Electrotechnical faculty
Speciality: Electrotechnical systems of electrical consumption
Master's work theme:
Scientific supervisor: Shlepnyov Sergey
In the last some years are given to questions of quality of electric energy very much a great attention. The electric power is used in all spheres of human life, possesses a set of certain properties and directly participates in creation of other kinds of products, influencing their quality. Last years there were many TVs, computers and other devices working on a direct current through the secondary power supply. They worsen quality of electric energy in a power line.
The work actuality is connected with absence of the analytical decision of problems of an estimation of electromagnetic compatibility and can help to open to experts theoretical aspects of a problem of improvement of quality of electric energy. The main objective — to investigate voltage in electric networks of Donetsk. The idea of work consists in use of techniques of the likelihood modeling, allowing to describe casual processes. Scientific value of work — development of the theory electromagnetic compatibility in a range of definition of characteristics of casual processes by means of statistical likelihood methods of calculation.
Voltage deviation — difference of actual power in the installed operating mode of system of an electrical supply from its rating value. Voltage deviation in any point of the network comes under the influence of slow changes in load, in accordance with its schedule.
The main requirement, shown to electrical supply system, maintenance of power U in admissible limits for the receiver is.
GOST 13109-97 establishes normally and maximum permissible values of the established deviation of pressure on clips of electroreceivers in limits accordingly ± 5 % and ± 10 % from network rated voltage.
The given type of switching is used during seasonal switchings as assumes disconnecting of the transformer from a network that it is impossible to do regularly, without depriving of electric voltage consumers. Switching without excitation allows to change transformer coefficient in limits from –5 % to +5 %. On low-power transformers it is fulfilled by means of two derivings, on transformers of average and big power by means of four derivings on 2,5 % on everyone [5]. Derivings are fulfilled on that side the power on which while in service is exposed to changes more often. Usually it is the side of the higher power.
Switchings without excitation are presented on fig. 1.
The given type of switchings is applied to the operative switchings linked to constant change of load (for example, day and night load on a network will be different). Depending on on what power and what power the transformer, regulation under load can change value of coefficient of transformation in limits from ±10 to ±16 % (approximately on 1,5 % for deriving). Regulation is carried out on the high voltage side as the current strength value there is less, and accordingly, the regulation device under load to fulfil easier and more cheaply. Regulation can be made both automatically, and manually.
The device circuit is presented on fig. 2.
The voltage can be regulated, changing a voltage line resistance. If the voltage line or its site consists of several parallel lines, that, disabling at o'clock of the minimum loads one of such lines, it is possible to increase power loss in a power line and that to reduce power for the consumer. Lowerings of a jet resistance of a chain and, therefore, at maximum loads can achieve power increase, applying longitudinal compensation of inductance of a line.
On fig. 3 the diagramme of change of pressure depending on change of transferred jet capacity is represented.
Electromagnetic compatibility of means — ability to function in the established electromagnetic conditions and not to create inadmissible electromagnetic hindrances for other means [1].
It is necessary to improve various ways electromagnetic compatibility if at least one indicator electromagnetic compatibility does not correspond to the normalized. It is enough to calculate or measure these indicators in these cases before improvement electromagnetic compatibility.
In the given work nonlinear characteristics therefore difficult use of analytical methods of an estimation which consider electromagnetic compatibility are considered [3]. Thereupon it is expedient to pass to statistical multifactor modeling which will be stated in more details.
The random variable can be completely described by means of the probability theory if allocation between separate values of this random variable is known. Any random variable is subordinated to this or that law of allocation.
The most meeting law of distribution — the normal law, which main feature that other laws of distribution come nearer to it under often meeting typical conditions. One of work problems — to find out, whether the random variable of a deviation of pressure submits to the normal law of distribution.
The normal law of allocation it is presented on fig. 4.
Figure 4 — The normal law of distribution
1. The primary goals of maintenance Ems are formulated. Check norms of GOST 13109-97 on one-minute deviations of voltage is executed.
2. The concept a voltage deviation is in full opened; its influence on electric equipment work, responsibility and indemnification measures is considered.
3. The basic problems connected with regulation of voltage in city networks are analyzed, and also recommendations about improvement of its quality are made.
4. It is planned to receive daily schedules that will allow to specify results of practical researches and to choose recommendations for the organization on improvement of quality of voltage.
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