ABB RELION REX640 Technical Manual page 1235

1MRS759142 C
REX640
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 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 Min Op voltage
delta setting. If a voltage in a phase is below the Min Op voltage delta setting, a new
Section 6
Supervision functions
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