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2 Functions
Measured value ac-
Four measuring inputs are available in the voltage circuit: three for phase-to-earth volt-
quisition voltages
ages and one input for the displacement voltage (e-n voltage of open delta winding)
or a busbar voltage. If the displacement voltage is connected to the device, the sum
of the three digitized phase voltages must equal three times the zero sequence volt-
age. A fault in the voltage transformer circuits is detected when
The factor k
ment voltage input and the phase voltage inputs (address 211 Uph / Udelta).
This malfunction is signalled as „Fail Σ U Ph-E" (no. 165).
Note
Voltage sum monitoring is only effective if an external displacement voltage is con-
nected to the displacement voltage measuring input.
Voltage sum monitoring can operate properly only if the adaptation factor Uph /
Udelta at address 211 has been correctly configured (see Subsection 2.1.2.1).
2.15.1.2 Software Monitoring
Watchdog
For continuous monitoring of the program sequences, a time monitor is provided in the
hardware (watchdog for hardware) that expires upon failure of the processor or an in-
ternal program, and causes a reset of the processor system with complete restart.
An additional software watchdog ensures that malfunctions during the processing of
programs are discovered. This also initiates a restart of the processor system.
If a fault is not removed by the restart of the processors, a new restart is attempted. If
the fault is still present after three restart attempts within 30 s, the protection system
will take itself out of service, and the red LED „Blocked" lights up. The Device OK
relay drops off and signals the malfunction by its „life contact".
2.15.1.3 Measurement Circuit Monitoring
Interruptions or short-circuits in the secondary circuits of the current and voltage trans-
formers, as well as faults in the connections (important for commissioning!), are de-
tected and reported by the device. To this end, the measured values are cyclically
checked in the background as long as no fault detection is present.
Current Symmetry
In healthy network operation it can be expected that the currents will be approximately
balanced. The monitoring of the measured values in the device checks this balance.
The smallest phase current is compared with the largest. Non-symmetry is detected
when
I
BAL. FACTOR I (address 2905) represents the allowable asymmetry of the phase
currents while the limit value BALANCE I LIMIT (address 2904) is the lower limit of
the operating range of this monitoring (see Figure 2-81). The dropout ratio is about
97%.
200
U
= |U
+ U
+ U
+ k
F
L1
L2
L3
allows for a difference of the transformation ratio between the displace-
U
| < BAL. FACTOR I as long as I
| / | I
|I
min
max
is the highest, I
the lowest of the three phase currents. The symmetry factor
max
min
·U
| > 25 V.
U
EN
max
> BALANCE I LIMIT / I
/ I
N
7SD610 Manual
C53000-G1176-C145-4
N
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