Post on 16-May-2015
description
Condition monitoring of longwall face support
RAVIKANT KUMAR 111MN0472
1. Introduction
2. Condition monitoring needs
3. Present status
4. Method of condition monitoring
5. Applicability
6. DATA processing and Interpretation
7. Conclusion
8. Refrences
TOPICS TO BE COVERED
INTRODUCTION
Despite the most refined maintenance strategies, equipment failures do occur.
The degree to which an industrial process or system is affected by these depends on the severity of the faults /
failures, the time required to identify the faults and the time required to rectify the faults.
Real-time fault detection and identification (FDI) and other methods offer maintenance personnel the ability to minimize,
and potentially eliminate one or more of these factors, thereby facilitating greater equipment utilization and
increased system availability.
What is condition monitoring ?
Condition monitoring (or, colloquially, CM) is the process of monitoring a parameter of condition in machinery (vibration,
temperature etc), in order to identify a significant change which is indicative of a developing fault.
It is a major component of predictive maintenance.
The use of conditional monitoring allows maintenance to be scheduled, or other actions to be taken to prevent failure and avoid
its consequences.
Condition monitoring has a unique benefit in that conditions that would shorten normal lifespan can be addressed before they
develop into a major failure.
What is to be done?
Understand the failure we want
to predict.
Identify a strategy that is appropriate to
the failure mode.
Identify a reliable indicator.
Action and review result.
When it is wrong to use CM?
When it doesn’t tell anything useful.
When we don’t understand the result.
When it adds cost to the cost of operation for no
operational improvement.
When we don’t use the result.
Longwall Maintenance-Current practices
As with all forms of mining, production downtime represents massive losses in potential revenue.
An effective maintenance program is seen in the industry as the key to a profitable and sustainable
longwall.
Maintenance is broadly categorized as either planned or reactive.
CONT…..
Reactive (or breakdown)
maintenance refers to the repair or
replacement of failed or faulty equipment
which interrupts longwall production.
Typically, one shift per week is assigned to
routine planned maintenance, with major overhauls of
machinery occurring at the end of each panel.
• It is these actions which are reported in the maintenance log of all unscheduled downtime.
• This maintenance is attended to by longwall operators, as each team typically includes specialists in both mechanical and electrical repairs.
Longwall Monitoring
Equipment monitoring is playing an increasingly significant role in the modern longwall.
By monitoring it is meant both the determination of the overall state of plant as well as measurement of individual properties; for example, the running
temperature of gearbox.
Condition monitoring of longwall equipment takes on two main forms: on-line and off-line.
On-line monitoring includes all sensor measurements recorded and transmitted to the surface using a PLC-driven, SCADA network.
All other measurement and monitoring, including regular maintenance inspections are classed as off-line.
On-line Monitoring
The on-line monitoring systems at longwall mines consist of a network of sensors and switches, which may be monitored from the surface or by operators
underground.
The interface allows users to view the overall operation, as well as monitor individual pieces of
machinery.
The system is designed to indicate simple faults such as an over-temperature trip by displaying
messages and changing the colour of the particular machine at fault.
ONLINE MONITORING
• SCADA• P-F Interval or Fault Detection Threshold(FDT)
Some popular methods of online monitorin
g:
•RATE OF MOVEMENT
•MICROSEISMIC MONITORING
OTHER IMPORTA
NT METHOD
1) SCADA-Supervisory Control And Data Acquisition
A SCADA system
performs four functions:
1. Data acquisition
2. Networked data
communication 3. Data
presentation
4. Control
Application of SCADA in longwall monitoring
This system is very expensive, both to purchase and maintain.
At present, the display is only looked at when production personnel indicate that the longwall
has stopped due to an unknown fault.
Data that is recorded, is rarely used, and undergoes no more than a visual analysis.
Over 300 analogue sensors are typically monitored by these SCADA systems.
Cont…..
In the past, data storage was considered one of the major pitfalls of archiving
all that was sampled.Today, however, this has been mitigated by
the inexpensive and very large capacity computer hard drives.
SCADA data is very very significant for Fault Detection AND Identification(FDI)
2) P-F Interval or FDT Method
A common curve that illustrates the behavior of equipment as it approaches
failure is the P-F curve.
The curve shows that as a failure starts manifesting, the equipment deteriorates to the point at which it can possibly be
detected (P).
If the failure is not detected and mitigated, it continues until a "hard" failure occurs
(F).
Cont…….
It is the window of opportunity during which an inspection can possibly detect the imminent failure
and address it.
P-F intervals can be measured in any unit associated with the
exposure to the stress (running time, cycles,
miles, etc).
Example
If the P-F Interval = 200 days and The item will fail at 1000 days,Then, the approaching failure begins to be detectable at 800 days.
Significance of P-F Interval
Reducing Equipment Downtime: The case for FDI
Available techniques to minimise equipment/process downtime are examined first.
After all, any maintenance program has the principle
goal of achieving the greatest possible equipment
utilization.
Available Techniques
1) Preventative Maintenance
The most common way that industries attempt is to improve machine availability is through preventative maintenance.
This consists of regular inspections, regular replacement of lubricant, filters etc. and occasional reconditioning of parts.
Preventative maintenance has proven very successful in prolonging the life of machinery, as well as showing
improvements in performance, such as the mean time between failures (MTTF) and mean time to repair (MTTR).
Cont…
2) Design Modification • It is possible to redesign machinery to alter
it’s inherent reliability.• That is, based on industry experience of
certain faults, redesign parts or entire machinery to reduce or stop the occurrence of the fault.
• Typically, machine design is the responsibility of the manufacturer, and is a very time consuming and costly operation.
3) Failure Prediction
Similar to weather forecasting, the knowledge of an imminent failure of a piece of machinery would allow machine operators to cease or change operation to minimize and potentially avoid any subsequent downtime.
There is an inherent risk in such a concept in that false or misleading predictions could cause additional downtime, and quickly lose operator confidence.
For a predictive system to be effective it must produce not only a prediction of an imminent fault, but provide sensible reason as to the prediction, so that operators may make an informed decision whether to act or ignore the suggestion.
Data processing and Interpretation
Since the data-driven approach does not assume an understanding of individual faults on data properties, large amounts of data must be collected.
If possible, the data should span an operational time for which a large number of example faults occur and exhibit an ordinary proportion of faults/failures per unit time.
The first concern in processing data is however the estimation of missing entries.
Cont….
In order to generate a list of classifications, one must attempt to determine the ‘state’ of the longwall at each observation.The only record of the activity of the longwall is the maintenance log, which details all unscheduled downtime at the longwall face.
Table 1 is an excerpt of the maintenance log corresponding to the condition monitoring data discussed earlier.
It records the time that the delay began and the duration of downtime experienced.
Conclusion
All longwall mines employ preventative maintenance.
It is one of the largest sub operations at any mine, and proves effective in that when less attention is paid to maintenance, more faults occur.
The optimum level of planned maintenance is difficult to determine because not all failures are age-related.
In fact, many failures follow an exponential distribution with a uniform failure rate that is not related to age.
Refrences
• Willsky, A S, (1976) A survey of design methods for failure detection in dynamic systems, Automatica, 12:601-61
• Bongers, D, (2004) Development of a Classification System for Fault Detection in Longwall Systems, PhD Thesis, The University of Queensland .
• Frank, P M, (1990) Fault diagnosis in dynamic systems using analytical and knowledge- based redundancy - a survey and some new results, Automatica, 26(3): 459-474 .