In power station practice "spinning reserve" is

Question

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Reserve generating capacity that is connected to bus and ready to take the load

Explanation: Spinning reserve refers to the extra generating capacity that is already synchronized to the grid and operating at partial load. This allows the generator to respond almost instantaneously to sudden increases in system demand or sudden loss of other generation units.

Working Principle: In a power system, units contributing to the spinning reserve run in parallel with the load-carrying units. By operating below their rated capacity, these generators can increase their power output by opening governor valves or increasing fuel input, thus stabilizing frequency when the system experiences a disturbance.

Key Formulas: $P_{Total} = P_{Load} + P_{SpinningReserve}$ — Total generation requirement considering reserves

Key Points: It is a critical component of power system security and reliability.; The response time is governed by the governor's speed regulation (droop characteristic).; It must be capable of reaching full capacity within seconds to minutes after being called upon.; Total Spinning Reserve must exceed the largest single contingency in the network.

Advantages: Maintains grid frequency stability during sudden load spikes.; Provides immediate support in the event of a contingency (N-1 criterion).

Disadvantages: Increases operational costs due to less efficient fuel consumption at partial loads.; Accelerates wear and tear on steam turbines due to varying thermal stresses.

Applications: Load Frequency Control (LFC) in modern AGC systems.; Grid balancing in transmission system operations.

Additional Info: Spinning reserve is distinct from 'Cold Reserve' or 'Standby Reserve' which are units not currently synchronized to the grid.. Option A is incorrect because spinning reserve is specifically 'in service' (synchronized). Option C describes 'Cold Reserve' or 'Ready Reserve', not 'Spinning' reserve.

Answer: B is correct — Spinning reserve represents generators that are synchronized, connected to the bus, and running at part-load, enabling rapid response to frequency deviations.

Exam Tip: Always distinguish between Spinning Reserve (synchronized, running) and Hot/Cold Standby (offline, requires start-up time). Exam questions often swap these definitions to test clarity.

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