The input signal MCBOP is supposed to be connected via a terminal binary input to the N.C.
auxiliary contact of the miniature circuit breaker protecting the VT secondary circuit. The MCBOP
signal sets the output signals BLKV and BLKZ in order to block all the voltage related functions
when the MCB is open independent of the setting of
OpModeSel
selector. The additional drop-out
timer of 150 ms prolongs the presence of MCBOP signal to prevent the unwanted operation of
voltage dependent function due to non simultaneous closing of the main contacts of the
miniature circuit breaker.
The input signal 89b is supposed to be connected via a terminal binary input to the N.C. auxiliary
contact of the line disconnector. The 89b signal sets the output signal BLKV in order to block the
voltage related functions when the line disconnector is open. The impedance protection function
is not affected by the position of the line disconnector since there will be no line currents that can
cause malfunction of the distance protection. If 89b=0 it signifies that the line is connected to the
system and when the 89b=1 it signifies that the line is disconnected from the system and the
block signal BLKV is generated.
The output BLKV can be used for blocking the voltage related measuring functions (undervoltage
protection, energizing check and so on) except for the impedance protection.
The function output BLKZ shall be used for blocking the impedance protection function.
13.2.7.2 Delta current and delta voltage detection
M13685-3 v7
A simplified diagram for the functionality is found in figure
392. The calculation of the changes of
currents and voltages is based on a sample analysis algorithm. The calculated delta quantities are
compared with their respective set values DIPU and DVPU. The algorithm detects a fuse failure if a
sufficient change in voltage without a sufficient change in current is detected in each phase
separately. The following quantities are calculated in all three phases:
• The change in voltage DV
• The change in current DI
The internal
FuseFailDetDVDI
signal is activated if the following conditions are fulfilled:
• The magnitude of the phase-ground voltage has been above VPPU for more than 1.5 cycles
(i.e. 30 ms in a 50 Hz system)
• The magnitude of DV in three phases are higher than the corresponding setting DVPU
• The magnitudes of DI in three phases are below the setting DI<
In addition to the above conditions, at least one of the following conditions shall be fulfilled in
order to activate the internal
FuseFailDetDVDI
signal:
• The magnitude of the phase currents in three phases are higher than the setting IPPU
• The circuit breaker is closed (52A = True)
The first criterion means that detection of failure in three phases together with high current for
the three phases will set the output. The measured phase current is used to reduce the risk of false
fuse failure detection. If the current on the protected line is low, a voltage drop in the system (not
caused by fuse failure) may be followed by current change lower than the setting DIPU, and
therefore a false fuse failure might occur.
The second criterion requires that the delta condition shall be fulfilled at the same time as circuit
breaker is closed. If this is an important disadvantage, connect the 52A input to FALSE , then only
the first criterion can enable the delta function.If the DVDI detection of three phases set the
1MRK 502 066-UUS B Section 13
Secondary system supervision
735
Technical manual
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