Functions
2.16 Underexcitation (Loss-of-Field) Protection (ANSI 40)
SIPROTEC, 7UM62, Manual
C53000-G1176-C149-7, Release date 03.2010
142
Delay Times
If the static limit curve consisting of the characteristics 1 and 2 is exceeded, the voltage regulator must first have
the opportunity of increasing the excitation. For this reason, a warning message due to this criterion is "long-
time" delayed (at least 10 s for 3004 T CHAR. 1 and 3007 T CHAR. 2).
If the excitation voltage is missing or too low, the rotor criterion picks up as well, provided that the excitation
voltage request feature has been enabled at address 3012 EXCIT. VOLT. ON and under address 3013 the
parametrized threshold Uexcit. < is undershot or the absence of the excitation voltage has been signalled
to the device by binary input. In all these cases tripping is possible with a short delay. This feature is set via
parameter 3011 T SHRT Uex<. The following messages and trip commands are typically assigned:
Table 2-8 Setting the Underexcitation Protection
Note
If very short time delays are selected, dynamic balancing procedures may cause unwanted operations. For this
reason, it is recommended to set time values of 0.05 s or higher.
Excitation Voltage Query
The excitation voltage monitoring feature is set to approx. 50 % of the no-load excitation voltage. If the gener-
ator is used for phase-shifting, an even lower pickup value must be chosen, depending on the application in
hand. It should also be noted that normally a voltage divider is connected between the device and the excitation
voltage.
with
U
Exc 0
No-load excitation voltage,
VD
Ratio
Voltage divider transformation ratio
Example:
U
Exc N
= 110 V
U
Exc 0
= 40 V
VD
Ratio
= 10 : 1
Characteristic 1 and 2 static stability undelayed Annunciation:
Exc < Anr
Characteristic 1 and 2 static stability long-time delayed
T CHAR. 1 = T CHAR. 2 ≈ 10 s
Trippings
Err<1 TRIP / Err<2 TRIP
Characteristic 1 and 2 Excitation Voltage
Failure
short–time delayed
T SHRT Uex< ≈ 1.5 s
Tripping
Err< UPU < TRIP
Characteristic 3 dynamic stability short–time delayed
T CHAR 3 ≈ 0.5 s
Tripping
Exc<3 TRIP
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