How to detect electrical equipment fault by temperature change?

1. Simple way to detect temperature changes

There are several simple ways to detect temperature changes.

(1) Use your hands to detect by feeling. The temperature reflected in this way varies greatly from person to person, so experience and habituation are important when testing equipment. If you often consciously experience the normal temperature of the device, it is not difficult to determine the abnormal temperature. In general, the temperature of Os can be touched by hand about 60℃.

(2) with stick temperature sheet or coated temperature coating to detect. Similar to the junction of the busbar, the blade of the isolation switch and other parts of the local heat, in the case of running with electricity can not be touched by hand, can stick a temperature sheet or coated with temperature paint, and then through its color changes with the temperature to detect the temperature. Recently there have been a lot of good temperature sheets and coatings on the market, and in the specified temperature can emerge a number of varieties, if affixed 2-3 kinds of temperature is about 60 degrees Celsius temperature can reflect the subtle changes in temperature.

(3) With a fixed installed temperature sensor or thermometer detection. In some special need to monitor the temperature of the parts, such as motor bearings and stator windings, transformer oil and various cooling clamps out of the population and other parts are generally installed ordinary thermometers or temperature sensors, through visual measurement or instrument can know the temperature.

2. Faults that can be found through temperature detection

Here are some examples of faults that can be detected by temperature changes.

A. When the temperature of the motor rises, you can know whether the temperature has changed by touching it and observing the temperature display instrument. However, the fault type is different for different inspection parts. It is divided into several parts for introduction. The temperature of the motor shell, internal winding, bearing, air inlet, exhaust and commutator surface is usually detected.

(1) The temperature of the shell and the inner winding is too high. It may be caused by over-load, single-phase operation, poor winding performance and insufficient air intake. Of course, the maximum allowable temperature of a motor varies depending on the insulation material used. In normal state, there is a large difference between the temperature of the y-class motor shell and that of the F-class motor shell. Therefore, it is not enough to judge whether the temperature is normal or not. It is necessary to understand the temperature resistance level to make a comprehensive judgment. For medium motors, the housing temperature is usually 30-40 cc lower than the internal winding temperature, so the internal temperature can be roughly extrapolated from the housing temperature.

(2) Bearing temperature is too high. If it is a rolling bearing, the temperature is too high may be caused by bearing damage and insufficient lubricating oil. If it is plain bearing, the reason may be metal wear, insufficient oil supply, poor oil cooler, cooling water cut off and so on. In addition, since the maximum allowable temperature rise of the bearing (the surface temperature rise of the bearing when the ambient temperature is 40℃) is specified as 4090, it can be considered that there should be no problem when the bearing housing temperature reaches 80℃. When heat resistant lubricating oil is used in rolling bearings, it is expected to be 10-20℃ higher than 80C.

(3) The exhaust air temperature is abnormal. When the motor adopts forced cooling, the exhaust temperature is an important monitoring data. The reasons for high exhaust temperature may be overload, high ambient temperature, insufficient cooling air flow, abnormal cooler, etc. Especially in the water-cooled cooler, internal rust, deposit scale and so on significantly reduce the cooling effect, must be opened at a certain time to clean.

(4) The surface temperature of commutator is too high. If the temperature of commutator and slip ring of dc motor and wire-wound motor is above specified limits, detailed inspection should be carried out as soon as possible. The high temperature of commutator and slip ring may be caused by abnormal brush pressure, abnormal vibration, current imbalance, insufficient cooling air volume, etc.

B. The temperature rise of electrical contact part is very common in electrical accidents, and electrical joints are very common in power equipment. For example, movable contacts of switchgear; Contact parts of circuit breakers and electromagnetic contactors; Wire and electrical connector (connection terminal), etc. Most of this kind of failure is due to vibration, insulation or aging of the connection screw loosening in the months and years, causing the increase of the contact resistance of this part, in many cases will be due to local heating at the joint and developed into equipment burning accident. Therefore, fastening measures should be taken regularly for parts where the temperature is expected to be too high. Especially for newly installed equipment, it is expected to be re-checked and tightened once within a year.

C. The temperature in the power distribution room is too high. An excessively high temperature in the power distribution room is often ignored. In rooms with a large number of control cabinets using semiconductors, special attention should be paid to failures due to increased indoor temperature. There are many examples where an unexplained control disorder can be rectified by adjusting the air-conditioning system properly. Air conditioning must be used for distribution rooms with control cabinets, etc., containing a large number of semiconductor components. It is hoped that the temperature will be properly managed from an energy saving point of view. The general rule is around 28℃, which makes most people feel comfortable.