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Electrical Tester online
August 2018
Stranded in a substation!

Stranded in a substation!

24 August 2018

Jill Duplessis - Global technical marketing manager and editor

You’re stranded in a remote substation and you can’t leave until it’s successfully commissioned. What instrument would you choose to have with you to help you tackle this daunting challenge? This scenario may seem a little unrealistic – after all, today’s employment laws make it difficult for even the most uncaring of bosses to condemn their employees to extended on-site exile. Nevertheless, commissioning a substation is no small task, so it’s not surprising that engineers undertaking this work may sometimes feel a little stranded, even if this doesn’t reflect reality. In such circumstances, having the right test equipment to hand is definitely a source of comfort!

Given the pressures of today’s dynamic energy market, electricity utilities are now, more than ever, expected to deliver the highest performance standards in all facets of their operations. This makes it essential for substation commissioning to be executed efficiently and expeditiously. The work ranges widely in scope and complexity and may for example include:

  • „commissioning new-build substations „  
  • commissioning mobile substations „  
  • commissioning modular substations
  • „installing additional electrical equipment and/or protection schemes „    
  • modifying existing electrical equipment and/or protection schemes „    
  • replacing existing electrical equipment and/or protection schemes

Commissioning of EHV transmission substations (e.g., >100 kV) and all installations of power transformers, which by default includes mobile and modular substations, often attracts considerable attention at corporate level in major utilities,  which is another good reason why efficient working is desirable.

Utilities have been installing equipment for over a hundred years so most have already formulated a commissioning process and there is usually little need to change this. The pillars of such a process will include attention to safety and the safeguarding of system integrity, complemented by the deployment of well-trained staff and an engaged workforce. Historically, the workforce involved in substation commissioning was a mix of skilled employees from several of the utility’s own internal departments, including protection/relay, substation design, substation construction and maintenance. More and more, however, utilities are calling on outside vendors to partly or even completely take over the responsibilities that would once have rested with their own staff. This means that effective management of the commissioning process is even more critical if a satisfactory outcome is to  be achieved. 

The commissioning procedure is a general guideline that outlines sequential steps to be followed during the commissioning process. The steps may, for example, include tasks such as marking prints to reflect functional test paths and voltage confirmation test requirements, developing a custom checkout guide that establishes test requirements for equipment and protection schemes, confirming relay and CT settings, and performing benchmark testing on new equipment and CTs.

Much of a commissioning engineer’s time is spent on-site during the assembly of key equipment such as transformers, circuit breakers, CCVTs, circuit switchers and disconnect switches. Transformers tend to take centre stage as proper handling and assembly validates their warranty and reduces the risk of future problems. They have very specific commissioning requirements that may include important tasks such as:

  • inspection and SFRA testing on arrival at site, before unloading from the transport vehicle „ 
  • transformer assembly witnessing „  
  • specification and/or agreement about the oil filling procedure to be used „  
  • confirmation of the correct operation of accessories such as pumps, fans, gauges, relays and alarms
  • review of acceptance testing

During the commissioning process, all devices require acceptance testing before being placed into service and this is once again particularly important for transformers. This is largely because transformers are almost always the highest value item of equipment installed in a substation, in some cases amounting to 60% of the total investment.

For all equipment, the testing specified by the manufacturer is performed during commissioning to meet warranty requirements and to ensure correct operation of the asset. Often additional testing is needed to ensure, for example, that the equipment meets its purchase specifications and that it was not damaged in transit. Tests may also be required to establish benchmark results, as these often significantly aid the evaluation of future test results when diagnostic tests are repeated during the operational life of the equipment, either as  part of a full health assessment or to investigate possible problems.

To make life easier for engineers tasked with carrying out the onerous work of substation commissioning, Megger has designed the TRAX test set with substation equipment and hierarchies in mind. As might be expected, transformer testing is central to the design. With the capability to  perform ten different tests on a transformer along with automatic, adaptive demagnetization of  the core, TRAX offers a complete solution in transformer testing.

Unique features include individual temperature correction (ITC), which is used to report true equivalent 200C power factor/tan δ results, and voltage dependency detection (VDD), which alerts users if unexpected voltage dependency is found during a power factor/tan δ test. TRAX can also perform true dynamic measurements on on-load tap changers. In fact, just about the only two transformer commissioning tests it can’t perform are SFRA tests and wideband DFR testing, for which the use of Megger FRAX and IDAX test sets, respectively, are recommended.

Circuit breakers, circuit switchers and instrument transformers are also important substation assets, and they have been fully taken into account in the design of TRAX, consolidating its position as a true all-in-one substation test set. TRAX provides instrument transformer testing capabilities for CTs and VTs, including turns ratio/polarity, excitation curves (saturation and kneepoint), winding resistance, voltage withstand, burden and power factor/dissipation factor. It also offers circuit breaker testing capabilities that include contact resistance measurements, three-phase main and PIR (pre-insertion resistor) contact time for breakers with a single break per phase, coil current analysis, contact travel/motion, and of course power factor/dissipation factor and capacitance tests.

On a good day, substation commissioning will proceed smoothly and stranded engineers will quickly be released from exile to return happily homeward. If things do go awry, however, TRAX provides all of the essential facilities and features needed to sort out the problems quickly and efficiently. It even has a manual mode, which allows users to take full control and operate the instrument as a six-channel multimeter with ten voltage and current generators and an integrated oscilloscope. So, if you’re heading intrepidly into the challenging territory of substation commissioning and you’re only allowed a single instrument as your companion, make sure it’s a TRAX!