3. The Basics of Electricity
•The pressure created by that power supply is called voltage.
•Voltage is the pressure applied to the circuit.
•Current is the Flow of the electricity in the conductor.
•Resistance is any restriction to the flow of the current in a conductor.
•Voltage, current and resistance are the three most fundamental components of electricity.
•Voltageis measured in volts,
•currentin amps
•resistancein ohms.
14. E-T-A Elektrotechnische Apparate GmbH
Part 1: General advantages of CBEs
Part 2: 1610/1170 versus Blade Type Fuses
ComparisonFuses vs. Circuit Breakers
15. What is a fuse?
A fuse is a device that protects against damage from excessive current. It contains a short piece of wire made of an alloy that melts readily. The flow of current through a fuse causes the wire to heat up and melts when excessive current passes through the fuse.
This action burns out the fuse and breaks the circuit. It also interrupts the flow of electricity because a fuse is always connected in series with the circuit it protects. A burned-out fuse which is commonly called a "blown" fuse must be replaced for the circuit to function.
ComparisonFuses vs. Circuit Breakers
16. E-T-A Elektrotechnische Apparate GmbH
Different types of fuses
Blade Type Fuses
Glass Fuses
SMT Fuses
Bolt-In Fuses
ComparisonFuse Types
17. CBEs: Usable many times
Fuses: Usable once only
Therefore prices cannot be compared on a one circuit breaker/one fuse basis.
ON -OFFON -OFF .........................ON -OFF ON -OFF ON -OFF ON -OFF ON -OFF ON -OFF ON -OFF ON -OFF ON -OFF
ComparisonFuses vs. Circuit Breakers
18. Convenient resetting of CBEs reduces downtime and service repair costs. There is no need of spares.
And: Risk of using temporary inappropriate substitutes is eliminated, warrenty costs are reduced.
Damned! Has anybody seen a spare fuse!
ComparisonFuses vs. Circuit Breakers
19. Most CBEs have a status indication.
Fuses don‘t!
E-T-A Type 1658
ON
OFF
ComparisonFuses vs. Circuit Breakers
20. Many types of CBEs are usable as ON/OFF switches
Fuses aren‘t!
The E-T-A series 3120is used to switch the grain millON and OFF, at the same time protecting the electric motors from overheating by overcurrents.
Example
ComparisonFuses vs. Circuit Breakers
21. CBEs: No hazard when the circuit breaker is unintentionally switched onto a short circuit.
Fuses: Installing a fuse with the load connected may cause an open intensive arc which is a potential hazard for personnel.
This fuse was plugged in on an existing short circuit. The arc destroyed the terminal block.
ComparisonFuses vs. Circuit Breakers
22. Many CBEs are available with auxiliary contacts.
Fuses aren‘t!
E-T-A 2210-S with two integral auxiliary contacts
Terminals of the auxiliary contacts
ComparisonFuses vs. Circuit Breakers
23. CBEs: Well adjusted to the load,
even in the event of high inrush
currents from capacitors and
motors.
Fuses: Trip upon inrush currents;
otherwise a higher current rating,
possibly requiring a larger wire
size, must be used, in which case
protection from low overloads is
no longer ensured
Diagram of start-up current of an
unloaded asynchronous motor
Diagramm: E-T-A Laboratory
24. Reset button / status indication
Manual release buttonwith colour coding
ComparisonFuses vs. Circuit Breakers
34. Medium-voltage circuit breaker can be classified by the medium used to extinguish the arc:
•Vacuumcircuitbreaker
•Aircircuitbreaker
•SF6circuitbreakersextinguishthearcinachamberfilledwithsulfurhexafluoridegas.
38. APPLICATIONS
B Type For protection of Resistive loads such as bulbs, heaters etc.
C type For protection of Inductive loads such as motors, air conditioners etc.
D type For protection of Cables and highly inductive loads which have high starting current such as transformers.
39. OVERCURRENT RELAY
•FUNCTION -The overcurrent relay is used to protect motors in case of:
•-Prolonged Overcurrent (105 to 125% Full Load Current)
•-Phase Unbalance
•-Phase Loss
44. Transformer Operation
Primary coil is supplied with a AC voltage.
Current drawn produces a magnetic field
Magnetic field transported to a secondary coil via a magnetic circuit
Magnetic field induces a voltage in secondary coil
V+
V+
53. Why do we laminate the core?
I
S
Large Number of flux lines cut
High voltage generated across core
Eddy currents are large & losses are great
54. Why do we laminate the core?
I
S
Small Number of flux lines cut
Low voltage generated across core
Eddy currents are small & losses are reduced
55. Losses due to Eddy Currents
2
e e m 1 P K f B t
Pe
Ke
F
Bm
t1
= losses in W/m3
= Constant
= Frequency
= Maximum Flux density
= Lamination thickness
57. Steel Types
Silicon steel is used for laminations
Silicon content 0 –6.5%
Why Silicon?
•Small hysteresis curve area
•Increases electrical resistivity
Reduced eddy current size
•Hardened grain structure
•Reduced workability
•Very low carbon levels <0.005% are called for or magnetic ageing will take place
Losses will increase with age
•Carbon can be removed by annealing in a hydrogen rich atmosphere
58. Grain Orientation
•Optimum properties are developed in the rolling direction
•Magnetic density is increased by 30% in the coil rolling direction
•Magnetic saturation is decreased by 5%
•Given codes such as M-0, M1, M-2, M-3, M-4 and M-6
•Similar magnetic properties in all directions
•less expensive
•Used in applications where the direction of magnetic flux is changing (motors and generators)
•Given codes from M-15 to M-47
Non-orientated
59. Grain Size
The larger the grain the less the hysteresis losses
2-10 W/kg @ 60 Hz and 1.5 tesla magnetic field strengthare common with a 150μm grain size
heat treatment increases the average crystal size
Excessive bending, incorrect heat treatment, or even rough handling of core steel can adversely effect its magnetic properties
60. Amorphous Steel
losses up to 30% of conventional steels
Made by pouring molten alloy steel on a rotating cooled wheel.
•high cost (about twice that of conventional silicon steel)
•lower mechanical properties
This cools the metal so quickly that crystals do not form
61. Lamination Coatings
•Increase electrical resistance between laminations
•Provide resistance to corrosion
•Act as a lubricant during die cutting
•Can be organic or inorganic (such as Magnesium oxide)
•Dependant on the heat treatment of the laminations
•Wheather it is immersed in oil
•The working temperature of the finished item
62.
63. Magnetostriction
A property of ferromagnetic materials that causes them to change their shape when subjected to a magnetic field
losses due to frictional heating
first identified in 1842 by James Joule
When a magnetic field is applied, the boundaries between the domains shift and the domains rotate, both these effects causing a change in the material's dimensions
The effect is responsible for the familiar "electric hum"
64. Winding types
•Three types?
•Magnetic leakage
Concentric
Higher voltage closest to Iron
70. Introduction
•In this lecture we consider various forms of rotating electrical machines
•These can be divided into:
•generators–which convert mechanical energy into electrical energy
•motors–which convert electrical energy into mechanical energy
•Both types operate through the interaction between a magnetic field and a set of windings
23.1
75. 75
Electric Motor Basic Principles
Interaction between magnetic field and current carrying wire produces a force
Opposite of a generator
Kelvin Peng
76. 76
2 pole brushed DC motor commutation
Kelvin Peng
78. 78
Conventional (Brushed) DC Motors
Permanent magnets for outer stator
Rotating coils for inner rotor
Commutation performed with metal contact brushes and contacts designed to reverse the polarity of the rotor as it reaches horizontal
Kelvin Peng
85. Introduction
•Three-phase induction motors are the most common and frequently encountered machines in industry
•simple design, rugged, low-price, easy maintenance
•wide range of power ratings: fractional horsepower to 10 MW
•run essentially as constant speed from no-load to full load
•Its speed depends on the frequency of the power source
•not easy to have variable speed control
•requires a variable-frequency power-electronic drive for optimal speed control
86. Construction
•An induction motor has two main parts
•a stationary stator
•consisting of a steel frame that supports a hollow, cylindrical core
•core, constructed from stacked laminations (why?), having a number of evenly spaced slots, providing the space for the stator winding
Stator of IM
87. Construction
•a revolving rotor
•composed of punched laminations, stacked to create a series of rotor slots, providing space for the rotor winding
•one of two types of rotor windings
•conventional 3-phase windings made of insulated wire (wound-rotor) » similar to the winding on the stator
•aluminum bus bars shorted together at the ends by two aluminum rings, forming a squirrel-cage shaped circuit (squirrel-cage)
•Two basic design types depending on the rotor design
•squirrel-cage: conducting bars laid into slots and shorted at both ends by shorting rings.
•wound-rotor: complete set of three-phase windings exactly as the stator. Usually Y-connected, the ends of the three rotor wires are connected to 3 slip rings on the rotor shaft. In this way, the rotor circuit is accessible.
89. Construction
Cutaway in a typical wound- rotor IM. Notice the brushes and the slip rings
Brushes
Slip rings
90. Rotating Magnetic Field
• Balanced three phase windings, i.e.
mechanically displaced 120 degrees
form each other, fed by balanced
three phase source
• A rotating magnetic field with
constant magnitude is produced,
rotating with a speed
Where fe is the supply frequency and
P is the no. of poles and nsync is called
the synchronous speed in rpm
(revolutions per minute)
120 e
sync
f
n rpm
P
101. •Other Motor Protection Devices
•Low Voltage Protection
•Phase Failure Protection
•Phase Reversal Protection
•Phase Reversal Protection
•Ground Fault Protection
102. •Other Motor Protection Devices
•Bearing Temperature Monitors & Protection
•Winding Temperature Monitors & Protection Devices
•Current Differential Relays (Phase Unbalance)
•Vibration Monitors & Protection
103. A Simple AC Generator
• We noted earlier that Faraday’s law dictates that if a
coil of N turns experiences a change in magnetic flux,
then the induced voltage V is given by
• If a coil of area A rotates with respect to a field B, and
if at a particular time it is at an angle to the field,
then the flux linking the coil is BAcos, and the rate of
change of flux is given by
23.2
t
Φ
V N
d
d
cos cos
d
d
d
d sin
t t
BA
dt
dΦ
104. • Thus for the arrangement shown below
t
Φ
V N
d
d
cos
d
d sin
d
d
NBA
t
NBA
t
Φ
V N
106. Relay Single Pole SinglThrow (SPST) is
the simplest with only two
contacts. Single Pole Double
Throw (SPDT) has three
contacts. The contacts are
usually labeled Common (COM),
Normally Open (NO), and
Normally Closed (NC)
107. Summary
In this course, we discussed:
•Common electrical hazards
•Standards relating to those hazards
•Electrical equipment defects/hazards
•Tools/techniques used in identifying hazards
