The whole concept of lightning defense is to management and direct the lightning surge electrical power so it does the least volume of damage or destruction. When it arrives to grounding SCADA programs, there are a fantastic lots of viewpoints on the matter, at least 50 percent of which have been motivated by apocryphal tales from the discipline. For a usual SCADA application, there are a few most important points to consider: (1) tower/mast top (2) antenna type (3) surge suppressor kind.
The principal intention of providing a widespread ground is to decrease any difference in electric potential between the antenna, tower, transmission cable, communications products and terra firma (floor). The surge arrestor, which is meant to be set up at or really near the cable stage-of-entry, is supposed to decrease the probable hurt to radio machines for dc pulse electrical spikes (surges).
A cable ground kit, mounted about halfway among the leading and the base of a transmission line, makes use of the person wire paths to ground, but is usually only considered for use on cable operates in surplus of 150 feet. (This is based on a calculation of distribution of recent on a guyed tower making use of mesh present community assessment.)
In-line surge arrestor When thinking about alternatives for lightning security, maintain in brain that lightning arrestors with dc continuity, this kind of as uncomplicated gasoline tubes and ¼ wave shorted stubs, may perhaps not be the finest decision, no make a difference how desirable the rate might appear, since the fuel tube arrestor would not turn on in time and the ¼ wave stub would ‘share’ surge current with the equipment.
The most successful type of lightning arrestor is “dc blocked”. That’s mainly because there is no heart conductor continuity from connector pin to pin. The inside coupling stops the sharing of very low-frequency surge existing with the tools. It also permits the dc blocked gasoline tube kind ‘impulse suppressor’ to hearth as the voltage reaches the turn-on threshold.
When a surge arrestor productively safeguards an specific internet site from surge injury, the device by itself may possibly be compromised, which is undoubtedly improved than having the radio tools broken. Having said that, the connection may perhaps very effectively not perform thereafter, because of to the nature of the protecting unit. This condition could demand that the surge system be replaced…a smaller rate to pay when in contrast to the price tag of the radio alone.
DC floor antenna There are a variety of yagi antennas that benefit from a folded dipole design for the active factor. With this layout, the center conductor is basically grounded to the antenna frame. If 1 checked resistance with an ohm meter across the protect and centre conductor, it would go through as a useless quick. Of system, to a radio it seems like a 50 ohm load!
Electrically, it will shunt to floor. That attribute need to be famous on the antenna information sheet, generally below the heading “lightning security”, as DC floor. The path to ground is by the mounting construction, which, as a matter of system, should really be electrically grounded.
Cable ground package-do we require it? “We floor the mast and use a name model lightning arrestor. Not long ago, the issue of grounding the antenna cables has arrive up. Is that a apply that you advocate, and why or why not?”
Numerous process integrators have been questioned this query, and as you can count on, several are undecided on the make a difference they are normally really organization in their beliefs, one particular way or the other.
Only a few operators have elected to specify a cable grounding package as part of the program ground. This commonly will involve slicing absent a modest part of the jacket in get to repair a floor lug right to the braid.
On towers that are much less than 150 ft, this more grounding technique adds only an incremental bit of transmission line floor. For most SCADA apps, the end end result is not worthy of the more time, equipment, and labour to set up it.
Empirical evidence indicates that the majority of SCADA end users, particularly in the Oil & Gas marketplace, discover that making use of a surge arrestor at 1 end of the transmission line and setting up a DC ground antenna at the other has demonstrated to be really sufficient and cost-effective.
Be positive to err on the aspect of caution when working with grounding difficulties. Surge suppressor makers are a quite fantastic useful resource, primarily when the web page is not a basic set up.
Grounding of communications machines can be fairly advanced and included, notably with high towers and/or several antenna techniques.
For 98% of SCADA apps, the grounding strategies outlined above are sufficient and secure.
