Understanding UPS Systems: The Basics

1) All UPS systems are not created equal.

To understand UPS systems, it’s important to first familiarize yourself with the different types of UPS units and how they work.

Standby UPS

A standby UPS is a reactive type of UPS. This UPS typically consists of a battery to provide a short-term source of electrical power, a rectifier or charger to maintain a battery voltage,, and a static switch to transfer load automatically between utility and the inverter with minimal disturbance.

This system may also have input and output isolation transformers, as well as filters, to provide the appropriate isolation and disturbance attenuation. Standby UPS systems also contain control circuits, sensors, and monitors. While generally reliable, this design of UPS passes utility power to your critical loads until there is a power disturbance, and then must rely on a switching device to transfer your equipment loads to battery to stay online and protected.

Line-Interactive UPS

This type of UPS monitors incoming voltage from the utility and provides automatic voltage regulation when low or high voltage conditions occur.

A line-interactive UPS preserves battery life, as it may not need to constantly switch to battery mode in places prone to brownouts on the grid. Line-interactive units also protect from power spikes and surges. Further, these units provide Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI) filtering.

This UPS is ideal for applications where you are not protecting mission-critical equipment, and the utility power is relatively clean and is typically inexpensive, suitable for a smaller office, for example.

Double-Conversion UPS

This type of UPS differs from a standby or line interactive UPS in several ways.

First, the primary power path in a double-conversion UPS system is the inverter instead of the AC utility mains. In this UPS, the input AC’s failure does not cause the transfer switch’s activation because the input AC is the backup source.

A double-conversion UPS system works by converting power from AC to DC and back to AC. This protects your facility at the highest level by isolating your equipment from raw utility power.

Since the unit is always online, this system provides power with zero transfer time to your equipment, making it ideal for facilities with mission-critical equipment or locations with poor or unreliable power conditions.

Double conversion UPS systems also have an internal static bypass. Because of this feature, if your UPS has a major failure, you can keep your critical loads online during a repair or replacement.

2) UPS total lifecycle costs vary based on systems and usage.

A number of factors can affect UPS total cost of ownership:

• Energy inefficiency is one of the most considerable controllable costs for UPS. A new UPS system can vary in efficiency from 85% to 98% in true, online mode. However, UPS systems—particularly when underutilized—can be enormous energy hogs, with as low as 40-50% efficiency in some legacy systems. At QPS, we can help you estimate your total cost of ownership, including the cost of wasted energy over the life of your system.
• Dust, debris, and moisture will sap overall efficiency. Electrical disruptions can also cause issues if not properly assessed.
• Irregular maintenance or poorly designed systems will also impact your UPS performance. Neglecting scheduled preventative maintenance will shorten your UPS lifecycle significantly while further inflating costs from the resultant frequent part replacements. Poorly designed systems bear the same results.
• Some systems may come standard with a three-year warranty rather than a one-year. Extending your initial warranty can lower your overall cost of ownership.

3) Your UPS is protecting more than just against power loss.

Your UPS also conditions your power and protects your equipment.

Why is power conditioning important? Because power anomalies from the utility can diminish performance. Power conditioning acts as a buffer to interference and smooths out potential power fluctuations before passing it to your location. Only a true online, double-conversion UPS will protect against all nine power anomalies.

The Nine common Power Problems Protected by Power Conditioning:

1. Power failure: Total loss of utility power.
2. Power sag: Short-term, low-voltage issues. This is similar to a person being sleepy after lunchtime.
3. Power surge or spike: Short-term high voltage beyond 110% of normal output. This is comparable to a person experiencing a caffeine high.
4. Undervoltage or brownout conditions: Reduced line voltage for an extended period, from a few minutes to a few days. This commonly happens during summer months as air conditioners can strain the power grid.
5. Overvoltage: Increased line voltage for an extended period, from a few minutes to a few days.
6. Electrical line noise: A high power frequency wave caused by RFI or EMI.
7. Frequency variation: A loss of stability in the power supply’s normal frequency of 50 to 60 Hz.
8. Switching transient: Instant undervoltage in the range of nanoseconds.
9. Harmonic distortion: Distortion of a normal power wave, typically transmitted by unequal loads.

4) UPS systems require regular maintenance.

To understand UPS systems, it’s important to first familiarize yourself with the different types of UPS units and how they work.

Pay attention to both the lifecycle of your equipment AND its parts. Each design’s lifecycle and its recommended maintenance frequency are as follows:

Static UPS Systems

The average lifespan for three-phase UPS systems is roughly 15 years. Many systems require semi-annual or annual maintenance. Replacement of UPS parts may also be affected by load on the system and its reliability.

There usually are three regular battery replacements in a static UPS system, done in year four, then in year eight, and again in year 12.

Note that battery replacements for the VRLA batteries included in these systems have their lifespans, further adding to the total maintenance cost.

Flywheel UPS System

The lifecycle for a flywheel UPS system is approximately 15 years, similar to that of a traditional UPS. Maintenance for this type of system is similar to that of a traditional battery UPS, with the exception of battery maintenance. While a flywheel eliminates the need for battery maintenance, it does have maintenance requirements of its own. Including inspections, oil pump replacement, filters and bearing replacements.

The bearings on a flywheel UPS system may also need to be replaced every five to eight years. This type of replacement requires specialized equipment and a prolonged downtime for the replacement, which can significantly add to expenses.