Conditions - ABB RELION 670 SERIES Applications Manual

1MRK 506 369-UUS -
25.1.2
Line distance protection REL670 2.2 ANSI
Application manual
high remanence level in a protection core CT can cause the following problems for
protection IEDs:
1. Unwanted operation of differential (i.e. unit) protections for external faults
2. Unacceptably delayed or even missing operation of all types of protections (for
example, distance, differential, overcurrent, etc.) which can result in loosing
protection selectivity in the network
No information is available about how frequent the use of the new iron core material is for
protection CT cores, but it is known that some CT manufacturers are using the new
material while other manufacturers continue to use the old traditional core material for
protection CT cores. In a case where VHR type CTs have been already installed, the
calculated values of E for HR type CTs, for which the formulas are given in this
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document, must be multiplied by factor two-and-a-half in order for VHR type CTs (i.e.
with new material) to be used together with ABB protection IEDs. However, this may
result in unacceptably big CT cores, which can be difficult to manufacture and fit in
available space.
Different standards and classes specify the saturation e.m.f. in different ways but it is
possible to approximately compare values from different classes. The rated equivalent
limiting secondary e.m.f. E
CT requirements for the IED. The requirements are also specified according to other
standards.

Conditions

The requirements are a result of investigations performed in our network simulator. The
current transformer models are representative for current transformers of high remanence
and low remanence type. The results may not always be valid for non remanence type CTs
(TPZ).
The performances of the protection functions have been checked in the range from
symmetrical to fully asymmetrical fault currents. Primary time constants of at least 120 ms
have been considered at the tests. The current requirements below are thus applicable both
for symmetrical and asymmetrical fault currents.
Depending on the protection function phase-to-ground, phase-to-phase and three-phase
faults have been tested for different relevant fault positions for example, close in forward
and reverse faults, zone 1 reach faults, internal and external faults. The dependability and
security of the protection was verified by checking for example, time delays, unwanted
operations, directionality, overreach and stability.
The remanence in the current transformer core can cause unwanted operations or minor
additional time delays for some protection functions. As unwanted operations are not
acceptable at all maximum remanence has been considered for fault cases critical for the
according to the IEC 61869–2 standard is used to specify the
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Section 25
Requirements
917