standard for vegetation clearance profile

Standard STNW0602 Ver 4

Ergon Energy Corporation Limited ABN 50 087 646 062

Network Asset Management Standard

Standard for Vegetation Clearance Profile

Approver David Nielsen: Group Manager Standards If RPEQ sign off required insert details below. Ergon Energy Certified Person name and Position Registration Number Anthony Sanders: Manager Line Standards 02835 Abstract: This Network Standard specifies Ergon Energy’s requirements for inspection and treatment of vegetation in the vicinity of Ergon Energy owned high voltage and low voltage power lines and communication and control cables.

It is not applicable to treatment and removal of vegetation in the vicinity of powerlines under construction, nor is it applicable to privately owned lines.

Keywords: Vegetation, clearance, profile, inspection clearance zone.


ii Standard STNW0602 Ver 4


Contents 1. Overview ....................................................................................................................... 1

1.1 Purpose .............................................................................................................. 1

1.2 Scope.................................................................................................................. 1

1.3 Vegetation Management Strategy....................................................................... 1

2. References.................................................................................................................... 1

2.1 Ergon Energy controlled documents ................................................................... 1

2.2 Other documents ................................................................................................ 2

3. Definitions, Acronyms, and Abbreviations................................................................ 2

3.1 Definitions ........................................................................................................... 2

4. Legal Responsibilities ................................................................................................. 4

4.1 Electrical Safety Regulation 2002 ....................................................................... 4

4.2 Compliance with Electrical Safety Regulation 2002 ............................................ 4

5. Clearance Profile Principles........................................................................................ 5

5.1 Clearance Profile Diagram.................................................................................. 5

5.2 Clearance Zone (V1)........................................................................................... 5

5.3 Regrowth Zone (V2)............................................................................................ 5

5.4 Low Vegetation Zone (V3) .................................................................................. 5

5.5 Risk Management Zone...................................................................................... 5

5.6 Overhang Risk Management Zone ..................................................................... 6

5.7 Corridor (Rural Areas Only) ................................................................................ 6

6. Factors Affecting Clearance Dimensions .................................................................. 7

6.1 Line Voltage........................................................................................................ 7

6.2 Line Type ............................................................................................................ 7

6.3 Line Sag & Sway................................................................................................. 7

6.4 Bushfire Hazard Areas........................................................................................ 8

6.5 Existing Rural Corridor Widths ............................................................................ 8

7. Treatment Prescriptions.............................................................................................. 9

7.1 Clearance Zone .................................................................................................. 9

7.2 Regrowth Zone ................................................................................................... 9

7.3 Low Vegetation Zone .......................................................................................... 9


iii Standard STNW0602 Ver 4


7.4 Risk Management Zone.................................................................................... 11

7.5 Overhang Risk Management Zone ................................................................... 11

7.6 Corridors ........................................................................................................... 11

7.7 Pruning and Removal of Trees ......................................................................... 12

7.8 Herbicide Treatment of Vegetation ................................................................... 12

7.9 Mechanical Clearing of Vegetation ................................................................... 12

7.10 Low Growing Vegetation................................................................................... 12

7.11 Stay Wires & Other Structures .......................................................................... 13

7.12 Climbable Trees................................................................................................ 13

7.13 Chipping............................................................................................................ 13

8. Inspection Prescriptions ........................................................................................... 14

8.1 Inspection of Vegetation near overhead HV ABC, CCT or Bare Conductors.... 14

8.2 Inspection of Vegetation near overhead LV ABC Service, Communication and Control Cables ............................................................................................................. 14

9. Clearance Profiles...................................................................................................... 15

9.1 Clearance Profile for Urban LV ABC and insulated services ............................ 15

9.2 Clearance Profile for Urban Bare LV mains and services ................................. 15

9.3 Clearance Profile for Urban Bare 11kV, 22kV and 33kV................................... 16

9.4 Clearance Profile for Urban 11kV ABC and CCT.............................................. 16

9.5 Clearance Profile for Urban Sub-Transmission Lines ....................................... 17

9.6 Clearance Profile for Rural Bare 11kV, 22kV and 33kV.................................... 17

9.7 Clearance Profile for Rural SWER.................................................................... 18

9.8 Clearance Profile for Rural 11kV ABC and CCT............................................... 18

9.9 Clearance Profile for Rural 33kV Sub Transmission ......................................... 19

9.10 Clearance Profile for Rural 66kV Sub Transmission ......................................... 19

9.11 Clearance Profile for Rural 110kV, 132kV (and above) Sub Transmission ...... 20

10. Quick Reference Lookup........................................................................................... 21


Page 1 of 21 Standard STNW0602 Ver 4


1. Overview

1.1 Purpose This Network Asset Management Standard specifies Ergon Energy’s requirements for inspection and treatment of vegetation in the vicinity of high voltage and low voltage power lines and communication and control cables.

Inspection and treatment of vegetation is to be carried out in accordance with this Standard and the Vegetation Management Strategy, as outlined in Section 1.3 below.

1.2 Scope This Asset Management Standard applies to treatment and removal of vegetation in the vicinity of existing Ergon Energy owned powerlines. It is not applicable to treatment and removal of vegetation in the vicinity of powerlines under construction, nor is it applicable to privately owned lines.

This latest version of the Standard for Vegetation Clearance Profile sees a further move towards optimisation of clearance distances, with increases in clearances only where needed, while maintaining a risk-based approach across the network. This is reflective of the need to reduce maintenance expenditure across Ergon Energy’s entire asset base in accordance with business direction.

This Standard replaces STNM002 Version 3.

1.3 Vegetation Management Strategy The clearance profiles in this Standard have been developed to assist in the implementation of the Ergon Energy Vegetation Management Strategy (SGNW0002) which aims to achieve compliance with legislation as outlined in Section 4, as well as ensure acceptable levels of system reliability.

2. References

2.1 Ergon Energy controlled documents BP000204R100 Corporate Risk Management Guideline

ES000905R100. Environmental Planning for Work Guide

NA000403R376. Access Tracks Construction Standards and Specifications

NA000403R380. Treatment of debris in Vegetation Management Maintenance Reference Standard

SGNW0002 Vegetation Management Strategy

SGNW0003 Bushfire Mitigation Strategy

STNW0011. Standard for Managing Private Electric Lines

STNW0601. Standard for Vegetation Management

STNW0603. Standard for Vegetation Management in Riparian Areas




2.2 Other documents Code of Practice: Safe Access in Tree Trimming and Arboriculture. Safe Work Australia.

ENA DOC 023-2009 ENA Guidelines for Safe Vegetation Management Work Near Live Overhead Lines

Code of Practice Working in the Vicinity of Overhead and Underground Electric Lines Safe Work Australia

3. Definitions, Acronyms, and Abbreviations

3.1 Definitions For the purposes of this standard, the following definitions apply.

Aerial Bundled Cable – ABC: Insulated cable manufactured to Australian Standard AS3560 or AS3599 Part 1 or AS3599 Part 2 used in substitution for multiple bare conductors.

Clearance Zone: The space surrounding a powerline that is to be generally kept free of vegetation.

Conductor: Cable or wire designed to transfer electricity, typically constructed of copper, steel or aluminium.

Corridor (a.k.a. Easement): An easement or corridor for transmitting, distributing or supplying electricity whether registered or unregistered.

Covered Conductor – CCT: As defined in AS6375 “Covered Conductor”. CCT is Covered Conductor Thick, which has a defined thickness of covering for high voltage lines. The covering is not “touch safe” and is generally managed the same as bare conductors.

Diameter Breast Height (DBH): Diameter measurement of a standing tree stem at 1.3m above the ground. The measurement is typically taken using a diameter tape or calipers, and is typically measured over bark.

Electric Line (a.k.a Power Line): A wire, conductor, or associated equipment used for transmitting, transforming or supplying electricity.

Hazardous Bushfire Area: Areas mapped by the Queensland Rural Fire Service based on a risk assessment of bushfire hazards. Additional areas may be mapped by Ergon Energy staff as hazardous based on historical knowledge of fire occurrence.

Hazardous Tree: a tree is considered hazardous if it has defects that are likely to cause failure, resulting in damage to Ergon Energy property, personal injury or death.

Inspection: Means the systematic inspection and assessment of a vegetation zone by a suitably experienced and qualified person to record vegetation condition and treatment and/or removal work requirements and negotiation with customers, landholders and property owners on access and tree removals where required. This can include desktop inspection and assessment using Geographical Information Systems (GIS), high resolution imagery and other technology.




Insulated Service Cable: A low voltage multi-core cable insulated by a medium other than an air space as defined in Australian Standard AS3000-1991-SAA Wiring Rules and used for the purpose of conveying electricity through a service wire.

Low Growing Species: Any plant that does not have the potential to grow to a height of more than 4 metres (within distribution line corridors), or; does not have the potential to grow into the clearance space.

Low Vegetation Zone: The space immediately below the clearance and regrowth zones which may contain trees that may or may not be capable of growing into the clearance zone.

Low Voltage: Voltage not exceeding 1000 Volts.

Mature Vegetation Height And Form: Vegetation which has reached approximately 75% of its full height and canopy growth and is of a desired height and form to meet obligations under Electrical Safety Regulation 2002.

Overhang Risk Management Zone: The space above the clearance and regrowth zone, in which vegetation overhanging the line must be risk assessed for stability. Overhanging limbs may pose a risk due to factors such as disease, fractures, dead wood and erosion or failure in adverse weather conditions.

Regrowth Zone: The space beyond the clearance zone that is to be cleared to allow for anticipated vegetation regrowth in the period leading up to the next scheduled pruning and treatment activity.

Risk Management Zone: The space outside the clearance, regrowth and low vegetation zones in which unstable trees or limbs may pose a risk to the electric line. This may be due to factors such as disease, fractures, dead wood, soil erosion or wind throw potential.

Rural Area: An area that is not an urban area.

Service Line: An electric line, including a connection to a service fuse, servicing a customer’s premises from the point of supply on Ergon Energy’s electrical network.

Sub Transmission Line: A power line that operates at a normal voltage equal or greater than 33kV, but not more than 132kV, for the purpose of transmitting electricity between zone substations.

SWER: Single Wire Earth Return; electric line style with a single conductor.

Tall Growing Species: An identified plant species which occurs within close proximity to a power line (typically within the corridor or risk management zone) that has the potential to grow into the clearance zone or reach a height capable of presenting an unacceptable risk to power supply or electrical safety.

Tree Size Classes: Trees scheduled for treatment are allocated a size class based on the diameter of its stem at breast height (DBH). Where a tree has multiple stems, the combined diameter of those stems should be used to determine size class. Areas of ground containing multiple individual plants with stems less than 100mm DBH, which are difficult to “group” to form a combined diameter, should be allocated under an hourly rate as agreed with the contractor. The classes are as follows:

• Class A: 100mm – 299mm DBH • Class B: 300mm – 599mm DBH • Class C: 600mm – 899mm DBH




• Class D: > 900mm DBH

Urban Area: An area of land which is predominantly: a. sub-divided into residential allotments which are not greater than 0.4 hectares or;

b. able to be used or developed under a planning scheme for residential, industrial or commercial purposes; or

c. provided with constructed streets and public utility services; or

d. located adjacent to roadways with a speed limit of less than or equal to 60km/hr

Vegetation Clearance Interval (a.k.a Cutting Cycle): The interval between successive inspection and treatment activities which Ergon Energy judges optimal for maintaining clearances between power lines and vegetation. It is usually a period of 12, 15, 18, 24, 36, 48 or 60 months depending on factors such as expected plant growth rates, or whether it is located in an urban or rural area.

4. Legal Responsibilities

4.1 Electrical Safety Regulation 2002 Ergon Energy has legal responsibilities to maintain safe clearances between vegetation and power lines under Section 148 of the Electrical Safety Regulation 2002, which reads:

Section 148: Trimming of trees near overhead electric line An electricity entity must ensure that trees and other vegetation are trimmed, and other measures taken, to prevent contact with an overhead electric line forming part of its works that is likely to cause injury from electric shock to any person, or, damage to property.

4.2 Compliance with Electrical Safety Regulation 2002 In order to comply with the Electrical Safety Regulation 2002, Ergon Energy aims to achieve the following outcomes from its vegetation management program:

• Having no climbable trees that, based on a risk assessment, would reasonably facilitate access to live conductors;

• Having no trees in contact with, or within arcing distance of, bare wire overhead conductors, likely to cause injury from electric shock to any person or damage to property;

• Having no tree in contact with bare overhead conductors which is likely to cause clashing of conductors; and

• Having no trees likely to damage the insulation on insulated cables.




5. Clearance Profile Principles

5.1 Clearance Profile Diagram The area in the vicinity of powerlines is divided into a number of zones, which are used for specifying and determining requirements for vegetation assessment and treatment. These zones are shown in Figure 1 below, and are described in the following section.

Figure 1: Typical Vegetation Clearance Profile Diagram

5.2 Clearance Zone (V1) The clearance zone is the space immediately surrounding an overhead conductor or cable that is generally to be kept clear of vegetation at all times. The clearance dimensions (Cl) for the Clearance Zone (V1) from the conductor or cable are specified in Table 1. The Clearance Dimension (Cl) applies radially from the conductor.

5.3 Regrowth Zone (V2) The regrowth zone is the space immediately beyond the clearance zone that is to be cleared to allow for anticipated vegetation regrowth during the vegetation treatment interval.

5.4 Low Vegetation Zone (V3) The low vegetation zone is the area immediately below the clearance and regrowth zones. There may be various species of trees or shrubs growing in this zone that may or may not eventually grow into the clearance zone.

5.5 Risk Management Zone The risk management zone is the space outside the clearance, regrowth and low vegetation zones in which unstable trees and limbs may present a risk to the safety and reliability of the powerline. The risk may be due to factors such as disease, fractures, dead wood and erosion or failure in adverse weather conditions.

Regrowth Zone (V2)

Low Vegetation Zone (V3)

Clearance Zone (V1)

Risk Management Zone


Overhang Risk Management Zone

Cl

Cl

Cl




5.6 Overhang Risk Management Zone The overhang risk management zone is the space above the clearance and regrowth zones, overhanging the line in which unstable trees or limbs may pose a risk to power supply or safety. These may be unstable due to factors such as disease, fractures, dead wood and erosion or failure in adverse weather conditions.

5.7 Corridor (Rural Areas Only) A corridor is a specified clearance width to which vegetation must be treated to. Used only in rural areas where span length and vegetation treatment intervals are generally longer, making prediction of required regrowth clearance dimensions otherwise too difficult. Corridor dimensions are measured from the centre line of the span.

Scalloping of corridor width is not required. A constant corridor width is to be applied along the entire span unless specified under Sections 6.4 or 6.5. Fauna habitat connectivity is to be maintained through retention of low growing species wherever possible.

Figure 2: Plan view of Rural Corridor Clearance Zone

RISK MANAGEMENT ZONE

ClearanceDimension

RURAL CORRIDOR




6. Factors Affecting Clearance Dimensions

6.1 Line Voltage The voltage level of the line influences the potential for electric discharge through arcing or conduction. The higher the voltage the greater the potential and hence need for greater clearance zone dimensions.

6.2 Line Type Insulated conductors reduce the risk of electric discharge. Use of aerial bundled cable or other insulated conductors reduces the necessary dimensions of the clearance zone. CCT is not considered to have sufficient insulation properties for reduced clearance dimensions.

6.3 Line Sag & Sway As shown in Figure 3, conductors have the ability to sag and sway; the extent of which is influenced by several line design and environmental factors:

• Span length (as determined by the distance between supporting structures) – influences both sag and sway. As span length increases, so does the weight of the line, leading to greater sag potential. Also as the span length increases, greater sideways sway movement is possible in a line.

• Conductor diameter – influences the weight of the line, and therefore how much it will sag. Therefore, the greater the voltage the greater the diameter and greater the line sag.

• Distance from supporting structure – influences both sway and sag. On level ground, the mid-point of a span experiences the most sag and sway, and requires greatest vegetation clearance effort. However, on sloping ground, the line will sag greatest closer to the lower supporting structure due to gravity, and will sway most at that same point.

• Conductor temperature – influences the expansion and contraction of the conductor material and affects line sag. As air temperature increases, or as electrical current increases, conductor temperature also increases leading to conductor expansion and greater sag.

These factors can be in a state of continual change, so an allowance is made in the clearance zone dimensions for the possibility of significant line sag and sway, with emphasis placed on the centre section of each span.

Figure 3: Sag and Sway




6.4 Bushfire Hazard Areas Ergon Energy does not generally require wider corridor dimensions in high bushfire hazard areas. However, if it is considered that widening of a corridor is necessary to address a site specific bushfire hazard identified under the Ergon Energy Bushfire Mitigation Strategy (SGNW0003), a request may be submitted to the Vegetation Strategist for approval. The request must include a documented risk assessment as per BP000204R100 “Corporate Risk Management Guideline”.

6.5 Existing Rural Corridor Widths Where existing corridor widths are greater than those specified in Tables 2 and 5, the existing corridor width should be applied so long as allocated budgets are not exceeded. In locations that have been most recently treated to an “interim narrow profile”, but have a wider original corridor design that is still visually evident, the original corridor dimension should be re-applied wherever possible.

For hourly rate style contracts, where budget constraints do not allow treatment to original corridor widths, the dimensions specified in this Standard shall be applied as a minimum.

For lump sum, “span rate”, or “SOR unit” style contracts, corridor widths shall be applied as per the contract specifications for each Vegetation Zone. Where such contract specifications do not exist for a Vegetation Zone, the corridor dimensions contained in this Standard are to be applied.




7. Treatment Prescriptions

7.1 Clearance Zone The primary aim of the vegetation management program is to exclude vegetation from the clearance zone. Where vegetation is growing into the clearance zone before it can be inspected and treated in the next cycle, or is deemed to have reached mature height and form and presents negligible risk to power supply interruption or safety, the following concessions are made:

• Vegetation brushing against low voltage lines or service lines having reached mature height is considered to be low risk, providing the tree is not climbable or capable of clashing conductors or damaging the conductor or attachments and should be excluded from treatment;

• While vegetation may occasionally encroach into the clearance zone of high voltage lines, it may not be permitted to touch or come within arching distance of such lines due to the increased safety risk; and

• Vegetation which comes into contact with insulated cables is considered to be low risk provided the contact does not threaten the insulation’s structural integrity through abrasion or other such processes.

No concessions are allowed for Sub Transmission electric line clearance zones. Clearance zone dimension requirements are specified in Table 1.

7.2 Regrowth Zone Variations in the uniformity of regrowth zone dimensions along particular power lines or between different power lines are permitted. The following factors will influence the dimensions of the regrowth zone along each span:

• the species of vegetation and the height and regrowth habits of that species;

• varying soil and environmental conditions along the line route;

• recent rainfall levels and expected rainfall levels in the next period between treatment times; and

• the nominated vegetation treatment interval.

7.3 Low Vegetation Zone Trees and shrubs in the low vegetation zone that are a known low or slow growing species and are not expected to grow into the clearance zone are not to be targeted for trimming, removal or herbicide treatment.

In urban areas, plant species growing within the low vegetation zone (V3) whether known to be tall growing or not are not to be treated or removed unless otherwise directed by the Vegetation Management Officer.

In rural areas, tree species growing within the low vegetation zone which are known to be tall-growing species are to be removed or chemically treated when most suitable for treatment effectiveness and cost efficiency. Trees occurring in gullies, or with slow growth rates, and have no chance of entering the clearance zone within the next 10 years are not to be treated.




Category Location Span length Clearance Zone (Cl) Dimensions (m) From conductor

Near Pole 1.0

Up to 40m 1.5

40-70m 2.0

Open Wire LV Mains and LV

Services Mid 2/3 of

Span > 70m 2.5

Near Pole 1.0

Up to 40m 2.0

40-70m 2.5

Open Wire 11kV, 22kV 33kV and

SWER Mid 2/3 of

Span > 70m 3.0

Near Pole 0.6 Up to 40m 0.6 40-70m 1.0

11kV ABC Mid 2/3 of

Span > 70m 1.4

Near Pole 1.0 Up to 40m 2.0 40-70m 2.5

11kV CCT Mid 2/3 of

Span > 70m 3.0

Near Pole 0.3 Up to 40m 0.3 40-70m 0.6

LV ABC and Services

Mid 2/3 of

Span > 70m 0.9

Near Pole 0.3 Up to 40m 0.3 40-70m 0.6

Communication& Control Cable

(Urban & Rural) Mid 2/3 of

Span > 70m 0.9

Near Pole 3.0 Up to 40m 3.0 40-70m 3.0

Open Wire 66kV to 132 kV Mid 2/3 of

Span > 70m 3.0

Table 1: Clearance Zone dimensions Urban & Rural areas




7.4 Risk Management Zone Where vegetation within the Risk Management Zone is identified during Inspection or Treatment as potentially presenting a higher risk than is acceptable, a risk assessment should be undertaken to confirm the level of risk and document appropriate remedial measures. Remedial measures can include limb or whole tree removal, extension of corridor width, or suggested network engineering solutions. As a guide:

• branches from trees outside rural corridors with potential to grow into the clearance zone in the cycle time will require treatment;

• all vegetation outside the rural corridor with high potential to fall into the clearance zone in the cycle time are to be subject to risk assessment following an industry recognised visual tree assessment procedure, this includes dead or dying trees. Vegetation which fails the risk assessment is to be removed or made safe and chemically treated if required to prevent regrowth; and

• in rural areas, “Class A”-sized trees outside the corridor that have the potential of growing into the clearance zone within the cycle time are to be treated.

7.5 Overhang Risk Management Zone Overhanging branches composed of seemingly sound timber are generally allowed to remain, with the following exceptions:

• Where overhang is permitted, all branches must be pruned to 4m above the conductors; and,

• Sub Transmission and Transmission lines are not permitted to have any overhang.

7.6 Corridors Corridors are to be applied in rural areas only; urban areas do not have an applicable corridor size. Vegetation which has the potential to enter the clearance zone is to be treated, except where concessions are made as per Section 7.1. In rural areas, the following minimum corridor widths apply either side of the centre line:

Rural Corridor Distance from Centre line (m) Bare Wire LV 4 SWER 4 11kV ABC and CCT 5

11kV, 22kV, 33kV 6 33kV Sub Transmission 6 66kV Sub Transmission 15

110kV (and above) Sub Transmission 20

Table 2: Rural corridor dimensions All tall growing species within the corridor are to be removed or chemically treated when most suitable for treatment effectiveness and cost efficiency. Where chemically treated, trees must not have the potential to fall into the clearance zone once dead.




7.7 Pruning and Removal of Trees Trees shall be pruned in accordance with Australian Standard AS4373 – 2007 “Pruning of Amenity Trees”.

In urban areas, removal of trees must follow Maintenance Reference Standard ‘Negotiation for the removal or herbicide treatment of unsuitable trees’ (NA00403R378). Removal should be considered where the vegetation:

• will continue to be hazardous to power supply or safety, or;

• is likely to be an ongoing management issue over three or more successive treatments; or

• is not anatomically suited to required pruning (ie. palm species).

Remaining stumps shall not be more than 50mm above and cut parallel to the ground unless required otherwise by the landholder or Vegetation Management Officer. Stumps in high pedestrian traffic areas should be cut to ground level to eliminate any tripping hazard. In urban areas, stump grinding should be considered if requested by the Vegetation Management Officer or customer to mitigate any safety hazard.

7.8 Herbicide Treatment of Vegetation Vegetation requiring management may be treated with herbicide provided:

• safe approach and vegetation clearance distances are maintained;

• the vegetation is not of recognised significant ecological, cultural or economic importance;

• the vegetation is assessed as unlikely to contact the conductors or fall into the clearance zone once the tree has died; and,

• the vegetation is assessed as unlikely to block any watercourse once it has died.

Stem injection, residual herbicide pelleting, foliar spray and all other methods resulting in standing dead vegetation are not to be used in urban areas.

In rural areas, cost effective herbicide application methods such as stem injection, herbicide pelleting, and foliar spraying are to be utilised wherever appropriate, except where such vegetation has the potential to fall into the exclusion zone, or across watercourses, roads, fences or other assets once dead. Methods such as vegetation height reduction or directional felling may be used to eliminate this potential.

Operators are required to follow operational requirements noted in STNW0601 ‘Standard for Vegetation Management’, STNW0604 ‘Standard for Vegetation Management in Riparian Areas’, as well as relevant legislation and agreements related to herbicide usage.

7.9 Mechanical Clearing of Vegetation While treatment of vegetation through selective herbicide use or hand clearing is preferred, it is acknowledged that in areas of dense regrowth or where access over terrain is difficult, that mechanical clearing using “mega mulchers”, “Pozitrac” or other suitable machinery may be necessary.

Vegetation treatment methods chosen are to be primarily based on efficiency and expected long term treatment costs.

When using mechanical clearing methods, operators are required to abide by operational requirements set out in the STNW0601 ‘Standard for Vegetation Management’.

7.10 Low Growing Vegetation Wherever possible, low growing vegetation species are to be identified and retained. Treatment methods should ensure as much low growing vegetation remains as possible, with selective stem injection, foliar spraying and removal being preferred over broad scale herbicides and mechanical clearing.




7.11 Stay Wires & Other Structures Vines and other vegetation with potential to enter the conductor clearance space or cause damage within the cycle time to any stay, pole, ground anchor or other overhead electrical distribution network structure are to be removed or treated with herbicide.

7.12 Climbable Trees In urban areas, where trees are assessed as able to be climbed and provide access to live conductors, risk assessments are required to be undertaken. Tree trunks or large branches that can be used to access the conductors are to be trimmed or removed where necessary. Trimming options must include removal of any lower branches within 3m of the ground which could be used in the climbing process.

7.13 Chipping Chipping of pruning residue is only to be undertaken where required and generally limited to within urban areas. In urban areas residue is to be removed as soon as practicable after pruning has occurred.

In rural areas, any debris produced is generally to be cut and laid flat away from structures, watercourses and standing vegetation. Refer to the Maintenance Reference Standard ‘Treatment of Debris in Vegetation Management (NA000403R380) for further instruction.




8. Inspection Prescriptions

8.1 Inspection of Vegetation near overhead HV ABC, CCT or Bare Conductors Table 3 shall apply when inspecting vegetation for all bare, HV ABC or CCT conductors.

Criteria

V1 Vegetation is inside the clearance zone

V2 Vegetation will encroach in the clearance zone before the next treatment cycle.

V3 Vegetation will encroach inside the clearance zone in future cycles.

Table 3: Inspection of Vegetation near Overhead HV ABC, CCT or Bare Conductors

Note: In urban areas, vegetation classified as V3 is not to be treated or removed unless directed otherwise by the Vegetation Management Officer. Note: Trees and branches in the Overhang Risk Management Zone or in the Risk Management Zone that have been identified as high risk from a visual assessment during inspection, are to be recorded as V2. 8.2 Inspection of Vegetation near overhead LV ABC Service, Communication and

Control Cables Table 4 shall apply when inspecting vegetation near overhead LV ABC, or service, communication or control cables where small branches and leaves are allowed inside the clearance zone.

Criteria

V1 Vegetation is inside the clearance zone and is already causing abrasion or deviation of the cables.

V2 Vegetation is either inside or just outside the clearance zone, is not presently causing abrasion or deviation of the cable, and is likely to cause abrasion or deviation of the cable before the next treatment cycle.

V3 Vegetation is either inside or just outside the clearance zone, is not presently causing abrasion or deviation of the cable, and is unlikely to cause abrasion or deviation of the cable before the next treatment cycle.

Table 4: Inspection of Vegetation near LV ABC, or Service, Communication and Control Cables




9. Clearance Profiles

9.1 Clearance Profile for Urban LV ABC and insulated services

Figure 4: Urban LV ABC and insulated services

9.2 Clearance Profile for Urban Bare LV mains and services

Figure 5: Urban Bare LV mains & services

Regrowth Zone (V2)


Clearance Zone (V1)




Cl

Cl

Cl

Cl

Clearance Zone (V1)

Regrowth Zone (V2)








9.3 Clearance Profile for Urban Bare 11kV, 22kV and 33kV

Figure 6: Urban Bare 11kV, 22kV and 33kV lines

9.4 Clearance Profile for Urban 11kV ABC and CCT

Figure 7: Urban 11kV ABC and CCT lines

Clearance Zone (V1)








Regrowth Zone (V2)


Clearance Zone (V1)

Cl

Cl

Cl

Regrowth Zone (V2)

Cl




9.5 Clearance Profile for Urban Sub-Transmission Lines

Figure 8: Urban Sub-Transmission 33kV, 66kV, 110kV, 132kV (and above)

9.6 Clearance Profile for Rural Bare 11kV, 22kV and 33kV

Figure 9: Rural Bare 11kV, 22kV and 33kV lines

Regrowth Zone (V2)




Clearance Zone (V1)

Cl

Cl

NO OVERHANG ALLOWED




Corridor (6m)


Clearance Zone (V1)

Cl

Cl

Cl

Corridor (6m)




9.7 Clearance Profile for Rural SWER

Figure 10: Rural SWER lines

9.8 Clearance Profile for Rural 11kV ABC and CCT

Figure 11: Rural 11kV ABC and CCT lines

Clearance Zone (V1)





Corridor (5m) Corridor (5m)

Cl

Cl

Clearance Zone (V1)

Corridor (4m)




Corridor (4m)

Overhang Risk Management

Zone




9.9 Clearance Profile for Rural 33kV Sub Transmission

Figure 12: Rural 33kV Sub Transmission lines

9.10 Clearance Profile for Rural 66kV Sub Transmission

Figure 13: Rural 66kV Sub Transmission lines

Corridor (6m)




Clearance Zone (V1)

Cl

Cl

NO OVERHANG ALLOWED

Corridor (6m)

Corridor (15m)




Clearance Zone (V1)

Cl

Cl

NO OVERHANG ALLOWED

Corridor (15m)




9.11 Clearance Profile for Rural 110kV, 132kV (and above) Sub Transmission

Figure 14: Rural 110kV, 132kV (and above) Sub Transmission lines

Corridor (20m)




Clearance Zone (V1)

Cl

Cl

NO OVERHANG ALLOWED

Corridor (20m)

Standard for Vegetation Clearing Profile



10. Quick Reference Lookup

Table 5. Minimum Clearance Zone and Rural Corridor Specifications.

Category Clearance (m) @ Pole

Clearance (m) Centre 2/3

<40m


40-70m


>70m

Rural Corridor (m)

from centre line

Remove all overhang?

Treatment of all tall growing species in

Corridor? Communication & Control Cable 0.3 0.3 0.6 0.9 N/A NO N/A

LV ABC & Services 0.3 0.3 0.6 0.9 N/A NO N/A

Bare wire LV Mains

LV Services 1.0 1.5 2.0 2.5 4.0 NO RURAL ONLY

SWER 1.0 2.0 2.5 3.0 4.0 NO RURAL ONLY

11kV ABC 0.6 0.6 1.0 1.4 5.0 NO RURAL ONLY

11kV CCT 1.0 2.0 2.5 3.0 5.0 NO RURAL ONLY

Bare Wire 11kV, 22kV, 33kV 1.0 2.0 2.5 3.0 6.0 NO RURAL ONLY

Sub Transmission 33kV 1.0 2.0 2.5 3.0 6.0 YES RURAL ONLY

Bare wire 66kV 3.0 3.0 3.0 3.0 15.0 YES RURAL ONLY

Bare wire 110kV and above 3.0 3.0 3.0 3.0 20.0 YES RURAL ONLY

standard for vegetation clearance profile

Documents