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Abstract

Content

1. General description of work

Relevance of the topic.Analysis of the device and the principles of operation of the known means of protection of the mine precinct electrical network from the short-circuit. shows that they all differ in a certain inertia due to the time delays necessary to measure the currents of the protected network and its comparison with the adopted setting. Therefore, the task of searching for new principles of overcurrent protection construction that will satisfy the safety issues of high-voltage networks acquires practical relevance.

In particular, in order to detect the acceleration of a short circuit, a method of controlling the rate of current rise can be applied. However, the increase in current is characteristic of other non-standard states, such as motor overload. On the other hand, the short-circuit is accompanied by a sharp displacement between current and voltage, but the instability of the phase relation of these parameters is also characteristic of such transient processes of starting an asynchronous motor or its overload. It is obvious that a simultaneous change in the phase relation and the parameter of the rate of current rise can be considered as information parameters about a short circuit in the power connection.

Scientific and practical relevance is the task of finding a new information parameter to build a maximum current protection with improved performance indicators. Objectively, we are talking about the protection of industrial power grids, which include a significant number of asynchronous motors.

Purpose of the study is the rationale for the method of accelerated automatic detection of the interfacial short circuit process in the mine area electrical network based on taking into account a set of parameters in the dynamics of their change.

2. Scientific position obtained during the study

2.1 Modeling of processes and theoretical substantiation of ways to improve speed overcurrent protection

The study of the features of information parameters that characterize the occurrence of a short circuit process in the connection of a mine precinct electrical complex should be carried out using the equivalent circuit of Fig.1. It is consistent with the principal provisions for such objects and most fully takes into account the active-inductive parameters of the transformer of the power substation, cable network before and after the short-circuit point, asynchronous motor, including its phase rotation EMF.

Figure 1 - The equivalent circuit of the connection in the electrical complex of the mine site in the event of a three-phase short circuit in it

Figure 1 - The equivalent circuit of the connection in the electrical complex of the mine site in the event of a three-phase short circuit in it

Study of the nature of the change in the phase relation between the phase current of the power grid and its voltage at the moment of occurrence of a short circuit can be performed, in particular, based on the use of the software product Electronic Work Bench.

The design model of the fragment of the electrical complex is presented in Fig. 2

Figure 2 - The design scheme of a fragment of the electrical complex in Electronic Work Bench

Figure 2 - The design scheme of a fragment of the electrical complex in Electronic Work Bench

A distinctive feature of such complexes is the presence of inductance, which in turn determines the phase displacement of the current relative to the voltage. During the short circuit process, the network configuration changes significantly, which, in turn, will lead to a change in the phase ratio of current and voltage. The specified phase relation can be considered as an information parameter for constructing an improvement in the protection device. In this regard, the scientific and practical interest is not only the value of this parameter, but also the dynamics of its change at the time and in the process of short circuit. Disturbing factors that must be taken into account are the power of the transformer substation, the cross section and cable lengths and the distance from the supply substation to the short circuit point. Accounting for these parameters will allow you to perform a comprehensive study of the process.

2.2 Algorithmization of the process of detecting short circuits using a phase-sensitive organ

Local network cables are the most vulnerable point of the entire power supply system of the mine.

All mine electrical equipment is housed in special shells that reliably protect it from any mechanical effects. But the cables that are operated in the mine electrical networks are not sufficiently protected from damage when moving downhole equipment, rock breaks or packs of coal. Damage to the cable insulation leads to interfacial leakage, which develops into short-circuit currents.

As a result of studies of the computer model of the mine precinct network, the nature of the change in the current component and short-circuit voltage was established. We noticed changes in the information parameters when changing the parameters of the different components of the mine precinct network.

Phase angle offset may also occur, in connection with the connection and disconnection of individual groups of consumers, as well as in connection with the launch of an asynchronous motor. However, the simultaneous change of these factors is possible only with a short circuit under the condition of a significant intensity of increase in current consumption. Thus, the construction of high-speed overcurrent protection should be based on the design of the circuits of its two channels: the current growth control channel and the control channel, the phase angle reduction.

In the case of simultaneously existing output pulses of both measuring channels, a control signal for the protective disconnection of the electrical installation is generated.

2.3 Structural scheme

After analyzing the model and processes in the place of cable damage, we came to the conclusion that at present the theory of short circuits does not take into account the dangerous processes occurring in the flexible cable, which in turn is the power cable of the induction motor, which in consequence of mine conditions can lead to an accident . That is, the technical protection solutions that are currently used in the mine provide for a certain period of protection operation, during which the supply of emergency power connection current will be maintained. However, in dangerous conditions of the mine, this period should be minimized.

We draw a block scheme of the electrical complex of the mine site (Fig. 5)

Figure 5 - Structural scheme of the electrical complex of the mine site

Figure 3 - Structural scheme of the electrical complex of the mine site

Conclusion

As a result of the conducted research, an analysis was made of the maximum current protection of the electrical engineering complex of a mine site and on this basis a device was developed for a fast-acting phase-sensitive maximum current protection of a mine electrical installation.

A mathematical model of a short circuit in a precinct network with a connected load was developed. The developed model allows to determine the magnitude of the phase angle between current and voltage, the nature of their changes. Since Since the industrial power grid contains active and inductive elements, during a short circuit, part of the inductive component of the network is abruptly removed from work, the angle between current and voltage changes dramatically.

In order to eliminate the influence of these factors, the device is supplemented with a functional unit that reacts to the rate of change of current in the power grid.

This master's work is not completed yet. Final completion: May 2019. The full text of the work and materials on the topic can be obtained from the author or his head after this date.

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