Generally, electrical circuits have components that have high thermal capacities, which prevents them from reaching very high temperatures very quickly, except during very large or prolonged disturbances. This, therefore, requires significant surge energies. In addition, the materials constituting the insulation of these components can operate at temperatures as high as possible. 200 ºc at least for short periods.
Electronic circuits, on the other hand, use components that operate at very low levels of voltage and power. Even small magnitude surge currents or transient voltages are enough to cause high temperatures and voltage breaks.
This is the case because of the very small electrical spacings between printed circuits and integrated circuits ( often in microns ) and the very poor temperature resistance of many semiconductor materials, which form the core of these components.
As such, a higher degree of surge protection is required if these devices are to operate safely in a normal electrical environment.
Thus comes the concept of Surge Protection Zones (ZPS).
According to this concept, an entire installation can be divided into zones, each with a higher level of protection and nested within each other.
As we move up the SPZ ladder, the surges get smaller and the protection better.
Zone 0: This is the uncontrolled area of the outside world with adequate surge protection for high voltage power transmission and major distribution equipment.
Zone 1: A controlled environment that adequately protects the electrical equipment present in a normal building distribution system
Zone 2: This zone has protection intended for electronic equipment of the more robust variety (power electronic equipment or discrete type control devices).
Zone 3: This zone houses the most sensitive electronic equipment and provides protection in the highest order possible (includes CPUs, distributed control systems, devices with ics, etc.).
We call this the zone protection approach, and we see these different zones with the appropriate order of magnitude reduction in surge current
as you descend through the zones, in the facility itself.
Note that in the uncontrolled environment outside our building, we would consider the amplitude to say, 1000A.
As we enter the first level of a controlled environment, called zone 1, we would get a reduction of a factor of 10 to possibly 100 A in surge capacity as we move to a more specific location, zone 2, maybe a computer room or a room where various sensitive hardware exists, we find another reduction by a factor of 10.
Finally, within the equipment itself, one can find another reduction by a factor of 10, the effect of this surge being basically one ampere on the device itself. IEEE C62.41 indicates a similar but slightly different approach to protection zones.
The idea of the zone protection approach is to use the inductive capacitance of the installation, i.e. The wiring, to help dampen the magnitude of the rising current, as we move away from the input of the installation service.
The transition between zones 0 and 1 is specified. Here we have a detailed image of the entrance to the building where telecommunications, data communications, and power cables enter from the outside to the first protected area.
Note that the Surge Protection Device (SPD) fundamentally suppresses all transients on any of these metal wires, referring all of this to the common service entrance ground, even when attached to the metallic water pipe system.
Likewise, the protection of zone 2 at the transition point of zone 1.
Here we are addressing the discrete level between the first level of controlled zone 1 and maybe the plug-in taking in zone 2, we can see that surge protection devices are available which handle telecommunications, data, and different types of physical connectors for each connector, including RJ telephone connector type as well as coaxial cabling
This is a common design error when there are two entry points and therefore two ground points are established for the AC power and telecommunication circuits.
The use of the TVSS devices at each point is very beneficial in controlling the line-to-line and line-to-ground overvoltage conditions at each entry point, but the arrangement cannot perform this task between entry points.
This is of paramount importance since the victim’s equipment is connected between the two points. Therefore, a common mode overload current will flow through the victim equipment between the two circuits despite the presence of the much-needed TVSS.
The minimal result of the above is data corruption. At maximum, there may be a risk of fire and electric shock from the equipment.
Regardless of the type of TVSS used in the above, and the number and type of individual and additional grounding cables, etc., used, the problem stated will remain largely as discussed above. The wires all have self-inductance and because of −e = L di / dt the conditions cannot equalize the potential between them under normal pulse/overvoltage conditions.
Such wires can self-resonate in quarter waves and odd multiples, which is also harmful. This also applies to metal pipes, steel beams, etc.
Grounding these nearby objects may be necessary to prevent side lightning, however.
Get progressive surge protection
From the above, it will be clear that the type of surge protection depends on the type of area and the equipment to be protected. We will illustrate this in more detail by example, starting from the uncontrolled zone of zone 0.
Let’s start by talking about what happens when a lightning strike hits an overhead distribution line.
Here in Figure 4, we see the image of the storm cloud unloading on the distribution line and points of application of a surge arrester by the electricity company at points 1 and 2. We notice that the operating voltage is here 11,000 volts on the primary line and the transformer has a secondary voltage of 380/400 V generally serving the consumer.
We need to understand what is called the traveling wave phenomenon. When lightning strikes the power line, the inherent construction of the power line makes it capable of withstanding 95,000V for its insulation system.
We call this the Basic Pulse Level (BIL).
Most 11,000-V construction equipment would have a BIL rating of 95 kV. This tells us that the insulation of the wires, the ties, and all the other parts, located near the live conductors, are able to withstand this high voltage.
Wave and sparks above the lightning applied to an 11 000-V line may have a spark characteristic of about 22,000 V . This high level of spark protection should allow the arrester to wait until the top of the 11,000-V operating waveform is exceeded before discharging energy into the earth.
The summit of the 11,000-VMS wave would be somewhere in the neighborhood of 15 000 V . When the voltage reaches the level of 22,000V and then stays there while the arrester performs its discharge, this voltage waveform moving on the power line moving very quickly at all points of the line. In places where there is a discontinuity in relation to the power line, such as points 3 or 4 of our chart, the wave motion will go to 22,000 V and will double again over the line 44 000 V.
This type of phenomenon is known as traveling wave reflection and it occurs at open parts of the circuit or even at the primary of transformers. When the primary of our distribution transformer serving the building reaches 44,000 V, the secondary supplying the building will be subjected to a surge.
Thus, points 5 and 6 of our table require us to: Think of certain types of lightning protection devices at the transformer secondary, the service entrance to the building, then further into the building, such as point 6 for that sensitive equipment is fully protected in this installation.