ABB RELION REX640, Техническое руководство, Страница: 1334 / 1960

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 fuse failure detection for that phase is not possible until the voltage
returns above the setting value.
Decision logic
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.
The fuse failure detection outputs
FUSEF_U
and
FUSEF_3PH
are controlled
according to the detection criteria or external signals.
Table 1275: Fuse failure output control
Fuse failure detection criterion Conditions and function response
Negative-sequence criterion If a fuse failure is detected based on the neg-
ative sequence criterion, the
FUSEF_U
out-
put is activated.
If the fuse failure detection is active for more
than five seconds and at the same time all
the phase voltage values are below the set
value of the
Seal in voltage
setting with
Ena-
ble seal in
turned to "True", the function acti-
vates the
FUSE_3PH
output signal.
Table continues on the next page
Supervision functions 1MRS759142 F
1334 REX640
Technical Manual