9-36 Setting the Relay Date Code 20001006
SEL-351 Instruction Manual
Current Transformer Ratios
Refer to Settings Sheet 1 of 23.
Phase and neutral current transformer ratios are set independently. If IN is connected residually
with IA, IB, and IC, then set CTR and CTRN the same.
For sensitive earth fault (SEF) applications (channel IN rated 0.05 A nominal), some thought
might be given to making the CTRN setting artificially high, to view small channel IN currents in
the event report. For example if CTRN = 10000, then 5 mA secondary into channel IN appears as
50 A primary in the event report (0.005 x 10000 = 50). Channel IN metering values are likewise
affected. All the neutral ground overcurrent elements operate off of secondary current values, so
the CTRN setting has no affect on their operation.
Line Settings
Refer to Settings Sheet 1 of 23.
Line impedance settings Z1MAG, Z1ANG, Z0MAG, and Z0ANG are used in the fault locator (see
Fault Location in Section 12: Standard Event Reports, Sag/Swell/Interruption Report, and
SER) and in automatically making directional element settings Z2F, Z2R, Z0F, and Z0R (see
Settings Made Automatically in Section 4: Loss-of-Potential Logic, Load Encroachment, and
Directional Element Logic). A corresponding line length setting (LL) is also used in the fault
locator.
The line impedance settings Z1MAG, Z1ANG, Z0MAG, and Z0ANG are set in W secondary.
Line impedance (W primary) is converted to W secondary:
W primary + (CTR/PTR) = W secondary
where:
CTR = phase (IA, IB, IC) current transformer ratio
PTR = phase (VA, VB, VC) potential transformer ratio (wye-connected)
or
PTR = phase-to-phase (VAB, VBC, VCA) potential transformer ratio (delta-connected)
Line length setting LL is unitless and corresponds to the line impedance settings. For example, if a
particular line length is 15 miles, enter the line impedance values (W secondary) and then enter the
corresponding line length:
LL = 15.00 (miles)
If this length of line is measured in kilometers rather than miles, then enter:
LL = 24.14 (kilometers)
Courtesy of NationalSwitchgear.com
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