9ee605a.13to141 department of technical education andhra pradesh name:v. narsimha reddy...
TRANSCRIPT
9EE605A.13to14 1
Department of Technical Education
Andhra PradeshName : V. Narsimha Reddy
Designation : Lecturer in EEE
Branch : D.E.C.E
Institute : GMR. Polytechnic Gajwel
Semester : VI Semester
Subject : Electrical Utilization & Automation
Code : EE605 A
Topic : Electric Heating
Duration : 100 Minutes
Sub topic : Methods of Temperature control
Teaching Aids : PPT, Diagrams, Animation
Revised By : K. Chandra Sekhar, L/EEE, GPT, HYD
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Recap
In the previous class you have learnt about
• Resistance heating
• Classification of resistance heating
• Applications of resistance heating
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ObjectivesObjectives
On completion of this topic ,you would be able to know
• Different methods of temperature control of resistance heating
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Temperature Control of Resistance Heating
• In resistance heating supply voltage and resistance of heating elements are independent parameters
• Current is a dependent parameter• The temperature of resistance furnace is
controlled by • Supply voltage• By varying the number of heating elements• Switching ON and OFF the supply
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Temperature Control Methods
Temperature control of resistance heating
Periodically switching on & off of the power
supply
By varying supply voltage
By varying resistance
By variable supply
By Auto-T/F or
Induction regulator
By series impedance
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Temperature Control Methods
Temperature control of resistance heating
Periodically switching on & off of the power
supply
By varying supply voltage
By varying resistance
By varying the number of
heating elements
By changing the
arrangement & heating
elements
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By Variable Supply Voltage
• If the furnace has separate generating set for electric
power supply, then variable voltage can be generated and
supplied to the furnace depending upon the temperature
• Voltage can be variable
• This is usually employed for large capacity furnace
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By Auto-transformer or Induction Regulator
V1=Primary side supply voltage.V2=Secondary output voltage.I1=Primary currentI2=Secondary current.
Fig.1
• FURNACE
• 4
• 3
• 2
• 1
• Supp
• l• y
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By Auto-transformer or Induction Regulator
• Fig 1 shows an auto - transformer
• By changing the position of the tap the voltage supplied to heating element will change and accordingly the temperature
• Supp
• l• y
Fig.1
• FURNACE
• 4
• 3
• 2
• 1
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1 – Phase Induction Regulator
• Fig 2 shows a single
phase induction regulator
• By changing the position
of rotor (primary) the
output voltage v2 will
change
• The change controls the
furnace temperature
Fig 2
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By Series Impedance
• A variable impedance will be connected in series with the furnace
• A part of voltage drop across the impedance included and the remaining voltage appears across the furnace
• Due to inclusion of impedance of the coil,the power factor reduces
• A capacitor is connected across the supply to improve the power factor i.e., Dotted Lines
Fig.3
• Supp
• l• y
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By Varying The Number of Heating Elements
• In this method the number of heating elements are changed by operating the switches shown in fig 4
• if the supply is reduced to all/few elements, the temperature also reduces and vice-versa.
Fig.4
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By Varying The Number of Heating Elements
• The number of heating elements are changed by
operating the switches shown in fig 4
• Each element is provided with one switch in fig 4 (a)
• One switch controls three elements in fig 4(b)
• If the supply voltage is reduced to few / all elements the
temperature reduces and vice – versa
• Non uniform heating taken place
• If uniform heating is required the even or odd number
elements should be switched off in fig 4 (b)
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V
V/2 V/2
V/4 V/4 V/4 V/4
V
V
Four parallel paths Two parallel paths
one parallel path
By Changing The Arrangement of Heating Elements
Fig.5
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By Changing The Arrangement of Heating Elements
• Fig 5 (a) shows the
arrangement of four
heating elements for a
single phase supply
• All the elements are in
parallel, the heat
produced will be equal to
ratingFig 5 (a)
V
Four parallel paths
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By Changing The Arrangement of Heating Elements
• If four elements are
arranged in two paths
shown in fig 5 (b)
• The heat produced will be
one – fourth
• Because the voltage
across each element is
v/2
Fig 5 (b)
V
V/2 V/2
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By Changing The Arrangement of Heating Elements
• If all four elements are
arranged in series shown
in fig 5 (c)
• The heat produced will be
one – sixteenth
• Because the voltage in
each element is v/4 Fig 5 (c)
V/4 V/4 V/4
V
V/4
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By Changing The Arrangement of Heating Elements
• Fig 6 shows circuit configuration for 3 phase system
• When the same elements are changed from delta to star, the power consumption reduced to one - third
Fig.6Connected in star Connected in delta
Three-Phase System
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Periodically / Intermittent On / Off
Final temperature α Time interval the switch remains ON Total time interval of the
ON/OFF cycle.
• The ON and OFF arrangement can be had by a thermostat switch.
• Which switches ON and OFF the supply at predetermined temperatures.
• Final temperature attained is proportional to ratio.
• The method is more efficient than series impedance method.
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Summary
In this class we have discussed about
• Methods of temperature control of resistance heating
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Quiz
1. When four elements connected in parallel produce heat
energy equal to the furnace. If the same four elements
are arranged in two paths then the heat produced will
be__________ that of the rated value.
a. Half
b. One-fourth
c. One-sixteenth
d. Equal
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Frequently Asked Questions
1) List the methods of controlling the temperature in resistance heating.
2) Explain the Auto T/F method of controlling the temperature.
3) Explain the method of controlling the temperature by varying the number of elements