Operation Principle - ABB Relion Technical Manual

1MRK 502 048-UUS A
17.9.6
Technical manual
Even if the AnalogInputType setting of a SMAI block is set to Current, the
MinValFreqMeas setting is still visible. This means that the minimum
level for current amplitude is based on VBase. For example, if VBase is
20000, the minimum amplitude for current is 20000 * 10% = 2000. This
has practical affect only if the current measuring SMAI is used as a
frequency reference for the adaptive DFT. This is not recommended, see
the Setting guidelines.

Operation principle

Every SMAI can receive four analog signals (three phases and one neutral value), either
voltage or current. The AnalogInputType setting should be set according to the input
connected. The signal received by SMAI is processed internally and in total 244 different
electrical parameters are obtained for example RMS value, peak-to-peak, frequency and
so on. The activation of BLOCK input resets all outputs to 0.
SMAI_20 does all the calculation based on nominal 20 samples per line frequency period,
this gives a sample frequency of 1 kHz at 50 Hz nominal line frequency and 1.2 kHz at 60
Hz nominal line frequency.
The output signals AI1...AI4 in SMAI_20_x function block are direct outputs of the
connected input signals GRPx_A, GRPx_B, GRPx_C and GRPx_N. GRPx_N is always
the neutral current. If GRPx_N is not connected, the output AI4 is zero. The AIN output
is the calculated residual quantity, obtained as a sum of inputs GRPx_A, GRPx_B and
GRPx_C but is equal to output AI4 if GRPx_N is connected. The outputs signal AI1,
AI2, AI3 and AIN are normally connected to the analog disturbance recorder.
The SMAI function block always calculates the residual quantities in case
only the three phases (Ph-N) are connected (GRPx_N input not used).
The output signal AI3P in the SMAI function block is a group output signal containing
all processed electrical information from inputs GRPx_A, GRPx_B, GRPx_C and
GRPx_N. Applications with a few exceptions shall always be connected to AI3P.
The input signal REVROT is used to reverse the phase order.
A few points need to be ensured for SMAI to process the analog signal correctly.
Section 17
Basic IED functions
691