Saudi State Grid requires 17.5kV ring main unit

Saudi State Grid requires 17.5kV ring main unit, with typical features as follows:

@Outdoor enclosure;

@There is a separate cable withstand voltage test terminal compartment;

@Adopting self powered protection unit;

@SF6 common box F+F+V (load switch+load switch+circuit breaker) combination;

@Ring network switch unit 630A, outgoing circuit breaker 200A;

@Refer to standard 32-SDMS-11.

The rated voltage of the Saudi State Grid standard ring main unit is 13.8kV, and the rated voltage of the equipment is 17.5kV. The rated frequency is 60Hz, the rated short-time withstand current is 21kA for 1 second, and the peak withstand current is calculated at 2.6 times 60Hz, with 21 * 2.6=54.6kA.

Adopting SF6 insulated box structure, it meets the IP54 protection level and can be directly used for outdoor applications. The upward flip structure is convenient for secondary control and protection operation.

Due to the installation of outdoor boxes and the need for an instrument room, the height of the switchgear should not be too high. Generally, the three position+circuit breaker cabinet is arranged vertically in China, and the height of the switchgear is relatively high. For low height products required by Saudi State Grid, the three position switch+vacuum circuit breaker is arranged horizontally on both sides to reduce height.

However, Saudi State Grid does not have high requirements for width. Compared to the conventional width of 350+350+350mm=1050mm in China, it can be appropriately enlarged. The overall width of less than 1.5 meters is acceptable and can refer to the size of LUCI switchgear as a design basis.

The three position switch and vacuum circuit breaker arc extinguishing chamber are arranged horizontally side by side as shown in the following figure.

For the load switch unit, due to the small size of the sulfur hexafluoride load switch and the generally large gas box, the grounding contact of the three position switch is connected to the sleeve at the front of the gas box of the switch cabinet through a copper rod as the cable withstand voltage test terminal. During the test, the load switch is in the closed position, and the test terminal is connected to the high-voltage testing equipment to directly apply high voltage to test the insulation level of the cable.

After the test is completed, remove the testing equipment, connect the grounding short circuit, reset the grounding switch to the grounding state, close the compartment door, and then operate the grounding switch to disconnect, achieving the normal function of the three position switch.

For the copper busbar connected to the cable withstand voltage test terminal, it needs to withstand short-circuit current, ensuring that it meets the grounding switch closing ability and dynamic thermal stability ability. That is to say, the cross-section of the copper busbar cannot be too small, otherwise it may burn out if it cannot withstand 1s 21kA thermal stability. Therefore, the cross-sectional area needs to meet the requirements.

For passive microcomputer protection, similar to the WIC1 type protection device, the opening operation of the circuit breaker is achieved through a low-energy trip coil. That is, when the external power supply is lost and the short-circuit current reaches the tripping requirement, the passive protection outputs an electromagnetic signal to drive the low-energy trip coil to operate the main shaft and achieve the opening of the circuit breaker.

In addition, there is also protection for the outer shell, which is not achieved through a separate ring main unit and outdoor box form, but through an integrated design, that is, the outer box and the ring main unit are designed as one, and the cable room is part of the outer box to meet the sealing and waterproof requirements. The upper flip type structure makes it easy to check the switch status, as well as the status and inspection of the microcomputer protection device and secondary circuit after opening.

Adopting the integrated form of power supply voltage transformer VT, the voltage transformer directly supplies power to the battery. The battery supplies power to the secondary control circuit and circuit breaker operation circuit through the power module, without the need for external power supply. The secondary control and status circuit adopt communication form, with one wire to achieve communication management with the external backend.