The heat dissipation design of high-power power frequency online UPS (hereinafter referred to as "power frequency UPS") is closely related to its structural characteristics (such as including power frequency transformers, low operating frequencies of power devices, etc.), especially in the high-power range (usually 100kVA and above), which directly affects the stable operation and service life of the equipment. The following provides a detailed explanation of the characteristics of the cooling system:
1、 Heat dissipation design and characteristics of high-power power frequency online UPS
The heat dissipation requirements of power frequency UPS stem from the heating characteristics of its core components - compared with high-frequency UPS, it contains power frequency transformers (input/output transformers) and power devices with lower operating frequencies (usually 50/60Hz), resulting in significant differences in the distribution of heat sources and heat dissipation pressure.
1. Main heat source: "Transformer+Power Device" dual core
The heating of high-power power frequency UPS mainly comes from two modules, and the heat distribution is relatively concentrated:
Power frequency transformer: This is the most prominent heat source of power frequency UPS. High power frequency transformers in the high-power range (such as 200kVA and above) generate large and continuous heat due to iron core losses (eddy current, hysteresis losses) and winding copper losses (resistance losses caused by current passing through the winding). Under full load, transformer losses usually account for 30% -50% of the total UPS losses, and the temperature can rise to 80-100 ℃ (depending on the insulation level, such as F-class insulation allowing a maximum temperature of 155 ℃ and H-class 180 ℃).
Power conversion devices: including rectifier bridges (such as thyristors, IGBTs), inverter IGBTs, etc. Due to the power devices of power frequency UPS operating at power frequency (50/60Hz), with low switching frequency (much lower than the kHz level of high-frequency UPS), low switching loss, but high conduction loss (due to high current at high power), the heating of rectifier and inverter modules is mainly "continuous stable heating" rather than the "pulse type switching heating" of high-frequency UPS.
2. Heat dissipation design: optimization for "large area, continuous heating"
The heat dissipation design of high-power power frequency UPS needs to match its heating characteristics, with the core being "efficient export of continuous heat". Common solutions are upgraded with the power range:
Medium and small power range (100-300kVA): forced air cooling is the main method
Adopting a "multi fan+optimized air duct" design: fans are usually configured redundantly (such as N+1) to avoid heat dissipation failure caused by a single fan failure; The air duct needs to cover the core heating areas such as transformers and power modules - for example, cold air is sucked in from the bottom/side of the equipment, filtered through a filter, first flows through the transformer (which needs to be guided by an air guide plate to cover the iron core and winding), then flows through the radiator of the rectifier/inverter module (aluminum fins to increase the heat dissipation area), and finally discharged from the top.
Some products will provide targeted heat dissipation for transformers, such as installing heat sinks on the transformer casing or setting up independent air ducts around it to avoid heat accumulation.
High power range (above 300kVA): air-cooled+auxiliary heat dissipation, or liquid cooled
When the power exceeds 300kVA, simple air cooling is difficult to meet the heat dissipation requirements, and an upgraded solution is needed:
Enhanced air cooling: using high-pressure centrifugal fans (instead of axial fans) to enhance airflow penetration; At the same time, heat pipes are installed on the heat sink of the power device (utilizing phase change rapid heat transfer) to efficiently dissipate the surface heat of the device to the air duct.
Liquid cooling assistance: Some industrial grade power frequency UPS systems (such as those used in new energy and heavy industry scenarios) adopt a hybrid cooling system of "air cooling+liquid cooling" - for example, for the inverter IGBT module with the most concentrated heat generation, a water-cooled plate is used for contact cooling (the cooling liquid circulates to remove heat), while the transformer still retains air cooling, balancing heat dissipation efficiency and cost.
3. Key factors affecting heat dissipation efficiency
The heat dissipation effect of high-power power frequency UPS is easily affected by external environment and its own state, and special attention should be paid to:
Environmental temperature: For every 10 ℃ increase in environmental temperature, the resistance of the transformer winding increases by about 4%, copper loss increases, and the heat resistance margin of the insulation material decreases. If the environmental temperature exceeds the design upper limit (such as 40 ℃), it is necessary to reduce the capacity (usually by 10% for every 5 ℃ increase), otherwise overheating protection may be triggered.
Smoothness of heat dissipation channels: The fan of high-power UPS has a large air volume. If there is a lot of dust in the environment, the filter mesh may become clogged (especially in industrial scenarios), resulting in a decrease in air intake; In addition, insufficient reserved space around the device (such as being too close to the wall or accumulating debris at the top) can hinder ventilation, and it is necessary to strictly follow the manual to reserve a heat dissipation distance (usually ≥ 0.5m in front, back, left, right, and top, ≥ 1m).
Load rate: Power frequency UPS has the highest efficiency and the best matching between heating and cooling under 50% -80% load; If the transformer and power components experience a sudden increase in heat generation due to long-term full load or overload (such as transformer losses being 2-3 times higher at full load than at light load), it is necessary to rely on the cooling system to operate at full power. At this time, the maintenance frequency of the fan and filter needs to be increased (such as cleaning the filter every month).
summarize
The heat dissipation design of high-power power frequency online UPS focuses on "dealing with the continuous heating of transformers and power devices", and achieves efficient heat dissipation through a "graded heat dissipation scheme" (air cooling/liquid cooling) and "air duct optimization". However, its heat dissipation efficiency is greatly affected by factors such as environmental temperature and dust; Environmental adaptability relies on "industrial grade component selection" (such as high temperature resistant transformers, three proof treatment) and "structural reinforcement design", which performs more stably in scenarios with wide temperature, high humidity, high dust, and vibration. Therefore, it is more suitable for industrial production, energy and other scenarios that require strict equipment reliability.
