Main schemes of power supply
At least once in life we heard expression from specialists "switched to back supply". What does it mean? It appears, it is about the scheme of power supply.
The main question of electric power distribution is the choice of the scheme. Correctly made scheme has to provide reliability of the power supply of consumers. All schemes which are found at the moment represent the design of separate elements: feeders, highways and branches.
Feeder - the line intended for electric power transmission from the distributing device to the distribution point, the highway or the separate electroreceiver.
The highway – the line intended for electric power transmission to several distribution points or electroreceivers attached to it in different points.
Branch – the line departing from the highway and intended for electric power transmission to one distribution point or the electroreceiver.
One of the main issues at design of electric utility power grids is the choice of schemes.
The main are main and radial.
In the drawing we gave the schemes which are most often found in practice below:
- and - radial with the one-sided power supply.
- - radial with the double-sided power supply
- in - radial and main (mixed)
- - main with the one-sided power supply.
At the main scheme of supply one line highway services several distribution points or the receivers attached to it in its different points.
At the radial scheme of power supply each line is kind of the beam connecting the node of network to the only consumer. Well, and in the general complex of network these schemes can be combined.
The radial scheme is applied in cases when there are separate nodes enough heavy concentrated loads in relation to which the substation occupies the central location. At the radial scheme separate powerful electroreceivers can receive the power supply directly from substation. With the direct power supply from substation all feed circuits of electroreceivers of high tension or from the distributing device of the highest tension on substation are among radial schemes.
It is possible to carry the following to advantages of radial schemes:
- Maximum simplicity.
- The emergency shutdown of the radial line does not affect power supply of other consumers.
But there are also shortcomings:
- Big expense of cable products and, therefore, high cost of system.
- At single radial lines reliability of power supply is low.
The main scheme of power supply is applied when loading has the concentrated character, but its separate nodes are located in the same direction in relation to substation and at rather small distances from each other. At the main schemes with concentrated loads joining of separate groups of electroreceivers as well as at radial schemes, it is made usually through distribution points. Placement of distribution points is important.
Here it is possible to list the following requirements:
- Extent of highways has to be minimum.
- Distribution points have to be placed in the places convenient for service.
- Cases of the return power supply of electroreceivers have to be minimized.
As well as in radial schemes, and in main there are advantages and shortcomings.
It is possible to carry the following to advantages:
- The cable expense is less.
- The best loading of lines.
- Difficulties when finding the place of damage.
- Lower reliability of power supply.
At the choice of schemes of power supply of consumers it is necessary to be guided not only what we considered above. The basic and, perhaps, the key factor of the choice is the category of power supply of this or that consumer. All of them are separated into 3 main categories.
1 category - consumers and electric units, having rummaged which in power supply can cause danger to life of people, significant material damage, disorder of difficult technology process, violation of functioning of especially important elements of municipal services. The metallurgical enterprises of chemical and mining industry, operating rooms, installations of water supply and the sewerage treat consumers and electric units of 1 category. From the list of consumers and electric units of 1 category the special group is allocated. Especially important state institutions, military facilities and objects of civil defense belong to this group.
2 category - consumers and electric units which break of power supply leads to the mass nedodopusk of products, mass idle times of workers and mechanisms, violation of normal activity of the large number city and villagers. Consumers and electric units 2 categories concern the enterprises of mechanical and light industry, educational, preschool institutions.
3 category - all this other consumers and electric units.
Consumers and electric units of the 1st category have to be provided with the electric power from two independent, mutually reserving power sources, and the break at violation of power supply of one of power sources can be only for the period of automatic recovery of the power supply.
Consumers and electric units of the 2nd category are provided with the electric power from two independent, mutually reserving power sources, and having rummaged in power supply has to make time necessary for inclusion of back supply actions of personnel on duty or the mobile team.
And for consumers and electric units of the 3rd category power supply can be carried out from one power source provided that breaks in power supply, necessary for repair or replacement of the damaged system element, do not exceed one days.Top