Siemens Siprotec 7VK61 Manual page 98

Functions
2.5 Under and over-voltage protection (optional)
Overvoltage positive sequence systemU
The device calculates the positive sequence system according to its defining equation
1
U = / ·(U
1 3
j120°
where a = e
The resulting single–phase AC voltage is fed to the two threshold stages U1> and U1>> (see Figure 2-22).
Combined with the associated time delays T U1> and T U1>> these stages form a two-stage overvoltage pro-
tection for the positive sequence system. Here too, the drop-out to pick-up ratio can be set.
The overvoltage protection for the positive sequence system can also be blocked via a binary input „>U1>(>)
BLK".
Figure 2-22 Logic diagram of the overvoltage protection for the positive sequence voltage system
Single-Phase Voltage Connection
Please bear in mind that the device is designed for a three-phase voltage connection. Single-phase connection
is also possible but no adjustments have been made in this respect. This must be taken into consideration when
setting the pickup value.
Overvoltage negative sequence system U
The device calculates the negative sequence system voltages according to its defining equation:
1
U = / ·(U
2 3
j120°
where a = e
The resulting negative sequence voltage is fed to the two threshold stages U2> and U2>>. Figure 2-23 shows
the logic diagram. By combining the associated time delays T U2> and T U2>> a two-stage overvoltage pro-
tection for the negative sequence system is formed. Here too, the drop-out to pickup ratio can be set.
98
1
2
+ a·U + a ·U )
L1 L2 L3
.
2
2
+ a ·U + a·U )
L1 L2 L3
.
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009