ANSI12000609-1-en.vsd
Comparator
If
f <= FreqHighLimit
AND
f > FreqLowLimit
Then
PICKUP
Comparator
I < PickupCurrentLevel
PICKUP
Signal Routing
Based on
Generator
Start or Stop
Detection Logic
and
Voltage Band Limit
Check Logic
V3P
I3P
CBOPEN
CBCLOSE
Comparator
If
FreqHighLimit <=
FreqLowLimit
Then
ERROR
BLOCK
LOADINIT
RESETACC
HOLDTIME
BFI_3P
ERROR
TRIPACC
TRIPCONT
STRORHLD
ACCTIME
ACCALARM
FREQOK FREQOK
Comparator
V
01
<= VHighLimit
AND
V
01
>= VLowLimit
VOLTOK
VOLTOK
TRIP
FREQ
Accumulation time
counter
Continuous time
counter
AND
Pickup & Trip
Output Logic
FREQ
PICKUP
LASTEVTD
ANSI12000609 V1 EN-US
Figure 369: Logical diagram
To achieve a proper operation, the set frequency high limit should be more than the set frequency
low limit. To avoid malfunction, a check is performed that
FreqHighLimit
is greater than
FreqLowLimit
. If not, the ERROR signal is activated.
FTAQFVR (81A) can be instantiated with one or more frequency ranges according to the turbine
manufacturer's specification. When the frequency falls in to the common zone when two frequency
ranges overlap it is necessary to block one instance and keep only one instance of FTAQFVR (81A)
active. The STRORHLD output is activated when either the BFI_3P output is active or when the
HOLDACC input signal is on. The STRORHLD output is connected to the input HOLDACC of the other
instance of FTAQFVR (81A).
Section 10 1MRK 502 066-UUS B
Frequency protection
684
Technical manual
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