Clark Electric Co.
(Office) 770.740.6009

Office Hours

Monday - Friday

7:00am-6:30pm EST


We have Extented

our Office Hours to Better

Serve you-our Valued

Customer


30 minute Service Window

Guaranteed on all Appointments


Serving Atlanta GA
Alpharetta GA &
Greater Metro Area

Licensed & Insured

24 Hour Service

Emergency Service Call
678.525-5814

Be there within an hour or less
Guaranteed!!




Electrical Contractor

Serving Georgia

 

Cumming

Buford

Suwanee

Alpharetta

Roswell

Johns Creek

Sandy Springs

Buckhead

Marietta

Kennesaw

Woodstock

Canton

Duluth

Norcross

Power Quality

The tolerance of data-processing equipment to voltage variations is often characterized by the CBEMA curve, which give the duration and magnitude of voltage variations that can be tolerated.
 
Ideally, voltage is supplied by a utility as sinusoidal having an amplitude and frequency given by national standards (in the case of mains) or system specifications (in the case of a power feed not directly attached to the mains) with an impedance of zero ohms at all frequencies.
 
No real-life power source is ideal and generally can deviate in at least the following ways:
 
  • Variations in the peak or RMS voltage are both important to different types of equipment.
  • When the RMS voltage exceeds the nominal voltage by 10 to 80% for 0.5 cycle to 1 minute, the event is called a "swell".
  • A "dip" (in British English) or a "sag" (in American English - the two terms are equivalent) is the opposite situation: the RMS voltage is below the nominal voltage by 10 to 90% for 0.5 cycle to 1 minute.
  • Random or repetitive variations in the RMS voltage between 90 and 110% of nominal can produce a phenomenon known as "flicker" in lighting equipment. Flicker is rapid visible changes of light level.
  • Abrupt, very brief increases in voltage, called "spikes", "impulses", or "surges", generally caused by large inductive loads being turned off, or more severely by lightning.
  •  "Undervoltage" occurs when the nominal voltage drops below 90% for more than 1 minute. The term "brownout" is an apt description for voltage drops somewhere between full power (bright lights) and a blackout (no power - no light). It comes from the noticeable to significant dimming of regular incandescent lights, during system faults or overloading etc., when insufficient power is available to achieve full brightness in (usually) domestic lighting. This term is commonly used to describe a reduction in system voltage by the utility or system operator to decrease demand or to increase system operating margins.
  •  "Overvoltage" occurs when the nominal voltage rises above 110% for more than 1 minute.
  • Variations in the frequency
  • Variations in the wave shape - usually described as harmonics
  • Nonzero low-frequency impedance (when a load draws more power, the voltage drops)
  • Nonzero high-frequency impedance (when a load demands a large amount of current, then stops demanding it suddenly, there will be a dip or spike in the voltage due to the inductances in the power supply line)
 
Each of these power quality problems has a different cause. Some problems are a result of the shared infrastructure. For example, a fault on the network may cause a dip that will affect some customers and the higher the level of the fault, the greater the number affected, or a problem on one customer’s site may cause a transient that affects all other customers on the same subsystem.
 
Other problems, such as harmonics, arise within the customer’s own installation and may or may not propagate onto the network and so affect other customers. Harmonic problems can be dealt with by a combination of good design practice and well proven reduction equipment.