4.58
SEL-700G Relay
Instruction Manual
Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
Zone 2 loss-of-field tripping typically is performed with a time delay of
0.5 to 0.6 seconds. Set 40Z2D equal to the necessary delay.
The 40DIR setting is hidden when 40XD2 < 0.
The 40Z2 Relay Word bit asserts without time delay when the measured
positive-sequence impedance falls within the Zone 2 mho circle defined by the
offset and diameter settings, and below the directional supervision line (if
used). The 40Z2T Relay Word bit asserts 40Z2D seconds after 40Z2 asserts.
The loss-of-field elements are disabled when the 40ZTC SEL
OGIC
control
equation equals logical 0. The relay allows these elements to operate when the
40ZTC SEL
OGIC
control equation equals logical 1. With the example setting,
the loss-of-field elements operate when the relay detects no loss-of-potential
condition.
Setting Calculation
Collect the following information to set loss-of-field.
➤
Generator direct axis reactance, X
d
, in secondary ohms
➤
Generator transient reactance, X'
d
, in secondary ohms
➤
Generator-rated line-to-line voltage, in secondary volts
(Vnom = 1000 • VNOM_X/PTRX)
➤
Generator-rated phase current, in secondary amps
(INOM setting)
➤
When a positive Zone 2 offset is necessary, you also need:
➢
Step-up transformer reactance XT, and system
reactance Xsys, in secondary ohms
➢
Generator-rated power factor
Recommendations
Two methods are available for loss-of-field protection: negative offset Zone 2
and positive offset Zone 2. Recommendations for both setting methods are
provided.
Loss-of-Field Protection Using a Negative Offset Zone 2.
When
setting Zone 2 with a negative offset, set the Zone 1 diameter equal to 1.0 per
unit impedance.
NOTE:
Typically, the X
d
is greater
than 1 per unit impedance. However, if
X
d
is less than or equal to 1 per unit
impedance, set the 40Z1P shorter so
that the worst-case stable power
system swing does not enter the Zone
1 characteristic.
Set the Zone 1 offset equal to half the generator transient reactance, X'
d
, in
secondary ohms.
Zone 1 loss-of-field tripping is typically performed with short or zero time
delay.
Set the Zone 2 diameter equal to the machine direct axis reactance, X
d
, in
secondary ohms.
NOTE:
The loss-of-field elements
require at least 0.25 volts of positive-
sequence voltage and 0.25 amps of
positive-sequence current to operate.
40Z1P
Vnom
1.73
INOM
---------------------------------
=
40XD1
X
d
–
2
------------
=
40Z1D
0.0 seconds
=
40Z2P
X
d
=
Summary of Contents for SEL-700G Series
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