Setting The Rated Current For The Protected Unit - ABB REM 543 Technical Reference Manual

ABB Network Partner
4.1.5.1.
REM 543 Protection,
Monitoring and Control
The last letter of the hardware version number specifies whether the machine terminal is
to be equipped with conventional matching transformers or with matching transformers
and sensor inputs. Refer to ordering information.
Each analogue channel is separately configured with the Relay Configuration Tool.
Both the measuring unit for each analogue channel and the type of signal to be meas-
ured are to be configured.

Setting the rated current for the protected unit

A separate scaling factor can be set for each analogue channel. The factors enable dif-
ferences between the ratings of the protected unit (generator, transformer, motor etc.)
and those of the measuring device (CTs, VTs etc.) The setting value 1.00 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 scaling the values too low will
affect 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 / I
nmd
where
Rated primary current of the measuring device (A)
I
nmd
I Rated primary current of the protected unit connected to the channel
np
Example:
Rated primary current of current trafo = 500 A:
Rated current of motor = 250 A:
Scaling factor for current channels:
The scaling factor is used for scaling regardless of the signal type connected to the ana-
logue channel.
The scaling factors for the analogue channels can be set via the MMI of the relay or
with the Relay Setting Tool. The MMI path for the scaling factors is: Main Menu/ Con-
figuration/ Protected Unit/ Ch 1: scaling, Ch 2 scaling...
Technical Reference Manual
np
Part 1, General
I = 500 A
nmd
I = 250 A
np
500 A / 250 A = 2.00
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