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Ansisse Zakaria
Faculty: Computer Information Technologies and Automatics (CITA).
Department: Mining Electrical Engineering and Automation behalf Ruvim Leybov (MEA).
Speciality: Automatic control of technological processes (ACP).
Theme of master's work:
Research of processes in a mine local electrotechnical complex
at occurrence short circuit and development the device of automatic switching-off of return power streams of asynchronous engines.
Scientific adviser: Ph.D Candidate of Technical Science Konstyantyn Marenych.
About author
Abstract of the Master’s Qualification Work
Research of processes in a mine local electrotechnical complex at occurrence short circuit and development the device of automatic switching-off of return power streams of asynchronous engines.
Survey of research and developments.
The vast majority of processes on Mining company performed using actuators. Therefore Electrical Complex Technology is an essential part of mine element ensuring the functioning of the whole enterprise. Modern electrical installations are characterized by miner middle and high levels of power and is not stationary during implementation of a number of technological operations. Therefore, power of induction motor drive is carried out by flexible shielded cables. In fact, this cable is only element of the electrical complex of mine. that has no means of protection, the most vulnerable in respect damage as a consequence of the external wind shell, and in connection with squeezing. In the latter case will be place internal damage to cable insulation. In both cases phase to phase short circuit occurs, which characterized extremely high currents and is a danger of explosion methane-air mixture, ignition equipment.
All known overcurrent provide identification of a short circuit and disconnect the damaged network from the power transformer. However, this does not stop the flow of current short-circuit in the chain of damage, because it would have place replenishment of damaged points on the inverse energy flux induction motor.
The urgency of this work is due to the necessity of automatic detection of damaged power cable induction motor and the suppression of its reverse energy flow from the switchgear engine.
The purpose and objectives of the study.
The aim of research is to study the processes in the "starter - flexible cable - induction motor, " in occurrence of phase to phase short circuit in the cable, the rationale for setting the correct information about damage cable and the parameters of automatic feedback suppression of energy flows in the engine during its protective disconnected from the network.
To achieve this goal it is necessary to solve the following problem:
- analysis performed on the device and features of operation of electrical mining district of the complex;
- analyze the technical possibilities of the known methods and devices, overcurrent protection of power Precinct electrical;
- investigate the processes in mining precinct electrical complex is damaged flexible power cable power induction motor and to identify the information parameter, an acceptable way to implement automatic suppression of the reverse power flow induction motor in the circuit breaker of the precinct mains;
- justify the control algorithm with an automatic suppression of the reverse power flow induction engine in the power circuit breaker of the precinct mains;
- The structural and Principal scheme automatic suppression of the reverse power flow induction motor in the electrical circuit breaker of the precinct;
Object of study is grid area mines, designed to transmit electricity from a precinct substation site to all consumers plot.
The subject of the study are the processes in the elements of the complex plot of electrical shafts, due to the emergence of phase to phase short circuit in the cable, power induction motor.
Research methods
Theoretical studies based on the classical positions of the theoretical foundations of electrical engineering, theory of electrical machines, electric drive, the theory of transients, the theory of mathematical statistics.
Scientific novelty of the results:
- has been further developed a mathematical model of electrical mining district of the complex, taking into account the influence of EMF of rotation on the value of the induction motor current in the circuit supplying power cable damage;
-scientifically based principles for identifying damage in the supply power cable, and automatic feedback suppression energy flux induction motor.
The practical significance of these results is to develop technical solutions to significantly improve the operational safety of the precinct electrical complex in the mine through the reduction of the lifetime of the short-circuit in the power supply cable induction motor Consumer.
SUMMARY OF WORK.
In the introduction the urgency of the theme of master's thesis, are the main provisions which define scientific and practical significance of research results
The first section discusses the electrical network technology section of mine as an object of study. The features of the district unit of electrical industry. Functionality of the equipment used, including specific tools for the mining industry protection from circuit at the touch of the elements of power, normally are under.
Analyzed in detail the well-known scientific work in the theory of short-circuit and overcurrent protection means. It was established that, for the industrial district power grid, including mine supply, there are no technical means of the automatic suppression of the reverse energy flows. On this basis justify the purpose and objectives of the study.
Figure 1 - Typical schemes of mining district of electricity, based on: a - starters, b - control station, in the - management station and actuators.
The second section Validated mathematical models short-circuit in mining precinct electrical complex, taking into account the impact of reverse power flow induction motor and the specific manifestations of an emergency, depending on the number of phases in circuit mode.
Established that the short-circuit can be represented by a set of successive states:
- occurrence of short circuit and the flow of current to the point of closure of the transformer;
- continuation of the feeding point of short circuit from the transformer and the current flow to the point of short circuit from the stator IM emergency accession(the process continues until the protective power failure on the part of the transformer);
- the appearance of currents flow due to reverse EMF IM after the protective power outage;
- fueling point short-circuit only on the BP disaster accession (the process takes place after switching off the contactor starter related accessions).
Investigation of the process can be accomplished through the use of design models of the corresponding states electrical complex area of the mine. As a base we take the scheme of substitution ETC in a state of three-phase circuit between power supply and consumer BP (Fig. 2) [2].
Until such time breaker AB voltage losses in the transformer 
, trunk cable 
defined by a set of currents in the respective functional units, including short-circuit current Loss tension in the flexible cable 
a circuit point of short circuit determined by the current short-circuit
emergency connection:
where 
- power factor of power station in short circuit mode in the accession;
- respectively, active and inductive resistances transformer, trunk, and a flexible cable (taking into account the length of the latter to the point
short-circuit);
- power factor alarm connection;
- short circuit power in the accession;
- sum of nominal capacities related consumer;
- Rated power factor of the adjacent (other customers).
Figure 2 - Equivalent circuit of the ETC in a state of three-phase circuit between the power source and a IM customer.
Phase voltage equation is short-circuited section of the form:
where 
- the resulting inductance of phase with the influence of the other two phases [2];
The solution of this equation can be represented:
where 
– impedance circuit short-circuit;
– shift angle relative to the current tension in the chain;
– phase inclusion short-circuit;
- circuit time constant short-circuit - parameter of the exponential decay rate of the free
component of short-circuit transformer.
Starting from the moment of short circuit IM emergency connection ceases to receive power and serves as the electricity installations, generating an exponentially decreasing back emf "shunted" section of the network to the point short-circuit In this section the processes are described by:
where
- the resulting inductance of phase with the influence of the other two phases;
The solution of this equation with respect to current:
is a free and decays with time constant:
Thus, the total current at short circuit in the interval from the beginning of the process to disable the automatic switch network consists of the following:
or
In this case, obratngy energy flow induction motor can be expressed in its rotation the EMF:
where P – number of pairs of magnetic poles IM ;
– stator currents and rotor;
– inductance of the main magnetic field, based on the phase of IM ;
A - Index of the phase «А».
These relations are the base for constructing a computer model of the process. The study of this model allowed option to receive information about the origin of three-phase short circuit, which is the process of short-term intensive reduction of current in the stator induction motor with a subsequent increase of the current intense.
Considering IM as a consumer of electricity generating plants, should take into account the individual nature of exponential decline back emf due to the corresponding time constants engines. However, in the range of the enabled state contactors KM1 - KMn starters (Fig. 2) all IM generate the reverse EMF of the total short-circuited net (Fig. 4). This is due to the existence therein of equalization of currents, which are caused by a common back emf BP. Model and the analytic expression obtained in the latter study [6] and should be adapted to the parameters of the load, which is an active-inductive resistance of the cables from BP to the point of short circuit.
In the interval after switching off the power contactors, magnetic starters point short-circuit carried back EMF induction motor emergency connection that takes into account the relevant part of the expression (9).
The third section is made algorithmization the automatic suppression of the reverse power flow induction motor in the event of a short circuit in the power cable to power in the circuit breaker, designed schematics of the device. Shows the operational requirements of the developed device and justify the factors of economic efficiency.
Conclusions and directions for further research.
In justifying the model structure of a short circuit in the power of electrical accession complex technological areas of mine included the significant factors of influence. These include the combined effect of the reverse EMF of induction motors related consumers forming the reverse flow of energy supply point of short circuit.
Obtained constitute a model for the sound sequence characteristic process states allow a change in the current chart at short-circuit during the entire interval of its existence, which is the subject of further study. In the future, the process model can be adjusted to study the nature of the change in the current two-phase short circuit in the force joining the ETC section of the mine.
Thus, as a result of the research addressed the problem posed by the study of processes in the "starter - flexible cable - induction motor" when a phase to phase short circuit in the cable, justified the correct information parameter on cable fault and the parameters of automatic suppression of the reverse energy flows into the engine during its breaker from the network.
This allows us to significantly improve the safe operation of the power of district electrical complex in the coal mine.
Remark
When writing this abstract of master's work is not yet completed. Final completion: December 2011. The full text of work and materials on the topic can be obtained from the author or his head after the specified date.
References
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