ABB 615 series Technical Manual page 874

Section 6
Supervision functions
868
Negative phase-sequence criterion
A fuse failure based on the negative-sequence criterion is detected if the measured
negative-sequence voltage exceeds the set Neg Seq voltage Lev value and the measured
negative-sequence current is below the set Neg Seq current Lev value. The detected fuse
failure is reported to the decision logic module.
Voltage check
The phase voltage magnitude is checked when deciding whether the fuse failure is a three,
two or a single-phase fault.
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 dV/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 dV/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 dV/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
1MAC059074-MB A
615 series ANSI
Technical Manual