Supply Power To A Fluorescent Lamp Engineering Essay

The following report contains the steps taken in designing, constructing and testing of a basic electrical system used to supply power to a fluorescent lamp. This report summarizes the method used to calculate the desired circuit parameters. Also, the design was implemented to achieve the required design objectives.

INTRODUCTION

An engineering approach was used in this design project and as such, it consisted the design, construction and testing of a basic electrical system used to supply power to a fluorescent lamp. The power factor of the system needed to be corrected to increase efficiency and this was explained in detail. Due to the high level of risk involved in this design project, precautions needed to be taken. Laboratory protocol, industry standards, codes of practice and occupational safety protocols was taken into account during this design project.

Course material from ECNG 1015 – Introduction to Electrical Energy Systems, ECNG 1006 – Laboratory and Project Design I and ECNG 1016 – Mathematics for Electrical Engineers was used in this design project.

In this report, all necessary mathematical models, and diagrams will be detailed. Also, the steps used to improve the power factor of the relay system will be accounted for as well as the main processes implemented in the system.

Background Theory

What is a fluorescent lamp? According to Sam’s F-Lamp FAQ, fluorescent lamps are a type of discharge tube similar to neon signs and mercury or sodium vapour street or yard lights.

The Different Types of Fluorescent Lamp Fixtures

There are basically three different types of fluorescent lamp fixtures. The three most used fixtures are listed as follows;

1. Instant Start

2. Rapid Start

3. Preheat fixtures.

Instant start

Instant start fixtures require a high voltage to be applied to the lamp to cause it to work. This high voltage must be above the specified voltage required for the lamp to light. This high voltage is required since the resistance of the gas may be high. Thus, the voltage being applied will force the gas to conduct and hence light. Sometimes, a potential difference is required to create a potential difference between instant start fixture and the lamp cathodes. This potential difference causes ionization to occur and this reduces the resistance of the lamp.

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The initial current which flows through the lamp causes the light to shine at maximum brightness. After the lamp turns on, the instant-start ballast will immediately regulate the voltage and current to the operating conditions of the lamps. OR Once current starts flowing through the lamps, the lamps illuminate at close to their full brightness. After a successful start, the instant-start ballast will immediately regulate the voltage and current down to the normal operating levels (QUOTE).

The average lamp life of an instant-start fixture is much shorter than that of a rapid start fixture. This is due to the fact that the instant-start fixtures use more energy than a rapid start fixture. It is also more efficient as it has a very efficient ballast. Caution must be used with respect to instant-start lamps in areas which utilizes occupancy sensors.

Rapid start

Rapid start is the name given to fluorescent fixtures with two or more lamps. When using this type of system, no starter switch is available for use. The ballast is used to maintain a steady current flow in the lamp at all times. In order for the lamp to start, a capacitor is used to ionize the gas, hence reducing the resistance of the flow of the gas.

The ballast allows the current in the lamp to flow when the gas is ionised. This current flow causes the lamp to glow dimly and also heats the gas. This heating of the gas generates light and this light is used to further ionize the gas. The ballast is also used to increase the start up process of lighting the bulb. All these process aid in decreasing the resistance of the gas and increasing the current flowing through the lamp. As brightness of the bulb can be thought of as directly proportional to the current flow. When the arc discharge occurs, the lamp is turned on and light is produced. However, the light given off wouldn’t be as bright since it takes a certain amount of time to ionise the gas. Hence, a couple of seconds would be required to achieve maximum brightness.

Applications that require constant turning on/off are best suited with rapid start lamps. Their long life and their ability to dim when required make them ideal for certain applications. However, these lamps consume power even when the filaments have burned out.

Preheat fixtures

A preheat fixture lamp is utilized in this project. Preheat fixtures usually consist of a starting circuit which allows current to flow through the cathodes to warm the filaments. A high voltage is sent through the tube and this creates an arc across the mercury vapour. This results in the atmosphere inside the tube to heat up and thus, electron activity from the gas increases. The electrons move rapidly through the tube and they carry the current as they move. The starter switch opens when the circuit is preheated for a short period of time (Henkenius, 2007).

Preheat fixtures are preferred as they use low cost performance phosphors. In using pre heat fixtures, the electrodes are damaged faster than other fixtures resulting in shorter life span. The type of ballast used in pre heat fixtures is either magnetic or resistive. It is recommended to avoid the use of pre heat fixtures as the maximum energy is not used.

Existing Types of Fluorescent Tubes

The following are some of the different types of fluorescent tubes;

T-5 – This type of fluorescent lamp is extremely powerful. It boasts low maintenance, low disposal costs and it allows for smaller fixtures to be used. These types of lamps have an average life of 35,000 hours based on 12 hours per start.

T-8 – This type of fluorescent lamp is used mainly for its sustainability. It boasts long life, a low level of mercury and it is energy efficient. The Philips T8 32W Extra Long life lamp and the Philips T8 25W will on average last longer than a standard 4’T8 32W lamp.

T-12 – This type of fluorescent lamp provides long life and high performance. It also comes in different sizes, shapes and types. An average life of 24,000 hours, 85 CRI and the highest lumen output are the features of this lamp.

T-16 – This type of fluorescent lamp is usually 60 inches long and has a diameter of 2 inches. A starter is needed for this type of lamp as it is a preheat lamp.

NEOLITEâ„¢ low-mercury – This type of fluorescent lamp is arguably one of the smallest fluorescent lamps ever made. This NEOLITEâ„¢ low-mercury lamp has an average life of 10,000 hours and its brightness is rated at 70 lumens per watt.

Dim Lights – This type of fluorescent lamp can be dimmed to about 20% of their full brightness. Thus, this type of lamp is considered an energy saver.

Circle Tube – This type of fluorescent tube uses a 4-pin connector. It is on average 8 to 12 inches in diameter.

U-tube – This type of fluorescent tube is shaped like a “U” as it name suggests. A tube which is bent into this U shape is much brighter than a normal tube of similar dimensions.

Requirements for the Operation of Fluorescent Lamps

The principles of operation of the system gave insight into some of the requirements needed for the operation of fluorescent lamps. These requirements are;

An electrical current is required to flow through the tube to power the system.

A ballast is required which controls the current flowing through the system and it provides the ‘voltage kick’ which creates the arc in the tube.

A starter switch is needed to turn on/off the system. Turning off the system cuts the current flowing to the ballast, hence turning the lamp off.

A relay is needed as its contacts control whether the circuit is open or close. In works together with the starter switch to control the lamp.

Advantages and Disadvantages of Different Systems

The Ballast

The ballast is considered one of the most important components of a fluorescent lamp, as it is used to start the lamp. Also, the current flowing through the circuit is controlled by the ballast as it regulates current flow. The ballast is extremely important in the circuit, as it corrects the power factor which increases the efficiency of electrical power consumption (quote). A fluorescent lamp without a ballast is considered a short circuit. Thus, there is a lot of current between the filaments and this causes the filaments to vaporise or the bulb to explode. Thus, the ballast can be seen as a core component in the fluorescent system.

There are typically two types of ballast used in fluorescent lamps. They are listed as follows;

Inductive Ballast

Electronic Ballast

Inductive Ballast

An inductive ballast connected with a starter is considered a series inductor. This type of ballast provides an inductive kick to jump start the lamp. This occurs when the current flowing through the ballast is interrupted. When this happens, a voltage is provided across the cathodes which are used to ionize the gas in the tube hence keeping the filaments hot.

According to www.infralight.com.au/ballasts.html, the inductive ballast has two benefits. They are listed as follows;

Its reactance limits the power available to the lamp with only minimal power losses in the inductor

The voltage spike produced when current through the inductor is rapidly interrupted is used in some circuits to first strike the arc in the lamp.

There are however disadvantages of using an inductive ballast. They are listed as follows;

The life span is significantly reduced

An “A” rated ballast will hum softly while a “D” rated ballast will hum loudly. According to www.freepatentsonline.com/y2008/0019113, the number of ballasts and their sound rating determines whether or not a system will create an audible disturbance which an inductive ballasts does.

Excessive heat is produced when in use

Electronic Ballast

According to www.ehow.com/about_6131466_electric-ballast-definition, An electrical ballast is a device that is used in gas discharge lighting systems to regulate the flow of current and to provide adequate voltage for the lights to function properly. The electronic ballast is typically preferred because it is more efficient than an inductive ballast. Furthermore, an inductive ballast requires a starter switch, less heat is lost, lamps do not flicker as often and the overall dimensions are smaller.

However, the electronic ballast has its disadvantages. When it is used in parallel, there is an increase in losses within the circuit. Sometimes, odd current waveforms are drawn due to a high current. Also, there is interference from the ballast and tubes in the circuit.

The electronic ballast is not used in the pre heat fixture system. Thus, it would have no effect in this design as an inductive ballast will be used.

Operation of the System

Inside a glass tube, there exists a pair of electrodes, a drop of mercury and some inert gas sealed at an extremely low pressure. The electrodes are sealed at each end of the tube. The electrodes are in the form of filaments which for preheat and rapid or warm start fixtures are heated during the starting process to decrease the voltage requirements and remain hot during normal operation as a result of the gas discharge (Goldwasser, 1999). The inert gas is usually argon. Phosphorous material line the inside of the tube. This material is used as it produces visible light due to ultra violet radiation upon it.

A relatively high voltage is required to initiate the discharge of the mercury/gas mixture. After this discharge, a relatively lower voltage is required to maintain it. The current which flows to the electrodes creates a voltage which acts across the electrodes. The electrons in the electrodes disperse from one side of the tube to the other. These excited electrons create energy and this energy changes some of the mercury to a gas. Electrons from mercury are special as they release photons which can be seen as ultraviolet light. Since the wavelength of ultraviolet light is so small, it cannot be seen by the naked eye. The ultraviolet light is made visible through the use of the phosphor powder coating. Photons released from the electrons are incident upon the phosphor coating and this causes the phosphor’s electrons to emit energy as it changes energy levels. This energy is usually given off in the form of heat. According to home.howstuffworks.com/fluorescent-lamp2, in a fluorescent lamp, the emitted light is in the visible spectrum — the phosphor gives off white light we can see. Manufacturers can vary the color of the light by using different combinations of phosphors. In a fluorescent lamp, the emitted light is in the visible spectrum — the phosphor gives off white light we can see. (Harris, 2009)

Switch

The switch system being used in this design project is the normally open and normally close switch. This switch controls the relay system as it closes the circuit when flipped. The lamp will then be turned on, as current is being supplied to the circuit.

Starter

Starters in pre heat fixtures are either automatic or manual and are used to light the lamp. When flipped, a voltage is applied to the circuit and this causes the lamp to light. A few things occur when the switch is flipped. Firstly, a current flows through the filaments and this causes the contacts to heat and open. This interrupts the current flow which in turn lights the bulb. The inductive ballast comes into play at this point. It regulates the current flowing through the circuit as the fluorescent tube now has a low resistance as it is lighted.

The starter used in preheat fixtures can be considered an on/off switch. It controls the period of time when the circuit opens/closes. As it is opened, the voltage causes ionisation of the mercury vapour due to the movement of electrons across the tube. The starter is very important as it determines whether the lamp flickers or not. This flickering can be attributed to the steady flow of electrons between the two filaments.

Figure :How starter works

Design process

Project plan

A project without any guidance or sequence is useless. Thus, a time management system was put into place in order to complete this design project. Before a system could be implemented, the project description must be known as well as the duration of the project. The design brief which entails everything the student needed to know about the project is stated in the following;

Students are required to design and build an electrical system in order to power a small fluorescent lamp. The system must incorporate an on/off switch utilizing a 110V relay (8-pin relay and base, 110V) to power the fluorescent lamp assembly (1X20 regular ballast type 110V fluorescent fixture). Students are required to;

Understand the load: its operation and existing types of fluorescent lamps

Determine the systems required for the operation of the lamp (use of an inductive or an electronic ballast

Develop a mathematical model for the relay based on the principle of operation of the vertical-lift contactor.

Design a start/ stop switch utilizing the relay to power the fluorescent lamp and discuss the importance of this switch in terms of safety.

Determine if the magnitude of the inductance is sufficient to light the fluorescent lamp.

Determine the magnitude of the force required to activate the relay and the load current to be supplied to the fluorescent lamp.

Measure the existing power factor of the load and improve the power factor to at least 0.9 lagging.

Investigate the effect of the fluorescent lamp assembly on the power system.

Supply a detailed explanation of the operation of the system using the system phasors to support your discussion.

QUOTE ELEARNING

Students are required to apply the knowledge gained from ECNG 1015 – Introduction to Electrical Energy Systems as well as the laboratory exercises that were performed during the semester.

Consideration must also be given to laboratory protocol, industry standards, codes of

practice, occupational safety protocols and risk assessment in undertaking this project.

3.2 Time Management Schedule

The following table illustrates the time management system used to complete this design project;

Week #

Designated Tasks Completed

1

Thorough research was done on fluorescent lamps to better understand the system.

A Safety and Risk Assessment was done with respect to the design project.

2

Specification sheets for acquired after collecting the required information from the ballast, relay, etc.

3

The start/stop switch was designed and used together with the relay to power the fluorescent lamp.

Key parameters were measured from the circuit.

4

A mathematical model of the relay system was determined. Using this model, the force required to activate the relay was determined. Also, the load current to get the fluorescent lamp to light was determined.

5

The existing power factor was measured and it was improved to 0.9 lagging with the use of a capacitor.

6

Proof read report and get accustomed to fluorescent lamp system in preparation for oral exam.

Table 1 showing Time Management System used to finish the design project.

Development of the Mathematical model of the Relay

A mathematical model of the system must be done as the system is required to operate within specified parameters. Firstly, a model of the relay was done to determine it parameters. The following indicates how this system was modelled;

Ampere’s Circuital Law states that the line integral of the magnetic field intensity, H, around a closed path in the magnetic field is equal to surface integral of the current density, J, over any surface bounded by the closed path (Defour, 2011).

This implies;

The magnetomotive force is a product of the number of turns in the coil and the current flowing through the coil.

=> [Eqn 2]

[Eqn 3]

Since we are using a ferromagnetic material, the magnetic field intensity H, can also be stated as;

[Eqn 4]

[Eqn 5]

[Eqn 6]

and F are constant in the above equation. This implies that is directly proportional to F, providing that all variables above remain constant.

[Eqn 7]

The above equation is similar to ohm’s law. Hence, the reluctance in this circuit can be treated as the resistance of the system, the force as the voltage through the circuit and as the current flowing through the circuit.

Figure : Magnetic equivalent circuit

Reluctance can also be stated as;

[Eqn 8]

If current is applied to the coil in the circuit above, the magnetic flux would vary. This change in magnetic flux is given by the equation;

[Eqn 9]

The above equation gives the change in magnetic flux for one turn of the coil. Hence, for N turns, the following equation is used;

[Eqn 10]

[Eqn 11]

[Eqn 12]

When equations 11 and 12 are substituted for and F, the following equation is formed;

[Eqn 13]

The inductance of the coil remains constant in the above equation. Hence, the flux linkage through the coil is directly proportional to the current flowing through the coil.

[Eqn 14]

When equation 13 is substituted into equation 14, the following equation is formed;

[Eqn 15]

However, V can be determined as the potential difference across the coil, R as the resistance of the coil and e as the emf of the coil;

[Eqn 16]

However,

[Eqn 17]

Figure : Electrical equivalent circuit

The above circuit can be used to measure power in the circuit. Power is the product of current flowing throught the circuit and the voltage across the circuit.

Multiplying equation 16 by the current flowing through the circuit gives the power as seen in the following;

[Eqn 18]

The following equation states that the energy supplied from the source to the field;

[Eqn 19]

The law of conservation of energy states that energy is always conserved. The following equation shows this conservation of energy;

[Eqn 20]

Flux linkage across the coil can be thought of as constant. This is flux linkage is assumed as the displacement of the armature occurs rapidly. Using Faraday’s law of Induction, the coil does not have an emf induced across it as λ is constant.

[Eqn 21]

The above equation implies that there is no energy flowing from the supply source to the coil. As such, equation 20 can be stated as follows;

[Eqn 22]

Taking into account the law of conservation of energy and the above equation, some energy must be lost from the magnetic field to the mechanical system. When a curve is drawn, the area under the curve illustrates the magnetic field energy lost to the system.

[Eqn 23]

[Eqn 24]

As varies, the energy lost is supplied by the coupling field. The following equation states the energy lost;

[Eqn 25]

=> [Eqn 26]

When equation 26 is substituted into equation 24, the force can be determined as follows;

[Eqn 27]

When equation 14 is substituted into equation 27;

[Eqn 28]

Consideration of System Requirements

Determination of the magnitude of inductance required to light the

Lamp

Since an inductive ballast is used in this fluorescent lamp system, it has a certain amount of inductance and resistance. Thus, the ballast can be considered as an RL circuit. The following diagram shows the equivalent circuit for the ballast;

Figure : Equivalent circuit for the ballast

The following equation is used to calculate the impedance of the circuit relay;

Determination of the magnitude of inductance when armature is turned on/off

Coil Inductance with Armature Off

The following equation is used to calculate the impedance of the circuit relay;

Coil Inductance with Armature On – Deenergize

The following equation is used to calculate the impedance of the circuit relay;

From the specification sheet, the inductance of the coil was specified as;

Inductance of Coil with Armature Off at 120V = 15.04H

Inductance of Coil with Armature On at 120V = 7.19H

The calculated values for the inductances vary significantly. This can be explained by taking into consideration the tolerance levels associated with the rated current. Also, the reaction time of the was slightly off and this resulted in a different current being taken than the actual current value.

Determination of the load current required to activate the relay

To determine the minimum current required to activate the relay, an analog voltmeter was used in series with the potentiometer. As the resistance of the potentiometer is not fixed, it was used to determine when the relay would activate. The resistance was varied and just as the relay was activated, the voltmeter was used and the minimum current required to activate the relay was determined.

The load current was determined as

Determination of the force required to activate the relay

The length of the air gap was determined to be approximately 1mm.

The minimum current required to activate the relay was determined as

Using the specification sheet, the inductance of the coil was determined;

Inductance of Coil with Armature Off at 110V = 13.38H

Inductance of Coil with Armature On at 110V = 5.69H

The following equation was used to determine the force required to activate the relay;

Thus, the force required to activate the relay is 1.03N.

Determination of key circuit parameters

Parameter

Unit

Value

Voltage across relay

V

99.5

Min. current to turn on the relay

mA

21.8

Resistance, R

Ω

1.464k

Coil Inductance (Armature off)

H

13.38

Coil Inductance (Armature on)

H

5.69

Length of Air Gap

m

0.001

Inductance of Ballast

H

363.82

Parasitic Resistance of Ballast

Ω

339.8

Table 3 showing key circuit parameters.

Design of start/stop switch

Relay

A relay is basically a circuit which is used to control/operate another circuit. The relay can be described as an 8-pin relay and base. A coil is located within the relay and it produces a magnetic field when current flows through it. This field causes a contact to change from its original location to another resulting in the circuit being opened or closed. The relay together with the starter was used to power the fluorescent lamp. The following diagrams illustrate the 8-pin arrangement of the relay used;

Figure : Arrangement of the 8-pin relay used

The above diagram on the left shows that this type of relay is a double pole double throw (DPDT) type relay. The double pole states that two contacts are closed while the double throw states that there are two different paths of conduction within the relay.

In this relay system, there are two switches being manipulated. When a voltage is dropped across contacts 2 and 7, a magnetic field is created within the relay. For this magnetic field to be created, the coil in the relay becomes energized and this produces the magnetic field which in turn manipulates the contacts. Contact 1 connects to contact 3 and contact 8 is connected to contact 6. Also, as seen on the diagram, contacts 4 and 5 remain normally closed until activated.

The relay is significant in this design project as it controls the current flow. Thus, no large current is exposed to any personnel.

(NOT SURE IF TO PUT TRADEMARK)

Switch

The following diagram illustrates the circuit used to design the start switch;

Figure : Schematic Diagram of Circuit Used

The switching circuit has three main switches;

Normally open switch (NO)

Normally closed switch (NC)

Start switch

The normally open switch indicates whether or not current flows through the circuit. When this switch is flipped, the contacts are connected allowing current to flow. The switch being used must be pushed down in order to complete the circuit to allow current to flow.

The normally closed switch will allow current to flow through the circuit normally. In contrast to the normally open switch, when the normally closed switch is pushed, the contacts become disconnected, interrupting the current flow.

The start switch is used to turn on/off the fluorescent lamp. If the contacts are connected, then current will flow. Thus, when the start switch is flipped, the fluorescent lamp will be turned on and hence light is given off.

In this design project, the normally open and normally closes switches were placed in series with the power supply and terminals 2 and 7. Contacts 1 and 6 were placed in parallel with the normally open switch as shown in the above figure and contacts 1 and 6 were placed across the normally closed switch. When the magnetic field is created in the coil, the contacts in the relay change position and connect to contacts 3 and 6. This configuration was used as the normally open and normally closed switch determines whether the fluorescent lamp is turned on/off.

When the normally open switch is pushed, the circuit is closed and the fluorescent lamp lights. When the normally closed switch is pushed, the circuit is open and the fluorescent lamp is turned off.

Explanation of the System

The voltage rms of the system was determined to be 117.5V. The real power of the system was determined to be 22.5W. The rms voltage determined is equivalent to the phasor voltage of the system. Hence, the phasor current can be determined as follows;

The supply voltage V, is calculated using the following equation;

Since this is a purely inductive load, the angle at which the current phasor lags the voltage phasor is determined as follows;

Hence, the voltage phasor is determined as follows;

The current flowing through the lamp is considered as the real current of the apparent current. The following equation is used to calculate this lamp current;

The reactive current flowing through the lamp is known to be out of phase with the supply voltage by an angle of . This reactive current was calculated using the following equation;

The real current calculated above is placed on the horizontal axis. Hence, it is seen that the voltage phasor is in phase with this real current. The following diagram illustrates the relationship associated with the apparent, reactive and real currents;

Figure : Phasor Diagram for System without capacitor

A capacitor was used in the design to correct the power factor to at least 0.9 lagging. This capacitor does not affect the power given off by the motor in the system and as such, the current is constant. However, as this capacitor was added, the current from the source decreased when compared to the first current attained. The fluorescent lamp still requires a steady current flow to maintain the specified power. Hence, a current also flows through the capacitor.

The system was required to be designed with a power factor of at least 0.9 lagging. Thus;

It should be noted that the current flowing through the capacitor reduces the reactive current.

Taking into account this corrected power factor, the following diagram illustrates the phasor diagram for the uncorrected power factor, corrected power factor and the capacitor current;

Figure; phasor diagram showing currents with the inclusion of a capacitor

As stated previously, with the inclusion of the capacitor, a new current will flow throught the system. This current is determined as follows;

As seen from the phasor diagram above, form a closed loop. Using Kirchhoff’s Current Law, the following equation was used to determine the current flowing through the capacitor;

Futhermore;

Hence, the capacitor need to correct the power factor to at least 0.9 lagging can be determined as follows;

The capacitor determined above is significantly different from the value used. This can be explained by considering that various power losses occur within the system. Also, this capacitance was calculated using theoretical values and not values obtained in the lab. Hence, there would be a difference.

From the above figure( phasor diagram for both power factors),