Advantages of the SF6 circuit breaker

Most of the electrical distribution substations with a voltage class of 6 kV and above were built in the 1960s. Nowadays, a large number of electrical installations, especially substations, need a complete reconstruction. This is primarily due to the fact that most of the equipment is outdated, not only morally, but also physically.

Circuit breakers are characterized by a low breaking capacity, as they have exhausted their resource for a long time. Relay protection it does not fully protect equipment and power lines, since most of its structural elements, that is, relays, have also served their service life. In general, technical re-equipment of electrical installations is necessary.

When planning work on the technical re-equipment of the substation, the question arises of choosing the type of switching devices, including high voltage circuit breakers.

Vacuum and SF6 circuit breakers are replacing oil circuit breakers as they are characterized by significant advantages.In this article, we will look at the advantages of the SF6 circuit breaker, comparing it to oil-based equipment with the same technical characteristics.

To make the comparison clear, we will give a concrete example. In the 110/35/10 kV substation, the outdoor 110 kV switchgear is being retrofitted. Oil switches of the MKP-110 type were originally installed in this electrical installation.

In accordance with the project for the reconstruction of the switchgear, it is planned to replace these switching devices with SF6 circuit breakers type 3AP1DT-126 manufactured by Siemens.

Let's look at the comparative characteristics of these switchgears to highlight the advantages of SF6 circuit breakers.

The first is the size of the switchgear. The overall dimensions of the SF6 circuit breaker are several times smaller than the dimensions of the oil pan. The weight of SF6 and oil devices is 17800 kg and kg respectively.

As for breaking capacity, the SF6 circuit breaker, despite the fact that it is several times smaller than the oil circuit breaker, is in no way inferior to it and even superior. So, the SF6 device under consideration is able to cut current up to 25 kA, while the number of allowable switching is 20 times. At the same time, the oil circuit breaker can interrupt the current up to 20 kA up to 7 times. After that, it is necessary to repair the switch, in particular, to change the oil.

The SF6 circuit breaker is easier to maintain. When the load current is turned off, SF6 gas does not lose its insulating properties, on the contrary, they improve somewhat, since dust is formed in the process of extinguishing the electric arc. This powder is essentially a good dielectric.

The MKP-110 oil switch drive is electromagnetic.At the time of switching on the switching device activating the solenoid creates a load in the control circuit up to several tens of amperes. The SF6 device is equipped with a spring drive. Maximum load current of closing and opening solenoids, driving motor of the circuit breaker not more than 4 A.

If a cable with a section of 25 squares is run to supply the operating current to the oil pan, then 2.5 squares is sufficient to supply the drive of the SF6 circuit breaker.

The correct opening and closing time of the SF6 circuit breaker is no more than 0.057 s and 0.063 s, and the oil circuit breaker is 0.06 s and 0.6 s, respectively.

Based on the above, there are several advantages of the SF6 circuit breaker:

— ease of use and maintenance;

— relatively low maintenance costs;

— small dimensions;

— high breaking capacity;

— large switching resource;

— little suitable time to switch off and on;

— long service life.