GB2491970A

GB2491970A - Detecting a loose connection in an electricity meter

Info

Publication number: GB2491970A
Application number: GB1210523.5A
Authority: GB
Inventors: Sanjaya Singhal; Kaushik Ghosh
Original assignee: Secure Meters UK Ltd
Current assignee: Secure Meters UK Ltd
Priority date: 2011-06-13
Filing date: 2012-06-13
Publication date: 2012-12-19
Anticipated expiration: 2032-06-13
Also published as: GB201109931D0; AU2012203454B2; GB201210523D0; MY183828A; AU2012203454A1; GB2491970B

Abstract

A loose electrical connection in an electrical apparatus such as an electricity meter is detected by measuring the rate of change of temperature in a housing that contains one or more electrical connections. The temperature sensor 17 measures the ambient air temperature inside the housing and a processor 14 computes the rate of change of temperature, or the acceleration of temperature i.e. the second derivative of temperature with respect to time. The rate of change or acceleration in temperature may be compared to a threshold stored in memory 15. A switch 18 may be activated to cut off the electricity supply if the temperature rate of increase or acceleration is too high, or an alarm signal may be generated. The current in the meter may be measured by current sensor 13 to compensate for changes in load. A thermal model of the apparatus may be used to determine the threshold.

Description

Apparatus and Method for Detecting a Loose Electrical don nection The present invention an apparatus end method for detecting a loose electrical connection in electrical devices. More particularly, the invention relates to sensing of the temperature in the electrical device and Using this information to determine whether there is a loose electrical connection that can potentially be a fire hazard. The invention is suitable for use in electrical devices such as electricity meters that have electrical.

bonnections carrying large currents.

Electricity meters or other similar electrical devices have electrical connections carrying large currents. Electricity meters that measure the consumption of electricity are well known. Many rely on electromagnetic or electronic principles)o measure the consumption. One of the problems that may be encountered particularly in electricity meters that handle large currents is the occasional incidence of a. loose connection (rogue joint) inside the meter at any electrical contact which can cause excessive heating leading to fire.

US 7,513,683 relates to a method, apparatus and system for detecting a problem or deteiloration in an electrical connection and, in particular, remote detection of a problem that results in a temperature above a predetermined level in an electricity.

meter: . . . . -The problem with this method is setting the predetermined level. Meters operateS at all sorts of ambient temperature and the rate of temperature rise in a meter depends not just on the ambient operating temperature but also upon the square of the current flowing through it. Since both these conditions are variable and unpredictable, setting a reliable predetermined value is difficult.

The present invention provides an apparatus and method to detect a potential risk such as a fire due to loose connections inside an electrical device as early as possible without the need for compariáon with a predetermined I preset value and to prevent it by switching off the load. . From a first aspect, the present invention provides an apparatus for detecting a looSe electrical connection, the apparatus comprising: a houáing comprising one or more electrical connections, a temperature sensor for sensing the temperature in the housing; a processor adapted to determine the temperature change in the housing in the basis of the sensed temperature and to further determine the rate of change of the temperature change, a memory to store values of temperature acceleration, one or more load disconnect switch wherein the processor is operable to detect that there is a loose electrical connection on the basis of the further determination.

The rate of change of the temperature change is preferably the acceleration of the temperature change and this is compared with values relevant to that particular apparatus and these values can be based on the load current of the apparatus or historical values of the acceleration and when the acceleration is higher than these values, it can. be deduced that there is a loose connection in the housing. This provides a comparison with a dynamic acceleration value particular to the apparatus which is being monitored and not a fixed level that may not be representative of the acceleration. . The apparatus is preferably an electricity meter and the meter further comprises means for measuring the current flow through the electrical connection.

The meter can continuously measure the acceleration of. the temperature5 change.

Embodiments will now be described with reference to the accompanying drawings, in which: Fig 1. shows a perspective cut away view of an electricity meter according to an embodiment; Fig. 2 shows a block diagram of an apparatus according to an embodiment; and Fig. 3 shows an example circuit of a load that is. being controlled.

In an embodiment of the present invention, electricity meter which may be either a conventional electromagnetic meter or a more modern electronic meter is provided which utilises a current transformer in order to detect consumption of electricity. It will be appreciated that this is simply an example of a device suitable for use with the present invention and that the present invention is capable of being utilised. with different types of electrical devices that have electrical connections carrying large currents.

Referring to Fig. 1, this shows a perspective view of a cut away portion of an electricity meter 10 which can be used in an embodiment. The meter 10 has a housing lOa including a number of components with electrical connections being formed in the meter. When the electricity meter is in use, heat can be generated at the various joints that provide electrical connectiOn. These points of connection are referred to as the "hbtspots". A number of possible locations for hotspots are shown in Fig. I by arrows A1 to A7. Referring to hotspot A1, heat from this hotspot A1 is transmitted by conduction to the bus bars 1112 attached. The bus bars 11,12 and the hotspot A1 radiate heat to other surrounding components. Air around the bus bars 11,12 is heated by conduction.

This principle applies at each of the remaining hotspots A7 to A7. When an electrical connection has deteriorated, the resistance at the connection can increase which in * turn can increase the temperature at the hotspot. It has been found that the ambient air around a particular hotspot in the meter 10 does not heat at. the same rate or to the same extent as the hotspot A1. Also, the temperature within the housing I Oa will vary due to varying currents flowing through the meter 10 andfor due to variation in the ambient conditions external to the housing (such as temperatures changes due to the weather).

Referring to Fig.2, the electricity meter 10 measures electricity consumption by detecting load current utilising a current detector 13 in the form of a current transformer whose output is fed to a computation section which is preferably constituted by a.

microprocessor 14. The result of the computation is then recorded and periodically stored in a memory 15. In addition, the meter 10 may be provided with communication means in the form of a transceiver 16 well known in the art to allow for the meter 10 to be read remotely through a communication link. The electricity meter described thus far is known, to those in the art.

Temperature in the meter 10 is a function of the ambient temperature in which it is operating and the current flowing through it. The ambient temperature at any instant is not known but the load current is known to the microprocessor 14 through the current detector 13.

The rate of heat dissipation from the meter 10 is a function of the meter design (thermal mass, materials used and their properties for transferring heat) and does not change from meter to meter if the meter design is the same. However, the rate will likely be different for different meter designs. A thermal model can be determined for each meter design and programmed into the microprocessor 14 and/or stored in the 30. memory 15 that can be embedded in the microprocessor or a separate memory unit.

Since information relating to the current flowing through the meter 10 is known from the current detector 13, the microprocessor 14 can calculate how much internal, heat is being generated by this current. Based on the thermal model stored in the * memory 15, the microprocessor 14 can calculate the expected temperature acceleration.

Diurna)tèmperature changes are not as rapid as the internal temperature change because of a loose contact and therefore measuring acceleration of temperature rise (rather than velocity) is a quicker method to establish whether loose connections have oOcurred. Therefore, in one embodiment, it is possible to determine the meter's own normal temperature on the basis of the load current without the need for a predetermined value being set for the meter because it uses the value of the current. and its own thermal model to determine its own normal' temperature.

The electrical connections in a meter tend to deteriorate over time creating the hot spots referred to above. When the meter 10 is first installed, the rate of temperature rise and acceleration of temperature rise both reflect good connections.

In another embodiment, data representative of the rate of temperature rise and acceleration of temperature rise can be stored in the memory 15 and over a period of time, the data can be collected to form historical reference data.

Detection of a loose connection is made when currently measured values are compared with this historical reference data and found to be higher than the reference data. Therefore, in this other embodiment, it is possible to detect a loose connection without the need for a predetermined value being set for the meter because it stores historical values of the temperature acceleration which. represent base-line' normal behaviour.

The electricity meter 10 is, provided with a temperature sensor 17 that is preferably a thermometer. The temperature sensor 17 is arranged in the housing lOa of the meter 10 and a' temperature & is read from the sensor 17 at a time t. The' temperature is read automatically by the microprocessor 14.

The microprocessor 14 is further adapted to measure the rate of change of temperature. i.e. d&/dt (the temperature gradient) and can store the measurements in the memory 15. The microprocessor 14 also measures the rate of change of the temperature gradient i.e. d261d9 which could be considered the acceleration of the 30' temperature, change and/or the second differential of the temperature change. The importance of measuring the acceleration is that the acceleration of the temperature change could be quite slow at the beginning and difficult to determine from the temperature gradient alone and the acceleration measurement can provide an early indication that a loose connection exists before a fire may occur. It can also be useful to distinguish between a temperature rise due to the ambient temperature external to' the housing lOa, rising (i.e. due to. diurnal temperature changes in. the environment in which the housing is.located) and a temperature rise due to a hotspot developing at an electrical connection in the housing iDa. The latter will have a higher acceleration of temperature change compared to the former.

The microprocessor 14 may be programmed to only carry out the hotspot detection at certain times of the day which can be fixed or variable.

The microprocessor 14 can also use the output of' the current detector 13 to determine when there are varying currents flowing through the meter 10 and determine if the temperature changes that may be sensed by the temperature sensor 17 are * . expected. Any impact of the current fluctuations due' to load current changes can be filtered out. Therefore, the microprocessor 14 compensates for changes in the current when determining the acceleration of temperature change and it is possible to * 15 determine whether the temperature change has occurred due to a natural temperature rise following on from a change in current flowing through the meter 10 or an unusual change due to a loose electrical connection. The current change can therefore be * measured and the current change is correlated with the temperature change) and a.

determination can be made on whether an alarm condition is to be activated on the basis of,the correlation. In various embodiments, there is therefore the ability to reject false alarms.

In response to a loose electrical connection being detected, the microprocessor 14 can cause the electricity meter 10 to switch off the entire load. A load switch 18 is * ,provided in, the meter 10 for this purpose. By being able to switch off the' supply automatically this provides increased safety in the environment in which the electricity meter 10 iè located by preventing a hazard such as a fire from occurring. Alternatively or in addition, an alarm can be sounded or the meter can send an appropriate signalto a remote central monitoring location such as the electriOity service provider through the transceiver 16 over a communications network. Appropriate action can then be taken by the service provider. . Sometimes a loose connection may be in a controlled circuit in the meter. A controlled circuit will be known to those skilled in the art and may be a water, heating circuit or an electrical space circuit in a meter. In this case, the current in the controlled circuit (which is known to the processor 14) can be used to switch off the controlled circuit only and cause less inconvenience to the user. Fig. 3 shows a diagram having two circuits (identified by numerals 1 and 2) being controlled with L representing live and N representing heutral in the meter 10.

It will be appreciated that the temperature sensor 17 may be embedded in the midroprocessor 14 as may be the memory 15. On the other hand, it is possible for the microprocessor 14 and the memory 15 to be located outside the meter 10 and provided in a separate unit away from the meter as long as the temperature sensor 17 is located within the housing of the meter so as to provide an accurate temperature of the ambient air in the housing.

Accordingly, the electrical device can determine the acbeleration of the temperature taking into account the variety of factors that affect the internal temperature of the device. . H 7

Claims

CLAIMS: 1. An apparatus, for detecting a loose electrical connection, the apparatus comprising: a housing comprising one or more electrical connections; a current supply S provided to the housing; a temperature sensor for sensing the temperature of ambient air in the housing a processor adapted to determine the temperature change in the housing on, the basis of the sensed temperature and to further determine the rate of change of the temperature change, wherein the processor is operable to detect that.there is a loose electrical connectio6on the basis of the further determination.
2. The apparatus according to claim 1, further comprising memory means for storing the temperature change over a period of time and / or a thermal model of the apparatus.
3. The apparatus according to, claim 2, wherein the memory means is adapted to store values of the rate of change of temperature change and the further determination can be compared, to the stored values.
4. The apparatus accdrding to claim 1, 2 or 3, further comprising means for measuring the current flow jn the housing, and means for measuring the heat generated by the current flow, wherein the processor is adapted to determine the rate of change of the temperature change on the basis of the generated heat.
5. The apparatus according to claim 4, wherein the current change is measured by the means for measuring the current flow in the housing, and the current chapge is correlated with the temperature change, and the processor is adapted to determine whether an alarm condition is to be activated on the basis of the correlation.
6. The apparatus according to any preceding claim, further comprising a load switch, wherin the processor is adapted to switch off the load switch when a loose electrical connection is detected thereby switching the load off. .
7. The apparatus according' to any preceding claim wherein the apparatus is an electricity meter.
8. The apparatus according to any preceding blairn wherein, the processor is adapted to determine the acceleration of the temperature change.
9. The apparatus substantially as hereinbefore described with reference to the accompanying drawings.
10. A method for detecting a loose electrical connection, comprising sensing the temperature in a housing that comprises one or more electrical connections through which current flows; determining the temperature change in the housing on the basis of the sensed temperature; determining the rate of change of the temperature change in order to defect that there is a loose electrical connection.
11. The method adcording to claim 10 further comprising storing the temperature change over a period of time and / or a thermal model of the apparatus.
12. The method according to claim 10 or 11 further comprising, measuring a change in current flow through the electrical connection, and determining the rate of change o the temperature change by compensating for the change in current.
13. The method according to claim 12 wherein the current change is measured, and the current change is correlated with the temperature change, and adetermination is made on whether an alarm condition is to be activated on the basis of the correlation.
14. The method according to any of claims 10 to 13 further cothprising switching off current to a load when a loose electrical connection is detected.
15. The method according to any of claims 10 to 14 including the step of determining the acceleration of the of the temperature change.