Scientific Supervisor: dr.sc., Grebchenko Nickolay

   Presently humanity practically cannot treat without the electric power, it has found the application in all areas of human activity, and its necessity for the further development of a human society is obvious. Since origin of power the question of trouble-free serve of electricity of necessary quality was an integral part of the general concept of electrification.

   It has not lost the actuality and for today. It gets a special actuality taking into account a situation of the Ukraine which has developed for today in power. In the conditions of permanent worsening technical condition of the basic power equipment which considerable part has developed the resource. It leads to increase in quantity of the damages which most part is made by short circuits (s.c.). In many cases the occurrence reason s.c. or the further development of failure deterioration of electric isolation of an electric equipment is. That why exposure and removal of isolation’s defects in good time will allow preventing the most part of damages thereby considerably having reduced expenses for repair or replacement of the equipment after damage. Increase of reliability of work of electric systems requires not only exposure of isolation’s defects in operating conditions, but also definitions of a place of occurrence of defect, i.e. findings of a concrete phase of joining with defect and distances from the joining beginning, for example a cable-engine, to a defect point.

   Qualifying work of the master is executed during 2009-2010 according to the scientific directions of department «Power plant" of Donetsk national technical university.

   The considerable stake of damages of joining a cable - the electric motor is connected with origin and development of local defects of isolation (on occasion to 90 % from total number of defects). For prevention of their development it is necessary to perform preventive works on restoration of dielectric properties of isolation in due time. It is possible to reach substantial reduction of time of carrying out of such works if we will provide revealing of the fact of appearance of local defect and a place of its occurrence on the working electric motor.
   Searching for a place of origin of defect on the disconnected electric equipment requires an extra time that is not always comprehensible not only for economic reasons, for example, because of shortages of vacation of production, but also on conditions of providing stability of work of loading. Sometimes, for example, at long switching-off of a feeding line 6–35 кV for search of a place of local defect of isolation or the threat of violation stability of the electric system arises up from the damage of other elements as a result of refuse.

   For defining of distance to the place of shorting on the earth apply remote [1], local [2], frequency [3] and other methods. The basic failings of modern methods are, as a rule, the impossibility of their use in operating conditions or impossibility of revealing of a place of short circuit in the presence of transitive resistance in a short circuit place.

   In this connection the task is put to develop concerning a simple method of revealing of defects of isolation in the working electric motor and a cable feeding it. Initial information should be parameters of operating condition.
   The purpose of carrying out of experimental researches is check of new methods of definition of parameters of local defects of isolation and reception of experimental dependences of parameters of operating conditions from parameters of local defects of isolation.

   Frequently quality of isolation is estimated only on size of its resistance that does not allow revealing the damages which are not accompanied by decrease of its resistance. However there are famous methods which allow to estimate more full quality of isolation thanks to the additional control of its capacity at giving of constant tension [4] or tension of various frequency [5]. Estimation of a technical condition of a winding of the electric car can be carried out on the transient arising up at a serve of a test signal on one of clips of a winding and the case [6]. But in system of own needs of power plants expediently specified methods to apply not separately for a cable and the engine, and simultaneously for all electric joining. There is also a device for the automatic control of isolation of electric system which works at increase of value of a current of loss anymore set [7]. But this device works at isolation deterioration in any point of a network and on any joining, that is the device cannot choose the damaged joining.

   Now in many organizations proceed works of perfection of relay defence , and new methods and diagnostics of working an electric equipment [1-3] are conducted. The special attention is given to search of a place of damage. For example, [5] the original method of definition of a place of single-phase short circuit on the earth is offered. It is focused on revealing of defects in lines. At the same time there are no the methods, allowing to reveal local defects of isolation in windings of electric motors and to define parameters of these defects (remoteness from the beginning of a winding and size of resistance of isolation in a defect place) in operating conditions.

   The report on a work theme is presented at conference by "Day of a science-2010" to DonNTU of chair power plants. Donetsk, DonNTU-2010.
   Except only said the report on Odessa the Internet of conference also has been given 2010.

   Researches were spent on the physical model of joining executed on the basis of the electric motor by tension 0,22 кВ which is connected through a cable to the dividing transformer of 0,38/0,22 sq. phases In a winding And strator of electro- engine are executed soldering on in various points which are deduced on special terminalchart of substitution of physical model of joining is resulted on fig. 8.1

Figure 8.1 - chart of substitution of physical model of joining a cable-engine
(animation: volume - 26.9 kbyte; size - 500х256; consists of 9 frames; a delay between frames - 120 msec; a delay between last and the first frames - 0 msec; quantity of recycle - 5)

   Treatment parametres of mode (phase currents and tension of phases in relation to the earth) it was carried out by means of an information input equipment in the personal computer which basis is made by payment Е-154 (the maximum integrated nonlinearity of transformation of 0,06 %). In each channel modules of a galvanic outcome and rationing of signals are established. Accuracy of transformation in these modules makes 0,05 %.
   The program of researches included experiences on modelling of local defects of isolation in various points of a cable and a winding stators the electric motor. As a result of carrying out of experiences of connection various soldering on puttee of stators through the resistor 200 Ohm with "earth" are received dependences of digital sequences on time which correspond to currents of phases IА, IВ, IС and tensions of phases concerning "earth" UA0, UB0, UC0. Digitization time is accepted equal 0,1 мs. These sequences are approximated by polynomial regress with use of a method of the least squares. For each parameter of a mode it was processed on 1000 points. As approach function the sinusoid by frequency of 50 Hz is accepted. The amplitudes received as a result of approximation and a phase of corresponding parametres is resulted in tab. 8.1.

Table 8.1 - parametres of operating conditions of joining a cable-engine at resistance of defect of isolation 200 Ohm

   The note. The experiences marked with an asterisk, are spent at presence coil short circuits in the middle of a winding stator EM. Number of the become isolated coils of 6 %. The current in the become isolated coils has made 1,4IНОhm/p>

   On fig. 8.2 and fig. 8.3 some results of physical modeling of defects of isolation in various points of the cable feeding electric motor are resulted.

Figure 8.2 - module of a current of zero sequence at change of a point of local defect

Figure 8.3 - Phase of a current of zero sequence in relation to a vector of tension UA at change of a point of local defect

   Principal cause of nonlinearity of the received dependences is redistribution of capacities of ways of course of currents through sites of a cable which are from the different parties of local defect.
   Presence of EM in controllable joining leads to that three-phase methods of revealing of defects of isolation, suitable loadings for other kinds, have low accuracy. It is caused by the static and dynamic asymmetry EM, shown that values of longitudinal resistance of phases EM are not equal each other and are not constant in time. For increase of accuracy of definition of remoteness b to a point of local defect it is offered to carry out calculation of longitudinal resistance ZA of a phase with defect of isolation for time moment tb value calculation b. Thus for calculation b values of parameters of a mode for the same moment of time tb are used. If for definition of vectors of parameters of modes approximation of current values in the digital form parameters for this purpose undertake 1-2 periods of industrial frequency is preliminary used. At calculation ZA it is necessary to consider a power failure from a current of zero sequence on site ZA from the beginning of joining to a defect point, i.e. On a site b*ZA.

   On fig. 8.4 the equivalent circuit of joining a cable-electric motor in the presence of Zdef on remoteness b from the joining beginning is resulted.

Figure 8.4 - Equivalent circuit of joining a cable-electric motor

   On the basis of an equivalent circuit resulted on fig. 8.4, the system of the equations describing a current condition is made. As a result of the decision of this system algorithms of definition of remoteness b (fig. 8.5 and 8.6) are received.

Figure 8.5 - Algorithm of definition of remoteness b at known Zdef

Figure 8.6 - Algorithm of definition of remoteness b at not unknown person Zdef

   In tab. 8.2 results of remoteness on the algorithm represented on fig. 8.5 are resulted.

Table 8.2 - Error of definition of remoteness b to a point of local defect (Rdef=200 the Ohm) in a winding статора the electric motor, %

1. Results of experimental researches of joining a cable - the electric motor are resulted at physical modelling of local defects of isolation in various points of a feeding cable and a winding stator electric motor.
2. Algorithms of calculation of remoteness of local defect and size of resistance of this defect are offered. Results of calculations of remoteness on the basis of experimental data have shown that the error of the developed algorithms does not exceed 7 %.

At writing of the given abstract a master’s work has not been finished yet. Date of the work’s final end is on December, 1st, 2010. Full text of work and materials on a theme can be received from the author or her supervisor after the named date.

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