ABB RED615 Technical Manual page 601

1YHT530004D05 D
615 series
Technical Manual
The module makes a phase-specific comparison between each voltage input and
the Seal in voltage setting. If the input voltage is lower than the setting, the
corresponding phase is reported to the decision logic module.
Current and voltage delta criterion
The delta function can be activated by setting the Change rate enable parameter to
"True". Once the function is activated, it operates in parallel with the negative
sequence-based algorithm. The current and voltage are continuously measured in
all three phases to calculate:
• Change of voltage dU/dt
• Change of current dI/dt
The calculated delta quantities are compared to the respective set values of the
Current change rate and Voltage change rate settings.
The delta current and delta voltage algorithms detect a fuse failure if there is a
sufficient negative change in the voltage amplitude without a sufficient change in
the current amplitude in each phase separately. This is performed when the circuit
breaker is closed. Information about the circuit breaker position is connected to the
CB_CLOSED input.
There are two conditions for activating the current and voltage delta function.
• The magnitude of dU/dt exceeds the corresponding value of the Voltage
change rate setting and magnitude of dI/dt is below the value of the Current
change rate setting in any phase at the same time due to the closure of the
circuit breaker (CB_CLOSED = TRUE).
• The magnitude of dU/dt exceeds the value of the Voltage change rate setting
and the magnitude of dI/dt is below the Current change rate setting in any
phase at the same time and the magnitude of the phase current in the same
phase exceeds the Min Op current delta setting.
The first condition requires the delta criterion to be fulfilled in any phase at the
same time as the circuit breaker is closed. Opening the circuit breaker at one end
and energizing the line from the other end onto a fault could lead to an improper
operation of SEQRFUF with an open breaker. If this is considered to be an
important disadvantage, the CB_CLOSED input is to be connected to FALSE. In
this way only the second criterion can activate the delta function.
The second condition requires the delta criterion to be fulfilled in one phase
together with a high current for the same phase. The measured phase current is
used to reduce the risk of a false fuse failure detection. If the current on the
protected line is low, a voltage drop in the system (not caused by the fuse failure) is
not followed by a current change and a false fuse failure can occur. To prevent this,
the minimum phase current criterion is checked.
The fuse failure detection is active until the voltages return above the Min Op
voltage delta setting. If a voltage in a phase is below the Min Op voltage delta
Section 6
Supervision functions
595