Maintenance:
In electrical engineering maintenance is defined as
a combination of actions to be carried out to replace, repair, service the
components of any electrical equipment so that it will continue to operate as
per specified standard i.e. stays in proper working condition
Objectives
of electrical maintenance Department
1. To minimize breakdown
of machines
2. To maintain the machine in perfect
working condition at the lowest possible cost
3. To operate the machine in such a
condition that they operate at its maximum capacity without any interruption
4.
To arrange training for the
executives and skilled workmen so that their operational efficiencies are
improved
5.
To make any machine reliable,
durable and safe
Functions
of maintenance Department
1.
To develop maintenance policies,
procedures and standards for the organization
2.
To carry out repairs and rectify or
overhaul planned equipment
3.
To prepare maintenance budgets
4.
To handle disposition of scrap or
surplus materials
5.
To keep record of all maintenance
work
Importance
of maintenance
1.
Due to lack of maintenance any
electrical equipment or machines may breakdown
2.
If machine is poorly maintained or
totally neglected in this respect it may breakdown totally in due course of
time. Sometimes replacement too will require high maintenance cost to put the
damaged machine and equipment parts
3.
If maintenance is properly
organized it will reduce the fault occurrence and hence increase the life
4.
Ensures the continuity of operation
United
States department of labor regulation (standard-29CFR) standard number 1926.431
title: maintenance of equipment under part safety and health regulation for
construction
“The employer shall ensure that all wiring
components and utilization equipment in hazardous locations are maintained in dust-tight,
dust-ignition-proof or explosion proof conditions as appropriate. There shall
be no loose or missing screw gaskets, threaded connections, seal or other
impairments to tight condition
Occupational
health and safety regulations 1995(plant regulation)
This regulation requires employers to ensure that
·
Hazards( potential for injury or
illness) associated with the installation , commissioning, erection, operation,
inspection, maintenance, repair, service and cleaning of nay new and existing
machine for use in the work place are identified
·
The risks( prone to injury or illness)
associated with the identified hazards are assessed and
·
Any risk is eliminated or reduced where
it is not practicable
The plant regulations require employers not to
depend solely upon the use of administrative control like training safety
procedure, safety signs, supervision or personal protective devices like
gloves, glasses to control risk unless the followings are not practicable to
measure
v Substituting
the machine with one which has a lower level of risk or
v Use
of engineering control to change physical characteristics of the machine to
eliminate risk or reduce risk or
v Isolation
of the machine from people
Steps
to consider:
Before Maintenance:
- Decide if work should be done by
specialist contractors, Never take or work for which your you are not prepared
so far to
- ·
Plan the work carefully before you start
ideally by using manufacturer’s instructions
- ·
Make sure maintenance staffs are
competent and have appropriate clothing and equipment
- ·
If maintenance work is performed before
startup or during shutdown , you can avoid many difficulties
Safe
working areas:
·
Provide safe access and a safe place of
work
·
Don’t just focus on safety of
maintenance workers, consider nearby people too
·
Set up signs and barriers and position.
people at key point if they are needed to keep other people out
Rules
to follow while maintaining electrical equipment
1.
Avoid contact with energized
electrical circuit equipment
2.
Treat all electrical device wires
as if they are live or energized-you never know
3.
Disconnect the power source before
servicing or repairing electrical equipment
4.
Use only tools and equipment with
non-metallic handles while doing maintenance or repair work
5.
Never use metallic pencil or ruler
wear rings or metal watchbands when working with electrical equipment
6.
minimize the use of electrical
equipment in cold room or avoid repair work in moisturized places
7.
if water or chemical is spilled
onto equipment shut off the power at main switch and unplug the equipment
8.
don’t store highly flammable liquid
near electrical equipment
Causes
of deterioration in electrical machines
1.
Ingress
of moisture :
Presence of moisture or humidity in
the air is root cause of problems like rust, rot, decay, decomposition. The
storage manufacture and transportation of materials, part of machines takes
place in humid environment which is not suited to the moisture sensitivity of
the material leading to deterioration of machine and their parts. Ingress of
moisture leads to many other problems like corrosion short circuit in
electrical equipment
2.
Contamination:
Contaminants are those unwanted
particles and materials which affects the performance of machine and its parts.
For example presence of solid particle like dirt, metal particle reduces the
quality of lubricant which increases the friction rather than decreasing it
which indeed deteriorate the machine and equipment
3.
Corrosion:
Corrosion is the process of
destruction of a metal or alloy surface by chemical or electrochemical reaction
with its environment. In most instances, the reaction is electrochemical in
nature: a flow of current between areas of metal surfaces through a solution
capable of conducting electricity. Higher humidity may lead to higher
condensation of water on metal surfaces. The concentration of molecule of water
vapor increases with increasing relative humidity. This molecular thickness of
layers of water eventually permits ionic conduction which accelerates the rate
of corrosion. With iron or steel the ferrous ion may react with hydroxyl ion in
water to form ferrous hydroxide and with oxygen to produce ferric hydroxide
(rust)
4.
Mechanical
Stress:
When certain part of machine or
whole machine body comes under continuous pressure or pressure of different
magnitude then ability of machine to stand for long time reduces. Pressure may
be internally generated or by some external means. Continuous stress causes
deformation of pressurized part. Brushes of generator comes under continuous
pressure which deteriorates the machine quality and performance if intensive
care is not given
5.
Electrical
fault:
In electrical machines and
equipment different type of electrical fault may occur which degrades the
machine quality and performance. For example problem may arise in transformer,
motor or other devices which employs coils and conductors, these usually
generate heat with time can malfunction. A corroded current carrying conductor
may draw less current than rated current because of increase in resistance
caused by decrease in cross-sectional area resulting in poor performance. Short
circuit in machine part may cause sudden rise of current which is harmful to electrical
equipment.
6.
Insulation
ageing :
Insulation strength may decrease as
the time passes by. When insulation comes under electro-thermal and
environmental stresses it may cause insulation system degradation and ageing.
Electrical stress is usually considered as the ageing factor so this external
factor may cause accelerated ageing. This degrades the machine quality. Same
insulation may offer less resistance after sometime than early days. Less
insulation strength brings problem in electrical machines.
7.
System
Surges:
In general a surge is a transient
wave of current, voltage or power in an electrical circuit. Every piece of
electrical equipment is designed to operate at a specified nominal voltage such
as 120vac, 240vac etc. Most equipment designed to handle minor variations in
their standard nominal operating voltage. However, surge can be very damaging
to nearly all equipment. Surge may be generated in switches contactors relay or
at loose connections which interrupts the performance of the machine or damage
it.
8.
Overheating:
Overheating is normally caused by
flow of excessive current, poor connections and insulation breakdown or by
frictional contacts. Continuous overheating may cause fire in the electrical
circuit or insulation failure in electrical equipment. Moreover, mechanical
strength of components of the equipment is also reduced when heated
continuously.
Types
of Maintenance:
1.
Corrective or breakdown maintenance
2.
Scheduled maintenance/routine
3.
Preventive maintenance
Corrective
maintenance or breakdown maintenance
It is a type of maintenance that
implies repairs are made after the equipment fails to perform its normal
function for example: an electric motor will not start. It allows a machine or
any other facility to run without much routine attention till its activity
breakdown and fail to perform its function
Under this condition production department request the maintenance
department to rectify the defect. The maintenance department inspects the
equipment, locates the fault and makes the necessary repairs. After removing
fault they do not attend the equipment again until another failure of breakdown
occurs. In this type of maintenance no attempt is made to prevent occurrences
of breakdown.
Typical
causes of equipment breakdown:
1.
Failure to replace worn out parts
2.
Incorrect installation or use of
equipment
3.
Faulty design construction
4.
Lack of lubrication
5.
Neglected cooling system
6.
Indifference toward minor faults
7.
External factors like too low or
high line voltage, wrong fuels etc.
8.
Indifference toward equipment
vibration, usual sound coming out of rotating part
Disadvantages
of breakdown maintenance
· The type, nature, place and time of
breakdown is of random nature. This practice leads to disruption of machine,
equipment etc.
· Impossible to plan work load,
distribution of maintenance work force for balanced attention of all equipment,
machine etc.
· Involves prolonged downtime due to lack
of requisite manpower and spares
· Leads to considerable output reduction
· Difficult to maintain quality of machine
· Increased chances of accidents, less
safety to both workers and machines
Scheduled
maintenance:
The maintenance provided for inspection, overhaul,
lubrication and servicing of certain machines or equipment at predetermined
dates is called scheduled maintenance. Aim of this maintenance is to minimize
breakdown. The frequency of such maintenance job is predetermined and schedule
or program of maintenance work to be done is prepared in advance considering
idle time of equipment e.g. when motorcycle runs for 1500km changing Mobil is
recommended.
It cannot ensure completion of work in time because
the nature of work to be done remains unknown. It may therefore, lead to
increased repair cost due to non-availability of requisite skills and materials
Advantages
of scheduled maintenance:
v Reduces
the number of faults
v Breakdown
is minimized and machine run at higher level of efficiency
v Predetermination
of date of maintenance work ensures to plan work load and work force in
balanced manner
Preventive
Maintenance:
It consists of routine actions to be taken in a
planned manner to prevent breakdown and to ensure efficiency to maximum in an
economical and practically possible way. Breakdown possibilities are inspected
and some actions are taken so as to prevent it from happening. Major objectives
of this maintenance are to prevent breakdown and to ensure operational accuracy
and safety. Preventive maintenance means proper maintenance it consists of
adoption of measures to know before breakdown and prevent them before they
occur than allowing breakdowns to happen and the take action
Types
of preventive maintenance:
1.
Routine
Maintenance:
It
should be carried out daily if possible. It includes visual inspection minor
repairs such as replacement of small parts and adjustment of equipment so that
it remains in operation. It includes all work required in cleaning of equipment
from dust and dirt, cleaning of fittings, tank cover, bushings of power
transformer, cleaning of fixed and moving contacts, replacement of burnt parts.
2.
Periodic
Maintenance:
It
should be carried out weekly, monthly, quarterly or half yearly depending upon
the requirement and condition of a machine. It includes inspection of loose
parts, ventilation, change of oil, checking of insulation etc.
3.
Overhauling:
It
should be carried out yearly or half-yearly. It consists of replacement or
renewable of main unit and part of electrical equipment or machines. It
involves work as rewinding of motor stator and rotor, replacement of bushings
of high voltage, circuit breaker and involves partial or complete dismantling
of the equipment
Advantages
of preventive maintenance:
1.
Reduction in breakdown
2.
Fewer large scale and repetitive
repairs
3.
Greater safety to employee because
of reduced breakdowns
4.
Low maintenance and repair cost
5.
Increased equipment life
6.
Work load of maintenance staff can
be properly planned
7.
Satisfactory maintenance of machine
and other equipment at low cost
Objectives
of preventive maintenance:
1.
To make plant equipment and
machines always available and ready for use
2.
Minimize the possibilities of
unanticipated interruptions
3.
Maintain the value of equipment,
machines and other facilities by periodic inspection, repairs, overhauling etc.
4.
reduce the work content of
maintenance job
5.
ensure safety of life of workmen
Elements
of preventive maintenance:
1.
Inspection:
Inspection
means to watch out for each defect it is carried out to detect worn out parts
of machine so as to plan its repair or replacement before it finally gives a
way and brings machine stand still. It is a means of preventing breakdown and
thus reducing the loss of production and repairs. Usually there will be sigs from
the part of machine where failure might happen in future
I.
External inspection:
It
is to watch out for each defect from abnormal sound. These checks can be
carried out while the machine remains in operation
II.
Internal inspection:
It
is Inspection of internal parts such as gear, brushes, bearings etc. This type
of inspection is carried out when the machine is under preplanned shutdown
2.
Overhauls:
It is one way of preventing
breakdown and lengthening the life of machine because it involves stripping of
a machine, cleaning it, rectifying its defects and replacing its worn out
parts. Inspection may refer to checks carried out between 2 overhauls
3.
Lubrication:
It ensures long life and safe
working of the machine or equipment. Lubricant converts solid friction into
fluid friction and thus reduces wear and tear of moving parts and cuts power
consumption. Proper lubrication, therefore guarantees long life of equipment
without failures
4.
Planning
and scheduling:
Every preventive maintenance work
should be pre-planned in details on the basis of the analysis done on the past
records. Repair and replacement can be planned about a week to month to year in
advance on the basis of inspectors report and request from the operating
department. While preparing maintenance schedule for a particular machine or
equipment, it is essential to refer manufacturers schedule for a particular
machine or equipment. It is essential to refer manufacturers drawing technical
date and workshop manuals and their recommendations should be followed strictly
5.
Record
and analysis:
Good record keeping is essential
for preventive maintenance. It helps to decide that degree and type of
attention that should be paid to an equipment
For this purpose following records
are generally maintained
a. Instruction
manuals
b. Drawings
c. Equipment
records
d. Equipment
history
e. Inspection
register
f. Log
book
6.
Training
of maintenance personal:
For the success of preventive
maintenance a sound training is essential for the maintenance personnel.
Therefore, the technicians and supervisors are trained to carry the
maintenance, inspection and repairs in systematic way.
Requirement
of good preventive maintenance
1.
Good supervision and administration
of maintenance department
2.
Priority of maintenance work should
be fixed after consultation with production department
3.
Correct, clear and detailed
instruction should be given to maintenance staff
4.
Sufficient stock or spares should
be kept
5.
Operators and maintenance staff
should be well trained
6.
Surrounding should be dust free and
clean with proper ventilation and illumination
7.
Failure information must be
available in order to have complete knowledge about causes of failure and their
effects. A systematic approach of
maintenance should be followed
Faults
due to poor maintenance:
1 .
Operating
temperature fluctuation:
If the temperature rises above
permissible temperature then the machine has to be operated at lower rating,
also insulation resistance degrades with rise in temperature and reduces the
life of insulation. This happens when dirt, dust is collected on windings and
blocks cooling system ducts.
2.
Insulation
resistance deterioration:
If measurement of insulation
resistance is not carried out frequently as per schedule, the moisture absorbed
by the winding or collection of grease on insulation etc. may not be detected
which reduces the life of insulation.
3.
Brush
sparking:
This may be due to dirty
commutator, mechanical unbalance, machine misalignment.
4.
Loose
commutator or loose bars:
Loose bars or commutator may cause
sparking on its surface which will have burns.
5.
Brush
adjustment:
If all the brushes are not fixed
with uniform and correct brush pressure, brush will get unevenly damage by
sparking
6.
Brush
clearance
If brushes are not placed at equal
distance and in magnetic neutral plane they will cause serious sparking as some
of the brush will not be then in magnetic neutral plane.
7.
Brush
staggering:
If improper brush seating is there,
between brushes and commutator it will cause unequal current to flow through
different brushes which will cause overheating and sparking which will destroy
the commutator surface film and brushes
8.
Brush
pressure:
At low brush pressure
it causes chattering and sparking commutator while too high pressure causes overheating and excessive wear of brushes and commutator
9.
Overloads
It will increase the operating
temperature of the machine, weak insulation strength and life at same time
continuous overload may set up a temperature which will cause commutator and
armature band to throw.
10. Over speed:
When machine works at speed beyond
the permissible limit, it will affect into throwing out of armature coil which
may also damage field winding
11. Vibrations and excessive end play:
Vibration which may be due to
unbalanced rotating masses or hall coupling not properly leveled will damage
the bearings at faster rate; will cause heating effect on bearings.
12. Cooling system:
If gas cooling or force water
cooling system is used for taking away the heat developed in electrical
equipment, malfunctioning of the same will result into development of high
winding and machine temperature which will damage the insulation.
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