Recommendations on UPS configuration for computer rooms

Recommendations on UPS configuration for computer rooms

1. Configuration Scheme Recommendations

1.1 Capacity

1.1.1 Related factors and explanations

When considering the capacity issue during UPS selection, list the relevant factors that determine the capacity and explain the specific relationship between each factor and the capacity. The factors that should be considered in determining the UPS capacity are: actual load capacity, load type, capacity utilization rate, environmental conditions, UPS type and actual load capacity, potential expansion requirements, etc. In practical applications, the following should be considered:

A. Actual load capacity

This is the most fundamental factor in determining the capacity of the UPS. The output capacity of the UPS must meet or exceed the load requirements to ensure normal power supply. In practical applications, it is necessary to consider whether the UPS uses centralized power supply or distributed power supply. The total load of centralized power supply should be the total power of all loads powered by the UPS in the computer room. If distributed power supply is used, it is determined according to the different loads carried by each UPS.

Usually the load capacity of electrical equipment is called apparent power, which is represented by S and the unit is VA. Apparent power includes active power P (unit W) and reactive power Q (unit Var), and the relationship between them is S2=P2+Q2. Here we call the ratio of active power to apparent power the power factor. The power factor of pure resistive load is 1, and the power factor of capacitive load is generally between 0.6 and 0.7.

B. Type of load

As mentioned above, different types of loads have different ratios of active power to reactive power, but the UPS needs to provide sufficient active power and reactive power to the load at the same time, so the actual output capacity is limited by the load type. For computer loads, the UPS can basically output the rated power. If the load is resistive or inductive, the output power of the UPS will decrease, and the UPS capacity needs to be increased. For example, a 1KVA UPS with a power factor of 0.7 can carry a full 1KVA with a computer load, but can only carry a maximum of 700VA with a pure resistive load (the active power is 700W at this time), and even less with an inductive load. Therefore, when calculating the load capacity, resistive and inductive loads that express power in W values ​​should be converted into VA values. The general calculation method is: VA value of resistive load = W value ÷ 0.7; VA value of inductive load = W value ÷ 0.3.

C. UPS capacity utilization

Since the computer room equipment has various nonlinear loads such as switching power supplies and various printer loads, these loads have large impact currents. If the power supply UPS capacity is too small, long-term overload operation will easily cause waveform distortion and overcurrent of the output final power device. In addition, the heat generated by overload will obviously be detrimental to system reliability. For high-power UPS, it is generally recommended to control the capacity utilization rate at 0.6~0.8.

Of course, the UPS capacity should not be too large. Although it is good for reliability to carry a very small load on the UPS, running it with too light a load will not only waste investment, but also cause the battery to discharge at a low current when the city power is off for a long time, which may cause deep discharge and damage.

D. Environmental conditions

The operating temperature of UPS should generally be controlled within the range of 0~40℃. If the temperature is too high and the ventilation conditions are poor, it will be unfavorable for heat dissipation and should be used at a reduced rating. In addition, the altitude also has an impact. When the altitude exceeds 1000m, the UPS should be used at a reduced rating of 5% for every 1000m increase in altitude.

E. UPS type and actual load capacity

Different types of UPS have different load capacities. The output capacity of the industrial frequency UPS is better, while the actual load capacity of the high frequency UPS is only 0.9 times that of the industrial frequency UPS.

Some other manufacturers' products may have actual load capacity lower than the nominal capacity. This is a product reliability issue, and users have to consider this factor when applying. Kehua has maintained a good reputation for many years. Its products have been strictly tested and quality-controlled, so users can rest assured. F. Potential expansion demand for equipment.

When configuring UPS capacity, you should consider the need for future equipment expansion and leave a certain margin so that you don't have to purchase UPS again when the load increases in the future. In addition, try to choose models with parallel function. If necessary, you can double the output capacity by paralleling UPS. At the same time, when configuring the input and output distribution cabinets of UPS, you should leave a certain margin for cables and circuit breakers to facilitate future expansion.

1.1.3 Considerations for Redundancy

What factors should be considered and what standards should be followed when considering capacity redundancy when selecting UPS.

1) Impact of impact load on UPS

For non-linear loads such as computers, the current waveform is a periodic non-sinusoidal wave, and the ratio of peak value to effective value (peak factor) can reach 2~2.5, which has a certain impact. Usually, the peak factor of UPS is 3:1, which is suitable for the peak factor requirements of non-linear loads such as computers in normal operation. However, when the load increases and the current waveform is irregularly superimposed, the current capacity of power supply equipment such as UPS is not enough to meet the instantaneous current requirements of the load, which will cause output waveform distortion. In this case, it is necessary to consider increasing the capacity of the power supply equipment to improve the current supply capacity.

In addition, computer loads will generate a surge current many times larger than usual when they are turned on, especially when multiple computers are turned on at the same time. This usually exceeds the UPS's peak factor tolerance. Therefore, when selecting UPS capacity, in addition to choosing a type with strong overload capacity, you also need to consider load fluctuations and surge margins, and appropriately increase the UPS capacity to withstand load fluctuations.

For some special loads (such as high-speed printers), a strong impact current will be generated during startup or operation, and the load capacity will increase several times (sometimes up to 6 times) instantly. For such loads, the margin should be further increased on the basis of the normal capacity margin ratio. Correct capacity redundancy has a great impact on the normal and stable operation of UPS and the working life of UPS. The chance of failure of a UPS system that often works under full load or overload is much higher than that of a UPS power supply with correct capacity redundancy.

2) The need for system expansion

If the UPS is initially selected without considering the margin, once the equipment is increased and exceeds the load capacity of the UPS, a new UPS must be purchased. This not only wastes the investment, but may also be limited by the site placement and bring many inconveniences in wiring and installation work.

Therefore, when choosing a UPS, you need to consider the possibility of capacity expansion within 2 to 3 years and appropriately increase the UPS power capacity. After all, the price of a UPS per KVA capacity decreases as the UPS capacity increases, and the cost of increasing capacity is much cheaper than buying a UPS of the same capacity alone. In addition, try to choose a model with a parallel function. If necessary, you can double the output capacity by paralleling the UPS. At the same time, when configuring the UPS input and output distribution cabinets, you should leave a certain margin for cables and circuit breakers to facilitate future expansion.