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Electrical Phases
When exploring Standby Power and UPS System Specifications, it is important to establish whether it is intended for a single-phase or three-phase electrical supply. In Part 3 - UPS System Specifications we are here to guide you through the UPS specifications.
Small UPS systems usually feature a single-phase input and output, while larger systems are equipped with three-phase input and output. In the mid-range, UPS systems typically have three-phase input and single-phase output.
Cooling Systems
When considering UPS system specifications, not all critical loads require protection by a UPS. Only systems that cannot tolerate brief power outages, such as servers, must be safeguarded by a UPS to prevent significant damage and issues. On the other hand, other critical systems that can handle a short power interruption, such as server room cooling systems, can and should be protected by a generator. Server room cooling systems are considered critical loads as a failure of the cooling system can cause a thermal shutdown of the servers, protecting them from overheating.
Power Conditioning
The primary role of an online UPS is to regulate fluctuations in the main power supply, which typically occur for brief periods of time. In the event of a complete power failure, the UPS system will rely on its battery to maintain a steady flow of power and, when paired with a generator, will provide seamless power until the generator takes over.
UPS System Specifications An online UPS will provide an uninterrupted electrical supply in case of main power failure and a seamless transition back to main power once the problem has resolved. Additionally, it features an automatic bypass to main power in the event of an overload or fault condition.
On-Line / Double Conversion Technology
One of the types of UPS systems is known as the On-line/Double Conversion Technology, which offers the highest level of power protection.
The UPS converts the incoming AC power from the main to DC power. The DC current powers the battery and the inverter, which then converts the DC back to AC and provides a regulated, clean, and conditioned AC output to the protected load.
The battery is always active, meaning that in the case of a main power failure, the battery continues to supply power to the inverter, providing an uninterrupted supply to the protected load without any switching. The UPS also includes a static bypass circuit, which serves as a failsafe mechanism by supplying AC main power to the load in the event of an overload or internal fault.
Online UPS systems are typically recommended for use with generators due to their tolerance to voltage and frequency variations that can be present with generators. Additionally, battery pack extensions can be used to extend runtime.
Offline / Standby Technology
An offline or standby UPS provides basic protection against problems with the main power supply. The AC main power passes directly through the UPS, which includes RFI filtering and limited spike protection.
In the event of a main power failure or if the AC main voltage falls outside the UPS operating range, the inverter starts up, closes a relay, and provides power to the load. When the AC main power returns, the main output is switched back to the main power, and the inverter shuts down. There is a brief interruption during the transfer to and from the inverter. The output when the inverter is in use is usually a square wave or stepped sine wave.
Offline units typically have power ratings ranging from 250VA to 2kVA and have limited communication capabilities. Although they are relatively cheap, they are typically recommended only for a single PC or workstation and home office applications.
Line-Interactive Technology
A line-interactive UPS provides more protection than an offline UPS, but it still does not provide complete protection against problems with the main power supply, unlike an on-line double conversion UPS system.
These UPSs operate similarly to an offline UPS, but they offer better spike protection. They also have a wider tolerance to voltage fluctuations thanks to a voltage-trimming transformer or similar device. This adjusts the incoming AC main voltage when it is too high or too low, preventing the UPS from switching to battery power unnecessarily and draining the batteries. In the event of a main power failure or if the incoming main voltage falls outside the operating limits, the inverter starts up and provides power as described in an offline system. The output waveform of a line-interactive UPS is usually a sine wave.
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