General; Requirements On Voltage Instrument Transformers; Requirements On Current Instrument Transformers; Choice Of Current Transformers - ABB REC 561 User Manual

ABB Network Partner AB
Version 1.0-00
October 1996
Function:

1 General

2 Requirements on voltage instrument transformers

3 Requirements on current instrument transformers

3.1 Choice of current
transformers
3.2 Conditions for the CT
requirements
Requirements and basic technical
data - REC 561
Basic
As an option, the REC 561 control terminal can include protection func-
tions, for example, breaker failure protection. The operation of a protec-
tion measuring function is influenced by distortion, so you must take
measures in the protection function to handle this phenomenon. One
source of distortion is current transformer saturation. In this control termi-
nal, take measures to allow for a certain amount of CT saturation with
maintained correct operation. This terminal can allow relatively heavy
current transformer saturation.
Protection functions are also affected by transients caused by capacitive
voltage transformers (CVTs). But because this terminal has a very effec-
tive filter for these transients, the operation is hardly affected.
You can use magnetic or capacitive voltage transformers.
Capacitive voltage transformers should fulfil the requirements according
to IEC 186A, Section 20, regarding transients. According to the standard,
the secondary voltage should drop to less than 10% of the peak value
before the short circuit within one cycle.
The terminal has an effective filter for this transient, which gives secure
and correct operation with CVTs.
Use the TPX or TPY current transformer — with an accuracy class of 5P
or better. The characteristic of the linearized TPZ current transformer type
is not well defined as far as the phase angle error is concerned. So contact
ABB Network Partner for confirmation that you can use the type.
Select the current transformer ratio so that the current to the protection
function is higher than the minimum operating value for all faults that are
to be detected. The minimum operating current for the protection function
is 20% of the nominal current.
The requirements for the protection functions are a result of tests per-
formed in a network simulator. The tests were made with an analogue cur-
rent transformer model with a settable core area, a core length, an air gap,
and several primary and secondary turns. The setting of the current trans-
former model was representative for TPX and TPY current transformers.
The results are not valid for TPZ.
1MRK 580 147-XEN
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