Mixed Deck — All EGSA Topics Flashcards

What is the purpose of a kW transducer in a generator paralleling system?

Answer: Convert real power output to a DC signal for the load sharing controller

A kW transducer converts the generator's real power (kW) output into a proportional DC signal used by the load sharing module to balance load between paralleled units.

When replacing a flexible exhaust coupling on a generator set, what characteristic is most important when selecting the replacement part?

Answer: Matching the original manufacturer's temperature and vibration rating

The replacement coupling must meet or exceed the OEM temperature and vibration specifications to ensure safe and reliable operation.

A diesel generator is running at 60 Hz at no load but drops to 59.4 Hz at full load. What is the governor droop percentage?

Answer: 1%

Droop % = (no-load speed − full-load speed) / rated speed × 100 = (60 − 59.4) / 60 × 100 = 1%.

What happens to a generator's terminal voltage waveform if one rotating rectifier diode in a brushless excitation system fails open?

Answer: Terminal voltage develops ripple at twice the exciter frequency due to half-wave rectification

A failed open diode converts three-phase rectification to an asymmetric configuration, introducing AC ripple on the DC field supply at twice the exciter frequency, which appears as terminal voltage modulation.

A reactive load bank test is performed primarily to evaluate the generator's ability to handle what type of load?

Answer: Inductive motor and transformer loads

Reactive (inductive) load banks simulate real-world motor and transformer loads that demand kVAR in addition to kW.

Which safety precaution is critical when working on a generator set that is paralleled with the utility grid?

Answer: Ensure the generator is properly isolated, synchronized protection is disabled, and permits are obtained before any work

When a generator is paralleled with the utility, isolation requires proper permitting, de-energization of all parallel paths, and confirmation that the unit is fully de-coupled before any maintenance work.

What is the purpose of load bank testing for generators?

Answer: To apply a controlled artificial load to verify generator performance and prevent wet stacking

Load bank testing applies a measured resistive, inductive, or combined load to verify the generator can handle its rated capacity and to burn off carbon deposits and unburned fuel (wet stacking) from underloading.

What maintenance action is required when diesel fuel stored in a day tank shows visible microbial contamination (dark slime)?

Answer: Drain, clean, and treat the tank, then refill with fresh fuel and biocide treatment

Microbial growth must be physically removed by draining and cleaning the tank; biocide treatment of contaminated fuel without cleaning will not eliminate the biofilm.

What is 'wet stacking' in diesel generator operation?

Answer: Accumulation of unburned fuel and carbon in the exhaust system due to prolonged operation at light loads

Wet stacking occurs when a diesel generator runs at light loads (below 30% of rated capacity) for extended periods, causing incomplete combustion. Unburned fuel and carbon accumulate in the exhaust, reducing performance and potentially damaging components.

During a voltage dip test, a generator's voltage recovers but takes longer than the manufacturer specifies. What is the most likely cause?

Answer: Sluggish AVR response due to incorrect gain setting

The AVR gain setting controls response speed; too-low gain causes slow voltage recovery after transient load application, exceeding the specified recovery time.

A natural gas engine prime mover uses which type of ignition system, unlike a diesel engine?

Answer: Spark ignition

Natural gas engines use spark ignition because natural gas has a higher octane rating and will not self-ignite under diesel compression ratios.

During a transfer switch maintenance inspection, what test verifies that the switch will correctly detect a utility outage and command generator start?

Answer: Simulated utility voltage dropout test with ATS in auto mode

A simulated utility dropout test confirms the ATS sensing circuit and time delays operate correctly before commanding generator start.

Which NFPA standard governs the testing and maintenance intervals for ATS equipment in health care facilities?

Answer: NFPA 99

NFPA 99 (Health Care Facilities Code) establishes inspection, testing, and maintenance requirements for ATS equipment in hospitals and other health care occupancies.

What is the significance of the short-circuit ratio (SCR) in a synchronous generator?

Answer: Ratio of field current at rated voltage to field current at rated short-circuit current

The SCR is the ratio of field current required for rated open-circuit voltage to that required for rated armature current at short circuit, indicating machine stiffness.

What is the primary concern when connecting a diesel generator day tank using flexible fuel lines?

Answer: Lines must be listed for fuel service, vibration-resistant, and properly supported to prevent fatigue failure

Flexible fuel connections must be rated for diesel service, resistant to vibration from the engine, and adequately supported to prevent cracking or fatigue failure over time.

Why is it important to monitor the diesel fuel cetane number for standby generator applications?

Answer: Cetane number indicates ignition quality; low cetane causes hard starting and rough combustion

Cetane number measures how readily diesel fuel ignites under compression; a low cetane number leads to delayed ignition, hard starting, and rough engine operation.

Which factor most directly determines whether a four-pole ATS is required instead of a three-pole ATS?

Answer: Whether the generator is a separately derived system with its own neutral-ground bond

NEC 250.30 requires the neutral to be switched when a separately derived system (generator with a neutral-ground bond) is used, preventing objectionable current from flowing on the grounding electrode conductors of both systems simultaneously.

A diesel generator set starts and runs normally but trips on high coolant temperature after 10 minutes of operation. Which maintenance action should be performed first?

Answer: Flush and refill the cooling system, and check for airlock

Air trapped in the cooling system prevents proper coolant circulation and is the most common cause of rapid overheating; flushing and bleeding the system is the first diagnostic step.

What is the role of a transformer in a power generation system?

Answer: To adjust the voltage levels for efficient transmission.

Transformers are essential in power generation systems for efficiently transmitting electricity over long distances. They step up the voltage from the generator for transmission, which significantly reduces current and minimizes energy loss due to resistance. Conversely, they step down the voltage at substations for safe distribution to consumers and industrial users.

A generator starts and runs normally but produces output voltage 15% below the nominal setting. After confirming AVR input power is present, what is the most likely fault?

Answer: Failed or misadjusted voltage sensing resistor in the AVR trim circuit

A failed or incorrectly trimmed voltage sensing circuit prevents the AVR from raising excitation to the correct level.