First, the pad mounted transformer brief
Box substation (referred to as pad mounted transformer) is a kind of high-voltage switchgear distribution transformer, low-voltage switchgear, energy metering equipment and reactive power compensation device according to a certain wiring scheme combined in one or several boxes in a compact complete set of distribution devices. It is suitable for the three-phase AC system with rated voltage of 10/0.4KV, as the line and the distribution of electric energy.
Box-type substation, also known as pre-installed substation or pre-installed substation. Is a high-voltage switchgear, distribution transformer and low-voltage distribution device, according to a certain wiring scheme arranged into one of the factory prefabricated indoor and outdoor compact distribution equipment, that is, transformer step-down, low-voltage distribution and other functions organically combined together, installed in a moisture, rust, dust, rat, fire, anti-theft, heat insulation, fully enclosed, movable steel structure box. It is especially suitable for urban network construction and transformation, and it is a new substation that rises after civil substation. Box-type substation is suitable for mines, factories, oil and gas fields and wind power stations, it replaces the original civil distribution room, distribution power station, and becomes a new complete set of transformer and distribution equipment.
Second, box-type transformer classification and the difference between American and European
Combined substation (referred to as American box transformer) preloaded substation (referred to as European box transformer) American box transformer is divided into two types according to the tank structure: common box type and divided box type, and European box transformer adopts ring network type and terminal type.
2.1 The concepts of assembly, Ovarium and beauty
(1) Assembled substation. The assembled substation puts the high and low voltage complete sets of devices and transformers into the metal box, and there is an operation corridor between the high and low voltage distribution devices. This type of box type variable volume is larger, has been less used.
Combined unit type substation. The high and low voltage distribution device of the combined device type substation does not use the existing complete sets of devices, but the high and low voltage control and protection electrical equipment is directly loaded into the box to make it a whole. Since the overall design is based on maintenance-free considerations, there is no need to operate corridors in the box. This can reduce the volume of the box type change, this type is European box change, is a commonly used type.
One type substation. A type substation is the so-called American box change. It is on the basis of simplifying the high and low voltage control and protection devices, the high and low voltage distribution device and the transformer body into the transformer tank together, so that it becomes a whole. This type of box type variable volume is smaller, and its volume is similar to that of ordinary oil-immersed transformers with the same capacity. Only about 1/3 of the volume of the same capacity European box.
2.2 Main differences between the United States and Europe
The high voltage protection is composed of plug-in fuse, backup fuse + load switch;
Obe, high voltage protection according to the load switching frequency, select pressure type, vacuum and SF6 load switch + fuse composition; The capacity is flexible.
The biggest difference between Meichange and Ouchange is in the high voltage part, Meichange high voltage wiring mode is only two, ring network (double power supply) or terminal power supply. The Oudian consists of an independent high-pressure unit, and the form can be customized according to customer requirements. Since each functional unit is independent, each unit (high voltage, transformer, low voltage) can be customized according to user requirements. Due to high pressure restrictions, as well as its own small size, the function is far less flexible than the European change. But it’s much cheaper than Oubian.
2.3 American box change characteristics
Advantages: small size, small footprint, easy to place, easy to camouflage, easy to coordinate with the environment of the community. It can shorten the length of low-voltage cable, reduce line loss, and also reduce the cost of power supply.
Disadvantages: low reliability of power supply; No electric mechanism, can not add distribution automation device; Capacitor free device, which is not good for reducing line loss; Because of the different civil foundation of the different capacity tank, it is inconvenient to increase the capacity of the tank. When the box becomes overloaded or the user increases the capacity, the civil construction needs to be rebuilt, and there will be a longer power outage time, increasing the difficulty of the project.
Application: American box transformer is suitable for multi-storey residential and other unimportant buildings with relatively low power supply requirements. According to our actual use, after the American box is converted into a small ring network switch station, it is fully applicable to the power supply needs of multi-storey residential buildings. Because it is the box change that fails, it has little impact on residents, but it is not suitable for small high-rise and high-rise.
2.4 European box change
Advantages: The radiation is lower than that of the American box, because the transformer of the European box is placed in the metal box to play a shielding role; Distribution automation can be set up, but also has the main advantages of the American box.
Disadvantages: large volume, not conducive to installation, has a certain impact on the environmental layout of the community;
Application: European box is suitable for multi-storey residential buildings, small high-rise buildings, high-rise buildings and other more important buildings.
Three, box high pressure part
3.1 High-pressure components:
- High pressure cable cabinet; 2. High voltage outlet cabinet; 3. High pressure ring network cabinet; 4. High pressure measuring cabinet
3.2 Main components of high voltage:
Live display DXN; Electromagnetic lock; High voltage arrester FV; High voltage load switch QF; High voltage fuse; High voltage grounding tool brake
3.3 High pressure metering cabinet:
Current transformer TA; Voltage transformer PT; fuse
3.4 Live display DXN
Display device by voltage; Sensors and displays; The voltage display device is composed of two parts, and the two parts are installed and connected. The voltage sensor is a pillar insulator of epoxy resin casting type. The voltage signal of 70V is extracted from the 10kV high voltage through the voltage sensor.
3.5 PT, CT and FU are used in the high-pressure metering cabinet
PT: Voltage Transformer JDZ-10 for voltage, electric energy measurement and relay protection
CT: Current transformer LZZJB9-10A fully enclosed pillar structure for electrical measurement and electrical protection
FU: High voltage fuse RN2-10/1ARN2 type indoor high voltage current limiting fuse, used for the protection of voltage transformer. Its cut-off capacity is 1000MVA. Instantaneous breaking during short circuit in such a way as to limit the line current to the minimum.
Four, Low pressure part
- Low pressure inlet cabinet; 2. Low voltage outlet line; 3. Low pressure compensation cabinet
4.1 Low Voltage Cable intake cabinet
Low-voltage inlet cabinet is composed of: three ammeter A; A voltmeter V; A universal transfer switch (for measuring voltage) a temperature controller WK; Closing button, opening button; Closing light, opening light isolation switch QS; Circuit breaker QF; Current transformer TA and other components.
4.2 Composition of low pressure compensation cabinet
Three ammeter A, a power factor meter COS; Power controller PK; Universal switch capacitor working indicator light; Isolation switch QS; Current transformer TA; Minitype circuit breaker QF switching capacitor contactor KM; Capacitor C; Arrester FV
4.3 Low Voltage Cable Outlet Cabinet
The low-voltage outlet cabinet can have multiple outlet lines. Each group of outlet lines has: an ammeter; A plastic-case circuit breaker; A current transformer
Five, box change prospect analysis
Box-type substation is the main direction of the current rural network transformation and future substation construction, but there are still some shortcomings in some aspects, which are reflected in:
(1) Fire prevention problem: box-type substation is generally fully sealed unattended operation, although all equipment is oil-free operation and equipped with remote smoke alarm system, but there are still fire hazards in the box, such as: Cables, compensation capacitors, etc., once a sudden fire, is not conducive to ventilation, is not conducive to fire fighting, so should consider the design of automatic fire extinguishing system, but this will increase the manufacturing cost of box-type substation.
(2) Capacity expansion problem: box-type substation due to the volume and manufacturing costs, the expansion margin of the outlet interval is small, if you want to increase 1 to 2 outlet intervals in the original box is more difficult, you must increase the box to do it.
(3) Maintenance problem: Because the box-type substation considers the manufacturing cost and the box volume limit in the manufacturing process, the maintenance space of the box-type substation is small, which is not conducive to equipment maintenance, especially emergency repair, which is the inherent deficiency of the box-type substation and can not be overcome.
In short, looking forward to the future, box-type substation in China’s vast cities, rural areas, industrial and mining enterprises, public building facilities will be widely used, it will be its advantages of cheap and fine by more and more people to use, so that China’s power grid operation level to a new level.