A fascinating flashback to a flying visit in the Netherlands with the CoroCAM 8UAV combined UV, visible and thermal camera mounted in a Gremsy T3 gimbal, lofted by an Aerialtronic’s Altura Zenith drone. The point inspection luckily did not show any major issues, unlike the example image included in the video, which shows a corona discharge co-locating with a hotspot.
When assessing what might at first appear to be a “new technology” in the power industry, it is reasonable of any client to seek a degree of evidence of its established provenance offshore and in the application to which it is intended to be applied in the ‘local’ context.
When that ‘new technology’ is in fact well established offshore but new to the local market, one must consider the question as to what would constitute a suitable level of information to inform, address, and allay in reasonable fashion any uncertainties or questions as to the suitability of the technology for the intended application and also the quality of its said provenance. Clearly, no technology will ever hold 100% of the market or technical opinion but it would be a fair observation that evidence of widespread uptake over a longer term, coupled with a selection of technical papers that all concur on the technical quality and advantages of the technology over alternative or conventionally-deployed solutions, should be deemed to be a tipping point to allow that technology’s confident and optimistic deployment locally.
The purpose of this paper is to convey the background, deployment level, international uptake, and technical evidence enough to allow one to embrace with confidence the ‘near 50Hz’ partial discharge cable diagnostic testing technology applied to both new and in-service condition assessment of one’s 11-33 kV cable population.
…AVO NZ proudly delivers this long-sought capability
HV Cable Assets constitute in many EDB’s and private networks one of the largest asset groups by replacement value. In some of the larger EDB’s this may represent as much as $1.5 to $2 billion. Alarmingly, and at odds with almost all other asset classes managed by such networks, almost nothing is known about the asset condition of each individual cable. Effective HV cable asset management is seriously fraught by this situation. With the parallel scenario of above-ground infrastructure management challenges now painfully troubling the Industry, the risks posed by not knowing the condition of HV cable assets is now a very pressing problem, given the age profile of such assets and the uncertain dynamic of asset aging modelling.
We all know the single most effective way to prevent power failures and shortened equipment lifespan is by keeping moisture to a minimum, along with heat and oxygen. It's fair to say that most equipment failure and subsequent losses (time, resources, etc) could be mitigated, through routine insulation testing.
When it comes to improving testing standards, the process is often long and expensive. Because of this, many industry players focus on improving test and measure equipment, which means we have very advanced tools that can often be let down by outdated regulations.
It also means when we do see updates to international standards, it's a very good thing and often welcome. One example is the adoption of DFR (Dielectric Frequency Testing) over traditional PF (Power Factor) and DF (Dissipation Factor), over 25 years after it was first introduced.
Q; What is the first trip test how is it used to evaluate my circuit breaker?
A: The first trip test uses small clamp-on current transformers that connect to the coil circuit and the load, or protection transformers on the circuit breaker while the breaker is still in service.The breaker is then tripped and the coil current is measured along with the voltage drop. The current extinction times of the three phases are also measured. The coil current trace and other parameters can be compared to previous measurements to see if the breaker is operating normally. This test ensures that no operation is left unmeasured and actually gives a picture of “real life” conditions and how the circuit breaker operates after remaining closed for months or even years.
Q: Since first trip evaluates “real life” conditions, do I still need to perform traditional offline timing on my circuit breaker?
A: Because first trip is relatively easy and quick, some people have tried to replace traditional timing tests with first trip testing. However, it is important to keep in mind that first trip testing complements but does not replace offline time and travel analysis. With first trip you are comparing previous measurements and trending, but time and travel analysis allows you to not only compare and trend results, but to actually verify that the circuit breaker is operating within manufacturer and IEEE/IEC specifications.
Q: You mention time and travel analysis, but connecting the transducer is often difficult. With this in mind, are travel measurements really necessary? Why can’t I just perform timing?
A: Timing ensures that the three phases are synchronized and that the contacts are opening at the correct time, but travel measurements provide a lot more information on how the contacts are actually performing. Travel verifies the stroke of the circuit breaker, as well as the velocity of the contacts. The circuit breaker times can be out of specification, but as long as the velocity of the interrupter is correct it will still be able to clear the fault. Additionally, travel will reveal mechanical issues such as overtravel and over damping. In order to simplify transducer connections, Megger provides a variety of transducers and connection adapters that fit multiple circuit breakers.
