INTERPRETING THE READINGS: Understanding the. CBEMA Curve. ” Determining Susceptibility”. Throughout the sphere of Power Quality you’ll hear the terms. The ITI, formerly CBEMA, curve was developed by the Information Technology Industry Council of the. United States of America. The curve describes an AC. Abstract: The ITI, formerly CBEMA, curve was developed by the Information Technology Industry Council of the United States of America. The curve describes an.

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E ventually, it became a standard design target for sensitive equipment to be applied on the power system and a common format for reporting power quality variation data. Moreover, the instrumentation to check compliance with the curve appears to be easier to design because of the simplified way the acceptable region is represented.

ITE equipment includes common office equipment such as computers and its related peripheral equipment. Simple cbea, such as a lightning strike, is easily indicated using a single point. During a power system disturbance, like a voltage sag, swell or a transient voltage for example, the DC bus voltage could go very low or very cbemx and in turn affect the reliable operation of the ITE equipment. H, HJ Elsevier After some minor modifications to the proposal, the ESC-3 working group approved this initial version of the curve, which remained unchanged until early in In the world of VAC that’s a whole 1kV approxand that’s kind of large!

This transient could occur during a temporary fault in the power system followed by clearing of the fault.

Normal functioning of ITE equipment is also not expected in region. This only applies to original works of the Federal Government and not to the work of any individual U. This transient typically results from the occurrence and subsequent clearing of faults in the AC distribution system. The interruption may last up to 20 milliseconds. From Wikimedia Commons, the free media repository. So we have presented two needs for a tolerance curve, both as the means to test a supply with the difference being before and after installation.


The magnitude of the transient is expressed as a percentage of the peak 60 Hz nominal voltage not the RMS value. The following other wikis use this file: As their frequency component is so high, wiring alone tends to provide huge attenuation let alone the filters found in most modern power supplies or transformers. Working right to left we’ll cover Type III category first. All conditions are assumed to be mutually exclusive at any point in time, and with the exception of steady-state tolerances, are presumed to commence from the nominal voltage.

To the right of this is longer term disturbances, and it can be seen that the more we progress to longer term disturbances, the less the deviation from the norm they may be.

Semiconductor wafer production is very sensitive to voltage sag voltage dip events and one voltage sag event could cost facility hundreds of thousands of dollars per voltage sag event.

Tables of content are generated automatically and are based on records of articles contained cbena are available in the TIB-Portal index. These two limits, therefore, represent the wide input voltage range most SMPSs now comfortably operate on. Some of which are unequal ground potentials, Electromagnetic Noise Interference etc.

The second the amplitude and duration of the reduced voltage.

Voltage Disturbance

Throughout the next 20 years that the original version was published, it grew in stature from a simple curve describing the performance of mainframe computer equipment PCs were not availableto a curve that was used to define everything from specification criteria for electronic equipment to the basis of power quality performance contracts between electric utilities and large industrial customers. It can be clearly seen how the shorter the time, the more distorion can be tolerated before disturbance is likely.


There are many other variables that could affect the reliable operation of IT equipment.

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File:CBEMA – Wikimedia Commons

High-Frequency Impulse and Ringwave This region describes the transients that typically occur as a result of lightning strikes.

By doing this it would appear as if these guys sure know how to make things complicated!

Please help stop this bad engineering practice. Voltage sags, dropouts, and steady state voltages in this region are not expected to damage the ITE equipment.

This curve provides an AC voltage boundary that most information technology equipment Cbems can tolerate or ride through without experiencing unexpected shutdowns or malfunctions. Basically, the CBEMA curve was originally derived to describe the tolerance of mainframe computer business equipment to the magnitude and duration of voltage variations on the power system.

When the short initially occurs, there are likely to be transients. View my complete profile. Newer Post Older Post Home. Any voltages in this range may be present for an indefinite cure and are a function of the normal loadings and losses in the distribution system.