Reactive power compensation - Critical Length of Cable Circuit

Transcription

1 APPENDIX 7 Reactive power compensation - Critical Length of Cable Circuit An underground (U/G) power cable has the capability to store and release electrical energy with the voltage variation; it works as a shunt capacitance generating a capacitive current which is in quadrature with the resistive or load current The capacitive or charging current has a limiting effect on cable rating capacity (MW). This effect is quantified by the fact that when intended to supply energy to a resistive receptor (active load consumer) in a radial network, via a power cable circuit, it is needed to inject a higher current at the source to compensate for cable capacitance. The charging current is calculated with the following equation: I C = ω CU 10 _ 6 where: Ic = charging current (A/km) = 2f ; f = System frequency C = capacitance per unit length (µf/km) U = Applied voltage (V) The charging current generates heat losses in cable which are of a significant magnitude in very long high and extra high A.C. underground power cable connections. As the capacitance and the charging current increase linearly with the length of the cable circuits the generated heat losses by the charging current could be as high as its entire thermal rating capacity. In other words, it could be said that for long and uncompensated cable circuits the entire

2 cable rating capacity could be consumed by the circulation of charging current; i.e. no real power transmitted without overheating the cable. The length of a cable at which its thermal capacity was consumed by the charging current is called critical length and it is calculated with the following formula: L C I ωc 3 U = 10 3 ( ) km where: C = capacitance per unit length (µf/km) = 2f ; f = System frequency U = Line (phase to phase) voltage (kv) I = phase current (A) (CIGRE WGB1-19/2004) The maximum transmitting power of a radial cable circuit is given by: P L S 2 G 2 2 _ 3 ( ). C. L. U. 10 = _ ω [MW] Where P L = Active power at load receptor (MW) S G = Apparent power at injecting point (MVA) C = capacitance per unit length (µf/km) = 2f ; f = System frequency U = Line (phase to phase) voltage (kv) L = Length of cable (km) (CIGRE WGB1-19/2004) It could be seen that the critical length L C is determined by the system voltage and frequency and by cable rating which is determined by the conductor size, environmental and installation conditions and cable capacitance. The larger active current transmitted on cable the longer the critical length; i.e. the charging current is of a lesser importance.

3 The calculated values of critical length and the loss of transmitted power, of a 40km 220kV cable system, by using the above equations, are of some significance for smaller cable sizes (300MVA rating) but for larger cables ( 600MVA carrying capacity) the impact is small. In Fig 1 is shown the typical critical length and the length at which the current rating is reduced by 20% for major high voltage cables (138 to 500kV voltage steps) based on North American experience. In addition to the heating effect of charging current the cable capacitance may have an impact on steady-state voltages across the power system to which the cable is connected. The voltage may rise, especially at low loads, due to charging current flowing through cable series inductances (material polarisation) and through system inductances (transmission lines and transformers); phenomenon known as Ferranti effect. The Ferranti effect is significant with long cables energised from one end. In this kind of situations the network voltage stabilisation is carried out by adjusting the voltage magnitude at generator by reducing the field excitation or by lowering the voltage taps on transformers. Figure 1 Critical length of 1000mm 2 U/G power cables (Power Technologies, Inc)

4 However in case of long cable circuits, the compensation of charging current requires installation of shunt reactors connected at one end or both end of cable circuits which are selected based on specialised system studies by taking into consideration cable specific data and system parameters. In case of overhead transmission lines (O/H TL) the rating capacity is influenced by the line inductance which is compensated by installation of series capacitors. Power cable, which is a capacitor, improves the O/H TL transmission capacity but, it presents the disadvantage of being of constant capacitance at constant voltage while the system requires variable adjustments

5 Appendix 8 Curriculum Vitae NAME: NATIONALITY: ADDRESS: Henry Kent Australian (born in Switzerland) 22 Avoca Street GLENBROOK, NSW 2773, AUSTRALIA Tel (2) Mobile (Preferred) henrykent@energyaction.com.au QUALIFICATIONS: Diploma in Electrical Engineering, NSW University of Technology Post Graduate Studies in Protection Engineering. Management and business training in various Institutions including Australian Graduate School of Management. Extensive experience in planning, design, asset management, construction and maintenance of transmission and distribution voltage underground cables and other network infrastructure. MEMBERSHIP OF PROFESSIONAL SOCIETIES Accepted to Institution of Engineers, Australia Convener of Australian Panel & member of CIGRE international Study Committee SC 21 HV Insulated Cables to 1990 Current member of CIGRE Australian Panel B1 Insulated Cables Former member ESAA Technical Advisory Committee Electro-magnetic Fields Current Secretary, ENA Power Poles & Crossarms Forum. LANGUAGES: English German some capacity EMPLOYMENT HISTORY : Electricity Commission of NSW [Generation &Transmission] : Prospect Electricity / Integral Energy [Distribution]

6 2000 Present: Consulting services to Utilities & Industry [Cable Design; Condition Assessment & Monitoring; Project Management and Training] COUNTRIES OF WORK EXPERIENCE: Australia, New Zealand, Singapore, Indonesia and United Arab Emirates CAREER HIGHLIGHTS: During some 40 years in the electricity supply industry responsibilities included: Design, construction, maintenance & refurbishment of transmission and distribution assets specialising in high voltage underground power cables. Development of specifications for cable infrastructure projects [some under Joint Venture] and tender evaluation. Implementation of network asset life extension strategies. Management of a stand alone Contracting Services Business within Integral Energy with an annual turn-over exceeding $A150 million [⅓ derived from external business]. Community consultation prior to construction of controversial overhead powerlines and underground cables. Development of industry guidelines for example, Electricity Supply Association of Australia document D(b) Work On Cables Under Induced Voltages and Transferred Earth Potential Six year term, , as Convenor of CIGRE Australian Panel 21 & member of CIGRE international Study Committee SC-21 HV Insulated Cables [representing the Australian & New Zealand cable industry internationally] Staff training and accreditation Specific highlights: Responsibility for the construction, maintenance & refurbishment of the extra high voltage cable network in the Sydney CBD and inner suburbs (comprising 500 kilometres of 132kV & 330kV oil-filled, gas-filled & polymeric cables) including project management of cable tunnel construction and cable installation. Introduction to Australia of innovative optical fibre technology Distributed Temperature Sensing and contribution (together with Tyree Optec & University of Sydney) in the commercial development of an application package. Engagement by the Inquiry into the Auckland CBD Power Supply Failure as chief technical consultant to determine the cause of failure of the 110kV oil filled & gas filled power cables in 1998.

7 Engagement by Rail Services Australia [now RailCorp NSW] to investigate condition of 33kV gas-filled cables Engagement by United Energy [now Alinta Vic] to report on in-house management practices related to underground cables Engagement as technical investigator to determine the cause of failure of Java-Madura 150kV submarine cable Project manager for the installation of 220kV XLPE cables, Taranki, NZ, being one of a number of cable projects won competitively by Integral Energy Contracting. Introduction of diagnostic methodologies associated with oil filled cables Presentation of technical papers at CIGRE, Paris Sessions; CIGRE symposium on diagnostics, Zermatt, Switzerland; CEPSI conference, New Zealand and to a number of Supply Industry forums in Australia Regular lecturer on cable technology at ESAA summer schools for engineers Co-ordinator of four international cable technology seminars in Sydney Establishment of apprentice training school & cable jointer training facility Change management of an organisation transitioning from a monopoly to a commercially competitive construction business Overseeing Corporation s performance to customer service level obligations, monitoring customer complaints and liaison with the industry ombudsman CONSULTING SERVICES TO UTILITIES & INDUSTRY, SINCE AUGUST /01: Consult to Electricity Supply Companies across Australia on supply chain management strategies - including e-procurement of equipment and services via live internet based auctions. 2001/02: Snowy Mountains Hydro Electric Authority, ACT, Australia:- Develop options for the installation of a spare 330kV cable at Tumut No.2 Power Station 2002: HMAS Success, Garden Island Sydney: Investigate damaged power & control cables on board while vessel under re-fit : TransGrid, NSW, Australia:- Assist TransGrid in tender assessment for the 330kV Sydney CBD cable reinforcement project 2002: TransGrid, NSW, Australia:- Assist TransGrid [and JPS] in a field trial to establish electro- magnetic field (EMF) mitigating measures 2002: Ergon Energy, Queensland, Australia:- Assess condition of 66Kv gas-filled cables in Townsville and recommend maintenance & replacement strategies 2002: Abu Dhabi Distribution Company, UAE:- Provide lectures (over a 5 month period) to professional staff & field operatives on life cycle issues related to power cables 2003: Promis Group, Dubai, UAE:- Present training course Power Cables Operation, Maintenance, Location & Fault Detection

8 2003: Mallesons Stephen Jaques, National Environment & Planning Group, Sydney, NSW, Australia:- Provide design & estimate for undergrounding 132kV overhead transmission line (to release land for development purposes) 2003: TransGrid, NSW, Australia:- Appointed Project Manager to retrofit a dynamic rating system to 330kV oil-filled cable [incl. assistance to Parsons Brinckerhoff in preparation of REF]. 2003: Blue Circle Southern Cement, Berrima, NSW: Investigate condition of recently installed, suspect, 33kV XLPE cables 2004: RailCorp NSW: Review and update in-house cable standards and procurement specifications advise on cable installation on railway bridge 2005: RailCorp, NSW: Assist in technical evaluation of tenders for cable supply 2006: TransGrid, NSW: Appointed Project Manager Replacement of 330kV Cable Joints involvement in preparation of estimates, REF & community consultation; co-ordination of many parties incl. JPS (Japan}; Energy Australia, Civil Works Contractor, Traffic Management, Cable Freezing Service. 2007: Engaged by Snowy Hydro to assist in preparation of Business Case to replace 330kV cables at T1 & T2 power stations 2007: Engaged by ElectraNet SA as Team Leader/Cables to assist in route selection & procurement of 275kV cable installation, Adelaide : Electricity Supply Association of Australia - in conjunction with various Universities:- Present Professional Development Course lectures on power cables & overhead line supports to present: Secretary ESAA [now ENA] Power Poles & Crossarms Forum

9 Name Education Other Training Membership of Professional Societies: Countries of Work Experience Experience 1994 Present (06/07/2007) George Bucea Diploma in Electrical Engineering, Bucharest Polytechnic Institute (1967). Special Training: Specialist training in extra high voltage polymeric and oil filled cable systems and high voltage apparatus. A total of over 24 months were spent working at cable and apparatus manufacturers in England, Italy, Germany, Japan and Finland during the years of 1973 to Training and specialising courses were attended at BICC, Pirelli, F&G Cables, Siemens, Alfa Cavi, CEAT, Nokia and Sumitomo. Member CIGRE AP-B1 High Voltage Cables Member CIGRE WG-B9 Life Expectancy and Diagnostics Member Institution of Engineers, Australia (1986 to 2006) Australia, Romania, Thailand, Singapore, Japan and New Zealand Principal Engineer/HV Underground Power Cable Projects, TransGrid, Sydney - Australia TransGrid became the registered business name of the Electricity Transmission Authority of NSW/Australia as from 30 May Responsible for the design, route selection, specification and contract administration of High Voltage cable installations up to and including 330 kv, throughout TransGrid s transmission system. Responsible for material inspection and testing carried out by cable manufacturers and contractors during manufacture, installation and commissioning to ensure that all is in compliance with the contract. Responsible for the investigation and development of new technologies in relation to high voltage cable systems and cable accessories in conjunction with cable manufacturers to achieve more reliable and cost effective products. Responsible for the investigation, testing and evaluation of the condition of TransGrid HV power cable systems and provide consultancy assistance to HV and EHV cable users from Australia and overseas.

10 Experience (cont d) Some of the most significant cable projects and investigations were as follows: 1. Since 1999 to 1995 I was responsible for design activity in relation to a 330 kv 750MVA 28km U/G power cable system for Sydney Central Business District. The work included: Route investigations and feasibility studies Evaluation of cable technology and setting a strategy for best tendering processes and technology selection Preparation of pre-qualification documentation for preselection of most reliable and cost-effective cable technology and of most competitive cable manufacturers. The investigated technology alternatives included XLPE, SCFF-paper and SCFF- PPL insulated cable types and GIL (gas insulated lines). Preparation of tendering documentation Evaluation of tenders The design for this cable circuit includes provision for on-line SCADA and condition monitoring system (CMS) in relation to the supervision of oil pressure, temperature/rating limitations and other supervisory systems. 2. Investigate the cable failure and specify/design remedial works of a 330 kv cable circuit as a result of cable-core movement (Sydney / ). 3. Investigations of cable network failure in Auckland, New Zealand (1998). Assist in preparation of the Report of the Ministerial Enquiry into the Auckland Power Supply Failure. 4. Member of the expert investigation teams employed to investigate and assess the performance of cable insulation of aged or faulty 132kV to 400 kv of cable systems in Sydney Australia, New Zealand and Singapore. 5. Organiser of the Cable Technology Seminars in Sydney, Australia in 1993, 1995, 1997 and 1998 (session dedicated to Auckland Power Failure). Presentation of technical papers. 6. Investigations of cable network failure in Singapore (2000 to

11 2006) and the on going diagnostic and technical advise to Singapore Power. Assist in preparation of technical documentation related to U/G Cable System Failure (66 to 400kV) Principal Engineer/HV Underground Power Cable Projects, Pacific Power Transmission Engineering Group, Sydney, Australia Experience (cont d) Same as above. Head of Extra High Voltage Cable Department, Electricity Ministry of Romania, Romania Responsible for design, procurement, installation, commissioning and maintenance testing of cable systems up to 400 kv. During this time I implemented development and training programmes to reduce the dependence of the Romanian Ministry on overseas technical assistance related range of works associated with HV & EHV cable systems. Within that period the total volume of HV underground cable network in Romania increased 10 fold, i.e. from about 45 km to more than 500 km by SCOF (Self-contained Oil-filled), XLPE (cross-linked polyethylene) and EPR (ethylene propylene rubber) were the most common cable systems used. The installation methods included all possible site conditions such as direct buried, tunnels, ducts, bridges, troughs, submarine (River Danube crossing) and buildings. Professional Engineer/High Voltage Network and Substations, Minister of Electricity Romania, Romania Responsible for maintenance and operation of distribution cable network and substations.

12 Publications 1. "110 kv Oil-filled Cable Handbook" Bucea, G, Editura Technica Bucharest, "Jointing Systems of H.V. Oil-filled Cable Systems" Constructii - Montaj, High Voltage Cables: Present and Future" - Electroenergetica "Techniques to Increasing the Current Carrying Capacity of H.V. Cables" Editura Technica MEE 1983 (Training Manual), "Management of High Voltage Cable Networks" Editura Technica MEE 1983 (Training Manual) "New Types of Insulations for HV Power Cables: PE, XLPE, EPR" Editura Technica MEE 1983 (Training Manual) "Repair the Damaged Submarine H.V. Cables Circuits at Danube Crossing /Romania", Bucea, G Energetica "Distributed Temperature Sensing of High Voltage Cables - Case Study from Sydney, Australia" H Kent and G Bucea, CIGRE /1992 Session. 9. Presentation of technical papers at Cable Technology Seminars Sydney, Australia 1993, 1995, 1997 and Shielding Techniques to Reduce Magnetic Fields Associated with Underground Power Cables - Case Study from Sydney,Australia G. Bucea and H. Kent. CIGRE /1998 Session 11. Preselection of cable type and cable manufacturers for the MetroGrid project in Sydney Australia Jicable, Conference/Paper A kv Cable System for the MetroGrid Project in Sydney,Australia CIGRE Conference/Paper Condition Monitoring Systems for 330kV Cables Supplying, Sydney CBD - TechCon 2004 Conference Sydney 15. Condition Monitoring System for TransGrid 330kV Cable - Powercon 2004 Singapore 16. Selection and Design of Cable System for HV & EHV

13 Underground Networks ESAA Summer School, Electrical Losses in Power cables Current dependent and voltage dependent losses. Cable Technology Seminar, Sydney Performance of XLPE-insulated HV & EHV Cable Systems. Comparative evaluation of IEC and North American related standards