Technical Questions and Answers for 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 special parallel device to complete the parallel work. It is generally recommended to use fully automatic parallel cabinets. Try not to parallel machines manually. Because the success or failure of manual parallel machines depends on human experience. Based on more than 20 years of experience in electric power work, the author boldly declares that the reliable success rate of manual paralleling of diesel generators is equal to zero. Never apply the concept of manual parallel operation to a large mains power supply system to a 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 unit oscillation.

3. Why do we require customers to carry out a fastening work for all electrical contacts after every 200 hours of operation of the unit?

Answer: Diesel generator set is a vibration worker. Moreover, it is useless for many domestically produced or assembled units to use double nuts. The use of spring washers is useless. Once the electrical fasteners are loose, a large contact resistance will be generated, resulting in abnormal 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 drop; if the generator inhales sand and other impurities, the insulation between the stator and rotor gap will be damaged, and the severe one will cause burning.

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

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 no grounding;

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

6. What problems should be paid attention to when using the neutral point ungrounded unit?

Answer: The 0 line may be charged, because the capacitive voltage between the live line 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 electricity custom.

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

Answer: 1) UPS is generally represented by apparent power KVA, firstly multiply it by 0.8 and convert it into the unit KW which is consistent with the active power of the generator;

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

3) If a generator with PMG (permanent magnet excitation) is used, the power of the UPS is multiplied 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 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 function?

Answer: No. At present, some of the units of the same brand even have it and some don't. Users must figure it out by themselves when purchasing a unit. ** Written as an attachment to the contract. Generally, low-cost machines do not have self-protection functions.

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

Answer: First check whether there is a factory certificate and a product certificate. They are the "identity certificates" of the diesel engine and must be available. Then check the three major numbers on the certificate 1) nameplate number; 2) body number (in reality, it is generally on the plane that has been machined at the end of the flywheel, and the font is convex); 3) oil pump nameplate number. Check these three numbers with the actual number on the diesel engine, it must be accurate. If you find any doubts, you can report these three serial numbers to the manufacturer for verification.

11. After the operating 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 for checking the real useful power of the unit is: the 12-hour rated power of the diesel engine is multiplied by 0.9 to get a data (kw). If the rated power of the generator is less than or equal to the data, the real useful power of the unit is determined by the rated power of the generator. If the rated power of the generator is greater than the data, the data must be used as the real useful power of the unit; 2) Check which self-protection functions the unit has; 3) Check whether the power wiring of the unit is qualified and whether the protective grounding is reliable. Whether the phase load is basically balanced.

12. There is a 22KW starter motor for an elevator, what size generator set should it be equipped with?

Answer: 22*7=154KW (the elevator is a model that starts directly with load, and the instantaneous starting current is generally 7 times the rated current to ensure that the elevator can move at a constant speed). (that is, at least a 154KW generator set should be equipped)

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

Answer: P**=3/4*P rated (that is, 0.75 times rated power).

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

Answer: 10℅.

15. The engine power of some generator sets is expressed in horsepower. How to convert between horsepower and 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(volt)*0.8) The simplified formula is: I(A)=unit rated power (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 in my country to express the capacity of transformers and UPS; 2) Active power is 0.8 times the apparent power, and the unit is KW, which is used in 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 it is only allowed to be used for 1 hour within 12 hours; 5) The economic power is 0.75 times the rated power , is the output power of the diesel generator set that can run for a long time without time limit. When running at this power, the fuel economy is the most, and the failure rate is the highest.

18. Why is the diesel generator set not allowed to run for a long time under the condition of less than 50% of the rated power?

Answer: The oil consumption increases, the diesel engine is easy to coke, the failure rate increases, and the overhaul cycle is shortened.

19. Is the actual output power of the generator based on the power meter or the ammeter when it is running?

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