NORTH RIVER NAMIB LEAD / ZINC PROJECT FEASIBILITY STUDY. Volume 1

Transcription

1 NORTH RIVER NAMIB LEAD / ZINC PROJECT Volume 1 Power Supply Distribution Earthing Proprietary Information This document has been prepared by and remains the sole property of. It is submitted solely for use in conjunction with the submission for which it has been prepared and is to be held proprietary to. The recipient agrees by receipt and/or use of this document to return it to upon request, and not to reproduce, copy, lend or otherwise disclose or dispose of the contents, directly or indirectly, and not to use it for any purpose other than intended for.

2 Power Supply Distribution Earthing Page: 2 of 13 TABLLE OF CONTENTS 1 OVERVIEW General Design Philosophy Standards and Codes Power System Power System Components and Equipment Plant Earthing and Lightning Protection System Substations and Transformer Enclosures Construction Power Supply Contractors Camp Power Supply...13

3 Power Supply Distribution Earthing Page: 3 of 13 1 OVERVIEW The previous Namib Lead Zinc operations made use of a dedicated 22kV transmission line for power supply. This existing line is not a viable technical option considering the critical condition that it s in, and the local Power supplier/authority (Erongo Red), have declared that the backbone network requires upgrading. The upgrade of network power line is in the planning phase, and the plant power will be carried by a 33kV line which will t-off from the upgraded network line, approximately 7,5km from the site. Erongo Red has confirmed the availability of grid power to the Namib Lead Zinc site. It has also stated that it is the CLIENT s responsibility to refurbish and upgrade the old 22kV transmission line which will provide dedicated power to the site. This cost has been included in the estimate. 1.1 General Design Philosophy The plant will be designed for reliable, safe, low maintenance operation in accordance with the project engineering strategy. The equipment will be designed to comply with the following basic criteria: Safety of personnel Safety of equipment Suitable for purpose (focused on most economical solution) Operability and compatibility with process requirements under the site conditions Maintainability

4 Page: 4 of 13 Minimisation of overall capital and operating costs Automated operating philosophy Reliability and continuity of supply and electrical operation at rated output for desired lifetime Possibility of future expansion Minimisation of spares holding 1.2 Standards and Codes The design and installation shall comply with all statutory regulations and will be subject to approval by the regulatory authorities where appropriate. The following standards shall be applicable as appropriate: South African National Standards (SANS) International Electrotechnical Commission (IEC) The following legislation (as amended) shall be complied with: Mine Health and Safety Act (Act 29 of 1996) Occupational Health and Safety Act (Act 85 of 1993) Minerals Act (Act 50 of 1991) See Electrical Design Criteria and equipment specifications for detailed lists of applicable standards and regulations. 1.3 Power System

5 Page: 5 of Power System Design The power system design is based on calculations with a view to ensuring: Correct current rating of cables, electrical equipment, etc. Correct kva sizing of transformers, Correct short time withstand current rating of equipment Correct voltage levels in the system during normal run and start-up of heavy motors The following computer aided studies will be conducted during the project execution stage: Load flow Fault study Protection relay settings (protection grading) Power Supply It is estimated that the total amount of electrical power required by the plant will be 1.8 MW maximum. The average load using diversity factor of 0.8 is estimated at 1.4 MW. The power required will be obtained from Nampower grid via a dedicated 33 kv Overhead Line constructed by THE CLIENT Plant Power Reticulation and Distribution

6 Page: 6 of 13 The power supply voltage of 33 kv will be stepped down to 525V. 525 V power will be used for plant reticulation as well as to supply electrical motors throughout the plant. It will be further stepped down to 400/230 V to supply small power and lighting as required. Ref. Appendix 1 Main Overall Power Distribution. Single Line Diagram. Drwg. No E Emergency Power Supply There are only 3 small motors that require emergency power in the plant. A 75 kva diesel generator is envisaged to supply emergency power for these loads as well as to instrumentation UPS and MCC control power supply UPS. All plant emergency light fittings will be provided with battery packs and will not be backed-up by diesel generator. The change-over between diesel generator and grid power will be manual. The above measures are based on cost savings but the diesel generator rating is sufficient to provide power to emergency lights if required (additional costs). It will also be possible to upgrade the system for the automatic change-over (additional costs).

7 Page: 7 of Power System Components and Equipment MV Switchgear There is no MV Switchgear within the plant area V Motor Control Centre Motor Control Centre (MCC) will be installed to provide starting facilities and power supply to the low voltage loads. Due to its size the MCC will require two 12 m containers. The two parts of MCC will be connected by busbars. The MCC will be installed in the containers at the place of manufacture. The MCC will be front access to minimise space requirements. The enclosure degree of protection will be IP42 minimum. The MCC will include a cubicle incorporating control interface equipment. All the motor starters installed in MCC will be of direct-on-line (DOL) starting type or VSDs for motors up to and including 90 kw. The motor starters will be equipped with moulded case circuit breakers, earth leakage protection and intelligent relays Simocode or equivalent. Motor running, stopped, tripped indication on motor starter door will be provided. The MCC will also incorporate feeders to VSDs for motors rated at above 90 kw, welding plugs and other 525 V loads. Where applicable, 525/400 V transformers will be fed from the MCC to provide power to lighting and small power consumers in the area. The transformers will be dry type and installed in the MCC containers.

8 Page: 8 of Transformer A 33/0.55 kv transformer supplying power to the plant will be oil immersed, two winding, core type transformer suitable for outdoor installation. The transformer rating will be 2500 kva. The transformer will be provided with padlockable off- load tap changer (OCTS) Miniature Substations There are no miniature substations within the plant area Medium Voltage Motors There are no MV motors required for the plant Low Voltage Motors The motors will be supplied from 525V, 3-phase, 3 wire, 50Hz power system. The motors will be of the totally enclosed fan cooled (TEFC) construction and provided with: IP55 rated enclosures Anti-condensation heaters where required Class F wiring insulation grade PT 100 temperature sensors embedded in the stator winding and bearings where required All the LV motors will be supplied by equipment suppliers as part of their scope.

9 Page: 9 of Variable Speed Drives The VSD s will afford at least IP20 degree of protection and their enclosures at least IP42. Each VSD will be equipped with a suitable port for control and monitoring via an associated PLC. All VSDs for motors rated at up to 90 kw will be installed in MCC cubicles. VSDs for larger motors will be installed in floor standing cubicles MV Cables There are no MV cables required within the Plant LV Cables The LV cables will be rated at 600 / 1000V. The cables will be PVC insulated, PVC bedded and PVC sheathed, fire retardant. Multi core cables will be steel wire armoured and single core cables aluminium wire armoured. Cables between secondary side of the distribution transformer and incoming terminals of 525V MCC will be XLPE insulated, PVC bedded and PVC sheathed, fire retardant, and unarmoured to reduce the number of cables required and ensure easy termination. All cables will have copper conductors Cable Racks Cable racks and accessories will be of a heavy duty industrial type, hot dip galvanised.

10 Page: 10 of 13 Cable racks will generally be routed along pipe racks where possible or attached to the buildings and structural steelwork in other cases. Where this is not possible the racks may be supported on uprights made out of steel profiles. The racks will preferably be mounted in a vertical plane (edge on) unless practically not possible. All cable racks shall be provided with sun shields (covers) protecting cables against direct exposure to solar radiation. Up to 20% of spare space on racks has been provided for future expansion Lighting and Small Power The 400 / 230V lighting and small power distribution circuits will be supplied from 525/400 V transformers as suitable. The lighting and small power distribution boards will be provided to supply small power and lighting loads throughout the plant. Lighting and small power cabling will be run on cable racks, in conduit or clipped directly to walls or structural steel where adequately protected. The electrical distribution in offices, control rooms and other personnel areas will be done by means of electrical wires run in under plaster conduits. Plant lighting will generally be provided in accordance with the following philosophy: Low ceiling internal fluorescent high ceiling internal and external high bay, high pressure sodium plant areas bulkhead, high pressure sodium, area lighting flood lights, high pressure sodium installed on high masts, poles, buildings or steel structures

11 Page: 11 of 13 Lighting will be designed to achieve the illumination levels in compliance with the relevant regulations 230V socket outlets will be protected by 30mA earth leakage units. Where they are located in plant areas these sockets will be housed in IP65 rated enclosures. 525V, three phase outlets (welding plugs) will be installed in strategic areas of the plant. They will be rated at 63A, provided with neutral and earth connections, housed in IP65 rated enclosures and protected individually by 30mA earth leakage units Power Factor Correction / Harmonic Suppression Not applicable. 1.5 Plant Earthing and Lightning Protection System Earthing The earthing system design will be such as to provide a uni-potential system with all equipment effectively being at a single earth potential. This will be achieved by tying together all earthing systems including structure, electrical equipment and instrumentation earth system. The interconnection of earth system will be radial to prevent the possibility of providing the routes for circulating currents. The detailed type of earthing system will be established upon conducting a soil resistivity survey on site.

12 Page: 12 of 13 Major electrical equipment such as the main transformer, MCC, etc. will be earthed directly to the earth mat by means of dual copper earth conductors. 525V motors will generally be earthed by means of the fourth cable core for the cables up to 50 mm 2 and by means of an external 50 mm 2 conductor for the motors supplied via larger cables. All earthing conductors within the plant area will be PVC insulated Lightning Protection The lightning protection system (where required) will be designed to protect the personnel and equipment against dangerous effects of the direct and indirect lightning discharge or induction from a passing charged cloud. 1.6 Substations and Transformer Enclosures Substations and MCC Rooms LV MCC will be located in specially prepared containers. All MCC containers will be ventilated (pressurised) by filtered forced-air systems. Air conditioning will be provided where required. The containers will be provided with the fire detection and protection systems and will have enough space to allow the future extensions of switchboards by at least two tiers and also enough space for access, maintenance and repairs.

13 Page: 13 of 13 The MCC containers will be provided with all safety notices, operating equipment, personal protection equipment, fire detection and protection equipment in accordance with relevant regulations Transformer Enclosures The main transformer will be located within outdoor enclosures located adjacent but not closer than 2 m from MCC Room. The transformer bay will comprise a concrete plinth for supporting the transformer, and a concrete or masonry bund wall at least 300mm above finished ground level, filled with crushed stone to a depth of 150mm. In addition transformer enclosure will have a brick wall on three sides extending at least 300 mm above the highest point of the transformer. The gate to the transformer enclosure will be padlockable and provided with all the required safety notices. 1.7 Construction Power Supply There is no construction power included in the Scope of Work (SOW). 1.8 Contractors Camp Power Supply Not included in the SOW.