NOTE: The sponsor of this content may contact you with more information on this topic. Click here to opt out from sharing your email address with this sponsor. (This link will not unsubscribe you from any other BIC email list).
Equipment that is started, stopped and/or operated incorrectly, or beyond its operating limits, will simply experience a higher failure rate. A reliability-focused operation’s team follows and enforces well-conceived standard operating procedures. The reliability-focused operation’s organization works closely with the maintenance contractor — particularly to provide inspection and operating health feedback on a regular basis — to the supplies design engineers, procurement specialists and strategic suppliers with the information they need to improve equipment operability. Reliability-focused management, however, is plagued with many obstacles. Among these obstacles are:
- Maintenance practices and schedules vary from site-to-site:
- What are your "Best Practices" and are they adequate? Are they consistent?
- Tests are conducted; data is stored away, but this process does not drive actions:
- Are we getting the RIGHT data to make a GOOD decision?
- Is the information getting to the right people?
- Can we effectively interpret the data … do we know what the tests are telling us?
- Are we dealing with many separate pieces of reliability information in reports, databases, computer folders, and/ or spreadsheets?
- Action plans are not in place to respond to issues identified:
- Are we following a reactionary maintenance program?
- Are our adopted test procedures pass/fail in nature, or do our test procedures offer diagnostic and predictive value?
- Do we have the experience to analyze diagnostic data and render informed predictions?
Addressing maintenance goals
Just where does your organization fall in the maintenance advancement path?
Corrective/Reactive Maintenance: Is maintenance only performed after a machine experiences problems or has failed?
Preventative Maintenance: Are actions performed on a time- or machine-run based schedule to detect, preclude, or mitigate degradation of a component or system with the aim of sustaining or extending its useful life and reduce the need for major repairs?
Condition Based Maintenance (CBM): Does your organization make attempts to evaluate the condition of equipment by performing periodic or continuous (online) equipment condition monitoring and then base your maintenance need on the actual condition of the machine rather than on some preset schedule
Predictive Maintenance (PdM): Does your organization concentrate on the monitoring and correction of root-causes of equipment failures?
The main goal of Predicted Maintenance is to allow convenient scheduling of corrective maintenance and to prevent unexpected equipment failures. The key is “Gather the right information in the right time frame". By understanding how assets are aging and knowing which equipment needs maintenance, maintenance work can be better planned (spare parts, people, etc.), and what would have been "unplanned downtimes" are transformed to fewer, more focused "planned downtimes", thus increasing plant availability. Other potential advantages include increased equipment lifetime, increased plant safety, fewer accidents with a negative impact on the environment, and optimized spare parts handling and workflow.
While maintenance can’t improve the reliability of equipment, it can ensure that the equipment’s inherent reliability —based upon design and operating context— is maximized. A reliability-focused organization doesn’t just employ modern techniques like Predictive Maintenance (PdM), Condition-Based Maintenance (CBM) and Preventative Maintenance techniques; instead, a reliability-focused maintenance organization works hard to optimize maintenance activities, with a focus on runtime activities. It also works closely with operations to ensure that the equipment is available to produce as much product as required, meet quality goals and —most importantly, satisfy customer demands.
Addressing information gathering needs
Medium voltage generators and motors typically provide many years of operation in utility and industrial applications before either the rotor or stator windings need to be replaced. If the machine is overloaded or subjected to a polluted environment — or had been poorly constructed — failure may occur in only a few short years due to premature aging. Over the past ten years or so, there have emerged several new tests and monitors they can detect (usually with months or years of early warning) aging problems that can lead to failures in rotating machines. Developing a testing regiment that implements these emerging technologies in combination with tried and true tests — such as insulation resistance, polarization index, and winding resistance testing — unexpected in-service failures can be all but eliminated, deriving maximum reliability from equipment.
A well-structured, reliability-focused maintenance program needs to address all of the fundamental failure sectors associated with the motor or generator system. These sectors include the rotor, stator, cables, and power circuit and power quality. Over the years, offline DC and AC tests have been used to evaluate insulation condition, but since these tests are done in the absence of mechanical or thermal stresses they are ineffective in discerning coil movement or stress coating deterioration. Offline tests are also used to detect rotor winding issues; however, they can be unreliable since the rotor is not spinning at the time of the test. Any well-structured condition-based maintenance program must include thermal, electrical, and vibration assessment in order to fully evaluate the asset and to uncover the majority of problems associated with the various failure sectors.
The information gathering elements of a predictive maintenance program would include:
- Periodic walkthrough inspections
- Oil sample analysis
- Infrared (IR) surveys
- UE greasing surveys
- Online machine analysis
- Offline machine analysis
Online or dynamic testing would include:
- Power quality
- voltage and current level
- voltage and current imbalance
- harmonic distortion
- Load Levels
- Rotor Analysis
- current signature analysis
- vibration monitoring
- Stator monitoring
- partial discharge monitoring
Offline or dynamic testing would include:
- Insulation integrity testing of cables
- Stator and rotor analysis
- winding resistance
- insulation resistance
- polarization index or dielectric absorption
- step voltage
- power factor/tan δ
- capacitance and inductance
- partial discharge
Common failure mechanisms
The following tables provide an overview of various failure mechanisms, their symptoms and detection tests used to identify them.
Failure mechanisms in cabling
- Thermal breakdowns
- Melting, discoloration, swelling, oxidation, delamination
- IR study, PD online & offline, Tan δ,
- Power Factor, visual inspection
- Contamination
- Partial discharges, ozone
- Insulation resistance, DA, Tan δ, PD online & offline, visual inspection
- Cable spacing
- Phase-to-phase short, partial discharges, white powder, tracking
- Insulation resistance, PD online & offline, visual inspection
Power circuit failure mechanisms
- High resistance connections
- at the local disconnect
- at the starter
- at the motor connection box
- Excessive heat, loss of efficiency
- IR study, Current imbalance measurements, phase resistance (micro-ohmmeter measurements)
- Defective contact surface
- Loose, oxidized, or corroded terminal connections
- Excessive heat, loss of efficiency
- IR study, Current imbalance measurements, phase resistance, micro-ohmmeter measurements, visual inspection
- Defective Power Factor Correction capacitors
- Loss of efficiency
- Phase inductance measurement (imbalance)
Information Utilization
A well-structured information gathering program will not bring about reliability objectives if there is no information utilization. Once issues are identified, actions must follow: work orders will need to be opened along with scheduling. There must be accountability for maintenance follow-up on condition based problems, validation on corrective work, and finally a change in the asset’s status. A typical workflow is shown in Figure 2.
Shermco addresses the obstacles
As stated earlier, reliability-focused management is plagued with many obstacles. Here is how Shermco Industries can help:
- Maintenance practices and schedules vary from site-to-site:
- Shermco has outlined a predictive/reliability program for rotating machines utilizing industry proven static and dynamic practices and procedures to obtain your reliability objective.
- Tests are conducted … data is stored away, but this process does not drive actions:
- Shermco Industries' skilled technicians’ gather information —our reliability engineers utilizes that information and gets it to the right people in your organization to deliver your reliability objective.
- Action plans are not in place to respond to issues identified:
- Predicted maintenance allows convenient scheduling of corrective maintenance, and prevents unexpected equipment failures. Shermco gathers the right information in the right time frame;
- By understanding how assets are aging and knowing which equipment needs maintenance; maintenance is better planned (spare parts, people, etc.) and what would have been "unplanned outages" are transformed to fewer, more focused "planned outages", thus increasing your plant reliability and productivity;
- Other advantages include increased equipment lifetime, increased plant safety, fewer accidents with a negative impact on the environment and optimized spare parts handling and workflow.
What is our next step in moving forward with making your reliability goals a reality?
For more information visit: www.shermco.com/sto
