Causes and monitoring methods of temperature rise of high-voltage switchgear

Ren Yunye (Accuray Electric Co.
, Ltd.
201801) Abstract: In the power transmission system, the high-voltage switchgear of power plants and substations plays a key role, and with the development of power grid equipment technology, high-voltage switchgear has also been widely used
.
In the process of using the switchgear, there is widespread overheating inside the switchgear, and due to the tightness of the switchgear, the temperature rise of the switchgear exceeds the standard in
areas with heavy loads.
In this paper, the reasons for excessive temperature rise and temperature monitoring methods are analyzed by taking the research object of high-voltage switchgear to analyze the causes of excessive temperature rise and temperature monitoring methods, which can effectively prevent the high-temperature failure of high-voltage switchgear and ensure the safety
of high-voltage switchgear.
Keywords: wireless temperature measurement, high voltage cabinet temperature measurement, intelligent control 1 IntroductionThe large-scale development of China's power system has increased the operating pressure of high-voltage switchgear, and with the reform and construction of the power grid, the number of high-voltage switchgear is increasing, increasing the probability of failure
.
At present, the switchgear used inside the power system must be treated by type test to the switchgear connected to the network, and the requirements are relatively strict
in terms of temperature rise.
According to the analysis of relevant theories, it can be seen that in the actual operation process, under normal circumstances, the load will not reach the design full capacity of the switchgear, let alone cause the temperature rise of
the switchgear.
However, this is not
the case.
According to the actual operation experience, with the continuous increase of load, the temperature rise of the switchgear increases
rapidly.
When the load exceeds 75% of the rated current of the switch, the temperature rise is especially pronounced in this case, and the standard requirements
have long been not met.
When the load is relatively low, the temperature rise phenomenon is not obvious
.
In actual operation, compared with the temperature rise data measured in the laboratory, the actual temperature rise level of the switchgear is generally relatively high, and in most cases, when the temperature rise exceeds the standard, the switchgear is even far from reaching the design full capacity
。 For high-voltage switchgear, the actual temperature rise of the switch contacts and busbar connection points is usually always higher than the test data, and the reasons are mainly manifested as: (1) Complete the type test in the laboratory, measure the corresponding data, in terms of duration, although the test time required for stable temperature rise is reached, but the site environment is complex, plus the test process, there is no temperature rise cumulative effect, can not be equivalent to the long-term operation of the site and continuous heating of the equipment
.
(2) There are differences
in the expansion effect of different metals.
The metal expansion system of steel bolts is much smaller than the metal expansion coefficient of copper and aluminum busbars, which is particularly prominent for bolt-type equipment joints, in the actual operation process, with the change of load current, temperature, in terms of expansion and contraction, due to certain differences between aluminum, copper and iron, to a certain extent, creep, that is, affected and restricted by stress, resulting in slow plastic deformation
of the metal 。 Practice has proved that when the operating temperature at the joint exceeds 80 °C, the joint metal expands due to overheating, and at the same time is affected by various factors, further producing tiny voids and early oxidative corrosion
.
When the load current decreases and the temperature decreases back to the original contact position, due to the coverage of the oxide film on the contact surface, the contact resistance becomes larger, and each temperature change cycle will further deteriorate the working condition of the joint, thus forming a vicious circle
.
(3) The tightening bolt pressure at the connection part is unreasonable
.
For conductor connections, in the consciousness of some installation and maintenance personnel, in the process of tightening the connecting bolts, it is believed that the tighter the bolts, the better, but this is not
the case.
Due to the small elastic coefficient of aluminum busbar, when the nut pressure reaches the critical value, if the material strength is relatively poor, when the pressure continues to increase, it will cause the contact surface to deform and bulge, so that the contact area is further reduced, the contact resistance is increased, and then the contact effect
of the conductor is affected.
(4) Due to the insufficient purity of the conductor raw materials, the conductivity of the conductor materials does not meet the requirements
.
(5) Other factors, such as in the process of processing, connecting and installing the busbar, the busbar contact surface treatment is not in place and uneven, thereby reducing the effective contact area, increasing the contact resistance and generating heat
.
The above conditions will cause the temperature rise of the high-voltage switchgear abnormal, so it is necessary
to strengthen the monitoring of the temperature rise of the operating switchgear and take timely measures to find the problem.
There is exposed high voltage in the high-voltage switchgear, the space is closed and narrow, and manual inspection and temperature measurement cannot be carried out, and the traditional temperature measurement method cannot effectively solve this problem
。 In order to solve this problem, the wireless temperature measurement method applied to the high voltage cabinet came into being, wireless temperature measurement is composed of two parts of temperature sensing device and display alarm device, temperature module includes temperature sensor and data transmitter, temperature module can be installed on any heating point in the cabinet, the use of wireless data transmission technology, can telemetry each important part of the heating problem including the contact in the switch cabinet, copper row joints and other non-visible parts, and can transmit the detection data in real time, by the display alarm device installed on the instrument door to receive the record
。 Using fieldbus technology, remote intelligent monitoring can also be realized, so that there is no need for manual on-site survey, there is no potential safety hazard, and the temperature of the high-voltage cabinet is monitored online in real time to avoid equipment failure
caused by high temperature 。 2 Functional characteristics of high-voltage switchgear intelligent control device Accuray Electric Co.
, Ltd.
ASD320/ASD500 intelligent control device with ATE400 wireless passive temperature sensor can be widely used in high-voltage switchgear electrical contact temperature monitoring, in addition to the intelligent control device also has a loop simulation diagram and switch status indication, high-voltage live display and nuclear phase, automatic temperature and humidity control, heating circuit fault alarm, opening and closing circuit integrity indication, opening and closing loop voltage measurement, Pre-divided pre-closed flash indication, human body induction automatic lighting, voice prompt, electrical parameter measurement, RS485 and Ethernet communication interface and many other functions, set operation, display in one, monitor the operation status of the high-voltage switchgear, and provide assistance
for the stable operation of the high-voltage switchgear 。 Wireless passive temperature sensor ATE400 adopts the principle of current induction to provide self-power, starting current is 5A, monitoring temperature range -50 °C ~ +125 °C, accuracy ± 1 °C, can be installed in the high-voltage cabinet switch contacts, copper row / cable joint to achieve temperature collection and upload, product operation is stable, through the test test of Xi'an High Voltage Electrical Apparatus Research Institute, obtained certification report
。 2.
1 Product model function 2.
2 Supporting products and ASD series products used with temperature and humidity sensor and wireless temperature receiver, can be used rail (DIN35mm) installation method, can also use bolt fixing method, wireless temperature sensor has a total of 5 kinds, respectively corresponding to bolt fixing, strap fixing, cable tie binding, alloy sheet fixing and other installation methods, as shown below The battery-powered wireless temperature sensor is installed in the heating part, and the sensor
that collects the temperature and transmits it wirelessly 。 At present, there are four types of wireless temperature sensors: CT induction power wireless temperature sensor installed at the circuit breaker contact, busbar, cable lap point and other large currents, the sensor wireless temperature receiver that collects the temperature amount and transmits it wirelessly3 SummaryHigh-voltage switchgear plays a vital role in power transmission in the power grid, and temperature is an important indicator
for the healthy operation of the switchgear.
Through the online monitoring of temperature, the abnormal state of the switchgear can be found in time, hidden dangers can be found and solved in time, and the safety of the power grid system can be avoided, so as to play an effective role in
the high-voltage switchgear 。 References:[1] Guo Yu and Liu Honglin, Analysis of online monitoring method for high voltage switchgear temperature.
Shandong Industrial Technology, 2017(19).
[2] Xie Liang.
Analysis of actual temperature rise of high voltage switchgear in operation[J].
Electric Power Safety Technology,2005(10).
[3] Chen Xiaoliang, Bao Ling, Gao Yongpeng.
Analysis of the reasons for the actual temperature rise of high-voltage switchgear exceeds the standard, SME Management and Technology, 2015(02).
[4] Accuray Enterprise Microgrid Design and Application Manual.
2022.
05 Edition Author Profile: Ren Yunye, male, Accuray Electric Co.
, Ltd.
, the main research direction is power distribution monitoring
.