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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On the other hand, voltages below the envelope are assumed to cause cugve load to drop out due to lack of energy. Generally, these transients result from application of heavy loads, as well as fault conditions, at various points in the AC distribution system.

The sharper the deviation, the higher the frequency.

ITIC Curve – Voltage Disturbance

In the center of the plot is the so called acceptable area. 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. The author then explains how to use the CBEMA curve for transients, short outages, and long-term disturbances. For a complete copy of the Application Note Click here References: Also, it is used as a reference to define the withstand capability of various loads and devices for protection from power quality problems.

Simple disturbances, such as a lightning strike, is easily indicated using a single point.

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If the file has been modified from its original state, some details such as the timestamp may not fully reflect those of the original file. ANSI too did not want to be left out of the arena, and came up with their own. In short, computers, programmable logic controllers PLCspower distribution units PDUsinstrumentation, telecom and other solid-state systems will operate reliably when applied properly.

This could include thyristor controlled heaters, some digital clocks etc.

File:CBEMA – Wikimedia Commons

The magnitude cbwma the transient is expressed as a percentage of the peak 60 Hz nominal voltage not the RMS value. Computers, programmable logic controllers, distributed processing units, instrumentation, and other sensitive solid-state systems are voltage and time sensitive. Told you, Power Quality is an electronics field, not a power engineering one!

The basis of this curve is supported by tests that were conducted on a representative sample of eight PC power supplies supplied by eight curvw manufacturers. Power Quality in Electrical Systems. A lightning strike, even when reasonably nearby, will often not damage equipment. This range is those deviations with extremely sharp rise and fall times deviate from and then return to the normal waveform extremely quickly.

This is because the curve is generally applicable to other equipment containing solid-state devices aside from being specifically applicable to computer-type equipment. Complicated disturbances need to be broken down in to various stages of the disturbance and indicated as separate points on the curve.

File:CBEMA Curve.png

Working right to left we’ll cover Type III category first. These two filters, between them, will establish the devices susceptibility to variations in the mains waveform – and the susceptibility is dependent on distortion vs.


The normal functional state of the ITE is not typically expected during these conditions, but no damage to the ITE should result. Call it by the device’s name if there is no name for it, but stop calling it ‘modified’. The rectified DC is stored in the bus capacitor. I have been working in an electric distribution utility for more than a decade. In other words, t he concept is that if the supply voltage stays within the acceptable power area then the sensitive equipment will operate well.

Furthermore, it must not be forgotten that the older mains transformer is also a rather large inductor followed by rectifiers and storage cap and such a curve is therefore also applicable to older power supplies.

Obviously, this is quite an extension from the initial intent of describing the power quality performance of typical mainframe computers. High-Frequency Impulse and Ringwave This region describes the transients that typically occur as a result of lightning strikes. Information technology equipment could include single phase computers, printers, scanners etc.

Low Frequency Decaying Ringwave: The longer the deviation, the more it can affect the capacitor. Voltage dropout includes both severe RMS voltage sags cbems complete bcema of the applied voltage, followed by immediate re-application of the nominal voltage.

Power Systems Engineering Research Center. Voltage sags occur when then there is some fault on the system or during starting of large loads motors etc.