Three Phase Appliance Protector

[[wysiwyg_imageupload:2163:]]The Project is contributed by Mr. Bharat Baravaliya

INTRODUCTION

Many of our costly appliances require three-phase AC supply for operation. Failure of any of the phases makes the appliance prone to erratic functioning and may even lead to failure. Hence it is of paramount importance to monitor the availability of the three-phase supply and switch off the appliance in the event of failure of one or two phases. The power to the appliance should resume with the availability of all phases of the supply with certain time delay in order to avoid surges and momentary fluctuations. The complete description of a three phase appliance protector is described here. User lines connected to power supply lines can be disconnected there from by a connect/disconnect switch. An isolation rectifier circuit connected across the each phase wit operational relays. Output of the rectifier circuit controlled by a timer and through that timer operates the switch. The timer restores the connection in failure of any one or two phases.

1. A protection device for an electrical machine appliance or installation, comprising:

Contactor switch connected between a plurality of supply lines and respective user lines to be protected and connectable to a load. An each isolating rectifier circuit element having an input side connected across each phase side point and a neutral point which can be at a ground potential, and an output side electrically isolated from coil side of operational relay along with led and free wheeling diode. A timer connected to an coil said operational relay and connected with contactor switch for automatically disconnecting said user lines from said supply lines upon the failure of any one phase or two phases, and for automatically reconnecting said user lines with said supply lines upon presents of all the three phases with certain time delay. An each isolating rectifier circuit is connected from secondary side of each step-down transformer. And a primary side of each step-down transformer is connected from each phase to neutral.

2. A protection device for an electrical machine appliance or installation, comprising:

A contactor switch connected between a plurality of supply lines and respective user lines to be protected and connectable to a load. An isolating rectifier circuit element having an input side connected across secondary side of step-down transformer, and an output side electrically isolated from coil said of operational relay.

CIRCUIT ELEMENTS

1. RELAY:-

Relay

Relay Insight

2. POLES CONTACTOR:

A contactor is an electrically controlled switch used for switching a power circuit, similar to relay except with higher amperage ratings. A contactor is controlled by a circuit which has a much lower power level than the switched circuit. Contactors come in many forms with varying capacities and features. Unlike a circuit breaker, a contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amps and 24 V DC to thousands of amps and many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side. Contactors are used to control electric motors, lighting, heating,
capacitor banks, and other electrical loads.

Operating Principle:

Unlike general-purpose relays, contactors are designed to be directly connected to high-current load devices. Relays tend to be of lower capacity and are usually designed for both normally closed and normally open applications. Devices switching more than 15 amperes or in circuits rated more than a few kilowatts are usually called contactors. Apart from optional auxiliary low current contacts, contactors are almost exclusively fitted with normally open contacts. Unlike relays, contactors are designed with features to control and suppress the arc produced when interrupting heavy motor currents. When current passes through the electromagnet, a magnetic field is produced, which attracts the moving core of the contactor. The electromagnet coil draws more current initially, until its inductance increases when the metal core enters the coil

The moving contact is propelled by the moving core; the force developed by the electromagnet holds the moving and fixed contacts together. When the contactor coil is de-energized, gravity or a spring returns the electromagnet core to its initial position and opens the contacts. For contactors energized with alternating current , a small part of the core is surrounded with a shading coil, which slightly delays the magnetic flux in the core. The effect is to average out the alternating pull of the magnetic field and so prevent the core from buzzing at twice line frequency.

Most motor control contactors at low voltages (600 volts and less) are air break contactors; i.e., ordinary air surrounds the contacts and extinguishes the arc when interrupting the circuit. Modern medium-voltage motor controllers use vacuum contactors.

Motor controls contactors can be fitted with short-circuit protection (fuses or circuit breakers), disconnecting means, overload relays and an enclosure to make a combination starter

Applications:

Lighting control

Contactors are often used to provide central control of large lighting installations, such as an office building or retail building. To reduce power consumption in the contactor coils, latching contactors are used, which have two operating coils.

One coil, momentarily energized, closes the power circuit contacts, which are then mechanically held closed; the second coil opens the contacts.

Magnetic starter

A magnetic starter is a contactor designed to provide power to electric motors. The magnetic starter has an overload relay, which will open the control voltage to the starter coil if it detects an overload on a motor. Overload relays may rely on heat produced by the motor current to operate a bimetal contact or release a contact held closed by a low-melting-point alloy.

The overload relay opens a set of contacts that are wired in series with the supply to the contactor feeding the motor. The characteristics of the heaters can be matched to the motor so that the motor is protected against overload. Recently, microprocessor-controlled motor protection relays offer more comprehensive protection of motors.When a relay is used to switch a large amount of electrical power through its contacts, it is designated by a special name: contactor. Contactors typically have multiple contacts, and those contacts are usually (but not always) normally-open, so that power to the load is shut off when the coil is de-energized. Perhaps the most common industrial use for contactors is the control of electric motors.

BASIC DIAGRAM OF CONTACTOR

The top three contacts switch the respective phases of the incoming 3-phase AC power, typically at least 480 Volts for motors 1 horsepower or greater. The lowest contact is an “auxiliary” contact which has a current rating much lower than that of the large motor power contacts, but is actuated by the same armature as the power contacts.

The auxiliary contact is often used in a relay logic circuit, or for some other part of the motor control scheme, typically switching 120 Volt AC power instead of the motor voltage. One contactor may have several auxiliary contacts, either normally-open or normally-closed, if required.

The three “opposed-question-mark” shaped devices in series with each phase going to the motor are called overload heaters. Each “heater” element is a low-resistance strip of metal intended to heat up as the motor draws current. If the temperature of any of these heater elements reaches a critical point (equivalent to a moderate overloading of the motor), a normally-closed switch contact (not shown in the diagram) will spring open.

This normally-closed contact is usually connected in series with the relay coil, so that when it opens the relay will automatically de-energize, thereby shutting off power to the motor. We will see more of this overload protection wiring in the next chapter. Overload heaters are intended to provide over current protection for large electric motors, unlike circuit breakers and fuses which serve the primary purpose of providing over current protection for power conductors. Overload heater function is often misunderstood. They are not fuses; that is, it is not their function to burn open and directly breaks the circuit as a fuse is designed to do.

Rather, overload heaters are designed to thermally mimic the heating characteristic of the particular electric motor to be protected. All motors have thermal characteristics, including the amount of heat energy generated by resistive dissipation (I2R), the thermal transfer characteristics of heat “conducted” to the cooling medium through the metal frame of the motor, the physical mass and specific heat of the materials constituting the motor, etc. These characteristics are mimicked by the overload heater on a miniature scale: when the motor heats up toward its critical temperature, so will the heater toward its critical temperature, ideally at the same rate and approach curve. Thus, the overload contact, in sensing heater temperature with a thermo-mechanical mechanism, will sense an analogue of the real motor. If the overload contact trips due to excessive heater temperature, it will be an indication that the real motor has reached its critical temperature (or, would have done so in a short while). After tripping, the heaters are supposed to cool down at the same rate and approach curve as the real motor, so that they indicate an accurate proportion of the motor’s thermal condition, and will not allow power to be re-applied until the motor is truly ready for start-up again.

Components

1. 555 timer IC: 555 Timer IC

2. Diode: Diodes Tutorial

3. Light-emitting diode:

Light Emitting Diode – LEDs

4. Transistor:

Transistor BC547

Transistor SL100

Transistor BC548

Transistor SK100

Transistor BC558

Transistor 2N2222

5. Capacitors:

Capacitor tutorial

Capacitor Insight

6. Resistor:

Resistor Tutorial

Transformer

INTRODUCTION:

A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer’s coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer’s core, and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or “voltage” in the secondary winding. This effect is called mutual induction

If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the number of turns in the primary (NP) as follows:

By appropriate selection of the ratio of turns, a transformer thus allows an alternating current (AC) voltage to be “stepped up” by making NS greater than NP, or “stepped down” by making NS less than NP. In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception.

Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household (“mains”) voltage. Transformers are essential for high voltage power transmission, which makes long distance transmission economically practical.

Basic principles:

The transformer is based on two principles: firstly, that an electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction).

Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.

FIG 3.2.1 TRANSFORMER

An ideal transformer:

An ideal transformer is shown in the adjacent figure. Current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron, so that most of the magnetic flux passes through both the primary and secondary coils.

Induction law:

The voltage induced across the secondary coil may be calculated from Faraday’s law of induction, which states that:

where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and ? equals the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic flux density B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer, the instantaneous voltage across the primary winding equals

Taking the ratio of the two equations for VS and VP gives the basic equation for stepping up or stepping down the voltage.

Ideal power equation :

The ideal transformer as a circuit element

If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient; all the incoming energy is transformed from the primary circuit to the magnetic field and into the secondary circuit. If this condition is met, the incoming electric power must equal the outgoing power.

Pincoming = IPVP = Poutgoing = ISVS

giving the ideal transformer equation

Transformers normally have high efficiency, so this formula is a reasonable approximation.

If the voltage is increased, then the current is decreased by the same factor. The impedance in one circuit is transformed by the square of the turn’s ratio. For example, if an impedance ZS is attached across the terminals of the secondary coil, it appears to the primary circuit to have an impedance of

. This relationship is reciprocal, so that the impedance ZP of the primary circuit appears to the secondary to be

Operation of transformers:

The simplified description above neglects several practical factors, in particular the primary current required to establish a magnetic field in the core, and the contribution to the field due to current in the secondary circuit. Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance. When a voltage is applied to the primary winding, a small current flows, driving flux around the magnetic circuit of the core. The current required to create the flux is termed the magnetizing current; since the ideal core has been assumed to have near-zero reluctance, the magnetizing current is negligible, although still required to create the magnetic field.

The changing magnetic field induces an electromotive force (EMF) across each winding. Since the ideal windings have no impedance, they have no associated voltage drop, and so the voltages VP and VS measured at the terminals of the transformer, are equal to the corresponding EMFs. The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the “back EMF”. This is due to Lenz’s law which states that the induction of EMF would always be such that it will oppose development of any such change in magnetic field.

Practical Considerations:

Leakage flux:

The ideal transformer model assumes that all flux generated by the primary winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings. Such flux is termed leakage flux, and results in leakage inductance in series with the mutually coupled transformer windings.

Leakage results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. It is not directly a power loss (see “Stray losses” below), but results in inferior voltage regulation, causing the secondary voltage to fail to be directly proportional to the primary, particularly under heavy load. Transformers are therefore normally designed to have very low leakage inductance

However, in some applications, leakage can be a desirable property, and long magnetic paths, air gaps, or magnetic bypass shunts may be deliberately introduced to a transformer’s design to limit the short-circuit current it will supply. Leaky transformers may be used to supply loads that exhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs; or for safely handling loads that become periodically short-circuited such as electric arc welders

Air gaps are also used to keep a transformer from saturating, especially audio transformers in circuits that have a direct current flowing through the windings. Leakage inductance is also helpful when transformers are operated in parallel.

It can be shown that if the “per-unit” inductance of two transformers is the same (a typical value is 5%), they will automatically split power “correctly” (e.g. 500 kVA units in parallel with 1,000 kVA unit, the larger one will carry twice the current).

Voltage transformers:

Voltage transformers (VTs) or potential transformers (PTs) are another type of instrument transformer, used for metering and protection in high-voltage circuits. They are designed to present negligible load to the supply being measured and to have a precise voltage ratio to accurately step down high voltages so that metering and protective relay equipment can be operated at a lower potential. Typically the secondary of a voltage transformer is rated for 69 or 120 Volts at rated primary voltage, to match the input ratings of protection relays

The transformer winding high-voltage connection points are typically labeled as H1, H2 (sometimes H0 if it is internally grounded) and X1, X2, and sometimes an X3 tap may be present. Sometimes a second isolated winding (Y1, Y2, Y3) may also be available on the same voltage transformer. The high side (primary) may be connected phase to ground or phase to phase. The low side (secondary) is usually phase to ground.

The terminal identifications (H1, X1, Y1, etc.) are often referred to as polarity. This applies to current transformers as well. At any instant terminals with the same suffix numeral have the same polarity and phase. Correct identification of terminals and wiring is essential for proper operation of metering and protection relays.

While VTs were formerly used for all voltages greater than 240V primary, modern meters eliminate the need VTs for most secondary service voltages. VTs are typically used in circuits where the system voltage level is above 600 V. Modern meters eliminate the need of VT’s since the voltage remains constant and it is measured in the incoming supply.

Transformer + Rectifier:

The varying DC output is suitable for lamps, heaters and standard motors. It is not suitable for electronic circuits unless they include a smoothing capacitor

Types:

Autotransformer, Poly-phase transformers, Leakage transformers, resonant transformers, Audio transformers, Instrument transformers.

THREE PHASE POWER SUPPLY

Introduction to Three Phase:

Electricity, which was considered to be a matter of pride for its possessor, merely fifty years ago, has become the most necessary and vital ingredient of twenty-first century human life .our dependency on electricity has increase to such an extent that we start our day by switching on an electrical appliance and end it by switching off the electric bulb. Innumerable electrical appliances such as a bulb, a tube light, fan, air-conditioner, mixer, washing machine, geyser, tele-vision and the list extends up to infinity.

The household appliances don’t need much power (electricity) to operate, and hence run well on single- phase electrical supply. But in day-today life we come across many situations in which large amount of power (electricity) is needed to perform the specified task such as in a flour mill, bore well pumps, factory machines etc. Here comes into operation another mode of power supply known as three phase power supply.

As you are aware, to transmit power with single-phase alternating current, we need two wires (live wire and neutral). However you would have seen that distribution lines usually have only 4 wires. This is because distribution is done using three phases and the 4th wire is the neutral. How does this help? Since the three phases are usually 120’ out of phase, their phasor addition will be zero if the supply is balanced.

WAVE FORM AND PHASOR DIAGRM OF THREE PHASE SUPPLY

It is seen from figure that in the balanced system shown, the three phases, usually designated R, Y, B corresponding to Red, Yellow and Blue, are equal in magnitude and differ in phase angle by 1200.

The corresponding phasor diagram is shown in figure (b). The voltage between any of the phases and the neutral is called the phase-to-neutral voltage or phase voltage Vp. It is usual to call the voltage between any two lines as the line-to-line voltage or Line voltage VL.

If the R-phase voltage is VR = Vp.0, then the remaining Phase voltages would be VY =Vp.-2p/3 and VB = Vp.-4p/3.

About Diode

A diode is an electrical device allowing current to move through it in one direction with far greater ease than in the other. The most common type of diode in modern circuit design is the semiconductor diode, although other diode technologies exist. Semiconductor diodes are symbolized.

A rectifier is used to convert A.C. to D.C. .The simplest of all is the Half-Wave Rectifier. A diode is conductive in forward–bias and it resembles open circuit in reverse–bias this property of diode is used to convert A.C. into D.C. As we can see in diagram.

PCB FABRICATION

MAKING OF PCB,DRILLING& SOLDERING OF COMPONETS:

For making PCB first of all consider the size of diode, resistor, relay, transitor, integrated circuit and all other required components before starting to draw PCB layout the jumpers shows the circuit become more accurate.

After drawing the PCB layout on paper it is to be drawn on the copper plate with the help of carbon paper. Size of copper plate is 6”4’ fix the carbon paper on th plate so that it should not move white drawing tracing on the copper plate to betake that is should be accurate and clear.

After completing this non-etching material should be applied on the layout the non-etching materials re nil polish, oil paint, marker etc. But mostly oil paint is preferred. Now the apply oil paint on the layout after applying the non- etching material on the layout the copper plate is then kept for some time drying purpose.

After drying the plate is really for etching procedure.

ETCHING:

This solution used for etching is fecl₃.The copper plate with non-etching material Is then kept in fecl₃solution observed it from time to tome we will remaining copper and the plate will be washed out wit fecl₃s solution the etching was done with in two hours. After etching the non-etching materiali.e. the etching tap is emoved from the layout with the help of blade so the PCB is ready for drilling

1. DRILLING:

After completing above work drilling is done with drill with the help of small drill set proper drilling is very necessary otherwise there is a chance of creaking of copper plate the holes of components can easily pass through the hole and make contact with soldering is being done with help of soldering iron and soldering rod.

2. SOLDERING TECHNICS:

First look PCB and components after determined the value of component is classified after this process input component on PCB one and solder it by low soldering iron.

After complete PCB work. We connect out side compones inthis way did soldering of my project three phase appliances protector.

The flare is very useful to solder to fix the soldering in proper plate .After connecting the components ends of components are cutting by cutter. We have no problem to make a soldering for project all the components soldered on proper prints.

3. MATERIAL REQURIED:

You will need the following for making PCB:

1. Copper plate board

2. Photo resist-redium.

3. Enamel tray for developing

4. Ferric chloride

5. Plastic tray for etching

4. TYPE OF PCB:

Only two type of PCB are most popular

1. Single sided boards

2. Double sided board.

The single board is mostly used in entertainment electronics where manufacturing cost is to be kept minimum control is neglected and single circuit can be accommodated on such boards. The number of jumper wires on the board should be minimum.

5. PCB SIZE:

The size of PCB is with thick it well list and not causes much problems. The constraints on the size of PCB is as follows.

1. Electric function

2. Testing and searching

3. Modifications

4. Equipments dimensions

6. PCB LAYOUT:

The rules for preparing layout for PCB are as follows.

1. Each and energy PCB layout should be prepared from wiring it from the components.

2. As far as possible the layout should be will delivered in the direction of signal flow. This will leads the shortest possible enter commendations.

3. The larger components should be planed to be placed first the space in between should be filled with smaller components.

4. The components which require input-output should come near the connector.

5. All components should be placed in such a manor that he disordering of other components is not required if they are to be replaced.

WORKING

Circuit diagram: Shown in the circuit diagram tab

As we give three phase supply to the circuit:

R phase passes through the step-down transformer X1. This step-down transformer reduces the voltage to 12V AC. Rectifier circuit rectifies the 12V AC to 12V DC. As the output appear at rectifier circuit 1 then LED glows. Rectifier circuit 1 gives the 12V DC to coil of relay RL1. When coil of relay RL1 gets triggered its pole connects to the NO.

Then phase Y given to pole of relay RL1 passes to transformer X2 through NO. Then Y phase passes from the step-down transformer X2. This step-down transformer reduces the voltage to 12V AC. Rectifier circuit rectifies the 12V AC to 12V DC. As the output appear at rectifier circuit 2 then LED glows. Rectifier circuit 2 gives the 12V DC to coil of relay RL2. When coil of relay RL2 gets triggered its pole connects to the NO.

Then phase B given to pole of relay RL2 passes to transformer X3 through NO. Then B phase passes through the step-down transformer X3. This step-down transformer reduces the voltage to 12V AC. Rectifier circuit rectifies the 12V AC to 12V DC. As the output appear at rectifier circuit 3 then LED glows. Rectifier circuit 3 gives the 12V DC to 555 timer. This 555 timer produces the delay to produce the output at pin 3 in order to avoid surges and momentary fluctuations. The time delay can be adjusted by the variable resistor connected at pin 6. The output at pin3 is given to the base of transistor.

Then this output is given to coil of relay RL3 through collector of transistor. When coil of relay RL3 gets triggered its pole connects to the NO. Then phase B given to pole of relay 3 passes to coil of 4pole contactor RL4 through NO.

When coil of contactor gets triggered it connects the three-phase supply to the load. When any one or two phase gets failure in three phase supply then this circuit fails in above operation. As the circuit fails in operation 4-Pole contactor RL4 automatically disconnects the three-phase supply to load.

CONCLUSION

The test system considered in the project is worked out for the best protection for the 3- phase appliance in absence of any of the phase. The main objective of this prospective protector is to maintain the efficiency of the appliance which we use with the 3- phase supply. The 4-pole contactor locking assures the presence of all the 3-phases. Remaining three relays placed for all the three phases show there working with a hissing sound and glowing LED’S. Due to any erratic action taking place there will be absence of any o the phase results in the un-locking of the 4- pole contactor with an rapid fast off sound. The 555 timer which we used in the destination tip of the circuit provides the time delay for each phase which would be around 4sec as the timer working in astable mode.For review time delay from the 555 timer we need to connect an variable resistor due to that time delay can subjected and maximum is upto 4 sec.A transistor is placed in need of a switch which is used for getting the output in the third phase. Using this protector scheme would be useful to protector the appliance and at the same time it would reduce the frequent money lending in fault occurrence or failure of the appliance.