Na7
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MiCOM P741, P742
2. CURRENT TRANSFORMERS
2.1 CT Saturation detection
Innovative methods are used to detect CT saturation in the P74x. The values associated with
the CT saturation algorithms are entered into the Peripheral Unit’s CT ratio menu column
and are used to define the CT’s characteristic. The algorithms for CT saturation detection are
executed in the peripheral units.
The first algorithm to be examined is the detection of variation of current.
The PU calculates the derived current and compares it to the magnitude of the waveform.
With 2400Hz sampling, maximum variation between 2 successive samples of sinusoidal
current can not exceed 14% of the previous period's magnitude.
FIGURE 19: CURRENT VARIATION
The magnitude of the current is the maximum value of the current measure during the last
period with a minimum of 50% of nominal current. A variation is detected is derived current
exceed 20% of this magnitude.
This instantaneous value is maintained 150ms for the first variation then 50ms for the next
ones, as shown as figure 20.
FIGURE 20: CURRENT VARIATION CRITERIA
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