Table of Contents
Advertisement
Requirements
5HTXLUHPHQWV
7UDQVIRUPHUV
*HQHUDO
The operation of a protection measuring function is influenced by distortion and mea-
sures need to be taken in the protection to handle this phenomenon. One source of dis-
tortion is current transformer saturation. In this protection terminal, measures are taken
to allow for a certain amount of CT saturation with maintained correct operation. This
protection terminal can allow relatively heavy current transformer saturation.
Protection functions are also affected by transients caused by capacitive voltage trans-
formers (CVTs) but as this protection terminal has a very effective filter for these tran-
sients, the operation is hardly affected at all.
9ROWDJH WUDQVIRUPHUV
Magnetic or capacitive voltage transformers can be used.
Capacitive voltage transformers (CVTs) should fulfil the requirements according to
IEC 186A, Section 20, regarding transients. According to the standard, at a primary
voltage drop down to zero, the secondary voltage should drop to less than 10% of the
peak pre-fault value before the short circuit within one cycle.
The protection terminal has an effective filter for this transient, which gives secure and
correct operation with CVTs.
&XUUHQW WUDQVIRUPHUV
&ODVVLILFDWLRQ
The performance of the REx 5xx terminal depends on the conditions and the quality of
the current signals fed to it. The terminal REx 5xx has been designed to permit relative-
ly heavy current transformer saturation with maintained correct operation. To guarantee
correct operation, the CTs must be able to correctly reproduce the current for a mini-
mum time before the CT will begin to saturate. To fulfil the requirement on a specified
time to saturation the CTs must fulfil the requirements of a minimum secondary e.m.f.
that is specified below.
There are several different ways to specify CTs. Conventional magnetic core CTs are
usually specified and manufactured according to some international or national stan-
dards, which specify different protection classes as well. However, generally there are
three different types of current transformers:
•
high remanence type CT
&KDSWHU
*HQHUDO
11
Advertisement
Table of Contents
