The final stage in the organization of the transport electrical network is the installation of distributing and converting devices. They can also be found at intermediate nodes of main lines, but this concept of branching of energy delivery circuits is most clearly manifested at the stage of direct supply of end objects. Input distribution devices (ASU) such as transformers, fuse switches, etc. are responsible for this function.
The concept and purpose of the ASP
As the name suggests, ASP systems perform the tasks of input and distribution of electricity at consumption facilities. Physically, the ASP is a set of technical means that provide power control, current conversion, its measurement in differentparameters and accounting. For a more complete understanding of what ASU is, it is worth familiarizing yourself with some modifications of devices and their purpose. So, at the basic level, the following classification is used:
- VRU-1. Input-distributing equipment in a complete set, which is used for operation outside the switchboard rooms. Such devices can be found on landings or in basements.
- VRU-2. Professional power control and distribution kits designed for use in control rooms. They can be used to ensure the operation of server rooms and technical wiring rooms.
- VRU-3. Small kits that can be part of an electrical panel in a suitable format.
The most commonly used means are VRU-1 and VRU-3. These are devices that are directly involved in the processes of receiving, accounting and distributing energy in 220/380 V networks with a frequency of 50 Hz. Some modifications additionally perform protective functions in cases of overloads and short circuits.
ASU operation principle
The work process begins with the reception of electricity from the main network. The power cable supplies current to the introductory automation in accordance with the standard values (rated current). Already at this stage, counters and other measuring instruments that measure the parameters of the current at the input can be included in the work. Again, it is worth recalling what an ASU is in terms of functionality. This is a complex of different devices, sometimes performingtasks of a completely different spectrum. In parallel with the measuring function, a protective function can be performed. So, the introductory switch as a whole controls the power supply and, when registering deviations from the standard values or the occurrence of emergency situations, turns off the machine. Technically, the switch is implemented in the form of a knife switch or disconnector - manual or automatic.
Next, a group of arresters enters the work, providing the connection of wires in phases. At this stage, the voltage parameters are necessarily fixed and, if necessary, they are corrected by transformers. Distribution is carried out in groups of wires by means of circuit breakers with different or similar ratings. The current parameters on each circuit depend on the needs of the consumer to which it leads. The task of branching is not determined by the separation of wires according to current characteristics, but by the need to separate energy in their directions for each supply point. Distribution automation ensures load uniformity between phases, fixing the demand factor of electrical networks, taking into account their maximum load.
Composition of the ASU
Practically all devices of this type are made in the form of a panel enclosed in a metal box. The following devices and functional blocks are placed on this base using pre-installed connectors and modules:
- Circuit breakers.
- Meters accounting for reactive and active energy.
- Current transformers.
- Transformers.
- Test devices.
- Electromagnetic starters.
- Measuring instruments (voltmeters, ammeters, multimeters, etc.).
Additional equipment depends on the specific set of functions of the device. For example, input-distribution devices with ATS (automatic transfer of a reserve) have several panels with control equipment for one-way service. A feature of such equipment is the ability to independently connect an auxiliary distribution cabinet with an uninterruptible power supply (UPS) in case of a blackout of the target object.
ASP characteristics
Most of the input-distribution systems are oriented to work in three-phase and single-phase networks with a power point from 100 to 400 A and a frequency of 50-60 Hz. As for power, the entry-distribution devices from 0.4 kV to 1 kV represent the initial level. They are used to service communal lighting systems, construction equipment at remote sites, etc. However, to supply large consumers, switchboards with ASUs are used, the power of which is at least 10 kV, and sometimes exceeds 25 kV. Also, the choice takes into account such characteristics as the connection time of the backup source (0.2-5 s), the degree of protection (from IP00 to IP31, depending on the part of the case) and electrical resistance (from 10 MΩ).
ASU residential buildings
To service multi-apartment residential buildings, devices for three-phase networks with variablecurrent, in which a dead-earthed neutral is provided. Among the main tasks in this case, one can single out the electrical protection of the line in cases of short circuits, overloads and emergency power outages. What is an ASU for a residential building in the physical version? This is a metal cabinet with provided grounding, in which meters, circuit breakers, fuse blocks, emergency panels for UPS input, load distribution sensors, etc. are installed.
Implementation of ASU at industrial facilities
First of all, multi-panel cabinets are used, designed for branched control of several power supply circuits. In this case, the power indicators and the degree of protection with insulation are higher, but in small enterprises or in separate workshops with normal operating conditions, household machines may well be used. But what is an ASU designed for operation at large public and industrial facilities? At the moment, cabinets of the ShchO-70 line of factory assembly are widely used. In terms of design, these are panels for one- and two-way control, which also provide for ATS automation and switches designed for long work sessions in a mode independent of the main power source.
Installation of ASU
Installation of the cabinet with ASU is carried out on the basis of the design scheme,compiled in accordance with the operating conditions at a particular place of use. First, mounting holes are drilled to fix the brackets and screws under the metal structure. According to the instructions, the installation of input distribution devices is carried out at a height of at least 30 cm, and a dielectric insulating overlap should be provided between the rear panel and the wall. There are also floor structures, the installation of which is carried out on a special foundation or platform, which is attached to a concrete screed.
Connecting equipment
After installing the housing of the ASU, the assembly and connection of the functional filling is carried out. An aluminum armored contour is used for cable entry. It is directly connected to the switch and control relay. Further, crimped wires depart from the relay to separate functional segments. The VRU-1 input and distribution devices have two input blocks that can be connected to different supply networks. But between them there must be an insulating partition. At the final stage, the routed and connected wires are fixed with nylon ties at the bottom of the shield.
Conclusion
ASP systems perform the important tasks of organizing electrical networks. The functionality of such equipment can be considered both as control and measuring, and as protective and control. Even 0.4 kV input distribution devices provide ample opportunities for monitoring the operation of the laid network, taking into accountvolumes of supplied energy both at the input and at the output. But the main task still lies in the physical distribution of power supply channels while ensuring a sufficient degree of reliability and safety of the equipment. In the latest ASP models, emphasis is also placed on improving the ergonomics of control with the expansion of automatic functions.
