Current Sensors; Supervision; Table 1: Current Metering Accuracy; Table 2: Zero-Clamping Limits - ABB UniGear Digital Commissioning And Testing Manual

PR IM AR Y T ES T IN G
4.2

Current sensors

Primary testing verifies the whole measurement chain including the sensor, cable connec-
tions and settings of the protection relay. Each current sensor has unique physical polarity.
Therefore, no polarity (physical test) is needed. The current sensor polarity can be changed
via parameter setting. Secondary winding resistance and magnetization curve tests are not
applicable either.
4.2.1

Supervision

In the protection relay, current metering is supervised by the CMMXU function. Metering ac-
curacy is stated in Table 1.

Table 1: Current metering accuracy

Characteristic
Operation accuracy
A measured value under the zero-point clamping limit is forced to zero. This allows the noise
in the input signal to be ignored. Read more details in the technical manual of the protection
relay.

Table 2: Zero-clamping limits

Function
Three-phase current measurement (CMMXU) 1% of nominal (In)
Residual current measurement (RESCMMXU)
Phase sequence current meas. (CSMSQI)
1 VLG 500 0 17 C
Value
• Depending on the frequency of the
measured current: f
• ±0.5% or ±0.002 × I
the range of 0.01...4.00 × I
Zero-clamping limit
1% of nominal (In)
1% of nominal (In)
CU R R E N T S EN SO R S
±2 Hz
n
(at currents in
n
)
n
1 9