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Technical Reference Manual, General
5()B
33
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A separate scaling factor can be set for each analogue 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
1
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 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 factor is not used for general measurement signals
connected to the analogue channel.
The scaling factors for the analogue channels can be set via the HMI of the feeder
terminal or with the Relay Setting Tool. The HMI path for the scaling factors is:
Main Menu/ Configuration/ Protected unit/ Ch 1: scaling,
Ch 2: scaling...
For storing the values listed above, refer to section “Storing of parameters and
recorded data” on page 27.
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When the feeder terminal is configured, the technical data of the measuring devices
is set in separate dialogue boxes in the Relay Configuration Tool. The set values will
affect the measurements carried out by the feeder terminal.
For storing the values listed below, refer to section “Storing of parameters and
recorded data” on page 27.
1. Prior to the Release 2.5 with two decimals only.
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
1
!
