The design of IEC ring network cabinet, the current Saudi Arabia, Russia and other countries for China-made ring network cabinet demand, various manufacturers are designing related products.
IEC standard ring network cabinet requirements generally have a common box, mechanical key interlocking, internal arc pressure release, cable voltage test dedicated interface, outdoor box and its size, etc., each region has different requirements, such as Southeast Asia requires a separate cable connection compartment.
Dedicated cable voltage test interface, the requirements of the cable room without opening the cover, without removing any cable connection casing accessories, etc., for high-voltage cable insulation test, using the application of AC frequency voltage or DC voltage 15 minutes test.
This requirement is more common, Saudi Arabia, Belgium, Malaysia and other countries have this requirement. Some only require the configuration of the load switchgear for ring-in and ring-out, and some also require the configuration of the transformer outlet circuit breaker or combination of electrical cabinet.
The specific requirements are as follows: each load break switch and circuit breaker shall be equipped with facilities for conducting applied high voltage tests and current injection tests on circuits connected to the switch.
The test facility shall be in the form of a 3-phase built-in test/earth bushing terminal enclosed in a cover which shall be fully interlocked with the operating handle to prevent access until the switch is in the “ground” position.
This is not a new feature, many older foreign ring mains cabinets have this design where the earth drain is connected externally to the gas tank via a bushing. As in RM6, the transparent casing connection also allows observation of the status of the earth switch.
This commonly used is the grounding switch shorting grounding row removed to the outside of the gas box, that is, the grounding switch as a disconnecting switch, the static cutter head insulation through the copper row through the casing out of the gas box, so that the three-phase static contacts are insulated from each other, to the ground, but also with the high-voltage cable is directly connected to the removal of the shorting row of the grounding through the casing, that is, you can carry out the cable withstand voltage test, the test is reconnected to a good grounding row, the switch to restore the grounding switch function. After the test and reconnection of the grounding row, the switch resumes its function as a grounding switch, realizing the grounding of the cable and ensuring the safety of cable maintenance.
The large space in the air box of the load switch cabinet facilitates the routing of the copper rows and the arrangement of the casing. Since the section from the static contacts of the earthing switch to the casing belongs to the part of the earthing switch that must withstand the short-term withstand peak withstand currents, the cross-sectional area of this section of the copper row connection must satisfy the values required for the thermal stabilization of the earthing switch, e.g., by means of a copper rod with a diameter of 16 mm, and at the same time, the copper rows must be kept at a safe insulating distance from the rest of the circuit.
After the casing has been led out of the gas tank, there are different designs. The simpler one is a separate compartment, which is dismantled and reinstalled manually by means of a grounding shorting strip, which is simple and reliable. There is also the use of knife gate form, knife gate to achieve three-phase shorting and grounding, this knife gate and cover and mechanical interlocking between the load switch, the grounding switch is closed, the cover can only be opened, the grounding row can be removed, the cover is open, the grounding switch can not be split, the load switch can not be closed.
Malaysia and other places require that the circuit breaker cabinet is also equipped with a cable voltage test port, unlike the Saudi Arabia program front layout, installed in the lower part of the agency box, the upper part of the cable room. As Malaysia requires cable rear side connection, and there is a separate cable connection compartment, so the pressure-resistant port is located in front of the lower part of the air box, the use of large knife gate form of connection to the grounding row.
This makes it easy to connect bus bars and bushings in the lower part of the circuit breaker’s air box, and makes the gate-type grounding connection simple and reliable.
There is also a requirement for a more cost-effective and reliable approach compared to passive microcomputer protection devices. The tripping control of the circuit breakers should be realized using only time-lapse fuses (TLF) with ratings of 7.5 A and 5 A. The ratings of the time-lapse fuses and CT link connections used for the different transformer capacities (kVA) used in the TNBs should be clearly displayed next to the TLF compartments.