Prime Mover and Governors Flashcards

A technician is setting up two paralleled generator sets of different power ratings to share a load proportionally. Which governor mode is essential for this application?

Answer: Droop mode

Droop mode allows for proportional load sharing between generators, especially those with different ratings. In droop mode, the governor allows the engine speed (and thus frequency) to decrease slightly as load increases. By setting the same droop percentage on both governors, each generator will take up a load proportional to its capacity, ensuring stable operation. Isochronous mode maintains a constant frequency regardless of load, which can cause issues with load sharing between paralleled units unless a dedicated load sharing controller is used.

What is the primary function of a governor on a generator's prime mover?

Answer: To maintain a constant engine speed under varying loads.

The fundamental role of a governor is to maintain the engine at a constant speed (RPM) by automatically adjusting the fuel supply in response to changes in the electrical load. This stable engine speed is crucial for maintaining a constant frequency (Hz) of the generated electricity.

A diesel generator experiences 'hunting,' where the engine RPM fluctuates up and down erratically under a steady load. Which of the following is the MOST likely cause related to the governor system?

Answer: An improperly adjusted gain or stability setting

Hunting is often caused by an improperly tuned electronic governor. The 'gain' or 'stability' setting controls how quickly the governor responds to speed changes. If set too high (too sensitive), the governor will over-correct for small speed deviations, leading to a continuous cycle of speeding up and slowing down, known as hunting. While a clogged fuel filter can cause erratic operation, improper governor adjustment is a more direct cause of the described oscillation.

Which of the following prime movers is characterized by its high power-to-weight ratio, fewer moving parts, and suitability for continuous, high-load operation, making it ideal for large-scale power plants?

Answer: Gas Turbine

Gas turbines are known for their high power output relative to their size, operational efficiency at high loads, and having fewer moving parts compared to reciprocating engines, which results in lower maintenance. These characteristics make them well-suited for continuous operation in baseload power generation applications.

A generator set is operating in isochronous mode. What will happen to the engine speed as a heavy electrical load is suddenly applied?

Answer: The speed will momentarily dip and then quickly return to the original set speed.

In isochronous mode, the governor's objective is to maintain a constant, exact speed (and thus frequency) regardless of the load. When a load is applied, there will be an initial, momentary dip in speed, but the governor will react quickly by increasing fuel to the prime mover to bring the speed back to the precise setpoint.

When paralleling two generator sets, the real power (kW) load sharing is primarily controlled by adjusting each unit's:

Answer: Governor speed setting

The distribution of the real power load (measured in kW) between two or more paralleled generators is managed by adjusting the governor speed settings. Raising the governor setpoint on one unit will cause it to take on a larger share of the kW load, while lowering it will cause it to shed load. The Automatic Voltage Regulator (AVR) controls the reactive power (kVAR) sharing.