Quantcast Power Quality

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Common solutions to the problem of electrical disturbances are filters, power conditioners, surge
arresters, capacitors, solid-state motor starters, adjustable frequency motor drives, uninterruptible
power supply systems, isolating transformers, and revisions to grounding systems. Since
disturbances by their definition last less that one minute (most last less than one second) it is
obvious that the distribution system must be designed and installed to operate automatically
without operator intervention to overcome the affects of disturbances. When outages occur, an
alarm or annunciator system should be used to provide operating or maintenance personnel an
indication of the time of occurrence and location of the outage. This will allow prompt
implementation of the restoration of electrical service to the affected area. The following
procedures must be in place for the personnel to follow, so that a systematic method will be used:
(a)
Report the problem and document the cause of the outage.
(b)
Change the system configuration as required to restore service.
(c)
Schedule repairs, if necessary.
(d)
Make the appropriate repairs or equipment replacements.
(e)
Restore the system to its normal operational configuration.
These personnel procedures should be performed in a timely and safe manner. When an outage
occurs on the electrical distribution system, a thorough investigation should be made to
determine the cause of the outage. The system configuration should be changed to remove
damaged equipment from service. The system power should be restored after a check for safety
has been made that determines that power can be restored. The safety considerations should
include checking for possible damage to equipment, both upstream and downstream of the
suspected fault location, and the changing of certain switching devices to the off position, so that
the unexpected return of power to certain equipment may not cause injury to personnel or
damage to equipment. These considerations should be a part of the operating procedures manual
discussed in paragraph 8.2.1.
8.2.4 Power Quality. Power quality is usually measured by the amount of deviation from the
nominal parameters that the steady-state power supply encounters. The usual parameters
measured are the voltage and frequency, since the current is a function of the load level on the
system. Measurements made on the system, or feeder voltage, usually include the magnitude.
The phase angle might also be included when a significant unbalance is suspected due to large
loading on single phases of a multi-phase system. The frequency magnitude is also measured. If
harmonics are causing a problem, then the various harmonic frequencies can be measured, as
well as the voltage of each harmonic. In order to perform the latter tests, sophisticated recording
devices with fast response times and frequency spectrum analysis capabilities must be used. If
the purchase of equipment is not deemed economical, then it can be rented from one of several
sources. Additionally, if power disturbances are causing operating problems, then special
transient recording devices must be used. These devices are used to record and monitor the
system parameters over a set time period and provide sufficient data to determine the probable
cause of the disturbances. This equipment is also costly; similar to harmonic analysis equipment,
8-5





 


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