MAINTENANCE IN POWERHOUSE

In the power stations, three types of maintenance practices are followed, namely, Preventive maintenance, predictive maintenance and breakdown maintenance.

1.PREVENTIVE MAINTENANCE:-

The preventive maintenance plan is implemented for a period, e.g. annually, monthly, and fortnightly, etc. as required by the power station. Normally power stations undertakes annual maintenance taking the advantage of the lean period of the river inflow. The preventive maintenance is done according to maintenance sheets provided by corporate office and also considers different maintenance jobs and OEM recommendations. The task is scheduled according to a time based maintenance strategy, i.e. the planned start and end dates are generated for each task on the basis for estimated effort. On completion of annual maintenance the report is prepared and sent to corporate office. In a similar manner quarterly, monthly, weekly, and daily maintenance is planned. The maintenance formats, filled after each periodic maintenance, are sent to O&M division, corporate office. the O&M division analyzes the reports and sends the comments on the maintenance carried out to the respective power stations.

2.PREDICTIVE MAINTENANCE:-

The power station has implemented condition monitoring system and it will be used to predict potential machine failures well ahead of breakdown.

The various parameters monitored by the power stations for predictive maintenance are:-

2.1ONLINE CONDITION MONITORING:

Vibration (Turbine & Generator). Air gap. Temperature of bearing, oil & winding. Inflow.

2.2OFF-LINE CONDITION MONITORING:

Analysis of lubricating oil. Analysis of transformer oil. Tan δ & power factor of bushings & windings. Partial Discharge Analysis.

Some of the condition monitoring benefits are:-

Provides early detection of machinery problem.

Lower machine maintenance cost. Higher availability. Improve operational safety. Reduce the quantity & severity of in service machine failure. Reduction in spares inventories. Reduced planned outage durations. Avoid revenue Loss. Overall profitability.

2.3STATUS OF CONDITION MONITORING IN O&M POWER STATIONS:-

Vibration and air gap monitoring - Chamera-I power station.Vibration monitoring system - Bairasiul power station. Uri power station.

Rangit power station.

Dissolved Gas Analysis Equipment - Chamera power station. Uri power station.Partial Discharge Monitoring - Chamera power station.(Stator winding) (On-Line Periodic).

3.BREAKDOWN MAINTENANCE:-

The breakdown maintenance of equipment is carried out when a fault occurs. This Breakdown maintenance module is initiated by alarms (temperature, pressure, level alarms), machine tripping and daily walk around inspections and generate fault reports.

After the completion of the maintenance, the complete history of the event is maintained in the database.When any breakdown occurs in the power station the following steps should be taken by the operation and maintenance staff:-

1.)Acknowledge all the alarms and trip annunciation.2.) Record all alarm and trip flags before resetting.3.) Prepare the trip report in the ISO format.4.) Locate the fault. 5.) Calculate the severity of fault and damage caused.

6.) Take IR value of generator and faulty motor or equipment and record.7.) If it is grid fault or no fault, synchronize the machine with proper intimation

to grid. In case of severity call maintenance division.

8.) Prepare the breakdown report with fault description.9.) After restoration prepare restoration and analysis report.

10.) Prepare history sheet for the breakdown and keep this in record.

11.)If the same problem arises frequently, report to the O&M Division. the O&M division analyzes the problem and sends the feedback to the design division for modification /necessary actions/ suggestion.

4.DISTURBANCE RECORDER:-

DR used as a tool for analyzing the performance of the power system and the related equipment during & after major disturbances.

The recording of monitored input is initiated by a power system disturbance e.g. a relay protection trip. DR can either be triggered by external triggers or by any of the event channel.

5.GLOBAL POSITIONING SYSTEM:-

GPS used for time synchronization of event logger, disturbance recorder, and clocks & energy meters.

6.COMPUTERIZED MAINTENANCE MANAGEMENT SYSTEM:-

Maintenance requirements for power stations are often extensive and complicated by the fact that the plants usually are located at geographically difficult and remote locations. The CMMS is required for maintenance of the power stations in a planned and coordinated manner.

The power station must have powerful communication systems (VSAT), internet etc., it will be possible to coordinate all types of manually managed activities into a single system so that information for decision making is available on anytime, anywhere basis. The solutions will handle large volumes of data efficiently. The solution will also be pro-active and used to alert users when special events occur in the plant. With the implemention of availability based tariff(ABT) structure, power station has to implement condition monitoring based maintenance strategy, therefore, for higher availability of machines in availability based tariff regime and lower maintenance costs. The CMMS will be linked to the SCADA system and Condition monitoring system. It will also be possible to reduce the amount of capital tied up in inventory while ensuring that critical spare parts are always available.

The complete system will include CMMS for each power station and one Corporate CMMS system with monitoring facility located at corporate office.

CORPORATE CMMS

TANAKPUR CMMS

SALAL CMMS

CHAMERA-I CMMS

LOKTAK CMMS

BAIRA SIUL CMMS

URI CMMS

RANGIT CMMS

DULHASTI CMMS

7.KNOWLEDGE BASE SYSTEM (KBS) :-

The knowledge base system designed for the CMMS, which is linked with all the modules of the CMMS, i.e. breakdown maintenance, predictive maintenance, preventive maintenance, inventory management, work management, automation and SCADA system, conditioning monitoring system, and database of CMMS.

The KBS of the CMMS have the rich experience of diagnosis of maintenance and all the information related to the equipment (date of commissioning, failure rate, type of failure, MTBF- Mean time between failures, MTTR-Mean time to repair, total running time, spares available etc.) The KBS utilizes artificial neural network or artificial intelligence based training technique, so that, the system may get richer in experience with the passage of time and provide quick and best solution for the diagnosis of the equipment failed. It is also possible for various plants of power stations to share their experiences in an organized form.

When any eventuality occurs such as breakdown or alarm from condition monitoring system the KBS will find the root cause of the problem and provide the possible diagnosis of the failure/ possible failure.

All the functionality regarding maintenance is included in the maintenance module as described in various maintenance techniques.

The integration of CMMS to the various maintenance strategies shall be as under:-

7.1PREVENTIVE MAINTENANCE:-

As explained before the preventive maintenance activity is scheduled as a time based maintenance activity with planned start and end dates. the CMMS will determine maintenance personnel or group for each scheduled task. The CMMS will closely monitor all the activities of maintenance. Cost and performance indicators will automatically be calculated from the progress of the maintenance activity.

There will be close collaboration with some external parties (sub-contractors) and inventory management system implemented at site. There will be facility to enter measurement while on round. The CMMS will generate alarms and reports on schedules slipped or not adhered and also upon the occurrence of any specified critical events. The module will produce a schedule for the year based on data fed and past time periods based on experiences.

7.2PREDICTIVE MAINTENANCE:-

The CMMS will have integration with condition monitoring system to be implemented at all power stations and corporate office for predictive maintenance.

The condition monitoring of user defined indicators or difference between two conditions will trigger maintenance work as per the solution provided by knowledge base system ( or standard library job). Work order will be generated when measurements fall outside warning limits and when tolerances are exceeded.

The control limits for conditions will be calculated using dynamic linear modeling or cumulative sum techniques. the CMMS will be able to import condition readings from condition monitoring system. the CMMS will produce comprehensive graphical representation of readings, control limits and calculated trends. The CMMS will have default safety library job generated on a calendar basis if no predictive jobs are generated. The various faults will be designated with user defined fault code so that structured analysis of fault can be done.

7.3BREAKDOWN MAINTENANCE:-

The breakdown maintenance is carried out after occurrence of a fault. with the integration of automation and SCADA system, module will pick all the alarms and ensure no alarm of relevance remains unnoticed.

When breakdown occurs the module will find out the root cause of the problem with the help of KBS system. the module will instruct work management module to issue maintenance requests and generate work order flow including planning, preparation, scheduling, execution and conclusion of work orders and tracking the entire history of work request and notifies through auto-generated e-mail (messenger) to maintenance department. the module will give operational location of equipment and time of fault, priority and person notifying the fault. the various faults will be designated with user defined fault close so that the structured analysis of the fault can be done.

8.PERT AND CPM:-

8.1PERT:-

PERT stands for programme evaluation and review technique and has been used most frequently in the aerospace industries, notably in research and development type of the programme. PERT takes uncertainties into specific account. it assumes that the activities and their network relationships have been well defined, but it allows for uncertainties in activity times. For each activity in the project network, not only is an estimate made of most practicable time required to complete the activity, but some measure of uncertainity is also noted in this estimate.

PERT calculates the expected value of an activity as a weighted average of the three time estimates, it assumes that the optimistic and pessimistic activity times t0 and tp and about equally likely to occur and most probable activity time tm is four times more likely to occur than either of the two. Therefore, expected time te of an

Activity = t0 + 4tm + tp ---------------- 6

The expected time, is what we would expect the activity duration to be on the average if the activity were repeated a large number of times. In most PERT applications, to be sure activities don’t get repeated a large number of times, they usually occur just once. But te is still the best estimate we can make of the time required for a single occurrence of an activity.

PERT is often oriented. In event-oriented networks, the events are the objects of interest and are appropriately described. An event is a point in time a milestone representing the beginning or the completion of some activity or group of activities.

The emphasis on evevts has its roots in the milestone method of management, in which programme progress is monitored in turns of success or failure in reaching certain important milestones at scheduled points in time.

8.2CPM:-

CPM stands for critical path method. It has been frequently applied to construction projects. the CPM was developed to solve scheduling problems in an industial setting. it was less concerned with the uncertainity problems and more concerned with costs of project, scheduling and how to minimize them. CPM does not make use of probabilistic job times; it is a “deterministic” rather than probabilistic model. CPM is activity-oriented. this means that in activity-oriented networks, the arrows representing activities or jobs are labled with some description of the activity. An activity represents a represent of work to be accomplished over a period of time.

It seems that there is some optimum project length between one with excessive direct costs for shortening jobs and one with excessive indirect costs for lengthening the project. the

CPM modal verifies this mathematically and it specifies a method for finding this optimum point-the point representing the lest-cost schedule.

A primary, schedule is generated in which all jobs are assigned at their early start times and with normal resources. this is maximum length schedule; it can be reduced only by expediting one or more of the jobs at added cost.

In power station during the annual maintenance of units, PERT and CPM are used. various maintenance activities carried out by power station are at first ascertained and listed. A detailed schedule depicting various activities and sub activities along with time taken in each activity is prepared by power station before undertaking maintenance work and all the resources of activities are arranged by the power station.

The proposed maintenance schedule is checked by O & M division and remarks/ comments if any required added in it. In this, it is ensured that all the activities which are essential for the power maintenance of power plant equipment must be there in schedule. Then the power station is requested to implement the schedule prepared for undertaking maintenance.

Independent activities are to be started simultaneously and there is no slack between interdependent activities. the time required for maintenance of each activity shall be average of last two previous years and the current year.

On completion of the maintenance, the actual time taken in each activity along with any unavoidable deviation in the schedule is prepared by the power station and sent to O & M division for examination. the O& M Division examines the final schedule and looks into the deviation if any in the maintenance schedule.

Thus this PERT chart can be used for the resources of activities.