1. What is the power factor of three phase generator? Can we add a power compensator to increase power factor?
Answer:
The power factor is 0.8. No, we can not because the charging and discharging of capacitor would lead to fluctuation of small power source and machine set oscillation.
2. Why we require our customer to fasten all of the electrical contacts after machine set run every 200 hours?
Answer:
Diesel generator set is a kind of vibration working device. Moreover, many sets produced or assembled in our country should be installed double nut and spring shim but actually they are not, which would result in abnormal machine set operation caused by high contacts resistance from electrical contacts loosen.
3. Why the generator room must be kept clean and no quick sand on the floor?
Answer:
If diesel engine draws dirty air, its power will fall off. If generator draws grains of sand or other impurities, the insulation among rotor clearance will be breakdown, even burned down.
4. How do the UPS and diesel generator match power to ensure stability of UPS output?
Answer:
1. Generally UPS is expressed by apparent power KVA, firstly multiplied by 0.8 to convert to the same unit as generator active power.
2. If general generators are applied, active power of UPS is multiplied by 2 to confirm the equipped generator power which is two times as UPS power.
3. If PMG (Permanent magnet) generator applied, power of UPS is multiplied by 1.2 to confirm generator power which is 1.2 times as UPS power.
5. Do all of the diesel generator sets have the function of self protection?
Answer:
No. At present markets, some of the products with same brand have this function but some don’t. Users must make this clear when purchase machine sets. A written material is preferred as contract attachment. Generally, machine sets with lower price do not have this function.
6. How to judge fake home-made diesel generators with poor quality?
Answer:
First, check if there are qualified certificate and product certificate which are identification of diesel generator and they are essential. Second, check three serial numbers on the certificates: 1. Date plate number. 2. Machine body number (usually it’s on the machine cut surface at flywheel side, which is in convex body). 3. Pump date plate number. Check these numbers with the actual ones on the generators. They must be accurate. If there are doubts, check and verify with manufacture.
7. Which three points does the operational electrician have to check after he takes over diesel generator sets?
Answer:
1. Check actual useful power of machine sets, then confirm economic power and reserve power. The way to check actual useful power: A number from rated power of diesel generator after 12 hours multiplied by 0.9, if generator rated power is less than or equal to this number, then the generator rated power is the actual useful power of this machine set. If generator rated power is greater than this number, then we must apply another number which is less than or equal as actual useful power.
2. Check which self protection function the machine set has.
3. Check if electrical connections are qualified, if protective grounding is reliable, if three-phase load is in a basic balance.
8. How many KWs generator set should be applied for an elevator with starting dynamo 22kw?
Answer:
22*7=154KW (elevator starts directly with load. Instant starting current is 7 times as rated current to ensure elevator making uniform motion. (154KW machine set is at least).
9. How to calculate optimal service power (economic power)?
Answer: P optimal =3/4*P rated (0.75 times as rated power) .
10: How much should engine power of normal generator set be larger than generator power according to national standards?
Answer: 10%.
11. Some of engine power of generator set is expressed by Horse power. How to convert Horse power into kilowatt?
Answer: 1 horse power=0.735 kilowatt, 1 kilowatt= 1.36 horse power.
12. How to calculate the current of three phase generator?
Answer:
I = P / (√3 Ucos φ ).
That is to say current= power(watt)/ (√3 *400(volt) * 0.8) .
Formula for reduction: I(A)= rated power(KW)* 1.8.
13. The relationships among apparent power, active power, rated power, ultimate power, and economic power.
Answer:
1. The unit of apparent power is KVA, by which we express transformer and capacity of UPS in our country.
2. Active power is 0.8 times as apparent power, whose unit is KW. It is applied into power generating equipment and power consumption equipment.
3. Rated power of diesel generator is the power that operates continuously in 12 hours.
4. Ultimate power is 1.1 times as rated power, but it is only available for 1 hour in 12 hours.
5. Economic power is 0.75 times of rated power, which is the output power of diesel generator set that can operate long time and no time limitation. When this power is in operation, fuel consumed is in minimum level and failure rate the lowest.
14. Under the condition of rated power less than 50%, why the diesel generator set can not be allowed to operate in long time?
Answer:
The increase of motor oil consumption, easy caking of diesel generator, higher rate of failure, the shortening of overhaul life.
15. Power meter and ampere meter, which one should be the criterion of actual output power when the generator is running.
Answer: The ampere meter. Take power meter as reference.
16. Engine and power generator, which should be blamed when the frequency and voltage are unstable?
Answer: Engine.
17. Engine and power generator, which should be blamed when the frequency is unstable?
Answer: power generator.
18. What’s wrong with the generator’s loss of excitation? How to deal with it?
Answer:
out of operation for a long time of generator that leads to the loss of magnetic remanence contained before leave the factory that excitation coil’s not able to build a proper magnetic field. Under this circumstance, engines are working well but can not be generating, which always happen among new machine sets or machines out of use for a long time.
Approaches: 1. press it if there is an excitation coil button. 2. Charge magnetism if there is no excitation coil button. 3. and overdrive for several seconds with a load lamp.
19. What are the main reasons that after run for a time, all of the factors are normal but the power falls?
Answer:
1. Air filter is too dirty to inhale enough air. To clean or change air filter is necessary.
2. Fuel filter device is too dirty to inject fuel quantity. To clean or change fuel filter is necessary.
3. Incorrect ignition time that needs to be changed.
20. What the problem lies in when a generator set has stable voltage and frequency but unstable current after on-load operation?
Answer:
The problem lies in the instability of customer’s load but the quality of generator is absolutely out of question.
21. What is the main problem if a generator set’s frequency is unstable?
Answer: The problem lies in the instability of rotate speed.
22. Which are the most important points should be paid attention when the diesel generator in operation?
Answer:
1. Water must be enough in the tank and keep the temperature within permitted.
2. Lubricate oil must be in place but no excess, and keep the pressure within permitted.
3. Frequency within about 500 Hz, voltage about 400V.
4. Three-phase current should be kept in rated range.
23. Which parts of diesel generator should be often changed or cleaned?
Answer: Diesel filter, motor oil filter and air filter.
24. What are the main advantages of brushless generator?
Answer:
1. No charges of carbon brush maintenance. 2. Resistance to radio jamming. 3. Failure reduction caused by loss of excitation.
25. What is the insulation grade of home made generator?
Answer: Home made machine-grade B; Marathon brand machine, Leroysomer brand machine and Stamford brand machine are of grade H.
26. What kind of gasoline engine’s fuel should be mixed by gasoline and motor oil?
Answer: Two-stroke gasoline engine.
27. Six systems that installed in diesel generator basic equipment.
Answer:
1. Gasoline lubrication system. 2. Fuel oil system. 3. Control and protection system. 4. Cooling and heat removal system. 5. Exhaust system. 6. Cranking system.
28. Why the motor oil and motor oil filter should be replaced after new machine used for a time?
Answer:
During running in period it is unavoidable that impurity would sink to the bottom of motor oil shell from which physical and chemical reaction would take place from gasoline and its filter.
29. Why we require customer to arrange the fire tube down-sloping 5-10 grades when assembling?
Answer: To prevent rainwater from entering fire tube to avoid heavy accident.
30. There are manual oil pump and exhaust bolt assembled. What are they used for?
Answer: They are used for removing air in the fuel pipe before start.
31. How to divide into different grades of diesel generator automation?
Answer:
Manual, self-starting, self-starting with commercial power transforming cabinet and distant range remote control, remote sense and remote monitor.
32. Why the standard of outgoing line voltage is 400V but not 380V?
Answer: Because there is voltage loss and reduction after line outgoes.
33. Why the airs in the diesel generator ground have to require being fluency?
Answer:
The output of diesel generator is influenced by air quantity and quality, and also generator needs enough air to be cool. So the ground has to be fluency.
34. When assembling motor oil filter, diesel filter and water oil separator, we can not rotate them tightly but only do until no oil leaking? Why?
Answer:
If rotate them tightly, then the seal ring would produce heat expansion and then great stress, which will result in the damage of filter shell or separator shell, even worse the damage of body nut that can not be repaired.
35. What is the advantage if customer purchased self starting but did not purchase automatic transforming cabinet?
Answer:
1. Once city power network fails, the generator set would start automatically that fasten manual power transmission.
2. If the illuminating line is connected at the front side of air switch, the equipment room illumination would not be influenced by power failure and convenient for the workers.
36. What conditions would be met for generator set to switch in to transmit power?
Answer:
1. Water cooler set and temperature reaches 56 ℃.
2. Air cooler set and machine body in tepefaction.
3. Normal voltage frequency and gasoline pressure in zero load.
37. What is the order of on-load after machine starts and power transmits?
Answer: Take load from small to large.
38. What is the order of load removal before the machine shut down?
Answer: Remove load from small to large, at last shut down the machine.
39. Why we can not shut down and start machine on-load?
Answer:
On-load shut down is emergency halt that attack stronger to machine set. On-load start is violation operation, which would damage generating equipment and power consumption ones.
40. What attentions should be paid when the diesel generator is in use in winter?
Answer:
1. Water tank can not be frozen. Apply special permanent antirust fluids and antifreeze or use electro-heat equipment to keep the temperature above 0℃.
2. Open flame is forbidden.
3. On-load preheating should be longer to transmit power.
41. What is three-phase four-wire system?
Answer:
There are 4 outgoing lines, 3 of which are front lines and the other is zero line. The voltage between front lines is 380V, and 220V between front line and zero line.
42. What is three phase short circuit? What kind of effects would be led to?
Answer:
There is no load between front fires. Direct short circuit is three-phase short circuit, whose effects are horrible, even machine destroyed and man killed.
43. What is inversely feeding, from which what effects would be led to?
Answer:
Inversely feeding, a kind of phenomenon that house generator transmit power toward city power network. There are two severe effects:
a) City power network is working, and then non-synchronous parallel operation will be produced after city power connected with house generator that must destroy machine set. If house generator has a large capacity then it will make city power vibrate.
b) City power network is under repairing. The repairing staff will be killed by electric shock when the house generator is in inversely feeding.
44. Why the test engineers have to fully check all of the fixed bolts and line interfaces if they are fixed?
Answer:
After a long trip, some of bolts and line interfaces may loosen or fall down, which would influence the test even damage the machine.
45. Which grade does electrical energy belong to? What is the feature of alternating current?
Answer:
Electrical energy is secondary; alternating current is confirmed by mechanical energy; direct current by chemical energy. Alternating current can not be stored, which can be used once found.
46. What is meaning of the general symbol GF of home made generator set?
Answer:
Double meaning.
a) Power frequency generator, available under universal power 50 Hz in our country.
b) Home made generator set.
47. Must the load taken by generators keep three-phase equilibrium in use?
Answer: Yes. The maximum deviation can not surpass 25%. Absence-phase operation is forbidden.
48. What are the four strokes in diesel generator?
Answer: Intake stoke, combustion stroke, power stroke, exhaust stroke.
49. What are the big differences between diesel generators and gasoline engine generators?
Answer:

1. Press object is different.
In the stage of compression stroke of diesel generator, air is under compression.
In the stage of gasoline engine generators of diesel generator, gasoline and air mixtures are under compression.
2. Different ignition.
Diesel generator ignites by atomized diesel spraying high pressure gas. Gasoline generators by spark plug.