中英文资料翻译
A Maintenance Optimization Program for Utilities’
Transmission and Distribution Systems
ABSTRACT: Today, preserving and enhancing system reliability and reducing
operations and maintenance costs are top priorities for electric utilities. As system equipment continue to age and gradually deteriorate, the probability of service interruption due to component failure increases. An effective maintenance strategy is essential in delivering safe and reliable electric power to customers economically. The objective of this paper is to provide a framework for a predictive, condition-based, and cost effective maintenance optimization program for transmission and distribution systems.
1 INTRODUCTION
In principle, improving system reliability and reducing Operations and Maintenance costs are top priorities of electric utilities. In an increasingly competitive power delivery environment, electric utilities are forced to apply more proactive methods of utility asset management. One of the main components of electric power delivery asset management is the capital budgeting and Operations and Maintenance of existing facilities. Since in many cases the cost of construction and equipment purchases are fixed, Operations and Maintenance expenditures is the primary candidate for cost cutting and potential savings. As system equipment continue to age and gradually deteriorate, the probability of service interruption due to component failure increases.
Electric utilities are confronted with many challenges in this new era of competition: rising Operations and Maintenance costs, growing demand on systems, maintaining high levels of reliability and power quality, and managing equipment aging.
Therefore, the health of equipment is of utmost importance to the industry because revenues are affected by the condition of equipment. When demand is high and equipment is in working order, substantial revenues can be realized. On the contrary, unhealthy equipment can result in service interruption, customer dissatisfaction, loss of good will, and eventual loss of customers. An effective maintenance strategy is essential to delivering safe and reliable electric power to customers economically.
2 RELIABILITY CENTERED MAINTENANCE (RCM)
During the late 1960’s, the aircraft industry was on the verge of manufacturing the first “jumbo jets”. The new 747’s were three times the size ofany other passenger jets currently in the air. The recognized size of the 747, its new engines, and its many technology advances in structures, avionics, and the like, all led to Federal Aviation Administration (FAA) to initially take the position that preventive maintenance on the 747 would be very extensive – so extensive, in fact, that the airlines could not likely operate this airplane in a profitable fashion. This problem led the aircraft industry to completely reevaluate its PM program. What resulted from this effort was a whole new approach that employed a decision-tree process for ranking PM tasks that were necessary to preserve critical aircraft functions during flight [3]. This new technique was eventually approved by the FAA and soon thereafter evolved into what is known as Reliability Centered Maintenance (RCM). RCM used by the airline industry led to major reduction in labor,material cost and inventory cost. Further it applied to nuclear power industry in the 1980’s. Today,RCM is the maintenance technique of choice for many industries including power industries.
Unlike the airline industry which had the advantage of being able to work with manufacturers to create an RCM program for a new generation of equipment, the utility industry, especially the electric power generation industry, has had to adopt RCM as a modification of long-established maintenance practices at existing plants [4]. Despite the costs associated with the implementation of these RCM programs in “midstream”, they have been found to pay for themselves in very short order.
RCM, as has been mainly applied to nuclear power plants, often requires the largest amount of maintenance because of safety and environmental considerations. However, with these successful programs now operating, fossil power plants and power transmission and distribution systems have recently been getting into the mix. Because these facilities face a less restrictive regulatory environment, they should be able to directly apply the streamlines forms of RCM much more easily, thus reducing the implementation costs.
The first step in revamping a maintenance program is to implement an RCM approach whichwill help establish priorities for a new program. Specifically, RCM is a set of methods and tools aimed at helping a utility to determine the minimum set of preventive maintenance tasks necessary to appropriately address critical equipment failures without compromising service reliability. RCM is a structured process used to determine optimal maintenance requirements for equipment in a particular operating environment. It
combines the strategies of corrective maintenance, preventive maintenance and predictive maintenance, and applies these strategies where each is appropriate, based on the consequence and frequency of functional failures. This combination produces a maintenance program which optimizes both reliability and cost effectiveness. For major pieces of equipment, such as power transformers, RCM may indicate that predictive maintenance is an attractive option, given the decreasing cost of sensor and diagnostic technology and the increasing cost of running the equipment to failure.
RCM is a condition-based maintenance program that focuses on preventing failures that are likely to be the most serious. RCM and Predictive Maintenance (PDM) analyses complement each other, and when they are performed concurrently, offer an excellent approach to maintenance optimization. In the last few years, the sophistication of monitoring equipment on the market and the falling price of electronics and computers have made the on-site monitoring applications a cost effective reality.
The very basic concepts and underlying principles of the RCM can be explained very easily. Its main methodology can be reduced to the following four points: 1) preserve system functions 2) identify dominant failure modes
3) prioritize function needs so that budget can be focused on preserving most critical functions
4) select only applicable and effective maintenance tasks Some of the benefits of RCM are: 1) Reduces major corrective actions
2) Eliminates unnecessary overhauls and routine tasks that provide little benefits 3) Optimizes the frequency of required overhauls
4) Increases use of predictive technology that help with resource planning 5) Decreases use of intrusive tasks that can induce equipment failures 6) Improves cost-effectiveness of routine tasks
7) Creates documented technical bases for maintenance programs
8) Allows easy implementation by incorporating existing maintenance practices that have proven to be cost-effective
9) Processes Knowledge, communications, and teamwork
Inexpensive solid state sensors are being developed, for example, that can be inserted in transformer oil to detect the presence of gases produced when insulation begins to deteriorate. Once the information from predictive maintenance technology becomes
available, it needs to be integrated with on-line data from across a power network and from historical records.
3 NEW TECHNOLOGIES
There are many technologies available today, and several new methods are being investigated to determine the equipment condition [5]. The following are just a few applications for monitoring power delivery equipment: Ultrasonic Noise Analysis
The presence of tones in the ultrasonic range can be an indication of leaks of air, gas, steam, and vacuum. Ultrasonic noise can be emitted as a result of friction between moving parts.
Partial Discharge Detection
This technology employs an electrical sensor to detect the initial insulation breakdown in electrical equipment such as insulators and terminators. Partial discharge detection is used to detect incipient failures before significant damage occurs. Transformer Gas-in-Oil Analysis
This is needed to keep the transformer on-line as much as possible. One indicator of abnormalities is the dissolved gas content in the transformer oil. Certain gas levels can indicate aging, the need for maintenance, or potential failure. Infrared Thermography
Thermography surveys involving the use of an infrared camera to detect hot spots in large motors used in power plants. Sound Intensity Measurement
Sound Intensity Meter is needed to identify potential problems in equipment and record the historical changes in sound and output of equipment
For transmission and distribution systems, sensors such as transformer fault gas analyzer might prove to be beneficial. This device provides real-time measurement of the four key gases associated with fault currents in transformer: carbon monoxide, hydrogen, acetylene, and ethylene. The next step is to incorporate an additional sensor to detect the presence of moisture which can reduce dielectric strength and lead to failure. This will be used with another device that measures the transformer loading so that the evolution of key gases and moisture can be characterized as a function of the load. With the moisture sensor and load current monitor we can develop accurate criteria for loading transformers under stressful conditions rather than having to rely on the overly conservative ratings now provided.
4 PROPOSED INTEGRATED APPROACH
An integrated approach for transmission and distribution systems would ensure that equipment or subsystems leading to serve a particular load would receive uniform and consistent level of maintenance in all departments, thus enhancing and optimizing the maintenance process.
In order to establish a maintenance program, the RCM process needs to be the driving point. Figure 2. Shows different strategies required for a maintenance optimization program. The classical RCM process involves identifying the systems to be studied, their functions, functional failures, failure modes, failure causes, and the maintenance task selectio.
The most critical pieces of equipment which affect the overall function of the system need to be identified. In other words, we need to identify equipment with severe consequences when failed. Also, critical customers and the equipment leading to their loads need to be identified. All equipment affecting these customers need to be analyzed, and the most critical pieces of equipment should be determined. We also need to understand the customer needs in terms of reliability, safety, power quality, cost, etc. These attributes must be weighted to determine the optimum maintenance policy to deal with these customers.
In order to optimize the utilities’ maintenance program, all relevant information must be used to most effectively initiate, schedule, track, record, and analyze maintenance tasks. An open communication protocol that enables various monitoring devices (regardless of the manufacturer) to talk to each other, with utilityoffices, and with control centers would best suit the needs of electric utilities by integrating various data sources and other software modules.
Currently, many large utility organizations perform some equipment diagnostic tests. Many have computerized their maintenance work management functions including retaining maintenance histories, logging significant operational activities, and maintaining a library of design information for equipment. The proper communication, integration and analysis of all of this information would result in more accurate recommendations concerning when to perform maintenance and/or how to operate a specific piece of equipment.
A typical problem in the industry is that, at times, a large amount of data is collected but it is not integrated and processed expediently for a quick evaluation. This results in the inability to make immediate Operations and Maintenances, therebyadding cost for the
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