Special Design of 36kV Switchgear

The IEC standard requires a 36kV power frequency withstand voltage of 70kV and a lightning impulse withstand voltage of 170kV. The minimum air clearance required by the IEC60076 standard is 320mm.

The North American standard voltage is 38kV, the power frequency withstand voltage is 80kV, and the lightning impulse withstand voltage is 150kV. There is no requirement for clear distance and creepage distance.

Although they are lower than the national standard of 40.5kV, power frequency of 95kV, and lightning impulse withstand voltage of 185kV, their overall dimensions are generally smaller than domestic 40.5kV switchgear.

IEC 36kV switchgear is generally 1000/1100mm wide and around 2500mm deep. The IEEE C37.20.2 standard metal armored switchgear for 38kV is generally 42 inches with a width of 1066mm and a depth of about 3000, which is slightly larger.

And the width of this voltage level switchgear is very important, directly determining the phase to phase distance. The phase spacing of 36kV circuit breakers is generally 275mm, while that of 38kV circuit breakers is generally 280/300mm.

In terms of system layout, the IEC 36kV layout is more compact, and the bus voltage transformer and line side voltage transformer are generally not separately switchgear, but are together with the circuit breaker switchgear.

The handcart type voltage transformer can be installed on the upper or lower part of the circuit breaker handcart, such as the American standard 38kV switchgear. The voltage transformer will be installed on the upper part of the switchgear and can be used for measuring the bus side voltage and line side. The bus side is directly connected to the horizontal busbar, while the line side is connected through insulated cables.

The American standard voltage transformer handcart needs to undergo a dynamic and thermal stability test of the contacts. In addition, the voltage transformer handcart requires a secondary disconnection before the handcart can be pulled out, usually using a key interlocking method.

There is also a requirement for the voltage transformer handcart to be pulled out of the cabinet, and the voltage transformer needs to be automatically discharged once to avoid personal injury caused by the stored charge of the voltage transformer. During the process of pulling out the beryllium bronze sheet on the upper part of the compartment, it automatically overlaps with the fuse connecting copper bar to achieve discharge. Therefore, American standard switchgear generally does not use fuse integrated voltage transformers.

The IEC switchgear mainly uses integrated voltage transformers with high-voltage fuses. In addition to the handcart, there are also voltage transformers that adopt a rotating knife switch structure. The main busbar of the tube type is located at the lower part of the switchgear, and the integrated contact box of the branch busbar is directly connected to the main busbar. The upper line side is directly connected to the grounding switch static contact. The current transformer is installed behind the cabinet, while the fuse integrated voltage transformer is installed in the raised cabinet behind the cabinet. After the voltage transformer rotates to the cabinet as a whole, the fuse cover can be opened for quick replacement.

One time scheme and layout, fixed voltage transformer without high voltage primary side fuse scheme, and rotating isolated voltage transformer (with fuse), achieve the connection and disconnection of voltage transformer through rotation.

Another design is to keep the voltage transformer stationary while the fuse tube rotates. The fuse tube drives the fuse to rotate, achieving connection and disconnection, and replacing the high-voltage fuse.

The knife switch type voltage transformer fuse system meets the application of bus and line side voltage transformers, saving the number of switch cabinets. The safety interlock device ensures that the fuse is discharged and grounded before opening the cylinder cover for fuse replacement, and vice versa. If the fuse cylinder cover is not closed, the fuse knife switch cannot be closed