Advantages of Continuous Monitoring of Partial Discharges ...

1 Abstract -- For over fifty years companies have beenperforming Partial discharge measurements on electricequipment in order to obtain information as to the quality ofinsulation on operating equipment. Partial discharge activityis a well-accepted indicator of insulation , trending of Partial discharge activity providesequipment owners the opportunity to reduce forced outagesand increase productivity of plant equipment. Traditionally,periodic testing is performed, but advances in technology allowthe Continuous Monitoring of Partial discharge Terms -- Partial discharge , motors, generators,switchgear, Continuous monitorI.

2 INTRODUCTIONLast year US industry spent over $600 billion on plant andequipment maintenance. According to industry experts, atleast $200 billion was wasted. Other industry statisticssuggest that 80% of all failures of plant and equipmentoccur on a random basis and only 20% of the failures areage related. This means that 80% of failures have not beenpredicted with current test and maintenance practices andtherefore have not been prevented. Can the situation beimproved?In today's competitive environment, increasing demands arebeing placed on the management of physical assets. Manythings have been done to improve the efficiency ofmaintenance work through the use of computerizedmaintenance management systems (CMMS), but they aremore focused on corrective and preventative (periodic) in technology are allowing new approaches tomaintenance.

3 These include reliability-centeredmaintenance, predictive maintenance, condition monitoringand expert systems. Trend setting organizations areincreasingly taking advantage of the convergence of thesenew technologies to implement proactive maintenanceprograms to improve their company's bottom such condition based maintenance technology is themeasurement, Monitoring and analysis of an electricalphenomenon know as Partial discharge (PD), a well-knownand accepted precursor or indicator to the failure ofinsulation systems in higher voltage electrical it has been successfully applied to equipmentrated as low as 2,300 volts, customer value is low.

4 Value iscreated at voltage levels of 4,000 volts and TRADITIONAL APPROACH OF PDMEASUREMENTST raditionally, PD measurements have been performed onequipment on a periodic basis, one to four times per periodicity is based on the analysis of the most currentreading, trend analysis, availability of resources, monitored equipment includes motors, generators,switchgear, cables, bus duct and of the deficiencies in performing periodic PDmeasurements as well as periodic off-line tests such asinsulation resistance and over potential testing are:1) Time duration between tests are typically six to twelvemonths (if on-line) and frequently much longer for off-linetests.

5 Many problems will manifest themselves in a muchshorter period of of Continuous Monitoring of Partial Discharges inRotating Equipment and SwitchgearClaude KaneCutler Hammer Predictive Diagnostics5421 Feltl Road, Suite 190 Minnetonka, MN 55343 Phone: 952-912-1358 Fax: 952-912-1355 Email: BlokhintsevCutler Hammer Predictive Diagnostics5421 Feltl Road, Suite 190 Minnetonka, MN 55343 Phone: 952-912-1334 Fax: 952-912-1355 Email: V. CarneyChemicals & Energy DivisionManager Electrical MaintenanceUS Steel GroupClairton Works - MS #42400 State StreetClairton, PA. 15025 Phone:[412]-233-1409 Fax: PozonskyCutler Hammer Engineering Service & Systems130 Commonwealth DrWarrendale, PA 15086 Phone: 724-779-5815 Fax: 724-779-5828 Email: During the performance of a periodic test a problem isdetected, one starts to ask the following questions: When did the problem start?

6 How fast is it degrading? Not only the velocity ofchange, but also the acceleration of change. How fast will it continue to degrade?The true answer is - one does not really know! In a periodicmode one will need, at least, two consecutive tests toestablish a rate of defect development which could meananother year of testing. Therefore, one does not haveenough qualitative and quantitative data to make a properjudgment at the time of problem detection, so arbitrarydecisions are ) In many cases PD activity is unstable. It may not beactive today, but active tomorrow.

7 Wide variations of PDactivity are frequently observed based on data fromcontinuous Monitoring . Many factors can affect PD few include: Voltage Load Temperature Humidity Vibration PressureAs more and more data is collected in conjunction withother dynamic factors, much is being learned. Correlationof the certain dynamics with PD activity provides additionalinsight and can improve accepted PD standards focus on off-line partialdischarge tests. OEM s test labs commonly have their owntest specifications and acceptance levels vary from OEM toOEM and are specific for specific insulation and PD standards dealing with on-line PD measurementsavoid the stating of specific levels or quantities to determineacceptability limits.

8 Instead, trending is order to perform proper trend analysis, one should makesure all dynamics are nearly identical at each testinginterval. This is very difficult, and sometimes impossible, toaccomplish and can be time consuming. At this time,knowledge on correction factors to account for the changein dynamics is more academic than practical. Anotherreason for the avoidance of establishing levels is that even avery low level of PD activity that is trending upward will beindicating the development of a defect. Conversely, a highlevel of PD activity that is stable should be of concern, butat least one knows that the problem or defect is not gettingworse, which should provide some level of ) Time consuming.

9 Taking periodic readings is laborintensive and frequently requires an expert to take andanalyze the data to extract valid information. Maintenanceorganizations that are being driven to do more with less arelooking for ways to increase reliability with fewerresources. The only true way to reduce maintenance costsis to take the "work" out of it, which is the essence ofcondition-based Continuous Monitoring OF PD ACTIVITYA Continuous Monitoring system will overcome all of thedeficiencies listed above and will be an effective conditionbased maintenance tool: Advantages include:1.

10 Finding a problem quickly. The monitor will identify aproblem in its earliest stages of defect will provide one with sufficient information as tothe growth rate and the severity of the Providing information as to which phase the defect is inand generally what type of defect such as: Corona Surface discharge Void type of defect (Insulation Delamination) Conductive tape deterioration (Slot discharge ) Loose high voltage connection that is arcingIt is even possible to localize even further the location of Since no labor is required to perform the tests, Continuous Monitoring allows the use of limitedresources to finding solutions to problems instead offinding Reducing unnecessary maintenance because themonitor will be constantly testing and will haveaccurate data on which to base Collecting more accurate data as tests are conductedunder real operating condition6.