Generators and UPS configuration issues

According to the UPS capacity, generally a traditional double conversion online UPS supporting the capacity of the  generator set than 2 to 4 times. Fact, the jaw tears general work in the 50% to 80% of rated capacity, and for generating set, its output power may be about 30% of the rated capacity.
Abstract: According to the UPS capacity, the general capacity than a traditional double conversion online UPS package generator sets 2 to 4 times. Fact, jaw tears general work in the range of 50% to 80% of rated capacity, and for generating set, its output power may be about 30 percent of the rated capacity. This will not only result in the capacity of the generator set can not take full advantage of the increased investment in equipment, resulting in the phenomenon of the "big horse cart", but they generator set is more prone to failure, maintenance, and reduce the reliability of the generator sets.
To improve the match between the problem with generators and UPS equipment, try to use the excellent performance of the generator while attention should be primarily on improving the UPS input characteristics and improve the connection between the two on.

According to the UPS capacity, generally a traditional double conversion online UPS supporting the capacity of the generator set than 2 to 4 times. Fact, jaw tears general work in the range of 50% to 80% of rated capacity, and for generating set, its output power may be about 30 percent of the rated capacity. This will not only result in the capacity of the generator set can not take full advantage of the increased investment in equipment, resulting in the phenomenon of the "big horse cart", but they generator set is more prone to failure, maintenance, and reduce the reliability of the generator sets. The reason is that in accordance with the characteristics of the diesel generators, if the long-term work in the small load, the cylinder temperature is low, the normal access of lubricating oil within the cylinder is not completely burned, and the fuel is not fully burn, causing the piston ring at, injector mouth at serious coke, cylinder wear increased, thereby accelerating the production of these parts failure, then the performance of the diesel diesel generator system, exhaust black smoke.
The diesel engine is less than 30% of the rated load, the economy deteriorated. Typically, the generator set work load exceeds 60% of the rated load of the diesel engine is more favorable.
Method to solve this problem is to correct the generator load input characteristics. Below, the specific introduction of several commonly used methods.
(1) to improve the system power factor
There are many ways to improve system power factor, introduces the following.
The first method is to set the auto switch cabinet, then the other load of the generator is first access in the UPS. This method is only applicable to high-power diesel generator system-UPS power supply system. Such a system, in addition to the UPS outside there are other properties of the load. This automatic switch cabinet to implement certain difficulties, and manufacturers maintenance engineers need a separate UPS and generator commissioning.
The second method is to increase the inductive reactance of a permanent to compensate capacitive load, commonly used in parallel wirewound reactors connected in parallel to the generator output board, it is very easy to implement and low cost, but whether it is a heavy load or light load , the reactor is always in the absorption of current and to influence the load power factor. Moreover, regardless of the quantity of the UPS, the quantity of the reactor is always fixed.
The third method is able to compensate for the inductive reactance of the capacitive reactance of the UPS installation of each UPS just contactor (option) in the case of low load controlled reactor access. This method can be more accurately set the reactor, but the number is large and the high cost of installation and control.
The fourth method is installed in the filter capacitor before the contact device, at low load disconnect. As the contact time must be precise, the control more complex, and can only be installed in the factory.
The fifth hybrid active filter the DHM in front of the UPS system configuration, input power factor of the entire power supply system is maintained at above 0.95, the input current harmonic control in less than 10%.
(2) to improve the input power factor of the UPS equipment
Talking about here is not used to increase the the UPS input of passive filter method. Traditional double conversion online UPS can be changed to a 6-pulse rectifier 12 pulse rectifier, this is an effective method to improve the UPS input power factor and reduce input current harmonic components, but it is the input you want to set the same filter, so can not fundamentally solve the matching problem of diesel generator systems with UPS. Described in chapter 4 of the method to improve the input power factor of the UPS, the most effective way to hundred, S C rectifier circuit input AC still changed to the high-frequency rectifier (PFC) circuit (as described in Chapter 2, Figure 2 -51 and Chapter 4, as shown in Figure 4-28), because this approach can be the UPS load input power factor increased to more than 0.95 regarded within the range of 0 to 100, when the UPS load exceeds 50A, can be increased to more than 0.98 and the input terminal without further passive LC filter, in such a system, the arrangement relationship between the capacity of the generators with the UPS can be reached 1.5:1.
(3) the elimination of the devices in the system start-up current impact
In the power supply system, the start of any high-power electrical equipment will form a large starting inrush current, serious pollution to the power grid, resulting grid voltage sag. Start grid after power supply system of the diesel generator system will affect the normal start of the diesel generator system, or even cause the UPS system failure. Figure 5-7 when the diesel generator system startup inrush current measured waveform.
Shown in Figure 5-7, the grounds of a 1OOkVA the electricity regulator the +1 Desk 8OkVAUPS composed UPS system. Grid power down the UPS genetically battery inverter power supply to the load, the electricity regulator enters shutdown state. Diesel generator system start-up start facing the electricity regulator and UPS to turn the diesel generator system powered by a battery inverter load current transfer process, the boot of a power regulator surge current amplitude package The change in characteristics of the envelope as follows: The maximum peak current is 135A, the duration is about 0.2s unipolar transient surge current. Generated by the UPS in the 2 boot inrush current, it appears in a boot inrush current disappeared after 3-4s. The start current generated by units 8OkVAUPS 2 input current slow start to climb the characteristics, the steady-state value of the input current is 5OA. Surge current test curve shows that pose the greatest potential threat to the safe operation of the generator to freedom 1OOkVA electricity regulator, and 8OkVA6 pulse type UPS with slow to start climbing modulation characteristics input current input harmonic wave current.
Linear transformers (including isolation transformer in the power supply system, the impact of the most serious current equipment startup, UPS input 12-pulse rectifier transformer and to compensate for transformer as the main exchange regulator), about the impact of current physical processes features and elimination of the way, see Section 3 of this chapter.
Another device to produce Inrush Current  UPS, the mains - diesel generator system-UPS power supply system, mains failure diesel generator system starts normally, the UPS access mainly manifested in two aspects , the load current from the battery inverter transfer of power to the diesel generator system, this shift may be a mutation of the diesel generator system load, the other does not rule out the load transfer process at the same time give the UPS battery charging, the changing the amplitude of the transient is greater than the normal UPS input current load power; Second is the impact of the capacitive current in the start of the the UPS input of passive filter. For the former, in order to reduce the impact of the UPS inrush current of the diesel generator system, usually require UH starts with a "soft start" function / start when the input current is slowly increased from zero rating. UPS along the slow start of the process is also very important to the stability of the diesel generator system-UPS system. Following Delta conversion UPS asked to explain the slow start the process in the case of diesel generator system powered hammer.
Because Delta Delta conversion UPS converter work in the high-frequency pulse-width modulation state, so the UPS power, it's slow-start process can be done very ideal input, as shown in Figure 5-8. Driven by a diesel generator for S1con480kUPS slow startup characteristics of the measured waveform.
UPS models: SlconDP3480E, 480kVM480kW.
UPS MCC load: full load 5OOkW.
Slow start: 105.
Diesel generator system: 625kV elbow 5OOkW.
Oil machine frequency change in load startup process: 0.25Hz.
ABB measured in October 2000 and December are two other brands in the United States high-power conventional double conversion UPS input slow start characteristics as shown in Figure 5-9. Wherein Figure 5-9 (a) is a measure, in October 2000, and Figure 5-9 (b) is a measure in December 2000. As can be seen from the figure, the two start waveform is not exactly the same, but the entire process by two harmonic jump to complete it is. Despite the The UPS delay the start time, but does not eliminate the problem of the diesel generator system load mutation.

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