9.1.7.4
Design
The voltage measuring elements continuously measure the three phase-to-neutral
voltages or the three phase-to-phase voltages. Recursive fourier filters or true RMS filters
of input voltage signals are used. The voltages are individually compared to the set value,
and the lowest voltage is used for the inverse time characteristic integration. A special
logic is included to achieve the
1 out of 3
,
2 out of 3
and
3 out of 3
criteria to fulfill the
PICKUP condition. The design of Two step undervoltage protection UV2PTUV (27) is
schematically shown in
.
PICKUP
PU_ST1_A
PU_ST1_B
PU_ST1_C
TRST1
PICKUP
PU_ST2
TRST2
TRIP
MinVoltSelector
Pickup
&
Trip
Output
Logic
Step 1
Pickup
&
Trip
Output
Logic
Step 2
Phase C
Phase B
Phase A
Phase C
Phase B
Phase A
Timer
t2
Voltage Phase
Selector
OpMode2
Time integrator
or Timer t1
Voltage Phase
Selector
OpMode1
1 out of 3
2 out of 3
3 out of 3
TRIP
TRIP
OR
OR
OR
OR
OR
OR
PICKUP
VA or VAB
VB or VBC
VC or VCA
Comparator
V < Pickup1
1 out of 3
2 out of 3
3 out of 3
PU_ST1
ANSI08000016-3-en.vsd
Comparator
V < Pickup1
Comparator
V < Pickup1
Comparator
V < Pickup2
Comparator
V < Pickup2
Comparator
V < Pickup2
ANSI08000016 V3 EN
Figure 132:
Schematic design of Two step undervoltage protection UV2PTUV (27)
Section 9
1MRK 502 048-UUS A
Voltage protection
286
Technical manual
