Toshiba GR200 Series Instruction Manual page 80

I c : Internal charging current
I f : Minimum internal fault current
†Note: The maximum erroneous differential current is mainly due to an internal
charging current. We shall discuss it in section 2.5.3(v). The user does not need to
consider a condition relating to the charging current flowing. This is because the
function of charging-current compensation can operate.
The user should set the same value for the [DIFL-I1] at all terminals; hence, if CT ratios
of all terminals are not identical, the user should set the [DIFL-I1] respectively so that the DIFL
characteristics of the primary side are coordinated.
Setting DIFL-I2 characteristic
(ii)
When setting [DIFL-I2], the user should have three considerations below:
(1) Maximum erroneous current generated during CT saturation upon occurrence of an
external fault. That is, the setting [DIFL-I2] should be set as small as possible; consequently,
the DIFL function does not operate undesirably by the generation of a maximum erroneous
current induced by CT saturation on the primary side when a through current flows due to an
external fault. Thereby, the user should set two times rated current (2×In†) for the [DIFL-I2].
(2) Maximum load current: A sufficient value should be set for the [DIFL-I2] such that it does
not encroach on load current.
(3) Maximum outflow current upon occurrence of an internal fault: This must be just
considered when the DIFL function operates for three-terminal double-circuit lines (‡), lines
with outer loop circuit(‡), or double-circuit lines with one-and-a-half busbar system (1.5CB‡).
That is, for the [DIFL-I2], the user should set a value larger than the possible largest value of
outflow current in case of an internal fault.
An outflow current flowing depends on the configuration or the operation in the power
system. Thus, the user has to check whether it is possible for the fault current to flow out of
the line. If so, the user must consider the influence when setting the [DIFL-I2].
†Note: The rated current (In) is defined while setting the VCT. For more information, see
the Chapter
‡Note: When the DIFL function is not used in those arrangements, the user does not
need to consider the outflow current flowing.
Setting DIFGL-I characteristic
(iii)
The user should set a value for the [DIFGL-I] by considering an earth fault current flowing in
Technical description: Transformer module for AC analog input
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6F2S1914 (0.49)
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GRL200 (Soft 033 & 037)