A UPS provides battery backup power to plugged-in equipment when the flow of utility electricity drops to an unsafe level or a complete outage occurs. UPS systems are available with different topologies.
Depending on topology, UPSs offer varying degrees of protection against common power anomalies including voltage sags and surges.
Line-interactive
When power fluctuates, this UPS type corrects it using its internal voltage regulator and then passes that regulated power to connected equipment. Because of the slight delay (around 4 milliseconds) when switching from utility to battery power, it’s ideal for areas where voltage fluctuations occur frequently.
Line interactive UPS systems offer a good balance between reasonable protection and moderate operating costs. They have a variable autotransformer that can adjust to normal and abnormal voltages, so they can tolerate high and low voltage brownouts and surges without dipping into reserve battery power.
They’re also more cost-effective than online UPS systems because they don’t condition power through the double conversion process. But because they rely on the battery to correct a voltage issue, they tend to drain their batteries more often than offline models. For that reason, this UPS technology is better for small to medium sized SMEs. It’s also the best UPS option for those looking to avoid a lengthy power outage or a full shutdown of equipment.
Standby
A standby UPS switches to battery power as soon as it detects a loss of utility input, so it offers the shortest protection time and is mainly used for non-critical home network and office equipment. This topology does not buffer equipment against common power anomalies like voltage surges/spikes and sags, so it is less effective than a line-interactive UPS in areas where such events are frequent.
It is also worth noting that this type of UPS frequently switches to battery power, which drains reserve battery capacity and reduces runtime. Additionally, it produces heat and there is a limit to how long the batteries can operate before they require replacement.
Whether protecting a network closet, server rack or data center, UPS systems can help organizations avoid the financial costs, customer frustration and business disruption that come with utility power outages. Understanding the different types of UPS systems and their capacities can help buyers make the right choice for their business needs.
Online
Online UPS systems deliver high-quality power that is not interrupted by AC power fluctuations. These systems utilize double-conversion inversion, which cleans any current that enters the system and ensures only the highest quality of DC power exits it. This helps protect equipment from AC power problems like voltage sags and spikes, over-voltage, frequency noise, harmonic distortion, and outages.
Incoming AC power enters the UPS and is immediately converted to DC power to be charged in its battery. When the power fails, this DC flows to the load through an inverter without any interruption, allowing equipment to continue operating as usual.
The online UPS topology is best for environments where critical IT equipment needs to remain up and running, or for sensitive applications that require a consistent power supply. These UPS systems can also be configured with a variety of additional features including management, monitoring, and redundancy options. These options help make the online UPS the most versatile and sophisticated uninterruptible power system available.
Bypass
A bypass switch is an essential equipment when used in conjunction with UPS systems and can be very useful in the event of maintenance or repair. It allows the UPS to be safely isolated and the power to the critical load maintained allowing engineers access to the system without disrupting the critical load.
Static bypass switches are fitted to most online UPS systems and provide a failsafe for the inverter, if it should fail the system will drop onto the mains input feed which ensures continuous power is supplied to the critical load. However operating on bypass does not filter or condition the power supply so should be used sparingly as it will expose the load to utility spikes, sags and brownouts.
External wrap around maintenance bypass systems can be rotary switches or circuit breakers and allow the UPS to be isolated for much more rigorous servicing & maintenance and complete replacement – again without disruption to the critical load.
