This curve provides an AC voltage boundary that most information technology equipment ITE can tolerate or ride through without experiencing unexpected shutdowns or malfunctions. Information technology equipment could include single phase computers, printers, scanners etc. 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 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 available , to 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.
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The intent was to derive a curve that can better reflect the performance of typical single-phase, V, 60 Hz computers and their peripherals, and other information technology items like fax machines, copiers and point-of-sales terminals. Also, it is used as a reference to define the withstand capability of various loads and devices for protection from power quality problems.
This is because the curve is generally applicable to other equipment containing solid-state devices aside from being specifically applicable to computer-type equipment. However, one should be careful and should keep in mind that the ITIC curve is not intended to reflect the performance of ALL electronic-based equipment. There are too many variables - power loading, nominal operating voltage level, and process complexity, to try to apply a one-size-fits-all ITIC curve. 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.
It is not intended to serve as a design specification for products or AC distribution systems. Other nominal voltages and frequencies are not specifically considered and it is the responsibility of the user to determine the applicability of these documents for such conditions.
Discussion A brief description of the individual conditions that are considered in the ITIC curve is provided in this section. 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. The timing between transients is assumed to be such that the ITE returns to equilibrium electrical, mechanical, and thermal before the next transient begin.
Any voltages in this range may be present for an indefinite period and are a function of the normal loadings and losses in the distribution system. This transient may occur when large loads are removed from the system or when voltage is supplied from sources other than the electric utility. Low-Frequency Decaying Ringwave This region describes a decaying ringwave transient which typically results from the connection of power factor correction capacitors to an AC distribution system.
The frequency of this transient may range from Hz to 5 kHz, depending upon the resonant frequency of the AC distribution system. The magnitude of the transient is expressed as a percentage of the peak 60 Hz nominal voltage not the RMS value. High-Frequency Impulse and Ringwave This region describes the transients that typically occur as a result of lightning strikes.
This region of the curve deals with both amplitude and duration energy , rather than RMS amplitude. The intent is to provide an 80 Joule minimum transient immunity.
Generally, these transients result from application of heavy loads, as well as fault conditions, at various points in the AC distribution system. The interruption may last up to 20 milliseconds. This transient typically results from the occurrence and subsequent clearing of faults in the AC distribution system.
No Damage Region Events in this region include sags and dropouts which are more severe than those specified in the preceding paragraphs, and continuously applied voltages which are less than the lower limit of the steady-state tolerance range. The normal functional state of the ITE is not typically expected during these conditions, but no damage to the ITE should result. Prohibited Region This region includes any surge or swells, which exceeds the upper limit of the envelope. If ITE is subjected to such conditions, damage may result.
Power Quality in Electrical Systems.
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. Also, the association designed the curve to point out ways in which system reliability could be provided for electronic equipment. Eventually, 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 best scientific interpretation of the curve can be given in terms of a voltage standard applied to the DC bus voltage of a rectifier load. In the center of the plot is the so called acceptable area. Voltage values above the envelope are supposed to cause malfunctions such as insulation failure, overexcitation and overvoltage trip. On the other hand, voltages below the envelope are assumed to cause the load to drop out due to lack of energy.
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