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Potapenko Alina
AUTHOR'S ABSTRACT
on a theme:
"Development of the device of protection against short circuits of a mine local network"
argument
Introduction
The analysis of object of research
Research of processes in object
Substantiation of basic assumptions
Substantiation of mathematical model of object of research
Results of modelling
Conclusions
The list of references
Introduction
Specific conditions of operation of underground electric installations of mines lead to their more frequent damages, than electroequipment of other enterprises. The most dangerous on the consequences are short circuits as they in conditions of mines underground developments not only cause damages of the miner equipment, but also can be the reason of fire or explosion.
In this work questions which concern to the theory of short circuits are considered, and also process of short circuit in the local electric system depending on set of influencing factors is simulated.
The analysis of object of research
The combined low-voltage electric network of a site of mine represents a complex of electromechanical installations, such as: a combine, the conveyor, stationary installations in structure of which electric motors work. For a feed of engines systems of electrosupply which in aggregate with electric drives make a low-voltage electrotechnical complex are provided. The scheme of a low-voltage electrotechnical complex of mine is presented on (fig. 1.).
Figure 1 - The scheme of mine low-voltage electrotechnical complex
The electrotechnical complex contains:
Limitation of space in mountain developments at insufficient light exposure considerably complicates installation, service and preventive repair of electric equipment. Untimely e limination of the arisen malfunctions in the electric equipment and erroneous actions of the attendants are the reasons of occurrence of short circuits (SC) in the miner electric equipment.
At SC there can be different unsafe consequences [2]:
Research of processes in object
Substantiation of basic assumptions
At calculation of model of an electric circuit we obviously neglect values of active resistance and reactance of the automatic switch, the actuator, believing, that these values are insignificant and do not render essential influence on results of calculations and results of modelling.
Substantiation of mathematical model of object of research
On fig. 2 the simplified scheme of the electric system of a site of mine is presented.
Figure 2 - The simplified scheme of an electric network of a site of mine
For researches we shall choose a site consisting of transformer substation ТСВП, the automatic switch АВ, one actuator ПВИ, the thyristor switchboard and the asynchronous electric motor of the mine machine the АД.
Let's transform the scheme shown above, having presented in the form of set of the structural blocks representing active and jet resistance. On fig. 3 the block diagram of an electric network of a site of mine is presented.
Figure 3 – The simplified block diagram of an electric network of a site of mine
On the processes occurring in a network, at short circuit following factors influence:
The simplified settlement scheme is presented on fig. 4.
Figure 4 - The simplified settlement scheme of an electric network of a site of mine
Considering the accepted assumptions we shall make the equations of mathematical model, using II Kirhgof’s law:
for 1-st contour:
-EA + EB = i1 ∙ RΣB + i1 ∙ RΣA + i2 ∙ RΣB + LΣA ∙ (di1/dt) + LΣB ∙ (di1/dt) + LΣB ∙ (di2/dt);
for 2-nd contour:
EB - EC = i2 ∙ RΣB + i2 ∙ RΣC + i1 ∙ RΣB + LΣB ∙ (di1/dt) + LΣC ∙ (di2/dt) + LΣB ∙ (di2/dt);
let:
1. LΣA = L1A + L2A + L3A + LEA;
LΣB = L1B + L2B + L3B + LEB;
LΣC = L1C + L2C + L3C + LEC;
2. RΣA = R1A + R2A + R3A + REA;
RΣB = R1B + R2B + R3B + REB;
RΣC = R1C + R2C + R3C + REC;
3. We shall accept LΣA = LΣB = LΣC
RΣA = RΣB = RΣC
Then LΣ = LΣA = LΣB = LΣC
Phase currents are equal:
iA = - i1;
iB = i1 + i2;
iC = - i3.
Results of modelling
As a result of modelling schedules of dependence of change in time of phase currents IА, IВ, IС have been received at three-phase SC (fig. 5-7).
Figure 5 - The Schedule of dependence in time of a current of a phase A
Figure 6 - The Schedule of dependence in time of a current of phase B
Figure 7 - The Schedule of dependence in time of a current of phase C
The sum of phase currents is equal to zero. Check:
Figure 8 – The Schedule of dependence in time of the sum of phase currents A, B, C
Conclusions
As a result of mathematical modelling transient of occurrence of short circuit in an electric network which is accompanied periodic and aperiodic by components of currents of short circuit is received.
The developed mathematical model can be used for more detailed studying process of short circuit on mines and creations of protection in view of all influencing factors.
The list of references