GO WITH THE FLOW…
WHAT TO INSPECT IN ELECTRICAL SUBSTATIONS AND LINES
While many know how critical it is to identify heat-related electrical problems prior to failure, too often they don’t inspect some of the most important equipment in a substation.
Typically we focus on the most critical equipment in a substation, equipment that, if it fails, will result in a wholesale outage. Transformers not only fit into this group but also are very susceptible to heat-related failure. Remember to inspect all the critical parts of the transformer:
Bushings: look for heat in the external connections as well as the more difficult to see internal connections in the bushing head and—as seen subtly at the base of the bushing—connections to the coils
Surge protection: look at segmented signatures with small rises in temperature as indicators of serious problems
Cooling systems: blockage or low oil in radiators will show up as cooltubes. Also, look at the fans after they have operated for 15 minutes or more. Failures in the cooling system are very costly because they rapidly result in damage to the transformer.
Tap changer tanks: normally these run at or below the temperature of the transformer. If a bad tap is carrying load, it will heat the changer tank but, beware, it may not be energized when you are inspecting!
Oil-filled circuit breakers (OCB) and voltage regulators are also critical to operations and can suffer heat-related failures similar to transformers.
Too often various disconnects and switches are neglected during an inspection. While their failure may not seem crucial, if a circuit needs to be opened and a disconnect is welded closed, there will be a serious problem! This equipment is very susceptible to damage because the localized heating in the jaw or latch end typically damages the metal and the trend to failure grows dramatically more rapid. All these devices depend on the spring tension of the metal to maintain viability of the electrical contact, and at temperatures as low as 200oF (93oC), annealing begins to occur and performance degrades.
Take your time, working with good conditions, to inspect all the equipment in your substation. You reap big returns on your investment and get through the peak season with improved reliability.