On-line PD Monitoring Makes Good Business Sense

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1 On-line PD Monitoring Makes Good Business Sense An essential tool for asset managers to ensure reliable operation, improve maintenance efficiency and to extend the life of their electrical assets. Executive Summary With the increasing age of electrical assets, on-line insulation condition monitoring has become an essential asset management tool. Compared to routine off-line diagnostic tests, on-line monitoring provides asset managers with continuous insulation condition status while electrical equipment is in operation. It indicates whenever operational stress factors are damaging electrical insulation and putting electrical assets at risk of failure. In this white paper, you will learn how on-line insulation condition monitoring has significant benefits for your organization. Not only can you optimize maintenance schedules based on actual asset condition, the reliable service life of your aging electrical assets can be maximized to help you get the most out of your investment. Introduction Electrical assets, including generators, motors, power transformers, as well as power cables and their accessories, are all exposed to a variety of environmental and operational stress factors throughout their service life. These stress factors cause aging and degradation in electrical insulation over time, which can eventually lead to the asset's early and unexpected failure. Dielectric diagnostic methods, particularly on-line partial discharge (PD) monitoring, make a crucial contribution to maintaining the operation safety and reliability of electrical equipment. They provide asset managers with evidence about changes in the dielectric condition of the insulation. Eventual defects can therefore be detected at an early stage to allow assets at risk of failure to be removed from service and repaired. This helps asset managers to avoid costly, unplanned maintenance and outages as well to extend the service life of equipment. Condition awareness is vital Not knowing the current condition or performance of an electrical asset may lead to premature failure, which leaves the organization with only one option to replace the asset, which is the most expensive option. It is therefore critical that organizations have a clear knowledge about the insulation condition of their electrical assets. On-line monitoring can identify changes and trends in insulation condition, which is indicative of a developing fault. Maintenance can be scheduled only when neccessary based on condition to prevent failure and to avoid its consequences. That is why many organizations are adopting on-line monitoring to access insulation condition status. It enables them to move away from routine, time-based maintenance to a more condition-based maintenance, OMICRON 2015 Insulation degradation is a major cause of asset failure. Shown here is an exploded bushing resulting from aging insulation.

2 scheduling downtime and repairs only when required. The economic benefits include greatly reduced maintenance costs, enhanced efficiency and maximized performance. Indications of insulation degradation Various statistics show that a significant percentage of in-service failures in electrical assets are related to defects in their insulation systems. And many insulation failures in electrical equipment are often the result of partial discharges (PD). These are small discharges that occur as the result of exposure to high electric field strengths and they can permanently damage the insulation. A certain amount of PD is normal and tolerable in electrical assets. However when PD exceeds accepted levels, it could be an indication that insulation degradation is taking place at a progressive rate. That is why in addition to insulation resistance, capacitance and power factor, PD has become a widely accepted measuring parameter for insulation diagnosis. PD often identifies voids, cracks or other flaws where electrical stresses exceed the dielectric strength of the insulation. Insulation damage 56% Causes of failure in rotating machines (Source: CIGRE, 2009 Survey of Hydro Generator Failures) Other 6% Thermal damage 17% Mechanical damage 24% Bearing damage 3% Tap changer 27% Windings 39% Bushings 17% Insulation 11% Causes of failure in power transformers (Source: Tenbohlen, S., Diagnosis of Electrical Assets, ETG Conference 2014) 2

3 Off-line PD testing During the production and commissioning of electrical equipment, off-line PD tests are frequently conducted by the manufacturer to verify the quality and reliability of the equipment. During equipment service lifetime, diagnostic PD measurements are also conducted off-line to check on insulation condition. These are conducted when the equipment is taken out of service during regularly-scheduled routine maintenance. The frequency of such diagnostic measurements is often determined by the importance of the asset and its prior maintenance history. These off-line PD measurements require not only special diagnostic equipment to conduct the tests, but since they are conducted when equipment is not operating, an external voltage source is also needed. This alone is often difficult to deploy on-site and adds significantly to the overall maintenance costs. Also important to consider is the significant amount of time required to prepare electrical equipment for testing, to perform the test and to return the equipment safely to service. Most significantly, normal operating conditions, such as load, operating temperature, vibrations etc., are not considered when the equipment is taken off-line for routine testing. Off-line PD testing offers only a snapshot of the insulation condition state at the time of the test. It does not indicate how the insulation performs fully loaded for extended periods under normal operating conditions. Detailed analysis of defects Off-line testing does have its advantages, however, including the ability to test insulation of electrical equipment at voltages above rated values in order to verify dielectric strength and to detect weaknesses under specific conditions. It is also beneficial for analyzing the severity of defects when detected and the likely consequences if no action is taken. Monitoring under real load conditions By comparison, on-line PD monitoring systems allow asset managers to collect a vast amount of information continuously without interrupting normal service. These monitoring systems record insulation condition data under real load conditions. Insulation deterioration occurring in operation can then be detected anytime and early action can then be taken in response to defects before they lead to failure. Periodic vs. permanent on-line monitoring There are two types of on-line PD monitoring systems available to choose from either periodic or permanent monitoring. Both types of monitoring offer continuous on-line assessments of PD levels and insulation condition during time intervals specified by the operator. Periodic PD monitoring enables operators to observe changes in PD activity over short, extended periods of time. Such a monitoring system is typically portable and can be used for different types of assets. When one asset has been monitored for a period of time, the system can be easily moved to the next asset to be monitored. With the monitoring software, asset managers can reliably assess the current insulation condition and identify which asset is most at risk of failure. For assets with increased PD levels, as well as those with special availability requirements or with unusual loads, a permanent continuous monitoring system can be installed to keep a constant eye on the condition state 24/7. Insulation condition status can be viewed anytime using a web interface to a secured server. A permanent on-line monitoring system typically consists of PD sensors designed for specific assets, a data acquisition device as well as monitoring and PD analysis software running on a central computer. Multiple assets can be monitored at the same time and the data compared using the same software. After installation, the monitoring system requires no human interaction and can be left for several years of reliable data collection. 3

4 Startup Decreasing failure rate Normal life Low constant failure rate End of life Increasing failure rate Early failures Chance failures Wearout failures Preventing early failure Ensuring reliable operation Extending lifetime Off-line diagnosis Diagnostic measurement and analysis when defects are detected Periodic on-line monitoring Periodic condition assessment to identify assets at risk Permanent on-line monitoring Continuous condition assessment Failure rate during asset life and implementation of on-line PD monitoring Periodic and permanent monitoring can be implemented across the complete asset life cycle to increase reliability, prevent premature failures and extend end of life. High Condition-based maintenance vs. time-based maintenance On-line condition monitoring indicates when action needs to be taken to prevent premature failure. It eliminates the "blind" periods between routine timebased maintenance checks when unknown stress conditions can result in failure. Insulation strength Low Condition trigger Operating stress Asset service life Condition-based maintenance t Time-based maintenance Failure t = Period between routine time-based maintenance checks 4

5 Alarm triggering when PD levels are too high Both types of on-line PD monitoring systems record measurement data over time and visualize trends in PD activity. An alarm is triggered only in case of service-relevant PD activity that exceeds acceptable limits. When acquired PD values are below pre-defined threshold values, they are colored in green in a dashboard style display. However when measured values are near or above user-defined threshold levels, they are colored either in yellow (warning) or red (alarm). A list of events that triggered the warning or alarm is provided in a log. The early detection of changes in PD activity enables asset managers to decide if and when to schedule downtime and make planned maintenance. Reducing the frequency of off-line tests The large amount of real-time data gathered by on-line monitoring systems can be used for precise condition assessment. Adding a permanent on-line PD monitoring system can therefore significantly reduce the requirement for frequent or routine off-line electrical testing. That is, by continuously knowing the exact insulation condition status, off-line tests only have to be conducted when a detected defect requires additional analysis. This saves not only time but also the expense associated with offline tests and taking electrical assets off-line. On-line monitoring software allows operators to view PD trends. Alarms are triggered if set thresholds are violated. Ideally on-line monitoring should be used from the beginning when an electrical asset is put into operation to continuously check for symptoms or evidence of an abnormal insulation condition throughout its service life. Off-line PD diagnostics can then be used primarily when an abnormal situation is detected to assess the severity of the problem. Taking the necessary equipment off-line can be planned in advance and based on necessity. Benefits of on-line PD monitoring On-line PD monitoring is an essential tool for effective maintenance and asset management with these benefits: > > On-line PD monitoring answers questions about the present condition of the equipment and its future performance. > > The large amount of real-time data gathered by on-line PD monitoring systems can be used for precise insulation condition assessment. > > On-line PD monitoring systems enable the effective comparison of historical data and the visualization of trends. > > On-line PD monitoring systems trigger an alarm when activity exceeds user-defined thresholds. > > Continuous knowledge of the insulation state saves time and money as maintenance can be scheduled only when required. > > Timely maintenance and repair can help to extend the service life of assets. 5

6 Economic benefits of on-line PD monitoring It is often necessary for asset managers to economically justify this type of condition monitoring activity to their organization in terms of the benefits gained. A PD monitoring system is an efficiency tool. Rather than contributing directly to increased revenue, it allows asset managers to detect abnormal conditions and to use the information to greatly minimize maintenance and repair costs as well as revenue loss. An equipment failure during operation causes a longer outage time and considerable cost expenditure for repair and replacement. The detection of pending faults is essential in order to reduce the failure rate and thus decrease the outage time as far as possible. In this respect, the purpose of on-line monitoring is to prevent major and catastrophic failures and convert them into issues that can be repaired at a reduced cost during a planned outage. Monitoring data also supports strategic decision making to ensure the safe, continued operation of electrical equipment beyond the service life specified by the manufacturer. This enables asset managers to optimize their investment in electrical equipment. Savings achieved Calculating the costs of total asset ownership takes into account not only the purchase of the electrical asset itself, but also the costs associated with its installation, training and overall maintenance. Adding to these costs is the level of risk based on the probability of a premature failure actually occurring and the negative economic impact of such an event. > > Risk = Cost of consequences x Probability of a failure > > Benefit = Annual cost of risk without on-line monitoring vs. Annual cost of risk with on-line monitoring The added cost of implementing on-line monitoring can be easily justified when one considers the costs incurred without monitoring for not only unplanned maintenance and outages but also unexpected failure. The table below shows how the different cost factors are affected by the application of on-line PD monitoring systems. Impact of on-line PD monitoring on asset life cycle costs Implementing an on-line PD monitoring system may add investment costs associated with an asset. However, considerably lower overall life cycle costs can be expected as a result of the information and the knowledge gained from using an on-line monitoring system. > > Investment in an on-line monitoring system > > Costs for planned maintenance and repair > > Costs for unplanned maintenance and repair > > Outage costs due to maintenance (+) ( ) ( ) ( ) > > Costs for off-line testing ( ) > > Insurance fees ( ) > > Premature equipment replacement ( ) 6

7 How OMICRON can contribute to your on-line PD monitoring success Advanced technology OMICRON periodic and permanent monitoring systems employ modern multi-channel synchronous and multi-spectral measurement techniques for reliable noise suppression and separation of multiple PD sources. This enables accurate detection of PD and related defects in electrical insulation. Customized solutions Periodic and permanent monitoring systems tailored to a variety of electrical assets and applications. OMS 605 Portable PD monitoring system for a variety of electrical assets OMS 600 Permanent PD monitoring system for generators and motors OMS 800 Permanent PD monitoring system for HV cable systems Periodic on-line monitoring MONTRANO Permanent dielectric condition monitoring system for power transformers Permanent on-line monitoring Knowledge and support Expert assistance with system design, installation, training, data analysis and interpretation. Conclusion Systems for periodic and permanent on-line PD monitoring identify mechanisms responsible for the deterioration of the insulation in electrical assets throughout their service life. Insulation defects and degradation can be detected at an early stage to prevent costly system failures through the early initiation of condition-based maintenance and repair. Asset condition monitoring information also helps to maximize equipment performance, extend equipment life, and decrease operating costs. Most importantly, it provides asset managers with greater peace of mind. 7

8 OMICRON is an international company serving the electrical power industry with innovative testing and diagnostic solutions. The application of OMICRON products allows users to assess the condition of the primary and secondary equipment on their systems with complete confidence. Services offered in the area of consulting, commissioning, testing, diagnosis and training make the product range complete. Customers in more than 140 countries rely on the company s ability to supply leading edge technology of excellent quality. Service centers on all continents provide a broad base of knowledge and extraordinary customer support. All of this together with our strong network of sales partners is what has made our company a market leader in the electrical power industry. OMICRON