Chinese-Style Box Substation

Overview

The Chinese-style box substation is a compact outdoor prefabricated step-up substation in which the oil-immersed transformer sits outside the enclosure while the HV and LV switchrooms are housed inside it. It keeps the small footprint and fast installation of the single-enclosure design while re-dividing the HV compartment, LV compartment and transformer connection area to meet domestic requirements for maintenance access and interlocking.

Construction

• Transformer unit: a fully sealed oil-immersed power transformer whose body, radiators and conservator sit on one side of or on top of the enclosure and cool by natural convection, with no forced-air fans that could fail and cause overheating; the tank keeps the Buchholz relay, pressure-relief valve and oil-level gauge accessible.
• HV unit: a separate HV compartment with a disconnector (with earthing switch) and a switch-fuse combination, or a vacuum circuit-breaker with CT/PT, surge arresters and live-line indication, meeting the requirements for a visible isolating gap and five-fold interlocking.
• LV unit: a separate LV compartment with an air circuit-breaker, moulded-case outgoing ways, capacitor compensation and smart metering.
• Enclosure and incomers: HV cables normally land on fully insulated elbow connectors or bolted terminations in the cable compartment, with busbar outgoing ways on the LV side; the enclosure is divided into HV compartment, LV compartment and transformer connection area with fire-resistant barriers, and the degree of protection is typically IP43–IP55, with protection against condensation, salt spray and dust.

Advantages

• Superior cooling: with the transformer outside the enclosure the dissipating surface is large and unobstructed, giving strong overload capability in hot, heavily loaded locations.
• Easy maintenance: the HV and LV compartments each have their own working space and can be opened for maintenance; oil level, Buchholz relay and other transformer indications are in plain view.
• Flexible protection: both compartments can take microprocessor relays and automation terminals (DTU/FTU) to Chinese grid standards, providing telemetering, telesignalling, telecontrol and teleadjustment.
• Varied HV connection: fully insulated elbow connectors or conventional bolted cable terminations suit different user practices.
• Robust enclosure: galvanised steel, stainless steel or non-metallic enclosures resist corrosion, condensation, salt spray and dust across widely varying climates.