**1. What are the conditions for parallel operation of two generator sets, 

and what equipment is used to achieve parallel operation?**  

Answer: The conditions for parallel operation require that the instantaneous voltage, frequency, and phase of the two units are identical, 

commonly referred to as the "three synchronizations." Specialized parallel operation equipment is used for this purpose. 

Fully automatic parallel operation cabinets are generally recommended, while manual parallel operation should be avoided as much as possible. 

The success or failure of manual parallel operation depends on human experience. Based on over 20 years of experience in the power industry, 

the author boldly asserts that the reliable success rate of manual parallel operation for diesel generators is virtually zero. 

The concept of manual parallel operation for large utility power systems must not be applied to smaller power systems, 

as their protection levels are entirely different.

**2. What is the power factor of a three-phase generator? Can power factor correction capacitors be added to improve it?**  

Answer: The power factor is 0.8. No, power factor correction capacitors cannot be added because the charging and 

discharging of capacitors can cause fluctuations in small power systems and lead to generator oscillations.

**3. Why do we require customers to perform tightening of all electrical connections every 200 hours of operation?**  

Answer: Diesel generator sets operate under vibration. Many domestically produced or assembled units lack necessary 

components such as double nuts or spring washers. If electrical connections become loose, it can result in high contact resistance, 

leading to abnormal operation of the unit.

**4. Why must the generator room be kept clean, with no loose sand on the floor?**  

Answer: Inhaling dirty air can reduce the diesel engine's power output. If the generator inhales sand or other impurities, 

the insulation between the stator and rotor gaps can be damaged, and in severe cases, this can lead to burnout.

**5. Why has our company generally advised against neutral grounding during installation since 2002?**  

Answer:  

1) The self-regulation capabilities of newer generators have significantly improved.  

2) Practical experience shows that units with neutral grounding have a higher lightning-related failure rate.  

3) The quality requirements for grounding are high and often difficult for ordinary users to achieve. 

    Poor grounding is less safe than no grounding.  

4) Neutral grounding can mask load leakage faults and grounding errors, 

    which would otherwise be exposed under high-current utility power conditions.

**6. What precautions should be taken when using units without neutral grounding?**  

Answer: The neutral line may carry voltage because the capacitive voltage between the live wire and the neutral point cannot be eliminated. 

Operators must treat the neutral line as a live conductor and not handle it according to utility power habits.

**7. How should the power matching between a UPS and a diesel generator be configured to ensure stable UPS output?**  

Answer:  

1) UPS units are generally rated in apparent power (KVA). Multiply this by 0.8 to convert it to active power (KW), 

    consistent with the generator's rating.  

2) For conventional generators, multiply the UPS's active power by 2 to determine the required generator power, 

    meaning the generator power should be twice the UPS power.  

3) For generators with PMG (permanent magnet generator) excitation, multiply the UPS power by 1.2 to determine the generator power, 

    meaning the generator power should be 1.2 times the UPS power.

**8. Can electronic or electrical components rated for 500V withstand voltage be used in diesel generator control cabinets?**  

Answer: No. The 400/230V voltage marked on diesel generator sets refers to the effective voltage. 

The peak voltage is 1.414 times the effective voltage, meaning the peak voltage of the generator is Umax = 566/325V.

**9. Do all diesel generator sets come with self-protection functions?**  

Answer: No. Currently, in the market, even within the same brand, some units include self-protection functions while others do not. 

Customers must verify this when purchasing a unit. It is advisable to document this in writing as part of the contract. Generally, 

low-priced units do not include self-protection functions.

**10. How can counterfeit or inferior domestic diesel engines be identified?**  

Answer: First, check for the factory certificate and product documentation, which serve as the engine's "identity proof" and are mandatory. 

Then, verify the three key numbers in the documentation:  

1) Nameplate serial number;  

2) Engine block serial number (usually embossed on a machined surface near the flywheel);  

3) Fuel pump nameplate serial number.  

These numbers must exactly match the actual numbers on the diesel engine. If any discrepancies are found, 

report the numbers to the manufacturer for verification.

**11. What three key points must the operating electrician verify after taking over a diesel generator set?**  

Answer:  

1) Verify the unit's actual usable power, then determine the economic power and backup power. 

    The method to verify actual usable power is: Multiply the diesel engine's 12-hour rated power by 0.9. 

    If the generator's rated power is less than or equal to this value, use the generator's rated power as the actual usable power. 

    If the generator's rated power exceeds this value, use this calculated value as the actual usable power.  

2) Verify the self-protection functions included with the unit.  

3) Verify whether the electrical wiring is compliant, whether the protective grounding is reliable, and whether the three-phase load is roughly balanced.

**12. For an elevator with a 22KW starting motor, what size generator set should be configured?**  

Answer: 22 * 7 = 154KW (Elevators are directly loaded starting devices, and the instantaneous starting current is typically 7 times 

the rated current to ensure smooth operation). Thus, at least a 154KW generator set should be configured.

**13. How is the optimal operating power (economic power) of a generator set calculated?**  

Answer: P_optimal = 3/4 * P_rated (i.e., 0.75 times the rated power).

**14. According to national standards, how much larger should the engine power of a generator set be compared to the generator power?**  

Answer: 10%.

**15. Some generator sets express engine power in horsepower. How is horsepower converted to kilowatts?**  

Answer: 1 horsepower = 0.735 kilowatts, 1 kilowatt = 1.36 horsepower.

**16. How is the current of a three-phase generator calculated?**  

Answer: I = P / (√3 * U * cos φ), i.e., current = power (watts) / (√3 * 400V * 0.8). A simplified formula is: I (A) = generator rated power (KW) * 1.8.

**17. What is the relationship between apparent power, active power, rated power, maximum power, and economic power?**  

Answer:  

1) Apparent power is measured in KVA and is commonly used in China to express the capacity of transformers and UPS systems.  

2) Active power is 0.8 times the apparent power, measured in KW, and is commonly used for power generation and consumption equipment in China.  

3) The rated power of a diesel generator set refers to the power it can continuously deliver for 12 hours.  

4) Maximum power is 1.1 times the rated power but is only allowed for 1 hour within 12 hours.  

5) Economic power is 0.75 times the rated power and is the output power at which the generator set can operate indefinitely without time restrictions. 

    At this power, fuel consumption is minimized, and the failure rate is lowest.

**18. Why is long-term operation of a diesel generator set below 50% of its rated power not allowed?**  

Answer: It leads to increased oil consumption, carbon buildup in the diesel engine, higher failure rates, and shorter overhaul intervals.

**19. During generator operation, should the actual output power be based on the power meter or the current meter?**  

Answer: It should be based on the current meter, with the power meter serving only as a reference.

**20. If a generator set's frequency and voltage are both unstable, is the problem with the engine or the generator?**  

Answer: The problem lies with the engine.

**21. If a generator set's frequency is stable but its voltage is unstable, is the problem with the engine or the generator?**  

Answer: The problem lies with the generator.

**22. What is generator demagnetization, and how should it be addressed?**  

Answer: Demagnetization occurs when a generator is not used for an extended period, causing the residual magnetism in the iron core to dissipate. 

As a result, the excitation coil cannot establish the necessary magnetic field. The engine runs normally, but no electricity is generated. 

This phenomenon is common in new units or those not used for a long time.  

Remedial measures:  

1) Press the excitation button if available.  

2) If no excitation button exists, use a battery to remagnetize the generator.  

3) Connect a light bulb load and run the generator at overspeed for a few seconds.

**23. After a generator set has been used for some time,

everything appears normal except for a decrease in power. What are the main causes?**  

Answer:  

a) The air filter is too dirty, restricting air intake. Clean or replace the air filter.  

b) The fuel filtration system is too dirty, reducing fuel injection. Replace or clean the system.  

c) Incorrect ignition timing. Adjust the timing.

**24. If a generator set's voltage and frequency are stable under load, but the current is unstable, where does the problem lie?**  

Answer: The problem lies with the unstable load from the customer, not the generator's quality.

**25. If a generator set's frequency is unstable, what is the main cause?**  

Answer: The main cause is the unstable speed of the generator.

**26. What are the most critical points to note when using a diesel generator set?**  

Answer:  

1) The radiator must have sufficient water and operate within the allowed temperature range.  

2) Lubricating oil must be at the correct level (not excessive) and operate within the allowed pressure range.  

3) Frequency should stabilize around 50Hz, and voltage should stabilize around 400V.  

4) The three-phase currents should all be within the rated range.

**27. Which components of a diesel generator set require frequent replacement or cleaning?**  

Answer: Diesel filter, oil filter, and air filter. (Some units also include a water filter.)

**28. What are the main advantages of brushless generators?**  

Answer:  

(1) No need for brush maintenance.  

(2) Resistant to radio frequency interference.  

(3) Reduced risk of demagnetization failures.

**29. What is the typical insulation class of domestic generators?**  

Answer: Domestic generators: Class B. Marathon, Leroy-Somer, and Stamford brand generators: Class H.

**30. Why do some gasoline engines require a mixture of gasoline and oil?**  

Answer: Two-stroke gasoline engines.

**31. What are the six basic systems of a diesel generator set?**  

Answer:  

(1) Lubrication system;  

(2) Fuel system;  

(3) Control and protection system;  

(4) Cooling system;  

(5) Exhaust system;  

(6) Starting system.

**32. Why do we strongly recommend that customers use the engine oil recommended by our company?**  

Answer: Engine oil is the lifeblood of the engine. Using substandard oil can lead to severe failures such as bearing seizure, 

gear damage, crankshaft deformation or breakage, and even total engine failure.

**33. Why do new units require oil and oil filter changes after some time in use?**  

Answer: During the break-in period, impurities can enter the oil pan, causing physical or chemical changes to the oil and oil filter.

**34. Why do we require customers to install the exhaust pipe with a 5-10 degree downward slope?**  

Answer: To prevent rainwater from entering the exhaust pipe, which could lead to serious accidents.

**35. What are the purposes of the manual fuel pump and air bleed bolt commonly found on diesel engines?**  

Answer: To remove air from the fuel lines before starting the engine.

**36. How are diesel generator automation levels classified?**  

Answer: Manual, automatic start, automatic start with automatic utility transfer cabinet, 

and remote three-control (remote control, telemetry, and remote monitoring).

**37. Why is the standard output voltage of generators 400V instead of 380V?**  

Answer: To account for voltage drop losses in the wiring after output.

**38. Why must the generator set's operating area be well-ventilated?**  

Answer: The diesel engine's output is directly affected by the quantity and quality of the air it intakes, 

and the generator requires sufficient air for cooling. Thus, the operating area must be well-ventilated.

**39. Why should tools not be used to overtighten oil filters, diesel filters, and fuel-water separators during installation? 

Hand-tightening until no leakage occurs is sufficient.**  

Answer: Overtightening can cause the sealing rings to expand under heat from oil immersion and engine operation, creating excessive stress. 

This can damage the filter or separator housing and, in severe cases, strip the engine's mounting threads, making repairs impossible.

**40. What are the benefits of purchasing an automatic start system without an automatic transfer switch?**  

Answer:  

1) If a utility power outage occurs, the generator will start automatically, reducing the time for manual power restoration.  

2) If lighting circuits are connected before the circuit breaker, the generator room lighting will remain unaffected during outages, facilitating operator work.

**41. Under what conditions can a generator set be closed and connected to the load?**  

Answer: For water-cooled units, the water temperature must reach 56°C. For air-cooled units, the engine body should be slightly warm. 

Voltage and frequency must be normal under no-load conditions, and oil pressure must be normal.

**42. What is the sequence for connecting loads after starting and energizing the generator?**  

Answer: Loads should be connected from largest to smallest.

**43. What is the sequence for disconnecting loads before shutting down the generator?**  

Answer: Loads should be disconnected from smallest to largest before shutting down the generator.

**44. Why should the generator not be shut down or started under load?**  

Answer: Shutting down under load constitutes an emergency shutdown, which can severely impact the generator. 

Starting under load is a violation of operational procedures and can damage both the generator and connected electrical equipment.

**45. What should be noted when using diesel generators in winter?**  

Answer:  

1) Ensure the radiator does not freeze. Preventive measures include adding specialized long-term anti-rust and antifreeze coolant or 

    using heating equipment to keep the room temperature above freezing.  

2) Never use open flames to warm the engine.  

3) Allow sufficient no-load warm-up time before connecting the load.

**46. What is a three-phase four-wire system?**  

Answer: A generator set with four output wires: three live wires and one neutral wire. The voltage between live wires is 380V, 

and between a live wire and the neutral wire is 220V.

**47. What is a three-phase short circuit, and what are its consequences?**  

Answer: A three-phase short circuit occurs when live wires are directly connected without any load. 

The consequences can be severe, potentially causing equipment damage and personal injury.

**48. What is backfeeding, and what are its two serious consequences?**  

Answer: Backfeeding occurs when a standby generator feeds power into the utility grid. The two serious consequences are:  

a) If the utility grid is not out of power, non-synchronized parallel operation between the generator and the grid can severely damage 

    the generator. If the generator is large enough, it may also cause grid instability.  

b) If the utility grid is out of power for maintenance, backfeeding can electrocute maintenance personnel.

**49. Why must technicians thoroughly inspect all fixed bolts and wiring connections before commissioning a generator set?**  

Answer: Generator sets may experience loose or missing bolts and wiring connections during transportation, which can affect commissioning or, 

in severe cases, damage the equipment.

**50. What level of energy is electricity, and what are the characteristics of alternating current (AC)?**  

Answer: Electricity is a secondary energy source. AC is converted from mechanical energy, while direct current (DC) is converted from chemical energy. 

A key characteristic of AC is that it cannot be stored; it must be generated and used immediately.

**51. What does the general symbol "GF" for domestic generator sets represent?**  

Answer: It represents two meanings:  

a) Industrial frequency generator sets suitable for China's standard frequency of 50Hz.  

b) Domestically produced generator sets.

**52. Must the load connected to a generator maintain three-phase balance during use?**  

Answer: Yes. The maximum deviation must not exceed 25%, and operation with a missing phase is strictly prohibited.

**53. What are the four strokes of a four-stroke diesel engine?**  

Answer: Intake, compression, power, and exhaust.

**54. What is the biggest difference between diesel and gasoline engines?**  

Answer:  

1) The substance compressed in the cylinder differs.  

In diesel engines, air is compressed during the compression stroke.  

In gasoline engines, a mixture of gasoline and air is compressed during the compression stroke.  

2) The ignition method differs.  

Diesel engines rely on atomized diesel fuel injected into high-pressure air for auto-ignition.  

Gasoline engines rely on spark plugs for ignition.

**Guangdong Longhong Electromechanical Equipment Co., Ltd. --- Manufacturer of Generators, Silent Generators, Guangzhou Generators   www.longhongpower.com**