Harmonic and Eco modes
Harmonics are also a problem here. In traditional UPS and some UPS systems that adopt advanced Eco forms, the load is not affected by the harmonic content of the mains voltage, and vice versa, the mains is not affected by the harmonic content of the load current. When running in the standard Eco form, both of these barrier functions fail. Data centers, hospitals, and industrial sectors have long been criticized for their large motor-driven equipment, such as chillers, fans, and water pumps, which generate voltage harmonics on the mains input circuit that should not affect the load. Usually, harmonic problems are not severe for most current data centers, but if the Eco form is used, it should be carefully analyzed or appropriate avoidance measures should be taken.
Although today’s IT loads have lower harmonic currents at rated loads, they still contain an appropriate amount of harmonic currents when operating in an energy-efficient form. If not fully considered and addressed, these harmonic currents may affect the entire power system.
Using Eco mode requires extra caution and careful analysis
All the issues mentioned in this article can be addressed through technical means. However, it is difficult to ensure that they will not become negative factors in detailed individual applications, so all aspects of electrical design should be fully analyzed and considered. The reduction in power maintenance caused by the use of Eco forms may be tolerable, but this issue must not be ignored. Most applications require the deployment of a series of complex devices, and their interconnection may not be perfect, so it cannot be guaranteed that the system can operate reliably in the Eco form without power maintenance. A highly standardized and pre designed electrical architecture allows for pre consideration and testing of relevant issues, making it more suitable to adopt the form of EcO.
The impact on reliability
The UPS system operating in Eco mode requires the activation of the inverter and power supply, as well as circuit switching, upon detecting a power issue. The frequency of power supply circuit switching depends on various factors, including the sensitivity of APCUPS settings, the quality of the main power supply, and the power interference caused by other equipment within the facility. Regardless of whether the power supply or circuit switching occurs once a month or once an hour, the APCUPS inverter will withstand the current surge caused by sudden load changes, resulting in instantaneous heating of the inverter and impacting the internal system of the UPS. The industry generally believes that transient heat is a major cause of power electronic system failures.
Even worse, this transient heat happens to occur during the peak demand for UPS operation (when there are often no other backup power options available). Therefore, we have placed the time when UPS is most in demand during the period when the risk of failure is most concentrated.
When the UPS operates in normal online mode instead of Eco mode, there will be no thermal shock or transient heat when the mains input fails. If the UPS inverter experiences a sudden failure, it is almost certain that the main power supply will still exist at this time, so the UPS will switch to the bypass and the load will not lose power as a result. The lifespan of many electrical components is affected by operating temperature and long-term current stress. When UPS operates in Eco mode, its rectifiers, inverters, related capacitors, and other devices are actually bypassed and not primarily supplying power to the load. This lowers the operating temperature of the UPS, which in turn extends its lifespan and reduces the failure rate.
However, it is important to recognize that the UPS failure rate is not directly related to the loss of UPS functionality or critical load power outages. UPS inverter or rectifier faults generally do not cause direct power loss to the load, as these faults mainly occur when the main power supply is supplying power normally, and UPS will protect the load by switching to a bypass. Therefore, reducing component damage is an advantage of Eco mode, but it may not necessarily offset or balance the risks of sudden temperature increases and thermal cycling mentioned earlier.