ABB Relion 670 Series RES670, Technical Manual

Page: 322 / 888

Frequency time accumulation protection function FTAQFVR (81A) is used to protect the
turbine against an abnormal frequency operation. During the startup and shutdown of the
turbine-generator set, FTAQFVR (81A) is blocked to avoid unnecessary accumulation of
time or tripping of generator. FTAQFVR (81A) is also blocked when the system positive-
sequence voltage magnitude deviates from the given voltage band limit, which can be
enabled with the
EnaVoltCheck setting. The overall logic of FTAQFVR (81A) is
explained in Figure 109 .
The frequency of the measured input voltage is monitored continuously and compared to
the set frequency band limits
FreqHighLimit and FreqLowLimit . When the measured
system frequency is above the FreqLowLimit setting and below the FreqHighLimit
setting, the
FREQOK
and
PICKUP
signals are activated. The
BFI_3P
signal is controlled
by the measured current and voltage input magnitude and the status of the circuit breaker
position.
FTAQFVR (81A) function will block
BFI_3P
signal activation and Accumulation of
time under two following conditions even if the system frequency falls within set band
limits.
• When the generator is not synchronized as indicated by the
CBOPEN
signal input:
Generator currents are considered to detect whether the generator is supplying its unit
auxiliary supply transformers or not. FTAQFVR (81A) function will be blocked
when the measured current magnitude drops below the setting
PickupCurrentLevel
and
CBOPEN
input is high. FTAQFVR (81A) remains blocked until the generator
returns to the operation condition. It can be verified by using the
CBCLOSE
signal.
Generator's start and stop detection logics for the
BFI_3P
output can be ignored by
disabling the CBCheck setting.
• When the positive-sequence voltage of the measured input voltage is outside the band
limit.
The
BFI_3P
output will be blocked if the EnaVoltCheck setting is enabled and the
system positive sequence voltage is not within the voltage band limits.
Voltage band limit check will be ignored for the
BFI_3P
output if the EnaVoltCheck
setting is disabled. The voltage band limits are set with the settings VHighLimit and
VLowLimit .
The output
VOLTOK
is activated only if the system positive-sequence voltage falls
within the voltage band limits and the EnaVoltCheck setting is enabled.
To avoid oscillations of the
BFI_3P
output signal, a hysteresis has been added with
current input comparison and voltage input comparison. It is also possible to block
FTAQFVR (81A) completely by activating the binary input
BLOCK and its function is to
reset all the binary outputs of FTAQFVR (81A) and freeze the accumulation time.
Time counters
FTAQFVR (81A) uses two time counters.
Section 10
1MRK 511 365-UUS A
Frequency protection
316 Phasor measurement unit RES670 2.1 ANSI
Technical manual