Percent Slope Setting - GE STD15C Instructions Manual

Determine
a.
b. For delta
(NOTE: For the location of fault assumed. a 11 the fault currant Is
.
Determine secondary CT voltage required
i
excitation curve of particular tap of current transformer
current.
error
,
should not
I
choose a higher tap on that set of
i
mismatch error, and percent ratio error.

PERCENT SLOPE SETTING

proper percent slope
The maximum range of manual taps and the load-ratio-control, or
a.
in percent.
b. The
The percentage slope tap
smaller of the through currents.
the 25 percent tap is used.
the
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burden on each CT. using the following expressions:
connected CT's
2R
CT'S
relay total burden (sea Table
N number of turns in bushing CT
bushing CT resistance per turn,
CT resistance per lead.
R control cable lead
CT current for 8 times tap setting.
8 relay tap rating
and relay current are the same, regardless of whether the
this secondary
the percent error In each CT by the expression:
20 percent on
is determined by the sum Of:
percent of mismatch of the relay taps.
should
In general, if the total error current does
If it
lead is used (as in
(at maximum
(at
(at
8 times tap setting.
set of If it does.
and repeat the calculations on selection of relay
greater than the ratio Of
20 percent, but not 35 percent. the
for example) the percent
temperature)
expected temperature)
by one CT. so that
are connected in
determine excitation
be
.
tap means.
error
20 Percent.
should be
or
to
about