Technical Data Of The Measuring Devices - ABB REX 521 Technical Reference Manual, General

1MRS 751108-MUM
4.1.6.2.
Protection Relay
Technical Reference Manual, General
When scaling factors are used, it should be noted that they affect the operation
accuracy of the relay. The accuracies stated in the description of each function block
(in the 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 / I
nmd np,
I Rated primary current [A] of the measuring device
nmd
I Rated primary current [A] of the protected unit connected to the
np
channel
Example:
Rated primary current of current trafo = 500 A:
Rated current of the protected unit = 250 A:
Scaling factor for current channels:
The scaling factors for the analogue channels can be set via the HMI of the
protection relay or with the Relay Setting Tool. The HMI path for the scaling factors
is: Configuration\Protected unit\IL1: scaling, IL2:
scaling...

Technical data of the measuring devices

The technical data of the measuring devices is set using the Relay Setting Tool or
via HMI. The set values (Configuration\Meas.devices\) will affect the
measurements carried out by the REX 521.
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• rated primary current (0...6000 A) of the current transformer
• rated secondary current (5 A, 2 A, 1 A, 0.2 A) of the current transformer
• rated current (5 A, 1 A, 0.2 A) of the current measuring input (= rated current of
the matching transformer of the protection relay)
• amplitude correction factor (0.9000...1.1000) of the current transformer at rated
current
• correction parameter for the phase displacement error of the current transformer
at rated current (-5.00°...0.00°)
• amplitude correction factor of the current transformer at a signal level of 1% of
the rated current (0.9000...1.1000)
• correction parameter for the phase displacement error of the current transformer
at a signal level of 1% of the rated current (-10.00°...0.00°)
where
REX 521
I = 500 A
nmd
I = 250 A
np
500 A / 250 A = 2.00
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