U.2.5
Date Code 20020501 User’s Guide SEL-421/SEL-421-1 Relay
Installation
Shared Configuration Attributes
Figure 2.3 Rear 3U Template, Fixed Terminal Block Analog Inputs.
(When using a vertical-mount relay, the right rear side is at the top.)
Figure 2.4 Rear 3U Template, Connectorized Analog Inputs.
(When using a vertical-mount relay, the right rear side is at the top.)
Secondary Circuits
The SEL-421 Relay is a very low burden load on the CT secondaries and PT
secondaries. For both the CT and PT inputs, the frequency range is 40–65 Hz.
The relay accepts two sets of three-phase currents from power system CT
inputs:
➤ IAW, IB W, and ICW
➤ IAX, IBX, and ICX
For 5 A relays, the rated nominal input current, I
nom
, is 5 A. For 1 A relays,
the rated nominal input current, I
nom
, is 1 A. Input current for both relay types
can range to 20 • I
nom
. The CT burden is 0.27 VA @ 5A and 2.51 VA @ 15 A
for the 5 A relay. The CT burden for the 1 A relay is 0.13 VA @ 1 A and 1.31
VA @ 3A. See the AC Current Inputs (Secondary Circuits) on page U.1.11 in
the User’s Guide for complete CT input specifications.
The relay also accepts two sets of three-phase, four-wire (wye) potentials from
power system PT or CCVT (coupling-capacitor voltage transformer)
secondaries:
➤ VAY, V B Y, a n d V C Y
➤ VAZ, VBZ, and VCZ
i3359a
i3372a
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