GB2186699A

GB2186699A - Temperature sensing means

Info

Publication number: GB2186699A
Application number: GB08703408A
Authority: GB
Inventors: Dennis Jaques
Original assignee: PJO IND Ltd
Current assignee: PJO IND Ltd
Priority date: 1986-02-14
Filing date: 1987-02-13
Publication date: 1987-08-19
Also published as: GB8603740D0; GB8703408D0

Abstract

The invention relates to a temperature sensing arrangement for the critical elements of a balanced three-phase electrical system, such as the cores of a cable or the windings of motors, generators and transformers, where any overheating can be a fire hazard and can cause the shut-down of electrically operated equipment. Temperature sensing means 1 such as resistance sensing elements, thermistors or thermocouples attached to the critical elements generate output signals that are a function of their temperatures, and hence the temperatures of the critical elements. These outputs are fed to monitoring means that preferably is a differencing circuit 3 able to sense the difference between the highest and lowest signal fed to it, and generate an output when the difference is at or above a predetermined maximum. It is also preferred to provide a high temperature selection circuit 5 able to detect that any one or all signals from the sensing means is above a predetermined maximum representing a safe working temperature for the critical elements, and generate a corresponding output. <IMAGE>

Description

SPECIFICATION Temperature sensing means This invention relates to temperature sensing means and is particularly concerned with the sensing of an increase in temperature of an electrical component in a multiple phase electrical system.

There are numerous examples where electrical power must be supplied to electrically operable equipment and where there can be considerable difficulties should the supply of electrical power be interrupted. For the most part cables used for the supply of electricity are of high quality and can be expected to remain in service without difficulty for considerable periods of time. However difficulties can be experienced at the junction or terminal of a cable and should there be any fault at a junction or terminal this can result in overheating of the cable to such an extent that there is breakdown of its insulation leading directly to cable failure.

This phenomenon is not uncommon in harsh working environments such as in deep mining and in the supply of electrical power to equipment at the coal face. In such environments not only is overheating of a cable potentially highly dangerous but also cable failure results in very costly down-time of the machine and lost production.

It is equally the case that there can be an unacceptable temperature rise resulting in overheating of critical parts of a balanced three-phase system, e.g. the windings of a motor or the windings of a transformer.

The object of the present invention is to provide a relatively simple and cost effective means of sensing the temperature of electrical components in a balanced multiple phase electrical system.

According to one aspect of the present invention, a temperature sensing means for the elements of a balanced multiple phase electrical system comprises sensing means attached to each of the elements of the system, each sensing means having an output signal that is a direct function of its temperature and by virtue of being attached to an element a direct function of the temperature of the element, the output signals from all the sensing means being connected to a monitoring unit, the output from which is a function of the signals emitted by the sensing means and hence a function of the temperature of the elements to which the sensing means are attached.

Thus, according to a second aspect of the present invention, a temperature sensing means for the cores of a multi-core cable comprises resistance sensing elements attached to each of the cores of the cable in advance of any junction or terminal to which the cable is attached, each resistance sensing element being connected to a monitoring unit the outputs from which are a function of the resistance and hence the temperature of the cores of the cable. Equally, in accordance with the first aspect of the invention the resistance sensing elements can be attached to any junction or terminal to which the cores of the multi-core cable are attached and whereby the temperature at the junction or terminal can be monitored.

Thus, once the cable and its attendant resi stance sensing elements is installed and connected to a junction or terminal, and the resistance sensing elements connected to a strategically located monitoring unit, the monitoring unit is callibrated to provide a zero output for so long as the cores are at the same temperature. If during operation the temperature of any one core increases by a an amount greater than any other core, this generates an output from the monitoring unit to signal to an operative a potential fault either in the cable itself or, more probably, at the junction or terminal. Additionaliy, if the cores are maintained at the identical temperature, but all simultaneously rise in temperature to beyond a pre-set threshold temperature, then again there is generated an output from the monitoring unit to signal a potential fault.This allows the cable and the terminal to be checked long before cable failure could occur.

In place of resistance sensing elements, the resistance of which rises as the temperature rises, other sensing means can be employed such as thermistors the resistance of which decrease as temperature rises, or thermocouples that generate an electro-motive force or current output that rises as the temperature rises. In the case of resistance sensing elements and thermistors the output from these sensing means can be a voltage or a current, and with thermocouples the output is an electro-motive force or a current, and consequently the circuitry of the monitoring means can be such as to accept either a voltage signal or a current or an electromotive force signal.

In accordance with a third aspect of the present invention, the temperature sensing means is for the critical parts of a balanced three-phase system e.g. three-phase motor windings on high power motors and generators, and individual three-phase transformer windings or the like. Here again by attaching sensing means to each winding any disproportionate rise in temperature of one or other of the windings can be signalled, as can the temperature of any one or all winding exceeding a pre-set limit.

Preferably, the monitoring unit is designed to be operated from a low power supply e.g., less than 6 watts, using a 110 volt or 220 volt AC supply. The output from the unit can activate a suitable visual or audible alarm but preferably it is designed to provide an electrical signal that can be transmitted over a low voltage cable back to a control centre.

The monitoring unit can be programmed to provide a number of signals. Thus, it can be programmed to signal that the temperature of any one element of the electrical system differs from any other element by a pre-set amount and by pre-set increments. It can also signal that the temperature of any one element has exceeded a pre-set safe working maximum, or that all the elements have simultaneously exceeded a pre-set safe working maximum.

One embodiment of the invention wiil now be described by way of example only, with respect to the accompanying, schematic drawing, and which is a circuit diagram in block form of a temperature sensing means in accordance with the invention.

In the drawing, resistance sensing elements 1 are each attached to e.g. the cores of a three-core cable, the resistance sensing elements providing a voltage output that is a function of its temperature and hence the temperature of a respective core and which are fed to a three-channel signal amplifier 2. Three amplified voltage signals are then fed to a differencing circuit 3 able to detect any difference between the three voltage signals fed to it and provide an output signal that is a function of the difference between the highest and lowest input voltage signal to it.The output from the differencing circuit 3 is fed to an appropriate relay or other switching device 4 the arrangement being such that if the difference in voltage detected by the differencing circuit is consequent upon the temperature of any one of the resistance sensing elements having been raised in comparison with any other of the resistance sensing elements by an amount greater than a predetermined maximum, the relay or other switching means is activated to provide an output signal to be fed to an appropriate alarm circuit of either a visual or an audible nature, or provide a signal to a control unit at a remote location, to allow appropriate remedial action to be taken.

In addition to the sensing means of the invention allowing the detection of a differential rise in temperature, it can also indicate an unacceptable rise in temperature of any one or all of the resistance sensing elements to beyond a safe working temperature. Thus, the amplified voltage output from the three-channel signal amplifier 2 can be fed to a high temperature signal selection circuit 5 able to select the signal from the resistance sensing element at highest temperature, there being an output signal from the high temperature signal selection circuit 5 to operate a relay 6 or similar switching device when the output from the high temperature signal selection circuit 5 is above a predetermined limit of a value equivalent to a safe maximum working temperature of the member to which the resistance sensing elements are attached.Here again, the relay 6 can activate a visual or audible alarm or can generate an output signal to be fed to a remote control unit and whereby to enable remedial action to take place.

It is preferred that the temperature sensing means of the invention operates from a low power supply. Thus, AC mains can be fed to a transformer 7 to provide a low power supply of less than 6 watts to a voltage regulating and monitoring circuit 8 providing power to the temperature signal amplifier 2, the differencing circuit 3 and the high temperature signal selection circuit 5. In the event that mains fails, or that the output from the transformer 7 falls below a pre-set minimum required for safe activation of the temperature sensing means of the invention, there is an output signal from the voltage regulating and monitoring circuit that is fed to a relay 9 or other appropriate switching device able to activate an appropriate audible or visible alarm circuit or feed a signal back to a control unit at a remote location.

Claims

1. A temperature sensing means for the elements of a balanced multiple phase electrical system comprising sensing means attached to each of the elements of the system, each sensing means having an output signal that is a direct function of its temperature and by virtue of being attached to an element a direct function of the temperature of the element, the output signals from all the sensing means being connected to a monitoring unit, the output from which is a function of the signals emitted by the sensing means and hence a function of the temperature of the elements to which the sensing means are attached.

2. A temperature sensing means for the cores of a multi-core cable comprising resistance sensing elements attached to each of the cores of the cable in advance of any junction or terminal to which the cable is attached, each resistance sensing element being connected to a monitoring unit the outputs from which are a function of the resistance and hence the temperature of the cores of the cable.

3. A temperature sensing means for the cores of a multi-core cable comprising resistance sensing elements attached to each of the junctions or terminals to which the cores of the cable are attached, each resistance sensing element being connected to a monitoring unit the outputs from which are a function of the resistance and hence the temperature of the cores of the cable.

4. Temperature sensing means for the windings of a balanced three-phase motor, generator, transformer or the like, comprising sensing means attached to each of the windings, each sensing means having an output that is a direct function of its temperature, and by virtue of being attached to a winding, a direct function of the temperature of the winding, the output signals from all the sensing means being connected to a monitoring unit, the output from which is a function of the signals emitted by the sensing means and hence a function of the temperature of the windings to which the sensing means are attached.

5. Temperature sensing means as in any of Claims 1 to 4, wherein the monitoring unit is a differencing circuit able to determine the difference between the highest and the lowest of the signals from the sensing means, and generate an output signal when a difference in the signals from the sensors is detected, and of a level determined by the degree of difference detected.

6. Temperature sensing means as in any of Claims 1 to 5, wherein an alarm circuit is provided, activated by the output from the monitoring unit when that output is above a predetermined maximum.

7. Temperature sensing means as in any of Claims 1 to 6, wherein there is provided a high temperature signal selection circuit to which the signals from the sensing means are fed, to generate an output signal on thede- tection of any one or more of the signals from the sensing means being at or beyond a predetermined maximum representing a safe working temperatue, said output signal activating an alarm circuit.

8. Temperature sensing means as in any of Claims 1 to 7, wherein a signal amplifier is provided between the sensing means and the monitoring unit.

9. Temperature sensing means as in any of Claims 1 to 8, wherein the monitoring unit operates on a lower power supply, and is connected to a transformer to which mains supply is provided.

10. Temperature sensing means substantially as hereinbefore described with reference to the accompanying drawing.