ABB RET 54 Series, Техническое справочное руководство, общее

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1MRS755225 Transformer Terminal
Technical Reference Manual, General
RET 54_
39
5.1.6.1. Scaling the rated values of the protected unit for analog
channels
A separate scaling factor can be set for each analog channel. The factors enable
differences between the ratings of the protected unit and those of the measuring
device (CTs, VTs etc.) The setting value 1.000 means that the rated value of the
protected unit is exactly the same as that of the measuring device.
When scaling factors are used, it should be noted that they affect the operation
accuracy and the dynamic measuring range of the terminal. The accuracies stated in
the description of each function block (CD-ROM “Technical Descriptions of
Functions”) only apply with the default values of the scaling factors. For example,
a high factor affects the operation of sensitive protection functions, such as the
directional earth-fault protection.
The scaling factor is calculated channel by channel as follows:
Scaling factor = I
nmd
/ I
np,
where
Example:
The scaling factors for the analog channels can be set via the HMI of the transformer
terminal or with the Relay Setting Tool. The HMI path for the scaling factors is:
Main Menu/ Configuration/ Protected unit/ Ch 2: scaling,
Ch 3: scaling...
For storing the values listed above, refer to Section “Storing of parameters and
recorded data” on page 36.
5.1.6.2. Technical data of the measuring devices
When the transformer terminal is configured, the technical data of the measuring
devices is set in separate dalog boxes in the Relay Configuration Tool. The set
values will affect the measurements carried out by the transformer terminal.
For storing the values listed below, refer to Section “Storing of parameters and
recorded data” on page 36.
I
nmd
Rated primary current of the measuring device (A)
I
np
Rated primary current of the protected unit connected to the channel
Rated primary current of current trafo = 500 A: I
nmd
= 500 A
Rated current of the protected unit = 250 A: I
np
= 250 A
Scaling factor for current channels: 500 A / 250 A = 2.000
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