Measurement Voltage Failure Detection - Siemens siprotec SJ62 User Manual

2 Functions

2.11.1.5 Measurement Voltage Failure Detection

Requirements
Purpose of the
Fuse Failure
Monitor
Functionality
189
Verification of the voltage phase rotation is done when each measured voltage is at
least
| V |, |V |, |V | > 40 V/√3.
A B C
Verification of the current phase rotation is done when each measured current is at
least:
|I |, |I |, |I | > 0.5 I .
A B C N
For abnormal phase sequences, the messages „Fail Ph. Seq. V" or „Fail Ph.
Seq. I" are issued, along with the switching of this message „Fail Ph. Seq.".
For applications in which an opposite phase sequence is expected, the protective
relay should be adjusted via a binary input or a programmable setting. If the phase se-
quence is changed in the device, phases B and C internal to the relay are reversed,
and the positive and negative sequence currents are thereby exchanged (see also
Section 2.21.2). The phase-related messages, malfunction values, and measured
values are not affected by this.
The function measurement voltage failure detection, in given briefly „Fuse Failure
Monitor" (FFM), only operates under the following condition.
• Three phase-to-ground voltages are connected; with phase-phase voltages and V
or single-phase connection, the function is disabled, as monitoring cannot occur.
In case of a measuring voltage failure caused by a fault or a broken wire in the voltage
transformer secondary system, zero voltage may be "seen" by individual measuring
loops. The displacement voltage element of the sensitive ground fault detection, the
undervoltage protection and the synchronization function in the 7SJ64 can thereby
acquire incorrect measuring results.
In grounded systems, the function „Fuse Failure Monitor" (FFM) can take effect,
unless three phase-to-ground voltages are connected to the device. Of course, super-
vision of the miniature circuit breaker and the Fuse Failure Monitor can be used at the
same time.
Depending on the settings and the MLFB, the FFM operates with the measured or the
calculated values V or I
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current being registered simultaneously, then there is an asymmetrical fault in the sec-
ondary circuit of the voltage transformer. The displacement voltage element of the
sensitive ground fault detection, the directional time overcurrent protection (phase and
ground function), the undervoltage protection and the synchronization function in the
7SJ64 are blocked. The latter, however is not blocked if Direct CO is selected and
therefore no measurement is required.
Note
On systems where the ground fault current is very small or absent (e.g. ungrounded
supply transformers), fuse failure monitoring must not be used!
. If zero sequence voltage occurs without a ground fault
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SIPROTEC 4, 7SJ62/63/64 Handbuch
C53000-G1140-C147-A, Edition 07.2015
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