CHOOSING LIMIT SETIINGS
When the PRIDE'Uni t is purchased,
the
user should spacify the desired limit settings.
These settings
will be stored in the
ROM
(Read Only Memory) on the M-0298 Memory Board before the relay is shipped to
tbe
user.
A
record of the settings and serial numbers of the boards will be kept on file by Beckwith
Electric.
Before installing, assure that the settings listed on the label match those ordered. In many
cases there will never be a need to change the settings; however if a change is desired, any of the
optiOns listed under the FIELD
AllJUSTMmI'
section may be employed.
In choosing the settings deSired,
the
following factors must be taken into consideration.
Due to variations in the load flow on a line, the phase angle at any point on the line will shift
relative to the phase at the substation bus. The transient effect observed on the line at any load
point will be a variation in the period of the ac voltage in the cycle during which the loading
changes.
A
frequency relay that is measuring the pariod of the power line potential will detect the
variation in
the
period and may indicate an over or under frequency condition.
The
PRIDE uses a unique digital filter to eliminate the effect of line phase shift. The PRIDE measures
tbe
pariod of each power line cycle and uses
the
digital filter (El:juation
5)
to smooth
the
data before
determining if the frequency is within the M-0290 setpoints.
The digital filter will produce a
transient OUtpllt for several cycles after a phase shift takes place.
However,
the
Power Loss software
will throw away a period that changes more than 273
AlS
from the previollsly measured period. This
corresponds to an apparent phase shift of
60.
A
phase shift of less than
6 0
will cause a temporary
response from the digital filter that could indicate an over or under frequency condition, if the over
frequency or under frequency setpoint i s within
1
Hz of
60
Hz. Therefore, the minimum time delay
settings of Figure
14
are reoommended for over frequency
and
under frequency settings close to 60 Hz.
The
Overvoltage setpoint must be at least 3% higher
than
the Undervoltage setlXlint, i.e., the minimum
voltage bandwidth is 3% total.
It i s not recommended that the Frequency Trip Timers be set less then 3 cycles or the Vol tage Trip
Timers set less then
15
cycles. This is to prevent short-time transient effects on the measured ac
line from caUSing nuisance trips.
Incorporated in the PRIDE is the capability to enable or disable certain functions.
This can be
accomplished either at the time of purchase bY ordering the functions deSired, or bY using the optional
M-0297/M-0397 Field Adjustment Unit. Refer to
the
M-0297/M-0397 Field Adjustment Unit Instruction Book
for further details on this unit.
The
following list shows the
PRIDE
functions that
can
be ordered (or programmed if using the
M-0297IM-0397) as either enabled or disabled.
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