AZT-9
14
ZPrAE Sp. z o.o.
4.2. Control of current circuit continuity (CTS)
Control of current circuit continuity is performed by measuring negative sequence to
positive sequence ratio.
This solution makes the measurement result insusceptible to the
values of current in measuring circuits. When values of current in three phases are similar
the ratio of negative sequence I2 to positive sequence is close to 0. In case of conductor
damage (current loss in one of the phases) this ratio increases rapidly. It makes it possible
to find the conductor damage and generate an alarm on a properly configured relay or
trigger the protection.
The following parameters can be set to execute CTS:
-
Threshold I2/I1
– energising threshold for negative sequence component
expressed as a percentage of positive sequence component.
-
Time tdel
– time delay between energising and activation of protection.
4.3. Breaker failure protection.
The AZT-9 protection device is equipped with an input that enables triggering of
energy storages by an external signal. The input is active irrespective of the supply mode
(by instrument transformers, auxiliary power supply). Thanks to the additional current
criterion and configuration of delay time the input can perform a function of breaker failure
protection.
Breaker failure protection can be set to the following values:
- Energising threshold – current value from current criterion necessary to activate breaker
failure protection,
- Time tdel – time delay between energising the input (when the current criterion is met)
and activation of protection,
- Time tres – reset time, time to the reset of operation time delay after energising signal
fades out. In case of operation and disappearance of energising signal – release time.
4.4. Detection of oversaturation of an instrument transformer (SAT)
Detection of oversaturation of an instrument transformer operates based on the
change of curve shape at the instrument transformer output in case of oversaturation. After
3 ms from the detection of maximum amplitude of a signal a window of oversaturation
detection is activated. Detection of oversaturation of the instrument transformer starts if the
oversaturation detection window is below the half of the maximum value of amplitude and
when the change of a signal in the oversaturation detection window is lower than ¼ of the
maximum value of amplitude.
Fig. 4.1. Example of instrument transformer oversaturation curve.
