In this article we will learn about the transient stability affecting factor of power system. we will also discuss about the important techniques for stability.
Transient Stability Affecting Factor of Power System
Factors Affecting Transient Stability and Techniques for Stability Important. Now we are going to discuss about the transient stability affacting factor of Power system.
Transient Stability Affecting Factor of Power System
Transient stability is a very important aspect of modern multimachine power systems. When a multimachine system becomes unstable, it is split into two groups of machines, which is go out of synchronism with each other while the machines within each group maintain synchronism. The grouping may differ with the fault location. Still, for a given fault location, the general behavior of a multimachine system is similar to that of a two-machine system. A two-machine system can be considered equivalent to a single machine connected to infinite bus. Therefore, the following conclusions, though based on a single machine connected to infinite bus, apply equally well to a multimachine system. These are some transient stability affecting factor of power system.
Factor Affecting Power System Stability
These are some Transient stablity affecting factor of system which are affect the stablity of power System
Effect of Generator Design
A heavy machine has greater inertia and is more stable than a light machine. In the present day competitive market the trend in generator designing is to achieve more power than from smaller machines. However, this trend is undesirable from the stability point of view. In earlier days, a large number of small machines were employed to derive large power. This was not a desirable feature from system stability considerations. A salient pole generator operates at lower load angles and is preferred to cylindrical rotor generators from considerations of stability.
Increase of Voltage
The amplitude of the power angle curve is directly proportional to the internal voltage of the machine. An increase in voltage increases the stability limit.It is basic Transient stablity affacting factor of power system.
Reduction in Transfer Reactance
The amplitude of the power angle curve is inversely proportional to the transfer reactance. This reactance can be reduced by connecting more lines in parallel. When two lines are in parallel and a fault occurs on one of the lines, some power is transferred over the healthy line except, when the fault is at the receiving end or sen ding end bus. This power transfer aids stability. Some features of the power system layout and bussing arrangement also help in improving stability. The use of bundled conductor lines helps in reducing reactance by series capacitors is another effective method of improving stability. However, the series compensation should be used only after its effects system voltage profile, over voltages during faults, end protection schemes have been studied. It is main transient stablity affecting factor of power system.
Rapid Fault Clearing
It is seen from the equal area criterion that stability is improved by decreasing the accelerating are A1 and increasing the reaccelerating are A2. This can be achieved by decreasing the fault-clearing angle (by using high-speed breakers) provided all the other factors remain the same.
Most of the faults on the transmission lines are of transient nature and are self-clearing. Modern circuit breakers are mostly of reclosing type. When a fault occurs, the faulted line is de-energized to suppress the arc in the fault and then the circuit breaker recloses, after a suitable time interval. Automatic reclosing increases the reaccelerating are A2 and thus helps in improving stability.
Stability Improvement Method of power system
Use of Double-circuit Lines
The impedance of double-circuit lines is less than of a single-circuit line. A double-circuit line doubles the transmission capacity. An additional advantage is that the continuity of supply is maintained over one line with reduced capacity when the other line is out of the service for maintenance or repair. But the provision of additional line can hardly be justified by stability consideration alone.
Use of Bundled Conductors
Bundling of conductors reduces to a considerable extent of the line reactance and so increases the power limit of the line.
Series Compensation of the lines
The inductive reactance of a line can be reduced by connecting the static capacitors in series with the line. It is to be noted that any measure to increase the steady-state limit P max will improve the transient stability limit. The use of generators of high inertia and low reactance improves the transient stability, but generators with these characteristics are costly. In practice, only those methods are used which are economical.
High-speed Excitation System
High-speed excitation helps to maintain synchronism during a fault by quickly increasing the excitation voltage. High-speed governors help by quickly adjusting the generation inputs.
Rapid isolation of faults is the principle way of improving transient stability. The fault is the principle way of improving transient stability. The fault should be cleared as fast as possible. It should be noted that the time required for fault removal is the sum of relay response time plus the circuit breaker operating time. Therefore, high speed is relaying and circuit-breaking arc commonly used to improves stability during fault conditions. it has now become possible to isolate the fault in less than two cycles (that is, 0.04 s for 50 Hz system). System stability can be further improved by making circuit-breaker recloseure automatic, as many faults do not re-establish themselves after restoration of supply. The time interval between line removal and reclosure should be reduced keeping in mind that the line must remain de-energized for a certain minimum time in order that the line insulation should recover fully.
Some Additional Transient Stablity Affecting Factor of System
In this method, an artificial electric load in the form of shunt resistors in temporarily connected at or near the generator bus. Such resistors partially compensate the reduction of load in a generator following a fault. The acceleration of the generation rotor is therefore, reduced. For this reason, these resistors are called braking resistors. This method is also known as “dynamic braking”. A control scheme connects the braking resistors to the generators through circuit breakers. The scheme also determines the amount of resistance to be connected and the duration of its connection. The braking resistors are connected immediately following the fault and remain in the circuit for few cycles. They are disconnected at the moment of reclosure when the system voltage has recovered.
Turbine Fast Valving or Bypass Valving
In the event of a fault, the generator output is reduced resulting in a high accelerating power. If the mechanical input power to the turbine could be momentarily reduced, the acceleration could be reduced. Fast valving is a means of reducing the mechanical input power to the turbine during the fault. Certain steam valves are rapidly closed (in 0.1 to 0.2) and immediately re-opened. This procedure increases the critical clearing time. it is also transient stability affecting factor of power system.
Majority of the line faults are single line-to-ground (LP) faults. In single-pole switching (also called independently pole operation), the three phase of the circuit breaker are closed or opened independently of each other. In the event of an LG fault, the circuit breaker pole corresponding to the faulty line is opened and the remaining two healthy phases continue to transfer power. Since most of the faults are transitory, this phases can be reclosed after it has been open for a predetermined time. The system should not be operated for long periods with one phase open. Therefore, provision should be made to trip the whole line if one phase remains open for a predetermined time. This is basic transient stablity affecting factor of power system.
High voltage direct current (HVDC) links are helpful in maintaining stability due to the following advantages
- D.c tie line provides a loose coupling between two a.c. systems to be interconnected.
- D.c. link may be interconnecting two a.c. systems at different frequencies.
- There is no transfer of fault energy from one a.c. system to another if they are interconnected by a d.c. tie line.
- Load shedding
If there is insufficient generation to maintain system frequency, some of the generators are disconnected during or immediately after a fault. Thus, the stability of the remaining generators is improved.
The unit to be disconnected unit is resynchronized and reloaded. Extra cost of a large steam bypass system is the limitation of this method. disconnection of some consumers, that is, load shedding (removal of load ), is also help in improving transient stability.
Hence these are trasient stablity affecting factor of power system.we have also studied about stablity improvement of power system. If you will find any incorrect in above article you must comment below in comment box.