Hitachi Relion 670 Series Applications Manual page 418
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Also See for Relion 670 Series:
- Applications manual (354 pages) ,
- Commissioning manual (284 pages) ,
- Product manual (192 pages)
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Section 22
Requirements
recommended that the current transformer should have an accuracy class which have an current
error at rated primary current that is less than ±1% (for example, 5P). If current transformers with less
accuracy are used it is advisable to check the actual unwanted residual current during the
commissioning.
22.1.6
Rated equivalent secondary e.m.f. requirements
With regard to saturation of the current transformer all current transformers of high remanence and
low remanence type that fulfill the requirements on the rated equivalent limiting secondary e.m.f. E
below can be used. The characteristic of the non remanence type CT (TPZ) is not well defined as far
as the phase angle error is concerned. If no explicit recommendation is given for a specific function
we therefore recommend contacting Hitachi Energy to confirm that the non remanence type can be
used.
The CT requirements for the different functions below are specified as a rated equivalent limiting
secondary e.m.f. E
according to other classes and standards are given at the end of this section.
22.1.6.1
Transformer differential protection
The current transformers must have a rated equivalent limiting secondary e.m.f. E
the maximum of the required rated equivalent limiting secondary e.m.f. E
³
E
E
al
EQUATION1412 V2 EN-US
³
E
E
al
EQUATION1413 V2 EN-US
where:
I
rt
I
tf
I
pr
I
sr
I
r
R
ct
R
L
S
R
In substations with breaker-and-a-half or double-busbar double-breaker arrangement, the fault
current may pass two main CTs for the transformer differential protection without passing the power
transformer. In such cases and if both main CTs have equal ratios and magnetization characteristics
the CTs must satisfy equation
412
according to the IEC 61869-2 standard. Requirements for CTs specified
al
æ
I
=
×
×
×
sr
30 I
R
ç
alreq
rt
ct
I
è
pr
æ
I
= ×
×
×
+
sr
2 I
R
ç
alreq
tf
ct
I
è
pr
The rated primary current of the power transformer (A)
Maximum primary fundamental frequency current that passes two main CTs and
the power transformer (A)
The rated primary CT current (A)
The rated secondary CT current (A)
The rated current of the protection IED (A)
The secondary resistance of the CT (W)
The resistance of the secondary wire and additional load (W). The loop resistance
containing the phase and neutral wires must be used for faults in solidly earthed
systems. The resistance of a single secondary wire should be used for faults in
high impedance earthed systems.
The burden of an IED current input channel (VA). S
and S
=0.150 VA/channel for I
R
75
and equation 77.
© 2017 - 2023 Hitachi Energy. All rights reserved
ö
S
+
+
R
R
÷
L
2
I
ø
r
ö
S
+
R
R
÷
L
2
I
ø
r
=5 A
r
1MRK506375-UEN Rev. N
that is larger than
al
below:
alreq
=0.020 VA/channel for I
=1 A
R
r
Railway application RER670
Application manual
SEMOD53723-1 v1
M11616-3 v4
al
SEMOD54689-4 v4
(Equation 75)
(Equation 76)
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