ALLPCB
The company focuses on production of intelligent distribution terminal products, development, manufacture, and sales of secondary equipment such as intelligent online fault detection and smart electricity software systems, and implementation of smart grid demonstration projects.
1. Modular construction and SF6-insulated load switches
Switchgear features a modular structure with multiple cabinet types available to users. These load switch cabinets are designed to meet distribution users' load requirements and provide complete distribution network automation interfaces and solutions.
Some SF6 load switches integrate three positions in one SF6 chamber for closing, opening, and grounding, improving reliability, safety, and applicability. The SF6 gas is sealed inside an epoxy housing, making the main switch body maintenance-free during its service life. An SF6 gas pressure gauge allows direct observation of internal SF6 pressure; an auxiliary pressure contact can also be fitted to monitor SF6 pressure changes via an electrical signal. The SF6-insulated three-position switch includes a pressure relief channel at its base to protect equipment and personnel in the event of an internal arcing fault.
2. Automated operating mechanisms
The control modules use a modular design. Spring-operated mechanisms, switch position indicators, central interlock systems, fuse trip mechanisms, motorized operating mechanisms, shunt trip coils, and auxiliary contacts simplify component maintenance. A reliable mechanical interlock module (central interlock system) enhances safety and reliability during operation and maintenance.
The switchgear structure is modular, divided into upper and lower units using plug-in construction with screw fastenings, which facilitates maintenance and component replacement. Connections between different modules are simple, easy to expand, and straightforward to install.
3. Functional module and parameter selection
1. Consider distribution automation requirements. Currently, the Chinese market's distribution switchgear automation level remains low; most distribution projects have little or no automated operation functionality. To accommodate future distribution automation, important substation and distribution projects should consider configuring 10 kV ring main unit switchgear to provide remote signaling, remote measurement, and remote control functions.
2. Consider neutral point grounding requirements. Previously, China’s 10 kV networks used ungrounded neutrals or arc suppression coil grounding. To improve distribution network safety and reliability, 10 kV systems at substations have been gradually converted to low-resistance grounded neutral operation. Therefore, selecting 10 kV ring main unit switchgear should take the neutral grounding method into account.
With an ungrounded 10 kV neutral, a single-phase-to-ground fault can be allowed to run for 1–2 hours without immediate tripping at the substation. During this period, the phase-to-phase voltages on healthy phases may rise to three times their normal value, so the selected ring main unit switchgear must have sufficient insulation levels. With low-resistance neutral grounding at 10 kV, single-phase-to-ground faults can produce relatively large fault currents through the faulted line, but protective relays can quickly clear the fault, keeping abnormal system time short. However, this also increases the number of outages and reduces supply reliability. Therefore, the ring main supply should be implemented and the selected ring main unit switchgear should have adequate rated current margins.
3. Selection of switchgear parameters. Distribution switchgear of the same type may offer different technical parameters. For example, some ring main units provide line-side rated currents of 400 A and 630 A. Switch operating mechanisms can be manual or motorized, and various accessories are optional. When ordering these switches, select technical parameters based on the system's operating mode and reliability requirements.
