Siemens SIPROTEC 7SD610 Manual page 164

Functions
2.11 Undervoltage and Overvoltage Protection (optional)
Note
For overvoltage protection it is particularly important to observe the setting notes: NEVER set an overvoltage
stage (U , U
L-E
permanent pickup which cannot be reset by any measured value operation. As a result, operation of the device
would be impossible!
Phase-to-earth overvoltage
The phase voltage stages can be switched ON or OFF in address 3701 Uph-e>(>). In addition to this, you can
set Alarm Only, i.e. these stages operate and send alarms but do not generate any trip command. The setting
U>Alarm U>>Trip creates in addition also a trip command only for the U>> stage.
The settings of the voltage threshold and the timer values depend on the type of application. To detect steady-
state overvoltages on long lines carrying no load, set the Uph-e> stage (address 3702) to at least 5 % above
the maximum stationary phase-to-earth voltage expected during operation. Additionally, a high dropout to
pickup ratio is required (address 3709 Uph-e>(>) RESET = presetting). This parameter can only be changed
in DIGSI at Display Additional Settings. The delay time T Uph-e> (address 3703) should be a few seconds
so that overvoltages with short duration do not cause tripping.
>> stage (address 3704) is provided for high overvoltages with short duration. Here an adequately high
The U
ph
pickup value is set, e.g. the 1
delay time T Uph-e>> (address 3705).
Phase-to-phase overvoltage
Basically, the same considerations apply as for the phase voltage stages. These stages can be used instead
of the phase voltage stages or additionally. Depending on your choice, set address 3711 Uph-ph>(>) to ON,
OFF, Alarm Only or U>Alarm U>>Trip.
As phase-to-phase voltages are monitored, the phase-to-phase values are used for the settings Uph-ph> (ad-
dress 3712) and Uph-ph>> (address 3714).
For the delay times T Uph-ph> (address 3713) and T Uph-ph>> (address 3715) the same considerations
apply as above. The same is true for the dropout ratios (address 3719 Uphph>(>) RESET). The latter setting
can only be altered in DIGSI at Display Additional Settings.
Overvoltage positive sequence system U
You can use the positive sequence voltage stages instead of or in addition to previously mentioned overvoltage
stages. Depending on your choice, set address 3731 U1>(>) to ON, OFF, Alarm Only or U>Alarm
U>>Trip.
For symmetrical voltages an increase of the positive sequence system corresponds to an AND gate of the volt-
ages. These stages are particularly suited to the detection of steady-state overvoltages on long, weak-loaded
transmission lines (Ferranti effect). Here too, the U1> stage (address 3732) with a longer delay time T U1>
(address 3733) is used for the detection of steady-state overvoltages (some seconds), the U1>> stage (ad-
dress 3734) with the short delay time T U1>> (address 3735) is used for the detection of high overvoltages
that may jeopardise insulation.
Note that the positive sequence system is established according to its defining equation
U = ·|U + a·U
1
/
1 L1
3
If the voltage at the remote line end is to be decisive for overvoltage detection, you can use the compounding
feature. This requires that address 137 U/O VOLTAGE is already set to Enabl. w. comp. (enabled with
compounding) when configuring the protection functions (Section 2.1.1.2).
164
, U ) lower than an undervoltage stage. This would put the device immediately into a state of
L-L 1
1
/ -fold of the nominal phase-to-earth voltage. 0.1 s to 0.2 s are sufficient for the
2
1
2
+ a ·U |. For symmetrical voltages this is equivalent to a phase-to-earth voltage.
L2 L3
SIPROTEC, 7SD610, Manual
C53000-G1176-C145-6, Release date 02.2011