UPS power input and output form and application
Time of issue:2021-12-31
At present, UPS can be roughly divided into three forms in terms of its input and output forms: single-phase input/single-phase output form, three-phase input/single-phase output form, three-phase input/three-phase output form.
The choice of the above three input and output forms is mainly determined by the load capacity. Single-in/single-out UPS ranges from 1KVA to 15KVA; three-in/single-out UPS ranges from 10KVA to 20KVA; and three-in/three-out UPS ranges from 10KVA to 500KVA. It can be seen that the input and output form is mainly based on the difference of UPS capacity and the adaptability to the field during field application. The input form mainly depends on the degree of influence on the on-site three-phase electric balance. The output form mainly depends on the UPS output wire diameter and the capacity of the power components. Generally, each single-phase output should be above 5KVA to ensure the effective load rate, or Taking into account the requirements of the three-phase load on the output form, a smaller single-phase output capacity is adopted.
1. Single-phase input/single-phase output form:
If the capacity is relatively small, a single-input UPS connected to any one-phase household mains will not cause trouble to the three-phase balance of the household mains power. However, the load capacity is small, and the UPS uses single-phase output to output its output. The wire diameter (current value) is not large, and single-phase inverter design can be used. Therefore, small-capacity (generally less than 15KVA) UPS adopts single-in/single-out forms.
2. Three-phase input/single-phase output form:
When the capacity is slightly larger, for example, a load larger than 20KVA, if it is connected to a single-phase input power, it will cause trouble to the field input power distribution balance. However, the three-phase input is adopted to automatically distribute the input current evenly, thereby effectively solving the balance. problem. However, single-phase output is not as large as possible. Single-phase inverter output requires a single-phase bypass input structure. When the UPS capacity is greater than 20KVA, a single-phase 20KVA bypass input requires a relatively large single-phase current. The bypass does not work during normal operation. Even unreasonable wiring and switch selection will not appear. Once the main circuit of the UPS fails or is overloaded and transferred to the bypass operation, the UPS will transfer the entire load to the bypass input circuit to supply power to the system Cause a serious imbalance. In severe cases, it may cause tripping, or fail to bypass due to potential unreasonable wiring and switch capacity. Have a reasonable front-end electrical configuration in time. It will also cause waste of power resources due to consideration of unbalanced configuration. Taking into account the requirements of single-phase bypass input balance and the current pressure of single-phase inverters, it is reasonable to output single-phase inverters within 20KVA. Therefore, UPS in the capacity range of 8-20KVA adopts single-phase inverters and single-phase bypass input with three-in/single-out forms.
When some users consider using large-capacity triple/single UPS, the main advantage they pursue is to improve the output utilization rate of the UPS and avoid output single-phase overload caused by output load distribution problems (when the total capacity is less than the total capacity of the UPS). Or because the on-site power line wiring is determined by special factors such as single or equal. At this time, in order to avoid the limitations of single-phase inverter UPS in terms of single-phase bypass input and insufficient single-phase inverter capacity, another three-phase input/single-phase output scheme is generally adopted. It adopts three-phase input/three-phase output UPS with output three/single transformer. Configure the three/single isolation transformer option on the UPS output side to meet the requirement of balanced three-phase input for the bypass input on the one hand, and relieve the current pressure of the inverter on the other hand. In addition, it also meets the output isolation requirements of some occasions. When using a three-in/single-out isolation transformer, the following points need to be paid attention to:
① The output capacity of the three-phase input/single-phase output transformer is 2/3 of the input capacity. If the output capacity requirements are met, the required three-in/three-out UPS capacity should be at least 1.5 of the single-phase output capacity of the system. Times. Otherwise, the single-phase output capacity of the transformer will be less than the output capacity required by the system. The operating principle of the three-in/single-out transformer is as follows:
The original schematic diagram of the three-phase input/single-phase output transformer is shown on the left. The primary side adopts a star-shaped three-phase input structure, and the secondary side adopts a structure where two identical phases are superimposed and one opposite phase is superimposed to synthesize a single-phase output. The output power of the A-phase, B-phase and C-phase of the primary side is converted to the secondary side to obtain the secondary side a-phase, b-phase and c-phase coil power with a mutual difference of 120 degrees. The vector whose power amplitude of the phase coils is equal and the direction is opposite to that of phase c is reversed and superimposed with the end of the same name of c to generate a total output power value that is twice the single-phase power. That is, the single-phase output is 2/3 of the three-phase input power.
② The technical requirements of the three single transformers are relatively high, so it is best to use imported products, especially the matching options produced by the same manufacturer.
The triple/single isolation transformer option produced by the original factory cooperates with the UPS mainframe to form a high-performance, high-reliability triple/single power supply solution. If you consider the possible parallel capacity increase requirements on site in the future, it should be purchased and installed for the first time Attention should be paid to the use of an output isolation transformer with a capacity of more than 2 times, so as to avoid replacement waste caused by insufficient output transformer capacity in the future capacity increase process.
3. Three-phase input/three-phase output form:
With the increase of the load capacity, on the basis of the input three-phase form, the output also adopts the three-phase form, so that the current of each single-phase output is not too large. In some special occasions, small-capacity three-phase output UPSs are also used, which are mainly designed for small-capacity three-phase loads. When purchasing a UPS with a three-phase output, the unbalanced load capacity of the UPS should be considered. Generally, a UPS with a 100% unbalanced load capacity should be selected. The different inverter structure of the UPS determines its unbalanced output load capacity. Currently, the UPS with a three-phase independent inverter bridge structure has a better unbalanced load capacity. Because the independent inverter bridge structure avoids the mutual influence of each phase caused by the traditional three-phase bridge + r/Y transformer structure, it completely becomes three 220V output inverters with independent output. Therefore, it has a more stable unbalanced load capacity.