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Which of the following triggers the failure of successive parts?
Brown out
Non-cascade tripping
Load shedding
Incipient fault in power transformer
Brown out
A brownout is a drop in voltage in an electrical power supply system. It triggers the failure of successive parts because as voltage drops, current drawn by constant-power loads increases to maintain the same output power, leading to overheating and cascading protection trips.
IEEE 1159
A brownout is a drop in voltage in an electrical power supply system. It triggers the failure of successive parts because as voltage drops, current drawn by constant-power loads increases to maintain the same output power, leading to overheating and cascading protection trips.
P=V├ЧIcos╧Х тАФ Relation between Power, Voltage, and Current
InewтАЛ=VdropтАЛ├Чcos╧ХPтАЛ тАФ Current increase during voltage dip
In power systems, many motors and electronic loads operate as constant-power devices. If the supply voltage V drops, the current I drawn must increase to keep power P=V├ЧI constant. This increased current leads to thermal stress in conductors and relay coils, potentially tripping downstream protective devices, which then forces the load onto remaining healthy feeders, causing their failure in a cascading sequence.
Brownout refers to a partial loss of power, distinct from a blackout.
Induction motors are particularly susceptible as they draw excessive current during low-voltage states.
Cascading failures occur when one feeder trip shifts the load burden to neighboring healthy feeders beyond their thermal capacity.
Voltage stability is critical for the coordination of protective relays.
Helps prevent total grid collapse by shedding load partially
Allows utility companies to avoid complete system blackout during peak demand
Risk of damage to electrical machinery due to overheating
May lead to a chain reaction of protection system operations (cascading failure)
Grid management during emergency energy shortages
Protection coordination studies in distribution networks
Brownout is defined as a voltage reduction between 10% and 25% for a period ranging from minutes to hours.
Option B (Non-cascade tripping) is designed to isolate faults locally without affecting other parts of the grid.
Option C (Load shedding) is a controlled procedure to prevent system-wide collapse, not a trigger for successive failures.
Option D (Incipient fault) refers to an internal fault in a transformer (like a Buchholz relay trigger) which is localized.
A is correct тАФ A brownout induces a voltage dip that causes constant-power equipment to draw excessive current, leading to thermal overloading and subsequent cascading failures of protective devices.
In power systems, always remember that for constant power loads, IтИЭV1тАЛ, so a voltage drop is inversely proportional to the current increase.
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