Custom Search
|
|
|
||
 the usage of modems. The software allows detailed analysis of system operations and production
of detailed reports showing almost all of the major parameters (voltage, current, power factor,
demand load, kVAR load, and energy consumption) for individually configurable report formats.
If such advanced recording devices are not installed, then the use of traditional chart recorders
should be considered for key operating parameters. The recorders should be used at least for
temporary periods to establish normal load cycles (time of daily, weekly, monthly, etc. peak
loads), system voltages, power factors, and currents during these conditions. Recording the
voltages, power factors, and currents during light load conditions is also important to determine
the overall operating profile of the system.
Use of relatively inexpensive microcomputer load flow analysis programs, which have only
become available in the last few years, can be very useful in determining the optimum operating
configurations for the electrical distribution system. With the knowledge of peak and minimum
load information and the use of the load flow analysis program, possible problems such as low
voltage, overloaded conductors and equipment, and alternative operating configurations, during
system forced and planned outages, can be analyzed and the appropriate corrective action
planned easily and quickly. In the past, these tools were not available to the operating personnel.
Many catastrophic failures occurred as a result, due to the lack of adequate and timely
information.
8.2.3 System Disturbances or Outages. Even though the electrical distribution system
normally operates for many days without any change in system configuration and without any
disturbances or outages to utilization equipment, there is always the chance of a fault or overload
that will result in an electrical disturbance or outage. The term outage, as used here, is the
complete absence of power at the point of use. The term disturbance is used for the temporary
departure from normal of one or more of the parameters of electric power at the point of use.
This includes such terms as sag, dip, surge, spike, impulse, noise, and phase shift. The more
usual disturbances involve line voltage impulses, noise, transients, steady-state voltage change,
or a combination of these disturbances. Studies indicate that 90 percent of the disturbances are
less than one second in duration and 80 to 85 percent involve only one phase of a three-phase
system. Disturbances are usually classified by time duration, with disturbances lasting over one
minute usually being classified as an outage. The ranges of classification involve an overlap of
the categories to some extent, although their use is not mandatory.
8.2.3.1 One Second to One Minute. These disturbances are usually attributed to severe
faults on one or more phases and are manifested by 50 to 100 percent voltage loss on one or more
phases. Often caused by lockout relays on circuit protective devices, this type of disturbance
results in an outage to the system on the cleared side of the fault, however, on the power source
side of the fault it is a disturbance. The cleared side of the fault refers to the system downstream
from the overcurrent or short-circuit protective device, which, when it operates, opens the circuit
and thus de-energizes the downstream system and clears the fault. The power source side of the
fault is the system upstream from the overcurrent or short-circuit protective device, and which,
8-3
|
 
|
|
|
||
