Analysis and treatment of the causes of internal dampness discharge in 35kV switchgear
Abstract:The article analyzes the original causes of internal discharge of 35kV indoor high-voltage switchgear in Lianzhou 35kV Xijiang Substation and proposes practical preventive measures, which are of positive significance to prevent such internal discharge of switchgear caused by moisture.
Introduction
With the continuous and rapid development of the national economy, the scale of the Shen network is expanding rapidly. As an important part of the power system, the operation of the substation is directly related to the safe and stable operation of the network.
35kV switchgear will be used more and more because of its advantages such as small space occupation and simple installation. This project fundamentally analyzes the causes of moisture in switchgear and manages the moisture problem from various aspects, which has good application prospects.
I. Current situation
35kV indoor switchgear has partially replaced the traditional open type switchgear due to its advantages of small space occupation and simple installation, and has been widely used in the power grid. Qingyuan Lianzhou Power Supply Bureau has two 110kV substations and three 35kV substations using indoor high-voltage switchgear for 35kV voltage level equipment. In the past eight years, the 35kV indoor switchgear of the 1,000 substations were all affected by moisture.
In the past eight years, the 35kV indoor switchgear of the substation has been exposed to moisture and exploded, causing the 35kV equipment of the whole station to be out of service and seriously affecting the normal power supply of customers (1 and 2). In response to this situation, Lianzhou Power Supply Bureau took measures such as installing air conditioners and moisture-proof lamps in the high-voltage room, adding heaters and strengthening blocking in the switchgear bus bar room.
Now the substation uses indoor type 35kv high-voltage cabinet, installs high-power heating and dehumidifying equipment at the bottom of the cabinet, and installs dehumidifiers, air conditioners and Shen cable trench blocking and other measures in the high-voltage room. Although the implementation of these measures to reduce the occurrence of accidents, but the equipment still has the following problems:
High-voltage cabinets still have the sound of local discharge, and the high-voltage room is filled with a strong ozone smell, indicating that the equipment still has discharge; regular local discharge tests on the equipment found that the local discharge data in wet weather seriously exceeded the standard (Figure 3);
Stop by inspection found that the switch contact box and wear plate bushing surface had sticky and discharge traces caused by humidity (Figure 4). The above phenomenon shows that the safety hazard of 35kV switchgear still exists, and measures must be taken to eliminate the hidden danger.
Second, the impact on the equipment and the possible consequences
If no measures are taken, in the rainy season weather, the switchgear operating environment is poor, the insulation performance of the insulation accessories inside the busbar room of the cabinet further decreases, which may occur in the phase discharge of high-voltage equipment, resulting in phase short-circuit fault, serious failure of the switchgear explosion, seriously affecting the safe operation of the equipment.
Three, cause analysis
1、Insulation margin is small:
The latest release of the National Energy Board < twenty-five key requirements for the prevention of power production accidents and the preparation of the interpretation of the explicit provisions: high-voltage switchgear such as the use of heat-shrinkable sleeve wrapped conductor structure, the part must meet the requirements of the net distance of air insulation (for 40.5kV not less than 300mm).
However, switchgear manufacturers use the method of compressed insulation margin in order to reduce the size of the cabinet during design. Some accident cabinets need to improve their insulation accessories to increase insulation strength due to insufficient safety distance.
2, the operating environment is more severe, the relative humidity exceeds the switchgear design using humidity:
In the design of high-voltage cabinets, in order to ensure the circulation of air inside and outside the cabinet, generally left with vents. However, in humid weather, moisture can easily enter the cabinet through these vents and increase the relative humidity inside the cabinet. The 35kV switchgear requires its operating environment to have a humidity level of no more than 70% dry. However, Lianzhou is in a region with frequent dry, warm and wet winds, where the temperature changes quickly and the average relative humidity inside the cabinet can reach 90% in wet weather, which is difficult to meet the technical requirements of the equipment. Damp season in the existing measures in the cabinet bus bar room can still occur condensation, put the day phenomenon.
Too much humidity inside the switchgear, insulation accessories insulation performance decline, may occur between the phase discharge of high-voltage equipment; switchgear internal insulation sheath and high-voltage equipment is not equal by bit, due to the moisture mix may occur with high-voltage equipment put by phenomenon.
IV. Improvement measures
In response to these problems, the following measures are proposed to ensure the safe operation of the switchgear.
1、Increase the insulation margin
It is suggested that 35kV switchgear be replaced with new type insulators, and all busbars in 35kV switchgear be sprayed with new type insulation coating paint by the weak links such as cable room insulators by using the opportunity of stopping by to increase their insulation strength. As shown in the figure below:
After spraying new type insulating material
Replace the new busbar shield wire to form equipotential to reduce the discharge phenomenon of insulation accessories due to potential difference. As shown in the figure below:
Old shield wire New shield wire
2、Optimize the operating environment of the equipment
For the bus bar moisture phenomenon, it is proposed to add a new cabinet condensation dehumidification device in the bus bar room of the high-voltage cabinet. When the change of humidity in the bus bar room inside the cabinet exceeds the set value, the condensing dehumidification device will be automatically activated to dehumidify the bus bar room, reduce the relative humidity inside the bus bar, reduce the condensation and discharge phenomenon inside the bus bar, so as to achieve normal local discharge data and ensure the safe operation of the equipment.
Through the above improvement process, no abnormalities such as discharge phenomena have been found so far. Reduce the condensation and discharge phenomena in the cabinet, so as to achieve the normal local discharge data and ensure the safe operation of the equipment.
Post time: Jun-25-2022
