SOPD Power System Operations 3

Question 1

A 500 kV line trips unexpectedly and operators observe voltage dropping on adjacent buses. What is the most likely cause of the voltage depression?

Accepted Answer

Loss of reactive power support that the tripped line was providing through its charging current

Answer

Transmission lines generate reactive power through their shunt capacitance; losing a line removes this reactive support and depresses voltage.

Question 2

Under what condition is a power system said to be operating in a 'voltage collapse' scenario?

Accepted Answer

When voltage instability leads to uncontrollable reduction in voltage despite increased reactive power injection

Answer

Voltage collapse occurs when the system can no longer supply adequate reactive power and voltage spirals downward beyond the point of recovery.

Question 3

What is the primary benefit of operating generators in 'droop control' mode rather than isochronous control?

Accepted Answer

It enables stable load sharing among multiple generators without hunting or instability

Answer

Droop control provides inherent load sharing by causing each generator's output to increase proportionally as frequency falls, preventing instability from competing governors.

Question 4

What does the term 'spinning reserve' mean in power system operations?

Accepted Answer

Unloaded generation capacity synchronized to the grid that can respond immediately to load changes

Answer

Spinning reserve is synchronized, partially loaded capacity that can increase output immediately without start-up delay.

Question 5

Which protective relay function is specifically designed to detect loss of excitation in a synchronous generator?

Accepted Answer

Loss-of-field relay (impedance-based, ANSI 40)

Answer

The ANSI 40 (loss-of-field) relay uses impedance measurement to detect when a generator has lost its excitation and begins absorbing reactive power.

(SOPD) System Operator/Power Dispatching Practice Test

(SOPD) System Operator/Power Dispatching Practice Test

SOPD Power System Operations 3