Gary Orlove wrote:Gary, in your experience would the CT heat into the main tank show up mainly in the top? I just recently had 2 Single tank 3 phase 23 kv feeder brkrs that had some heat on them. Oil showed nothing as far as gasses go. Bottom of tank could be 6-7 degrees cooler than top. On one of them I have one particular bushing that is warmer than the others, But with the other the whole head of the breaker and all 6 bushings are fairly consistent in temp. I was just surprised that the heat appears to be going half way down the tank.
ING OIL CIRCUIT BREAKERS
Function: A circuit breaker is designed to open (trip) during a fault condition, which protects transformers or other sensitive equipment in the circuit. It is also in the circuit to allow the utility or facility to energize or de-energize a transformer or bus section while under load. The internal mechanism is designed to break and extinguish the arc that is created during the trip operation.
Unique Characteristics: The individual phase tanks are filled with transil oil. This oil insulates the voltage from the grounded tank and extinguishes the arc during the trip operation. Some of the breakers have CTs installed at the base of each bushing. The CTs should be equally warm and will transfer some heat to the main tank. The degree of heating is proportional to the loading of the circuit breaker.
IR Analysis: The circuit breaker is not a heat source under any load condition, the phase tanks should be equal in temperature and ambient. Any temperature rise should be investigated and should be considered serious. The heating of a phase tank usually indicates high resistance of the main contacts that are misaligned or out of adjustment. Normally, some burning and pitting of the main contacts is evident at this point. A dissolved gas analysis of the oil is used to confirm the condition of the contacts.
Oil level indicators should be checked. If the oil level indicator is not visible in the site glass, try to determine the level using IRT. A portable heat source may have to be used to obtain IR level information. If the level cannot be confirmed, the condition should be considered serious.
Most control cabinets have heaters that should be checked for normal operation. See http://www.compsys.com/enews/knewspro.nsf/v/RGAY-5TGSEL
Case Study (avoided cost $225,200)
A thermography survey detected a 7C temperature rise on a main generator oil circuit breaker. One tank was warmer than the other two. The thermographer from the plant passed over this anomaly for two reasons. First, the plant has a 10C limit on taking action; and secondly, and more importantly reason is, the thermographer was an I&C technician, who was following the guidelines for reporting thermal anomalies in the plant. He didn't understand the operation of the switchyard equipment. The substation thermographer did a survey the next day, and he rated the problem as 'critical'. The scheduling for these jobs was done from two different offices; the overlap in equipment surveyed was by chance. The unit was removed from service and an inspection revealed severe burning and misalignment of the main contacts. Any temperature rise above ambient on an OCB must be investigated.
Infrared Training Center