Technical Paper Presentation- ERC Forum
- 1. 2013 Electrical Regulatory Compliance Forum Low Voltage Current Transformer Testing for Regulatory Compliance Razmi Marzook Electrical Engineer (Metering) Endeavour Energy, NSW
- 2. Abstract The low voltage current transformers (LV1 CTs) installed in metering installations are required to be tested for accuracy2 for regulatory compliance in accordance with the National Electricity Rules (NER). This has been a challenging project from the planning to implementation stage, when Australian Energy Regulator (AER) introduced a civil penalty provision for non-compliance in 2012. The sample size of 10% was selected from the LV CTs population to be tested in-situ based on their age incurring a power outage for the customer’s supply. The benefits of secondary injection outweighed the conventional primary injection method to determine the accuracy of the CTs. Statistical analysis was performed on the obtained field test results. This paper discusses the management of the performance of LV CT accuracy testing in-situ and the challenges faced in its process.
- 3. Introduction Low Voltage (LV) Current Transformers (CTs) are installed to step down the high currents in the primary side to a lower secondary current to be measured by a transformer connected electricity meter in metering installations in customer’s switchboards. The LV CTs of rating up to 3000 Amps primary to 1 or 5 Amps are used in situations where the anticipated energy consumption exceeds 100 Amps per phase as per Service and Installation Rules of NSW. The measurement of accuracy of a metering installation is very vital in the National Electricity Market (NEM) and this does not solely depend only on the meter alone whereas the minimum accuracy requirement of National Electricity Rules (Rules/NER) stipulates overall error inclusive of the CT.
- 4. Introduction The Chapter 7 of NER, Metrology Procedure, Part A and associated regulations require all new CT’s must meet the requirements of relevant Australian Standards, it should type tested until a valid pattern approval is issued by National Measurement Institute (NMI) and tested for accuracy within the limits of measurement of uncertainties at least every 10 years (time based) or based on an asset management strategy approved by Australian Energy Market Operator (AEMO) for all Type3 1-6 metering installations. The Responsible Person in the NEM shall be a financially responsible market participant (retailer) or Local Network Service Provider (LNSP) and shall be the responsible party who ensure the regulatory compliance in accordance with the rules when testing the CTs. Australian Energy Regulator (AER) is responsible for the compliance and enforcement with respect to the rules.
- 5. Background Until 2011across the industry, the majority of the CTs installed at premises were not accuracy tested with in the 10 year interval mainly due to the challenges faced in the testing task. AEMO brought this issue to AER’s attention. Subsequently, in consultation with the industry in the form of a Current Transformer Testing Working Group (CTTWG), AEMO developed a document on alternative testing minimum requirements for LV CT metering installations and AER released a Compliance Bulletin No.6 on Instrument Transformer Testing.
- 6. Introduction AER published bulletin permitted all RPs to either test a representative 10% sample of LV CTs population from all family types during financial year 2012-2013 or undertake an alternative testing practice approved by AEMO. AEMO’s alternative testing approach is to test LV CTs by sample testing, variables or attributes method. As part of a sample testing process, this method requires performing an in service test4 (inspection of sites) at all LV CT metering installations of Type 4-6 and, in addition test all LV CT meters installed in Type 3 & 4 sites. The AER bulletin also stated issuing of an infringement notice of $20,000 or instituting proceedings in a court in relation to a breach of the electricity rules, in which identify provision of civil penalty an amount not exceeding $100,000 and an amount not exceeding $10,000 for every day that the breach continues.
- 7. LV CT Testing Process
- 8. CTs Specification The specification of a LV CT includes family characteristics listed below. A thorough investigation in terms of these specifications is necessary to prepare a LV CT test plan as part of the Metering Asset Management Plan (asset maintainace strategy) to cover field testing across all family types of the CT population in order to seek AEMO/AER concurrence. The availability of historical information and data records helps to build an effective master plan for the implementation and operation.
- 9. CTs Specification • Australian Standard (AS) of manufacture: AS C.45-1950, AS 388-1968, AS1675-1974, AS60044.1-2007 • Type & Ratio: Type A - 150/300/600:5, Type B - 400/800/1200:5, Type B - 200/800/1200:5, Type C – 1000/2000/3000:5, Type S - 200:5, Type T – 800:5 and Type W – 1500:5 • Taps on CTs: Multi taps, Single tap (extended range) • Diameter: 24mm, 32mm, 45mm • Class: BM, AM, BM/AM/AM (AS C.45), 0.5M, 0.5ME2, 1M (AS1675), 1.0, 1.0 0.5, 0.5S (AS 60044.1) • Burden (VA): 5, 10, and 15 • Power Factor of burden: Unity (AS1675), 0.8 (AS 60044.1) • Winding: Non-Compensated, Compensated
- 10. Test Points and Limits of Error
- 11. Development of Safe Work Methods Testing staff are appropriately authorised under the Electrical Safety Rules to carry out the testing of CTs in-situ. Prior to commencement of testing, a worksite hazard and risk assessment shall be carried out so that any hazards and risks associated with the testing to be assessed and controlled by the safety control measures to ensure testing can be carried out safely. All staff is required to wear safety clothing and footwear and rescue kits shall be available for immediate use. Insulating PPE, i.e. approved rubber gloves, insulating mat (comply with AS/NZS 2978), approved eye protection shall also be used as required. It shall be ensured that CTs do not have open circuit secondaries while primary circuit is alive and secondary voltage level shall be recorded. It is very important to check the connections, using non-retractable fully shrouded lead connectors wherever possible and to connect all earthing points of test equipment to a suitable common earth.
- 12. Primary Injection Method 2.5Comparator 10 Variac Injection Transf. CT under Test STD Burden Box Test Set Standard CT 15 30
- 14. Test Environment The LV CT customers are located across a large geographical area in the electricity network and hence the operation of the testing process is involved with long distance travel for pre inspection of the site and testing purposes. The test methodology requires the customer’s load outages and site access to customer’s main switchboard is necessary for testing the CTs. This depends on the customer’s support and corporation towards compliance due to the fact that their normal processes are to be disrupted. The pre inspection of the site prior to organising the testing with the customer’s help to assess the site condition and the feasibility to carry out the tests such as sufficient natural light, adequate space, the design of the switchboard and the construction of the CTs installed. Due to the fact that, some of the switchboards were built in two to four decades ago, the challenges facing in reality in the LV CT testing process is to overcome these factors.
- 15. Test Management The management of tests, project support and to review the progress in order to achieve the targets is a real challenge. There are lots of activities in the back office and also in the field that are needed to be performed such as contacting customers, requesting for load shut down and scheduling and organising a suitable time and date to carryout tests. It has been very effective to meet the customer directly by the test staff to discuss the requirement of the test and to organise an appointment for the outage. The majority of the customers have been very corporative and in certain instances, the customer’s request written undertaking of the requirement. The selections of premises to be tested are performed by a database based on the CT’s age and service orders are created automatically with the help a computer system. The scheduling and asset management tools for records management are very helpful to operate the testing process efficiently and effectively.
- 16. Test Results The accuracy test results of the LV CTs, ratio error and the phase angle error were found to be within the limits of error specified by the AEMO for in service compliance testing of CTs irrespective of their manufacture standards and the accuracy class. When the LV CT’s accuracies are available, the calculation of the overall accuracy requirement for the metering installations could be performed with the help of a computer based system. The test results are submitted to AEMO for further analysis and AER will assess whether a further 10%, or another sample size of LV CTs, should be tested by RPs who have adopted this approach.
- 17. Discussion Metrology in the NEM itself is very challenging in view of national and jurisdictional regulation in addition to the ongoing competition in the metering business. The implementation of National Energy Customer Framework (NECF) in NSW in July 2013 introduces some non-negotiable regulations in the areas of customer’s interruptions. The electricity network businesses are endeavoring to keep the electricity price increases to in par with the CPI while meeting the regulatory compliance which contributes to cost implications due to investment in the resources. When AER finailise the next course of action towards the continuation of LV CT testing based on the assessment of the test results of the current program, there would be many challenges ahead in the future.
- 18. Acknowledgement The author appreciates the fullest support of the management, field and back office staff at Metering Information branch at Endeavour Energy to complete the interim solution to LV CT testing.
- 19. Thank You