Table 383: SAPTUF (81L) Non group settings (basic)
Name Values (Range) Unit Step Default Description
GlobalBaseSel 1 - 12 - 1 1 Selection of one of the Global Base Value
groups
10.1.6 Monitored data
PID-3901-MONITOREDDATA v6
Table 384: SAPTUF (81L) Monitored data
Name Type Values (Range) Unit Description
VLevel REAL - kV Level of measured voltage
FREQ REAL - Hz Measured frequency
10.1.7 Operation principle
M13354-3 v8
Underfrequency protection SAPTUF (81) is used to detect low power system frequency. SAPTUF
(81) can either have a definite time delay or a voltage magnitude dependent time delay. If the
voltage magnitude dependent time delay is applied, the time delay will be longer if the voltage is
higher, and the delay will be shorter if the voltage is lower. If the frequency remains below the set
value for a time period corresponding to the chosen time delay, the corresponding trip signal is
issued. To avoid an unwanted trip due to uncertain frequency measurement at low voltage
magnitude, a voltage controlled blocking of the function is available from the preprocessing
function, that is, if the voltage is lower than the set blocking voltage in the preprocessing function,
the function is blocked and no PICKUP or TRIP signal is issued.
10.1.7.1 Measurement principle
M13354-6 v7
The fundamental frequency of the measured input voltage is measured continuously, and
compared with the set value,
PUFrequency
. The frequency function is dependent on the voltage
magnitude. If the voltage magnitude decreases below the setting
MinValFreqMeas
in the SMAI
preprocessing function, which is described in the Basic IED Functions chapter and is set as a
percentage of a global base voltage parameter, SAPTUF (81) gets blocked, and the output
BLKDMAGN is issued. All voltage settings are made in percent of the setting
VBase
, which should
be set as a phase-phase voltage in kV.
To avoid oscillations of the output PICKUP signal, a hysteresis has been included.
10.1.7.2 Time delay
M13354-10 v8
The time delay for underfrequency protection SAPTUF (81) can be either a settable definite time
delay or a voltage magnitude dependent time delay, where the time delay depends on the voltage
level; a high voltage level gives a longer time delay and a low voltage level causes a short time
delay. For the definite time delay, the setting
tDelay
sets the time delay.
For the voltage dependent time delay the measured voltage level and the settings
VNom
,
VMin
,
Exponent
,
t_MaxTripDelay
and
t_MinTripDelay
set the time delay according to figure 362 and
equation . The setting
TimerOperation
is used to decide what type of time delay to apply.
1MRK 502 066-UUS B Section 10
Frequency protection
667
Technical manual
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