CONTEMPORARY TOOLS FOR ANALYZING THE CONDITION OF ELECTRICAL EQUIPMENT

ABSTRACT

This comprehensive article explores the world of electrical equipment maintenance with a specific focus on Switchgear (SWG) and the maintenance of large motors and generators, crucial components in various industries. The article underscores the critical relationship between equipment reliability and overall business success. It highlights the challenges in achieving high levels of reliability, often necessitating complex redundancy methods with associated costs. The piece delves into common practices and vendor recommendations for equipment maintenance, offering insights into innovative solutions.

The article discusses the importance of continuous monitoring and outlines three primary monitoring approaches: online, offline on-site, and offline in the workshop. It also examines the degradation mechanisms of SWG, motors, and generators, focusing on common causes of motor failure and emphasizing the centrality of stator insulation in equipment reliability.

The article introduces advanced diagnostic tools, such as the LEAP (Life Expectancy Analysis Program) test and Partial Discharge analyzers, explaining their significance in assessing stator insulation and overall equipment health. It underlines how these tools empower businesses to make informed decisions, optimize resource allocation, and minimize downtime, ultimately extending the service life of electrical assets.

The article concludes by emphasizing the cost-effectiveness of these technologies, particularly in large-scale applications and with expensive equipment. It underscores the importance of transitioning to condition monitoring and using these tools in scenarios where conventional maintenance is challenging or economically unviable.

Keywords: Electrical equipment maintenance; Equipment reliability; Switchgear; motors and generators; Online monitoring; Offline monitoring; Common causes of motor failure; LEAP test; Partial Discharge analyzers; Downtime mitigation; Condition monitoring; Equipment service life extension.

Ensuring Uninterrupted Operations: The Pursuit of Electrical Equipment Reliability

Reliable operation of electrical equipment is the cornerstone of a safe and prosperous business, regardless of the industry it operates in. The link between the reliability of equipment and the overall success of a company is undeniable. It's a symbiotic relationship - the better the reliability of your electrical equipment, the lower the probability of costly downtime, crippling blackouts, and disruptive production upsets. In essence, equipment reliability paves the way for a company's growth and sustains its competitive edge in a dynamic marketplace.

In the quest for absolute reliability, it's important to acknowledge that achieving 100% uptime is an elusive goal. Even the most exceptional companies aspire to maintain their key performance indicators at a remarkable level, often exemplified by the awe-inspiring "Five Nines" reliability standard, or 99.999, which represents an astonishingly high level of availability [1].

However, the pursuit of such lofty reliability standards frequently necessitates the adoption of intricate methods such as N+1 and 2N redundancy [2]. While these methods are highly effective in enhancing reliability, they come at a cost - a substantial increase in capital expenditures (CAPEX). Companies must allocate significant resources to bolster redundancy levels, which can strain budgets and impact long-term financial sustainability. In this article, the electrical equipment maintenance common practices are covered, with a specific focus on Switchgear (SWG) and the maintenance of large motors and generators - components that are indispensable in various industrial applications. These electrical assets are the lifeblood of many operations, and their uninterrupted performance is paramount for sustained reliability and profitability.

Mitigating Risks Through Continuous Monitoring

One key to mitigating the risks associated with aging, insulation degradation, and contamination with substances like dust and oil is continuous monitoring. Implementing a proactive monitoring strategy can significantly enhance equipment reliability. In this regard, two primary monitoring approaches come into play:

1. Online Monitoring: Continuous online monitoring is a valuable tool for assessing the health of electrical equipment. However, it's essential to note that partial discharge monitoring, a critical aspect of this approach, is most effective for equipment operating at voltages lower than 6kV.

2. Offline Monitoring On-Site: Offline monitoring on-site involves various diagnostic tests to assess equipment health. Standards such as IEEE 62.2.19 are instrumental in guiding these tests. Techniques include insulation resistance testing (commonly performed with a megger), polarization index measurement, and power factor analysis.

3. Offline Monitoring in Workshop: Some diagnostic tests are better suited for workshop conditions, where equipment can be inspected and tested in a controlled environment. These tests include the Tum Tum surge test, partial discharge testing [3] for medium voltage equipment, and high potential testing, which helps assess the integrity of insulation.

Review of Switchgear and Motor/Generator Degradation Mechanisms:

Understanding the underlying degradation mechanisms of Switchgear and large motors and generators is pivotal in ensuring their long-term reliability. Typically, these mechanisms result from a combination of factors, including thermal stress, electrical stresses, environmental conditions, and mechanical wear and tear.

1.1 Common Causes of Motor Failure of motor/generators:

As we delve deeper into equipment reliability, it's essential to address one of the most prevalent challenges in the realm of electrical equipment: motor failure. According to [4], motor failure can be attributed to several factors, with the following being the most common:

1. Bearing Failure (51%): Bearing failures account for over half of all motor failures. These issues often result from poor or improper maintenance practices. Common factors contributing to bearing failure include overgreasing, the use of the wrong lubricant, misalignment, excessive greasing, shaft overload, vibration, and overheating.

2. Stator Winding (16%): Stator winding issues, including overloading and overheating, are responsible for a significant portion of motor failures. Understanding the operational limits and maintaining proper cooling and insulation are critical in mitigating these risks.

3. External Conditions (16%): External factors such as ambient temperature, humidity, and contamination play a notable role in motor failures. Monitoring and controlling environmental conditions can help prevent such failures.

4. Rotor Bar (5%): Rotor bar problems can stem from various factors, including starting frequency, overloads, and under voltage conditions. Proper maintenance and operational practices can mitigate these risks.

5. Shaft Coupling (2%): Misalignment is a common issue with shaft couplings, both mechanical and electrical. Addressing misalignment through proper installation and regular checks can prevent failures in this area.

Picture 1. Common Causes of Motor Failure

Mitigating Stator Insulation Problems: A Critical Imperative

As can be seen from the chart above (picture 1) the common causes of motor failure, two factors persistently take center stage: stator winding issues and the influence of external conditions. Remarkably, both of these aspects are often intricately linked to the criticality of stator insulation. As we explore the complexities of this relationship, we find that stator insulation is not just a component but a linchpin in the reliability of electrical installations. Its significance arises not only from its role as a protective barrier but also because it consistently ranks as the most expensive part of the entire installation.

The Costly Proposition of Stator Insulation

Stator insulation, while often overlooked, is the guardian of electrical equipment. It ensures the integrity and reliability of motors and generators. Surprisingly, it constitutes a significant percentage of the total cost of these installations [5]. This fact alone emphasizes the paramount importance of maintaining its reliability.

1.2 Common Causes of SWG:

According to statistics published by IEEE [6] the most fundamental reason for SWG failure is exposure to dust, moisture and various contaminants that can lead to partial discharge and subsequent equipment overheating, eventually resulting failure. Obviously, prompt and thorough bus cleaning could mitigate the risk of equipment failure (pictures 2 and 3).

Picture 2. Common causes of Insulated SWG failure

Picture 3. Common causes of bare SWG failure

2.1 Common practice for motor and generator maintenance

To truly grasp the criticality of stator insulation, let's turn to the recommendations of equipment vendors and the best practices adopted by industry giants. Our journey through a wealth of insights and expertise is represented through comprehensive tables that shed light on the essential nature of inspections and monitoring. The maintenance intervals are often defined by operating hours (runhours) for rotating equipment and just time for static equipment, but in the article the simplified version is represented.

In tables 1-3 you can find usual preventive maintenance plans [5, 7]. It is important to mention that maintenance plans might differ from company to company and from equipment to equipment, but general approach is the same.

Table 1.

Generator maintenance plan

Table 2.

Motor maintenance plan

Motor and generator maintenance plans might look similar but in realm generators are much more complicated and sophisticated pieces of equipment and require more testing and attention in general.

2.2 Common practice of SWG

Table 3.

Switchgear maintenance plan

3. The Challenge of Timely Inspections

Yet, the reality of industrial operations often presents a challenge: timely inspections are not always feasible. Imperfect equipment design, operational constraints, and the need to avoid costly production downtime can create hurdles to regular assessments of stator insulation. However, the dilemma remains: even in such scenarios, it is of crucial importance to know the condition of electrical equipment.

This is where innovation in the form of Partial Discharge analyzers and the LEAP (Life Expectancy Analysis Program) test enters the stage. These diagnostic tools are not just solutions; they are the key to unlocking the hidden mysteries of stator insulation and SWG conditions.

3.1 LEAP Test

The ABB LEAP test is a combination of a number of different electrical tests such as insulation resistance test, PI, Hi-pot a combination of this is designed to define a detailed condition of stator insulation. What makes this test unique and precise is the database that ABB has. ABB analyzes data of tested motor with data that the company has gathered within years of its operation. A huge history and a diverse database allow ABB to state 80% confidence of the LEAP test results [8]. As a result of LEAP test ABB share reports where the detailed condition of the insulation is described and expected life of operation for equipment with and without recommended maintenance. This information is beneficial for clients to define a course of further actions if needed (picture 4).

Picture 4. Reliability expectation

3.2 Partial discharge analyzer

Companies like EA technology [9] have developed products that allow online monitoring of partial discharge on SWG. The UltraTEV family of products is used as an example (picture 5). These products all include an ultrasonic sensing function. The products come with several narrow band ultrasonic sensors. All of these sensors go to a measuring circuit which provides a quantitative measurement of the energy in a 2 KHz band centered at 40 KHz. Additional circuitry then heterodynes the signal down to be centered at 1.6 KHz without changing its nature. This is available via the headphone jack on the unit. A volume control and mute function is provided. When connected to a set of high-quality headphones, this output allows the user to hear what is normally above the range of human hearing. The built in sensor and flexible sensors are designed for short distance detection through air. Additionally, the device is equipped with a screen where a user has two scales that help a user to define the presence of a partial discharge.

Picture 5. PD analyzer

The Transformative Impact

The LEAP test, developed by ABB, takes diagnostics to a whole new level. This sophisticated analysis program considers a myriad of factors, including load, temperature, and environmental conditions, to predict equipment life accurately. It goes beyond mere maintenance; it's a crystal ball, revealing the future health and longevity of motors and generators.

But why are these innovative tools so beneficial? The answer is simple: they empower businesses to make informed decisions, prioritize resources effectively, and minimize costly downtime. By proactively assessing stator insulation and overall equipment health, companies can implement condition-based maintenance strategies, targeting specific issues and avoiding unnecessary overhauls or replacements. In doing so, they not only reduce operational costs but also extend the service life of their invaluable electrical assets.

Additionally, this means of preventive maintenance might be extremely beneficially money-wise. Often prompt repair is less expensive than a complete replacement (of course it is applicable mostly for powerful, tailor-made equipment). Thus, by timely identifying potential issues and preventing major failures from happening or/and increasing equipment work life by doing proper maintenance, an equipment owner could avoid losing money for equipment replacement and possible downtimes.

In the realm of SWG, Partial Discharge testing is particularly effective in scenarios where access to SWG busbars is limited, making it a viable alternative to ensure the reliability of these critical assets. By exploring these cutting-edge approaches, we empower businesses to uphold equipment reliability, even when faced with formidable maintenance challenges, allowing them to operate seamlessly and thrive in a demanding and dynamic operational landscape.

Therefore, it becomes evident that innovation is the key to ensuring the longevity and performance of critical assets. By embracing cutting-edge tools like Partial Discharge analyzers and the LEAP test, businesses can transform their maintenance practices, enhance operational efficiency, and secure their investments in electrical installations for the long haul. The future of reliability lies in our ability to adapt, innovate, and prioritize the preservation of our most valuable assets [2].

Conclusion

In conclusion, it is important to acknowledge that the implementation of modern electrical equipment monitoring and diagnostic systems may come with significant costs. This includes the acquisition of specialized equipment, staff training, and data accumulation. Additionally, in the case of systems like LEAP, there is an ongoing financial commitment for inspections.

However, it's worth emphasizing that such investments can be justified in specific scenarios:

• Transitioning from preventive maintenance to condition monitoring can lead to cost savings without compromising the reliability of equipment.
• Monitoring the condition of equipment in locations where full-scale maintenance is challenging or economically impractical can prevent costly equipment replacements.

It's essential to bear in mind that these technologies, such as Partial Discharge analyzers and LEAP, tend to demonstrate their economic efficiency on a larger scale and with more expensive equipment. Nevertheless, their use as a complement to regular maintenance can be critical for timely detection of potential issues, such as winding faults. Therefore, these technologies should be considered as an investment in equipment reliability and long-term efficiency.

References:

1. Diekmann, K. (2023) Five nines ranked among World’s most elite, Five Nines Technology Group. Available at: https://fivenines.com/2021/02/five-nines-ranked-among-worlds-most-elite/ (Accessed: 18 September 2023).
2. Kapur, K.C. et al. (1977) Reliability in Engineering Design. Publisher: Wiley.
3. (2023) Other discharge phenomena. In: Practical Partial Discharge Measurement on Electrical Equipment., pp. 85–91. doi:10.1002/9781119833345.ch4.
4. Butcher, J. (2021) Common Causes of Motor Failure & How to Prevent Them. Energy Management Corporation.. Available at: goemc.com/2021/04/09/common-causes-of-motor-failure-how-to-prevent-them. Accessed 18 Sept. 2023.
5. Klempner, G. and Kerszenbaum, I. (2018) Generator design and construction. In: Handbook of Large Turbo‐Generator Operation and Maintenance. Publisher: Wiley-IEEE Press, pp. 53–168. doi:10.1002/9781119390718.ch2.
6. ABB (2021) Preventive maintenance synchronous motors and generators. ABB Library. Available at: abb.com/motors-generators/service/maintenance (Accessed: 18 September 2023).
7. IEEE (2007) Recommended practice for the design of Reliable Industrial and commercial power systems. Institute of Electrical and Electronics Engineers. New York, N.Y.
8. ABB (2010) ABB Life Expectancy Analysis Program (ABB LEAP) - Standard level for stator winding on high voltage motors and generators. Available at: https://library.e.abb.com/public/eac21fe89b8b8068c1257b2f003d772f/ABB_FactFile%20LEAP_02_low%20res.pdf (Accessed: 18 September 2023).
9. EA Technology Pty Ltd. (n.d.) Product Brochure: UltaTEV® Plus2. EA Technology Pty Ltd. Available at: https://eatechnology.com/australia/products/high-voltage-solutions/partial-discharge-detection/ultratev-plus/ (Accessed: 18 September 2023).