Anhui Erzheng Electric Co., Ltd. presents six distinct application features of packaged substations.

1. Application Background

Box-type substations differ from conventional civil-engineering distribution rooms; their main characteristics are:

(1) The substation shall be designed, manufactured, and installed at the manufacturer’s facility, with internal electrical wiring completed on site.

(2) The substation has undergone the prescribed type-test assessment.

(3) The substation has been verified through factory acceptance tests.

2. Overall Structure of the Box-Type Substation

In a packaged substation, the compartment housing the high-voltage switchgear is generally referred to as the high-voltage compartment; the compartment housing the transformer is generally referred to as the transformer compartment; and the compartment housing the low-voltage distribution equipment is referred to as the low-voltage compartment. These three compartments can be arranged in two configurations within the packaged substation: the “well” configuration and the “square” configuration, which correspond to the so‑called European‑style and American‑style arrangements, respectively.

3. Medium-voltage switchgear inside the packaged substation

In box-type substations, a combined switchgear assembly consisting of a load switch and a fuse is used for terminal connections; for ring-network connections, a ring-network power-supply unit is employed. A typical ring-network power-supply unit is equipped with load switches and comprises two load-switch cabinets serving as incoming and outgoing feeders, along with a transformer-protection cabinet that also incorporates a load switch and a fuse, all integrated into a single switchgear assembly. Given the nationwide initiative to promote ring-network power supply in urban grid construction and renovation projects—aimed at minimizing power outages—the ring-network power-supply unit is expected to experience substantial growth.

SF6 ring-main units are characterized by significantly enhanced personal safety, easy installation, minimal maintenance, space savings, and substantial economic benefits. Distribution cabinets include high-voltage distribution cabinets, low-voltage distribution cabinets, combined high- and low-voltage distribution cabinets, JP cabinets, integrated distribution boxes, and packaged transformers.

A ring-network power supply unit consists of bays, typically comprising at least three bays: two cable inlet/outlet bays and one transformer circuit bay.

Urban distribution networks typically employ ring mains; where overhead lines are used, these can be routed to the vicinity of the ring-main unit and then connected via cable for both incoming and outgoing feeders. In general, busbars and switchgear are enclosed within an SF6-insulated housing. This enclosure protects the equipment from external environmental influences, thereby enhancing its reliability; moreover, the use of SF6 insulation allows for a compact footprint. Additionally, the relatively low gas pressure simplifies sealing and other related design challenges.

4. Transformer Matching and Heat Dissipation Measures

Box-type substations typically employ step-down transformers to reduce the voltage from 10 kV to 380 V/220 V, with transformer capacities ranging from 50 to 1,600 kVA; common capacities for such units are 80 to 630 kVA. Preferred choices include oil-immersed transformers of the S11 class or higher—featuring full sealing, maintenance-free operation, low noise, and excellent cost-effectiveness (noise level ≤ 50 dB)—or newer dry-type transformers such as the SCB10 series. When dry-type transformers are used, the transformer room must be equipped with an effective cooling system. Currently, provincial regulations mandate the use of S11-series distribution transformers; in some cases, amorphous alloy transformers are also employed due to their exceptionally low no-load losses—only about one-quarter to one-third of conventional transformers. However, these amorphous alloy transformers are 1.3 to 1.6 times more expensive. With ongoing advancements in manufacturing technology and subsequent cost reductions, amorphous alloy transformers are expected to eventually dominate the market.

There are two common configurations for transformer installations: one involves exposing the transformer to the open air while keeping it enclosed within a cabinet, which facilitates easy replacement (European-style pad-mounted substation); the other entails mounting the transformer inside a sealed compartment (American-style pad-mounted substation). In the latter configuration, to prevent solar radiation from raising the compartment temperature, the walls are insulated with thermal insulation materials, and a double-layer panel construction is employed. The roof is designed as an air-louvered or insulated roof structure, with internal ventilation ducts and equipped with an automatic forced-exhaust ventilation system—either axial fans or centrifugal fans. Typically, the operation of these ventilation systems is automatically controlled by a temperature-monitoring device in the transformer compartment, with the setpoint calibrated at 80% to 90% of the allowable operating temperature; under normal indoor conditions, heat dissipation relies on natural ventilation.

5. Functional Features of the Low-Voltage Side

On the low-voltage (0.4 kV) side, outgoing line protection can be implemented using multiple air circuit breakers or knife-fuse switches; an automatic cyclic switching reactive power compensation device is provided, with a compensation capacity typically equal to 30% of the transformer’s rating; and an energy metering cabinet is included.

Equipping low-voltage switches with intelligent controllers enables early-warning functionality, provides signaling and operational control, and also includes metering capabilities.

6. Enclosure Manufacturing Process

Poor adhesion and short service life of the surface protective coating limit the use of ordinary steel plates in outdoor packaged substations. While some enclosures are made from stainless steel, aluminum alloy, or polystyrene composite panels, the adoption of non-metallic enclosures—such as glass-fiber-reinforced cement boards, glass-fiber-reinforced plastic panels, and color-coated panels—has become a prevailing trend. When using glass-fiber-reinforced cement boards or glass-fiber-reinforced plastic panels, a smooth, waterproof drip edge can be incorporated into the roof to enhance natural lighting and prevent rainwater from entering.