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3 Operation Theory
PCS-978 Transformer Relay
3-23
Date: 2013-01-16
usually an internal fault, so blocking mode 2 can ensure differential protection operate correctly if
there is an internal fault in situation 4.
3) The difference between blocking mode 1 and 2 is the operation of differential protection in
situation 3. Situation 3 may be an internal fault or inrush current, blocking mode 1 can distinguish
through its perfect criteria (refer to manual for details). Therefore, we recommend user to use
blocking mode 1, i.e. self-adaptive blocking mode.
Users can select blocking mode 1 or blocking mode 2 in PCS-978 according to their requirements.
3.2.3.12 CT Saturation Detection
There are two CT saturation conditions, i.e. transient CT saturation and stable CT saturation. If an
external fault or an inter fault occurs, primary current of CT increases greatly and secondary
current of CT consists of fundamental component, DC component and harmonic component. The
decaying DC component results in remanent magnetism in magnetic core, and with the
accumulation of remanent magnetism CT goes into CT saturation state called transient CT
saturation. With the time passed, the DC component decays to zero almost and CT is still
saturated caused by AC excitation, which is called stable CT saturation.
According to our lab tests, it is found that the second harmonic component is greater than the third
harmonic component at CT transient saturation stage and the third harmonic is greater than the
secondary harmonic at the CT stable saturation stage. Therefore, the second and third harmonics
both can be used to detection CT saturation.
In order to prevent an unwanted operation of sensitive biased differential protection caused by
transient or steady state saturation of CT during an external fault, the second and third harmonics
of secondary current of individual CTs are used for the protection equipment to discriminate
saturation of three-phase CT. If CT saturation is detected, then sensitive biased differential
element will be blocked.
st
xb
sat
rd
st
xb
sat
nd
I
K
I
I
K
I
1
_
3
_
3
_
1
_
2
_
2
_
Equation 3.2-16
Where:
st
I
1
_
is the fundamental component of one phase current of some side.
nd
I
2
_
is the secondary harmonic of the same phase current.
rd
I
3
_
is the third harmonic of the same phase current.
xb
sat
xb
sat
K
K
3
_
2
_
,
are fixed coefficients of secondary and third harmonics respectively.
If any harmonic of one phase current meets the above equation, it will be considered that it is CT
saturation to cause this phase differential current and sensitive percent differential element will be
Содержание PCS-978
Страница 1: ...PCS 978 Transformer Relay Instruction Manual NR Electric Co Ltd ...
Страница 2: ......
Страница 6: ...Preface PCS 978 Transformer Relay IV Date 2013 01 16 ...
Страница 10: ...Preface PCS 978 Transformer Relay VIII Date 2013 01 16 ...
Страница 62: ...3 Operation Theory PCS 978 Transformer Relay 3 p Date 2013 01 16 ...
Страница 250: ...4 Supervision PCS 978 Transformer Relay 4 b Date 2013 01 16 ...
Страница 264: ...4 Supervision PCS 978 Transformer Relay 4 14 Date 2013 01 16 ...
Страница 266: ...5 Management PCS 978 Transformer Relay 5 b Date 2013 01 16 ...
Страница 272: ...5 Management PCS 978 Transformer Relay 5 6 Date 2013 01 16 ...
Страница 334: ...6 Hardware Description PCS 978 Transformer Relay 6 60 Date 2013 01 16 ...
Страница 370: ...8 Human Machine Interface PCS 978 Transformer Relay 8 d Date 2013 01 16 ...
Страница 404: ...8 Human Machine Interface PCS 978 Transformer Relay 8 34 Date 2013 01 16 ...
Страница 406: ...9 Configurable Function PCS 978 Transformer Relay 9 b Date 2013 01 16 ...
Страница 446: ...10 Communication PCS 978 Transformer Relay 10 26 Date 2013 01 16 ...
Страница 448: ...11 Installation PCS 978 Transformer Relay 11 b Date 2012 10 09 ...
Страница 456: ...11 Installation PCS 978 Transformer Relay 11 8 Date 2012 10 09 ...
Страница 458: ...12 Commissioning PCS 978 Transformer Relay 12 b Date 2012 12 07 ...
Страница 468: ...12 Commissioning PCS 978 Transformer Relay 12 10 Date 2012 12 07 ...
Страница 470: ...13 Maintenance PCS 978 Transformer Relay 13 b Date 2012 10 09 ...
Страница 474: ...13 Maintenance PCS 978 Transformer Relay 13 4 Date 2012 10 09 ...
Страница 476: ...14 Decommissioning and Disposal PCS 978 Transformer Relay 14 b Date 2012 10 09 ...
Страница 478: ...14 Decommissioning and Disposal PCS 978 Transformer Relay 14 2 Date 2012 10 09 ...
Страница 480: ...15 Manual Version History PCS 978 Transformer Relay 15 2 Date 2013 01 16 ...