hager hw+, Руководство пользователя

Страница: 85 / 120

85
6LE007331A
Alarm management
11.1 Overload pre-alarm PTA
The Sentinel trip unit is used to manage 4 types of alarms:
• Overload pre-alarm PTA
• Overload alarm
• Trip alarm
• System alarm
Sentinel electronic trip units are configured to signal an overload pre-alarm to warn that the
load current is approaching a programmed trip threshold (90% of Ir). Preventive measures
(load-shedding, maintenance, etc.) can then be taken before the circuit breaker trips and thus
avoid any power outage.
The overload pre-alarm PTA is defined by two parameters:
• The PTA threshold equivalent to 90% Ir
• The PTA time delay equivalent to 50% tr
It is activated for a load current when the intensity and duration falls in a pre-trip warning
zone .
Overload pre-alarm zones
This pre-trip warning zone is bounded on one hand by the threshold and time delay of the
PTA overload pre-alarm and on the other hand by the Ir pick-up and tsd time delay.
The
pre-warning monitoring zone starts from the PTA threshold. Any load current which
appears in the monitoring zone is taken into account in the form of a thermal image of the
current and increases as the load of the Sentinel trip unit increases.
t
tr
tsd
6xIr Ii / Isd I
50% tr
90% Ir
PTA
50% tr
90% Ir
Normal load zone
Pre-warning monitoring zone
Pre-trip warning zone