The first issue of the CoronaGram is the start of another new adventure for me and I will endeavor to make it interesting for you. Please spread the word if you find this useful and forward the corona information we are able to provide, if you have a concern please tell me first.
The Corona Technology Course website and the CoronaGram are brought to you by Ox Creek Energy Assoc Inc. who present the Corona Technology Courses for industry and utilities.
Corona is the result of an increasing or steady-state high voltage electrical field applied to air resulting in the eventual ionization of the air -which is corona- and can be identified by audible sound, primarily ultraviolet light, ozone and nitric acid formation. The ozone can react/breakdown some materials such as the sheaths on fiber optic cables and potentially the covering on non-ceramic insulators. The inception voltage, existence and severity of corona is influenced by "relative air density" or RAD and the papers referenced on the Corona Technology Course website.
An analogy from the hydro-turbine world, where corona would be equated to cavitation, where small very powerful implosions of low pressure areas in water occur that can destroy the strongest steels by blowing tiny fragments out over time. The cavitation occurs in low pressure areas and can completely remove the blades from a stainless pump impeller. As the equipment gets further from the design tolerance the cavitation rate typically grows worse rapidly and efficiency dwindles.
What can we decide when we see corona? That energy is being consumed, efficiency is decreasing. An individual instance of corona typically does not consume significant power and may be random. Random is another part of the problem with corona complaints or RFI/TVI which can occur and when the technician has time to look there is nothing to find because the RAD has changed.
Technology is a wonderful thing, the device to make corona troubleshooting possible when RAD is different on any given day must be somewhere down the path we are following. When we let this new device tell us the temperature, air pressure, humidity, atmospheric pressure and any other contributing variables, then make the line connections and then push the button to begin the sequence and go observe with a corona camera the transmission line, substation, or distribution line where the complaint may have originated from. This technology will also enable the transmission line maintenance company to certify to the ISO the tested voltage and leakage or losses for a transmission line for a RAD range, adding the infrared maximum temperatures for a rated current will result in a Transmission Line or Substation Voltage and KVA Certification.
If corona is not random, but is occurring consistently in a spot on a bright sunny day then action is definitely required to understand what the cause is and the magnitude of the losses. The causes of sunny day corona can be corners too sharp for the applied voltage (frequently at transformer and breaker connectors, switch hardware), applied voltage above the component rating (69 kV on 35 kV insulators), damaged components (punctured insulators put greater stress on the remaining insulators in the string), corona between ground wires and structure or on steel fence posts (ice on insulators or shorted insulators raising ground/step potential), contamination on insulators and conductors (airborne road salt or other chemicals, transmission and distribution lines over roadways may need to be relocated underground for the over the roadway span, substation insulators may need to be cleaned), bird caged vertical cable drops, corrosion on conductors, …
The story I was told "the young engineer right sized the conductors and on a rainy day there was no output power from the transmission line all input was consumed in losses."