ABB REG670 - Monitored Data

10.4.6 Monitored data
Table 324: FTAQFVR Monitored data
Name
Type Values (Range) Unit Description
FREQ REAL - Hz Measured frequency
value
ACCTIME REAL - s Accumulated time for
frequency band limits
LASTEVTD REAL - - Accumulation time for
last event of frequency
within band
10.4.7 Operation principle
Frequency time accumulation protection function FTAQFVR is used to protect the
turbine against an abnormal frequency operation. During the startup and shutdown of
the turbine-generator set, FTAQFVR is blocked to avoid unnecessary accumulation
of time or tripping of generator. FTAQFVR 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 is explained
in Figure 270.
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 START signals are activated. The START
signal is controlled by the measured current and voltage input magnitude and the
status of the circuit breaker position.
FTAQFVR function will block START 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 function will be blocked
when the measured current magnitude drops below the setting CurrStartLevel
and CBOPEN input is high. FTAQFVR 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 START 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 START output will be blocked if the EnaVoltCheck setting is enabled and the
system positive sequence voltage is not within the voltage band limits.
Section 10 1MRK502052-UEN B
Frequency protection
560
Technical manual