Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
Which of the following is the long term stability in a Load driven system?
Rotor-angle stability
Short term voltage stability
Frequency Stability
Long-term voltage stability
Long-term voltage stability
Quick Summary: Long-term voltage stability refers to the ability of a power system to maintain steady voltages at all buses after being subjected to a disturbance, especially when involving long-term equipment responses like transformer tap changers and thermostat-controlled load devices. It is essentially a load-driven phenomenon where the system struggles to restore voltage levels because the restoration mechanisms (like tap changers) attempt to increase load consumption, potentially leading to voltage collapse.
Long-term voltage stability refers to the ability of a power system to maintain steady voltages at all buses after being subjected to a disturbance, especially when involving long-term equipment responses like transformer tap changers and thermostat-controlled load devices. It is essentially a load-driven phenomenon where the system struggles to restore voltage levels because the restoration mechanisms (like tap changers) attempt to increase load consumption, potentially leading to voltage collapse.
P=V2×G
Q=V2×B
In a power system, when a disturbance causes a voltage dip, automatic load-restoring devices such as tap-changing transformers and thermostatic controls act to restore the consumed power to pre-disturbance levels. If the system's transmission capacity or reactive power reserves are insufficient to meet this increasing demand, the voltage continues to drop. This cycle of restoration-attempt and voltage-decay continues over minutes, characterizing the long-term stability time-frame.
Long-term stability operates on a time scale of minutes to hours.
Major factors include transformer tap changers, generator field current limiters, and thermostatic load control.
Voltage collapse occurs if the load power-voltage characteristics exceed the maximum power transfer capability of the network.
It is fundamentally driven by the system's inability to restore reactive power balance after slow-acting equipment attempts to recover load.
Predictability through long-term simulation tools (e.g., PSS/E, ETAP).
Allows for strategic placement of reactive support (SVC/STATCOM).
High computational cost for time-domain simulation.
Complex interaction between discrete (tap changers) and continuous (generator) variables.
Power system planning for peak load scenarios.
Setting under-voltage load shedding (UVLS) relay thresholds.
Rotor-angle stability is concerned with synchronism, whereas voltage stability is concerned with bus voltage magnitude.
Frequency stability relates to the balance of real power (Generation vs Demand).
D is correct — Long-term voltage stability is fundamentally characterized by the slow, load-driven processes such as transformer tap changing and thermostatic demand recovery that can lead to voltage instability if the system cannot meet the restored load requirements.
Always remember: Frequency is a system-wide parameter linked to active power (P↔f), while Voltage is a local parameter linked to reactive power (Q↔V).