Power system stability

For coherent machines the equivalent inertia constant(H) is given by 

• 1. H₁H₂

• 1. H1 - H2

• 1. H1 + H2

• 1. H1/H2

Transient state stability is generally improved by

• 1. Using high speed governors on machines

• 1. Using low inertia machines

• 1. Dispensing with neutral grounding

• 1. Any of the above

The synchronizing power is _________ when two alternators are running in synchronism.

• 1. Negative

• 1. Positive

• Zero

• 1. Cannot be determined

Equal area criteria and Swing equation are used for _______ and _________ stability respectively

• 1. Steady state, Transient

• 1. Transient, Steady state

• 1. Both are used for steady state stability

• 1. Both are used for transient stability

Explanation:

Equal area criteria and Swing equation are used for transient and steady-state stability respectively.

The ability of a synchronous power system to return to stable condition and maintain its synchronism following a relatively large disturbance arising from very general situations like switching ON and OFF of circuit elements, clearing of faults, etc. is known as transient stability.

Steady-state stability is defined as the capability of an electric power system to maintain its initial condition after a small interruption or to reach a condition very close to the initial one when the disturbance is still present.Consider a lossy transmission line with V₁ and V₂ as the sending and receiving end voltages, respectively. Z and X are the series impedance and reactance of the line, respectively. The steady-state stability limit for the transmission line will be

• Greater than (V1V2)/X

• less than (V1V2)/X

• equal to (V1V2)/X

• equal to (V1V2)/Z

The power transfer capability of a transmission line is the most affected by _______.

• 1. Shunt conductance

• 1. Capacitance

• 1. Resistance

• 1. Inductance

Stability of a system is not affected by

• 1. Reactance of line

• 1. Losses

• 1. Reactance of generator

• 1. Excitation of generator

The angle δ in the swing equation of a synchronous generator is the

• 1. angle between stator voltage and current.

• 1. angular displacement of the rotor with respect to the stator

• angular displacement of the stator mmf with respect to a synchronously rotating axis

• 1. angular displacement of an axis fixed to the rotor with respect to a synchronously rotating axis.

A 100 MVA, 11 kV, 3 phase, 50 Hz, 8 pole synchronous generator has an inertia constant H = 4 seconds. The stored energy in the rotor of the generator at synchronous speed will be

• 1. 100 MJ

• 1. 400 MJ

• 1. 800 MJ

• 1. 12.5 MJ

Steady state power limit is

• P=EV/X

• P=EVsind/X

• P=EVcosd/X

• P=EVsin30/X