Electrical Maintenance and Repair EEP424 (Answers and questions)

Table of Contents

Maintenance and repair

Maintenance is defined as a combination of actions carried out to restore an item of equipment to an acceptable condition after deterioration has taken place. Economics of maintenance: since industrial organization exists to make profit by the use of equipment and labour to convert raw material of relatively low value to finish product of higher value, the need for the maintenance of such equipment is inevitable.

Briefly explain the economics of maintenance

Thus, the economics of maintenance can be seen as the practice of achieving maintenance needs within optimum cost implications. Reliability is the percentage of failure per 1000 hours of use. A well maintained or machine will operate long before the failure rate sets in and vice-versa. Hence, a well maintained machine has probability of being available for use at point in time Through its relationship with plant availability which is a direct cost maintenance.

Through the cost of maintenance resource which can be considered as direct cost of maintenance motor.Through its relationship with the useful life of plant, the longer the life of the plant, the greater is the life cycle probability In the design of maintenance planning functions, the following among numerous function are of importance Mapping out repairs strategies Furnishing forecasts Setting up preventive maintenance schedule Planning investment Setting up repairs schedules Construction Process planning, locating errors, establishing job cost measures, eliminating weak point, checking work carried out if required, maintenance cost estimation, writing reports , storage of data and commissioning procedures.

The factors to be considered in deciding a maintenance policy include;Operational requirement; which refers to the function equipment has to perform and the condition under which operates. Equipment characteristics: This include reliability, complexity, safety precaution etc. Tool and test equipment; the provision of appropriate tools and test equipment influence the maintenance of equipment considerably. Maintenance personnel; maintenance personnel also affect the maintainability of equipment if is/are not readily available Quality is defined as the degree of excellence.

Define quality in engineering maintenance and explain forms of quality

Quality management is the totality of action taken to ensure that quality (degree of excellence is delivered) .

i. Quality planning: Involves identifying the customer and establishment their requirements.

Quality control: Here, the final product or service is measured and compare with the requirement(s) an any shortfall or derivation is corrected

Quality improvement- By systematic identification of quality imperfection in the process and permanently resolving them a new and lower level of waste is attained.

Outline the reason for keeping the record of workdone on machine.

The reason for the work done record keeping are as follow

(i) It confirms that routine maintenance tasks have been carried out and helps to avoid duplication of work.

(ii) It indicates the amount of time and money Spent in maintaining each item, other items and equipment might have passed the age of economic viability.

(iii) It highlights recurring faults which may indicate the need for designed out maintenance.

(iv) It gives the opportunity to record any spare materials used for stock control purposes. Conceptioning is the formulation of idea about what the design that leads to the realization of the equipment in mind.

Commissioning is the beginning of usage of particular equipment in which in which clearly puts an end to the investment and power in return on investment. To maximize profit, the period between conceptions to commissioning should be small as possible while the operating life and total returns on investment should be as large as possible. Once the equipment is commissioned, the operating life (hence return on investment) is a function of the level of maintenance applied.

The two types of manufacturer’s manual are: The operational manual: it is a pamphlet that describe the operation part of the machine. It also spells out system of operation that must be followed in order to effectively operate the machine. The service and maintenance manual; it specifies the signs and symptoms to be observed during normal working conditions of the machine. It will also list the parts that will be frequently replaced for the efficient running of the machine.

(i) Specification of maintenance periodic Internal.

(ii) Step-by-step sub-guide for faults location.

(iii) Isolation of defected parts procedures.

Fault possible causes Remedy Trip out at start Overload has tripped out the circuit breaker or blown fuse Low voltage Loose terminal Reduce reset circuit breaker or replace Check plate values for proper supply Tighten up the connections Mechanical noise or vibration

Fault possible causes Motor is running on single phase Shaft running out in a sleeve bearing Remedy Trip Stop the motor, check for open circuit or correct phase voltages. Check the shaft and look for excessive end play and correct

The procedure for the manual is as follows:

Title dismantling of electrical motors for routing repair service work
Aim
Introduction
Procedure
Table
Table of content
Observation
Conclusion
Certification.

What is cell, primary and secondary cell

Cell: Is a device that gives electrical voltage Battery: is a combination of cell to boost the supply

Primary Cell: is a source of electrical energy once runs out of power cannot be recharged. Secondary cell: can be recharged once its runs out e.g accumulator in a motor car.

precautions to be taken in charging room

Room must be well ventilated
Vent plug must removed
No naked light should be brought near charging batteries
Always add acid to water (not water to acid).
Mix electrolyte in a non-corrosive container capable of withstanding heat
Protective clothing should be used in the charging

One core of a twin cable has a low resistance Fault to the earth, and the other core is in good electrical condition.L= length of the complete loop of cablex= fault distance from the near endss=slider loop lengthr=Slider distance from the fault end. Then, r/s = X(m)/x(m)(when the balance is established).: r/s= n/x = Rx/s (m)

Explain how effective earthing system can prevent or minimise earth fault

Murray-loop and Varley-loop tests employ the principle of Wheatstone bridge. 20. It is noted from practice that during the earth fault, current of about 16 times normal usual current flows and its dangerous to the equipment to carry such ‘ heavy’ and equally hazardous to the personnel. Hence, if earthling is properly done check test (maintenance), it can save time and money for repair that good result from some situation of bad earthling.

list and explain three relevant maintenance techniques to be employed according to the nature of equipment or plant

( i) Preventive maintenance : Is planned maintenance on a predetermined schedule. The purpose is to maintain the equipment in good condition, to prevent breakdown that would occur had the preventive maintenance not been done Also to keep safety and environmentally sensitive equipment in top shape.

(ii) Predictive maintenance – is condition monitoring on a predetermined schedule, while the equipment is operating.

Preventive maintenance requires the equipment to be shut down, but Predictive maintenance does not. Condition monitoring means that the condition of the equipment is monitored with an instrument or analyser and the results are compared to a pre-established physical parameter or limit.

(iii) Breakdown maintenance – pure breakdown maintenance, often called. Failure” reactive maintenance or run to means that the equipment is repaired when it breaks down. This is the most expensive and least productive approach to maintenance. Breakdown wastes time and money because the work has to stop. Repair is costlier than maintenance because when equipment his deteriorated, it usually involves changing of I most cases while the maintenance in other had usually involves cleaning and lubrication of parts. The repair is costly because it brings about time wasting and redundancy.