Solution configuration for data center UPS power supply

Solution configuration for data center UPS power supply

When professionals consider the capacity of UPS power supply during the selection process for data center UPS power supply, they first determine the size of the UPS power supply capacity. Then, they consider various factors such as the type of load, load capacity utilization, environmental conditions, type of uninterruptible power supply (UPS), actual load capacity, and potential expansion requirements for specific problem analysis.

The actual load capacity is the fundamental factor that determines the size of the UPS power supply capacity. The output capacity of the UPS power supply must meet or exceed the load requirements to ensure normal power supply. In practical applications, it is necessary to consider whether the UPS power supply uses centralized power supply or distributed power supply. For centralized power supply loads, the total load should be the cumulative power of all loads powered by the UPS power supply in the data center. For distributed power supply, the load capacity is determined based on the load carried by each UPS power supply.

The load capacity of electrical equipment is usually referred to as apparent power, denoted as S, with the unit VA. Apparent power includes active power P (unit W) and reactive power Q (unit Var), and the relationship between their magnitudes is S2 = P2 + Q2. Here, the ratio of active power to apparent power is called power factor. The power factor of purely resistive load is 1, and the power factor of capacitive load is generally between 0.6 and 0.7.

As mentioned above, different types of loads have different proportions of active power and reactive power. However, the UPS power supply needs to provide sufficient active power and reactive power to the load at the same time. Therefore, the actual output capacity is limited by the load type. For computer loads, UPS power supplies can basically output the rated power. If the load is inductive or capacitive, the output power of the UPS power supply decreases, and it requires a larger UPS power supply capacity. For example, a 1 KVA UPS with a power factor of 0.7 can fully load 1 KVA with computer load, but it can only carry a maximum of 700 VA (where the active power is 700 W) with purely resistive load, and even lower with inductive load. Therefore, when calculating the load capacity, for resistive and inductive loads represented in watts (W), their VA values should be calculated as follows: VA value for resistive load = W value + 0.7; VA value for inductive load = W value + 0.3.

I. UPS power supply capacity utilization rate

Due to the various nonlinear loads of computer room equipment, such as switching power supplies and various types of printer loads, these loads have large current surges. If the capacity of the supplied UPS power supply is too small and it operates under long-term overload conditions, waveform distortion may occur, and it may cause overcurrent in the output stage power devices. In addition, the heat generated by overload significantly affects the system reliability. For high-power UPS, it is generally recommended to control the capacity utilization rate between 0.6 and 0.8.

Of course, the UPS power supply capacity should not be excessively large either. Although having a very small load on the UPS power supply is beneficial for reliability, running under excessively light load not only wastes investment but also, during long power outages, the batteries discharge at a low current, which can lead to deep discharge and damage.

II. UPS power supply environmental conditions

The operating temperature of the UPS power supply should generally be controlled within the range of 0 to 40°C. If the temperature is too high or the ventilation conditions are poor, it is not conducive to heat dissipation and the capacity should

 be derated. In addition, altitude also has an impact. After exceeding 1000 meters above sea level, the UPS power supply should be derated by 5% for every 1000 meters of elevation.

III. Types of UPS power supply and actual load capacity

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

In addition, some manufacturers' products may have actual load capacities lower than the nominal capacity. This is a reliability issue with the product, and users have to consider this factor when applying it. Kehua, as a company, has maintained a good reputation over the years. Its products have undergone rigorous testing and quality control, so users can rest assured. When configuring the UPS power supply, the capacity should take into account potential expansion requirements for the equipment. Sufficient margin should be reserved so that if the load increases in the future, there is no need to purchase UPS power supplies again.

It is advisable to choose models with parallel operation capabilities, and if necessary, the output capacity can be multiplied by parallel operation of UPS power supplies. Also, when configuring the input and output distribution cabinets for the UPS power supply, cables and circuit breakers should have some spare capacity to facilitate future expansion.

IV. Impact of transient loads on UPS power supply

For nonlinear loads such as computers, the current waveform is periodic and non-sinusoidal, and the peak-to-effective value ratio (crest factor) can reach 2 to 2.5, indicating a certain level of transience. Usually, the crest factor of UPS power supplies is 3:1, which is suitable for the crest factor requirements of non-linear loads such as computers during normal operation. However, when the load increases and the current waveform becomes irregular, the current capacity of the UPS power supply and other power supply equipment may not be sufficient to meet the instantaneous current requirements of the load, resulting in output waveform distortion. In this case, it is necessary to consider increasing the capacity of the power supply equipment to improve its current supply capability.

In addition, computer loads generate a significantly higher surge current during startup, especially when multiple computers are turned on simultaneously. This often exceeds the peak factor tolerance of the UPS power supply. Therefore, when selecting the capacity of the UPS power supply, in addition to choosing a type with strong overload capacity, load fluctuations and additional margin should be considered, and the UPS power supply capacity should be appropriately increased to withstand load fluctuations.

For certain special loads, such as high-speed line printers, they can generate strong surge currents during startup or operation, causing the load capacity to increase several times (sometimes up to 6 times). For such loads, additional margin should be added based on the normal capacity margin ratio. Proper capacity redundancy has a significant impact on the normal and stable operation of the UPS power supply and the working lifespan of the UPS power supply. UPS power supply systems that frequently operate at full load or overload are much more prone to failures than UPS power supplies with correct capacity redundancy.

V. Need for system expansion

If the initial selection of UPS power supply did not consider the margin, and as equipment increases, it exceeds the load capacity of the UPS power supply, a new UPS power supply must be purchased, which not only wastes investment but may also be restricted by site layout and bring inconvenience to wiring and installation work.

Therefore, when selecting a UPS power supply, it is necessary to consider the possibility of expansion within 2 to 3 years and appropriately increase the power capacity of the UPS power supply. The price of UPS power supplies per unit KVA capacity decreases as the UPS power supply capacity increases, and

 the cost of adding capacity is much lower than purchasing a UPS power supply with the same capacity separately. Additionally, it is advisable to choose models with parallel operation capabilities, and if necessary, the output capacity can be multiplied by parallel operation of UPS power supplies. Also, when configuring the input and output distribution cabinets for the UPS power supply, cables and circuit breakers should have some spare capacity to facilitate future expansion.

By considering the factors and following the standards mentioned in the professional introduction above, you should have a clear understanding of the selection factors and standards for UPS power supply configuration in computer data centers.