For example, what is the difference between voltage stability and voltage security?
For any power system, main control are active power(KW) control, and reactive power control(KVAR). Active power can be increased by increasing torque angle (delta), one can get maximum power transfer at delta equals to 90 degree(steady state limit) which is theoretical (cannot be reached) because with little disturbance, system will be unstable. Hence the stability limit(below 90 degree) at which system can remained stable(in synchronisam ) or bare the maximum disturbance of torque angle (delta) is called transient stability limit at which system normally operates.
Efficiency, reliability, and voltage control point view,0.8 lag is considered to be the best power factor. With increase in torque angle (increased KW), if the increased KVAR demand is not satisfy the power factor will more lagging,hence more current demand and the relatively,increased voltage drop will reduced supply voltage, hence for power system security(voltage) constant reactive power control is also needed, with increased KW demand,
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in practical field Power system stability means, system will stable in any loading condition or in load fluctuation,
Not think about generation, because you have an estimated idea about generation so grid construction is according to that .
but protection depends on both side, i mean load side and generation side. No estimation, any thing can happens on any time.
Modern active power(KW) and reactive power(KVAR) control are done economically from load dispatch centers, system are rigid with large inertia with ability to bare quite large disturbance. Normally online monitoring with "load frequency control" is enough to keep system stable(nothing can happen,system would be quit reliable).
Stability relates to the system response to load, while security has to do with what influences from outside can do to you system's ability to supply e.g. terrorism..
The system adequacy is associated with the planning of power systems for long-term facility expansion, short-term marketing , and operational planning including
unit commitment and economic dispatch among available generation systems. Meanwhile, the system is subjected to different kinds of uncertainties within an operation, which may have planned or unplanned sources. The planned outage
can be due to the maintenance of sub-systems and components.
Moreover, the unplanned uncertainties can be induced by generation-demand unbalance, load forecasting, renewable power uncertainty, failure of any component, short-circuit, large load changes and so on. The occurrence of any contingency in the system may cause system variables violation.
These violations could be line thermal over-loading, system busses voltage, generator rotor angels, and system frequency.
They are associated with the different phenomena in the power system and may disturb the power delivery. Therefore, the system must be able to withstand and/or response to any sudden contingency to maintain power delivery. This ability is called power system security
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