ABB RELION SMU615 Technical Manual page 155

1MRS758407 C
The module makes a phase-specific comparison between each voltage input and
the
corresponding phase is reported to the decision logic module.
Current and voltage delta criterion
The delta function can be activated by setting the
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
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
and the magnitude of dI/dt is below the
at the same time and the magnitude of the phase current in the same phase
exceeds the
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 SEQSPVC 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
voltage delta setting. If a voltage in a phase is below the Min Op voltage delta
setting, a new fuse failure detection for that phase is not possible until the voltage
returns above the setting value.
Decision logic
SMU615
Technical Manual
Seal in voltage setting. If the input voltage is lower than the setting, the
Min Op current delta setting.
If voltages are Wye-connected, it is recommended to scale the default
values of voltage-based settings with 1/sqrt(3) because the default
setting values apply for Delta-connected settings.
Supervision functions
Change rate enable parameter
Voltage change rate setting
Current change rate setting in any phase
Voltage change
Min Op
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