may be based on a recorded average current value, which may be used to impute a predicted number of remaining switching events based on a lookup table. In another example, the predicted number of remaining switching events may be based on the number of recorded switching events and an initial remaining percentage contactor life estimate (e.g., by calculating the average percentage contactor life used for each switching event). The recorded current values ​​may be used in other ways to predict the number of remaining switching events.

[0019] In one embodiment, a user may be notified if the predicted number of remaining switching events falls below a threshold. For example, the user may be notified via a warning light on the electrical device, a message displayed on a user interface (the user interface may comprise a display on the electrical device, a handheld device, or other display), an electronic message, or other means. In another embodiment, the predicted number of remaining switching events may be converted to a predicted duration of use of the electrical device before the contactor requires replacement. For example, the average time increment between each switching event may be known and used to convert the predicted number of remaining switching events to a duration. In one embodiment, the method may include recording the date and time of the switching event. In one embodiment, a user may be notified if the predicted duration of use falls below a threshold. For example, the user may be notified via a warning light on the electrical device, a message displayed on a user interface (the user interface may comprise a display on the electrical device, a handheld device, or other display), an electronic message, or other means.

[0020] Outputting the percentage remaining contactor life estimate may include at least one of communicating the updated percentage remaining contactor life estimate to a controller and notifying a user of the percentage remaining contactor life estimate. Notifying a user may include displaying the percentage remaining contactor life estimate on a user interface (e.g., on the electrical appliance or via a handheld device).

[0021] The current value may include a maximum current in a period that includes the switching event command. In one embodiment, the current value may include a maximum current from multiple current samples measured before and after the switching event command and at or before and after the switching event command. For example, the current value may include a maximum current from a first current measurement before the switching event command, a second current measurement at the switching event command, and a third current measurement after the switching event command. The current value may include a maximum of a current vector recorded over a defined period that includes the switching event. The current vector may include three or more current values. For example, the current vector may include two to ten current values. In one example, the defined period may be about 10 milliseconds, but may be shorter or longer. In another embodiment, a sensor may be used to detect a maximum current during a defined period (such that an actual maximum current during a defined period is detected rather than selecting a maximum current value from multiple current samples). In another embodiment, the maximum current may be measured at a predetermined time relative to the switching event command, for example, where the time of the maximum current is predicted based on previous measurements.

[0022] The percentage of the total contactor life estimate attributable to the switching event may be further based on a voltage value. The voltage value may be indicative of the system voltage or the voltage across the open electrical contactor at a time proximate to the switching event, as previously described. The voltage value may be a nominal voltage (e.g., where the electrical contactor is known to switch at a given voltage) or may be measured. If the voltage value is measured, the voltage value may include the voltage at the time the current value is measured. For example, the current value may include a maximum current in a period of time that includes the switching event command, and the voltage value may include the voltage measured at the time of the maximum current.

[0023] Attributing a percentage of the total contactor life estimate to switching events based on the current value may be accomplished by comparing the current value to a predetermined list of calibrated current values ​​that correspond to known percentages of the total contactor life. Attributing a percentage of the total contactor life estimate to switching events based on the current and voltage values ​​may be accomplished by comparing the current and voltage values ​​to a predetermined list of calibrated current and voltage values ​​that correspond to known percentages of the total contactor life.

[0024] In one embodiment, the attributable percentage may be a percentage from the list corresponding to the calibration current value closest to the current value at the time close to the switching event. In another embodiment, the attributable percentage may be determined from two percentages from the list corresponding to the two calibration current values ​​closest to the current value at the time close to the switching event. For example, if the current value is between the calibration current values ​​of a given list, the updated remaining percentage contactor life estimate may be determined by linear interpolation (which may be performed on a logarithmic scale). This may be based on the assumption of linearity (on a logarithmic scale) between the percentage of total contactor life at the closest current value above the switching current and the percentage of total contactor life at the closest current value below the switching current.

[0025] The predetermined list of calibrated current values ​​corresponding to a known percentage of the total contactor life may correspond to a voltage at which a switching event occurs. Each of the multiple predetermined lists may correspond to a different voltage. Similarly, the total contactor life as a function of current may correspond to a voltage at which a switching event occurs. The predetermined list of calibrated current values ​​corresponding to a known percentage of the total contactor life (or the total contactor life as a function of current) may be a single switching event (between an open and closed state, or between a closed and open state), or a double switching event (between an open and closed state, and between a closed and open state).

[0026] Referring to FIG. 4, a schematic graph is shown showing possible relationships between the percentage of total contactor life (used in switching events) versus current for three voltages. The solid line is at the lowest voltage, the dashed line is at the highest voltage, and the dashed line is at voltages between the lowest and highest voltages. The percentage of total contactor life used in switching events increases with current. For a given current, the percentage of total contactor life used in switching events is greater at higher voltages. In the example shown, linearity is assumed between the data points (this may occur on a logarithmic scale). There may be more data points than shown, and linearity may or may not be assumed between the data points.

[0027] Referring to FIG. 5, a schematic graph is shown showing possible relationships between the total lifetime of a contactor (as the total number of switching events) versus current, for three voltages. Each point on the graph shows the expected total number of switching events at a given current and voltage that the contactor can undergo during its lifetime, assuming that each switching event occurs at the same given current and voltage. The solid line is at the lowest voltage, the dashed line is at the highest voltage, and the dashed line is at a voltage between the lowest and highest voltage. The lifetime decreases with current. For a given current, the lifetime is shorter at higher voltages. In the example shown, linearity is assumed between the data points (this may occur on a logarithmic scale). There may be more data points than shown, and linearity may or may not be assumed between the data points.

[0028] A predetermined list of calibration current values ​​corresponding to a known percentage of the total contactor life may be determined based on a predetermined list of calibration current values ​​corresponding to a known total contactor life as a total number of switching events (percentage of total contactor life=100 / total number of switching events).

[0029] In another embodiment, a predetermined list of current values ​​corresponding to a known percentage of the total contactor life may be determined from the total contactor life as a function of current and voltage, hi another embodiment, the total contactor life as a function of current is known and may be used to attributing a percentage of the total contactor life estimate to switching events based on the current values.

[0030] In another embodiment of the disclosure, there is an apparatus for monitoring contactor health. An electrical contactor of an electrical device is switchable in a switching event between an open state and a closed state or between a closed state and an open state. In response to a switching event command, the apparatus is configured to determine a current value indicative of a current flowing in the closed electrical contactor at a time proximate to the switching event. The apparatus is further configured to attribute a percentage of a total contactor life estimate to the switching event based on the current value, the total contactor life estimate being an estimate of a total life of the contactor. The apparatus is further configured to determine an updated percentage remaining contactor life estimate by subtracting the percentage of the total contactor life estimate from the initial percentage remaining contactor life estimate. The updated percentage remaining contactor life estimate includes an estimate of a life of the contactor after the switching event, and the initial percentage remaining contactor life estimate includes an estimate of a life of the contactor before the switching event. The apparatus is further configured to output the percentage remaining contactor life estimate.

[0031] The apparatus may be further configured to perform any of the methods presented elsewhere herein.

Claims

1. 1. A method for monitoring contactor health of an electrical contactor of an electrical device, the electrical contactor being switchable in a switching event between an open state and a closed state or between a closed state and an open state, and in response to a switching event command, the method comprising: determining a current value indicative of current flowing through the closed electrical contactor proximate to the switching event; attributing a percentage of a total contactor life estimate to the switching event based on the current value, the total contactor life estimate being an estimate of a total life of the electrical contactor; determining an updated percentage remaining contactor life estimate by subtracting the total percentage remaining contactor life estimate from an initial percentage remaining contactor life estimate, wherein the updated percentage remaining contactor life estimate comprises an estimate of the life of the electrical contactor after the switching event and the initial percentage remaining contactor life estimate comprises an estimate of the life of the electrical contactor before the switching event; and outputting the updated percentage remaining contactor life estimate.

2. The method of claim 1 , wherein the current value comprises a maximum current during a period of time that includes the switching event command.

3. The current value is before, after and at the time of the switching event instruction, or The method of claim 2 , comprising: a maximum current from a plurality of current samples measured either before and after the time of the switching event command.

4. The method of claim 2 , wherein a maximum current is measured at a predetermined time relative to the switching event command.

5. The method of claim 1 further comprising recording the current value.

6. 6. The method of claim 5, wherein the current value is recorded by incrementing one of a plurality of bins, each bin corresponding to a current range, and the bin that is incremented corresponds to a current range that includes the current value.

7. transmitting the recorded current value to a controller; and notifying a user of the switching data based on recorded current data from a previous switching event.

8. The method of claim 7, further comprising predicting the remaining life of the electrical contactor using a distribution of a plurality of bins, wherein the remaining life is: the estimated number of remaining switching events, and and an estimated remaining period of use of the electrical equipment before the end of the life of the electrical contactor.

9. The method of claim 8 , further comprising notifying a user if the life of the electrical contactor falls below a threshold number of remaining switching events or a threshold remaining usage period.

10. outputting the percentage remaining contactor life estimate; communicating the updated percentage remaining contactor life estimate to a controller; and notifying a user of the percentage remaining contactor life estimate.

11. 2. The method of claim 1, wherein the attributing a percentage of a total contactor life estimate to the switching event is further based on a voltage value, the voltage value representing a system voltage or a voltage across the electrical contactor in the open state at a time proximate to the switching event.

12. 2. The method of claim 1, wherein the attributing a percentage of a total contactor life estimate to the switching event based on the current value is accomplished by comparing the current value to a predetermined list of current values ​​that correspond to known percentages of a total contactor life.

13. 13. The method of claim 12, wherein if the current value is between current values ​​of the predetermined list of current values, the updated percentage remaining contactor life estimate is determined by assuming linearity on a logarithmic scale between the percentage of total contactor life at the closest current value above a switching current and the percentage of total contactor life at the closest current value below the switching current.

14. The method of claim 12 , wherein the predetermined list of current values ​​corresponding to known percentages of total contactor life is determined from total contactor life as a function of at least one of current and voltage.

15. 1. An apparatus for monitoring contactor health of an electrical contactor of an electrical device, the electrical contactor being switchable in a switching event between an open state and a closed state, or between a closed state and an open state, the apparatus comprising: determining a current value indicative of current flowing through the closed electrical contactor proximate to the switching event; attributing a percentage of a total contactor life estimate to the switching event based on the current value, the total contactor life estimate being an estimate of a total life of the electrical contactor; determining an updated percentage remaining contactor life estimate by subtracting a percentage of the total contactor life estimate from an initial percentage remaining contactor life estimate, wherein the updated percentage remaining contactor life estimate comprises an estimate of the life of the electrical contactor after the switching event and the initial percentage remaining contactor life estimate comprises an estimate of the life of the electrical contactor before the switching event; and outputting the updated percentage remaining contactor life estimate.

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