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Power Distribution Equipment Complete Distribution System
Oct 25, 2017

What power distribution equipment is required for a complete distribution system

Box type substation

The structure of box - type substation

Usually the power supply capacity of 315 ~ 630kVA, the use of outdoor compact box-type substation, power supply capacity of 750 ~ 5000kVA, then do not use compact box substation

Box-type substation has three main components (see Figure 5): high-voltage switchgear, transformers and low-voltage switch (power distribution) devices. Box-type substation can be wired after the arrival of the use, you can save a lot of on-site and technical services.

Box-type substation, usually buried in the underground a cement structure, and in the ground box height of 2.5m or so. "German" box-type substation is buried underground 1m, exposed ground height of not more than 1.6m. "German-style" substation has the advantage of box change and environmental coordination without affecting the line of sight, the disadvantage is the flood season, water can be immersed in the box, hazardous equipment.

Box-type substation of the overall layout in two forms: one is modular (European); the second is one (American). The combination is a high-voltage switchgear, transformers and low-voltage switch (power distribution) devices for each room (see Figure 9). Integral refers to the transformer as the main body of the fuel tank, fuses and load switches into the tank and the body into one body, the box is fully enclosed structure, the transformer is generally three-phase five-column.

Medium voltage switchgear

If the box-type substation is in the terminal wiring, use the load switch fuse combination (described in the third section); if the ring network wiring, the use of ring network power supply unit. The structure of the ring power supply unit is shown in Fig. 6, which consists of at least three intervals, namely two cable access intervals and one transformer circuit interval (load switch + fuse). By disconnecting the switches A and B, it is possible to isolate the fault section and restore the power supply to the normal circuit in time. The fuse F protects the internal fault of the medium voltage / low voltage transformer and the direct short circuit of the secondary terminal of the transformer, On the fuse and the transformer also from the isolation and grounding effect.

transformer

Box-type substation transformer is a step-down transformer, generally 10kV down to 380V / 220V, directly for users to use. Transformer capacity as 160 ~ 1600kVA, the transformer can be oil-immersed transformers, flame-resistant transformers, epoxy dry-type transformers. In the case of strict fire protection requirements, such as in the high-rise buildings can not use the oil with the electrical appliances, so the use of vacuum, SF6 switch, dry-type transformers. As the S9 series distribution transformer load loss than the ST series of distribution transformers about 25% lower, to actively use it. In order to reduce the no-load loss of the distribution transformer, the use of amorphous alloy core transformer, amorphous alloy core transformer than the silicon steel core transformer no-load loss (in the evening), while the remaining time, Reduce the 60% to 70%, no-load current down about 70%.

Transformer ventilation and cooling can be used natural ventilation and mechanical forced ventilation of two, from the economic considerations, of course, should be optimized to consider the natural ventilation.

Low voltage switchgear

The low-voltage switchgear is housed in a low-pressure chamber and a main switch (main switch) and 4 to 8 feeder switches in the low-voltage switchgear. The power is sent to the user by the feeder switch.

Low-pressure indoor also equipped with low-pressure metering device and static compensation device A: the minimum opening time and the maximum fuse time intersection B: the maximum breaking time and the minimum fuse time intersection due to overhead lines exposed to the atmosphere, susceptible to lightning, insulation susceptible to industry Contamination, by the wind blowing easy to touch with the trees, so the failure rate is extremely high, in order to reduce the failure, in the city network generally use underground cable.

In the ring network unit, a cable connector is provided for connecting the cable and the ring power supply unit. For safety, the cable connector is closed.

High-voltage XLPE cable insulation (XLPE) cable accessories in the 20th century, 60 years after the fastest-growing technology of the power cable varieties, accessories with terminals and connectors. High-voltage XLPE cable with accessories, in the city power grid transformation and box-type, large-scale industrial and mining substation and other transmission and distribution systems widely used, but China's XLPE cable and accessories and the international advanced level there is still a certain gap.

Monitoring and control unit

Box-type substation installed in the outdoors, the box temperature, humidity outside the box by the environmental impact. If the high pressure chamber and low pressure chamber condensation, then endanger electrical insulation and lead to break failure. While the transformer temperature exceeds the first degree, it will affect the pressure output power. So the box should be installed temperature and humidity monitoring device, when a certain humidity and dew point temperature, issued a command to make the temperature regulator action; when the temperature exceeds a certain range, issued a command to start the fan, forced exhaust. Condensation controller installed in the box shown in Figure 7.

If necessary, the tank is also installed FTU, remote control, communication interface, through the FTU acquisition fault information, remote control, news port, and control center contact to achieve protection, feeder feeder energy measurement, timely reporting to the control center slip Electric energy measurement, timely report to the control center tributary load situation; and receive control center command, switching power compensation unit.

Automatic splitter

Automatic vacuum splitter

In the box-type substation section has been mentioned, the load switch can be combined, the normal load current, it can not break short-circuit current.

The automatic splitter is composed of a load switch of an electrifying spring operating mechanism, an automatic splitter controller and an auxiliary device. It is a function that can memorize the number of times through the fault current and reach the set number of times after no voltage and no Current in the case of automatic opening of the switch device, it has a closed short-circuit current and breaking and closing load current capability. The splitter is used to automatically isolate the fault area in a 10kV distribution system.

Automatic splitter by arc different media can be divided into air, oil, SF6 and vacuum four types.

Automatic Segmenter and Automatic Recloser Used in Radiation Distribution Network

 (1) Set the X time limit 10s of Q01 to Q03, the X time limit of Q04, and the fault occurs in the second paragraph.

 (2) A fault occurs, recloser (QR) detected after the fault trip, all sections of power, sub-device due to power off and sub-gate.

 (3) The automatic recloser (QR) is superimposed after the first coincidence interval delay, and each of the finder Q01 to Q04 is closed in accordance with the preset delay time, that is, Q01 after 10 s, Q02 is After 20s, Q03 after 30s, Q04 in 10s +30 s = 40s closing, complete the line power supply.

 (4) If the permanent fault, because Q04 closed on the fault line, so that the recloser again trip, so all sectors once again power, sub-gate again gate, but then Q04 controller in the Y time limit Detection and loss of voltage, and make it locked in the sub-gate state.

 (5) After the second reclosing of the recloser, Q01 ~ Q03 are closed in turn to complete the normal power supply of the above section. Since Q04 is in the sub-gate state, the fault zone has been separated from the grid, so the reclosing of the recloser success.

Circuit breakers, automatic recloser (12kV)

Vacuum circuit breakers

Circuit breaker is a switchgear that can handle, carry and disconnect the normal current of the running circuit, and can also shut down, carry and disconnect the specified short-circuit current within the specified time. In other words, when the circuit breaker in the closing state, it should be a good contact with the conductor, can withstand the normal load current and the provisions of short-circuit current under the heat and electric power; in the closed state, as soon as possible within a short time break fault Short circuit current, in the sub-gate state, as short as possible to meet the provisions of the short-circuit current, and the circuit breaker contact does not occur welding; can be used as a separate main protection equipment.





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