The final stage in the organization of the transportation electrical network is the installation of distributing and converting devices. They can also be found at intermediate nodes of the trunk lines, but this concept of branching of the energy delivery circuits most clearly manifests itself at the stage of direct supply to the final objects. For this function, input-distribution devices (ASUs) such as transformers, fuse switches, etc.
The concept and purpose of ASU
As the name implies, ASU systems perform the tasks of input and distribution of electricity at consumer facilities. Physically, ASU is a complex of technical means providing power control, current conversion, its measurement in various parameters and accounting. For a more complete understanding of what the ASU is, it is worth familiarizing yourself with some modifications of the devices and their purpose. So, at the basic level, the following classification is used:
- VRU-1. Fully equipped induction and distribution equipment, which is used for operation outside switchboard rooms. Such devices can be found on stairwells or in basements.
- VRU-2. Professional energy monitoring and distribution kits designed for use in panel rooms. They can be used to ensure the operation of server rooms and technical wiring utilities.
- VRU-3. Small kits that may be part of an electrical panel in a suitable format.
Most often, VRU-1 and VRU-3 are used. These are devices directly involved in the processes of reception, metering and distribution of energy in 220/380 V networks with a frequency of 50 Hz. Some modifications additionally perform protective functions in cases of overload and short circuit.
The principle of the ASU
The workflow begins with the reception of electricity from the mains network. The power cable supplies current to the input automation in accordance with standard values ββ(rated current). Already at this stage, counters and other measuring devices that measure the input current parameters can be included in the work. Again, it is worth recalling what the ASU is in terms of functionality. This is a complex of different devices, sometimes performing tasks of a completely different spectrum. In parallel with the measuring function, a protective function can be performed. So, the input switch as a whole controls the power supply and when registering deviations from standard values ββor the occurrence of emergency situations, it 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 comes into operation, providing a 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 circuit breakers with different or similar ratings. The current parameters on each circuit depend on the needs of the consumer to whom it leads. The task of branching is not caused by the separation of wires according to the characteristics of the current, but by the need for diluting the energy in its directions for each supply point. Distribution automation ensures the uniformity of loads between phases, fixing the demand coefficient of electric networks taking into account their maximum load.
The composition of the ASU
Almost all devices of this type are made in the form of a panel enclosed in a metal box. On this base, through the pre-installed connectors and modules, the following devices and functional blocks are placed:
- Circuit breakers.
- Meters that record reactive and active energy.
- Current transformers.
- Converters.
- Testing devices.
- Electromagnetic starters.
- Measuring instruments (voltmeters, ammeters, multimeters, etc.).
Additional equipment depends on the specific set of device functions. For example, input-distributing devices with ABP (automatic reserve input) have several panels with control equipment for one-way maintenance. A feature of such equipment is the ability to independently connect an auxiliary distribution cabinet with an uninterruptible power supply (UPS) in the event of a blackout of the target object.
Characteristics of ASU
Most input-distribution systems focus on working in three-phase and single-phase networks with a point power of 100 to 400 A and a frequency of 50-60 Hz. As for power, the input level is represented by input-distribution devices from 0.4 kV to 1 kV. They are used to service public lighting systems, construction equipment at remote sites, etc. However, to supply large consumers they use switchboards with switchgear, the power of which is at least 10 kV, and sometimes exceeds 25 kV. Also, the selection takes into account such characteristics as the backup source connection time (0.2-5 s), degree of protection (from IP00 to IP31 depending on the part of the case) and electrical resistance (from 10 MΞ©).
ASU residential buildings
For servicing apartment buildings, devices for three-phase networks with alternating current are used, which provide for grounded neutral. Among the main tasks in this case, we can distinguish the electrical protection of the line in cases of short circuits, overloads and emergency power outages. What is ASU for a residential building in physical performance? This is a metal cabinet with provided grounding, in which meters, breakers, protection units, emergency panels for inputting the UPS, load distribution sensors, etc. are installed. In modern designs, the key parameters of the power supply are provided on the doors of such boxes.
Implementation of ASU at industrial facilities
First of all, multi-panel cabinets are used, designed for the branched control of several energy supply circuits. Power indicators and the degree of protection with insulation in this case are higher, but in small enterprises or in individual workshops with normal operating conditions, household machines may well be used. But what are ASUs designed for operation at large public and industrial facilities? Currently, cabinets of the SchO-70 line of factory assembly are widely used. From the point of view of design, these are panels for one- and two-way control, which also include automatic switchgear and circuit breakers, designed for long working sessions in a mode independent of the main power source.
Installation of ASU
The installation of the cabinet with the ASU is carried out on the basis of the design scheme drawn up in accordance with the operating conditions at the specific place of use. First, the mounting holes are drilled to fix the brackets and screws for the metal structure. According to the instructions, the installation of distribution and 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 floor structures, the installation of which is carried out on a special foundation or platform, which is attached to a concrete screed.
Hardware Connection
After installing the ASU case, the assembly and connection of the functional filling is performed. An aluminum armored circuit is used to enter the cable. It is directly connected to a switch and a control relay. Further, the pressed wires leave the relay for separate functional segments. The input and distribution devices of the ASU-1 provide two input units that can be connected to different supply networks. But between them the insulating partition should be kept. At the final stage, the divorced and connected wires are fixed with nylon ties in the lower part of the shield.
Conclusion
ASU systems perform critical tasks of organizing electrical networks. The functionality of such equipment can be considered both as a control and measuring device, and as a protective control device. Even 0.4 kV input-distribution devices provide ample opportunities for monitoring the operation of the laid network, taking into account the amount of energy supplied both at the input and output. But the main task still lies in the physical distribution of energy supply channels while ensuring a sufficient degree of reliability and safety of equipment operation. Recent ASU models also focus on improving control ergonomics with the expansion of automatic functions.