Brian D. Sparling, Senior Member of IEEE, and Regional Manager with Dynamic Ratings Inc.
The challenges facing substation owners and operators for the past years are unrelenting and are summed up in one sentence: “Reduce operating costs, enhance the availability of the generating and transmission equipment, and improve the supply of power and service to the customer base.” All this, in an environment where the available resources are inexorably decreasing and the pressure from the shareholders and the competition mount steadily. Critical oil-filled electrical equipment, such as transformers, shunt reactors, current transformers, circuit breakers and bushings, are key elements of an electrical power system. The reliable and continued performance is the key to profitable generation and transmission of power. The early detection of incipient faults in these assets can create economic benefits that have a measurable impact on the results required to meet these formidable challenges.
Thus continuous on-line monitoring Intelligent Electronic Devices (IEDs) have become commonplace and, with improvements in sensor technology and with built-in intelligence, have demonstrated their ability to meet the challenges. However, there are still some myths and misunderstandings surrounding the application of and benefits to be gained with these devices. These need to be brought out and discussed. During my twenty-plus years in this field, there persist what I call myths surrounding the use and at times misuse of these IEDs. In this article, I will try to bring out the most frequent of these myths.
Myth: If I use these IEDs, it will prevent the failure of my transformer or circuit breaker.
False
The truth is, if a piece of equipment is on its way to a failure, and nothing is in place to advise the owner of its imminent failure, then it will fail. There are of course protection devices (so-called transformer protection relays, etc.) to advise the owner of its failure (or failure to perform its function). These devices do nothing to protect or save the equipment. Their sole purpose is to remove that piece of equipment as quickly as possible from the system to avoid system problems. In other words, they are system protection relays and are not designed to protect the transformer.
A properly selected and applied monitoring IED is there to provide the early warning of a developing fault within the equipment. The warning to the owner is there to initiate some investigation and corrective action. One of the primary reasons for the use of the IED(s) is to reduce the risk of unexpected failure, not to stop a failure from occurring.
Another truth: These IEDs can and do provide early warning of symptoms of a potential defect, but the transformer failed anyway, occasionally catastrophically. This has happened more than once. The primary reason is that the system was not connected to an alarm annunciator, or into an RTU, because the job (installation and commissioning) was, in my words, NOT completed. By NOT completed I mean that no means of communications were connected to (at a minimum) the relay alarm outputs, or via Serial or Ethernet communications networks to some device to pass on the alarms. Speaking of alarms, another failing to complete the job item is training of the operators, or others to be able to respond to the alarm. These systems will deliver “new types” of alarms that some operators have never been trained in, i.e. how to respond to alarms they have not seen before. Some deeper understanding of the alarm and the consequences of ignoring these alarms must be communicated to those who are responsible.
Table 1 presents an example of such an alarm statement, with a recommendation of next steps, to ultimately making an informed decision. These two are only the beginning; a listing of ALL possible alarms needs to be defined and operators trained.
Myth: If I use these IEDs on my equipment, they will advise me of ANY defect or malfunction of that equipment.
False
The truth is, primary equipment has many failure modes and a good many are VISUAL. When performing an FMEA (failure modes and effect analysis), and all possible failure modes are listed, then lined up with technology and/or methods that can be used to detect the symptoms of those failure conditions, I have found that between 30 % and 40 % of failure modes are VISUAL in nature.
Table 1. Example of alarm statements, with recommendations of next steps necessary for making informed decisions
| Alarm condition | Diagnostic | Prognostic | Recommendations |
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The DGA Monitor HI relay has been triggered because of one of the following:
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