Lightning Protection Article-e

Logical Analogy and Electrical Argumentation about Steel Tower as Down Conductor is in Accordance with Standard Installation Lightning Protection System

An article for consideration

By: Januargo National CME and Design HCPT Project

Contents I. Introduction ................................................................................................................. 3 II. Logically Analogy ....................................................................................................... 5 III. Standard References .................................................................................................. 10 IV. Electrically Argumentation Regarding Tower as “down conductor” ........................ 11 V. Currently Cases and The Analysis ............................................................................ 14 VI. Conclusion and Solusion Proposal ........................................................................... 16

Author : Januargo S. Baskoro Date : Feb 04, 2008

2

I. Introduction As everybody understood that high building such as telecommunication tower is something that “inviting“ lightning. Inviting means that when there is no high building at some area then lightning doesn‘t come to there unless high level ionization in air at the area carry the ion to jump from cloud to earth. But if the ionization isn‘t happened then lightning jumping only between cloud to another cloud. Lightning is a jumping ion which normally spread at the surface of cloud to the counterpart ions which have inverse polarity toward neutralization condition. At some cloud are not always have same polarity of ion, for example one group of cloud consist of negative ion (-) then another group of cloud could consist of positive ion (+). Whenever the two of group become closer until a distance which the energy of charged are strong enough to jump, so lightning between clouds are exist. But if, in the way of running cloud doesn’t meet the counterpart ion, then the ions are going down because of earth gravitation effect and forming a path from cloud to earth thus lightning may be happened from cloud to earth because earth is an extraordinary ions source. The occurrence of lightning from cloud to earth is more possible if there is a better way to reach, those are a high building and tower.

Figure 1. Lightning between clouds

Author : Januargo S. Baskoro Date : Feb 04, 2008

3

Figure 2. Lightning between cloud to earth

Figure 3. Lightning from cloud to earth via tower

Author : Januargo S. Baskoro Date : Feb 04, 2008

4

II. Logically Analogy In accordance with previous explanation that lightning is electrical ions that jump each other with counterpart ions to find neutral condition. The moving ions become an electric current when it is passed by a conductor. Basic understanding of electrical behavior is always corresponding to liquid behavior because liquid is visible to be analyzed of its movement. Electricity is flowing from higher potential to lower potential. Similar with this that liquid is flowing from higher pressure of place to lower pressure of place. Moving electricity need a conductor, liquid need a pipe to move nicely as expected. Size of conductor is defining of ability to conduct the electric current, size of pipe is also defining of pipe ability to be passed by liquid. Logical analogy of lightning protection system at telecommunication tower that on struck by lightning can be corresponded with water tank system with its pipe channels and dissipation pipes as shown in Figure 4. The picture is showing how liquid from top tank flow to bottom via pipe channel, P1 and P2, and the liquid is dissipated completely if the dissipation pipes are enough.

Figure 4. Logical analogy lightning protection system as tank system with the liquid.

But, when number of dissipation pipes is reduced then liquid will flow to out side via any pipe that connected to the system as shown in Figure 5. If any part of the out side pipe consist small cross section and thin, then at that part will receive big pressure thus the leakage possibility on it can be exist. The illustration is shown in Figure 6.

Author : Januargo S. Baskoro Date : Feb 04, 2008

5

Figure 5. Liquid flowing to outside via a pipe that connected to the system.

Figure 6. A small pipe exist at outside pipe. In Figure 4, 5 and 6 shown system that using 2 kind of channel pipe, P1 and P2. Assuming that using 1 channel pipe, P2, is enough actually then usage of channel pipe, P1, giving an extra channel excessively, meaning, the availability of P2 may be removed because P1 is so bigger than P2. Figure 7, 8, and 9 are showing the system with single channel pipe.

Author : Januargo S. Baskoro Date : Feb 04, 2008

6

Figure 7. Tank system in figure 4 with single down pipe.

Figure 8. Tank system in figure 5 with single down pipe.

Figure 9. Tank system in figure 6 with single down pipe.

Author : Januargo S. Baskoro Date : Feb 04, 2008

7

If the tank system that shown in figures above to be translated in electric drawing according to the agreement in the beginning of this discourse are shown in Figure 10, 11, 12, 13, 14 and 15.

Figure 10

Figure 11

Author : Januargo S. Baskoro Date : Feb 04, 2008

8

Figure 12

Figure 13

Figure 14

Author : Januargo S. Baskoro Date : Feb 04, 2008

9

Figure 15

III. Standard References 1. IEC 62305-3, Protection against lightning – Physical damage to structures and life hazard. Is a standard reference regarding lightning protection system. In point (4.3) says: “Steelwork within reinforced concrete structure is considered to be electrically continuous provided that the major part of interconnections of vertical and horizontal bars are welded or otherwise securely connected. Connections of vertical bars shall be welded, clamped or overlapped a minimum of 20 times their diameters and bound or otherwise securely connected……… ……… For structures utilizing steel reinforced concrete (including pre-cast, prestressed reinforced units), the electrical continuity of the reinforcing bars shall be determined by electrical testing between the uppermost part and ground level. The overall electrical resistance should not be greater than 0,2 Ω , measured using test equipment suitable for this purpose. In section (5.3.5) says: “The following parts of the structure should be considered as natural downconductors: a) the metal installations provided that – the electrical continuity between the various parts is made durable in accordance with 5.5.2.”1

1

The number of connections along the conductors shall be kept to a minimum. Connections shall be made secure by such means as brazing, welding, clamping, crimping, seaming, screwing or bolting. Author : Januargo S. Baskoro Date : Feb 04, 2008

10

2. SIEMENS, Installation guide line - Earthing, lightning and equipontential bonding for mobile radio base stations. Is a Siemens standard guide line for Lightning Protection System in BTS. In section (2.2.2.2) says, “For a metallic tower (Greenfield site, see chapter 4)2, there is no need to install a down conductor in order to conduct the lightning current to earth, as the tower structure itself will perform this task.”

3. HARGER, Lightning Protection Specification Wireless Communication sites. In section (I.A) says, “The tower legs should be utilized as down conductors as they provide an acceptable path of conductance.”

4. POLYPHASER, Exploring the need for tower down conductor. In their experiment concluding, “There could be other reasons for a separate down conductor such as: • ……… • ……… But not to “protect” the tower from lightning.”

5. Jay M. Jacobmeyer, P. E, April 1, 2007, in his article that published by MRT says: “Installing down conductors from high on the tower: Installers are sometimes told they must install a copper down conductor from the antenna to the earth electrode system. The author has seen more than 200 feet of AWG No. 2 wire installed on a tower to meet this misguided requirement. True, copper has better conductivity than galvanized steel, but the impedance of the tower is much lower than No. 2 copper wire for two reasons: the larger surface area of tower members creates lower inductance and the multiple current paths to the ground create lower overall impedance.”

More and more references can be taken, from internet, but haven’t been included.

IV. Electrically Argumentation Regarding Tower as “down conductor” Conductor is a medium that conduct electric current from a point with higher potential to another point with lower potential. The best medium that can do the task is metal, but non metal also could carry the electric current eventhough not well enough. 2

Chapter 4 is Greenfield sites installation examples.

Author : Januargo S. Baskoro Date : Feb 04, 2008

11

Capability of conductor to conduct ions is different depending on the material composed and it is called conductivity. Conductivity is formulated as:

σ = nqμ where, n is number of electric charge carries, q is the charge of the ion, μ is the mobility of the charged species.

Conductivity is not familiar at people’s ear and it is not understood generally. People can understand about resistivity that simply inverse of conductivity,

ρ=

1

σ

And resistance is an extrinsic property of a device which is represented by the equation R=ρ

l A

where, R is resistance of material ( Ω ), ρ is resistivity of material ( Ω .m), l is length of material (m) and A is its cross sectional area (m2) once more simply equation that taken from basic electronic knowledgement about paralel combination of resistance is, 1 1 1 1 = + + ... + R R1 R 2 Rx According to Table 1, shown that each material such as Copper, Aluminium, and Steel has different resistivity, those are -

Copper = 1.7241x10-6 Ω .cm or equal with 1.7241x10-8 Ω .m Aluminium = 2.284x10-6 Ω .cm or equal with 2.284x10-8 Ω .m Steel = 10.4x10-6 Ω .cm or equal with 10.4x10-8 Ω .m

So, for copper cable with cross-sectional area 50 mm2 and its length is as height as tower, let’s say 80 m, the resistance value can be calculated as R = 1.7241 × 10 −8 ×

80 50 × 10 −6

R = 2.75856x10-2 R = 0.027586 Ω

Author : Januargo S. Baskoro Date : Feb 04, 2008

12

Then for resistance value of Aluminium cable with cross-sectional area 70 mm2 is,

R = 2.284 × 10 −8 ×

80 70 × 10 −6

R = 2.6103x10-2

R = 0.026103 Ω

Thus for galvanized steel that has dimension 50mm x 3mm is,

R = 10.4 × 10 −8 ×

80 150 × 10 − 4

R = 5.5467x10-4 R = 0.055467 Ω Base on standard value of resistance for down conductor that states not bigger than 0.2 so the value as result of calculation above are so much less, in that means the three of those component are acceptable to be used.

Table 1. Resistivity of material

Author : Januargo S. Baskoro Date : Feb 04, 2008

13

If the resistance calculation is simply implemented to tower shown as follow. For example 72 m 4 legged Angular Tower, many angular tower have same type of top 10 m section, and the top section has smallest size of legs than bottom section. From tower data, each top leg is using angle bar 80 x 80 mm with thickness of 8 mm, see Figure 16.

Figure 16. Angle bar 80mm x 80mm x 8mm The section area is,

A = (80 x8) + (72 x8) = 1216 mm2 = 12,16x10-4 m2 Assume that as height as tower are using leg with same type angle bar, so the resistance of single leg is, R = 10.4 × 10 −8 ×

72 12.16 × 10 − 4

R = 0.006158 Ω And value of all leg as paralel combination is 1 1 1 1 1 = + + + R 0.006158 0.006158 0.006158 0.006158

1 4 = R 0.006158 4 R = 0.006158

R = 0.001539 Ω This is a very small value (remember the calculation was assuming that tower use same smallest size of leg as long as height of tower, so the actual could be smaller than the calculation) and it is acceptable to be used as down conductor.

V. Currently Cases and The Analysis So many reports about damage accident that caused by lightning hit the tower such as 1. KWH meter in tower location is burn. 2. Neighbor’s electric equipments are burn, like TV, Radio, Water pump, Lamp etc.

Many opinions arise that says: Author : Januargo S. Baskoro Date : Feb 04, 2008

14

1. 2. 3. 4.

“It is happened because of tower doesn’t equip with down conductor” “It is happened because there is no control pit and the grounding bar is not copper” “It is happened because the grounding resistance is not below than 1 Ω “ “It is happened because of electromagnetic effect when lightning is striking”

Opinion 1, It is denied with the explanation in section III and section IV. Opinion 2, It is said without analysis and logically thinking. Opinion 3, The value of 1 is not mentioned in installation standard of lightning protection system or in any standard. IEC 62305-3 standard is defining grounding resistance value as 10 Ω and PUIL (Indonesia Standard) is defining grounding resistance value as 5 Ω . Technical explanation of this value is too long to be mentioned in this discussion. Opinion 4, From the fact in the field, known that portion of damage devices is at power part, for example, TV burn, radio burn, water pump burn, lamp burn, etc. Which is electromagnetic field does not cause that defection. Electromagnetic effect as impact from lightning may cause, human brain disruption, defection on electronic device such as computer, digital radio etc, but not in power part. So clearly clarified that all of the defections in these cases are not impacted by electromagnetic field effect.

So, the analysis of the accident is, When the lightning striking tower, lightning current is carried down to earth via down conductor, any down conductor type as mentioned or the tower itself can do the job. In earth, the lightning current is dissipated through the electrodes. The capability of electrode to be thru by lightning current depend on surface wide of the electrode that contacted with earth and impedance of earth self. If number of electrodes are much enough, so the lightning current can be dissipated immediately, otherwise the currents are looking for any conductor connected that can be passed, and the alternative selected path is PLN line toward outside tower area to the neighbor. If the currents that flowing to outside are big, the defection as mentioned can be happened particularly if current pass a small conductor or big inductance. Because KWH meter has a coil conductor as inductor inside, so it create high impedance when a momentary current flow and burn it. Inductor and impedance are not explained in this writing.

Author : Januargo S. Baskoro Date : Feb 04, 2008

15

Every PLN users are suppose to install lightning protection system in their area, but unfortunatelly it is not done in Indonesia, so when something happen as impact of the lightning in their neighbor, it may impact to them too.

V. Conclusion and Solusion Proposal Several conclusion are taken after all clarification above, 1. Tower as down conductor is in accordance with installation standard of lightning protection system. 2. All currently defection cases are not caused by the installation lightning protection system without separate down conductor. Those are caused by poor installation of lightning protection system underground. 3. The value of grounding resistance can not be taken as the only reference. The number of grounding electrode is one of other consideration. 4. Poor installation of lightning protection system in PLN user, so when lightning happened in some place, the damage devices can be happened in other place surrounding. The author would like to propose two solusions for rectification, 1. Install more standard rods in the tower area as other path for lightning current to be dissipated by earth. The number of additional rods are using “trial an error“ method because nobody knows the big of lightning current is striking. And also, the author never did specially the lightning research and never got detail training about lightning, but this discourse is based on references, basic electrical and logically thinking. 2. Install more standard rods at nearest PLN pole which the line is connected to the site. And pull grounding from each line at the pole via arrestor device. This is intended to intercept lightning current that flowing to out side before touching eighbor devices.

Author : Januargo S. Baskoro Date : Feb 04, 2008

16