Description
2.8 Electronic trip unit ETU
3VA27 molded case circuit breakers & 3WL10 air circuit breakers
64
Manual, 10/2018, L1V30499596002-01
DST - directed short-time protection
Directed (directional) short-time protection DST behaves like short-time-delayed short-circuit
protection (ST) except that the tripping current and the delay time depend on the direction of
power flow. The user can define which direction is the forward direction. Based on this, it is
possible to define individually the current operating values and time delays in this forward
direction (FW) and in the backward direction (BW). This ensures differently selective
behavior of the device depending on the direction of power flow.
Voltage unbalance V-NBA
The voltage unbalance protection function provides protection from unwanted unbalance of
the voltage between the phases and load unbalances in the distribution and at the load. It
can open the circuit breaker with a constant, definable delay time t
nba(U)
if a phase-to-phase
voltage (U
ph
-U
ph
) deviates by more than the set operating value U
nba
from the arithmetic
mean of the phase-to-phase voltages. The deviation of the operating value from the mean
value is stated as a percentage [%].
Underfrequency protection (f
u
)
Underfrequency protection responds with a definable definite-time delay t
u
(f) as soon as the
line frequency falls below the operating value f
u
.
The operating value is described as factor < 1 of the line frequency - settable to 50 Hz or
60 Hz.
In this way, the distribution board can be protected from impermissible deviations in the line
frequency.
Overfrequency protection (f
o
)
Overfrequency protection responds with a definable definite-time delay t
o
(f) as soon as the
line frequency exceeds the operating value f
o
.
The operating value is described as factor > 1 of the line frequency - settable to 50 Hz or
60 Hz.
In this way, the distribution board can be protected from impermissible deviations in the line
frequency.
Undervoltage protection (V
u
)
The undervoltage protection responds with a definable definite-time delay t
u
(U) as soon as a
phase-to-phase voltage (U
ph
-U
ph
) falls below the operating value U
u
.
The operating value is described as factor < 1 of the rated voltage U
n
of the power system.
The rated voltage U
n
can be variably set from 100 V to 690 V.
In this way, the distribution board can be protected from impermissible deviations in the line
voltage.
