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Voltage Sags:

What Are They?

How Do They Affect Business?

Voltage Sags

Definition(ANSI std. 1100-1992) A RMS reduction inthe AC Voltage, at the power frequency, forduration from a half a cycle to a few seconds.

1. Voltage can drop below normal level

for several cycles and can affect thecritical load to cause shutdown.

2. With electronically controlledequipment, voltage under 20% below

normal will result in shutdown.

Well, now you know what a voltage sag is, butwhat causes them?

Commonly they are caused by a fault in thepower distribution system. Lightning strikes,tree or animal contact with power lines orvehicle contact with a pole can cause thesefaults. Motor starts can also cause sags buttheir magnitudes are usually not severe enoughto cause equipment to drop off line or operateerratically.

As long as the fault is present, the facility willexperience a sag in voltage. As soon as thefault is cleared (usually within a few cycles) thefacilitys power will return to nominal levels.

Unfortunately the damage has already beendone! Much of todays modern electronicprocessing equipment is very sensitive to

voltage fluctuations.

Each occurrence can cost a business manydollars in damaged product, lost production,customer dissatisfaction, increasedmaintenance, and possibly extra man-hours forcleaning up and resetting equipment.

The types of equipment that are sensitive tothese voltage sags include most devices foundin a typical manufacturing environment.

Process controllers that regulate watertemperature by controlling chillers can beaffected causing major problems in someindustrial applications.

Electronic chip testers, when tripped could take

as much as 30 minutes to restart due to theircomplexity. Also, the chips involved in the testcan be damaged.

DC drives used in many processes, includingprinting presses and plastics manufacturing aresensitive.

The plastic extrusion process is a commonprocess that is particularly susceptible to sags.The entire process is usually automated, and an

interruption can cause very expensive cleanupsand restarting requirements. Typically eachevent could cost $10,000 or more, and a plantfed from a distribution system could experience20-25 events per year!

Programmable logic controllers are animportant category of equipment because mostprocesses are often completely controlled bythese devices. Sensitivity varies widely, butits the weak link in the chain scenario, with

some devices shown to trip for voltages as highas 90% for a few cycles!

Machine tools can be very sensitive to voltagevariations. Often complicated machines, orrobots are used in the drilling, cutting, andmetal processing used in producing specializedparts. Voltage variations can seriously affect

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the quality of the part being machined. Also,many of these machines are intentionally set todrop out at voltage levels as high as 90% due tosafety concerns! Theres no telling what arobot will do when operating on low voltage!

SolutionsSo what can be done? Well there are severalthings that can be looked at by the utility andtheir customers.

For the utility, there are two options, preventthe faults, and modify the fault clearingprocess.

Fault prevention includes tree trimming, adding

line arresters, insulator washing, and addinganimal guards. This really amounts toimproving the design and maintenance of thetransmission and distribution systems.

Improvements could be made to the faultclearing process, including adding linereclosers, eliminating fast tripping, adding loopschemes, and modifying feeder design. Thesemay reduce the number and/or duration of sags,but utility faults can never be eliminatedcompletely.

For the customer, the solution usually involvessome sort of power conditioning for theirsensitive loads.

Until recently these options included:

Motor-Generator sets (M-G sets)

Uninterruptible Power Supplies (UPSs)

Constant Voltage Transformers (CVTs)

Magnetic Synthesizers

Superconducting Storage Devices (SSDs)

Each of these solutions has their pros and cons.The cons typically involve initial and ongoingcosts. For instance the UPS, probably the mostcommon power-conditioning device, has theongoing problem of battery maintenance and

replacement. Also, if the UPS is the offlinetype, it wont be able to switch to batteriesquick enough, and youll still see a sag of shortduration. It also is very expensive and takes upa lot of real estate.

CVTs have a lower cost, but will only helpwith minimal sags to 80%.

The other solutions also have inherentlimitations and prohibitive costs, which makethem not the remedy of choice for manybusinesses. (Many businesses will just livewith the problem!)

Now there is another choice that has more

benefits, with fewer of the problems and costs.Its manufactured in the U.S.A. by SoftSwitching Technologies, and solves 92% of thepower problems affecting the industrialenvironment today!

The Dynamic Sag Corrector uses patentedtechnology to help sensitive equipment to ride-through voltage sags down to 50%, and outagesup to 0.15 seconds.

It has a power range of 1.5 kVA to 2000 kVA!It has no batteries or moving parts, and usesvery little power when not correcting sag. (Itseffectively offline until it senses a voltage sag,and then switches on in less than 1 cycle!)

In their September/October 1998 issue, PowerQuality Assurance Magazine said about the

DySC:

The Dynamic Sag Corrector (DySC)

described in this article has significantadvantages over existing technologies thatshould make it a very popular method of

protecting facilities from short-durationvoltage sags

Technology usually solves the problems itcreates!