GB2619722A

GB2619722A - Switch condition monitoring

Info

Publication number: GB2619722A
Application number: GB2208641.7A
Authority: GB
Inventors: An Yuan; Moore Robin
Original assignee: L C SWITCHGEAR Ltd
Current assignee: L C SWITCHGEAR Ltd
Priority date: 2022-06-13
Filing date: 2022-06-13
Publication date: 2023-12-20
Also published as: GB202208641D0

Abstract

A switch (see also figure 1) comprises at least one current breaking contact arrangement 16 and at least one non-current breaking contact arrangement 14 arranged to break electrical contact with a timing difference before the current breaking arrangement. At least one sensor or transducer 18 is arranged to detect the timing difference. The non-current breaking arrangement (figure 3) may comprise a sprung contact 3 and a moving contact. The sensor/transducer may detect movement of the sprung contact as the moving contact separates from it. A drive mechanism (motor 13, shaft 2, shaft 10) may connect the contact breaking and non-contact breaking arrangements and cause the contact breaking arrangement to open after the non-contact breaking arrangement. The current breaking arrangement (figure 4) may comprise a fixed contact 4 and a movable contact 5 connected to the drive mechanism by an overtravel arrangement such that the separation of the fixed/movable contacts is delayed from initiation of the drive. The sensor/transducer may detect the interval between the separation of contacts between the contact breaking and non-contact breaking arrangements. The sensor/transducer may be an accelerometer or position/displacement sensor. Sensor data may be transmitted to a remote monitor to determine an actual or potential deterioration of the switch condition.

Description

Switch Condition Monitoring Technical Field

[0001] The present invention relates an electrical switch and an arrangement for monitoring its condition.

Background

[0002] Switches such as high-current DC switches may be used for a variety of applications, such as in railway trackside equipment designed to isolate and bond the supply rails on three and four rail systems. Remote monitoring of the condition of such equipment is desirable, as this can result in fewer planned maintenance procedures and fewer interruptions to services due to breakdowns. Reducing the number of maintenance procedures is very important with respect to health and safety because the procedures often require access to the side of the railways with the associated dangers of passing rolling stock. Remote monitoring of high-current switches is also desirable in other applications, such as industrial applications.

[0003] The condition of switchgear and distribution equipment can be monitored by measurement of temperature of certain components. For example, the temperature of electrical contacts when passing current can be a good indication of their condition. The surface of the contacts can become eroded, particularly if the contacts are used to interrupt the electrical current. The erosion can result in an increase in electrical resistance. Once the resistance reaches a critical point a thermal runaway situation can arise. However, temperature monitoring may not be suitable in certain circumstances, such as where no current is flowing.

Summary

[0004] Aspects of the invention are defined by the accompanying claims.

[0005] At least some embodiments of the invention, a switch comprises a plurality of contact pairs arranged in parallel. At least one contact pair is designed to interrupt current and is therefore referred to hereafter as a current-breaking contact pair. One or more other contact pairs are designed purely to conduct current and may not function well if they interrupt current and are therefore referred to hereafter as non-current-breaking contact pairs. When the switch is opened, the non-current-breaking contact pair(s) are opened slightly before the current-breaking contact pair(s), thus ensuring that the current is interrupted only by the current-breaking contact pairs.

[0006] The switch may be modular in design; for example, the number of non-current-breaking contact pairs may be chosen according to the nominal current.

[0007] The contacts can be opened or closed manually, or may be driven by a motor, such as an electric motor. The non-current-breaking contacts may be driven directly by the motor and the current breaking contacts may be driven by the motor via a mechanism that quickly separates the current-breaking contacts, for example a spring-driven and/or over-centre mechanism.

[0008] The timing between the opening of the non-current-breaking contact pairs and the current-breaking contact pairs may be important for the correct operation of the switch. If the time delay is too long the current, which may be considerable especially for higher-rated switches and/or under fault conditions, can cause overheating and subsequent damage to the current-breaking contact pairs. If the time delay is too short, there is a possibility the current can be interrupted by the non-current breaking contact pairs.

[0009] Variations in the timing of the opening of the contacts can be caused by wear or faults developing, for example in the driving mechanism which opens and closes the contacts. Variations in the timing of the opening of the contacts can also be indicative of contact wear.

Excessive contact wear can be a cause of overheating and therefore the switch should be subjected to maintenance or replaced before this occurs.

[0010] In at least some embodiments, the time delay between the operation of non-contactbreaking and contact-breaking contact pairs is measured. If the switch were always opened with current flowing it could be possible to measure the time delay by monitoring the current and measuring the time between the opening of the current-breaking contacts and the non-current-breaking contacts. However, the switch may, in normal operation, open when no current is flowing. Hence, one or more sensors or transducers may detect non-electrical properties of the contact pairs.

[0011] In at least some embodiments, two separate transducers or sensors are used to measure the timing between the opening of non-current-breaking and current-breaking contacts. There are many possible transducers or sensors which could be used. A similar type of transducer could be used to monitor both events or, if more appropriate, different types of transducers can be used. An accelerometer may be used to detect when the non-current breaking contacts open. A Hall effect potentiometer may be used to detect when the current-breaking contacts open.

[0012] The interval between the sensed time of the non-current-breaking contacts opening and the current-breaking contacts opening may then be calculated and used to monitor the condition of the switch.

Brief Description of the Drawings

[0013] Specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a perspective view of one example of a switch to which embodiments of the invention may be applied, comprising both current-breaking and non-current-breaking contacts; Figure 2 is a perspective view of an array of conducting members for making contact between pairs of non-current-breaking sprung contacts, for use in a switch of the type shown in Figure 1; Figure 3 is a close-up view showing two of the conducting members making contact between respective pairs of sprung contacts; Figure 4 is a perspective view of one of the current-breaking contacts; and Figure 5 is a schematic diagram of a switch in an embodiment of the invention.

Detailed Description of Embodiments

[0014] Figures 1-4 show one example of a switch to which embodiments of the invention may be applied, while Figure 5 shows schematically an embodiment of the invention applied to this switch.

[0015] The switch may be a high-current DC switch suitable for various applications, such as electric railways or trams, renewable energy, electric vehicle charging, DC distribution networks and industrial processes such as aluminium smelting and arc furnaces. The switch comprises a non-current breaking contact arrangement 14 and a current-breaking contact arrangement 16, arranged electrically in parallel. The non-current-breaking contact arrangement 14 may comprise one or more non-current-breaking contact pairs arranged in parallel. The current-breaking contact arrangement 16 may comprise one or more current-breaking contact pairs arranged in parallel.

[0016] The switch may be driven between open and closed positions by a rotatable axle or shaft 2, that is rotated manually or by a drive motor 13.

[0017] A range of such switches, referred to respectively as Otter 051L to OWL, were available on the applicant's website on 9th June 2022 at http://www.lcswitchgear.co.uk/productiotter-dc-switch-os11-os7r/ [0018] The 0S1 switch has two current-breaking contact pairs and two non-current-breaking contact pairs. The nominal current rating of the 051 switch is 800 A and the nominal current increases as more contact pairs are added, with the 057 switch having seven pairs of noncurrent breaking contacts, with a nominal current of 4,400 A and capable of breaking 13,200 A at 900 V under fault conditions.

[0019] Each of the non-current-breaking contact pairs comprises a conducting member 1 which rotates about the drive shaft 2 at or near its midpoint. As the conducting member 1 rotates in one direction to a closed position, each end la, lb of the conducting member 1 is inserted between a respective set of two sprung contacts 3, as shown in Figure 3. The ends la, lb of the conducting member 1 may taper in cross-section in a direction towards the contacts 3, for example like a knife blade, to facilitate insertion of the ends la, lb. When the conducting member 1 is in the closed position, current passes from one pair of sprung contacts 3, along the conducting member 1 to the other pair of sprung contacts 3. The shapes of the contacts 3 and the conducting member 1 are such that a first end la of the conducting member 1 makes contact with its pair of sprung contacts 3 before a second end lb makes contact with its pair of sprung contacts 3.

[0020] When the conducting member 1 is rotated in the opposite direction, the circuit between the two pairs of sprung contacts 3 is interrupted. The second end lb of the conducting member 1, which made contact with its pair of sprung contacts 3 after the first end la, breaks the circuit between the two pairs of sprung contacts 3. As the second end lb moves out of contact with its pair of sprung contacts 3, these sprung contacts 3 move or vibrate. In an embodiment of the invention, this movement or vibration is be detected by a suitable transducer or sensor 18, as shown schematically in Figure 5. It has been found that the most suitable transducer is a small accelerometer, but acceptable results may be obtained with a displacement sensor.

[0021] As shown in Figure 4, the current-breaking contact pairs each comprise a fixed contact 4 and a moving contact 5. The moving contact 5 rotates about a shaft 10 so as to make or break contact from the fixed contact 4. The shaft 10 is rotated by a drive mechanism 15 which is coupled to the drive shaft 2. The drive mechanism 15 preferably acts to quickly break the moving contact 5 from the fixed contact 4 so as to reduce arcing, for example by means of an over-centre mechanism which translates the continuous rotation of the drive shaft 2 to a sudden rotation of the shaft 10 once the drive shaft 2 reaches a predetermined degree of rotation, for example corresponding to a position when the non-current braking contacts pairs are open. Arcing, which is likely to occur between the fixed contact 4 and the moving contact 5 as the current is broken, is inhibited by an arc splitter plate 11 and an arc chute 12.

[0022] The moving contact 5 is pivotally mounted on a contact carrier 6 and is biased towards the fixed contact 4, for example by a spring 9. The pivotal mounting of the moving contact 5 about the contact carrier 6 allows the shaft 10 to over-rotate after the moving contacts makes contact with the fixed contact 4. This provides an overtravel or lost motion arrangement, increasing the tolerance of the angular position of the shaft 10 when the switch is in the closed condition. The spring 9 also determines the contact force within a defined range. When the drive mechanism is initiated to separate the contacts 4, 5, the initial rotation of the shaft 10 does not move the moving contact 5 in relation to the fixed contact 4. Once the shaft 10 has rotated through an angle equivalent to the degree of overtravel, the moving contact 5 starts to move, increasing the effective moment of inertia of the drive mechanism and resulting in a transient reduction in the angular velocity of the shaft 10. In an embodiment of the invention, this reduction in angular velocity of the shaft 10 is detected using a suitable rotational displacement transducer or sensor 17, as shown schematically in Figure 5. Good results have been obtained using a Hall effect potentiometer, but acceptable results may be obtained with a different type of displacement transducer. It has been found that in practice the contacts 4, 5 separate shortly before the reduction in angular velocity is detected. This delay may be substantially constant so that the time of opening the contacts 4, 5 may be accurately determined by deducting the known delay from the time the reduction in angular velocity is detected.

[0023] The interval between the determined time of the non-current-breaking contacts 14 opening and the current-breaking contacts 16 opening may then be calculated and may be subjected to a test, for example the interval may be compared to a normal range of intervals for correct operation of the switch and/or a change may be detected in the interval relative to one or more previously measured intervals. If the test indicates an actual or potential deterioration in performance of the switch, an error condition may be indicated. The testing and/or indication of an error condition may be done locally, for example by means of one or more processors integrated with or locally connected to the switch. Alternatively or additionally, some or all of the data from the sensors or transducers 17, 18 may be transmitted to a remote or central monitoring facility where the data can be analysed and any maintenance necessary can be determined. The switch may include or be connected to a transmitter or network interface 19 for transmission of the data, which may be by a wired connection or wirelessly using for example a wireless network, such as a mobile data network.

[0024] Other parameters of the switch may be monitored using suitable sensors or transducers. For example, the temperature of the electrical contacts 4, 5 may be monitored using a suitable temperature sensor. Because of the high voltages involved, a non-contact infrared sensor or an array of sensors capable of measuring the temperature of more than one area, such as the Omron D6T range of sensors, is particularly suitable for this task. Other parameters which may be used to monitor the condition of the switch include ambient temperature and humidity, the number of operations performed by the switch, whether each switching operation interrupted the current or not and/or how much current was carried by the switch and for how long.

[0025] Alternative embodiments which may occur to the skilled person on reading the above description may nevertheless fall within the scope of the following claims.

Claims

Claims 1. A switch comprising at least one current-breaking contact arrangement, and at least one non-current-breaking contact arrangement arranged to break electrical contact with a timing difference before the current-breaking contact arrangement, the switch including at least one sensor or transducer arranged to detect said timing difference.
2. Switch of claim 1, comprising a first said sensor or transducer arranged to detect a state of the at least one current-breaking contact arrangement and a second said sensor or transducer arranged to detect a state of the at least one non-current breaking contact arrangement.
3. Switch of any preceding claim, wherein at least one said non-current-breaking contact arrangement comprises a sprung contact and a moving contact, and at least one said sensor or transducer is arranged to detect movement of the sprung contact as the moving contact separates therefrom.
4. Switch of any preceding claim, wherein the at least one current-breaking contact arrangement is connected to the at least one non-current-breaking contact arrangement by a drive mechanism that opens the at least one current-breaking contact arrangement after the at least one non-current-breaking arrangement has been opened.
5. Switch of claim 4, wherein at least one said current-breaking contact arrangement comprises a moving contact and a fixed contact, the moving contact being connected to the drive mechanism by an overtravel arrangement such that separation of the moving contact from the fixed contact is delayed from initiation of the drive mechanism to separate the contacts, and at least one said sensor or transducer is arranged to detect a change in the drive mechanism as the moving contact is separated from the fixed contact.
6. Switch of any preceding claim, wherein at least one of said first and second sensors comprises an accelerometer.
7. Switch of any preceding claim, wherein at least one of said first and second sensors comprises a position or displacement sensor.
8. Switch of any preceding claim, including a transmitter arranged to transmit data derived from said at least one sensor or transducer to a remote monitoring facility.
9. Switch of any preceding claim, including a monitor arranged to use said timing difference to monitor a condition of the switch.
10. Switch of any preceding claim, comprising a high-current DC switch.