Nine Power Problems Handled By Uninterruptible Power Supplies

#	Problem Category	Causes and Other Information	S	L	O
1	Power Failure - A Total Loss Of Utility Power	Caused by lightning strikes, downed power lines, grid over demands, natural disasters, accidents.	Y	Y	Y
2	Power Sags - Short Term Low Voltage	Triggered by the startup of large loads, utility switching, utility equipment failure, or power service that's too small for the demand. Power sags involve voltages 80 to 85 percent below normal for short periods of time (one or more cycles). Possible causes are heavy equipment being turned on, large electrical motors being started, and the switching of power mains (internal or utility). A power sag can have effects similar to those of a power surge.	Y	Y	Y
3	Power Surge - (Spike) Short Term High Voltage Above 110% of Nominal	Can be caused by a lightning strike and can send line voltages to levels in excess of 6000 volts. Can be triggered by a rapid reduction in power loads, heavy equipment being turned off, or by utility switching. The results can potentially damage hardware. High voltage spikes occur when there is a sudden, rapid voltage peak of up to 6,000 volts with a duration of 100mS to 1/2 cycle. These spikes are usually the result of nearby lightning strikes, but there can be other causes as well.	Y	Y	Y
4	Under-voltage - (Brownout) Reduced Line Voltage for Extended Periods of a Few Minutes to a Few Days	Can be caused by intentional utility voltage reduction to conserve power during peak demand periods, or other heavy loads that exceed supply capacity. A reduction in the mains voltage without a complete loss of power. A brownout is a steady lower voltage state. An example of a brownout happens during peak electrical demands in the summer, when utilities can't always meet the requirements and must lower the voltage to limit maximum power.	N	Y	Y
5	Over-voltage - Increased Line Voltage for Extended Periods of a Few Minutes to a Few Days	Over-voltage can be triggered by a rapid reduction in power loads, heavy equipment being turned off, or by utility switching. A power surge that takes place when the voltage is 110% above rated RMS voltage for one or more cycles. The most common cause is heavy electrical equipment being turned off.	N	Y	Y
6	Electrical Line Noise - High Frequency Waveform Caused by RFI or EMI Interference	Can be caused by either RFI or EMI interference generated by transmitters, welding devices, SCR driven printers, lightning etc. Random, sporadic, or multi-frequency electrical signals that become part of a transmission making the signal or information more difficult to identify. Electrical Line Noise is defined as Radio Frequency Interference (RFI) and Electromagnetic Interference (EMI) and causes undesirable effects in circuits of computer systems. Sources of the problem include electric motors, relays, motor control devices, broadcast transmissions, microwave radiation, and distant electrical storms.	N	N	Y
7	Frequency Variation - A Change in Frequency Stability	Resulting from generator or small co-generation sites being loaded and unloaded. A frequency variation involves a change in frequency of more than 3Hz from the normally stable utility frequency of 60Hz. This may be caused by erratic operation of emergency generators or unstable frequency power sources.	N	N	Y
8	Switching Transient - Instantaneous Under-voltage (Notch) in the Range of Nanoseconds	Normal duration is shorter than a spike and generally falls in the range of nanoseconds. Switching transients take place when there is a rapid voltage peak of up to 20,000 volts with a duration time of 10 to 100 microseconds. They are commonly caused by arcing faults and static discharge. In addition, major power system switching disturbances initiated by the utilities to correct line problems may happen several times a day.	N	N	Y
9	Harmonic Distortion - Distortion of the Normal Waveform generally Transmitted by Nonlinear Loads	Distortion of the normal line waveform, generally transmitted by non-linear loads. Switch-mode power supplies, variable-speed motors and drives, copiers and fax machines are examples of non-linear loads. The presence of harmonics that change the AC voltage waveform from a simple sinusoidal to complex waveform. Harmonic distortion can be generated by a load and fed back into the AC mains, causing power problems to other equipment on the circuit.