Which of this power plant is started first after system black out

Question

Examoogle · Accepted Answer

Hydro

Explanation: Hydro power plants are utilized as 'black start' units because they can be started independently without requiring an external electrical supply. Unlike thermal or nuclear plants, which require auxiliary power to run boilers, feed pumps, and cooling systems, hydro plants rely on gravity-fed water to rotate turbines.

Working Principle: In a black start scenario, the governor system of a hydro turbine uses a small battery-powered actuator to open wicket gates. As water flows through the turbine, it spins the generator, producing voltage to build up the system frequency. Once stable, this 'cranking' power is used to energize transmission lines to restart larger, non-self-starting thermal plants.

Key Formulas: $P = \eta \rho g Q H$ — Power output equation where $P$ is power, $\eta$ is efficiency, $\rho$ is density, $g$ is gravity, $Q$ is flow, and $H$ is head.

Key Points: Black start capability refers to the ability of a power plant to start without support from the external grid.; Thermal plants require 'cranking power' for boiler feed pumps, fans, and cooling systems.; Hydro units possess high inertia and fast-start characteristics suitable for grid restoration.; Diesel generators or gas turbines can also serve as black-start units in some grid configurations.

Advantages: Independent startup capability; Rapid response to grid frequency fluctuations; Essential for restoring power during total collapse

Disadvantages: Geographically limited to sites with water reservoirs; High initial infrastructure cost; Dependent on hydrological availability

Applications: Grid restoration after major blackout; Emergency supply for local distribution grids

Additional Info: A 'Black Start' unit acts as a 'reference' source for the grid during the restoration phase.. Option A (Thermal) is incorrect because boilers require electricity for startup.. Option B (Nuclear) is incorrect due to stringent safety regulations and massive auxiliary power requirements.

Answer: C is correct — Hydro power plants serve as the designated black start source due to their ability to start without an external electrical grid connection.

Exam Tip: Always remember that 'self-starting' ability is defined by the absence of need for external excitation or motor-driven auxiliaries, which is the defining characteristic of Hydro and some Gas/Diesel plants.

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