University of Connecticut Computer Center
	Electrical Disturbances

• DEFINITION OF TERMS -

  There are several different types of electrical disturbances. Below are the definitions of some of them.

• Blackout - A blackout is a complete loss of power. In some cases this includes any drop in voltage below 80V, since most equipment will not operate below 80V.
• Sag or Brownout - A sag or brownout is a decrease in voltage levels which is usually of short duration but can last from fractions of a second to hours.
• Spike - A spike is an instantaneous (usually no longer than one-millionth of a second) and tremendous increase in voltage levels.
• Surge - A surge is a short-term (usually 1/120 of a second) increase in voltage levels, usually of short duration (usually a fraction of a second).
• Electromagnetic Interference (EMI) and Radio Frequency Interference (RFI) - EMI and RFI, commonly referred to as "electrical noise" is a disruption in the smooth (sine wave) current expected from utility power.

• CAUSES OF ELECTRICAL DISTURBANCES -

  Below is a brief description of the causes of the various types of electrical disturbances.

• Blackout - Blackouts can be caused by excessive demand on the power grid, lightning storms, ice on power lines, equipment failure or any accident which brings down a power line.
• Sag or Brownout - Sags or brownouts can be caused by heavy equipment coming on line, short circuits, undersized electrical circuitry, or when the utility company deliberately decreases voltage levels in order to cope with peak load times (rolling brownouts). Brownouts generally occur during the summer heat waves.
• Spike - Spikes are generally caused by a nearby lightning strike, or if utility power lines are downed in a storm or as a result of an accident.
• Surge - A surge is usually caused when high-powered appliances in the area are turned off. They can also be caused by short circuits or undersized electrical circuits.
• Noise - EMI and RFI noise can be caused by lightning, load switching, generators, transmitters, transformers and industrial equipment.

• EFFECTS ON COMPUTER EQUIPMENT -

  Below is a brief explanation of the ways that power disturbances affect computer equipment.

• Blackout - Blackouts may cause loss of current work in RAM or cache, possible loss of the hard drive File Allocation Table (FAT) resulting in total loss of data stored on drive (which may or may not be recoverable).
• Sag or Brownout - A loss of optimal voltage could cause frozen keyboards, dim or bright lights, shrinking display screens and unexpected system crashes resulting in the loss or corruption of data. Sags or brownouts also reduce the efficiency and life span of electrical equipment, particularly motors. According to Glenn Cross of the Willimantic office of Connecticut Light and Power, planned brownouts by the company are usually preceded by plenty of warning and result in a 5% voltage reduction on the entire system. Assuming that you were receiving normal voltage prior to this reduction, a voltage drop of 5% should not cause any problems.
• Spike - A spike can cause catastrophic damage to hardware (e.g., burn out your PC circuit boards), as well as loss of data and processing errors.
• Surge - Surges can stress delicate components and over time could wear out components. In addition, surges can contribute to data errors, dim or bright lights, and shrinking display screens.
• Noise - Electrical noise can introduce glitches and errors into executable programs and data files, but it is not harmful to the equipment.

• HOW TO PROTECT AGAINST ELECTRICAL DISTURBANCES -

  Below are some devices that can help protect against electrical disturbances. In all cases, it is also necessary to protect your data and programs by backing them up frequently to external backup devices.

• Blackout - a UPS (uninterruptible power supply) continues to provide power (battery) when there is a loss of electrical power. While a UPS provides power for a limited duration, that time can be extended by combining a UPS with a generator.
• Sag or Brownout - A regulating UPS continues to provide the required voltage even when there is a drop in voltage. For extended usage, one could combine a generator with a UPS. Unstable voltage can also be protected by use of a voltage regulator, which is now built in to most power supplies.
• Spike - A surge suppressor/diverter is used to protect equipment from transient over-voltages present on AC power, data or telephone circuits.
• Surge - A surge suppressor/diverter is used to protect equipment from transient over-voltages present on AC power, data or telephone circuits.
• Noise - In many cases a UPS can smooth out noisy power sources. Another solution is the use of a communication line surge suppressor.

• MORE INFORMATION ON UPS AND SURGE SUPPRESSORS

Surge Suppressors

Surge suppressors guard against spikes and surges that come through the AC outlets by absorbing excess electricity and diverting it to the ground line, away from your computer and peripherals. There are two types of surge suppressors: the floor model (which resembles the conventional power strip) and the console model (which sits under your monitor).

One should be careful in the use of surge suppressors. It has been found that spot placement of surge suppressors can actually increase the incidence of electrical problems. If the equipment is not properly grounded when a surge suppressor shunts a surge to ground, it elevates the ground potential. The differences in ground voltages can cause electrical currents to flow in the ground circuit, which can damage non-protected devices. Therefore, if one device on a circuit is protected by a surge suppressor, they all should be protected.

UPS (Uninterruptible Power Supply)

UPS's are used to protect against decreases in voltage (either blackouts or brownouts/sags). A UPS switches your system over to battery power when it senses certain electrical problems. A UPS usually provides about 5 - 15 minutes of battery power. This usually provides you with enough time to save your files and perform a controlled system shutdown. In general, a UPS is capable of performing the following functions: absorb relatively small power surges, smooth out noisy power sources, continue to provide power during power sags/brownouts, provide power for some time during blackouts. Additionally, some UPS or UPS/software combinations can perform additional functions including the monitoring and logging of the status of the power supply.

In general, there are three different types of UPS devices.

1. Standby power supply (SPS) - In this type of device, power is usually derived directly from the power line until power fails, at which time a battery powered inverter turns on to continue supplying power. The time it takes for the inverter to come 'on line' varies by unit. The battery is charged when line power is available. Generally, a standby power supply does not compensate for voltages withing the 103-132 VAC input window, and therefore are not useful in dealing with minor fluctuations in voltage.
2. Hybrid UPS systems - In this type of device, when normal operating line power is present, the supply conditions power using a ferroresonant transformer. This transformer maintains a constant output voltage even with a varying input voltage and provides good protection against line noise. The transformer also maintains output on its secondary briefly when a total outage occurs.
3. True UPS system - In this type of device, power is supplied continuously from an inverter. There is no switchover time, and they provide the best isolation from power line problems.

• COPING WITH ELECTRICAL DISTURBANCES AT THE UNIVERSITY OF CONNECTICUT

• Computer Center - The UPS system at the University of Connecticut Computer Center has battery backup only, and is intended to give the Computer Center time to come down in a scheduled manner in the event of power fluxes, failures or reduction in power flow. The UPS system is not designed to keep the Center running for long periods after a power interruption; it is intended for short-term outages of 10-15 minutes. In the event of reduction or loss of street power, the UPS batteries would kick in to cover the loss of power. Computer Operations would then call Facilities Management to determine the anticipated time frame for power reduction or loss. If the outage or reduction is expected to last more than 10 minutes, Computer Operations would then begin the shutdown procedures and power off the computing equipment. Once the systems and attached devices have been turned off, Computer Operations would then trip the battery circuits to stop the drain on the batteries and preserve their integrity.
  
  
• Individual Departments and Offices - The best way to determine what preventative measures you should take is to first assess your own situation and to balance your critical needs with the cost involved. In addition to computer equipment you may wish to assess non-computer equipment, as well. With respect to computers, it is wise to get in the habit of doing frequent backups of your programs and data to an external device to minimize the negative effects of electrical disturbances.
  • How critical is it for you to continue to work if the power were down? If you cannot survive even a short-term outage (less than 4 hours) resulting in a manageable loss in production with reasonable backup procedures in place, then a backup generator would be required, as well as a UPS, since it would take some minutes for the generator to kick on.
  • How critical are the programs and data stored on your hard drive? If restoring your programs and data to the most recent backups made would still impose a hardship, then you should invest in a UPS which would provide you with enough uninterrupted power to permit you to back up your critical applications and data. If more time is required then a backup generator would also be necessary.
  • Could you cope with the effects of nuisance interruptions (noise, spikes, surges), which generally do not last very long but which could still cause damage? Depending on your analysis, you may wish to invest in a UPS and/or surge suppressor.