Computerized scheduling guides service firms and plant electricians, achieving effective maintenance with practical economy.
Key to successful electrical maintenance at the Westinghouse Electric Corp. Electronic Systems plant, Baltimore, Md. is a carefully developed computerized scheduling plan. This comprehensive plan guides engineers who bring in electrical service firms as needed as well as activities of in-plant maintenance electricians.
The heart of the program is computerized scheduling covering electrical preventive maintenance (EPM) of all power distribution equipment, related components, and certain production systems. The maintenance computer center also regularly sends EPM workorders to the electrical maintenance department, where it's determined whether maintenance will be done "in-house" or delegated to an outside service firm.
How computerized maintenance works
Several years ago, Charles Gantt, maintenance supervisor, gradually updated a list of all power system equipment in the plant, itemized integral parts of each piece of equipment, and specified maintenance procedures. Time intervals for maintenance were based on experience with the equipment.
Because of the huge quantity of electrical equipment to be maintained, the gathering and organization of this information was a herculean job. After a planning meeting with Facilities Engineering, it was determined that the simplest method was to list equipment by major categories. For example, groupings selected included outdoor substations, outdoor transformers, indoor unit substations, busways, panelboards, motor-generator sets, batteries, etc. Then, sub-group listings were developed, such as indoor substation Circuit Breakers (CBs), indoor transformers, terminations, protective relays, control circuits, etc. Finally, maintenance procedures for each of these were developed and scheduled.
This information was sent to Terry Wade, Supervisor of Maintenance Planning, who set up a computerized scheduling program. The program consists of two major parts.
* A main schedule that lists all major components, ID numbers, location, designation, description, schedule and similar data (as shown in the diagram on page 46).
* A work order for each piece of equipment or system, providing safety directions, instruction on maintenance procedures, dates, space for remarks, etc. The work orders are generated automatically according to schedule and sent to the maintenance supervisor. About 30 to 40 EPM work orders arrive at the electrical department each month, about a month before the work is to be done. When maintenance by in-plant electricians is completed, a report is made on the work order, which is reviewed by the maintenance supervisor. The supervisor then sends it back to central computer maintenance, or holds it for further action if necessary.
Outside service firms do maintenance
Facilities Engineering, headed by John N. Harvey, Supervisory Engineer, Electrical Section, gets very much involved with electrical maintenance. Together, they help solve difficult problems, decide when to call in service companies, and investigate design or equipment changes that will enhance reliability or save money.
Because of the huge size and growing complexity of the electrical power systems, outside service firms are brought in to perform maintenance on large groups of equipment, or for specialized procedures. For example, specialists do all maintenance on the 34kV outdoor substation, on over 60 indoor unit substations, on protective relays, and on other equipment or systems that require specialized expertise or test equipment. Basic maintenance on selected equipment is done by in-plant electricians.
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According to Harvey, the use of the computerized maintenance plan combined with judicial selection of which work will be done by in-plant electricians or by outside service firms results in significant advantages. First, the plant operates with high reliability and minimum downtime, which effectively saves the high cost of unscheduled downtime.
The procedures conducted by outside firms are well done because these firms are specialists; work done by in-house electricians is effective and efficient because they know the equipment. An extra benefit is that this allows the maintenance department to keep a steady number of employees. As a result, high reliability and efficiency of operation is obtained at the lowest possible costs.
Maintenance techniques
Typical examples of maintenance procedures done by in-plant electricians include the following.
Infrared thermography. The electrical department has found that one of the fastest and most effective maintenance procedures is infrared thermography. Within the plant are thousands of feet of distribution busway rated 480/277V and 208/120V. Attached to these busways are hundreds of plug-in CBs of all sizes supplying a variety of loads. Electricians using infrared scanners view all sections of the busways and related CBs according to work order schedule. CBs are highly reliable; however, after many years of operation, particularly where vibration or contamination is present, a plug connector can loosen. When this happens, the connection point begins to develop a higher resistance, resulting in heating. Any spot that is hot, including an occasionally bus-bar joint, is easily seen through the infrared scanner, and the location is recorded for investigation and correction if needed. The scanner is also used to check motors, generators, panelboards, switches, transformers, and other selected equipment.
Electronic maintenance. Electronic technicians are plant electricians who have attended schools, courses, and training classes to become qualified in the maintenance and troubleshooting of electronic equipment. Their main job is to maintain and troubleshoot plant electronic systems, microprocessor-based equipment, and other complex devices. For example, they maintain an extensive electrical monitoring system, scores of programmable controllers, and any equipment furnished with solid-state controls. They also do certain electrical maintenance on power equipment or systems when needed.
Motors and controls maintenance. Vibration analysis is used extensively to check all motors and rotating equipment. Most of this work is done by HVAC technicians who have been trained to use the vibration analysis instruments. This test technique has become the preeminent method of determining the condition of motors and rotating machines. A base-line value amplitude and frequency of vibration is established for each machine. Then, tests are made regularly and compared to the base values. If an obvious deviation is found, further investigation is initiated. Vibration analysis can indicate and locate imbalance, misalignment of couplings or bearings, bad bearings, bent shafts, bad gears and belts, and mechanical looseness.
Brush maintenance. Plant electricians maintain the generators. Many of the generators providing 400 Hz and 50 Hz are of the revolving armature type, which supply output power from the rotating armature. As a result, the generators are furnished with slip rings and brushes that must be regularly maintained. The slip rings require little maintenance other than inspection to assure that their color is correct and that there is no wear. However, the carbon brushes must be regularly (monthly) checked to assure that they do not become too short, break, or allow a brush holder or brush shunt to rub on a slip ring.
Battery maintenance. All battery banks are maintained by the plant electricians. They've found that the best procedure is to perform a load test every six months. This test tells the capability of the battery under load and has become the standard test for battery maintenance. The electricians have dispensed with checking cells for water and/or acid content as well as other no load tests.
Outside firms' maintenance work
Outside firms are brought in to provide complete maintenance service of the outdoor substation, such as cleaning insulators and the checking of knife-blade switches, oil circuit breaker, and main power circuit breaker operation as well as outdoor transformer oil conditions.
During the plant's holiday shutdowns, large outside service crews and technical specialists come in to do a complete service on the 60 indoor unit substations. This includes checking power circuits and components of primary and secondary circuit breakers, testing of all protective relays, performing insulation-resistance and high-potential tests of components and distribution conductors.
RELATED ARTICLE: FACILITY BACKGROUND INFORMATION
At this huge manufacturing plant, which encompasses over 2.5 million sq ft, the major product is radar and related systems for both defense and commercial applications. As a result, only the highest product quality is acceptable. To achieve this, it's essential to maintain maximum dependability of power systems, test labs, and production operations at all times.
The plant incorporates the latest in production systems, quality control, and development facilities. Support systems are similar, including programmable controllers, online monitoring, and electronics.
Paradoxically, much of the plant power system equipment is old; however, most components have been thoroughly modernized and updated. For example, at unit substations, old-design 5kV power circuit breakers have been upgraded from electromagnetic protection to solid-state. A new on-line, microprocessor-based monitoring system provides audible and visual status of most power distribution equipment and critical devices. Older but expensive equipment have been kept and are meticulously maintained. As an example, numerous motor generator sets that convert 60 Hz to 50 Hz or 400 Hz have revolving armature alternators that use brushes to provide output voltage. These brushes are very carefully maintained in the program.
