56 common questions about diesel generator sets


1. What are the conditions for the parallel use of two generator sets? What device is used to complete the parallel work?

Answer: The condition for parallel use is that the instantaneous voltage, frequency, and phase of the two machines are the same. Commonly known as “Three Simultaneous”. Use a dedicated parallel device to complete the parallel work. It is generally recommended to use fully automatic parallel cabinets. Try not to manually parallelize. Because the success or failure of manual parallelization depends on the human experience. With more than 20 years of experience in electric power work, the author boldly asserts that the reliable success rate of manual paralleling of diesel generators is equal to 0. Never apply the concept of manual paralleling of the large mains power supply system to the small power supply system, 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 vibration of the unit.

3. Why do we require the customer to carry out a tightening of all electrical contact parts after every 200 hours of operation of the unit?

Answer: Diesel generator sets are vibration workers. Moreover, many domestically produced or assembled units are useless to use double nuts. The spring washer is useless. Once the electrical fasteners are loosened, a large contact resistance will be generated, resulting in the normal operation of the unit.

4. Why must the generator room be 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 particles, the insulation between the stator and rotor gaps will be damaged, and in severe cases, it will be burned.

5. Why since 2002, has our company generally does not recommend users to use neutral grounding during installation?

Answer: 1) The self-regulation function of the new generation generator is greatly enhanced;

2) In practice, it is found that the lightning failure rate of the neutral point grounding unit is relatively high.

3) The grounding quality requirements are relatively high, which cannot be achieved by ordinary users. Unsafe work grounding is worse than not grounding.

4) The unit with the neutral point grounded will cover up the leakage fault and grounding error of the load, and these faults and errors cannot be exposed under the condition of large-current power supply of the mains.

6. What should be paid attention to when using a unit with an ungrounded neutral point?

Answer: The 0 wire may be charged because the capacitive voltage between the live wire and the neutral point cannot be eliminated. The operator must regard the 0 lines as a charged body. It cannot be dealt with according to the habit of commercial electricity.

7. How to match the power of the UPS and the diesel generator to ensure the stable output of the UPS?

Answer: 1) UPS is generally expressed by the apparent power KVA. First, multiply it by 0.8 and convert it into a unit KW consistent with the active power of the generator.

2) If a general generator is used, multiply the active power of the UPS by 2 to determine the power of the allocated generator, that is, the generator power is twice the power of the UPS.

3) If a generator with PMG (Permanent Magnet Machine Excitation) is used, multiply the power of the UPS by 1.2 to determine the power of the generator, that is, the power of the generator is 1.2 times the power of the UPS.

8. Can the electronic or electrical components marked with a withstand voltage of 500V be used in the control cabinet of diesel generators?

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. Are all diesel generator sets equipped with a self-protection function?

Answer: No. At present, some units of the same brand in the market have or not. Users have to figure it out for themselves when purchasing a unit. It is best to put it in writing as an attachment to the contract. Generally, low-cost machines do not have self-protection functions.

10. How to identify fake and inferior domestic diesel engines?

Answer: First check whether there is a factory certificate and product certificate. They are the “identity certificate” of the diesel engine when it leaves the factory, and they are necessary. Check the three major numbers on the certificate again: 1) Nameplate number; 2) Body number (generally on the plane machined at the flywheel end, and the font is convex); 3) Oil pump nameplate number. Check these three major numbers with the actual numbers on the diesel engine, and they must be accurate. If any doubts are found, these three serial numbers can be reported to the manufacturer for verification.

11. After the electrician takes over the diesel generator set, which three points should be verified first?

Answer: 1) Verify the real useful power of the unit. Then determine the economic power, and reserve power. The method of verifying the real useful power of the unit is: to multiply the rated power of the diesel engine for 12 hours by 0.9 to obtain 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 which self-protection functions the unit has.

3) Verify whether the power wiring of the unit is qualified, whether the protective grounding is reliable, and whether the three-phase load is basically balanced.

12. There is an elevator starter motor of 22KW, what size generator set should be equipped?

Answer: 22*7=154KW (the elevator is a direct start-up model with load, and the instantaneous starting current is generally 7 times the rated current to ensure the elevator moves at a uniform speed). (that is, at least a 154KW generator set should be equipped)

13. How to calculate the optimal use power (economic power) of the generator set?

Answer: P best=3/4*P rated (ie 0.75 times rated power).

14. The state stipulates that the engine power of the general generator set should be larger than the generator power? Answer: 10℅.

15. The engine power of some generator sets is expressed in horsepower. How to convert between horsepower and international unit kilowatt?

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

16. How to calculate the current of the three-phase generator?

Answer: I = P / (√3 Ucos φ )

That is, current = power (watts) / (√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) The active power is 0.8 times the apparent power, and the unit is KW, which is used for power generation equipment and electrical equipment in my country.

3) The rated power of the diesel generator set refers to the power that can run continuously for 12 hours.

4) The maximum power is 1.1 times the rated power, but only 1 hour of use is allowed 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 a time limit. When running at this power, the fuel economy is the most economical and the failure rate is the lowest.

18. Why is the diesel generator set not allowed to run for a long time below 50% of the rated power.

A: The oil consumption is increased, the diesel engine is easy to carbonize, the failure rate is increased, and the overhaul period is shortened.

19. Is the actual output power of the generator in operation based on the power meter or the ammeter?

Answer: The ammeter shall prevail, the power meter is only for reference.

20. The frequency and voltage of a generator set are unstable. Is the problem with the engine or the generator?

A: It’s the engine.

21. The frequency of a generator set is stable and the voltage is unstable. Is the problem with the engine or the generator?

Answer: It is the generator.

22. What is the matter of generator loss of magnetism and how to deal with it?

Answer: If the generator is not used for a long time, the residual magnetism contained in the iron core before leaving the factory will be lost, and the excitation coil cannot establish the proper magnetic field. At this time, the engine runs normally but cannot generate electricity. This kind of phenomenon is a new machine. Or there are many units that are not used for a long time.

Treatment methods: 1) Press the excitation button if there is an excitation button, 2) If there is no excitation button, use the battery to magnetize it, 3) Load a light bulb and run it at Overspeed for a few seconds.

23. After the generator set has been used for a period of time, it is found that everything else is normal but the power has dropped. What is the main reason?

Answer: a. The air filter is too dirty and the inhaled air is not enough. At this time, the air filter must be cleaned or replaced.

b. The fuel filter device is too dirty and the fuel injection volume is not enough, so it must be replaced or cleaned.

c. The ignition time is not correct and needs to be adjusted.

24. When a generator set is under load, its voltage and frequency are stable, but the current is unstable. What is the problem?

A: The problem is that the customer’s load is not stable, and the quality of the generator is absolutely fine.

25. The frequency of a generator set is unstable, what is the main problem?

A: The main problem is that the speed of the generator is unstable.

26. What are the most important points that must be paid attention to in the use of diesel generator sets?

Answer: 1) The water in the water tank must be sufficient and keep working within the allowable temperature range.

2) The lubricating oil must be in place, but not excessive, and keep working within the allowable pressure range.

3) The frequency is stable at about 50HZ, and the voltage is stable at about 400V.

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

27. What are the parts of the diesel generator set that need to be replaced or cleaned frequently?

A: Diesel filter, oil filter, air filter. (Individual units also have water filters)

28. What are the main advantages of brushless generators?

Answer: (1) The maintenance of carbon brushes is eliminated;

(2) Anti-radio interference;

(3) Reduce the loss of magnetic failure.

29. What is the general insulation level of domestic generators?

A: The domestic machine is B grade; the Marathon brand machine, Leroy Somer brand machine and Stamford brand machine are H grade.

30. What kind of gasoline engine requires gasoline and oil to be mixed?

Answer: Two-stroke gasoline engine.

31. Which six systems are included in the basic equipment of diesel generator sets?

Answer: (1) Oil lubrication system;

(2) Fuel system;

(3) Control and protection system;

(4) Cooling and cooling system;

(5) Exhaust system;

(6) Starting system;

32. Why do we try our best to advise customers to use the oil recommended by our company in our sales work?

Answer: Oil is the blood of the engine. Once the customer uses unqualified oil, the engine will cause serious accidents such as the seizure of the bearing bush, the tooth of the gear, and the deformation and fracture of the crankshaft, until the whole machine is scrapped.

33. Why should the oil and oil filter be replaced after a new machine has been used for a period of time?

Answer: During the running-in period of the new machine, it is inevitable that impurities will enter the oil pan, which will cause physical or chemical changes in the oil and oil filter.

34. Why do we require customers to incline the exhaust pipe downward by 5-10 degrees when installing the unit?

A: To prevent rainwater from entering the exhaust pipe, resulting in major accidents.

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

36. How to divide the automation level of diesel generator sets?

Answer: Manual, self-start, self-start plus automatic mains conversion cabinet, long-distance three remotes (remote control, telemetry, remote monitoring.)

37. Why is the outlet voltage standard of the generator 400V instead of 380V?

Answer: Because the line after the outlet has voltage drop loss.

38. Why is it required to have smooth air in the site where the diesel generator set is used?

Answer: The output of the diesel engine is directly affected by the quantity and quality of the air inhaled, and the generator must have sufficient air for cooling. Therefore, the use of the venue must be smooth air.

39. Why is it not appropriate to use tools to screw the above three devices too tightly when installing the oil filter, diesel filter, an oil-water separator, but only by hand to prevent oil leakage?

Answer: Because if it is screwed too tightly, the sealing ring will thermally expand under the action of oil bubbles and the body heating, resulting in great stress. Causes damage to the filter housing or the separator housing itself. What’s more serious is the damage to the body screw that cannot be repaired.

40. What are the benefits of the customer who purchased the self-starting, but did not purchase the automatic conversion cabinet?

Answer: 1) Once the power outage occurs in the city network, the unit will automatically start to speed up the manual power transmission time;

2) If the lighting wire is connected to the front end of the air switch, it can also ensure that the lighting of the computer room is not affected by the power failure, 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: TIn the water cooling unit, the water temperature reaches 56 degrees Celsius.

The air-cooled unit and the body are slightly hot.

The voltage and frequency are normal at no load. Oil pressure is normal. before closing the switch and sending power.

42. What is the load sequence after power on?

Answer: The load is carried in order from large to small.

43. What is the unloading sequence before shutdown?

Answer: The load is removed in order from small to large, and finally shut down.

44. Why can’t it be turned off and turned on with load?

Answer: Shutdown with load is an emergency shutdown, which has a greater impact on the unit. Starting with load is an illegal operation, which will cause damage to the power generation equipment and electrical equipment.

45. What should be paid attention to when using diesel generators in winter?

Answer: 1) Pay attention that the water tank must not freeze, and the prevention methods include adding special long-term anti-rust, anti-freeze, or using electric heating equipment to ensure that the room temperature is above the freezing point.

2) Baking with open fire is strictly prohibited.

3) The no-load preheating time should be a little longer before power transmission.

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 zero wire. The voltage between the live wire and the live wire is 380V. 220V between a live wire and a neutral wire.

47. What is the 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 terrifying, and in serious cases, it will lead to the destruction of the machine and the death of people.

48. What is the so-called reverse power transmission? What are the two serious consequences?

Answer: The situation where the self-provided generator sends electricity to the city network is called reverse electricity transmission. There are two serious consequences:

a) If there is no power outage in the city network, the power supply of the city network and the power supply of the self-provided generator will be paralleled asynchronously, which will destroy the unit. If the capacity of the self-provided generator is large, it will also cause shocks in the city network.

b) The city network has been out of power and is being repaired, and its self-provided generator sends electricity backward. The maintenance personnel of the power supply department will be electrocuted.

49. Why must the commissioning personnel check whether all the fixing bolts of the unit are in good condition before commissioning? Are all line interfaces intact?

Answer: After the unit is transported for a long time, sometimes it is inevitable that the screw bolt and the line interface will be loose or dropped, which will affect the debugging and damage the machine.

50. Which level of energy does electric energy belong to? What are the characteristics of alternating current?

Answer: Electric energy is a secondary energy source, alternating current is converted from mechanical energy, and direct current is converted from chemical energy. The characteristic of alternating current is that it cannot be stored, and it is now used.

51. What does the general symbol GF of the domestic generator set mean?

Answer: Represents dual meanings:

a) The power frequency generator set is suitable for the general power 50HZ generator set in my country.

b) Domestic generator sets.

52. Must the load of the generator be kept in a three-phase balance during use?

Answer: Yes. The maximum deviation shall not exceed 25%, and it is strictly forbidden to operate without phase.

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

Answer: Inhale, compress, do work, 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.

The diesel engine compresses the air during the compression stroke stage;

The gasoline engine compresses the gasoline and air mixture during the compression stroke stage.

2) The ignition method is different.

Diesel engines rely on atomized diesel to ignite high-pressure gas spontaneously;

Gasoline engines rely on spark plugs for ignition.

55. What does “two votes and three systems” in the power system refer to?

A: The second vote refers to the work ticket and the operation ticket. That is, any work and operation performed on electrical equipment. The work ticket and operation ticket issued by the person in charge of the shift must be collected first. The parties must execute by vote.

The three systems refer to the shift system, the patrol inspection system, and the regular switching system of equipment.

56. When, where, and who was the inventor of the world’s first practical diesel engine? What is the current situation?

Answer: In 1897, the world’s first diesel engine was born in Augsburg, Germany, and was invented by Rudolf Diesel, the founder of MAN. The current English name of the diesel engine is the founder’s name, Diesel.

MAN is the most professional diesel engine manufacturing company in the world, with a single-engine capacity of up to 15000KW. It is the main power supplier for the marine shipping industry. Large diesel power plants in China also rely on MAN, such as Dongjiang Power Plant in Huizhou, Guangdong (100,000 KW). Foshan Power Plant (80,000 KW) are all units provided by MAN.

At present, the world’s earliest diesel engine is stored in the exhibition hall of the German National Museum.

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