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The combined low-voltage electric system of a site of the mine is a system of flexible cables which are characterized by presence of the generallow-voltage transformer substation, automatic switches and set of actuators according to the number of electric consumers. Asynchronous engines with phase and short-circuited rotors are applied as electroconsumers.
The greatest number of damages happens in a mine local system in comparison to other sites of electrosupply of mine.
Principal cause of occurrence of short circuit in underground electric installations is mechanical influences.
The The flexible cables installed directly in faces have an enormous breakdown susceptibility.
Conditions of operation of the electric equipment in underground shaft of mines define special requirements for construction of the protection system of local system against currents of short circuit.
Some means of maximal current's protection are built in the equipment to protect underground electric installations against currents of short circuit.
One of the tasks of maximal current's protection is to prevent dangerous action of currents of short circuit through intact elements of underground electric installations.
Teristor's regulators of pressure (ÒRP) have received a widly used now. They are used as the devices of smooth start-up functioning in the mode "soft-start"of the asynchronous engine. They are applied to improve operational parameters of electric drives.
Advantages of teristor's regulators of pressure are the simplicity of the power scheme and system of the engine.
Function teristor's regulators of a pressure is connected with realization of the principle of phase regulation of pressure on load. It means that its size can be changed from zero up to rating value corresponding to alteration of unlocking teristor's corners from 180° to 0°. Thus, the current of short circuit depends on the parameter of tiristor conductivity on the outlet tiristor's regulators of a pressure as well, and maximal current's protection should have function of correction of level operations.
The current of short circuit can appear lower due to the size on load under deep regulation of a target pressure of tiristor's regulators of a pressure than nominal starting current of asynchronous engines. It will lead to protection failure.
Dependence on change of a current of short circuit from electric system parameters show essential decrease in a current of short circuit with increase in a corner of tiristors unlocking and lengths of a cable.
It demands the development of additional technical decisions with the purpose to correct sensitivity of maximal current's protection. The basic scheme adapted to an electrotechnical complex with tiristor's regulators of a pressure is presented in figure 1.
Figure 1 - The basic scheme of the device maximal current’s protection
The given device dynamically allows to correct a level of operations of maximal current's protection depending on a corner of unlocking tiristors.
Thus, the developed device allows to increase accuracy of operation of maximal current's protection in the low-voltage local electric system containing tirister's regulators of pressure, in particular, the device of smooth start-up of asynchronous electric drives - "soft-start".
The mining combined electric systems supply all mine with electric power. All mining works are impossible without electricity service, because it controls all technological processes.
The developed device meets modern requirements and has five steps of correction so it will provide reliable system switching-off if short circuit arises.
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