GB2301231A

GB2301231A - Thermal olfactory alarm for electril motor winding

Info

Publication number: GB2301231A
Application number: GB9510735A
Authority: GB
Inventors: Patrick Shui-Chung Wang
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 1995-05-26
Filing date: 1995-05-26
Publication date: 1996-11-27
Also published as: DE29609351U1; GB9510735D0; CN1146652A; JP3031563U

Abstract

A thermal olfactory alarm is associated with a winding of an electric motor to provide an indication of undue temperature rise of the winding. The alarm may include two or more temperature rise steps, progressing from advance warning to critical. The alarm does not affect operation of the motor but provides the operator with an indication of an overheating situation developing to enable the operator to take corrective action or at least be aware of a dangerous situation developing.

Description

ELECTRIC MOTOR WITH THERMAL INDICATION This invention relates to electric motors and in particular, to an early warning system indicating potential motor failure due to overheating.

Electric motors are prone to overheating which shortens motor life and may Icad to premature failure should the overheating be excessive or sustained due to heat deterioration of the insulation or lubricating systems.

Overtemperature cut out switches such as bimetal strips, positive coefficient thermistors and fusels, protect the motor by stopping current when excessive heat or excessive current which leads to heat build-up is detected. However, there is no warning that such a condition is approaching. Excessive heating is normally associated with excessive current which occurs, for example, by operating under overload or stall conditions or excessive load cycling, i.e., stopping and starting with a high duty cycle which does not allow the motor to cool down between starts. Also, in some circumstances, the motor users want to be aware that the motor is approaching overload or is overloaded before damage occurs and without the motor being made inoperative.

This can be achieved by providing an olfactory alarm which is arranged to emit a noticeable odour when the winding reaches a predetermined temperature. The olfactory alarm can be arranged to give an indication of increasing temperature of the motor winding by either increasing the rate at which odour is released as the temperature continues to rise within reason or by emitting one or more different odours as the temperature continues to rise.

The predetermined temperature would be between the normal operating temperature range of the motor and the temperature at which damage may occur to the motor.

Usually the first sign of overheating is the smell of burning varnish as the wire of the winding overheats, followed by smoke when the varnish catches on fire and/or plastic parts or other low temperature items start to melt and catch on fire. In severe cases, the insulation is degraded causing electrical shorting and fire.

However, while the varnish or wire insulation will emit an odour (which is distinctive), when it is heated beyond its capacity., this is once the motor has overheated and damage has been caused to the insulation.

Accordingly, the present invention provides an electrical motor comprising a stator assembly, a rotor, a winding associated with at least one of the stator assembly and the rotor and an olfactory alarm associated with the winding, arranged to release a noticeable odour when the winding reaches a predetermined temperature.

The release of the noticeable odour before the motor reaches critical temperature causing damage to the winding, etc., gives ate indication of a potentially dangerous situation, allowing corrective measures to be instigated.

Preferably, the olfactory alarm comprises a substance coated on the wire of the winding, mixed with the insulation of the wire of the winding or impregnated into the winding after the winding has been wound.

Preferably, the olfactory alarm comprises a substance which releases a noticeable odour at about 180"C.

Preferably, the olfactory alarm is arranged to release a noticeable odour at more than one temperature to provide an indication of the rise in temperature of the winding past a predetermined temperature.

Preferred embodiments of the invention will now be described by way of example only.

A typical electric motor has a rotor, a stator assembly and one or more windings associated with the rotor and/or stator assembly. For example, a brush type PMDC motor has a permanent magnet stator assembly and a wound rotor or armature mounted on a shaft of the motor and associated with a commutator for connecting the winding to an external power source. A brushless PMDC motor has permanent magnets fitted to the rotor. The stator assembly comprises a flux ring and a stator winding to provide the rotating magnetic field to turn the rotor. The current through the winding is controlled by an electric circuit to switch the current sequentially through coils of the winding to create the rotating magnetic field. In a universal motor, the stator assembly and the rotor both have windings to provide the magnetic fields.In other a.c. motors, the stator assembly incorporates a winding to provide the stator magnetic field.

In all these motors, there is a winding formed by coils of wire coated with an insulating material, usually electrical varnish, through which electric current is passed to generate a magnetic field to cause the motor to operate, i.e., to cause the rotor to move with respect to the stator. Current passing through the winding causes the winding to heat up. The motor is designed to run at a predetermined temperature chosen depending on the application of the motor. The various components of the motor including the wire of the winding are chosen to withstand operation at this temperature plus a safety margin. For example, the wire of the winding may be rated at 2000C which means that it will withstand continuous operation at 2000C although it will also withstand short periods of time at higher temperatures.However, operating above this temperature will run the risk of burning or charring the insulation (varnish) of the wire, reducing its insulation properties. Prolonged exposure to high temperatures may lead to insulation failure and the possibility of the varnish or other parts of the motor catching on fire.

Although the smell of burnt varnish has a peculiar and noticeable odour, by the time this odour is detected, damage to the motor has occurred and the motor should be withdrawn from service.

By installing an olfactory alarm, the temperature of the motor can be determined without touching the motor and without special instruments such as infrared thermometers or PTC's while allowing the motor to continue to operate. This gives advance warning of a possible overload situation, allowing the operator to reduce load or increase ventilation to enable the motor to cool down and avoid thermal failure or to predict possible life expectancy at current loading depending on the situation.

The olfactory alarm, comprises a substance which is in thermal contact with the winding and which emits or releases a noticeable odour or aroma when it reaches a particular temperature. This gives the operator notice that the motor has reached a particular operating temperature, signalling the need to reduce the load or to provide better ventilation or cooling.

The rate of release of odour may be arranged such that a small volume of odour is released at a predetermined temperature and the rate of release increases as the temperature increases pass the value to give an indication that the temperature is continuing to increase.

In addition or alternatively, the olfactory alarm may contain one or more different substances, or the substance contains one or more different chemicals, arranged to release noticeably different odours as the temperature continues to rise, i.e., a first odour may be released at an initial rate when the temperature of the winding reaches an initial predetermined value indicating a high temperature situation exists. As the temperature continues to rise, the rate of odour release increases. Once the temperature reaches a final predetermined value, a final odour is released indicating that a critical temperature has been reached and possible motor failure is imminent. A number of intermediate steps may be introduced to provide a progressive indication of temperature rise. Ideally, each new odour is more pungent than the previous odour signifying a greater risk to the motor.

The substance or substances of the olfactory alarm may be coated onto the wire of the winding, like a second insulation coating or mixed with the insulation material before the insulation is applied to the wire. Altclnatively, the winding may be impregnated with the substance or substances after the winding has been wound. In the later arrangement, the substance or substances may form at least a part of an encapsulating material protecting the winding from atmospheric contaminants and aiding insulation of the wire from metal parts of the motor, etc.

Other embodiments and variations of the invention will become apparent to those skilled in the art and it is intended that all such variations should be covered by the invention as defined by the appended claims.

Claims

1. An electric motor comprising: a stator assembly; a rotor; at least one winding associated with at least one of the stator assembly and the rotor; and an olfactory alarm associated with the winding arranged to release a noticeable odour when the winding reaches a predetermined temperature.

2. An electric motor as defined in Claim 1 wherein, the olfactory alarm comprises a substance coated on wire of the winding.

3. An electric motor as defined in Claim 1 wherein, the olfactory alarm comprises a substance and the winding is impregnated with the substance.

4. An electric motor as defined in any one of the preceding claims wherein, the olfactory alarm releases a noticeable odour at about 1 800C.

5. An electric motor as defined in any one of the preceding claims wherein, the olfactory alarm is arranged to release noticeable odour at more than one predetermined temperature value to provide an indication of the temperature of the winding.

6. An electric motor as defined in any one of the preceding claims wherein, the olfactory alarm is arranged to increase the rate of release of the odour as the temperature increases past the predetermined temperature.

7. An electric motor as defined in Claim 6 wherein, the rate of release of odour is proportional to the increase in temperature past the predetermined temperature.

8. An electric motor as defined in any one of the preceding claims wherein, the substance of the olfactory alarm comprises zinc oxide.

9. An electric motor incorporating an olfactory alarm substantially as hereinbefore described.