Transmission and distribution (T&D) equipment and networks undergo significant stress during operations and can experience poor performance if not properly assessed at the installation stage. This has encouraged utilities to adopt a wide range of testing and measurement (T&M) tools and methods in order to ensure reliable operations of T&D equipment. Leading utilities share their T&M experience and priorities…
What have been your organisation’s key priorities with respect to testing and measurement of transformers and meters?
For a transmission utility, the operational performance of the entire equipment is the key priority. Hence, diagnostic testing becomes a key focus area for critical equipment. Besides, the routine testing of all protection devices is an important practice followed by our organisation.
Along with the conventional equipment testing practices, tests like sweep frequency response analysis and excitation at high voltages of transformers, capacitance and tan delta measurement for other critical equipment, dynamic contact resistance measurement of breakers, etc. have also become routine. With the increase in the number of diagnostic tests, it has been a challenge to interpret test results and establish a correlation to ensure corrective action in a timely manner. Therefore, developing expertise in this area is a key priority for us.
Even though online oil testing equipment is used for dissolved gas analysis, there are no separate standards to refer to these test results and following conventional benchmarks may not be as correct a method for interpretation. This remains an open area for exploration.
The power system protection segment has changed a lot over the years. Meanwhile, the tests for checking these protection systems have also changed. Maharashtra State Electricity Transmission Company Limited (MSETCL) is using automated test kits for testing all numerical protection devices. All new substations have substation automation systems built around IEC 61850. Test kits capable of GOOSE (generic object oriented substation event) testing are being used. The overall performance of these automated test kits has been satisfactory.
The use of software tools for the testing of communication in and out of substations is required as many legacy protocol devices are still in service and cannot be replaced immediately. Protocol testing tools for MODBUS, IEC 104, IEC 103 and IEC 61850 will also be required. Developing protection and automation equipment verification laboratories is an option utilities can consider for the verification of automation and communication equipment capabilities. New testing tools and equipment will be required for this purpose. With optical ground wire becoming the norm for the communication backbone, the testing of these wires would require the introduction of new test kits in the utility.
Apart from these, improvements in meters and equipment for routine troubleshooting at substations are a small but important focus area. Direct current (DC) earth fault locators need to be simplified.
In the domain of energy meter testing too, the verification of the communication capabilities of meters and the verification of adherence to data protocol would require new tools. Further, device language message specification and verification tools for availability-based tariff meters would need to be introduced.
Eastern Power Distribution Company of Andhra Pradesh Limited (APEPDCL) has adopted the following testing procedures with regard to the testing and measurement of transformers and meters:
Measurement of transformers:
- Measurement of insulation resistance
- Measurement of winding resistance
- Open circuit test
- Short circuit test
- Ratio test
- Magnetic balance test
- Vector group verification test
- Measurement of losses through power analyser
- Measurement of no load losses
- Measurement of load losses
- Measurement of guaranteed maximum losses at 50 per cent load
- Measurement of guaranteed maximum losses at 100 per cent load
- Testing of dielectric strength/break down voltage of transformer oil
- Testing of acidity of transformer oil
Testing and measurement of meters:
HT TVR meters
All high tension (HT) trivector (TVR) meters being procured are of 0.2S class. Hence, the kWh, kVArh, kVah parameters are being calibrated with more accurate ZERA electrical resistance system (ERS) testing kits, which are being calibrated at the National Accreditation Board for Testing and Calibration Laboratories (NABL). All current transformers (CTs), power transformers (PTs) and CTPT sets are also being tested for confirming the ratios and polarities. All HT TVR meters owned by the utility are tested annually.
LT CT-operated meters
All low tension (LT) CT-operated meters are being tested after commissioning for accuracy with service accucheck ERS testing kits, which is also calibrated yearly at the NABL.
LT three-phase and single-phase direct meters
LT three-phase and single-phase direct meters are being tested with a 0.05S class fully automatic meter test bench made by Itron, Inc.
Kerala State Electricity Board (KSEB) Limited’s key priorities with regard to equipment and meter testing functions have been ensuring safe operations, accuracy and reliability, maximising the useful life of assets, and assuring that the equipment performs as per standards.
Higher failure rates of distribution transformers (DTs) were one of the major issues plaguing the state’s distribution system. To this end, the utility has been able to reduce the failure ratio from 4.34 per cent in 2006-07 to 1.57 per cent in 2016-17 by making the acceptance test more stringent.
KSEB Limited has achieved 100 per cent metering for all its consumers. More than 12.3 million consumer meters are connected to the system. The meter failure rate is 7 per cent. The quality of meters, though not compromised, is affected by the procurement policy based on the lowest rate. In the given environment, efforts are being made to bring down meter failure rates by imposing much superior standards for acceptance tests.
T&M is a critical and typically vast area for the sector. In the context of the distribution segment, T&M is being deployed with regard to the materials used for the supply and sale of electricity. The key priorities of an organisation with regard to T&M are the accurate measurement of electricity and quality assurance of related material supplies. The major technocratic items in this respect, mainly transformers and energy meters, have therefore been our priority. They undergo 100 per cent testing before being put to use. The testing standard for transformers and meters is different. Power transformers are tested at NABL-accredited testing laboratories like the Central Power Research Institute (CPRI)/Electrical Research and Development Association (ERDA). However, in the case of distribution transformers and energy meters, only percentage/sample testing is done at NABL laboratories, and 100 per cent testing is done at the organisation’s level. For other materials, percentage/ sample testing is done at NABL laboratories and only verification is done at the organisation’s level.
The key priority for accurate measurement of electricity is the selection procedure with regard to meter suppliers. This procedure involves sample testing along with tendering of meters at both levels, that is, at the organisation’s lab and at NABL laboratories (like CPRI/ERDA, etc.), as well as post-order “type testing” at NABL laboratories. Further, the instrument transformers (CTs, PTs) are used with meters for the measurement of electricity and thus, undergo 100 per cent testing conducted by the organisation’s concerned testing sections prior to putting them to use. The installed meters in use are periodically tested to assure accuracy.
The key priority for the quality assurance of material supplies is the pre-delivery inspection and acceptance testing as per Indian Standards (IS) of each batch of supplies. The testing is done at the manufacturer’s site by the organisation’s inspector.
Are the existing test facilities adequate to meet the sector’s requirements?
Even though the existing test facilities are adequate, there is scope for further improvement, such as the establishment of MSETCL’s own NABL-accredited state-of-the-art oil testing and interface meter testing laboratory.
Yes, existing facilities are adequate to meet APEPDCL’s requirements.
The present testing facilities are adequate to deal with the requirements of acceptance and routine tests prescribed in the standards. However, KSEB Limited proposes to upgrade the testing system in all its laboratories with state-of-the-art technology, and attain NABL accreditation for all its labs in the near future, which distinction is now limited to only one of its labs (TMR in Angamali). The need to upgrade the facility for complete tests for CTs and PTs has already been recognised. In order to contain the DT failure rate, the utility’s testing facility for DTs requires improvements.
For organisational-level T&M, the organisation has equipped area store-level facilities with power analysers and other equipment for 100 per cent testing of DTs. The tests are conducted at the six area stores of the organisation. For meter testing, the organisation has two HT meter testing divisions at its regional headquarters, which are equipped with high accuracy rotating substandard (RSS) meters and portable primary/secondary injection kits for testing of HT meters and MEs. For LT meter testing, the company has LT meter testing laboratories at eight circle headquarters out of its 15 circles; three are equipped with fully automatic testing benches facilitating accurate and faster testing of LT meters including the testing of consumer-contested meters. Further, for periodic on-site testing of installed meters in use, each of the circle headquarters is equipped with at least one portable RSS meter and the city circle/divisions are equipped with the portable ones.
These testing facilities may not be fully adequate, as for materials other than DTs and meters, there are no internal testing facilities and, therefore, definitely need strengthening, expansion, addition as well as advancement. Moreover, the establishment of NABL accreditation level testing laboratories at the regional headquarters is currently under process.
What are the key issues and challenges being faced in the T&M domain?
The issues and challenges are as follows:
- Currently, online monitoring of certain dissolved gases in transformer oil has been incorporated for some transformers. The challenge is to cover more transformers for online monitoring along with the monitoring of additional dissolved gases.
- Soft integration of diagnostic test data from all the transformers and the development of algorithms for centralised monitoring of the health of transformers.
- To increase the number of mobile testing units for interface meters.
- To adapt to the new metering system, as proposed by the Forum of Regulators in its report on scheduling, accounting, metering and settlement of transactions in electricity.
- Implementation of technical specifications for interface meters and automated meter reading as proposed by Power System Operation Corporation Limited.
The key issues are as follows:
- There is no movable testing equipment available for the measurement of “no load” losses and load losses of DTs and PTs in the field.
- There is no movable testing equipment available for the testing of dielectric strength of transformer oil in the field.
- Communication of meters with modems has become a priority for online billing and analysis works. If all meters are provided with RS-232 ports, the fixing of modems can be achieved without any hurdle.
NABL accreditation has already been attained for KSEB Limited’s lab in Angamali. The immediate challenge is to attain accreditation for the remaining four labs. Most of the testing labs do not have an HV testing facility for DTs, which acts as an impediment to the periodic verification of the manufacturers’ claims. However, this issue will eventually be addressed.
The long testing time requirement at NABL-accredited laboratories is a key issue due to the limited availability of laboratories like CPRI/ERDA in the organisation’s vicinity and the overloading of the available laboratories with large pendency. In addition, there are mistakes in testing at NABL-accredited testing laboratories, even in sensitive testing like sound transmission class rating test, accuracy tests, etc., due to overcrowding at the available NABL-accredited testing laboratories. In the T&M domain, the defining of jammer conditions for various energy meters and testing of meters against jammers is a key challenge as diverse and stronger jamming techniques/devices are being introduced and NABL-accredited testing laboratories do not cover such testing. Besides, the organisation has issues and challenges of its own for setting up adequate facilities and ensuring faster testing with reduced requirement of testing expenditures such as:
- Setting in-house regional-level standard testing laboratories for materials like transformers, meters, cables and conductors.
- Obtaining NABL accreditation for such laboratories.
- Upgrading the existing facilities for accurate and faster testing.
- Expanding the existing testing facilities at least up to the circle level.
- Providing mobile laboratory van facility for the testing of other equipment/ items.
- Forming a separate testing team for inside and outside testing work.
- Material sampling through software to eliminate human intervention.