Table 3.

STCOMET on-board metrics vs. IEC 61000-4-30 requirements (class S) [33].

Parameter	IEC 61000-4-30			STCOMET Metric Main Features	Correction Algorithms
	Measurement Range	Time Interval (t.i.)	Maximum Error
Frequency Period	42.5 ÷ 57.5 Hz (for 50 Hz syst.)	10 s (not overlapping)	−Number of integer cycles during the 10-s t.i. divided by their cumulative duration −Harmonics and interharmonics are attenuated	−Measurement from zero-crossing (voltage channel, with a low pass filter). −Frequency range between 32.55 and 81.38 Hz −Resolution of 8 μs −Period is calculated as the mean of the last eight measured periods	−Single frequency value is obtained as period reciprocal (on-board metric) −Frequency measurement is calculated as the mean of the single frequency values over 10 s
RMS	20 ÷ 120% Udin	200 ms (10 cycles for 50 Hz) no gaps	−The r.m.s. value includes, by definition, harmonics, interharmonics, etc. −Every 10/12-cycle interval shall be contiguous and not overlapping −Not used for dips, swells, voltage interruptions, and transients	−RMS measurement is obtained from voltage/current samples −Voltage/current are not filtered −Integration time is 10 cycles −RMS value is updated every 128 μs	−No modifications of on-board metric −Measurement reading is updated every 10 cycles, in order to have not overlapping t.i.
Dips Swells Interruptions	---	---	−The basic measurement shall be the RMS over a half cycle or full cycle (Urms(1/2) or Urms(1)) −Measured data are maximum/residual voltage (i.e., the max./min. voltage value during the event) and duration (i.e., the difference between start and end times of the event) −For interruptions only duration is measured	−The fundamental component of voltage (RMS) is compared to a 10-bit threshold −An internal time counter is incremented until the momentary voltage value is below/above the threshold −Maximum/residual voltage is not calculated −Interruptions measurement is not on-board	−(Urms(1)) has been implemented −Urms(1) is compared with the event threshold to obtain event start, end, and duration −An internal counter is incremented until Urms(1) value is below/above the threshold −Urms(1) measurement is used to store the residual/max. voltage
Harmonics	10 ÷ 100% of harmonic limits, up to 40th order	200 ms (gaps allowed) ± 0.03% max. synchr. error (optional)	−DFT/FFT −t.i. synchronized to the power system frequency −Rectangular window (Hanning in case of loss of synchronization	−Not on-board	−New algorithm (see Section 3.2)