ABB RELION 620 Series Technical Manual page 611

1MAC504801-IB E
620 series ANSI
Technical Manual
• 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
line from the other end onto a fault could lead to an improper operation of the fuse failure
supervision 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
The fuse failure detection outputs FUSEF_V and FUSEF_3PH are controlled according
to the detection criteria or external signals.
Section 6
Supervision functions
605