Abstract
Introduction (Motivation)
In the energy sector under the survivability of the object is understood the property to withstand perturbations without allowing them to cascade development with a massive malnutrition consumers [1]. Persistence unit load, we assume the ability of consumers and their automatic defenses to counteract disturbances that may lead to crash it off.
One way to ensure the survivability of the site is a load switch (ATS). Power supply unit load should be restored not only damaged the main power supply or the disappearance of the voltage on the supply side, but also in cases that lead to the circuit breaker (when disconnecting the power supply due to false or non-selective tripping relay - RH, inadvertent breaker, the erroneous actions of the staff in the process of repair or commissioning, as well as damage to insulation in circuits operating current). High technical and economic efficiency and simplicity of schemes ABP led to their wide application in power systems and networks of industrial enterprises.
Effects of AVR devices should be single (in order to prevent multiple inclusion of backup power be eliminated if a short circuit) and only happen after you turn off the switch operating element of the tire consumers (to eliminate the power supply to the damaged element), so it usually start running from the auxiliary contacts in the actuator switch.
The unit should complement the protection of minimum voltage, which controls the voltage on the tire consumers in the case of his disappearance, acting on the circuit breaker of the working power source [2], if he stays on.
Vitality Power System (EPS) envy is its structure, configuration, reliability of electrical equipment, tools and automatic RH, as well as the qualifications of the staff, the stability margin, a reserve of active power [3].
When a short circuit network elements and the denial of triggering a range of protective switching devices (CAD), through which flowed through fault current, are so-called chain of the accident [4]. The 25 EPS and two ECO former USSR for 5 years were recorded 75 such incidents. And 81% of cases they occur because of damage to the network and failures in the functioning of APC [5]. They accounted for 90% of the damage to consumers of electric energy [6].
The degree of disorder in the functioning of plant accidents and violations referred to in the depth [5-7]. The depth of the chain of the accident depends on the location of the CP and the number of dead to the switchgear, through which flowed through the current emergency and set in motion their current protection. It can be characterized by the number of intact falsely disconnected consumers (section tires), or their loss, are associated with nedootpuskom electricity, downtime and disorders cycles.
Therefore, issues associated with assessing the survivability of load nodes real substation, there is an actual scientific problem.
Objective
Get the new dependency node survivability load on the frequency and duration of the appearance of short-circuit in the protected element of the network security features, through which passes through the current emergency and the timing of their diagnosis.
To achieve this goal it is necessary:
1. A mathematical model for survivability node load.
2. Getting engineering formulas with which we can estimate the survivability of the node load.
3. Example of calculating the reliability of the node load.
Scientific novelty
A new relationship for assessing the site load substation 110/10 kV.
Practical value
We propose an engineering method to evaluate the survivability of the node load substation 110/10 kV.
Results
Robustness index can serve as a frequency of the system of chain of accidents with different depth of a power failure [6]. The frequency of their occurrence in the short-circuit in the protected element of the network and the denial of triggering a number of APC, through which flowed through fault current is determined by the formula [8].
(1)
where λj- setting the flow of independent short circuit in the j-element of that network λs.i - the failure flow parameter in the triggering of the i-th APC; θi— time between preventive check-ups off of i-th APC together with its relay protection system, or ABP; m-number of APC, through which flowed through fault current (the effect of their primary or a backup RE required), or the number of sectional switchgear with ABP, failed to include; n - number of units elektooborudovaniya receiving elektoenergiyu on this download site.
Equation (1) is valid under two conditions:
- Intervals between appearances in the short-circuit element network and the time intervals between failures in the triggering of APC does not contradict the exponential probability distribution function with parameters respectively λj, λs.i;
- θiλs.i<0,1.
In cases where the second condition can utilize the services of the department of electricity industry and the cities of Donetsk National Technical University of mathematical models in the form of linear differential equations, allowing to predict the probability of chain (cascade) accident nearly any depth in the energy and network industries. It also developed the principle of constructing equivalent circuits for the evaluation of complex emergency situations and methods of collecting and processing the necessary statistical information. In deriving (1) adopted the following assumptions: - Security appliance can fail only when they are in standby mode; - If at the time of injury in the network, to which must respond to the RE, she was in good condition, it is unlikely her failure in the alarm mode [9,10].
Failures in systems of rare-earth and drive the switch detected and eliminated only by an absolutely reliable preventive checks. Refusal in triggering APC will understand this, which leads to failure to disconnect the damaged part of the network when in range of the short-circuit its relay protection [11].
If possible prevention systems disable APC will be the same, the formula (1) becomes :
The probability of cascading failure Q (t) at time t can be determined by the expression :
If Ht <0.1, then Q
Ht.
Example 1. Consider the scheme of power supply sections of tires I and II in Figure 1. 
year-1; λs.0=λs.1=λs.2=λs.3=λs.4=λs.12=λs.13=λs.14=0,098 year-1.
Necessary to determine the likelihood of accidental disconnection section tires I and II in the year when short-circuit in one of the elements of the network, receive electricity from the tire section I, ie probability of the accident chain.
Solution. When CP in one of the j (j =) RE elements triggered switching devices 14,13,12, and one of the switchgear (1-4) extending from the section of tire I.
Section I and II of a switch, switching devices 14, it does not work Blajan to place short-circuit switching device through which flowed through fault current, and switches 12 and 13.
By formula (2) when m = 3 we find:
From the expression (3) compute the probability of a chain (cascade) of the accident within 1 year, ie Emergency shut-off sections I and II, with a short circuit in one of the elements of the network, receive electricity from Section I. Since Ht <<0.1 we obtain:
Q(t)
H·t=H·1=3,32·10-7.
Conclusions
1. The results of calculation showed that if under observation for 1 year will be N = 3 * 106 power supply systems, similar to that shown in Figure 1 (the sum parameter flow and short circuit in electrical lines that receive electricity from Section I, will be 3 year -1 and the failure flow parameter in the triggering of protective switchgear - 0,098 yr -1), then statistically happen KZ in one of the elements that receive electricity from used tires I. This will lead to an emergency disabling sections I and II, ie happen chainlike (cascading) off undamaged consumers.
2. As can be seen from the calculations, the probability of coincidence in time and space of three or four random events is small. Therefore, when assessing the survivability of the node load is proposed to be ignored.
3. Changing the timing of prevention systems off the protective switchgear from 1 to 0.25, the site allows you to improve the survivability of the load factor of 16.
References
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When writing this master's work was not completed. The final work is available from the author or supervisor since December 2010.