Description
2.8 Electronic trip unit ETU
3VA27 molded case circuit breakers & 3WL10 air circuit breakers
Manual, 10/2018, L1V30499596002-01
63
Thermal memory
The electronic trip units have a thermal memory for the overload protection function (LT) to
protect equipment from overheating due to overload.
The thermal memory maps the circuit breaker's thermal state as determined by the load
current. It shortens the delay time of the protection function, considering the existing thermal
load of the circuit breaker. This can be the case after fast reclosure of the circuit breaker
following an overload trip. The size of the overcurrent that caused the trip and therefore the
amount of overheating is considered.
The thermal memory can be disabled on electronic trip units of the 6-series. The thermal
memory should remain activated in normal operation. It is the responsibility of the
commissioning engineer/company operating the installation to provide additional thermal
overload protection for the downstream power distribution system while the thermal memory
is deactivated.
Enhanced protection functions expanded with the MF Advanced metering module for ETUs of the
6-series.
The protection functionalities of the ETUs of the 6-series can be enhanced if the ETU is
expanded with the MF Advanced metering function. In this way, complex protection functions
can be generated based on simultaneous processing of current and voltage signals and the
circuit breaker becomes a central control and protection element in the installation.
The enhanced protection functions can be set to the operating modes: "closed", "only alarm"
or "open".
With open contacts, too, signals can be provided if the voltage is sensed on the line side to
detect anomalies or faults in the voltage applied before the main contacts of the circuit
breaker are closed.
Reverse active power protection: Reverse power protection (RP)
If the power flows through the device in the opposite direction to the direction of power flow
defined as 'normal,' the reverse power protection RP detects this and can trip the circuit
breaker when an operating value for the active power is exceeded. The user can freely
define the direction of power flow in the parameters.
For reverse power protection RP, the direction of the power flow is determined continuously
in the ETU based on the power factor (PF) by evaluation of the current and voltage signal
and the active and apparent power are placed in relation to each other. Based on the sign of
the PF or the phase displacement angle
φ between the current and voltage signal, deviating
or reversing power flows are identified. Besides the RP protection function, the DST
protection function is also a typical application for this.
Power factor PF
avg
- alarm
A warning signal can also be transmitted as soon as a defined deviation of the averaged
power factor PF
avg
of the 3-phase system of < 1 is reached, i.e. increasing generation of
reactive power and an undesired large phase difference between the current and voltage.
Corrective action can be derived from this (e.g. reactive power compensation).
