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2.6 Frequency Protection
GRT100 provides underfrequency or overfrequency protection and/or alarms for load shedding or
for detecting such an overfrequency condition caused by disconnecting load from a particular
generation location.
The frequency element FRQ comprises two frequency elements 81-1 and 81-2, the former is used
for tripping and the latter for alarms.
Figure 2.6.1 shows the scheme logic of the frequency protection. The tripping element 81-1
outputs underfrequency and overfrequency trip signals L1 and H1. Either underfrequency or
overfrequency protection is selected by setting the scheme switch [FRQ-UF1] to “ON” or “OFF”.
The alarm element 81-2 outputs underfrequency and overfrequency alarm signals L2 and H2.
Either underfrequency or overfrequency alarms are selected by setting the scheme switch
[FRQ-UF2] to “ON” or “OFF”.
Frequency protection can perform time-delayed tripping of up to five breakers. Any of the breaker
tripping signals FRQ-1 to FRQ-5 can be blocked by the scheme switch [FRQ1] to [FRQ5]
settings.
Note: Models 203 and 204 are not provided with FRQ-4 and FRQ-5.
Alarm signal FRQ-A can be blocked by the scheme switch [FRQA] setting.
Frequency protection is blocked under the condition that the system voltage is lower than the
setting of the undervoltage element UV.
[FRQ-UF1]
[
FRQ-UF2
]
+
+
TFRQL
0.00 - 60.00s
0 t
≥1
&
&
&
&
+
[
FRQ1
]
1
1
81-1
81-2
H1
H2
L2
L1
UV
89
90
91
92
119
1
ON
ON
Note: Models 203 and 204 are not provided with FRQ-4 and FRQ-5.
≥1
FRQ-OF ALARM
FRQ-UF ALARM
FRQ A
257
356
355
+
[
FRQ-UF2
]
ON
OFF
FRQ-1
≥1
&
TFRQH
0.00 - 60.00s
0 t
TFRQA
0.00 - 60.00s
0t
+
[
FRQ2
]
FRQ-2
&
+
[
FRQ3
]
FRQ-3
&
+
[
FRQ4
]
FRQ-4
&
+
[
FRQ5
]
FRQ-5
&
+
[
FRQA
]
&
&
&
FRQ-OF TRIP
FRQ-UF TRIP
FRQ TRIP
249
354
353
+
[
FRQ-UF1
]
ON
OFF
&
&
Figure 2.6.1 Scheme Logic of Frequency Protection