Steam turbines & Electric motors
“How can we rev you up?”
A Group F’s Production
http://www.revak.com/powergenpics.htm
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Presentation Outline
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Typical Applications
Types of Drives
Physical Principles
Troubleshooting
Safety
Operability
Capital & Operating
Costs
We’re going to make
Motors and Turbines
jump through hoops for
you!
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So where do drives live in
Chemical Engineering Land?
They live next to…
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Pumps
Compressors
Fans
Conveyor belts
Crushers
Mills
And many more places…
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Types of Drives
Electric Motor
Steam Turbine
& Many More!!!
Source: http://fsvpix.homestead.com/FSVtodaypix.html
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Drives sub-types
Electric Motors
• Constant Speed:
– A/C Squirrel-Cage
Induction, Synchronous
A/C, etc.
• Variable Speed
– Two-Winding, SingleWinding ConsequentPole, etc.
Steam Turbines
– Condensing, Noncondensing, Automatic
Extraction turbine, etc.
Source: http://www.gi4xsf.freeserve.co.uk/imgen/imgen.htm
A Squirrel Cage Induction
Motor. Squirrels not
included. No, it doesn't run
on squirrels either. 5
Physical Principles
Electrical Motors
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Physical Principles: Electric
Motors:
• The rotor is wound with wire
• Current flows through the wire to create an
electromagnet
•
Motor rotation is achieved through magnetic forces.
Source: http://www.howstuffworks.com/motor3.htm
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Ways the Speed of Electric
Motors are Varied
• Wound-Rotor Induction
Motor
– Efficiency is sacrificed for
controllability
• Gearbox control
– Gear shift to change
rotation speed.
– Discrete Operating Curve
(Step-curves).
– Cheaper
Source: http://www.anaconsystems.com/text/pr11402eagle.html
Source: http://www.bostongear.com/
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How the Wound-Rotor
Induction Motor Works
• Rotor is an electromagnetic (wound with
wires)
• Windings are connected to a slip ring
which is connected to brushes
• Brushes are connected to a resistance
which may be varied
– Reduces current through the rotor
– Reduces magnetic strength of the rotor
– Reduces the speed of the rotor
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How Gearboxes Vary the
Speed of Rotating Equipment
• The shaft coupling connects to the gear
box
• The gear box varies the speed of
rotation with gears of varying diameters
• Smaller gears = larger rotation speed
• Larger gears = smaller rotation speed
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Physical Principles
Steam Turbines
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Physical Principles: Steam
Turbines:
• High Pressure Steam
expands through a
governor valve and a
nozzle.
• Experiences an
increase in velocity
and momentum
• Pushes the impeller
to drive the turbine.
http://home.pacifier.com/~rboggs/HP.GIF
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Methods Varying of Steam
Turbine Speed
• Throttling valve
• Multi-valve
machines
– Basic
– With overload
– With stage valve
Salisbury, K.J., Steam Turbines and Their Cycles.
Krieger Pub. Co., c 1950.
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How Throttling Machines
Work
• Flow controlled by varying valve
position
• Increased steam flow rate results in
greater impeller speed
• Efficiency greatly reduced at low
steam rate
Display
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How Multivalves Machines
Work
• Flow split into smaller diameter pipes and
controlled by on/off valves
• Valves operated in sequence by a camshaft
• When one valve closes flow is reduced
– Resistance across each valve remains constant
• Total pressure drop from feed steam into the
turbine remains constant
• More efficient at low flow rates than throttling
Display
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Physical Principles
Connecting the drives
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Coupling – From Useless
Spinning to Useful Shaft Work
Many coupling types –
Focus on Grid Couplings:
• Horizontal Split Cover
– Small Footprint
– Easily Installed
• Vertical Split Cover
Source: http://www.lovejoy-inc.com/catalog/gd.pdf
– Ideal for High Speeds
• Full Spacer Design
– Extremely useful for pump
applications.
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Coupling Selection Procedure:
Step 1:Determine:
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Mover type(Motor/Turbine Type).
Duty requirements.
Equipment Characteristics (Shaft sizes)
Misalignment – Possible?
Likelihood of excessive vibrations.
Ambient conditions
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Coupling Selection Procedure:
Step 2: Determine Coupling Material Types:
1. Metallic
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Stiff rotation – Light inertial loads
Non-tolerant to misalignment.
High Temperature Applications.
2. Elastromeric
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Soft rotation – High inertial loads
Allows for misalignment
Low Temperature Applications.
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Packing– Preventing fluid
leakage
• Packing = Sealant on shaft bases to
prevent leakage of process fluid and
reduce misalignment, example: O-ring
• Sealant material:
– Must be relatively inert to reaction with
environment and process fluid.
– Low temperature applications: polymeric,
rubbery material
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Troubleshooting
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Troubleshooting Workshop
The efficiency of a turbine in the boiler
house has decreased, and Dave has
observed vibrations. He shuts down the
unit for maintenance and observes
water pooled in the bottom of the
turbine.
What may have happened?
How can the problem be prevented?
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Common Problems with
Steam Turbines
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Vibration
Cycling of the governor
Sticky valves
Temperature bow
Erosion
Excessive rotation speed
Electrostatic discharge
Steam condensation
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Common Problems with
Electric Motors
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Vibrations
Mechanical & Electrical Overload
Short-circuits
Excessive rotation speed
Locked Rotor
Under-Voltage
Sparking
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Trouble-shooting Causes:
Vibrations
Possible Causes:
• Turbine misalignment
• Unbalanced turbine
• Rubbing parts
• Lubrication problems
• Steam condensation
• Settling of the foundation
• Cracked or worn parts
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Troubleshooting:
Causes of
Excessive Rotation Speed
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Mechanical Overload
Steam flows which are too high
Loose gears or loose bearings
Decoupling
Aged gears (worn gears)
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Troubleshooting:
Causes of Equipment
Overload
• Electrical
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Current surge
Short circuit
Rotor sticking
Etc.
• Mechanical
– Excessive steam flow
– Pressure increase in the steam
– Etc.
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Troubleshooting: Sparking
• Charge accumulation
• Poor contacting between the stator and
the rotor
• Short circuit
• Etc.
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Safety
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Safety: Electric Motors
Different area classifications require
different motor enclosures
– Open, drip-proof
– Weather-protected, types I and II
– Totally enclosed motor
Packing & casing around the coupling
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Safety: Steam Turbines
• Slug of water may damage the turbine
– Moisture separator prevents water from
entering the turbine
• Rotor imbalance
• Need to prevent high inlet pressure
• Temperature bow
– Bends the shaft
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Cost and Operating Range
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Operability - Steam Turbines
• Operating Window
– Typically Operate
below 538ºC
(1000 ºF)
– Keep above dew
point of process
fluid.
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Operability – Electric Motors
• Trade-off between
Torque and
Speed.
– Typical motors
have an optimal
point of max.
power between
max torque and
speed.
Source: http://www.airmotors.com/template.cfm?page=1
Power a Torque*RPM
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Capital Cost
• Principal Correlating
Factor:
– Drive Power (bhp).
• Auxiliary Factors:
– Electrical motors:
• Rotation Speed
(RPM),
• Enclosure
Type/Design
– Steam Turbines:
• Pressure (psig)
• Superheat (ºF)
“So, how much would the
squirrel cage induction motor
cost, if we wanted squirrels?”
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Operating Cost:
Factors Affecting the
Operating Cost:
• Electric Motors:
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Price of Electricity
Age of the Motor (efficiency)
Coupling alignment
Bearing wear
• Steam Turbines:
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Cost of Steam
Blade degradation
Coupling alignment
Bearing wear
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When to choose what?
• Requirement: small torque and low flows.
– Electric motors easily fitted into process.
• Requirement: large torque and high flows
– Steam turbines prove to be more efficient.
• Excessive amounts of high pressure steam in
process – Steam Turbines to minimize cost.
• If sufficient budget and steam – build both
and alternate to minimize cost.
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Considerations in Drive
Selection
Steam Turbine
• Pressure and Temperature of steam
available
• Desired pressure and temperature
exiting the turbine
• Steam cost, and turbine efficiency
• Flexibility in turbine speed
• Level of control required
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Considerations in Drive
Selection
Electric Motor
• Cost of electricity
• Required Power
• Efficiency and applications (pump, fan, etc.)
• Time in service
• Required flexibility of speed
• Variable Speed is 4 times more expensive
than single speed (at 3000 hp)
• Maintenance
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References
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Perry, H. Perry’s Chemical’s Handbook, 7th Edition, McGraw-Hill, New York, NY.
c1984.
Salisbury, K. J., Steam turbines and their cycles, Krieger Pub. Co., 1974, c1950.
http://www.lovejoy-inc.com/catalog/m.pdf
http://www.vem-uk.com/1024/frameload.htm?frame2=/1024/products.html
http://www.bostongear.com/
Microchip WebSite, http://www.microchip.com/1010/index.htm
http://www.microchip.com/1010/suppdoc/design/mtrcntrl/menufaq/mtrtypes/
Premium-Efficiency Motors Initiative website,
http://www.cee1.org/ind/motrs/motrs-main.php3
Energy Advisor website, http://www.ladwp.com/energyadvisor/PA_35fig.html
Drive system Inc.website, http://www.drivesys.com/asdis.html
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Multivalve Machine
F1/3
From
Boiler
F1
F1/3
P2
P1
F1/3
F1=F11+F12+F13
1/2
1/2
F1=v1(DP/r) + v2(DP/r) + v3(DP/r)
1/2
Multivalve Machines
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Throttling Machine
From Boiler
P1
P2
F1
F1=v(DP/r)
1/2
Throttling Machine
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Troubleshooting Explanation
• Steam condensing within the turbine.
– A temperature drop in the steam
• Poor insulation
• Reduction in boiler efficiency
• Etc.
– An excessive pressure drop across the
nozzle
• A blockage in the nozzle
• Decrease in inlet steam pressure
• Etc.
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Troubleshooting Solution
• Monitor the steam pressure and
temperature from the boiler
– Increase boiler load if either is too low
• Check and fix the insulation where
applicable
• Monitor the pressure drop into the
turbine
– Clean nozzles and other parts if necessary
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