The best solution for switchgear temperature monitoring

Switchgear heating fault causes and key monitoring points

High-voltage switchgear as the core equipment of the power system, in the process of long-term operation, its conductive connection parts are very easy due to mechanical vibration caused by bolt loosening, contact surface oxidation corrosion, installation process defects or long-term overload operation, and the phenomenon of increased contact resistance. According to Joule's law, the current through the high impedance contact will produce a cumulative thermal effect. If not detected and dealt with in time, this hidden temperature rise will accelerate the aging of insulation materials, and ultimately lead to insulation breakdown, short-circuit, or even cause serious switchgear explosion.

In order to prevent such accidents, the following are critical heat generating areas where temperature monitoring is necessary:

• Breaker contacts:In particular, the contact surfaces of the plum blossom contacts and the movable and static contacts are very susceptible to heat generation due to wear and tear or insufficient contact pressure as a result of frequent opening and closing operations.
• Busbar Lap Points:High impedance points are easily loosened at the copper row connection bolts inside the busbar room due to thermal expansion and contraction and micro-vibration.
• Cable Termination Glands:Connectors located in the cable room, which are heavily influenced by the construction process, are a high risk area for overheating faults.
• Disconnect switch contact fingers:When left in operation for long periods of time, fatigue of the contact finger springs or oxidation of the surface can cause an abnormal temperature rise.

1. Fluorescent fiber optic thermometry (recommended)

This is the current high-pressureSwitchgear monitoringIt is the most advanced and stable technology in the world. It utilizes the measurement of the afterglow time of rare-earth fluorescent substances as a single-valued function of temperature.

Technical characteristics:The technology is “intrinsically safe” in that the probe consists of a quartz fiber and fluorescent material and is completely insulated without any electronic components. It is inherently immune to high-voltage electromagnetic field interference, resistant to high voltage, and does not require batteries or inductive power, which fundamentally solves the problem of high-voltage insulation and electromagnetic compatibility. Its data transmission is accomplished through optical signals, which requires no calibration for long-term operation and has a life expectancy of more than 20 years.

2. Wireless radio frequency temperature measurement technology (ZigBee/433MHz)

Wireless temperature measurement was the early mainstream solution, transmitting data via radio frequency signals emitted by wireless sensors mounted on contacts.

Technical characteristics:Sensors are active electronic devices. There are usually two ways of power supply: battery power (there is a risk of replacement cycle and high temperature leakage) or CT inductive power extraction (bus current is small and can not start, there is a monitoring dead zone). In addition, the metal shell of the switchgear cabinet has a shielding effect on radio frequency signals, which can easily lead to packet loss or unstable data transmission.

3. Surface Acoustic Wave (SAW) passive temperature measurement technology

Utilizing the piezoelectric effect, radio waves are emitted by the reader to excite the sensor, which reflects an acoustic signal with temperature information.

Technical characteristics:It realizes the “passivation” of the sensor side and does not need batteries. However, its core disadvantage is that the transmission distance is extremely short (usually only a few meters), and the installation location requirements are harsh, easily blocked by the metal structure of the switchgear cabinet and interference. In addition, the cost of SAW technology readers is usually high.

4. Infrared thermometry

The surface temperature is measured by detecting the infrared energy radiated by the object, which is mainly categorized into in-line infrared probes and infrared temperature measurement windows.

Technical characteristics:Non-contact measurement. Its main defect lies in the “field of view” limitations, must ensure that the probe and the measured point of no obstruction between. At the same time, long-term operation of the lens ash, copper surface oxidation rate changes will significantly reduce the accuracy of temperature measurement, maintenance workload.

5. Fiber Bragg Grating (FBG) temperature measurement technology

Measurements are made using the temperature-sensitive nature of the wavelength of the fiber Bragg grating.

Technical characteristics:It has the insulation and anti-interference advantages of fiber optic sensing. However, fiber grating is also very sensitive to “stress”. Vibration during switchgear operation or bending stress during installation can easily cause wavelength drift, resulting in false temperature readings (cross-sensitivity issues), and is not as good as fluorescent fiber in terms of vibration resistance.

Comprehensive performance comparison table of 5 monitoring programs

Conclusions and recommendations

Considering the safety in high-pressure environment, the stability of long-term operation and the cost of post maintenance.Fluorescent fiber optic temperature measurement technologyIt is the optimal solution for switchgear temperature monitoring at present. It perfectly solves the contradiction between strong electromagnetic interference and high-voltage insulation, and is suitable for long-term use in unattended substations.

If you need to purchase high performance fluorescent fiber optic temperature measurement products or obtain detailed technical solutions, please consult: Fuzhou Innotonics.