Ofil's Corona Detection Solution
For detecting and predicting problems on high & medium voltage systems, DayCor® corona cameras come in useful. During the past decade it has been proven that DayCor® cameras render in real time and on the fly meaningful concrete information about existing processes that emit partial discharge. Observing the emitted discharges let engineers discover existing problems and predict failures that if left unattended develop into imminent failures. And yet, one of the expected features of testing equipment is the ability to differentiate between false and true alarm signals. Indeed, can a camera as sensitive to UV signals as DayCor® handle this righteous demand?
Acknowledging the need for sifted information led Ofil develop a new approach to corona detection. This approach is called "Corona Detection Solution" and it involves the ability to pinpoint corona sources and analyze findings. To be able to pinpoint corona sources Ofil offers the most UV sensitive corona cameras. And, to be able to analyze findings Ofil offers the Corona-Base software. Corona-Base is programmed to enable identifying trends and find answers that are based upon stored cases of inspection findings.
Corona-Base is a database application that manages inspection findings and media collections in an easy-to-use all-in-one environment. With Corona-Base it is easy to document inspections, store findings, follow-up cases, and look-up components history, report actions and analyze trends. Corona-Base assists in creating priority levels, distinguish between important and urgent and basically manage assets in a timely economic manner.
Nevertheless, more than a basic understanding of corona formation is needed in order to be able to benefit from Ofil's Corona Detection Solution. CITI, Ofil's educational initiative supplements the recommended knowledge by providing theoretical and practical background of the physicals and electrical processes that lead to corona discharge as well as of the outcome of such discharge activity. 20 PDHs and a UViGrapher diploma are granted to CITI graduates after completing the course. Trained UViGraphers are qualified certified UV inspectors that know how to benefit from UV inspections and turn raw data into executive decisions.
SWITCHGEARS - CASE STUDYIn January 2009 at IE's 161 kV substation a 22kV Circuit Breaker (Air insulated) with insulating epoxy boards showed a consistent discharge to ground. The discharge was detected by the control desk of IE and a tripping from one of the cabinets was located. The case was documented in IE's corona-base as an example how to treat similar detected symptoms.
A suspicious noise was heard from one of the cabinets causing the maintenance team to open the circuit breaker's metal cabinet. With bare eyes the considerable damage and material degradation could immediately be observed, yet in order to investigate what caused this havoc and exactly where is the root IE used a DayCor®.
The DayCor® instantaneously displayed a huge UV discharge with a count of 4500 UV events/min located between the epoxy insulating boards to the "R" & "T" phases of the circuit breaker. The initial local corona discharge has deteriorated and developed into arcing with tracking and carbonization of the epoxy board.
Investigation led IE to conclude that this was a case of a design issue:
- Air gap was trapped between the epoxy boards and 2 of the phases of the Circuit breaker
- Sharp edges in the epoxy boards created high enough local E-field to initiate corona discharge
- The combination of high local electric field, humid unventilated conditions, and presence of air gap fed the ongoing corona discharge, creating micro arcs and arcs, changing the insulation properties of the boards, damaging the material and creating considerable noise
As a result, IE retrieved in their database all similar cabinets and changed their design removing the side metal boards.
In follow-up check no corona activity was detected. IE closed the case knowing that if the root cause were not treated on time a flashover leading to an unscheduled shut-down could have been expected, and the life time of all similar switch gears were restored to their original plan.