Ieee std 1159-1995, ieee recommended Practice for Monitoring Electric Power Quality

Figure 12ÑExample of voltage ßuctuations caused by arc furnace operation

---

IEEE
MONITORING ELECTRIC POWER QUALITY
Std 1159-1995
25
overall level of effort required of the project. The objective may be as simple as verifying steady-state volt-
age regulation at a service entrance, or may be as complex as analyzing the harmonic current ßows within a
distribution network. The resulting data need only meet the objectives of the monitoring task in order for the
monitoring to be successful.
The procedure for deÞning monitoring objectives differs by the type of study. For diagnostic monitoring to
solve shutdown problems with sensitive equipment, the objective may be to capture out-of-tolerance events
of certain types. Evaluative or predictive monitoring may require collection of several voltage and current
parameters in order to characterize the existing level of power quality.
Measurement of electromagnetic phenomena includes both time and frequency domain conducted parame-
ters, which may take the form of overvoltages and undervoltages, interruptions, sags and swells, transients,
phase imbalance, frequency aberrations, and harmonic distortion. Non-conducted environmental factors can
also have an effect on load equipment, although these types of disturbances are not considered in this docu-
ment. Such factors include temperature, humidity, electromagnetic interference (EMI), and radio frequency
interference (RFI).
5.2 Need for monitoring power quality
There are several important reasons to monitor power quality. The primary reason underpinning all others is
economic, particularly if critical process loads are being adversely affected by electromagnetic phenomena.
Effects on equipment and process operations can include misoperation, damage, process disruption, and
other such anomalies. Such disruptions are costly since a proÞt-based operation is interrupted unexpectedly
and must be restored to continue production. In addition, equipment damage and subsequent repair cost both
money and time. Product damage can also result from electromagnetic phenomena requiring that the dam-
aged product either be recycled or discarded, both of which are economic issues.
In addition to resolving equipment disruptions, a database of equipment tolerances and sensitivity can be
developed from monitored data. Such a database can provide a basis for developing equipment compatibility
speciÞcations and guidelines for future equipment enhancements. In addition, a database of the causes for
recorded disturbances can be used to make system improvements. Finally, equipment compatibility prob-
lems can create safety hazards resulting from equipment misoperation or failure.
Problems related to equipment misoperation can only be assessed if customer disturbance reports are kept.
These logs describe the event inside the facility, the type of equipment that was affected, how it was affected,
the weather conditions, and the losses incurred. A sample disturbance report is shown in Þgure 13.