Operation and Maintenance Objectives and Activitives

The distribution system constitutes the interface of a utility with consumers who judge the performance of the utility by the performance of its distribution system. Therefore, proper operation and maintenance of the power distribution system is essential. Any failure on this account may deprive the user of electric supply and lead to chaotic conditions. There are two types of maintenance: Preventive Maintenance and Breakdown Maintenance.

• Preventive Maintenance is maintenance done prior to the onset of Monsoon and after the end of Monsoon.

• Breakdown Maintenance is done on breakdown in the installation.
In this section, we discuss the general O&M objectives and activities for the power distribution system.

You will agree that the prime goal of a power utility, like any other business, is to achieve consumer satisfaction with optimum effort and costs while maintaining reasonable profit levels. The operation and maintenance (O&M) practices of a utility contribute significantly in attaining this goal. These activities should help in improving the reliability and maintenance of plant and equipment, maximising capacity utilisation, increasing operating efficiency,and reducing operating and maintenance costs.

The objectives of O&M for distribution systems may thus be spelt out as follows.


 

The O&M strategy adopted by a utility can be evaluated in terms of certain parameters, which are given below

 

Activities Involved in Operation and Maintenance
The following activities are involved in the operation and maintenance of the Distribution System:

• continuity of service;

• technical operation and maintenance;

• training and retaining of operational staff;

• renewal of maintenance contract;

• upkeep of spare parts inventory;

• record keeping of faults in the network/equipment problems, solutions,modifications and enhancements;

• close monitoring of budgeted expenditure;

• preparation, continuous updating and proper maintenance of operational and network data;

• record of protective and isolating devices installed and their relay settings;

• record of schedule of maintenance and preventive and routine maintenance of network elements;

• development of spare parts;

• development of maintenance practices, tools and procedures for trouble free operation; and

• record of transformer/switchgear oil testing and its parameters.

Utilities should have manuals for O&M to ensure efficient and trouble free operation of the system/equipment. These manuals should contain the following information:

• factory and site test certificates for each item of the system with reference to relevant design calculation and quality assurance standards;

• maintenance instructions for all plants and other preventive and corrective maintenance procedures;

• maintenance and inspection schedules for all items/equipment giving type of works required on a weekly, monthly, annual basis; and

• proforma of the required maintenance record sheets for all the component/equipment.

We now outline the modern approach to operation and maintenance of power systems.

Renovation and Modernisation (R&M) and Life Extension Schemes

Basically, the deterioration of electrical components in the distribution system is related to electric, thermal, mechanical, chemical, environmental and combined stresses. Hence, failure of equipment could be due to insulation failure, thermal failure, mechanical failure or any combinations thereof.The concept of simple replacement of power equipment in the system, considering it as weak or a potential source of trouble, is no longer valid in the present scenario of financial constraints.Renovation, modernization and life extension of existing substations,sub-transmission and distribution network and field equipment outside the substations is one of the cost effective options for maintaining continuity and reliability of the power supply to the consumers. Renovation and modernisation (R&M) is primarily needed to arrest the poor performance of the substation equipment (mainly transformers and switchgears), which are under severe stress due to poor grid conditions, poor and inadequate maintenance and polluting environment.

In this changed paradigm, efforts today are being directed to explore new approaches/techniques of monitoring, diagnosis, life assessment and condition evaluation, and possibility of extending the life of existing assets, i.e., generator, circuit breaker, surge arrestor, oil filled equipment like transformers, load tap changer, etc., which constitute a significant portion of assets for generation, transmission and distribution system Assessing the condition of the equipment is the key to improving reliability. The knowledge of equipment condition helps to target the maintenance efforts to reduce equipment failures. Reduction of failures of equipment improves reliability and effectively extends the life of equipment.

Hence, utilities are continuously in search of ways and means other than conventional methods/techniques to assess the condition of equipment in service. Thus, remedial measures can be taken in advance to avoid disastrous consequences thereby saving valuable resources.For assessing normal operation, strategic planning and scheduling,three major tasks need to be identified:

• incipient failure detection and prevention − supervisory function, monitoring;

• identification of malfunction or fault state − offered by diagnostic techniques; and

• planning for repair, replacement and upgrading − life assessment and condition evaluation techniques.

Researchers and manufactures have come out with various condition assessment, diagnostic monitoring, preventive maintenance, predictive
maintenance (PDM) techniques for the equipment to reduce the risk of failure and extend their effective life and thereby help utilities overcome the challenges they face. Various condition assessment tools are used to establish the health of equipment using latest on line and off line diagnostic testing techniques/technologies.

Predictive maintenance is gaining popularity as it helps eliminate unscheduled downtime of expensive equipment and reduces the overall cost of maintenance. This approach, sometimes called ‘condition-based maintenance’, relies on planned inspections, testing, analysing and trending of the relevant equipment parameters. In most cases, these parameters can determine the equipment’s health and must be followed up by proactive actions that change the way the equipment is operated to reach the goals set out. In other words, the performance of the equipment is analysed to determine its condition and predict when it will need attention.

The techniques so developed are grouped under Residual Life Assessment(RLA) techniques. The potential of such techniques is tremendous and their benefits are so many that utilities cannot ignore their importance in the present scenario.The main objective of RLA is to determine the condition of a set of equipment (e.g., transformers) in order to identify the most vulnerable component/equipment. Based on the evaluation, utilities can develop a strategic replacement plan for a particular population of equipment. The aim should be to maximize the availability and utilization by avoiding unexpected failures and at the same time minimizing risk. Strategies for life assessment are quite complex and involve many aspects (both user-oriented and manufacturer-oriented). Their details are beyond the scope of this course.

In the next section, we introduce the concepts of grid management, load scheduling and load balancing. However, you may first like to revise the ideas presented in this section.