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
What is the main cause of voltage instability?
Generators
Transformers
Loads
Line losses
Loads
Quick Summary: Voltage instability is primarily caused by the inability of the power system to maintain steady voltages at all buses under normal conditions and after being subjected to a disturbance. This is fundamentally driven by the system's inability to meet the reactive power demand of the loads.
Voltage instability is primarily caused by the inability of the power system to maintain steady voltages at all buses under normal conditions and after being subjected to a disturbance. This is fundamentally driven by the system's inability to meet the reactive power demand of the loads.
Qdemand=f(V) — Reactive power demand as a function of voltage
Vbus≈Vs−VsPR+QX — Approximate voltage drop at the receiving end
Voltage instability occurs when the load characteristic is such that a change in load power or system configuration leads to a progressive and uncontrollable drop in voltage. As the load demands more reactive power (Q) than the system can supply at a given voltage level, the voltage at the load bus decreases, which in turn causes the load to demand even more reactive power, eventually leading to a voltage collapse.
Voltage instability is essentially a reactive power support problem.
Induction motors and air conditioners are major contributors to voltage instability due to their constant power load characteristics.
Static Var Compensators (SVC) and STATCOMs are used to provide rapid reactive power support.
The nose point of the P-V curve represents the point of voltage collapse.
Power system stability analysis
Design of shunt compensation equipment
Voltage collapse often happens in systems heavily loaded with inductive motors.
Option D (Line losses) is a consequence of high current, but voltage instability is specifically the inability of the system to provide necessary reactive power under load conditions.
C is correct — Voltage instability is primarily triggered by the load's demand for reactive power exceeding the power system's capability to supply it.
Always remember: Frequency is a global parameter (same everywhere), but Voltage is a local parameter (varies from bus to bus), making voltage stability a local bus-level issue.