Abstract on the theme of the final work
Plan
2. General stability analysis units at small load disturbances.
3. Basic mathematical relations for the static stability analysis of load units.
3.1. Calculation of the stability of asynchronous and synchronous motors.
1 Introduction
Determination of conditions of stability of electric power load is one of the stages neobidnyh general analysis of energy systems, determining the capacity of transmission lines, choice of controls, regulations, etc. Such studies are performed both at different stages of design and during operation - mainly to clarify the area of permissible modes.
Calculations of load resistance as required in the design of electricity industry to develop measures that are unique resorts continuity manufacturability processes in various modes of operation and businesses of various perturbations.
Stability analysis of power systems generally involves analysis of the stability of static or dynamic as generators and motors. In power systems possible cases when the violation of stability of generators does not lead to violations of engines. At the same time, possible system situations that cause inhibition and subsequent cut-off large groups of engines while maintaining the parallel operation of generators. Therefore the problem of sustainability is very important dvuhuniv.
The objective is to analyze the static stability of industrial customers from dyhunnym load in the presence of synchronous and asynchronous motors.
For the purpose of the study were asked and addressed the following objectives:
• Software development for the study of theoretical static stability of the secondary criteria;
• development of software for the design of the definition of static stability conditions by small fluctuations;
• development of guidelines for making laboratory work to studyth static stability conditions more simple electrical system.
The feature of load units calculations of stability is the use of computers using appropriate mathematical models. Mathematical description of the propulsion load zkladayetsya depending on the number of engines that are enabled in the node. We must distinguish three main cases [7].
1 A small group of engines. Engines vvoditsya directly in the calculation: each of them considered their equations and parameters.
2. Groups from many engines that serve one production. Such groups are replacing a small number of engines.
3. Powerful nodes load. Their description for calculating stability is based on concrete data on the composition and parameters of the load distribution network by using some parameters obtained by statistical analysis.
Use of industrial enterprises napivprovodnykovyh converters, arc furnaces for melting of direct heating of steel, electric plants cause large consumption of reactive power. Therefore, the analysis of electromechanical transients must consider the impact on the stability of reactive power components of electrical loads.
In practice, stability investigation units used complex load calculation models [4] describing a simpler scheme odnouzlovogo. Such models allow to reproduce the main features of transients in electric motor and consider the effects of other electro.
Complex computational load containing the equivalent equation of asynchronous and synchronous motors, as well as static load. Under static loading understand the burden that has no magnetic fields, rotating: lighting, electrical, municipal and household appliances, capacitor batteries, inductive and active support network elements.
2 General provisions stability analysis for small units of loading perturbations
Small disturbances may occur under the influence of power (voltage and frequency changes) and as a result of changing the system itself and its elektrospozhyvachiv in terms of process (the change of power lines, Operational switching, etc.). Under these conditions, electrical properties and electro unit load type significantly affects its stability.
Static stability of the industrial unit load calculated as follows [1]:
- Replace the node load estimated model and define its parameters;
- Allocate substantial parameters and criteria of stability for the scheme, electricity
- Assess the possible mode of critical importance for stability of essential variables.
Unit load of induction motor model zamischyuyut calculated as the equivalent induction motor. Uncertainty replacement depends on how its implementation [3]. The choice of criterion depends on the purpose replacement problem which is solved and the required accuracy. In approximate calculations can use statistical parameters of the equivalent engine [2].
Raznotypnist synchronous motors in units of load is small. This allows them to take into account the actual parameters and normal parameters. In the approximate calculation of load resistance nodes use the average values of synchronous motors. They differ depending on the type of engine (yavnopolyusni, neyavnopolyusni).
Unit load, which is asynchronous and synchronous motors, represents a complex model estimated. Its parameters can be set in lieu of individual component load characteristic that describes static characteristics. For approximate calculations, we can use average values of model parameters are given in [1].
Fugure 1 - Computational model unit load
Resistance unit load by analyzing the pattern of all the assistant power supply system and the parameters of its regime. Depending on the specific conditions of power calculation scheme reduce to one of the main types listed in img. 1
This enables the use of stability criteria praktychniy. Thus, the four computational models otymuyut uzla load yaui differ stability criterion:
1. Model, where the voltage in the node load is an independent variable, regardless of the mode of electro, which allows to calculate stability independently for each specific group of electro at its main criterion (img. 1, a).
2. Model, where specific groups of electro radially connected to an external resistance tires node load, the voltage at which an independent variable mode (img. 1, b).
3. Model, where specific groups of electro-called "associated with the node to an external load resistance and is independently variable regime emf. zhderela supply (img. 1, c).
4. Model, where the load node contains all the typical components and source of reactive power (DRP) (img. 1, d).
3 Main mathematical relations for the static stability analysis of load nodes
3.1 Stability calculation of asynchronous and synchronous motors
Violation of static stability in its early stages can be characterized by variable (aperiodychnym) changing display settings, such as increasing the angle of the load when the power drive mechanism above the maximum value. Under certain conditions prayed as violations of the static stability at the onset and growth parameters of vibration mode (oscillatory violation). The main reasons that cause breach aperiodychnoho type is the growth of capacity, increasing the external resistance znachnye and often reduce tension in the node load. Of course stock for static stability is assessed value of allowable load voltage reduction at the point of power under normal condition the unit, or unlock when some power lines [8].
Voltage clamp on the engines and independent of the operating mode of motor emf. called critical power () if they meet the boundary aperiodychnoyi stability. Critical behavior for synchronous motor, called "deal with the source of emf. constant resistance, defined by the following expression
Independent evaluation of host resistance load for certain groups of asynchronous and synchronous motors running for the calculation model according to Fig. 7.1 a and b. The significant independent variable in this case is the voltage at node tire load. To assess its stability using the main criteria of stability:
and 
It should take into account the characteristics of the cast and their loading mechanisms.
For induction motors (or equivalent) The basic requirement
is a violation of the stability equation 
. When Ммх=соnst engines and direct connecting to
the tire unit load critical parameters that correspond to the boundary regime
of its static stability, defined by the formulas:
When you turn the engine to load the site through its own external support zzov1, and zzov2 zzov3 (img. 1, b) calculation of boundary parameters and stability of the regime is the same with these resistances.
If resistance to neglect, then. Calculated formula in this case have the form:
(1)
With the known characteristics of the mechanism of Ммх = f (s) boundary mode parameters found by solving the equation system:
(2)
Given the expression for calculating the boundary sliding
and equations (1) after appropriate transformations of equations (2) takes the form:
(3)
Calculating the system of equations (3), One can determine the parameters of Us CD and su to the boundary for the stability of the regime, where all the static stability boundary sliding is more su boundary sliding at M <Mmax / (1 xzov / xs).
In approximate calculations consider. Then after the solution of equations (7.3) we obtain
. (7.4)
> When p = 0 there is a case of personal expression 
and to determine the
critical voltage is converted to the corresponding expression obtained from
(1).
The critical voltage is determined by inference engine
shutting ravenstva current stator and rotor current consolidated 
. As
,
and taking into account (1)
,
expression for the critical voltage clamp on the engine can be written as:
. (5)
Static stability of synchronous motors connected to the node
with the same load voltage and frequency at threshold condition is violated 
. Subject
and
this condition can be represented as follows:
. (6)
If no devices AER derivative engines 
and for the
static stability boundary corresponds to the angle mode 
when
(7)
Electromotive force in destinies of its value at idle is determined by the expression
(8)
where 
;
.
(9)
and always less than the critical voltage is defined by the expression (7) In the absence of AER, since the transition resistance is much smaller than the synchronous.
The presence of an external resistance when connected to the node load of asynchronous and synchronous motors reduces the threshold for static stability maximum active power and increases the value of critical voltage at load node. This in turn makes more strict requirements for voltage stability.
Figure 2 - Determination of the critical voltage of load node without account of power compensating devices
Figure 3 - Determination of the critical voltage of load node light power compensating devices
4 Conclusions
In this master's work deals with methods of evaluation of static stability of all these computational models of host load. In an environment of universal mathematical processor MathCAD 7.0 Developed software for specific calculations. Using the developed programs vykonyutsya static stability calculations using different criteria node load substation Avdeyevka - 35. At this stage of the master's work is not complete.
5 List of sources
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