56 Common Questions About Diesel Generators

1. What are the conditions for paralleling two generator sets? What device is used to complete the paralleling work?
Answer: The condition for paralleling is that the instantaneous voltage, frequency and phase of the two machines are the same. Commonly known as "three simultaneous". Use a special paralleling device to complete the paralleling work. It is generally recommended to use a fully automatic paralleling cabinet. Try not to use manual paralleling. Because the success or failure of manual paralleling depends on human experience. With more than 20 years of experience in power work, the author boldly stated that the reliable success rate of manual paralleling of diesel generators is equal to 0. The concept of manual paralleling of large power supply systems of municipal power must not be applied to small power supply systems, because the protection levels of the two are completely different.

2. What is the power factor of the three-phase generator? Can a power compensator be added to improve the power factor?
Answer: The power factor is 0.8. No, because the charging and discharging of the capacitor will cause fluctuations in the small power supply. And unit oscillation.

3. Why do we require customers to tighten all electrical contacts after every 200 hours of operation of the unit?
Answer: Diesel generator sets are vibrating machines. Moreover, many domestically produced or assembled units do not use double nuts when they should. Spring washers are not used when they should. Once the electrical fasteners are loose, a large contact resistance will be generated, causing the unit to operate abnormally.

4. Why must the generator room be kept clean and free of floating sand on the ground?
Answer: If the diesel engine inhales dirty air, the power will decrease; if the generator inhales impurities such as sand, the insulation between the stator and rotor gap will be damaged, and in severe cases, it will burn out.

5. Why has our company generally not recommended users to use neutral point grounding during installation since 2002?
Answer: 1) The self-regulation function of the new generation of generators has been greatly enhanced;
2) In practice, it has been found that the lightning failure rate of neutral point grounding units is relatively high.
3) The grounding quality requirements are high and ordinary users cannot do it. Unsafe working grounding is worse than no grounding.
4) The unit with neutral point grounding will cover up the leakage fault and grounding error of the load, which cannot be exposed under the condition of high current power supply of the mains.

6. What should be paid attention to when using the unit with ungrounded neutral point?
Answer: The 0 line may be charged because the capacitive voltage between the live wire and the neutral point cannot be eliminated. The operator must regard the 0 line as a charged body. It cannot be handled according to the mains practice.

7. How to match the power of UPS and diesel generator to ensure the stability of UPS output?
Answer: 1) UPS is generally expressed in apparent power KVA. First multiply it by 0.8 to convert it into the unit KW consistent with the active power of the generator.
2) If a general generator is used, the active power of UPS is multiplied by 2 to determine the power of the generator, that is, the generator power is twice the UPS power.
3) If a generator with PMG (permanent magnet excitation) is used, the generator power is determined by multiplying the UPS power by 1.2, that is, the generator power is 1.2 times the UPS power.

8. Can electronic or electrical components marked with a withstand voltage of 500V be used in diesel generator control cabinets?
Answer: No. Because the 400/230V voltage marked on the diesel generator set is the effective voltage. Its peak voltage is 1.414 times the effective voltage. That is, the peak voltage of the diesel generator is Umax=566/325V.

9. Do all diesel generator sets have self-protection functions?
Answer: No. At present, even in the market, some units of the same brand have and some do not. Users must clarify this themselves when purchasing a unit. It is best to write it in written form as an annex to the contract. Generally, low-priced machines do not have self-protection functions.

10. How to identify counterfeit and fake domestic diesel engines?
Answer: First check whether there is a factory certificate and product certificate. They are the "identity certificates" of the diesel engine when it leaves the factory and are required. Then check the three major numbers on the certificate: 1) nameplate number; 2) engine number (usually on the plane machined by the flywheel end, the font is convex); 3) oil pump nameplate number. Check these three numbers with the actual numbers on the diesel engine, and they must be accurate. If there are any doubts, report these three numbers to the manufacturer for verification.

11. After the operating electrician takes over the diesel generator set, which three points should he verify first?
Answer: 1) Verify the real useful power of the unit. Then determine the economic power and standby power. The method for verifying the real useful power of the unit is: multiply the 12-hour rated power of the diesel engine by 0.9 to get a data (kw). If the rated power of the generator is less than or equal to this data, the rated power of the generator is determined as the real useful power of the unit. If the rated power of the generator is greater than this data, this data must be used as the real useful power of the unit.
2) Verify what self-protection functions the unit has.
3) Verify whether the unit's power wiring is qualified, whether the protective grounding is reliable, and whether the three-phase load is basically balanced.

12. There is an elevator starting motor of 22KW. How big a generator set should be equipped?
Answer: 22*7=154KW (the elevator is a direct load starting model, and the instantaneous starting current is generally 7 times the rated current to ensure that the elevator moves at a uniform speed). (That is, at least a 154KW generator set should be equipped)

13. How to calculate the optimal power (economic power) of the generator set?
Answer: P best = 3/4*P rated (that is, 0.75 times the rated power).

14. According to national regulations, the engine power of a general generator set should be how much greater than the generator power? Answer: 10℅.

15. The engine power of some generator sets is expressed in horsepower. How to convert horsepower to the international unit kilowatt?
Answer: 1 horsepower = 0.735 kilowatts, 1 kilowatt = 1.36 horsepower.

16. How to calculate the current of a three-phase generator?
Answer: I = P / (√3 Ucos φ)
That is, current = power (watt) / (√3 *400 (volts) * 0.8).
The simplified formula is: I (A) = rated power of the unit (KW) * 1.8

17. What is the relationship between apparent power, active power, rated power, maximum power, and economic power?
Answer: 1) The unit of apparent power is KVA, which is used to express the capacity of transformers and UPS in my country.
2) Active power is 0.8 times the apparent power, and the unit is KW, which is used in my country for power generation equipment and power-consuming equipment.
3) The rated power of a diesel generator set refers to the power that can be continuously operated for 12 hours.
4) The maximum power is 1.1 times the rated power, but it is only allowed to be used for 1 hour within 12 hours.
5) The economic power is 0.75 times the rated power, which is the output power of the diesel generator set that can run for a long time without time restrictions. When running at this power, fuel is the most economical and the failure rate is the lowest.

18. Why are diesel generator sets not allowed to run for a long time at less than 50% of the rated power?
Answer: The oil consumption increases, the diesel engine is prone to carbonization, the failure rate increases, and the overhaul cycle is shortened.

19. When the generator is running, the actual output power is based on the power meter or the ammeter?
Answer: The ammeter is the standard, and the power meter is only for reference.

20. The frequency and voltage of a generator set are both unstable. Is the problem with the engine or the generator?
Answer: It is in the engine.

21. The frequency of a generator set is stable, but the voltage is unstable. Is the problem with the engine or the generator?
Answer: It is in the generator.

22. What is the reason for the generator demagnetization? How to deal with it?
Answer: The generator has not been used for a long time, resulting in the loss of residual magnetism contained in the iron core before leaving the factory. The excitation coil cannot establish the proper magnetic field. At this time, the engine runs normally but cannot generate electricity. This phenomenon is more common in new machines or units that have not been used for a long time.
Treatment method: 1) Press the excitation button if there is an excitation button, 2) If there is no excitation button, use a battery to magnetize it, 3) Carry a light bulb load and run it at overspeed for a few seconds.

23. After using the generator set for a period of time, it is found that everything else is normal but the power is reduced. What is the main reason?
Answer: a. The air filter is too dirty and the air intake is insufficient. At this time, the air filter must be cleaned or replaced.
b. The fuel filter is too dirty and the fuel injection is insufficient. It must be replaced or cleaned.
c. The ignition timing is incorrect and needs to be adjusted.

24. There is a generator set with stable voltage and frequency after loading, but unstable current. What is the problem?
Answer: The problem is that the customer's load is unstable, but the quality of the generator is absolutely fine.

25. What is the main problem of a generator set with unstable frequency?
Answer: The main problem is that the speed of the generator is unstable.

26. What are the key points that must be paid attention to when using a diesel generator set?
Answer: 1) There must be enough water in the water tank and it must be kept within the allowable temperature range.
2) The lubricating oil must be in place but not excessive, and it must be kept within the allowable pressure range.
3) The frequency is stable at around 50HZ, and the voltage is stable at around 400V.
4) The three-phase current is within the rated range.

27. What are the parts of a diesel generator set that need to be replaced or cleaned frequently?
Answer: Diesel filter, oil filter, air filter. (Some units also have water filters)

28. What are the main advantages of brushless generators?
Answer: (1) No need for carbon brush maintenance;
(2) Anti-radio interference;
(3) Reduce demagnetization failure.

29. What is the insulation level of domestic generators?
Answer: Domestic generators are Class B; Marathon, Leroy Somer and Stanford are Class H.

30. What gasoline engine requires a mixture of gasoline and engine oil?
Answer: Two-stroke gasoline engine.

31. What six systems are included in the basic equipment of a diesel generator set?
Answer: (1) Engine oil lubrication system;
(2) Fuel system;
(3) Control and protection system;
(4) Cooling and heat dissipation system;
(5) Exhaust system;
(6) Starting system;

32. Why do we try our best to recommend customers to use the engine oil recommended by our company in our sales work?
Answer: Engine oil is the blood of the engine. Once the customer uses unqualified engine oil, it will cause serious accidents such as engine bearing seizure, gear toothing, crankshaft deformation and fracture, and even the whole machine will be scrapped.

33. Why do you need to replace the engine oil and oil filter after a new machine has been used for a period of time?
Answer: During the running-in period of a new machine, impurities will inevitably enter the oil pan, causing physical or chemical changes in the engine oil and oil filter.

34. Why do we require customers to tilt the exhaust pipe downward by 5-10 degrees when installing the unit?
Answer: To prevent rainwater from entering the exhaust pipe and causing major accidents.

35. Generally, diesel engines are equipped with manual oil pumps and exhaust bolts. What are their functions? Answer: Used to remove air from the fuel pipe before starting.

36. How are the automation levels of diesel generator sets divided?
Answer: Manual, automatic start, automatic start plus automatic AC power conversion cabinet, long-distance three-remote control (remote control, telemetry, and remote monitoring.)

37. Why is the standard of the generator's output voltage 400V instead of 380V?
Answer: Because there is voltage drop loss in the line after the output.

38. Why is it required that the use site of the diesel generator set must have smooth air?
Answer: The output of the diesel engine is directly affected by the amount and quality of the air inhaled, and the generator must have sufficient air for cooling. Therefore, the use site must have smooth air.

39. Why is it not advisable to use tools to tighten the above three devices too much when installing the oil filter, diesel filter, and oil-water separator, but only to tighten them by hand until there is no oil leakage?
Answer: Because if it is tightened too tightly, the sealing ring will expand thermally under the action of oil bubbles and the temperature rise of the body, generating great stress. This will cause damage to the filter housing or separator housing itself. Even more serious is that the body nut is damaged and cannot be repaired.

40. What are the benefits if the customer purchases the automatic starter but does not purchase the automatic conversion cabinet?
Answer: 1) Once the city grid is out of power, the unit will automatically start to speed up the manual power supply time;
2) If the lighting line is connected to the front end of the air switch, it can also ensure that the lighting in the machine room is not affected by the power outage, so as to facilitate the work of the operator;

41. What conditions must the generator set meet before it can be closed and powered?
Answer: For water-cooled units, the water temperature reaches 56 degrees Celsius.
For air-cooled units, the body is slightly hot.
When no-load, the voltage and frequency are normal. The oil pressure is normal. Only then can it be closed and powered.

42. What is the order of loading after starting the machine and powering it?
Answer: Loads are loaded in order from large to small.

43. What is the order of unloading loads before shutting down?
Answer: Loads are unloaded in order from small to large, and finally shut down.

44. Why can't you shut down or start the generator with load?
Answer: Shutting down with load is an emergency shutdown, which has a greater impact on the unit. Starting with load is an illegal operation and will cause damage to both the power generation equipment and the electrical equipment.

45. What should I pay attention to when using a diesel generator in winter?
Answer: 1) Pay attention that the water tank must not freeze. Preventive methods include adding special long-term anti-rust and antifreeze or using electric heating equipment to ensure that the room temperature is above the freezing point.
2) Open flame baking is strictly prohibited.
3) The no-load preheating time should be slightly longer before power can be supplied.

46. What is the so-called three-phase four-wire system?
Answer: There are 4 outgoing wires of the generator set, 3 of which are live wires and 1 is neutral wire. The voltage between the live wires is 380V. The voltage between the live wire and the neutral wire is 220V.

47. What is a three-phase short circuit? What are the consequences?
Answer: There is no load between the live wires, and a direct short circuit is a three-phase short circuit. The consequences are very terrible, and serious ones can cause the machine to be destroyed and people to die.

48. What is the so-called reverse power transmission? What are the two serious consequences?
Answer: The situation where the self-provided generator sends power to the city grid is called reverse power transmission. There are two serious consequences:
a) The city grid has not been shut down, and the city grid power supply and the self-provided generator power supply are asynchronously paralleled, which will inevitably destroy the unit. If the self-provided generator has a large capacity, it will also cause the city grid to vibrate.
b) The city grid has been shut down for maintenance, and the self-provided generator reverses power. This will cause the maintenance personnel of the power supply department to be electrocuted to death.

49. Why must the commissioning personnel fully check whether all the fixing bolts of the unit are fixed intact before commissioning? Are all the line interfaces intact?
Answer: After the unit has been transported over a long distance, it is inevitable that the bolts and line interfaces will be loose or fall off, which will affect the commissioning at the least and damage the machine at the worst.

50. Which level of energy does electric energy belong to? What are the characteristics of alternating current?
Answer: Electric energy belongs to secondary energy. AC is converted from mechanical energy, and DC is converted from chemical energy. The characteristic of AC is that it cannot be stored and is now used.

51. What does the general symbol GF of domestic generator sets mean?
Answer: It represents two meanings:
a) Industrial frequency generator sets are generator sets suitable for my country's general power of 50HZ.
b) Domestic generator sets.

52. Must the load carried by the generator maintain three-phase balance during use?
Answer: Yes. The maximum deviation shall not exceed 25%, and it is strictly forbidden to operate in a missing phase.

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 a diesel engine and a gasoline engine?
Answer: 1) The pressure objects in the cylinder are different.
Diesel engines compress air during the compression stroke;
Gasoline engines compress a mixture of gasoline and air during the compression stroke.
2) Different ignition methods.
Diesel engines rely on spraying atomized diesel to high-pressure gas for self-ignition;
Gasoline engines rely on spark plugs for ignition.

55. What does the "two tickets and three systems" of the power system specifically refer to?
Answer: Two tickets refer to work tickets and operation tickets. That is, any work and operation performed on power equipment. You must first obtain the work ticket and operation ticket issued by the person in charge on duty. The parties must execute according to the ticket.
The three systems refer to the shift system, the patrol inspection system, and the regular equipment switching system.

56. When and where was the world's first practical diesel engine born, and who was the inventor? What is the current situation?
Answer: In 1897, the world's first diesel engine was born in Augsburg, Germany. It was invented by Rudolf Diesel, the founder of MAN. The current English name of the diesel engine is the name of the founder, Diesel.
MAN is the most professional diesel engine manufacturer in the world today, with a maximum single-unit capacity of 15,000KW. It is the main power supplier for the ocean shipping industry. China's large diesel engine power plants also rely on MAN, such as the Dongjiang Power Plant in Huizhou, Guangdong (100,000 KW). The Foshan Power Plant (80,000 KW) are all units provided by MAN.
Currently, this world's earliest diesel engine is stored in the exhibition hall of the German National Museum.