| Uninterruptible
Power Supply - Q&A |
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1.Power Quality Problems |
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The following is an overview of the typical power quality problems encountered. Give special attention to the unit type vs. the problems addressed for each type of power problem.
| Power uality Problem | Description | Effect | Will the Cell Power or UPS Solve? | | Temporary Interruption | Planned or accidental total loss of utility power in a
localized area of the community. Seconds to minutes. | Equipment shutdown, loss of work and data, file and hard disk and operating system (OS) corruption, loss of fiber optic, T1 and ISDN connections. | Off-line - Yes
Line-interactive - Yes
On-line - Yes | | Long-Term Interruption | Planned or accidental total loss of utility power in a localized area of the community. Minutes to hours. | Equipment shutdown, loss of work and data, file and hard disk and OS corruption, loss of fiber optic, T1 and ISDN connections. | Off-line - No
Line-interactive – 95%
No On-line - Yes | | Momentary Interruption | Very short planned or accidental power loss. Milliseconds to seconds. | Computer hangs, computer and network equipment
reboots or hangs, loss of work and data, file and hard
disk and OS corruption. | Off-line - Maybe
Line-interactive - Maybe
On-line - Yes | | Sag or Under-Voltage | A decrease in utility voltage Sags -- Milliseconds to a few seconds Under-voltage -- Longer
than a few seconds | Shrinking display screens, equipment hang or reset, equipment power supply damage, Computer hangs,
computer and network equipment reboots or hangs, loss of work and data, file and hard disk and OS corruption. | Off-line - No
Line-interactive - Yes
On-line - Yes | | Swell or Over-Voltage | An increase in Utility voltage Swell -- Milliseconds to a few seconds
Over-voltage -- Longer than a few seconds | Permanent equipment damage, Computer hangs, computer and network equipment reboots or hangs, loss of work and data, file and hard disk and OS corruption. | Off-line - No
Line-interactive - Yes
On-line - Yes | | Transient, Impulse or Spike | A sudden change in voltage up to several hundred to
thousands of volts.
Microseconds. | Network Errors, Burned or damaged equipment and
circuitry, Computer hangs, computer and network
equipment reboots or hangs, loss of work and data, file and hard disk and OS corruption. | Off-line - Yes
Line-interactive - Yes
On-line – Yes, Higher level of protection. | | Notch | A disturbance of opposite polarity from the waveform.
Microseconds. | Slow LAN due to excessive errors, audible noise in
telephone and audio equipment. | Off-line - No
Line-interactive - No
On-line - Yes | | Noise | An unwanted electrical signal of high frequency from other equipment Sporadic. | Slow LA N due to excessive errors, audible noise in
telephone and audio equipment. Equipment hangs. | Off-line - No
Line-interactive - No
On-line - Yes | | Harmonic Distortion | An alteration of the pure sinewave (sinewave distortion), due to nonlinear loads such as computer
switching power supplies. | Causes motors, transformers and wiring to overheat, lowers operating efficiency of office equipment, | Off-line - No
Line-interactive - No
On-line - Yes |
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2.How to Choose an Uninterruptible Power Supply (UPS ) |
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An uninterruptible power supply or (UPS) is the best way to protect your computer hardware and documents from power fluctuations. It also lets you continue to work during brief power failures. You can sometimes find wattage and volt-amperage of your computer equipment in the manual or on a sticker on the chassis .Whether you need EMI and FRI protection depends on the quality of your electricity and the amount of other electronic equipment in the vicinity of your computer.
Mains power is continually plagued by surges, sags, spikes, transients, EMI, RFI and even complete failure, all of which affect sensitive electronic equipment. The key benefits to having UPS protection and support are: Avoiding costly hardware damage-Avoiding date corruption and loss Avoiding costly and inconvenient down time Enabling remote monitoring and control of power requirements Enabling unattended orderly shutdown in the event of mains failure .
There are basically three types of UPSs: Standby, Line-interactive, and On-Line.
Standby : sometimes called off-line with this type if power supply, power comes directly from the A/C outlet until the voltage sages or the power fails .After the power sags or fails, a battery powered inverter almost immediately turns on the continue to supply you with power Batteries are charged , as necessary , when direct A/C power is available .Even while power is coming directly from A/C outlet, the UPS provides protection from voltage spikes and surges .Standby units are the low coat solutions in the UPS family .
Line-interactive: Just like the standby units, line-interactive UPSs provide protection form spikes and surges, as well as supplying auxiliary power if voltage sag or a blackout occurs. Unlike the standby units, line-interactive UPSs provide automatic voltage boost when the power dips, without accessing the batteries .This feature provides continuous lined conditioning, promotes longer battery life, and eliminates electronic noise that can cause minor application errors and loss of date.
On-line: On-line UPSs provide the highest quality of power protection by using a double-conversion technique. The UPS takes the incoming A/C power and recreates it by converting the voltage to D/C, then conditioning the power to eliminate noise , sags ,or surges , and finally , converting it back to A/C before it exists the UPS.
Since the power runs continuously through the inverter, there is no transfer or switching time to battery mode in event of a blackout.
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3.How do I select the right UPS for my equipment |
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1. if you have a limited budget , choose a standby ( also called off-line) UPS that switches to battery power when power goes out . And choose an on-line UPS if you need unlimited backup power.
2. Select a line-interactive UPS if your needs fall between the two other types. Determine the total power needs ( in watts and volt-amperes ) of equipment you will connect to the UPS. Choose a UPS that equals or exceeds the total power requirements of the equipment that you will connect to it.
3. Compare the following five specifications for different models: maximum surge current, surge suppression, suppression response time. Battery recharge time, and number of AC outlets.
4. Find out if the unit under consideration has a replaceable battery , and if the battery is user-replaceable .And compare battery operating times ( how long the UPS will keep equipment running after power failure).
5. Look for a unit with modem surge protection and electromagnetic interference (EMI) and radio-frequency interference (RFI) noise reduction if you need those features.
6. Check for alarms or LEDs that indicate wiring problem, whether the equipment is running on UPS battery , and whether the battery is low.
7. if you are buying a more expensive unit, get one with software that automatically saves documents, closes applications , and turns off equipment when power goes out.
8. Compare warranties.
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