Arcteq AQ-C255, Инструкция по эксплуатации

Страница: 304 / 420

5.5 Monitoring functions
5.5.1 Current transformer supervision
The current transformer supervision function (abbreviated CTS in this document) is used for monitoring
the CTs as well as the wirings between the device and the CT inputs for malfunctions and wire breaks.
An open CT circuit can generate dangerously high voltages into the CT secondary side, and
cause unintended activations of current balance monitoring functions.
Figure. 5.5.1 - 153. Secondary circuit fault in phase L1 wiring.
The function constantly monitors the instant values and the key calculated magnitudes of the phase
currents. Additionally, the residual current circuit can be monitored if the residual current is measured
from a dedicated residual current CT. The user can enable and disable the residual circuit monitoring at
will.
The blocking signal and the setting group selection control the operating characteristics of the function
during normal operation, i.e. the user or user-defined logic can change function parameters while the
function is running.
The function uses a total of eight (8) separate setting groups which can be selected from one common
source.
The operational logic consists of the following:
• input magnitude processing
• threshold comparator
• block signal check
• time delay characteristics
• output processing.
The following conditions have to met simultaneously for the function alarm to activate:
• None of the three-phase currents exceeds the I
set
high limit setting.
• At least one of the three-phase currents exceeds the I
set
low limit setting.
• At least one of the three-phase currents are below the
I
set
low limit setting.
• The ratio between the calculated minum and maximum of the three-phase currents is below
the I
set
ratio setting.
A AQ Q-C255 -C255
Instruction manual
Version: 2.06
302 © Arcteq Relays Ltd
IM00035