Schweitzer Engineering Laboratories SEL-700G Series, Instruction Manual

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4.59
Date Code 20170814 Instruction Manual SEL-700G Relay
Protection and Logic Functions
Group Settings (SET Command)
Set the Zone 2 offset equal to the Zone 1 offset.
Set the Zone 2 time delay long enough to avoid an incorrect operation during a
worst-case stable power system swing condition, typically 0.5 to 0.6 seconds
or according to the recommendations of the generator manufacturer.
In this case, the 40DIR setting is hidden.
The Relay Word bits 40Z1T and 40Z2T are configured to trip the field breaker
and the generator breaker in the factory-default logic (see Trip/Close Logic
Settings for details). You must change the setting if your application requires a
different action.
Loss-of-Field Protection Using a Positive Offset Zone 2.
When setting
Zone 2 with a positive offset, set the Zone 1 diameter:
Set the Zone 1 offset equal to half the generator transient reactance, X'
d
, in
secondary ohms.
Traditionally, the Zone 1 delay for this type of scheme is 0.25 seconds.
Use the direct axis reactance and XS, the sum of the step-up transformer
reactance XT and system reactance Xsys, to set the Zone 2 diameter.
Use the total reactance of XS to set the Zone 2 offset.
Traditionally, the Zone 2 delay for this type of scheme is approximately 60
seconds (it is advisable to conduct system studies to determine the best time
delay when using the positive offset method).
The relay applies a shorter delay if the Zone 2 element picks up at the same
time that the relay detects an undervoltage condition. This logic is discussed in
the following text. In this case, the 40DIR setting is necessary. Set 40DIR
equal to -20 degrees or the arc cosine of the minimum rated power factor,
whichever is smaller.
When applying loss-of-field protection with a positive Zone 2 offset, you can
use the time-delayed Zone 1 Relay Word bit, 40Z1T, and the long-time-
delayed Zone 2 Relay Word bit, 40Z2T, directly in the generator breaker and
field breaker tripping SEL
OGIC
control equations.
40XD2
X

d
–
2
------------

=
40Z2D 0.5 seconds =
40Z1P 1.1 X
d
X

d
–
2
------------

+

=
40XD1
X

d
–
2
------------

=
40Z1D 0.25 seconds =
40Z2P 1.1 X
d
XS

+

=
where
XS XT Xsys + =
40XD2 XS

=
40Z2D 60.0 seconds =