MI 2892 Power Master
Theory and internal operation
181
5.2.5
Interharmonic voltage
The level of interharmonics is increasing due to the development of frequency converters and similar
control equipment. Levels are under consideration, pending more experience. In certain cases
interharmonics, even at low levels, give rise to flickers (see 5.2.7), or cause interference in ripple control
systems.
5.2.6
Mains signalling on the supply voltage
In some countries the public distribution networks may be used by the public supplier for the
transmission of signals. Over 99 % of a day the 3 s mean of signal voltages shall be less than or equal to
the values given in the following figure.
Figure 5.29: Mains signalling voltage level limits according to EN50160
5.2.7
Flicker severity
Under normal operating conditions, in any period of one week the long term flicker severity caused by
voltage fluctuation should be P
lt
≤
1 for 95 % of the time.
5.2.8
Voltage dips
Voltage dips are typically originated by faults occurring in the public network or in network users
installations. The annual frequency varies greatly depending on the type of supply system and on the
point of observation. Moreover, the distribution over the year can be very irregular. The majority of
voltage dips have duration less than 1 s and a retained voltage greater than 40 %. Conventionally, the
dip start threshold is equal to 90 % of the nominal voltage of the nominal voltage. Collected voltage dips
are classified according to the following table.
Table 5.10:Voltage dips classification
Residual
voltage
Duration (ms)
10 ≤ t ≤ 200 200 < t ≤ 500
500 < t ≤
1000
1000 < t ≤ 5000 5000 < t ≤ 60000
90 > U ≥ 80
Cell A1
Cell A2
Cell A3
Cell A4
Cell A5
80 > U ≥ 70
Cell B1
Cell B2
Cell B3
Cell B4
Cell B5
