Inrush-Current Detection (87T-HB2)
When a transformer is switched on, an inrush current with a DC component flows, since the flow cannot
change itself instantaneously. The inrush current develops in all phases and appears immediately as differen-
tial current. The direct-current time constant can amount to several seconds with large transformers. The
following figure shows typical waveforms.
Inrush current also flows when a parallel transformer is switched in (sympathetic inrush) or after clearance of
an external fault (recovery inrush).
Inrush current is detected by measurement of 2nd harmonic current as this is at a high level in the inrush
current. If the proportion of the 2nd harmonic exceeds the setting value blocking occurs. The harmonics
develop differently in the different phases. If high 2nd harmonic current is detected in any phase, it may be
necessary to block all phases simultaneously.
[dw_7SR5_function87TStructureOfTheFunction3, 1, en_US]
Figure 5-50
Typical Inrush Current Curve
If a transformer is operated with a voltage that is too high, it can be modulated up into the non-linear part of
the magnetization characteristic curve. An increased magnetizing current i.e. differential current results and
this can lead to protection mal-operation.
Protection and Automation Functions
5.22 87T Transformer Differential Protection
Reyrolle 7SR5, Transformer Protection Device, Device Manual
309
C53000-G7040-C015-1, Edition 11.2019
Содержание Reyrolle 7SR5
Страница 8: ...8 Reyrolle 7SR5 Transformer Protection Device Device Manual C53000 G7040 C015 1 Edition 11 2019 ...
Страница 24: ...24 Reyrolle 7SR5 Transformer Protection Device Device Manual C53000 G7040 C015 1 Edition 11 2019 ...
Страница 132: ...132 Reyrolle 7SR5 Transformer Protection Device Device Manual C53000 G7040 C015 1 Edition 11 2019 ...
Страница 142: ...142 Reyrolle 7SR5 Transformer Protection Device Device Manual C53000 G7040 C015 1 Edition 11 2019 ...
Страница 338: ...338 Reyrolle 7SR5 Transformer Protection Device Device Manual C53000 G7040 C015 1 Edition 11 2019 ...