Standard: Distribution Design Manual Vol 4 Underground Cable Distribution

Transcription

1 Standard: Distribution Design Manual Vol 4 Underground Cable Distribution Standard Number: HPC-5DC

2 Document Control Author Name: Anthony Seneviratne Position: Standards Engineer Document Owner (May also be the Process Owner) Name: Justin Murphy Position: Manager Power System Services Approved By * Name: Justin Murphy Position: Manager Power System Services Date Created/Last Updated June 2014 Review Frequency ** 3 yearly Next Review Date ** June 2017 * Shall be the Process Owner and is the person assigned authority and responsibility for managing the whole process, end-to-end, which may extend across more than one division and/or functions, in order to deliver agreed business results. ** Frequency period is dependent upon circumstances maximum is 5 years from last issue, review, or revision whichever is the latest. If left blank, the default shall be 1 year unless otherwise specified. Revision Control Revision Date Description A 17/06/2014 Initial Document STAKEHOLDERS The following positions shall be consulted if an update or review is required: Manager Engineering Services Manager Assets Management Services NOTIFICATION LIST The following shall be notified if an update or review is required Engineering & Projects Operations Page 2 of 47 Print Date: 18/12/2013

3 TABLE OF CONTENTS FOREWORD INTRODUCTION General Design Objectives DESIGN PROCESS AND INPUTS Safety in Design Network Requirements Planning Equipment Installation Requirements Cable Route Termites Equipment Location Equipment Compatibility Environmental and Approval Management ELECTRICAL EQUIPMENT USED FOR UDS INSTALLATIONS Medium Voltage Ring Main Unit (RMU) Switchgear Outdoor RMU Kiosks Indoor RMUs MV Cables, Joints and Terminations MV Feeder Cables MV Transformer Cables MV Cable Joints MV Terminations Non-Loadbreak Terminations Load break Terminations Types of Substations Modular Packaged Substations (MPS) Non MPS Arrangements Customer Owned Substations Single Phase Padmount Transformers kva Single Phase (SPUDS) Transformer kva Rural Underground Transformer Service Pillars LV Cables, Joints and Terminations Page 3 of 47 Print Date 23/06/2014

4 3.5.1 LV Feeder Cables: LV Service Cable LV Street Light Cables Other LV Cables LV Cable Joints/Terminations VOLTAGE REGULATION Voltage Tolerance Limits Statutory Voltage Tolerance Limits Voltage Drop Criteria Effect of Different Load Cycles Voltage Drops and Line Currents in LV Feeders General Effect of Load Unbalance Voltage Drops/Line Currents in Meshed Networks Voltage Drop Limits for LV Networks MV Voltage Regulation Design Approach Computer Modelling Voltage Control Equipment UNDERGROUND DISTRIBUTION SCHEMES (UDS) Design Procedure Transformers Initial Requirements Transformer Selection Mixed Loads Example Regions other than Esperance LV Network Design Primary Aim Challenge for Network Designers Use of Computer Packages Aspects of Electrical Design Determination of Cable Size Selection of LV Feeder Routes Proximity to Loads Utilisation/Loading Typical Route Lengths Page 4 of 47 Print Date 23/06/2014

5 5.3.8 Interconnection with Other Feeders Pillar/Cabinet Positioning and Alignment Other Considerations Typical Design Issues MV Design MV Cable Requirements MV Network Systems Radial Feeder System Ring Main System Hybrid System Satellite Substations Automation Design Outputs Outputs - MV/LV Layouts Outputs - Cable Ducts DETERMINATION OF RECOMMENDED LOAD DEMAND VALUES Estimation of Load Demand Effect of Load Diversity on Maximum Demand Residential Load ADMDs Determination of ADMD when standard values are not used Non-Residential Load Demands Residential Lot Classification LV FEEDER PROTECTION Introduction Feeder Protection Policy LV Fuse Selection Policy Prescribed Fuse Sizes (MV and LV) Maximum Lengths of LV Feeders General Equivalent Length of LV Feeders Feeder Equivalent Length Calculation Maximum Equivalent Lengths What if the Maximum Allowable Length is Exceeded? Calculation of Fault Currents at End of LV Feeders Fault Current Ready Reckoner Typical LV Fuse Time-Current Characteristics Page 5 of 47 Print Date 23/06/2014

6 8 INSTALLATION REQUIREMENTS STREET LIGHTING APPENDIX A REVISION INFORMATION APPENDIX B CURRENT RATING OF UNDERGROUND CABLES B.1 Continuous Current Rating B.1.1 Rating Factors for depth of laying direct in the ground B.1.2 Rating Factors for depth of laying direct in a duct B.1.3 Rating Factors for variation in Thermal Resistivity (3 core cables laid directly in the ground) B.1.4 Rating Factors for variation in Thermal Resistivity (1 core cables laid directly in the ground) B.1.5 Rating Factors for variation in Thermal Resistivity (3 core cables laid in duct buried in the ground) B.1.6 Rating Factors for variation in Thermal Resistivity (1 core cables laid in duct buried in the ground) B.1.7 Rating Factors for Variation in Ambient Temperature B.1.8 Rating Factors for Variation in Ground Temperature Page 6 of 47 Print Date 23/06/2014

7 FOREWORD This volume is one in a series of five volumes, which together, form the Horizon Power Distribution Design Manual. The DDM is intended to be a comprehensive reference manual for distribution design work carried out by professional engineers and technical support staff. The five volumes are: Volume 1: Quality of Electricity Supply Volume 2: Low Voltage Aerial Bundled Cable Volume 3: Supply to Large Customer Installations Volume 4: Underground Residential Distribution (URD) Volume 5: Overhead Bare Conductor Distribution The DDM will also serve to initiate "newcomers" to distribution work in Horizon Power without them having to start from scratch. It serves to establish "standards" for design work to ensure that we get the best value from our facilities - not only in terms of initial cost, but also in terms of component availability, length of service life and cost-effective maintenance. In addition to this, the DDM will also serve as a teaching aid for courses run by Horizon Power. This volume describes the engineering process involved in designing and providing electricity supplies using underground cables. It describes the design process in detail, making use of standardised design information for use with routine work. Page 7 of 47 Print Date 23/06/2014

8 1 INTRODUCTION 1.1 General This document describes the engineering process involved in designing distribution underground networks. These networks typically originate from Zone substations as medium voltage feeders and are stepped down to low voltage networks through distribution transformers. Low voltage distribution networks then transmit power to customer installations, though some customers are supplied directly from the medium voltage networks. Although, underground cables do not account for a significant proportion of Horizon Power's networks at present, Horizon Power's policy mandates underground power supplies in all sub divisions including residential, rural residential, commercial and industrial. There are variations to this policy in the case of larger lot sizes greater than 10 hectares, which can be found in Horizon Power s Underground Distribution Schemes Manual. Underground assets are capital intensive, both for Horizon Power and its customers and they need to be properly designed and constructed. It is imperative that a high level of engineering is put into their designs, particularly because cables are buried and are not visible. Effort expended during design could avoid unnecessary expenses and ensure that the requirements (Horizon Power's and its customers ) are catered for. Each cable network may require different design considerations, configurations, layouts, etc. As such, there may be many different ways to approach a design. The information contained in this manual will assist the designer to develop a structured design approach, and ensure that the optimum configuration is selected at all times. 1.2 Design Objectives The objectives of underground cable design are to: a) Reduce cost to customers; b) Reduce life cycle costs; c) Provide greater durability, with due consideration to location in rocky, saline and marshy soils; d) Ensure safety of workers and the general public (safety in design); e) Promote environmental compatibility; f) Ensure electromagnetic field compatibility; g) Promote public acceptance (e.g. easements); and h) Attain and exceed the required supply quality and reliability standards. Page 8 of 47 Print Date 23/06/2014

9 The following factors are to be considered before the design can commence: a) Potential number of customers and total load; b) Estimation of potential load growth; c) Availability and/or requirement for interconnections; d) Selection of voltage for line operation; e) Size and location of loads (Bulk supply, transformers); f) Selection of route; g) Length of cable route; and h) Life cycle costs. Note: The size and type of cable to be used will be dictated by the capacity (load) to be carried by the cable during its lifetime together with voltage drop, thermal rating and fault rating considerations. Page 9 of 47 Print Date 23/06/2014

10 2 DESIGN PROCESS AND INPUTS This section covers the various considerations and inputs needed as part of design. The steps involved in the design of an underground cable network will depend on the individual project and the context in which the design is performed. It is an iterative process, with the designer making some initial assumptions, e.g. cable type and rating, which may later be adjusted as the design is checked and gradually refined. Delivering an optimum arrangement that meets all constraints as the final outcome. Horizon Power mainly uses underground cable simulation software to aid the design process. 2.1 Safety in Design Whenever design work is undertaken to construct new distribution network assets, or modify existing assets, demonstration of due diligence with respect to safety is required. This must cover the full life cycle of the asset that is created or the remaining life of the modified asset and thought about early in the design stage. The essential elements covering a designer s responsibility in ensuring the safety of the asset during its life cycle are addressed in the document, Guideline Safety in Design - HPC-2DC Network Requirements Design shall take into account both present and future network requirements. This information is typically covered in the relevant planning report, design specification and equipment specifications Planning For new distribution networks or extension to existing distribution networks, planning is carried out during concept development stage. Details covered in the planning reports that need to be considered include but not limited to: a) Load size; b) Load distribution centres; c) Load cycle; d) Nature of load; e) Required transfer capacity; f) Potential interconnection point; and g) Automation requirements Equipment Design specification and equipment specifications play a role in capturing requirements that need to be addressed during design. This includes the following: a) Equipment and cable rating for normal load, emergency load and for fault conditions (selection of medium voltage cables as feeders based on continuous current rating is covered in Appendix A ); b) Equipment or cable operating conditions (e.g. Broome versus Esperance); Page 10 of 47 Print Date 23/06/2014

11 c) Network tolerance limits (e.g. statutory voltage tolerance limits); d) Standard installation requirements (refer to clause 2.3); and e) Protection grading requirement. In special cases, there may also additional requirements such as: i. Customer request for a higher security supply; and ii. Coordination with road lighting design 2.3 Installation Requirements Installation condition has a significant impact on the overall technical design of an underground distribution network. Factors that must be considered by designer include but not limited to the following: a) Ambient air and ground temperature; b) Soil type and terrain such as: sandy, rocky, water table, etc.; c) Soil or backfill thermal resistivity; d) Cable installation arrangement (i.e. numbers of circuit within same easement, use of conduit, installation depth, etc.); e) Space requirement for installation of ground mounted equipment; f) Termites activity; g) Environmental risk such as fire, flood, acid sulphate soil and erosion; h) Pollution such as dust, salt and noise; i) Proximity to other utility assets and congestion level from existing services; j) Proximity to metallic/conductive structures; k) Proximity to occupiable structures; and l) Soil salinity Cable Route Evaluate the terrain to determine issues with ground. For example, suppose a medium voltage underground cable is to be constructed to supply a customer remote from a zone substation, and the line route traverses an area of rock, it would seem prudent for the designer to consider the issues involved in embedding cables in rock and the associated cost Termites Termite protection must be installed in all areas prone to termite attack Equipment Location Equipment must be suitable for the environment in which it operates. For example, a ground mounted transformer with open bushings may not be suitable for use outside a cement plant or quarry, where the build-up of fly-ash or dust may lead to nuisance tripping or a disproportionately high level of maintenance. Others include mines sites, with open air blasting, etc. Page 11 of 47 Print Date 23/06/2014

12 The location of ground mounted substations and other equipment shall take into consideration access, fire separation, touch and step potential, and other related issues. (Refer to Substation Installation Technical Requirements HPC-9DJ and Distribution Line Earthing Standard HPC-9DC ). 2.4 Equipment Compatibility Standard equipment shall be used as much as possible. In certain cases however, use of non- standard equipment may be required to deliver the required outcome or to deliver the most cost-effective solution. In such cases, equipment compatibility must be considered. Where unusual conditions or other circumstances warrant using alternative equipment the disadvantages in terms of readily available replacements and operational issues must be considered. Cable accessories such as joints and terminations for example, can only be used for cables within a certain size range. Other factors that need to be considered include but not limited to: a) Equipment s rated voltage b) Equipment s normal load and fault rating In cases where non-standard equipment is required as part of the design, the designer should seek formal approval from the Standards Group prior to proceeding with the final design. 2.5 Environmental and Approval Management Environmental sensitive areas, land usage, condition and ownership issues along a cable installation route can have a significant impact on the overall project cost and timeline. Relevant factors that need to be considered by designers include but not limited to the following: a) Aboriginal heritage sites or areas; b) Area with bio-security weeds, pests and disease spread risk (i.e. dieback disease); c) Threatened ecological communities, sites with declared rare flora and fauna; d) Land with native title; e) Protected wetlands; f) Waste management areas; and g) Registered and/or private lands. Prior approvals are typically required to perform work at or close to these sites. Where vegetation clearing is required, a permit shall also be obtained prior to proceeding with the clearing. Current statutory processes require a range of approvals to be obtained prior to commencement of works. Due to the time taken to obtain these approvals, these issues must be considered at the commencement of a project. As per the Western Australian Distribution Connections Manual (WADCM Section 6.12) environmental and heritage impacts must be investigated and managed by the applicant for power supply and their agent. Page 12 of 47 Print Date 23/06/2014

13 3 ELECTRICAL EQUIPMENT USED FOR UDS INSTALLATIONS 3.1 Medium Voltage Ring Main Unit (RMU) Switchgear 22 kv and 33 kv RMU switchgear is used for switching of the medium voltage network. They are used as a "standalone" kiosk or incorporated into a RMU integrated package substation (only option is currently available as a packaged substation). 11 kv networks shall make use of 22 kv switchgear Outdoor RMU Kiosks The commonly used outdoor RMU combinations at 22 kv and 33 kv are: a) 2 switches plus 1 fuse switch (2+ 1); b) 2 switches plus 2 fuse switches (2+2); c) 2 switches plus 3 fuse switches (2+3) only at 22 kv; d) 3 switches plus 0 fuse switches (3+0); e) 3 switches plus 1 fuse switch (3+1); f) 3 switches plus 2 fuse switches (3+2); and g) 4 switches plus 0 fuse switches (4+0); 22 kv and 33 kv RMUs are incorporated into either 3, 4 or 5 way kiosks (e.g. 2+2). RMUs are installed in a freestanding aluminium kiosk mounted on a steel frame. This steel frame is buried in the ground to provide a firm foundation and allows easy access to the cables and terminations below the switchgear Indoor RMUs Indoor compounds comprising brick enclosures with roof are used to house RMUs and transformers. They are generally used to cater for larger loads (> 630 kva). Extensible and non-extensible MV RMUs are also installed within buildings owned by customers. 3.2 MV Cables, Joints and Terminations MV Feeder Cables (a) 3 x 1 core, 95 mm 2, 185 mm 2, 400 mm 2 aluminium and 240 mm 2 copper XLPE insulated, PVC/HDPE sheathed cables are used on 22 kv networks. (b) 3 x 1 core, 185 mm 2 aluminium and 240 mm 2 copper XLPE insulated, PVC/HDPE sheathed cables are used in 33 kv networks MV Transformer Cables (a) 3 X1 core, 35 mm 2 aluminium XLPE insulated, PVC/HDPE sheathed, cables are use on 22 kv systems (b) 3 X 1 core 50 mm 2 aluminium XLPE insulated, PVC/HDPE sheathed, cables are use on 33 kv systems Page 13 of 47 Print Date 23/06/2014

14 3.2.3 MV Cable Joints Currently, all MV straight-through joints, including transition types, use heat shrink materials, except where otherwise approved. All cable joints shall be installed in accordance with details outlined in the Underground Cable Installations Manual: HPC- 5DJ , and the manufacturer's instructions supplied with joint kits. Where not published in specific detail clarification shall be sought from the supplier. In any case, sound engineering practice shall be used MV Terminations All pole top cable terminations and some transformer terminations use heat shrink materials, except where otherwise approved. Separable insulated connectors (non-ioad break type) are used for terminations on transformers (satellite and ringmain), Modular Packaged Substations (MPS), small single phase pad mount transformers (SPUDs) and ringmain switchgear with integral bushings Non-Loadbreak Terminations The MV connectors, bushings and apparatus used in Horizon Power's underground system are shown in table below: Type of Connector Connector Function Non-Load Bushing Non-Load Elbow break break Mounted on the MV side of transformer to connect cables Terminates the XLPE cable to allow connection with the MV bushing Dead-End Plug Dead-End Receptacle Used to protect the non load break elbow when it is not connected to a transformer bushing Used to protect the transformer bushing when there is no non load break elbow connected to it Load break Terminations Load break terminations are currently not used by Horizon Power. 3.3 Types of Substations Horizon Power may require that the supply arrangement to an installation be via a particular "type" of substation, i.e.: "District" Substation (With LV street feeds to/from the substation); "Sole Use" Substation (With no LV street feeds); or "Customer Owned" Substation (Supplied at distribution MV voltage levels). Page 14 of 47 Print Date 23/06/2014

15 Consideration may also be given to installing a pad-mount or Modular Package Substation (MPS) in lieu of the more common brick enclosure substations. There may be cost advantages as well as land/space advantages with this option. The decision as to which type is selected depends on several factors, including: a) Size of customer's load; b) Location of customer's load centre on the property, and distance of the same from the street boundary; c) Type and nature of loads within the installation (disturbing, passive, etc.); d) Nature of Horizon Power's existing distribution network and loading levels on other substations in the vicinity; e) Horizon Power's need to connect LV street feeds to/from the substation; f) Fire separation requirements LV street feeds may be required to/from a substation for the following reasons: a) The customer requires a "back-up" LV supply to the installation; b) There will be future developments and load growth in the immediate area; c) The customer's load is expected to increase in the future; d) Ease of maintaining equipment in the substation (e.g. with street feeds into the substation, the customer's load can be partly met while the MV switchgear is being maintained); etc Modular Packaged Substations (MPS) a) A MPS comes complete with a single transformer and LV switchgear. It is housed in a self contained metal enclosure and is installed on an inverted, direct buried concrete culvert. If MV switchgear is required, this is also housed in a self-contained metal enclosure which is installed adjacent to the transformer on a direct buried steel mounting frame. b) MPS s are used only as District Substations. They are not used as Sole Use substations and are not fire rated. c) MPS is the preferred arrangement for a District substation with a maximum load of 630 kva after allowing for future load growth, and where there is no requirement for the substation to be fire rated Non MPS Arrangements a) A Non MPS arrangement comprises a combination of one or more transformers plus LV switchgear and MV switchgear as required. Each of these items is a separate component housed in a self contained metal enclosure. The transformer is installed on an inverted, direct buried concrete culvert. The LV and MV switchgear enclosures are installed on direct buried steel mounting frames. b) Non MPS components are not installed as a single package. They can be installed either as a cluster substation or in a fire rated enclosure (see Section 6). In the latter case, the culvert and switchgear mounting frames are not required. Page 15 of 47 Print Date 23/06/2014

16 c) Non MPS arrangements can comprise multiple transformers, with 1000 kva being the largest individual transformer size. They can be used as both District and Sole Use substations. A Non MPS arrangement shall be used where; A Sole Use substation is required; or Multiple transformers are required; or The maximum load is greater than 630 kva after allowing for future load growth; or The substation is to be fire rated Customer Owned Substations Typically, for loads greater than 4 MVA, a Customer Owned substation shall be provided. Neither the MPS nor the Non MPS arrangements are suitable for Customer Owned Substations. Horizon Power shall provide extensible MV switchgear necessary for connection to the network. The equipment shall be installed in a switch room constructed by the customer, along with the customer s own MV switchgear (See DSM-3-22 for details). Where a customer s load is less than 4 MVA, MV outdoor ground mounted switchgear can be considered. (See DSM-3-23 for details). A Customer Owned Outdoor Ground Mounted Substation cannot be upgraded for loads above 4 MVA. In the event that the customer s load increases above 4 MVA, the substation shall be converted to a MV Indoor Ground Mounted Substation, which will require a switch room to be built. In areas with overhead networks only, MV outdoor aerial mounted switchgear may be used (See DSM-3-24 for details) Single Phase Padmount Transformers The padmount single phase transformer is available in both 10 kva and 25 kva units for 12.7 kv Single Wire Earth Return (SWER) operation or for 22 kv "Two Phase" operation. The transformers are supplied configured for 240 volts, but can be re-configured to 480 volts for "sole use" applications kva Single Phase (SPUDS) Transformer The transformer is mounted on a hot-dipped galvanised steel base. The HV side of the transformer is equipped with either 2, 3 or 4 x 200 A tapered bushings which allow connection with separable non loadbreak elbow connectors. An internal, oil-immersed HV fuse is fitted inside the transformer tank. The unit is fitted with an externally operated, off-load tap-changer with steps of 0, ±2.5% and ±5.0%. The LV feeder cables, outgoing from the LV compartment, are protected by one "Red Spot" fuse (100 Amp) for 240 V or two "Red Spot" fuses (63 Amp) for 480 V. For further information refer to SPUDS design and operation manual. Page 16 of 47 Print Date 23/06/2014

17 kva Rural Underground Transformer The transformer is mounted on a concrete base. The HV side of the transformer is equipped with 2 x 200 A tapered bushings which allow connection with separable non-loadbreak elbow connectors. An internal, oil-immersed HV fuse is fitted inside the transformer tank. The unit is fitted with an externally operated, off-load tap-changer with steps of 0, ±2.5% and ±5.0%. The outgoing mains from the LV compartment, are protected by one "Red Spot" fuse (50 Amp) for 240 V or two "Red Spot" fuses (32 Amp) for 480 V. 3.4 Service Pillars Customer service pillars facilitate the connection of house services, customer bulk supply cables or interconnections of main LV street cables. In dusk to dawn street lighting areas, some may also provide supplies to streetlights. The service pillars are of a dark-green, polyurethane construction, with base partly buried in the ground. Figure 3-1 shows typical pillars. Figure 3.1 Typical Pillars There are two types of service pillar: 1) "Mini" Pillar (with tunnel terminal blocks): Tunnel block accepts up to 5 outgoing circuits (to 35 mm 2 copper cable), usually connected as follows: Pillar on cable side of road: Connect incoming 3 core 25 mm 2 cable from LV feeder; and Connect outgoing 2 x 3 phase or 2 x 1 phase services; and outgoing 3 core 25 mm 2 road crossing service cable Page 17 of 47 Print Date 23/06/2014

18 Pillar on other side of road: Connect incoming 3 core 25 mm 2 road crossing service cable; and Connect outgoing 2 x 3 phase or 2 x 1 phase house services 2) Universal" Pillar (with links and tunnel terminals): The universal pillar can be used as: an "interconnector" pillar with provision for solid links, to form a normally open or closed network point. a location to reduce the size of LV cable; to service a large single load (e.g. multiple dwelling lot) with LV HRC fuses (J type) to 315 A The universal pillar also contains tunnel terminals for service cables, as per "mini" pillar. Note: both "mini" pillars and "universal" pillars have provision for a fused terminal for an adjacent lighting column. 3.5 LV Cables, Joints and Terminations LV Feeder Cables: (a) 120 mm 2, 3 core, solid Aluminium conductor, Copper screened neutral (Wave Wound), 0.6/1 kv, XLPE insulated, PVC sheathed (b) 185 mm 2, 3 core, solid Aluminium conductor, Copper screened neutral (Wave Wound), 0.6/1 kv, XLPE insulated, PVC sheathed (c) 240 mm 2, 3 core, solid Aluminium conductor, Copper screened neutral (Wave Wound), 0.6/1 kv, XLPE insulated, PVC sheathed (d) 630 mm 2, 1 core, solid Aluminium conductor, Copper screened neutral (Wave Wound), 0.6/1 kv, XLPE insulated, PVC sheathed LV Service Cable 25 mm 2, 3 core, solid Copper conductor, Copper screened neutral (Wave Wound), 0.6/1 kv, XLPE insulated, PVC sheathed LV Street Light Cables Single core 10 mm 2 and 16 mm 2 stranded copper, XLPE insulated, helical copper wire neutral screen, PVC sheathed Other LV Cables For minor branch and road crossing services use: 25 mm 2, 3 core, solid Copper conductor, Copper screened neutral (Wave Wound), 0.6/1 kv, XLPE insulated, PVC sheathed cable. Page 18 of 47 Print Date 23/06/2014

19 3.5.5 LV Cable Joints/Terminations There are many variations of joints and terminations being used which are summarised below: 1) feeder cable straight through and breeches joints; 2) feeder cable to service cable tee joints; 3) feeder cable pole terminations (to bare and LV ABC overhead conductors); 4) feeder cable termination at universal pillar; 5) feeder cable termination at fused switch; 6) service/street light cable termination at mini pillar; 7) service/street light cable terminations (to bare and LV ABC overhead conductors); and 8) service/street light cable straight through and tee joints. Page 19 of 47 Print Date 23/06/2014

20 4 VOLTAGE REGULATION 4.1 Voltage Tolerance Limits Statutory Voltage Tolerance Limits Horizon Power declares the voltage level at a customer s point of supply as within ± 6% of the nominal 240 V single phase and ± 6% of the nominal 415 V three phase. As such, the maximum and minimum phase-to-neutral voltage levels at any point of supply on the LV network shall be within 225 V and 254 V for single phase supplies and within 390 V and 440 V for three phase supplies (under normal network conditions). In accordance with AS , Horizon Power expects to adopt the new voltage standard 230 V +6%, -10% for single phase and 400 V +6%, -10% for three phase supplies sometime in the future. When planning and designing a residential distribution network, the designer has to ensure that the voltages at any point of supply on the network will be within the statutory voltage tolerance limits, under normal network conditions. 4.2 Voltage Drop Criteria Impedance in each of the following components of the distribution system leads to voltage drop: 1) Medium Voltage Feeder; 2) Distribution Transformer; 3) Low Voltage Network; 4) Customer Service Leads/Cables. After a distribution system has been constructed, there are only two locations where voltage levels can be adjusted: a) at the zone substation (bus-bar voltage set-point and the use of Line Drop Compensators), and b) at the distribution transformers (off load tap changers). It is therefore important that the non-adjustable parts of the system be designed adequately to fully utilise the voltage control equipment at these locations to keep the customers voltages within the statutory voltage tolerance limits. Table 4.1: - Voltage Drop Limits with respect to nominal voltage Non-Adjustable System Components Maximum Voltage Drop Limits Medium Voltage Feeder 5.0% Distribution Transformer 4.0% Low Voltage Network 5.0% Customer Service Cable 2.0% Thus to compensate for voltage drops caused by components in Table 4.1, the Automatic Voltage Regulator (AVR), Line Drop Compensator (LDC) and distribution transformer taps are set accordingly. Page 20 of 47 Print Date 23/06/2014

21 With a 2% voltage drop assumed for customer service cables, coincident voltage drops, when taken together with zone substation LDC Buck/Boost and distribution transformer tap options are considered a reasonable balance to achieve: a customer s voltage at the meter panel between ± 6% of the nominal 240 V. Maintenance and Emergency Voltage Limits are shown in Table Effect of Different Load Cycles The majority of customers in a typical area will have similar, normal load patterns. Some, however, will have load patterns which vary and in extreme cases could be completely opposite to the normal pattern. These are usually single customer loads. Such loads of relatively small magnitude with respect to the total feeder load (or of relatively large magnitude with respect to the total distribution transformer load) can be catered for by adjusting the tap settings on the transformer supplying the load. Instances could also arise where a particular MV feeder load profile becomes dominant and masks the normal load profile of the remaining feeders on the zone substation. Such a feeder could influence the response of the LDC, to the detriment of the remaining feeders and their individual loads. This problem falls into network load modelling and is not dealt with in this manual. 4.3 Voltage Drops and Line Currents in LV Feeders General A three phase, four wire distribution system servicing a large proportion of single phase residential loads together with three phase commercial/industrial loads is subject to rapidly fluctuating currents. These currents produce corresponding rapidly fluctuating voltages on the system Effect of Load Unbalance It is inevitable that an imbalance between the line currents on the three phases of a feeder will occur if the feeder services a large number of single-phase loads (e.g. residential loads). This imbalance in the line currents leads to a current which flows in the neutral conductor, which adds to the voltage drop caused by the current flowing in the phase conductor. The voltage drop calculation (in LV DESIGN software) takes into account this added voltage drop caused by the load unbalance, as necessary Voltage Drops/Line Currents in Meshed Networks A Null Point is a point on the meshed portion of the network, through which no line current flows - the voltage drop from the transformer to either side of the null point is also the same. Page 21 of 47 Print Date 23/06/2014

22 In practice, the location of the null point in the meshed portion of the network can change as the loads on the meshed portion vary during the day. However, during times of peak load, the location of the null point would be approximately at the same position. The location of the null point in the meshed portion of the network signifies that the voltage drop from the transformer to either side of the null point is within the maximum allowable limit. Hence, once the location of the null point is known, the network can be assumed to be opened at this point and the cable sizes are appropriate to ensure that the voltage drop to the null point (and hence to all other points on the meshed portion of the network) remains within the maximum allowable limits Voltage Drop Limits for LV Networks One of the voltage drop criteria is that the maximum allowable voltage drop limit for the LV network is 5.0%. This translates to a phase-to-neutral voltage drop of 12 V between the transformer LV terminals and the Point of Supply of any load on the network. This limit, however, applies for normal or steady state conditions. In general, the network designer shall ensure that the design of the network conforms to the voltage drop limits shown in Table 4.2. Table Maximum Voltage limits for LV Networks Condition Voltage Limits (Phase to Neutral) % Volts Max (V) Min (V) Normal or Steady State ± Maintenance ± Emergency ± When designing the network, maintenance or emergency conditions must also be considered. Interconnection with adjacent networks is necessary to maintain the supply. 4.4 MV Voltage Regulation Design Approach The design approach is generally as follows: (a) Determine loads for maximum, lightly loaded and maintenance conditions. (b) For least cost option, check that voltage remains within limits for the various loads. (c) If voltage goes outside limits try various options. (d) Compare options to determine optimum solution Computer Modelling In many instances the cable electrical data is entered into a suitable computer program for analysis such as Horizon Power s Power Factory (Digsilent) program. This calculates the voltage variations for each option. The designer still needs to compare the options. Page 22 of 47 Print Date 23/06/2014

23 Voltage Control Equipment Some voltage control is built into the standard system equipment as follows: (a) Distribution Transformers: Out of service manual tap changes of ±2.5% and ±5%. (b) Zone Substation Transformers: Typically ±10%, ±13% or %. In urban areas it has been standard practice to utilise the above two measures only and choose appropriate conductor sizes and distribution transformer location/quantity to provide satisfactory voltage regulation. These are covered in Clause LV Network Design. Where longer lines are used it can become uneconomic to increase the conductor size. Additional forms of MV voltage control may become the lowest cost option. The three options usually considered are as follows: a) Capacitors -typically used for lines of moderate length (effective when permanently in service) b) Reactors - typically used for very long lightly loaded lines (effective when permanently in service) c) Regulator - can be used to raise or lower voltage (output voltage varies to suit load conditions) Page 23 of 47 Print Date 23/06/2014

24 5 UNDERGROUND DISTRIBUTION SCHEMES (UDS) 5.1 Design Procedure The Underground Distribution Schemes Manual (UDSM) sets out the procedure for a subdivision that is to be supplied with electricity from Horizon Power s network. The UDSM covers the policies, processes, practices, requirements and equipment that are relevant to designing underground distribution systems and it shall be referred to when designing Underground Distribution Schemes. The challenge for the designer is to produce the most economical selection of equipment, location and cable size that will adequately service the loads within the constraints of achieving Horizon Power s "quality of supply" objectives. (Refer to HPC-5DC : Distribution Design Manual Volume 1 Quality of Electricity Supply). Section 6 Determination of Recommended Load Demand Values, provides information about determining loads for underground distribution schemes. General steps involved in design are summarised below: 5.2 Transformers Initial Requirements Count the lots in the development from which the total number of transformers can be calculated (refer to HPC-3DC : Information Electrical Design for Distribution Networks: After Diversity Maximum Demand). Based on the number of lots to be serviced by a transformer, do a rough grouping of the lots and select tentative transformer locations. Relocate transformers after Step (b) to optimise loading on the LV distribution cables available. Identify non-residential loads such as pumps, shops, schools etc. Identify discrete or sole use transformer loads. The transformer substation should be located as near as possible to the electrical load centre of a group of lots in order to best balance the loads between feeders. This is achieved by locating the transformer close to road intersections and junctions. The designer must be prepared to regroup lots and change transformer locations as the design develops. Standard transformer ratings used by Horizon Power for underground distribution schemes are: i. 160 kva MPS and non MPS ii. 315 kva MPS and non MPS iii. 630 kva MPS and non MPS iv kva non MPS Note: The above transformers are available as indoor or outdoor units Page 24 of 47 Print Date 23/06/2014

25 5.2.2 Transformer Selection The designer must also be aware of other factors that may affect transformer selection and location unique to the subdivision under development, such as: 1) Isolated pockets of UDS that may be serviced from: Satellite substations; Spare capacity from adjacent non residential loads; and Spare capacity from adjacent separate developments. 2) Pockets never likely to be expanded and satisfactorily serviced from a 315 kva substation (i.e. no future 630 kva requirement). 3) Topographical features and ground conditions prohibiting installation. 4) Strategies adopted by developers for different schemes Mixed Loads If the full utilisation of Horizon Power assets is to be achieved then mixed loads are inevitable. Different peak load times for mixed loads must be taken into consideration when selecting transformer ratings or grouping of lots Example 1 How many residential lots can be supplied from a substation feeding a high school? Available information: School maximum demand is 220 kva (clause 6.3.2) School is supplied from a 315 kva transformer ADMD for Esperance is 3 kva Residential peak occurs between 5:30 and 6:30 PM. School load has been measured at 20% peak during domestic peak. Transformer kva = (No. of lots x ADMD) + (220 x 20%) Hence, No. of lots = {315 - (0.2 x 220)} / 3.0 = 90 lots now and ultimately No. of lots = {630 - (0.2 x 220)} / 3.0 = 195 lots with 630 kva transformer It appears that about 195 lots may be mixed with a high school load provided that a 630 kva transformer replaces the 315 kva transformer sometime in the future. However, the school peak occurs at 11:30 am when the domestic load has been measured at 50% maximum demand, Therefore, No. of lots = ( ) / 1.5 = 63 lots now and ultimately = ( ) / 1.5 = 273 lots with 630 kva transformer Page 25 of 47 Print Date 23/06/2014

26 An analysis of the above shows that certain options exist depending on the particular circumstance of the subdivision requirements. 1) 63 lots could be serviced now from a 315 kva substation to be upgraded later to a 630 kva substation. This would underutilise the 630 kva transformer unless, as is often the case, there was a requirement for spare capacity (up to 132 lots) at a later stage of development. 2) 195 lots could be serviced now from a 630 kva transformer saving the cost of upgrade but incurring additional capital costs and early transformation losses. In general, it may be prudent not to take advantage of the 120% overload capacity of the transformer. This allows for contingencies, common in mixed load applications Regions other than Esperance It is standard practice to install 630 kva transformers initially because the flat load profile due to air-conditioning allows little scope for cyclic rating use. 5.3 LV Network Design Primary Aim The primary aim when designing a LV network is to select and locate equipment that will adequately service both present and future customer loads and also satisfy the reliability and quality of supply standards stipulated by the Electricity Industry (Network Quality and Reliability of Supply) Code Challenge for Network Designers The challenge for any network designer is to avoid over/under design of the network. Over design is costly in terms of unnecessary capital investment, whilst under design leads to high losses, costly investigation and rectification of Quality of Supply related complaints. Extra effort expended in optimising the design of LV networks results not only in the efficient utilisation of capital costs but also impacts on the MV network, affecting the number and location of distribution transformers Use of Computer Packages Typically, the design studies and calculations are carried out using specially written computer programmes, for the more complex cases or where accurate results are required. Alternatively, manual calculations can sometimes be used, especially for simpler cases or where only estimates are required. LV DESIGN is a PC based computer program, written specifically for studying LV networks. It is particularly suited for underground distribution scheme designs, with distributed loads along the LV feeder. The program automatically accounts for load unbalance and diversity. However, it can also be used to calculate the voltage drops and line currents caused by large commercial loads. LV DESIGN can be used to investigate the impact of new large loads within residential estates, e.g. shopping centres, pumps, etc. Page 26 of 47 Print Date 23/06/2014

27 GIS (Geospatial Information System) is one of Horizon Power's prime computer systems. Various distribution plant items are recorded in the system for most parts of the state, e.g. transformers, MV and LV cables and many other assets. Customer property boundaries are also recorded in the GIS database. GIS can be used by the designer to obtain information quickly about the existing supply system around a new proposed installation, from which, various supply alternatives can be considered. GIS can also be used to down-load information on the supply system onto Power Factory (Digsilent) for later analysis Aspects of Electrical Design The electrical design of distribution feeders generally involves the following aspects: 1) Estimation of load demands; 2) Selection of distribution transformer; 3) Planning of network layouts; 4) Calculation of Voltage Drops and Cable Currents; 5) Selection of cable sizes to satisfy the voltage drop and current capacity requirements; and 6) Selection of fuse/protection device (if applicable). These aspects are explained in the following sections Determination of Cable Size The size of LV cable is chosen to ensure that all of the following criteria are satisfied: 1) Voltage drops during peak network load times being within maximum allowable limits (and during minimum load times being within minimum allowable limits) - Refer to Section 4 2) De-rated current carrying capacity of cable being adequate so that load currents will be within the capacity, not only during steady state conditions, but during maintenance/emergency conditions when the LV network is interconnected with others (Refer to Appendix B); 3) Other cable current ratings (e.g. summer, winter) not being exceeded, wherever applicable ( Refer to Appendix B and cable manufacturers data); 4) Cable impedance satisfying the LV fuse/protection requirements (so that at times of fault at the end of the feeder, the fault current will be large enough to be seen by the LV fuse and hence, cleared in time to prevent damage to the cable ( Refer to Section 7) Selection of LV Feeder Routes When selecting LV feeder routes, the designer should take the following into account: Page 27 of 47 Print Date 23/06/2014

28 Proximity to Loads The feeder route should be chosen such that it will start to be loaded as close to the transformer as possible. This is facilitated by locating the transformer as close to heavy load centres as possible or as close to the centre of gravity of a group of loads. Feeder routes where the feeder only picks up loads after a considerable distance away from the transformer should be avoided (as this causes larger voltage drops than necessary in the initial part of the feeder) Utilisation/Loading LV feeder routes must be chosen such that the transformer will service the required number of loads determined on the basis of design load demand values (refer to Section 6 Determination of Recommended Load Demand Values and HPC-3DC Electrical Design for Distribution Networks: After Diversity Maximum Demand) Typical Route Lengths The length of a LV feeder affects the: 1) voltage drop on the feeder; and 2) fault current at the end of the feeder. Very long LV feeders should generally be avoided since this would only result in medium voltage drops than necessary, cause improper operation and lead to possible conductor burnouts. Designs may require up to 500 m route lengths. However, route lengths in excess of 400 m are unusual and may indicate poor substation location. Cable routes should be selected so that feeders start to pick up load as close to the substation as possible. This can be achieved by locating the substation close to the electrical load centre of a group of residential loads or non residential loads. Cable routes that pick up loads at significant distances from the substation entail substantial voltage drops to occur. This can impact adversely on conductor costs and losses Interconnection with Other Feeders If a transformer becomes unserviceable, its LV network has to be supplied by adjacent transformers until repairs can be effected or a replacement put into service. As such, the LV network should be provided with sufficient numbers of interconnecting points (e.g. via the use of removable solid links, fuse switches) to allow lateral interconnections between LV networks of adjacent transformers. When selecting LV routes, the designer should select routes which can assist in the provision and location of these interconnecting points, if possible. The interconnection criteria generally used by Horizon Power is to ensure that the backbone feeder of any transformer can be interconnected with other LV feeders from adjacent transformers, at least twice. If the number of interconnections cannot be provided due to certain constraints, the designer should consider using a smaller transformer size instead. Page 28 of 47 Print Date 23/06/2014

29 5.3.9 Pillar/Cabinet Positioning and Alignment When selecting the LV feeder route, the designer must also give consideration to the positioning of Pillars and Cabinets Other Considerations Sometimes, in order to mitigate the excessive voltage drops caused by large motor starting currents, it may be necessary to connect up large motors (e.g. large reticulation and sewerage pumps) via a dedicated LV feeder. A similar requirement may be called for to mitigate any interferences caused by potentially disturbing electrical loads to other customers on the same LV feeder, e.g. light industrial customers with arc-welders, thyristor controlled motor speed drives, large motors. On the other hand, from the nature of the load itself, or due to special requests from the customer for a more secure supply arrangement, certain loads may need to be serviced via dedicated LV feeders or from sole-use transformers (e.g. small hospitals, retirement villages, bulk cold food storages) Typical Design Issues When designing the LV feeder and street lighting, voltage drops with various cable sizes are calculated. If the voltage drop at the end of a radial LV feeder exceeds the prescribed limits the following alternative design choices are possible: a) Adjust lot grouping or change transformer boundaries b) Relocate the transformer to a site nearer the electrical load centre of the grouped lots. c) Upgrade cable size d) Check current flows against the current rating of the cables e) Check LV feeder protection fuse size 5.4 MV Design MV Cable Requirements When designing the MV layout, the shortest and most direct MV cable routes should be selected. If the design is for a large UDS: a) a detailed and comprehensive study of the existing and proposed MV feeders supplied from adjacent zone substations shall be carried out to determine the effect of the new load on the overall MV network and system security; b) in the overall area concept plan, the location of all the transformers and all existing MV mains adjacent to the subdivision (obtained from GIS) shall be marked; c) transformers that are to be supplied as "satellites" from the adjacent overhead MV mains and the transformers that are to be "ring main" Page 29 of 47 Print Date 23/06/2014