Steady State Stability MCQ Quiz in বাংলা - Objective Question with Answer for Steady State Stability - বিনামূল্যে ডাউনলোড করুন [PDF]

Concept:

Steady-state stability: The stability of a system refers to the ability of a system to return to its steady-state when subjected to a small disturbance.

The steady-state stability limit is given as

\(SSSL = \frac{{{V_1}{V_2}}}{X}\)

A higher value of the steady-state stability limit indicates higher steady-state stability.

Methods to improve steady-state stability:

• Higher excitation voltages: Higher excitation values give high SSSL value and hence the steady-state stability will improve.
• Upgrading voltage on the existing transmission system or opting for higher voltages on the new transmission system.
• The use of an additional parallel transmission line reduces transfer reactance X, thereby increases it.
• The use of a transformer with lower leakage reactance improves a steady-state stability limit.
• Series capacitive compensation of transmission line reduces transfer reactance X and hence steady-state stability limit increases.
• The use of bundled phase conductors reduces the reactance thereby increasing the stability limit.

Explanation:

Steady-state stability of a power system is

\({P_{max}} = \frac{{EV}}{X}\)

We can increase the steady-state stability by decreasing the reactance X.

In a double circuit line where two transmission lines are connected in parallel,  the reactance is less than the single line circuit and hence the stability can be improved.

Therefore, ​both Statement I and Statement II are individually true and Statement II is the correct explanation of Statement I

Maximum steady state power that can be transmitted over the line

\({P_{max}} = \frac{{\left| {{V_s}} \right|\left| {{V_R}} \right|}}{{\left| z \right|}} - \frac{{{{\left| {{V_R}} \right|}^2}}}{{\left| z \right|}}cos\theta\)

\(\theta = {\tan ^{ - 1}}\left( {\frac{2}{2}} \right) = 45^\circ\)

\({P_{max}} = \frac{{{{\left( {220 \times {{10}^3}} \right)}^2}}}{{2\sqrt 2 }} - \frac{{{{\left( {220 \times {{10}^3}} \right)}^2}}}{{2\sqrt 2 }} \times \frac{1}{{\sqrt 2 }}\)

Before fault

Steady state stability power limit

\(\begin{array}{l} = \frac{{{E_V}}}{{{X_{eq}}}} = 6.25\\ \frac{{1.0 \times 1.0}}{{\left( {0.12 + \frac{X}{2}} \right)}} = 6.25 \end{array}\)

⇒ x = 0.08 p.u.

After fault steady stability

Power Limit \(= \frac{{1.0 \times 1.0}}{{0.12 + 0.08}} = 5.0P.u\)

Steady-state stability of a power system is

\({P_{max}} = \frac{{EV}}{X}\)

We can increase the steady-state stability by decreasing the reactance X.

In a double circuit line where two transmission lines are connected in parallel,  the reactance is less than the single line circuit and hence the stability can be improved.

Therefore, Statement I is true but Statement II is false.

Steady state stability is defined as the capability of an electric power system to maintain its initial condition after small interruption or to reach a condition very close to the initial one when the disturbance is still present.

The steady state stability is very important in planning and designing of the power system, in developing special automatic control device, putting into operation new elements of the system, or modifying its new operating condition.

The estimation of steady state limit is important for power system analysis.The power system analysis includes the checking of an electrical power system in a specified steady state, the determination of its stability limits and qualitative estimation of the transient. It also estimates the choice of type of the excitation system and its controls, the modes of control, the parameter of the excitation and automation control system.

The selection of the stability is made by the requirements of the stability limit or quality of electrical energy under steady state condition or during the transient. The steady state limit refers to the maximum flow of power through a particular point without causing the loss of stability when the power is increased very gradually.

When all the machines in one part run together, then they are treated as one large machine connected at that point. Even, if the machines are not connected to the same bus bar and are separated by large reactance, they are also considered a large machine. The large system in a power system is always supposed to have a constant voltage and is treated as an infinite bus.

Steady-state stability limit = \(\frac{{{V_1}\;{V_2}}}{X}\)

More steady-state stability represents more transient stability of the system.

Steady-state stability limit of the system can be increased by the following methods:

• Upgrading voltage on the existing transmission system or opting for higher voltages on the new transmission system.
• The use of an additional parallel transmission line reduces transfer reactance X, thereby increases it.
• The use of a transformer with lower leakage reactance improves a steady-state stability limit.
• Series capacitive compensation of transmission line reduces transfer reactance X and hence steady-state stability limit increases.
• The use of bundled phase conductors reduces the reactance thereby increasing the stability limit.

सही उत्तर है- भयानक और घना

सही उत्तर है- पशु और पेड़-पौधे

Concept

The maximum power that can be transferred through a power system is:

\(P_m={EV\over X}\)

where, E = Induced EMF in an alternator

V = Infinite bus voltage

X = Total reactance

Calculation

Given, E = 1.6 pu

V = 1 pu

X = 0.6 + 0.2 pu

\(P_m={1.6\times 1\over 0.8}\)

P_m = 2 pu