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Trip value recorder
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The main objective of line protection and monitoring terminals is fast, selective and re-
liable operation for faults on a protected object. Besides this, information on the values
of the currents and voltages before and during the fault is valuable to understand the se-
verity of the fault.
The trip value recorder in the REx 5xx series of terminals provides this information on
the HMI and via SCS/SMS. The function is an optional software module in the terminal.
The function calculates the pre-fault and fault values of currents and voltages and pre-
sents them as phasors with amplitude and argument.
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Pre-fault and fault phasors of currents and voltages are filtered from disturbance data
stored in digital sample buffers.
When the disturbance report function is triggered, the trip value recorder function starts
to calculate the frequency of the analog channel U1. If the calculation fails, a default
frequency is read from database to ensure further execution of the function.
Then the sample for the fault interception is looked for by checking the non-periodic
changes. The channel search order is U1, U2, U3, I1, I2, I3, I4, I5 and U5.
If no error sample is found, the trig sample is used as the start sample for the Fourier
estimation of the complex values of currents and voltages. The estimation uses samples
during one period before the trig sample. In this case the calculated values are used both
as pre-fault and fault values.
If an error sample is found the Fourier estimation of the prefault values starts 1.5 period
before the fault sample. The estimation uses samples during one period. The postfault
values are calculated using the Recursive Least Squares (RLS) method. The calculation
starts a few samples after the fault sample and uses samples during 1/2 - 2 periods de-
pending on the shape of the signals.
The pre-fault time (tPre) should be at least 0.1 s to ensure enough samples for the esti-
mation of pre-fault trip values.
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