Sugar Refinery Chimney Replacement: Lightning Protection ... · REFINERY CHIMNEY REPLACEMENT -...

REFINERY CHIMNEY REPLACEMENT - LIGHTNING PROTECTION, RISK ANALYSIS & DESIGN STUDY

EARTHING, BONDING, LIGHTNING & SURGE PROTECTION CONFERENCE 2012 1

Sugar Refinery Chimney Replacement: Lightning Protection, Risk Analysis & Design Study

Authors:

Frank Anthony Auditoré (Tony)1, Michael Leonard Swan2 1LineTech Consulting (New Zealand) 2New Zealand Sugar Co (New Zealand)

Presenter:

Frank Anthony Auditoré (Tony)1 1LineTech Consulting (New Zealand)

Earthing, Bonding, Lightning & Surge Protection Conference 2012, 18th & 19th September 2012, Ridges, Auckland, New Zealand

Summary:

LineTech Consulting was requested by New Zealand Sugar Co (NZS) to undertake a study to investigate the consequence of a direct lightning strike to the proposed replacement Stainless Steel Chimney (SSC) and insure the safety of personal working in this area . The objective of this study was not to protect the SSC from lightning. By its design, material composition, profile and location; there were no economic means of protecting the SSC against direct lightning strikes. However, this study attempted to quantify the magnitude of the possible risks that the surrounding plant and equipment were subjected to in the event of the SSC being struck by lightning. Furthermore, the study proposes mitigation measures against possible overvoltage damage in the form of effective earthing.

The CDEGS simulation concludes that an effective Lightning Protective System (LPS) as described in Scenario 2 as the best solution. That is earthing in the immediate area of the SSC with four 6 m 38 mm Ø copper coated earth electrodes. In addition, all SSC steelwork and reinforcing had to be solidly bonded.

The study proposed an effective LPS design. In addition, it proposed surge protection for all main power in-feeders that supply plant and equipment. Lastly, it also included operational safety guidelines that reduce the risk of injury to public and occupational persons.

The study included a risk assessment done in accordance with AS/NZS 1768:2007 Section 2 Assessment and Management of Risk Due to Lightning – Analysis of Need for Protection . As the acceptable risk was far less than the total risk 0.0238 > 0.00001 the results require the design of a shielding system for the SSC. It is emphasised that it is not feasible to shield the SSC from direct lightning strikes. Therefore mitigation measures have to be applied.

The above risk assessment is extremely conservative and does not take into account environmental shielding effects or any applied mitigation such as the installation of surge protection. Therefore a risk assessment based on a holistic approach has been adopted. This method applies the risk assessment process detailed in AS/NZS 1768:2007 and was calculated using the supplied calculation spreadsheet.

The spreadsheet calculations consider the following 4 scenarios:

I. Lightning strikes to the SSC without any surge protection installed on the power supply or electrical equipment. Results were not acceptable with the Loss of Life risk = 3.17 E

-5.



II. Lightning strikes to the SSC with surge protection installed on the power supply and electrical equipment. Results were acceptable with the Loss of Life risk = 9.49 E

-8.

III. Lightning strikes to the Boiler House without any surge protection installed on the power supply or electrical equipment. Results were not acceptable with the Loss of Life risk = 3.74 E

-5.

IV. Lightning strikes to the Boiler House with surge protection installed on the power supply and electrical equipment. Results were acceptable with the Loss of Life risk = 1.03 E

-8.

Surge protection on the point of entry includes surge arresters at both the supply transformer (415 V side) and entry into the Boiler House 415 V mains board.

The surge protection for electrical equipment within the Boiler House is situated at the 415 V mains board. Any electrical equipment that is outside of the Boiler House and supplied from the Boiler House 415 V mains board requires additional surge protection at the equipment itself. For example: Surge protection will need to be installed on the drive of the chimney draught fan.

The boiler house adjacent to the SSC required adequate earthing. The condition of the existing earthing was not obvious due to the age of the premises and an accurate assessment would have been costly. An effective and low cost solution was to install earth electrodes on the outer four corners of the building.

1. Background

Depending on the shielding effect of the surrounding topography, tall structures are susceptible to lightning strikes. The SSC is considered a high risk structure for a lightning strike. A direct lightning flash to the SSC will cause a potential rise in the vicinity of the chimney. It may also result in dangerous and damaging electrical transients to plant and equipment remote from the SSC. Figure 1 illustrates the extent of the area of NZS. The lightning discharge current through the SSC can also induce voltages and currents in remote conductors due to electric and magnetic coupling. The “victims” of such overvoltages include power and communication cables and terminal electronic equipment.

The historical plant performance of the New Zealand Sugar Refinery did not indicate any previous damage to plant and equipment due to a direct lightning strike to the old chimney. However, there were no facts provided that prove previous technical malfunctions have not been due to overvoltage surges - from local faults or faults from the incoming supply. It was strongly proposed that NZS install surge protection. This surge protection would be against overvoltages due to both direct lightning strikes to the SSC as well as from surges from the local distribution supply. The application of surge protection consisted of the selection of coordinated surge suppression devices.

2. Scope of the design

The objective of this study was not to protect the SSC from lightning by standard engineering such as the “rolling sphere method”. By its design, material composition, profile and location; there are no economic means of protecting the SSC against direct lightning strikes. However, this study does attempt to quantify the magnitude of the possible risks that the surrounding plant and equipment are subjected to in the event of the SSC being struck by lightning. Furthermore, the study proposes mitigation measures against possible overvoltage damage in the form of effective earthing.

The design objective was to design an earth grid for the SSC that has minimum transient electromagnetic field oscillation with reduced electric field and potential magnitude. Three scenarios were investigated. These include the SSC without earthing (Scenario 1), SSC with earthing in the immediate area (Scenario 2), and enhanced earthing with additional remote electrodes (Scenario 3).



Figure 1: Aerial View of New Zealand Sugar Co

3. Design process

A lightning strike normally begins with a stepped leader, a low-energy stroke that progressively propagates downward toward the ground in discrete steps, of about 50 m in length for each step. At this stage the stepped leader traverses a path to ground without regard to local terrestrial features until it reaches within about 10 – 100 m of the earth or the top of an above ground structure. At that stage, a more powerful return stroke emanates from ground, meeting the stepped leader. The electrical circuit is then completed, & it is possible that several repetitive strokes flow along the established path. Only within 10-100 m of the ground does the geometry & electrical characteristics of the ground & structures affect the lightning's striking point. By reviewing Figure 1: Elevation of Chelsea Sugar Refinery it becomes obvious that the number of terrestrial features in the form of buildings and vegetation are numerous. The figure contains the old chimney which is taller than the proposed SSC.

Because lightning is a high-frequency phenomenon, it is not simple to predict its behaviour. An acute change in direction of a ground conductor may create a high-frequency impedance that diverts the current to another & less obvious path such as the buildings surrounding the SSC. Figure 1 illustrates the area of water (inland and coastal) that surrounds the refinery. These water surfaces offer highly probable areas for lightning to strike.

The effectiveness of charge dissipating devices to de-ionize the immediate atmosphere surrounding lightning air terminals is often debated amongst scientific researchers. Charge dissipation terminals are claimed to mitigate direct lightning strikes by dissipating the charge of static electricity into the atmosphere through the process of ionization (point discharge principle). This affects the region within the 10 – 100 m as discussed in the previous slide. The process of dissipation effectively lowers the probability of streamers forming in time to be first to complete the path of the lightning strike. From the former discussion, the top edging (6 mm thick & 1,550 mm Ø) of the SSC does offer good charge dissipation.

The engineering program modules HIFREQ and FFTSES of CDEGS software package were used for this study. The methodology contains the following three computation steps:

Chimney

REFINERY CHIMNEY REPLACEMENT

EARTHING, BONDING, LIGHTNING & SURGE PROTECTION CONF

� Frequency Decomposition of the Time Domain Signal� Computation of the Frequency Domain Electromagnetic� Computation of the Time Domain Electromagnetic Fiel

The transient behaviour of the SSC subjected to a ltheory approach. The lightning strike double exponential model. The dynamic electromagnetdecomposing the lightning discharge current into itFast Fourier Transform with the CDEGS FFST module. and earthing conductors, the scalar potentials and selected frequencies of the frequency domain spectrand electromagnetic fields were obtained using the

The input time signal was analysed by converting it into thsampling exponent was to a power of 2. The selection of the time durationcriteria. These were:

− The time duration determines the frequency resoluti

− The time duration should be selected so that the inwindow

The study considered a voltage surge was . To be conservative a time step of 0.1 300/0.1 = 3000 sampling points.

Reviewing the results – Figure 2 illustrates the effect of variable frequency on tthe earthing system. Figure 2 (a) illushigh above the extended earthgrid compared to the hearthing is more effective for dissipating high fre

(a): 3,333 Hz

Figure 2: Potential Profiles at Varying Frequencies

The results of numerous CDEGS studies revealed thatfour electrode design as illustrated in Figure 3.


EARTHING, BONDING, LIGHTNING & SURGE PROTECTION CONFERENCE 2012

Decomposition of the Time Domain Signal Computation of the Frequency Domain Electromagnetic Field Response Computation of the Time Domain Electromagnetic Field Response

The transient behaviour of the SSC subjected to a lightning strike was investigated utheory approach. The lightning strike was simulated by injecting a 30 kA current surge based double exponential model. The dynamic electromagnetic field response was decomposing the lightning discharge current into its frequency domain spectrum using the Fast Fourier Transform with the CDEGS FFST module. The discharge current distribution in the SSC and earthing conductors, the scalar potentials and the electromagnetic fields wereselected frequencies of the frequency domain spectrum. Thereafter, the time domain scalar potentials

obtained using the inverse Fast Fourier Transform.

analysed by converting it into the discrete frequency spectrum. The to a power of 2. The selection of the time duration was determined by two

The time duration determines the frequency resolution and is represented by the relationship

The time duration should be selected so that the input signal is very small at the end of the time

which corresponds to Hz. The rise time of the . To be conservative a time step of 0.1 was chosen which corresponds to a

2 illustrates the effect of variable frequency on the potential profile of Figure 2 (a) illustrates that at the low frequency (3,333 Hz), the voltage profile i

high above the extended earthgrid compared to the high frequency (6,813,333 Hz) in (b). Localised earthing is more effective for dissipating high frequency voltages.

(b): 6,813,333 Hz

Potential Profiles at Varying Frequencies

The results of numerous CDEGS studies revealed that the most effective earthing method was the four electrode design as illustrated in Figure 3.

LIGHTNING PROTECTION, RISK ANALYSIS & DESIGN STUDY

4

investigated using the field simulated by injecting a 30 kA current surge based on the

obtained by quency domain spectrum using the forward The discharge current distribution in the SSC

were computed at um. Thereafter, the time domain scalar potentials

e discrete frequency spectrum. The determined by two

on and is represented by the relationship

put signal is very small at the end of the time

Hz. The rise time of the chosen which corresponds to a

he potential profile of the low frequency (3,333 Hz), the voltage profile is

igh frequency (6,813,333 Hz) in (b). Localised

the most effective earthing method was the

REFINERY CHIMNEY REPLACEMENT

EARTHING, BONDING, LIGHTNING & SURGE PROTECTION CON

Figure 3: Proposed Detail Design

3.1 Applied standards

The following local and international guidelines and

• AS/NZS 1768: 2007 Lightning protection

• AS/NZS 3000: 2007 Wiring Rules (Incorporating Amendment No.1)

• Electricity Engineers’ Association of New ZealaPractice June 2009

3.2 Quantification of probability of a direct strike to

NZS is located in a geographical area where the lightning ground flash density is maximum of 0.10 flashes/km

2/year


EARTHING, BONDING, LIGHTNING & SURGE PROTECTION CONFERENCE 2012

Figure 3: Proposed Detail Design

local and international guidelines and standards were applied in the study:

AS/NZS 1768: 2007 Lightning protection

Wiring Rules (Incorporating Amendment No.1)

Electricity Engineers’ Association of New Zealand (EEA): Guide to Power System Earthing

Quantification of probability of a direct strike to SSC

area where the lightning ground flash density is expected to be /year. This value is obtained from AS/NZS 1768:2007 Figure 2.4

LIGHTNING PROTECTION, RISK ANALYSIS & DESIGN STUDY

5

applied in the study:

(EEA): Guide to Power System Earthing

expected to be a AS/NZS 1768:2007 Figure 2.4



Average Annual Lightning Ground Flash Density Map of New Zealand (page 27). This is reproduced in Figure 4.

Figure 4: Expected Average Annual Lightning Ground Flash Density

Any risk assessment presents itself with a challenge due to the probabilistic nature of lightning, the lack of data of lightning strokes to the proposed replacement chimney and no known practical method of providing 100% shielding from lightning. The available flashes/km

2/year from AS/NZS 1768:2007 is

to be considered an average value.

However, the probability of it being struck is a function of its ground surface area, height, the striking distance between the points of the downward-moving stepped leader and the chimney and soil conditions (from both a soil resistivity and composition point of view). Due to this fact it is advisable to apply the more conservative value of annual lightning flash density (Ng) = 0.10 flashes/km

2/year.

In the absence of a predetermined path, lightning strikes will be attracted to many earth-bound conductors. As previously mentioned, within the NZS property there are a number of alternative striking possibilities for lightning to terminate to ground as shown in Figure 5 and Figure 6. The method of lightning protection does not eliminate the possibility of a strike but it does provide a lower risk of injury to personnel and damage to equipment.

Charge dissipation terminals mitigate direct lightning strikes by dissipating the charge of static electricity into the atmosphere through the process of ionization (point discharge principle). This affects the region within the 10 – 100 m as previously discussed. The process of dissipation from the edge of the SSC effectively lowers the probability of streamers forming to complete the path of the lightning strike.



Figure 5: Relative height of SSC to Immediate Building

Figure 6: Relative height of SSC to Immediate Building

The environmental factor (Cd) was applied in the calculations. This is conservative as it represents an isolated structure with no other structures or objects within a distance of 3 x height from the structure. E.g. structure in a rural area.

The probability of lightning striking a particular structure situated on the ground is calculated by multiplying the object’s lightning-attractive area (Ad) by the local ground-flash density (Ng) and the environmental factor (Cd).

This was estimated by the following:

Where:



��

��

Note that the length (L) and breadth (B) of the SSC are conservatively taken as the diameter of the SSC.

�� !�"��

#� ��

$% �� &� &&&''(�%)*+,-�.-*)/+.�-0�-1+�223�4+*�5+6*��

4. Comprehensive risk assessment

The above assessment is extremely conservative and does not take into account environmental shielding effects or any applied mitigation such as the installation of surge protection. Therefore a risk assessment based on a holistic approach has been adopted. This method applies the risk assessment process detailed in AS/NZS 1768:2007 and was using the supplied spreadsheet.

The spreadsheet calculations consider the following 4 scenarios:

I. Lightning strikes to the SSC without any surge protection installed on the power supply or electrical equipment.

II. Lightning strikes to the SSC with surge protection installed on the power supply and electrical equipment.

III. Lightning strikes to the Boiler House without any surge protection installed on the power supply or electrical equipment.

IV. Lightning strikes to the Boiler House with surge protection installed on the power supply and electrical equipment.

Each is considered below:

I. Lightning strikes to the SSC without any surge protection installed on the power supply or electrical equipment The result for Loss of Life was calculated as 3.17 E

-5 (see RED arrow) which is clearly higher

than the acceptable risk of 1 x E-5

. However, when surge protection is installed at the electrical point of entry and on all the electrical equipment the overall risk improves – see scenario II below.

II. Lightning strikes to the SSC with surge protection installed on the power supply and electrical equipment The result for Loss of Life was calculated as 9.49 E

-8 (see GREEN arrow) which is clearly lower

than the acceptable risk of 1 x E-5

. It can be concluded that by installing surge protection at the point of entry and on all the electrical equipment results in the Loss of Life risk becoming acceptable.

Surge protection on the electrical point of entry includes surge arresters at both the supply transformer (415 V side) and entry into the Boiler House 415 V mains board.

. Any equipment that is outside of the Boiler House and is fed from the Boiler House 415 V mains board will require additional surge protection at the equipment itself. For example: Surge protection will need to be installed on the drive for chimney draught fan.



III. Lightning strikes to the Boiler House without any surge protection installed on the power supply or electrical equipment The result for Loss of Life is 3.74 E

-5 (see RED arrow) which is clearly higher than the acceptable

risk of 1.0 E-5

. However, when surge protection is installed on the point of entry and equipment the overall risk changes.

IV. Lightning strikes to the Boiler House with surge protection installed on the power supply and electrical equipment The result for Loss of Life is 1.03 E

-8 (RED arrow) which is clearly lower than the acceptable risk

of 1.0 E-5

. It was concluded that by installing surge protection on the point of entry and on all equipment makes the Loss of Life risk more than ‘acceptable’.

Once again as in I & II, surge protection on the point of entry includes surge arresters at both the supply transformer (415 V) and entry into the Boiler House mains board. Similarly, note that the surge protection on equipment within the Boiler House is at the 415 V mains board. Any equipment that is outside of the Boiler House required additional surge protection at the equipment itself. For example the chimney forced draught fan motor.

5. Lightning Protection System Design

An effective LPS design provides for a predetermined (or highly probable) lightning conduction system and the effective dissipation of the lightning discharge current to earth. In addition, it also provides surge protection for all main power in-feeders that supply plant and equipment. Lastly, a LPS should also include operational safety guidelines that reduce the risk of injury to public and occupational persons. These are individually addressed below.

5.1 LPS – lightning conduction & discharge current dissipation

The design reviews the main elements of a LPS surrounding the SSC and is as follows:

5.1.1 Air terminals

The application of air terminals is to achieve a high probability of intercepting a direct lightning strike. Due to the high profile of the SSC, this is naturally achieved without any additional extension to the SSC. The SS cylinder with a diameter of 1,550 mm and 6 mm thickness provides a large inception area for a direct strike. The leading edge of the 6 mm SS has effective ESE properties.

Although not essential to the lightning performance of this particular LPS, a lightning terminating point on the rim of the SSC may have been installed. Such a system is the ERITECH

© INTERCEPTOR SI

ESE lightning terminal. If installed, the terminal should have been mounted on the top of a 2 m mast ERITECH

© ER2-2000-SS and secured to the SSC by means of two mast brackets ERITECH

© ALOF-

1-GS (702175) mounted 500 mm apart. The brackets secured to the SSC by means of SS bolts and fastened with double SS nuts. The mast would protrude 1.4 m from the edge of the SSC. No connecting lead from the terminal would have been required to connect the 2 m mast to the SSC.

5.1.2 Down conductor

Down conductors are used to convey lightning current towards the earth. It is sound practice that existing building metalwork should be used as far as possible, especially steel frames and reinforcing steel in reinforced concrete columns, supplemented where necessary by external down conductors. Due to the conductive characteristic of the SSC it is not necessary to provide a separate down conductor. The entire length of the SSC is regarded as the down conductor.

The reinforcing of the SSC foundation is also connected to the welded assembly of the hold down cage for the SSC. This results in the SCC being solidly bonded to the reinforcing. The separate reinforcing steel sections are bonded to each other by means of wiring them solidly to each other at numerous locations.



5.1.3 Earthing electrodes

The earth termination resistance should be less than 10 �. The earthing system consists of the following earth electrode system: Four electrodes are placed on the surrounds of the chimney foundation. One electrode is placed at each foundation corner. These electrodes are copper-bonded will a high fault current capacity. A typical product is the ERITECH

© Reference code 3,0M34 – 34 mm

Ø. The cable connection between the electrode and the SSC is made with rod-to-cable clamps. Inspection pits are provided at each electrode connection (four). Facilities are made at the base of the SSC to support four tower earth clamps that were used to connect the earthing cable onto the SSC.

A Ground Enhancement Material (GEM) was applied around each electrode in a trench width of 20 cm to improve the soil resistivity characteristics and ultimately the earthing resistance. The tips of the earthing rods should be accessible to inspect the connecting conductor. This is achieved by installing an ERITECH

© Earth Rod Inspection Box PIT-03. Ground potential equalisation was not considered

necessary as the four electrodes are equally positioned from the source of the lightning discharge current.

In addition to the above installation, the boiler house adjacent to the SSC required adequate earthing. It is constructed with steel columns and beams with are supported on concrete foundations. The condition of the earthing was not obvious due to the age of the premises and an accurate assessment would have been costly. The outer four corners of the building was supplied with earthing electrodes and the main steel supports where bonded in a manner similar to the electrode design as described above.

5.2 Surge protection of plant & equipment

The historical plant performance of the New Zealand Sugar Refinery does not indicate any previous damage to plant and equipment stemming from a direct lightning strike to the old chimney. However, there are no facts provided that prove previous technical malfunctions have not been due to overvoltage surges - from local faults or faults from the incoming supply. Considering production outage times due to a serious overvoltage incident and the subsequent failure of plant or equipment, it was proposed that NZS install surge protection. This surge protection is against overvoltages due to both direct lightning strikes to the SSC as well as from surges from local distribution supply. The application of surge protection consists of the selection of coordinated surge suppression devices. The categories for surge arrester ratings are illustrated in Table 1.

Table 1: AS/NZ 1768:2007 Lightning Clause 5.6.3.7 Section 5 – Application of SPD’s

TABLE 5.1

Recommended Surge Ratings for A.C. Power Systems

SPDs per phase

Category SPD location Imax rating (kA)

A Long final sub circuits & electricity supply outlets 3 – 10

B Major sub mains, short final sub circuits & load centres 10 – 40

C1 Service entrance, other than below 40

C2 Service entrance, building fed by long overhead service lines, or is a large industrial or commercial premises

40 – 100

C3 Service entrance, building in a high lightning area, or fitted with a LPS

100

WEIDMULLER supplied the SPD product range which covers Category A through to Category C3. It was proposed that the distribution supply within the refinery was inspected and where no surge



suppression exists a maintenance strategy be implemented to install such protection. The installation of an effective LPS system does require that surge protection be included.

The surge arrester ratings are illustrated in Table 6 and Table 7.

Table 6: Proposed Surge Suppression Devices for Main Incoming Supply

Main Incoming Supply 11 kV/415 V TSG Triggered

Spark Gap* PU I Varistor 3 Pole

with Relay**

T1 No. 1 Refinery Transformer 500 kVA Cat # 8960480000 Cat # 8859010000




Table 7: Proposed Surge Suppression Devices for Main Circuit Supply

Main Circuit Supply 280 V

PU II Varistor Type PU II 3R280V* Cat # 8859650000 PU II Varistor Type PU II 1R280V** Cat # 8859700000 PU III Varistor Type PU III 230V*** Cat # 8860330000

6. Operational safety guidelines

6.1 Awareness programmes

NZS has in their existing safety awareness sessions provision of information on the dangers of lightning and the importance to keep within safe zones during normal and adverse weather conditions. In particular, “safety walkways” and access to the boiler house are included. Maintenance inspection of surge suppression equipment and earthing points are also included in routine maintenance inspections.

6.2 Safe walkways & fencing

Current practice to demarcate “safe walks” for pedestrians on the existing roads should continue. The existing location of these “safe walks” adjacent to the existing chimney offer safe clearance from side strikes in the event of a direct lightning strike to the SSC. These are illustrated in Figure 7. In addition to the safe walkways, temporary fencing restricting access to the SSC during installation was also erected.



Figure 7: “Safe Walks” Demarcation Adjacent to SSC�

6.3 Restricted access

For purposes of this study the consequence of damage assumes a limited number people and the duration that they are in the boiler house during severe weather conditions. This situation is regarded as an unsafe event. However, it is not possible to prevent maintenance and construction activities during such periods of potential lightning activity. The only cautionary measure is to make maintenance staff aware of the dangers and if possible they are to avoid contact to steelwork that is directly connected to the SSC during Lightning storms.

6.4 Safe Distance Demarcation��

An appropriate safe demarcation distance from the SS Chimney would prevent a contact voltage or a lightning side flash striking a bypassing employee or contractor in the event of a lightning stroke to the SS Chimney. For a worst case scenario a SS Chimney surge impedance of 300 � can be assumed. For a lightning discharge current of 30 kA, a possible voltage of 900 kV can be realised. Applying McAuley’s rod-to-rod gap equations, the positive and negative polarity critical flashover (CFO) for 2.0 m is:

�789 � �� :� ; �� <��=��>

�78? � :@ ��= ; �� <�A��>

The above values are consistent with a minimum CFO voltage of 570 kV/m.1 The minimum

demarcation distance of 2.5 m from the SS Chimney is sufficient to provide a safe passageway for personnel against expected lightning strokes.

Any maintenance or inspection work scheduled during threatening lightning conditions on the SS Chimney shall be postponed and rescheduled.

1 Andrew Hilerman – Insulation Coordination for Power Systems ISBN 0-8247-9957-7



6.5 Earthing of SS Chimney Flexible Ducting

Both sides of the flexible ducting was securely connected to each other by means of a single 95 mm2

flexible copper cable – similar to the cable applied to the main earth conductors at the base of the SS Chimney. This is illustrated in of Figure 8 and Figure 9 (demarcated by means of a yellow line). Connection was applied in two convenient locations on each of the flexible ducting – a total of four earth connecting bridges (two on each of the flexible ducting). Locations considered regular visual inspection and testing of the earth connections during routine maintenance.

Figure 8: Earthing of Flexible Ducting

Figure 9: Earthing of Flexible Ducting



7. References

1. J. A. Laver and H. Griffiths; The Variability of Soils in Earthing Measurements and Earthing System Performance; Power Engineering (2001) 57-61

2. B.BabyPriya and A.Chilambuchelvan; Modelling and Analysis of DFIG Wind Turbine 3. Harmonics Generated in Grids; B.BabyPriya et al. International Journal of Engineering and

Technology Vol.2(3), 2010, 185-189 4. Georgios C. Christoforidis, Dimitris P. Labridis, Senior Member, IEEE, and Petros S. Dokopoulos,

Inductive Interference on Pipelines Buried in Multilayer Soil Due to Magnetic Fields From Nearby Faulted Power Lines; Member, IEEE; IEEE TRANSACTIONS ON ELECTROMAGNETIC COMPATIBILITY, VOL. 47, NO. 2, MAY 2005

5. AS/NZS 60479.4 – 2010 IEC/TR 60479-4, Ed.1.0 (2004), table A.2 – Comparison of electrical and lightning injury, page 13

6. AS/NZS 1768: 2007 Lightning Protection. 7. AS/NZS 3000: 2007 Wiring Rules (Incorporating Amendment No.1). 8. IEEE 80: 2000 IEEE Guide for Safety in AC Substation Grounding. 9. Hileman, A.R.; Insulation Coordination for Power Systems; Marcel Dekker, New York; 1999.

10. Electricity Engineers’ Association of New Zealand (EEA): Guide to Power System Earthing Practice June 2009.

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