Overvoltage events in electrical distribution systems are
not new things, however they have not been regarded as particularly dangerous
for the operating of industrial systems until now. The rising complexity
of technological equipment, their aggregation into automatic production
lines or one another close joining operational systems, along with the
considerable amount of overvoltage-sensitive electronics in stated equipment,
significantly increase the danger and amount of damage following overvoltage
events. Regarding industrial operations, the sources of overvoltage events
1.- storm activity- lightning strikes
2.- switching processes in distribution systems
3.- initiated by technological processes, generally switching processes
of power components
The frequency of overvoltage events could be very different, moreover
by 8-9 place values.
In addition to the low frequency of dangerous overvoltage events,
which result in the necessity for long-term monitoring of the state of
the mains, the positions in which we monitor the overvoltage events are
also important. As the number of monitoring points grows, so does the
number of devices needed, as it has been stated, only long-term monitoring
can give a sufficient objective reflection of the state of the mains in
terms of overvoltage surges.
In a preferred way we recommend to monitor the appearance of overvoltage
surges in these points:
- Operating places with a danger of fire or explosion. It is advisable
to provide these places with overvoltage protection devices when they
are installed. The PPI equipment is suitable for mounting to all inputs,
because it has integrated overvoltage protection category C, but the neutral
conductor must be installed to all phases separately, too.
- The main distribution boxes the low voltage side of the electric connection
registers overvoltage events coming from the external distribution network.
- The subsidiary distribution boxes, from which the places of operating
systems are supplied, at which short-term shut-down also leads to serious
interruption of the production process and marked damage. The subsidiary
distribution boxes, which supply the composite and expensive (especially
CNC) technological equipment, which damages have a very serious service
(time and costs), and consequently also threaten significant loss of production.
- The points of electrical distributions, which can generate antenna effects
regarding close lightning strikes, especially if the construction does
not insure sufficient shielding.
In evaluating information (numbers of pulses) obtained by the PPI equipment
we recommend to principally consider the following circumstances:
- the duration of monitoring - short-term monitoring, for only days
or weeks has only very restricted value
- the appearance of storm activity in a close surroundings during monitoring
- the mounting point of the equipment - the overvoltage surges coming
from the external distribution network are attenuated by branching and
by the length of the leads, correspondingly this is also valid in relation
to the sources of overvoltage surges in an indoor distribution network.
The counter registers overvoltage events and at the same time protects the conductor to which it is connected against overvoltage. This conductor also acts as the power supply for the electronic circuits of the counter. If there is a power failure the counter is failproofed for two hours by its resident back-up power supply. At the end of this time period the counter is reset. This equipment is primarily intended for the long-term monitoring the occurrence of overvoltage surges in factory mains, mainly due to random events.
The level of overvoltage surge, which is registered with this equipment, is specified by the minimal value of flowing current and by applied varistor module. The parameters listed below are detached for the 8/20 current waveform, which is standardised for overvoltage protection class C according to VDE 0675-6, class II according to IEC 61643-1. The equipment is installed by mounting it on a DIN-rail and connecting it to the L, PE conductors or only by connecting it to the L, PE conductors. The information about the state of the counter is easily readable on the three-digit LED display.
The counter registers overvoltage surges, which initiate the current through the earthing conductor min. 20 A. According to the voltage of the applied varistor module 275V, 385V or 550V the minimal value of overvoltage, which is registered by the equipment is 650V, 950V or 1400V.
The equipment registers all overvoltage surges, whose energy responds to the 8/20 waveform and peak current value min. 20A.
The significant advantage of using the PPI equipment is that during the monitoring of overvoltage events, it also ensures protection against overvoltage surges in the position of its mounting. After an sufficiently long period it is possible to install type PU C or PU B serial-producted overvoltage protection instead of the PPI equipment and use the equipment for monitoring at another position of the mains.