The methods of definition of the parameters of series or parallel capacity compensative devices for perfection of characteristics of an electrotechnical complex “extended feeding line – asynchronous electric drive” is presented. Use of these devices allows to improve the real characteristics of the electric drive, increase its energy coefficients in state modes and the static stability so that dynamic properties are satisfactory. Functional diagrams of compensative devices and principle of their operation has been presented.
The cases of feeding of powerful asynchronous (induction) motors (IM) of important mechanisms are rather often on works of extractive, wood-working and others industries. It can result in perturbation of stability of asynchronous electric drives (ED) of such mechanisms in different modes because of the raised voltage failure in a feeding supply (cable or air line). The specified problem has the special urgency at a feed removed low-voltage (380, 660 or 1024 V) ED, when the mechanism characterizes by big flywheel masses or causes significant value of the idling torque. To such mechanisms can be referred coal combines, gang-saw frames, piston pumps, stamp presses, drag conveyors and others. In this paper the methods of a choice of variant and parameters of capacitor compensa-tive devices (CD) for the perfection of characteristics of the electrotechnical complex (ETC) “extended feeding line (FL) – asynchronous ED”, that provide the optimally probable on technical and economic reasons level of voltage on IM terminals, near the voltage of a con-ventional power supply (PS). As PS it can be the local distributive transformer or place of pa-rallel inclusion of other powerful IM. The generalized functional scheme of ED is submitted in a fig.1. The control of CD is carried out with the help of the control system СS, in which the information of IM stator cur-rent value received with the help of the sensor S, and also the prior information about a tech-nological work cycle of ED and ED initial condition is used.
The suggested algorithm of the decision of a task of reduction of FL influence on a level of voltage on IM terminals, is submitted in a fig.2.
For definition of electromagnetic IM parameters RV, XV resistances are taken. They define parameters, equivalent to them, – complete FL resistance
and corner 
,
describes a ratio between active and inductive components of complete resistance. Overload capacity values of voltage deviations were determined from a position of maintenance of re-quired stability of work according to [4].
Parallel, series and (in exclusive cases) mixed (series for the start-up period and parallel in the state modes) as alternative variants of compensation, and also appropriating cases of use of the parallel (fig.3) and series (fig.4) CD, were considered.
On the circuits (fig. 3, 4) are shown: K – switching devices (electromagnetic switches or semi-conductor keys); CLR – cur-rent-limiting reactor; CB – bank of cosine capacitors; DR – discharge resistors; SR – shunting resistor.
The place of CD setting (fig.1) depends on a variant and number of compensation steps. The algorithm of choice of a preferable compensation variant is submitted in tab.1. Thus, in case of use of series compensation the place of CD setting in FL
limits may not be rigidly regulate, in other cases it should be whenever possible closer to IM terminals.
3.1. ED with step parallel compensation
Parallel CD provides three steps of compensations with RP 52,1 kVAr, 86,4 kVAr, 445,9 kVAr. Section of CB, which appropriate to minimal step of compensation , is always in work. Steps of compensation appropriate the full compensa-tion of RP in idling ( ) and in nominal ( ) modes and 10% IM voltage deviation dur-ing starting ( ). Initial condition of ED: speed of IM rotor is equal to zero; switches K0, K2, K3 are in open state (see fig.3). Position of K1 is not regulated. For ED starting switch K0 closes, IM stator current raises fast to start value. With de-lay, appropriate to period of attenuation of current high-frequency components [7] (not more, than 20 – 50 ms), switches K1, K2, K3 close. Thus the starting step of CB is in work. Af-ter IM current decreasing at level appropriate to linear part of characteristic [(1,5…2,0)ISH ] the shutoff of starting step of CB carries out by K3 closing, thus switch to step , appropriating to nominal state mode, carries out. After closing of section CB3 it closes on discharge resistor DR3. Minimal step of compensation works at long-continued period of load reduction, for that at appropriating IM current decreasing by K2 closing section CB2 cuts off. For ED braking switch K0 opens.
The CB of series CD has nominal RP 685,9 kVAr, that is rather more than RP value of IM in starting mode, and allows to provide 10% voltage deviation of IM voltage during start-ing. The SR 1 Ohm provides the guarantee exception of self-excitation in starting pe-riod [7]. Initial condition of ED: speed of IM rotor is equal to zero, switch K0 is in open state, switch K1 is in close state (K1' is open) (see fig.4). For ED starting switch K0 closes, thus the series CD is in work. Current of IM raises to start value. After IM current decreasing at level appropriate to linear part of characteristic [(1,5…2,0)ISH ] the shutoff of series CD carries out by K1 closing. Discharge of series CD provides through resistor SR. For ED braking switch K0 opens. Use of series compensation in state modes isn’t considered as design mode.