Download Motor Quality Guide your questions answered

Motor_Qual_brochure 1/5/02 4:43 pm Page 1
Motor Quality Guide
your questions answered
Motor_Qual_brochure 1/5/02 4:44 pm Page 2
Introduction
● Reliability is by far the most important aspect of
a motor
The only time the motor is really noticed is when it fails. Unplanned downtime
can cost as much as a new motor every five minutes, rapidly adding to the life
cycle cost.
● The support and know-how of the manufacturer can
be as important as the product quality
For a healthy bottom line, it is important to select quality motors that won’t let
you down, from a manufacturer with an adequate support infrastructure.
● Purchase price is insignificant when compared to the
overall life cycle cost
The AC motor is the workhorse of industry. It is a fit-and-forget item, expected to
last for many years. Its life cycle cost is mainly made up by the electricity it
consumes - for every £1 you spend buying the motor, you will typically spend
£100 running it over a 10-year life cycle.
There is more to motors than
meets the eye
2
Motor_Qual_brochure 1/5/02 4:44 pm Page 3
What do you need from a manufacturer?
There are three major aspects to quality - materials, systems and people
information when you need it. After sales
support and service systems should also
be available 24/365 for a fast and
efficient service.
Quality materials
The life expectancy of a motor can
exceed 20 years, which is why the use of
quality materials is of paramount
importance. The motor is the prime
mover and the reliability of the plant will
depend on the quality of the motor.
However there is more to motors than
meets the eye. For this reason, care
should be taken when selecting a motor
supplier. A quality motor, correctly
selected and dimensioned, will provide
many years of trouble free performance.
Making the right choice
How you can recognise a quality motor
is something we aim to explain over the
next 10 pages, enabling you to make an
informed choice. Making the wrong
choice can result in lower motor life
expectancy, higher running costs and
increased downtime.
Remember that quality normally
comes at a price. While making the right
choice may result in a one-off cost
increase when purchasing, making the
wrong choice could result in ongoing
operational cost increases for the life of
the motor.
Quality people
Motors are utilised in hundreds of
applications under a variety of conditions
and appropriate advice is essential to
select the right motor for the job.
A good manufacturer will have wide
industry experience and will be able to
give adequate advice for the particular
conditions and demands of your industry
sector. You should also expect
knowledgeable advice on issues such as
starting methods, variable speed drive
considerations such as bearing currents
and harmonics, as well as the
wider issues affecting the correct
selection of motors.
The manufacturer you use
needs to have a full range
of motors to cover all
your applications
Quality
systems
Fast and
efficient
access to
information
and support is
essential for any
business. Online
documentation, ordering and
delivery tracking systems
should be available 24 hours a
day, 365 days a year, to provide
3
Motor_Qual_brochure 1/5/02 4:45 pm Page 4
Quality means reliability
Motors should never fail. Unfortunately, they do, some more than others
A motor is only as good as its constituent
parts. Here, it really is a case of getting
what you pay for. About 55% of the price
of a motor goes towards materials, while
15% is used for labour and another 30%
for other costs, e.g. R&D, logistics and
general overheads.
This chapter outlines what makes a
good motor, and what to look out for
when buying motors.
Reliability - why should I care?
If you need a motor for a water pump
that runs once a year on a non-critical
application, reliability will not be a big
issue. Providing the motor is right for the
application, the running hours will never
mount up and the materials will almost
certainly last regardless of quality. But if
you are responsible for the 24/365
operation of a paper machine, or a
processing plant, with a downtime cost of
£10,000 per hour, you will appreciate the
importance of reliability. And if you are
selecting motors as an OEM, you will be
putting your company’s reputation at risk
Of the motor’s key components, the bearings and the
winding are the ones most exposed to wear
by selecting a low quality motor. It will
be your company that gets the blame, not
the motor manufacturer, when the
product fails.
As much as 55% of the motor’s price goes towards
materials, while 15% goes to direct labour and 30%
towards R&D, logistics and general overheads. For this
reason it is difficult to cut costs substantially without
affecting performance
4
Motor_Qual_brochure 1/5/02 4:45 pm Page 5
Product quality
First of all, the quality of the product is
secondary to the quality of the advice
you receive when selecting your motors.
The world’s finest materials will not help
if the motor is wrong for the job. Make
sure that your motor manufacturer has
experienced engineers who are available
to help you with selection.
Bearings
Check:
Regardless of the type of bearing, it needs to be
adequately greased. The quality, frequency and amount
are all critical factors; excessive greasing reduces bearing
life just as insufficient greasing does
What is the quality of the bearing?
Do you know the bearing manufacturer?
Is bearing life defined to L1 or L10?
Does the motor have a grease
outlet?
with the original grease. Special grease is
available for operation in hot or cold
ambient temperatures. Your motor
manufacturer should be able to provide
specific advice on lubrication.
Over-greasing can have just as
disastrous consequences as insufficient
greasing, particularly in fast running
applications. When too much grease is
added, the bearing elements do not have
enough room for heat expansion, which
causes friction and overheating. Some
motors have a grease relief valve to
avoid this happening.
Bearings should come from a
reputable manufacturer. ABB uses
bearings from, for example, SKF, NTN,
and NSK. Along with a small number of
other companies, these are among the
world’s premier bearing manufacturers.
L1 and L10 are the most common
measures for bearing life (reliability) used
by bearing manufacturers. L10 means that
90% of bearings achieve or exceed the
calculated bearing lifetime; L1 means that
99% of bearings achieve or exceed the
calculated bearing lifetime. The improved
reliability is achieved by more frequent
re-greasing intervals.
Actions:
Ask your motor supplier to recommend:
Bearings dimensioned for the
appropriate load
Internal bearing clearance suitable for
the temperature
Grease suitable for the temperature
Choose re-greasable or sealed-for-life
bearings as appropriate
The most common cause of motor failure
is bearing problems. The life of the
bearing depends on many different
factors, the main one being the quality of
the bearing. It also depends on selecting
the right type of bearing for the
application and load in question, and
correct greasing for the application.
Bearings can be either re-greasable or
sealed for life. The re-greasable bearing
will give a longer service life, providing
that the end-user has a suitable
maintenance infrastructure. If not, sealedfor-life bearings are preferable. These are
also required in for instance dusty
environments. The bearings should only
be re-lubricated with grease compatible
5
Motor_Qual_brochure 1/5/02 4:46 pm Page 6
Product quality (continued)
Winding
Check:
Winding insulation - Class F is better
than Class B
Withstand voltage above 1400 V is
beneficial for variable speed drive
operation
Good slot fill
Poor slot fill
A good slot fill is one of the characteristics of a
good winding
Actions:
Deg. C
Choose high efficiency for a lower winding
temperature; this gives long winding life
as well as low running costs
155
130
The second most common cause of
failure is the winding. At the end of a
long service life, the insulation system,
including varnish, that insulates the
copper wire in the windings will start to
break down and a short circuit may occur.
If this happens, a high quality motor can
in many cases be rewound without too
great a reduction in efficiency. The
materials and constructions used will allow
the removal of the old winding and
rewinding and impregnation of the motor.
A low quality motor can also be
rewound but typically with much greater
losses in efficiency, due to lower quality
electrical steel used in the stator
laminations.
Years
Winding lifetime
A lower internal temperature extends the life of
the motor
The windings can be insulated to
different standards; Class F (155°) and
Class B (130°) are the most common.
Most motors are manufactured with Class
F insulation material but designed to run
no hotter than with Class B temperature
rise. The cooler the motor runs, the longer
the insulation system will last and the
longer the motor will operate.
Efficiency - the other side of temperature rise
A low running temperature means the motor requires less cooling, enabling the use of a smaller fan. This
results in low heat losses and high efficiency. High efficiency means lower energy costs, giving lower
operational costs. Low temperature rise comes from using high quality materials and production methods and
comes at a price. However, the additional cost for using a high efficiency motor is often repaid in reduced
energy costs in less than a year. Take the following example:
Purchase cost, 90kW high efficiency motor (95%)
£5,532
Purchase cost, 90kW average efficiency motor (92%)
£4,273
Difference in purchase price
£1,259
Daily running cost, 95% efficiency
£131
Daily running cost, 92% efficiency
£138
Saving, per day
£7
Payback time
6 months
6
Motor_Qual_brochure 1/5/02 4:46 pm Page 7
Product quality (continued)
• Random winding pattern
• High quality slot insulation,
impregnation systems and phase
insulation systems
The integrity of the winding is measured
in withstand voltage and is usually in the
region of 1200 V.
Motors with withstand voltage of 1400 V
and above are available and offer increased
reliability. This is especially important to
help withstand the voltage spikes produced
by some variable speed drives.
The normal running temperature in
high quality motors running at full load
can be as low as 60-80° C, while lower
quality motors can run in excess of 90° C.
Although this still meets the criteria of
Class B temperature rise, it could run considerably hotter than a quality motor of
the same size. Theoretically, a reduction of
10-15° should double the life of the winding, as well as the re-greasing intervals.
The life of the winding also depends to
a large extent on the production
techniques used in the manufacturing
process. A compact winding with a good
slot fill, i.e. high density of copper, gives
the best performance. Automated winding
equipment, as used on smaller size
motors, gives a higher density slot fill than
hand winding and gives a repeatable
quality time after time.
The characteristics of a good
winding are:
• Small overhang
• High quality grade of copper wire
• Good slot fill ratio. The more copper
wire in the slot, the better the metalto-metal transfer of heat, and the
cooler the running temperature of
the motor.
Stator electrical steel
The stator is made up of laminations, thin
slices of low loss steel with an insulated
coating. These should be uniform and as
thin as possible to maximize the strength
of the magnetic fields in the stator. They
must be perfectly aligned to give straight
channels for the slot fills. The stack of
laminations should be rotated periodically
to compensate for the effect the grain in
the metal has on the magnetic field.
C
180
15
155
130
10
Hotspot temperature margin
10
Permissible temperature rise
80
105
125
Maximum ambient temperature
40
40
40
B
130
F
155
H
180
120
40
Insulation class
Maximum winding temperature
The stator is made up by laminations of low loss steel
with an insulated coating
A higher insulation class gives better protection
against high temperatures and extends motor life
7
Motor_Qual_brochure 1/5/02 4:46 pm Page 8
Product quality (continued)
normal operation, as this can cause
moisture to build up inside the motor and
affect reliability. Your motor supplier
should be able to advise on whether IP65
is appropriate.
Frame
Check:
Examine casting for blowholes and
imperfections upon delivery, reject if
unsatisfactory.
Cast iron motors should be made of
suitable standard cast iron, e.g. ENGJL-200/GG 20/GRS 200
Aluminium motors should be made of
low copper content aluminium
(max 0.3%)
Noise - an invisible pollutant
Most responsible employers aim to reduce the
noise in their workshops. For example, the
recommendations issued by the UK’s Health and
Safety Executive set a maximum value of 85dbA
1 metre from the motor. Limits are continually
moving downward and your supplier should be
able to advice on the most recent regulations. The
noise levels should be printed in motor
catalogues. It is worth noting that an increase in
the noise by 3db is perceived as a doubling of the
noise. A difference in noise levels between two
motors of, say, 3db is therefore significant.
Actions:
Ask your supplier for advise on the correct
frame material for your application
Noise level
db(A)
The casting should be smooth and free
from blowholes. Apart from being
unsightly, blowholes trap air, which
hinders the transfer of heat. They can also
reduce the strength of the material, leading
to weak points and potential fracture.
100
Total noise
Fan noise
Bearing noise
90
Magnetic noise
80
70
60
50
40
0.2
0.5
1
2
5
10
20
50
100 200
500 1000 2000
Power, kW
Enclosure
The standard enclosure for motors is IP54.
This protects against water splashing.
Some motor manufacturers use IP 55
as standard. This additionally protects
against water jets.
Many users specify IP65 motors.
This means the enclosure is dust tight.
While this is appropriate in some
applications, it is unnecessarily air tight for
Components that raise noise level
Low noise motors can make a significant impact
on overall noise levels
Aluminium motors should use low
copper content aluminium to minimise
corrosion. Modern alloys contain as little
as 0.2-0.3% copper; a lesser quality alloy
can contain as much as 2.5%, typically
corroding at ten times the rate. Cast iron
motors should be made of high-grade cast
iron.
Painting
Actions:
Ask your supplier for a paint specification
appropriate for your application
The motor needs to be painted according
to appropriate specifications. Process
industry and offshore, for instance, needs
The casting should be smooth and free
from blowholes
8
Motor_Qual_brochure 1/5/02 4:46 pm Page 9
Product quality (continued)
a higher specification paint. A suitable
cover for aluminium motors in general
industrial application would be a twopack polyurethane acrylic varnish, while
for cast iron motors, a two-pack epoxy
primer followed by two-pack epoxy
topcoat is recommended.
Terminal box
Check:
Ensure that the terminal box is large
enough to enable rapid installation
with the type a cable used in your
application
If you have ever fitted a motor under
time pressure, for instance while standstill
costs were mounting up, then you will
appreciate the importance of the design
of the terminal box. The terminal box
should be large enough to accommodate
the bends of heavy gauge cables and
have cable entry from two or four sides.
Shaft
Check:
Can your supplier offer a range of shaft
materials for different applications?
The shaft material is selected according to
application. Normally, the shaft is a hot
rolled steel bar turned to the correct
dimensions. Stainless steel shafts are
available for use offshore or in chemical
plants. If strong radial forces are expected,
high tensile shaft material is available. Your
selected manufacturer should be able to
give advice on permissible loadings on
the shaft and suitable shaft materials.
Fan
Check:
A generously sized terminal box helps installation and
is particularly useful when time is at a premium.
Are original fans available as spare parts?
Can the fan be re-fitted once removed?
Some motors also come with a gland
plate which can be easily moved from
one motor to another, making re-glanding
of cables a thing of the past. In addition,
a spacious terminal box offers better
protection against short circuit.
The fan must be large enough to produce
adequate cooling, but too large a fan
reduces efficiency and increases noise. To
achieve the optimum balance, ABB varies
the blade size and pitch between models.
For this reason, a broken fan cannot be
replaced with any standard fan. The
appropriate fan for the model should be
obtained; using a standard fan can
increase fan losses by as much as 20%.
Check how the fan is fitted - it will
need to come off when the bearings are
replaced. A fan fitted to the shaft using a
keyway and grub screw can be removed
and re-fitted many times.
Accessories
Check:
Availability of accessories and ease
of fitting
Some motors are easier to modify than
others. You may want to add for example
monitoring or protection devices, check
how easily this can be achieved.
9
Motor_Qual_brochure 1/5/02 4:47 pm Page 10
Support and backup
Having quality support and backup is as
important as having a quality product.
The help of an engineer can be
invaluable when specifying the motor, as
this can prevent problems later on. The
engineer is part of a team and should be
supported by other engineers in-house,
who in turn should be supported by the
R&D department at the factory. Only this
way can you be sure you have the
backup you need for all eventualities.
Ensure that your supplier has backup of manpower as
well as products in stock
Issues affecting motor selection
Check:
up to 400 kW are stocked at ABB’s
central stock locations in Europe and can
be delivered within 24 hours.
Does your motor supplier know about
the wider issues affecting your industry?
Your supplier should be able to advise
you on all the wider issues that affect
motor selection, such as the Climate
Change Levy and Enhanced Capital
Allowances; health and safety issues,
such as noise; the ATEX directive for
explosion proof motors; ISO 14001, the
standard for environmental management
systems; the WEEE directive, relating to
the recycling of waste electrical products;
WIMES, the water industry’s mechanical
and electrical specification; and for
exporting OEMs, EPCA, the motor
efficiency norms in North America.
Production lead times
Check:
Are modifications and custom builds
available?
It is not always that stock motors are
appropriate for the application.
Sometimes, modifications or custom
builds may be necessary. It is important
that your chosen manufacturer can deliver
these within a reasonable time frame.
Some examples of ABB’s lead times:
• Fitting heaters or thermistors - four
days delivered
• Custom builds - normally six to eight
weeks delivered
Stock availability
Check:
Is a wide range of motors available
with short delivery times?
On-line services
Your chosen supplier should have a wide
range of motors, available in quantity at
short notice. All of ABB’s national
distributors stock motors up to 37 kW for
local availability. Some of them stock
sizes as large as 132 kW; these can be
delivered nationwide overnight. Motors
10
Check:
Is your supplier e-commerce enabled?
Some manufacturers enable you to deal
with them online, helping you reduce
administrative costs. If you do business
online, make sure your motor supplier
does, too.
Motor_Qual_brochure 1/5/02 4:47 pm Page 11
Support and backup
• Data sheets
• Type tests
• Certificate of conformity
• CE certification
• Machine certificate
• Speed/torque curves
• Flameproof certificate
• Noise curves
• Drawings, general arrangement
• Type test
The supplier should also be able to
handle your custom documentation and
produce dedicated speed/torque curves
for your application.
Your supplier shouldn’t just ship motors; he should
also be a reliable source of information for all your
application needs
After sales services
Warranty
Check:
Check:
Does your supplier have a reasonable
structure for after sales support?
Does your supplier have a clear
structure for handling claims?
After sales service may seem a long way
away while the motor has yet to be
specified, however sooner or later the
need will arise, and you should make
sure your chosen supplier has an
adequate support infrastructure.
Complicated warranty procedures are not
unheard of in the motor industry. Ensure
that your supplier has knowledgeable
field staff that can help with your
warranty claims, as well as a clear
internal structure for handling warranty
claims professionally. ABB’s warranty
claim procedure is outlined on the
internet at www.abbmsp.com
Documentation
Check:
Is the right documentation available?
If a service agent is used, it is the
manufacturer’s responsibility to ensure
that standards are maintained.
Your supplier should be able to provide
documentation within a reasonable
timeframe, such as:
To handle all aspects of customer service, your supplier needs a team structure, which can look something like this:
Technical support
Logistics
After sales
Application knowledge
Order handling
Warranty cases
Dimensioning
Progress reporting
24/7 support
Comments on specifications
Documentation packages
Repair/modification
Design capability
Proof of delivery
Service
Local representation
Stock profile
11
ABB Automation Ltd
9 The Towers
Wilmslow Road
Didsbury
Manchester M20 2AB
United Kingdom
Tel: +44 (0) 161 445 5555
Fax: +44 (0) 161 448 1016
www.abb.co.uk
MOTBRO-03/2002
Motor_Qual_brochure 1/5/02 4:43 pm Page 12