Misunderstandings to be aware of when installing metal oxide arresters

With the widespread development of urban and rural power grid transformation, metal oxide arresters (hereinafter referred to as MOA) have been widely used in 10-500kV power grids. MOA has many advantages such as low residual voltage, no continuous current, simple structure, small size, light weight, easy installation, operation and maintenance. However, in the process of our contact with some users, we found that some units have improper installation when using MOA, which makes MOA unable to play its due protective role and even prone to accidents, threatening the safe operation of the power grid. The correct and incorrect installation methods are illustrated as follows.

1 Comparison of correct and incorrect installation methods of pillar-type bases

In the installation method shown in Figure 1, there is no insulating pad above the connecting plate on the base, and the operating current flowing through the MOA is directly grounded without passing through a counter or an online monitor, so that the counter or the online monitor cannot record the number of MOA operations or monitor the MOA operating current.

The installation method shown in Figure 2 adds an insulating pad above the connecting plate on the base. The operating current flowing through the MOA is grounded through a counter or an online monitor, which can accurately record the number of MOA actions or monitor the operating current of the MOA. This is the correct installation method.

2. Comparison of installation accuracy of counter or online monitoring instrument

In the installation methods shown in Figures 3 and 4, the high and low voltage terminals of the counter or online monitor are connected to the same potential of the MOA. No current flows through the counter or online monitor, making them ineffective and causing the MOA to be ungrounded, which in turn fails to protect the power system. The installation method shown in Figure 5 is the correct installation method.

Comparison of 3 MOA high voltage wiring methods

Due to different levels of attention, the safety distance is considered when wiring MOA with voltage levels above 110kV, but not enough attention is paid to the safety distance of MOA with voltage levels of 35kV and below, especially for MOA installed indoors. The safety distance is not enough for the wiring method shown in Figure 6 (leading down to the power line), which is very harmful:

① It is easy to cause harm to the human body or nearby equipment. ② The high-voltage lead wire is easy to discharge to the lower flange of the MOA, causing grounding fault or overvoltage.

Figure 7 shows the correct installation method (connecting the power line upwards), which ensures sufficient safety distance.

The above describes the more common incorrect installation methods of MOA. The main purpose is to remind users to read the instructions provided by the manufacturer in detail during actual application to avoid accidents or other unnecessary failures due to improper installation. For MOA, in addition to mastering the correct installation method, users should also conduct inspections and maintenance during operation. Before the thunderstorm season every year, MOA preventive tests should be carried out to check whether the components of MOA are in good condition and whether the parameters meet the requirements. If counters or online monitors are installed, they should also be checked to see if they are working properly.

As long as the user unit correctly masters the installation method and operation and maintenance methods of MOA, MOA can play an excellent protective role and contribute to the safe and stable operation of the power system.