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Diagrams using Triac 15 1.5.The structure of resistance furnace 16 Chapter 2: Introduction of 3-phase AC voltage regulator circuit 17 2.1.. Advantages of electric furnace compared to fur

ELECTRIC POWER UNIVERSITY

DEPARTMENT OF CONTROL ENGINEERING AND

NGUYỄN QUANG HUY BÙI XUÂN HUY

HA NOI, 12/ 2020

ELECTRIC POWER UNIVERSITY

DEPARTMENT OF CONTROL ENGINEERING AND

NGUYỄN QUANG HUY BÙI XUÂN HUY

HA NOI, 12/ 2020

COMMENT (Of instructive lecturer)

Ha Noi, day month year 202

The lecturer

COMMENT

(Of review lecturer)

Ha Noi, day month year 202

The lecturer

INTRODUCTION

Since ancient times, people have known how to create fire -an invention using heat has greatly influenced the development history of mankind Having a method

of creating fire that allows people to heat, cook food and craft objects, and weaponagainst other animals, is a stepping stone for humans to move forward a newcivilization Today, in the 21st century, in addition to the basic applications of heat,people have researched to bring heat energy into industry and production, heatenergy can be used to heat, dry, process waste Therefore, the use of this energysource rationally and effectively is essential The resistance furnace is widely used

in industry because it meets many practical requirements In a resistance furnace,the most important technical requirement is the adjustment of the furnacetemperature This is also the power electronics project that we are choosing toresearch The project was done under the enthusiastic guidance of teacher NguyenDuy Trung to help us complete this project The project is divided into thefollowing three main parts

1. Brief introduction about structure and operating principle of electric furnaceand furnace resistor

2. Circuit design and calculation

Chapter 1: Overview about the structure and operating of resistance furnace

1

1.1. Introduce about the electrical furnace 1

1.1.1 Definition 1

1.1.2 Advantages of electric furnace compared to furnace using fuel 1

1.1.3 Disadvantages of electric furnace 2

1.1.4 Classificationresistance furnace 2

1.2. Working principle of resistance furnace3

1.3. The structure of resistance furnace4

1.3.1 Funace cover 5

1.3.2 Lining 6

1.3.3 Heating wire 7

1.4. Some diagrams control resistance furnace 13

1.4.1 Diagram using Thyristor 13

1.4.2 Diagrams using Triac 15

1.5.The structure of resistance furnace 16

Chapter 2: Introduction of 3-phase AC voltage regulator circuit 17

2.1 Three-phase AC voltage regulator circuit 17

2.2 The relationship between control angle and load power 18

Chapter 3: Calculate and design power circuit 23

3.1 Selection semiconductor valve 23

3.2 Design the power circuit 27

3.2.1 Overcurrent protection 27

3.2.2 Overvoltage protection 28

Chapter 4: Design and calculate control circuit30

4.1 Operating principle of control circuit 30

4.2 Principle of control 30

4.2.1 The principle of linear vertical control 30

4.2.2 “Arccos” vertical control principle 31

4.3 Control circuit 31

Chapter 5: Simulation in Psim 9.0 and Conclusion41

5.1.Simulation in Psim 41

References document

Chapter 1: Overview about the structure and operating of resistance

Electric furnaces are widely used in technical fields:

- Producing high quality steel

- Production of fero alloys

- Heat treatment and chemical heat treatment

- Igniting items before rolling, forging, and spinning

- Producing casting and powder metal

In other industrial sectors:

- In light industry and food, electric furnaces are used to manufacture andplating articles and prepare food

- In other fields, electric furnaces are used for the production of hydroproducts glass, ceramics, refractory materials, etc

Electric furnaces are not only present in industries but also increasinglypopularly used in human daily life in a stylish way rich and diverse: electriccookers, rice cookers, electric water heaters, solidifying equipment, electric dryingetc

1.1.2. Advantages of electric furnace compared to furnace using fuel:

Electric furnaces have the following advantages:

- Able to create high temperatures

- Ensuring large heating speed and high productivity

- Ensuring even and accurate heating due to easy adjustment of electric modeand temperature

- Sealed

- Ability to mechanize and automate the process of material loading andunloading shipping items

- Ensuring hygienic working conditions, good working conditions, andcompact equipment

1.1.3. Disadvantages of electric furnace:

- Electric energy is expensive

- Requires a high level of qualifications to use

1.1.4. Classificationresistance furnace

• Classification according to the method of heat emission:

- Direct-acting resistance furnace

- Indirect-acting resistance furnace

• Classification by working temperature:

- Low temperature furnace: the working temperature of the furnace is below

- Average furnace: the working temperature of the furnace is from to

- High temperature furnace: the working temperature of the furnace is over

• Classification by place of use:

- Furnaces used in industry

- Furnaces used in the laboratory

- Furnace for household use

• Classification according to the working characteristics:

- The Furnace works continuously

- The furnace works interrupted

Figure 1.1: Graph of operating temperature of the resistance furnace

• Classification according to furnace structure:

- Chamber-shaped furnace

- Well-shaped furnace

1.2. Working principle of resistance furnace

The resistance furnace works on the basis of when an electric current ispassed through a wire or the conductor there would emit some heat according toJoule-Lenz law:

In this formula:

- Q: Heat amount in joules (J)

- I: Current in Amperes (A)

- R: Resistance is in Ohm(

- T: Time in seconds (s)

From the above formula we see resistor R can play the role: burning object(in this case, it is called direct heating) or line heating (when the wire is heated itwill transfer heat to the object heated withradiation, storage, heat orthermosynthesis This school is call is indirectly heating)

The first case is uncommon because it only uses dikes to heat single-shapedobjects simplified (cross-section of a rectangle, square and circle)

The second one is much more pcommon in industrial practice, so when wetalk about resistance furnace we need mention to the material of the heating wire-the part heat emission of furnace

Figure 1.2: The principle of the furnace is to heat directly and indirectly

1.3. The structure of resistance furnace

Conventional resistance furnaces consist of three main parts: the furnace cover,the lining and the heating wire

Figure 1.3: Picture of well-shaped resistive furnace

Figure 1.4: Structure of well-shaped resistive furnace

1.3.1. Furnace cover:

The resistive furnace shell is a rigid frame that mainly assists the load in theprocess furnace working On the other hand, the furnace also uses a dyke to keepthe insulation loose and secure Complete or relative sealing of the furnace Forfurnaces that work with protective gases, it is necessary that the furnace shell becompletely sealed for normal resistive furnaces, furnace shell closure only requiresreduction of total heat loss and avoid the draft of cold air into the furnace,especially along the height of the furnace In specific cases, the resistance furnacecan cause the furnace cover to be uncovered The furnace shell should be strongenough to withstand the load of the lining and the furnace load (object furnace) andmechanical devices mounted on the furnace shell

- Rectangular furnace shell is usually used in chamber furnace, continuousfurnace, vibrating bottom furnace, etc

- Round furnace shells are used in well furnaces and some cover up furnaces,etc

- Round furnace shell withstand the internal impact better than rectangularfurnace shell when the same amount of metal to manufacture furnace shell.When the furnace shell is structured round, steel is often used thick sheet 3

to 6 mm when the diameter of the furnace shell is 1000-2000 mm and 8 - 12

mm when the road furnace shell glass is 2500 - 4000 mm and 14 - 20 mmwhen furnace shell diameter is about 4500 - 6500 mm

When it is necessary to increase the rigidity of the round furnace shell, washersare used strengthened with shaped steels The casing is built up using U, L shapedsteel and shaped steel plate suitable shape The furnace shell can be sealed, maybenot depending on the requirements of the furnace The processing method of thisfurnace shell is mainly welding and canopy

1.3.2. Lining

The resistance furnace lining usually consists of two parts: a refractory and aninsulating material The refractory part can be constructed of standard bricks,shaped bricks and special shaped bricks according to the shape and size of thefurnace chamber Sometimes peoplecompacted with refractory powders andadhesives called compaction blocks Compressed block can be done in the furnaceand can also be done externally through the molds

The refractory part should meet the following requirements:

- Withstand the maximum working temperature of the furnace

- Has a large enough heat resistance when working

- Having enough mechanical strength when loading the object and placing thetransporting equipment in the thing working condition

- Ensure the ability to attach durable and firm heating wire

- Having enough chemical resistance when working, withstand the effects ofgas and gas influence of the heating object

- Ensures the ability to positively heat negatively This is especially importantfor the furnace work cycle

The insulation is usually between the furnace shell and the refractory part.Master purpose of this section is to reduce heat loss Particularly for the bottom,the insulation requires must have a certain mechanical strength and the other partsgenerally do not require.

The basic requirements for insulation are:

- Negative thermal conductivity

- The ability to minimize heat

- Stable on physical and thermal properties under specified workingconditions

The insulation can be built with insulating bricks, which can be filled withpowder insulating heat

1.3.3. Heating wire

Figure 1.5: Some basic parameters of the wire material

Requirements of heating wire material:

- Resistant to high temperatures

- Great mechanical strength

- Having large resistivity (because the small resistivity will lead to long wiresdifficult to arrange in the furnace or the wire section is small, not durable)

- Coefficient of thermistor is small (because the resistance will change withtemperature, to ensure the life of the furnace)

The material for the incinerator can be:

- Cr-Ni, Cr-Al alloys with furnaces working temperature below

- Compounds: SiC, MoSi with the furnace with working temperature of

Monolithic Mo, W, C (graphite) with furnace with working temperaturehigher than

Resistor wire size calculation: Starting from furnace capacity, we calculate thefurnace capacity consumed from the grid

Productivity of furnace:

- ,: the initial and heating temperature of the heater.

Useful capacity of the furnace:

- k: the reserve factor, taking into account the voltage drop in the network, theresistor due to aging increase.

k = 1,2 ÷ 1,3 for continuous working furnaces

k = 1,4 ÷ 1,5 for cyclical furnaces

From the P power, an approximate single-phase incinerator power density can

be calculated That is the possibility heating of a wire per unit of time per wiresurface area

With:

- m: number of phase

- : surface area (surrounding area) of single-phase incinerator []

From the capacity of the furnace, the size of the incinerator to be fitted can becalculated With an oven with numbers symmetrical phase, the power of the phasewill be:

On the exothermic relation, the combustion wire capacity level across the

surrounding area so:

With:

- L: length of heating wire (m)

- C: heating wire circumference (m)

On the relation between electrical parameters:

(1)

Inferred:

With: S is area of the incinerator cross section, [m2]

Balance (1) and (2), we have:

The left hand side of the (3) is the wire size parameters The first factor of the rightside is s electrical parameters, the following factor on the right side tells the wire's thermal relationship The furnace wire used in the resistance furnace may have a circular or rectangular cross-section and the size shown in table 1:

Working temperature in furnace

(0C)

Size of heating wire (mm)

Round wire(diameter d)

Rectangular wire(size a.b), (m = )

(2)

(3)

1100-1200

123-44-56-77-8

Table 1: The cross section of the wire is used in the resistance furnace

Instead of (3) and find d, we have:

With rectangular wire:

Instead of (3) we have:

And b = ma; usually m = 5 ÷ 15

1.4. Some diagrams control resistance furnace

1.4.1. Diagram using Thyristor

 Diagram of the star load using thyristor with neutral

- Advantages: The voltage across the semiconductor valves is smaller than theother scheme because the voltage applied to the semiconductor valve is thephase voltage.

- Disadvantage: This diagram is on the neutral wire having high orderharmonic current, when the opening angle of the valve differs from zerowith interrupt load current and this type of connection scheme is onlysuitable for the load type Three-phase has four output terminals

Figure 1.7: Diagram of the star load using thyristor with neutral

 The diagram of the star connection using the thyristor non-neutral

- Disadvantage: Here the current flows between the phases together, so at thesame time must supply the control pulse for two thyristors of two phases atonce The supply of control pulses like that, double During difficultclamping in the circuit, even switching of mains phase order is possiblemake the schematic not work

Figure 1.8: The diagram of the star connection using the thyristor

non-neutral

 Triangular load diagram using thyristor

- Advantage: The number of semiconductor valves in all modes will decrease.Simplifies control signals Are not Wide or pulse control pulse requiredconfirmed to ensure the operation scheme Just 1 single pulse is enough

- Disadvantage: However, if the triangle connected Thyristor will have themaximum opposite voltage to bear is from 1.5Vm to 3Vm

Figure 1.9: Triangular load diagram using thyristor

1.4.2. Diagrams using Triac

 Triac loading star diagram with neutral

Similar to the diagram of the star load using 2 neutral connection thiristors.Advantages in terms of symmetrical controls and simplified pairing.

Figure 1.10: Triac loading star diagram with neutral

Similar to the diagram of the star connection using 2 thyristors connectedopposite without neutral Advantages in terms of symmetrical controls andsimplified pairing

Figure 1.11: Non-neutral triac load star diagram

Similar to the diagram of the star connection using the triangular connectionthyristor Advantages in terms of symmetrical controls and simplified pairing

Figure 2.6: Triangular load diagram using Triac

1.5. Selection of AC voltage regulator

With the non-neutral star dynamic circuit, current flows on the line with theline so the control is like a single-phase regulator so the control circuit is simple

So we choose the scheme: 3-phase voltage regulator using thyristor without neutralwith the star load:

Figure 2.2: The diagram of the star connection using the thyristor

non-neutral

Chapter 2: Introduction of 3-phase AC voltage regulator circuit

2.1. Three-phase AC voltage regulator circuit

Furnace loading capacity:

So to change furnace capacity need to change Uf or Rt In practice to change theoutput power of the load we often use to change Uf When there is an AC source,

in order to be able to change the voltage on the load we can use an alternatingvoltage regulator using a semiconductor valve Adjusting the output voltage on theload is similar to rectifiers, i.e changing the valve opening point compared to thezero voltage of the supply voltage, so this is also called the phase control method(changing the valve opening angle )

Because the diodes only direct the one-way direction, but the output voltagerequires AC, so k uses diodes instead of triac, but triac cannot control the openingangle of the valve, so we replace with thyristors connected in parallel

Valves T1, T2 in turn lead the current in one direction to determine the currentthrough thyristo pairs is alternating The thyristor valves are pulsed with 180degrees difference to ensure that the current through the valve pair is perfectlysymmetrical

In industrial practice, the ac voltage regulator circuits all use the star load ordelta load 3-phase AC voltage regulator circuits

Figure 2.1: Graph of output voltage form of a resistive load alternating voltage

regulator circuit

2.2. The relationship between control angle and load power

Furnace loading capacity:

Where I is the r.m.s.value of the load current This current varies according to 2

of the following 3 rules

- If each phase has a conductor (or the whole circuit has 3 valves)

- If there are only two spouts (or the whole circuit has 2 valves)

With: is line voltage amplitude

is phase difference angle between voltage and current at time review

• Conductive range with α = 0÷60: In this range there will be periods with

3 valves and 2 pilot valves alternating

Based on the graph, we can determine the relation between load output power

P and control angle :

• Conductive range with α = 60÷90

There are always only two valves in this range