The equipment and facilities supporting today’s critical infrastructure are vital to modern society. This article provides testing and maintenance tips to ensure systems are kept in top condition.
Power plant owners have been striving to align their maintenance practices with North American Electric Reliability Corp. (NERC) requirements, initially outlined with section PRC-005, “Protection System, Automatic Reclosing, and Sudden Pressure Relaying Maintenance,” passed in 2016. These standards require the development of a Protection System Maintenance Plan (PSMP), the execution of that plan, and the creation of report records that are subject to audit every three years. Since then, the NERC electrical system maintenance requirements have expanded in scope.
Keeping current with NERC requirements and determining the PSMP details, equipment lists, and testing procedures have historically presented challenges that power plants struggle to address. There are many resources that identify and define which electrical maintenance tasks and testing should be performed on electrical assets. The most frequently referenced sources are the American National Standards Institute/InterNational Electrical Testing Association’s “Maintenance Testing Specifications For Electrical Power Equipment” (ANSI/NETA MTS-2019), and the National Fire Protection Association’s “Recommended Practice for Electrical Equipment Maintenance” (NFPA 70B). Additional testing and maintenance recommendations can be found in NERC Protection and Control (PRC) and Modeling, Data, and Analysis (MOD) standards, as well as in Institute of Electrical and Electronics Engineers (IEEE), American Society for Testing and Materials (ASTM), National Electrical Manufacturers Association (NEMA) standards, and in equipment manufacturers’ literature.
Yet, even with all this information at your fingertips, creating a detailed electrical system maintenance plan can be a challenge. The reference documents aren’t always clear and concise. Furthermore, testing specifications do not always agree. The process can be confusing.
Additionally, while these documents provide a good basis for which maintenance and tests should be performed, they do not cover the details of proper test techniques. They also do not consider the type of power distribution system or the criticality of the equipment. Some systems may include redundant feeds and transformers to increase their reliability and decrease the impact should equipment fail. Equipment supplying power to critical infrastructure may require more maintenance and testing, for example, than equipment feeding administrative offices.
Testing and maintenance are about risk aversion, and the desired level of reliability (or acceptable rate of failure) must be established to determine the testing and maintenance scope. To ensure an effective testing and maintenance program, the following factors should be considered: Criticality of equipment served, age of equipment, condition of equipment, operating environment of equipment, history of equipment, and system configuration.
Businesses operate within a limited budget and can typically only support equipment outages for limited time periods. Therefore, budget and time constraints must be considered when determining which equipment should be tested, and what tests and maintenance tasks should be performed.
Strategies for Maintenance Scheduling
Once the foundation of the plan is established with a list of equipment and the prescribed tests to be performed, a maintenance scheduling strategy will need to be applied. NERC provides parameters for three basic maintenance planning strategies: time-based maintenance, condition-based maintenance, and performance-based maintenance. Choosing the right strategy for your system and operational criticality depends on your budget and a variety of other parameters.
Time-Based Maintenance. Time-based maintenance refers to maintaining or reconditioning an item to restore its performance and reliability at a fixed time, interval, or usage regardless of its condition. Maximum maintenance or testing intervals are applied for components or groups of components. The interval may have been developed from prior experience or a manufacturer’s recommendation. The verification interval also can be based on other factors, including experience of the particular asset owner or collective experiences of several asset owners who are members of a country or regional council. Usually, the maintenance intervals are fixed and range in number of months or years.
Condition-Based Maintenance. Condition-based maintenance looks for physical or other evidence that a failure is occurring or is about to occur. It is the process of gathering and monitoring information available from modern microprocessor-based relays and other intelligent electronic devices that monitor batteries, partial discharge, and protection system elements. A combination of visual inspections and monitoring devices will generate system health information during normal operation, and the information can be assessed either onsite or at a convenient location remote from the substation. Time-based and condition-based maintenance are often effectively used in combination.
Performance-Based Maintenance. Performance-based maintenance programs require auditing processes like those included in widely used industrial quality systems. These systems track the performance of protection systems and require the owner to demonstrate how they analyze findings of performance failures and aberrations, and implement continuous improvement actions. A performance-based maintenance process may justify longer maintenance intervals or require shorter intervals relative to a time-based strategy.
Maintenance Testing and Standards Compliance
Reliable and accurate documentation of test procedures and test data is vital to an effective testing and maintenance project. Depending on the apparatus and tests being performed, variations of a given test or test procedure may be applied. Some tests or procedures will yield similar and accurate results, while others may not provide the expected results or may include or exclude components that affect the results. Testing professionals can sort through the noise to find meaningful data.
Subjecting an organization to regulatory fines or penalties, or worse yet, subjecting employees to an unsafe work environment are unacceptable outcomes. Creating or updating a comprehensive compliance program takes time, knowledge, and expertise. Compliance specialists stay abreast of changing regulations and use their expertise to tailor services to a critical facility’s unique needs.
Once a compliance program is created, documenting the testing and maintenance procedures and results, and then producing routine reports is critical to realizing the full benefits of the program. These reports will be necessary for compliance audits and provide important verification information if an incident should occur. The test report summarizes project activities, test data, analysis, and recommendations. Other than test stickers, the report is the only evidence that electrical testing took place, so the documentation process must be accurate and reliable. Measurement values and units, as well as any observations, must be recorded.
1. Electrical testing involves more than simply hooking up test equipment and recording data; experienced technicians carefully examine components for signs of damage, deterioration, excessive wear and/or heating, and other deficiencies. Courtesy: Electrical Reliability Services
In addition to performing the electrical tests (Figure 1), an experienced tester will carefully examine the apparatus and note any signs of damage, deterioration, excessive wear, excessive heating, and other deficiencies. These inspections should be clearly documented on the test datasheet. The equipment owner should assume that if the inspections and tests are not documented, they likely did not occur.
During the project, test data must be constantly reviewed by the technician to ensure all test parameters are met, and any equipment with troubling test data is immediately identified and brought to the attention of the owner. This is where the guidance of a Level III or Level IV NETA-certified technician is required. Senior testers can ensure the data is accurate and make sound recommendations based on their years of experience. When less than acceptable test data is discovered, an immediate retest is often warranted to verify the data and ensure the test data has not been affected by a test method, a defect in the test equipment, or other external influence.
Once the test data is verified, the project lead and owner’s representative must communicate to determine the best course of action and record these conversations in the test report. The documentation process must involve minimal transcription of information from one source to another to avoid introducing additional errors. While some testing companies continue to use paper test forms on projects and then input the data into a computer system at a later time, the most accurate and efficient process involves direct input of test data into a reliable database during testing.
The key to success in using a data management system is to use standardized forms and a common database where all data can be stored, backed up, mined, and retrieved. This database should not reside solely on a local laptop or office computer; it must be synchronized to a commercial data architecture system with redundancy and regular backup processes to avoid losing the data or placing the data at unnecessary risk of corruption.
Optimizing Maintenance Budgets and Outages
Many maintenance procedures require servicing de-energized electrical equipment during scheduled shutdowns. Offline maintenance can be challenging to schedule and coordinate with operational demands. Incorporating an online maintenance program between offline services can help prioritize repairs and replacements, and optimize the work during an outage.
There are four predictive maintenance tests that should be part of any maintenance program. The four components are visual inspection, partial discharge testing, infrared/thermographic survey, and insulating fluid sampling and analysis. These tests can reduce the need for offline services, improve system performance, reduce the risk of system failure, and help optimize budgeted expenditures.
These predictive maintenance tests can be performed while the system is online. They are non-destructive, non-invasive, and examine electrical equipment under normal operating conditions. Ideally, these tests should be coordinated between planned outages so the resulting data can be used to inform and help prioritize offline service needs.
In combination, these four activities can identify variations in properties that are indicators of impending asset failure. If performed by a qualified testing agency, they can be executed efficiently and cost-effectively. The benefits include evaluation under normal operating conditions, collection of trending data for predictive assessments, identification of issues before significant problems occur, identification of equipment to be prioritized during maintenance outages, data collection that allows for extending the time between scheduled outages, and improved budget allocation toward the most critical maintenance needs. Additionally, predictive maintenance services can be performed more frequently than offline services, and thereby reduce the risk of incidents and system-related outages, improving employee and public safety, increasing peace of mind, and preventing problems that could affect your company’s reputation and operational credibility.
Increasingly, high reliability is required, and systems must be designed with adequate redundancy in mind. To meet the demands that users have for these systems, certain testing and maintenance tasks must be performed. If a high level of reliability is required from a system design that lacks sufficient redundancy, additional or more detailed testing and maintenance (and time and money) will be required. When considering these important factors and decisions, and in order to ensure the reliable, efficient operation of these systems and equipment, owners and operators should work with a testing and maintenance service provider to establish a customized scope of work for a testing and maintenance program. ■
—Leif Hoegberg is director of Engineering and Technical Support for Vertiv’s Electrical Reliability Services (ERS). He is a Level IV NETA-certified technician with more than 30 years of electrical engineering, operations, and field service experience.