DEFINATIONS & DESCRIPTIONS. VOLTAGE STABILIZER AUTOMATIC-1Kva Technicians hand-book DEFINATIONS and DESCRIPTIONS

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1 DEFINATIONS & DESCRIPTIONS VOLTAGE STABILIZER AUTOMATIC-1Kva Technicians hand-book DEFINATIONS and DESCRIPTIONS 1

2 LOAD INPUT VOLTAGE OUTPUT VOLTAGE INPUT CURRENT OUTPUT CURRENT INPUT VOLTAGE RANGE OUTPUT VOLTAGE RANGE LOW VOLTAGE CUT-OFF HIGH VOLTAGE CUT-OFF ON-TIME DELAY TIME DEFINATIONS Any equipment connected to the stabilizer and which draws power from the stabilizer is load. This is the voltage coming from the main to the stabilizer. This is the voltage available at the output terminals of the stabilizer. This is the current drawn from the mains by the stabilizer. This is the current drawn by the load from the stabilizer. All input voltages (150V-280V) for which the stabilizer gives output within the output voltage range. The voltage ( V) which the stabilizer is designed to deliver when the input: within the specified input voltage range. The stabilizer is designed cut-off the output voltage when the input voltage falls below 150V+/-. The stabilizer is designed to cut-off the output voltage when input voltage goes beyond 280V +/- 5V. The stabilizer is designed to delay the supply of mains to output terminal (2min +/-20 secs) before starting in case of initial starting, mains failure or high/low voltage cut-off coming into operation. This is an automatic operation The ON delay can be avoided (by passed) by pressing a switch manually to obtain the output instantaneously. 2

3 TRANSFORMERS Transformers are used to step up or step down a-c voltage. Transformers are constructed of two coils wound on the same iron core as shown in Fig below. The voltage is the stepped up or down i.e. applied to coil F which is called the primary coil of the transformer. When an a-c voltage Vp is connected to the primary coil, a current Ip flows through the coil. This current creates a magnetic field which passes around the iron core and through the secondary coil S. As the field due to the primary cases and falls with the continual rising and falling of the a-c current, it cut across the winding of the secondary coil and induces a voltage Vs across the coil. If the secondary coil has more turns into the primary, then the voltage will have been stepped up and the output voltage Vs will be greater than input voltage Vp. On the other hand,if secondary has few turns than primary, then Vs will be less than Vp and the voltage will be stepped down. The number of turns in the secondary (Ns) delivered by the number of turns in the primary (Np) is called the turns ratio T of the transformer: T= Ns/Np The total ratio tells us how much the voltage is stepped up or down To find the output voltage multiply the input voltage by turns ratio Vs = T x Vp In order towards the output voltage depends on the ratio of the primary winding and secondary winding turns expressed as: Vs = Ns Vp Np The voltage of a system can be controlled by changing the turns ratio of a transformer. The transformer windings may be provided different taps and by selecting the taps turns ration can be changed. 3

4 The main transformer used in the voltage stabilizers has a single continues winding which is used as primary as well as secondary winding. This is called an Autotransformer. Its theory and principle operation is similar to that of a two winding transformer. The portion AB is used as primary winding and portion BC as secondary winding Fig (a) shows a step down and (b) a step up arrangement TAP CHANGING N 8 = Number of turns for secondary winding N P = Number of turns for primary winding By changing/selecting suitable tappings for input and output in a auto-transformer having different tappings, desired output voltage can be obtained. A simple tap changing device is a selector switch. As shown figure above number of turns of primary and secondary can changed through switch S1 and S2 respectively. Thus the output voltage can be kept in a specified range by changing turns-ratio through tap changing. Tap changing can also be done automatically and instantly with the help of relays. Different arrangements of tap changing are made in the stabilizers, with the help of relays, which are controlled by electronic control circuits to obtain an output within the range of volts from an input range of 150 to 280 volts. This is explained in detail while discussing the individual stabilizers. 4

5 RELAYS A relay is an electrically operated switch. Instead of operating a switch by hand to turn it on or off, an electromagnetic devise is used to the same. A relay has coil of many turns of insulted copper wire wound around a piece of iron called the core. This coil with its iron core is the electromagnet. The iron core becomes a magnet when a current flows in the coil that is when the coil is emergenced and the relay is said to the operate. When current quits flowing in the coil that is, when the coil is de-energized the iron core looses its magnetism and the relay has to release. An iron are called the armature in front of the core is pulled down, when the relay generate which is turn closes or open the contacts of the relay, which were in just opposite state when the relay was de-energized (released) construction. Closing or opening a contact is similar putting switch on or off. Only a small amount of current is needed through the coil to operate the relay, but this on control (make/break) a larger current through its contacts. Double pole, single throw Double pole, double throw SCHEMATIC DIAGRAM Relays the switches come in various combinations of poles and throws. The numbers of poles are determined by the number of sets of contacts it operates at one time. A relay is called a single throw when its contacts opens/closes when the relay operated; and it is called double throw when the set of contacts closes circuits in both energized and nonenergized positions. While showing in systematic diagrams the status of the contacts are shown when the relay is nonenergized (released) condition.(no= Normally Open, NO = Normally closed contacts) 5

6 RESISTORS/POTENTIMETERS Resistors are used in just about every electronic circuit. They control the amount of current in a circuit, keeping it within desired value. If the resistance is high, the current will be low: if the resistance is low, the current will be high. Fixed resistor Variable resistor A variable resister also called Potentiometer is one, which has a field value between the two end terminals, and has a third terminal from a slider contacts (which is marker with an arrangement schematics drawings). Changing the position of the slider the resistance between the slider terminal and the other two and terminals can be varied within the minimum resistance value. The value of resistors is given in ohms(ω) and the same is indicates by colour bands or Figures on the body. Their were handling capacity in watts is also important. CAPACITORS Capacitors are among the very widely used electronic component. The a-c signal passes through a capacitor while the d-c is blocked out. Capacitors are also able to store electricity and then feed it back to the circuit required. Capacitors come in a wide variety of shapes and sizes. However all capacitors are essentially the same: two conducting surfaces separated by a thin insulator called a dia-electric. There are two basic kinds of capacitors and those that are not electrolytic. Electrolytic capacitor Disc capacitor Electrolytic have much larger capacity than the others, and their terminals are married (+) and (-). Proper polarity must be observed while connecting in circuits. Capacitors which are not electrolytic don t have a polarity mains, since make no difference which way they are connected. 6

7 SEMICONDUCTOR DIOES This is the simplest of all semiconductor devices. Diode conduct in only one direction (neglecting small reserve current) Fig shows schematic symbol and for the diodes. Its forward resistance is quite low while its reserve resistance is exactly high. In the schematic to a choose the arrow point in the conventional direction of current flow (which is opposite to the direction of electron flow.) RECTIFIER CIRCUITS Connecting an a-c to d-c is called rectification. Two types of rectifier circuits discussed in the next page. HALF WAVE RECTIFIER CIRCUIT Positive current half cycle thru Load. Negative current Half cycles does not appear in output. Half -wave rectifier The simplest of all rectifier circuits is the half have rectifier shown in the figure. The transformer has the proper turns ratio for the desired secondary voltage. During the half of the a-c cycle when the transformer secondary polarity is as shown in figure, the diode will conduct and current will flow through the load. The diode is forward biased in this condition. During the other half of the a-c cycle, the diode cannot conduct (it is said to be reverse biased) and no current flows through the load. The result of the above action that a series of positive half-cycle pulses are developed across the load and no load, current flows during the negative half of each cycle, giving d-c at the output. 7

8 Full-wave Rectifier Current path: Positive half-cycle Negative half-cycle Full-wave Rectifier Fig. above illustrates the basic operation of the full-wave rectifier. Note that the circuit requires the use of a centre-tapped transformer secondary winding. During positive half cycles when the top end of centre-tapped secondary is positive with respect to the centre-tap current flows through the circuit indicated by transformed arrows (conventional). Current flows through D1 and causes the positive half- cycle to appear across the load. There is no flow of current through during this part of cycle. During negative half-cycle, the bottom end of the transformer secondary winding becomes positive, with respect to the centre-tap and now current will low through D 2 as shown by dashed arrows. Current always flows through one diode only and both the half-cycle flows through the load in the same direction giving a-c output. BRIDGE RECTIFIER CIRCUITS Current path: Positive half-cycle Negative half-cycle A bridge rectifier circuit is shown in fig. above. The solid arrows show the current path (conventional), when the secondary winding is positive and dashed arrows show the current path for the other half-cycle, when the top of the secondary winding is negative. The current always flows through two diodes. Current for both the half cycles flows through the load in the same direction giving d-c at output. 8

9 ZENER DIODES Zener diodes are most commonly used as voltage regulators and voltage limiters. They are specially designed for sudden break down of resistance when the designed reverse voltage is reached. They are normally used with reverse biasing. Zener diode keeps the voltage across itself constant with variations in current flow through it. This property is very useful as a voltage regulator. If the voltage applied across a zener diode is lower than its break down voltage the zener current remains very small till its break down voltage. When break down occurs the resistance of zener decreases to leap the voltage across it at constant for the input voltages of higher value. The important specification for zener diode are the zener break down voltage (Ez) the minimum zener current for good regulation (Izm) the maximum safe current that the zener can handle (Izm) and wattage ratting. TRANSISTORS The transistor can be recognized by its three leads. The three leads are called base (B),emitter(E) and Collector (C) The transistor is called an active device, meaning that it performs amplification. A small current flowing between the emitter and base leads will allow a much larger signal current to follow between the emitter and collector leads. The emitter s job is simply to emit current into the transistor. The base controls the amount to curve that flows from the emitter to the collector. The collector finally collects all the current in the transistor and transfers it to some type of load, such as a relay coil/ a speaker. 9

10 OPERATIONAL AMPLIFIERS The operational amplifier (called the Op-amps in short) is a high gain amplifier that will amplify d-c signals as well as a-c signals. Symbol of an operational amplifier is shown in the fig. Operational amplifiers have two inputs marked in the figure. A signal V1 applied to input 1 is reversed in phase (inverted) upon passing through the operational amplifier. A signal V2 applied to input 2 retains the same phase in going through the amplifier. Minus (-) sign on the schematic is used to indicate phase reversal (inverting) and plus (+) sign for the non inverting input. If two signals V1 and V2 in phase with each other are applied simultaneously to the two operational amplifiers inputs, the amplifiers signal V 0 is the the difference between V1 and V2. One input signal subtracts from the other because one signal is inverted in the output and the other is one. The output voltage is equal to V1-V2 multiplied by the amplifier gain. OPERATIONAL AMPLIFIERS AS VOLTAGE COMPARATORS It is often necessary to have some means of indicating when two voltages in an electronic circuit are equal. A voltage comparator using an operational amplifier is a simple circuit that can do the job. There are number of application for such comparators, one popular use is as voltage regulators, The operational amplifier comparator can be used in two basic ways as shown in fig below: (a) (b) In (a) above, the input voltage (Ein) is applied to the non-inverting input while a reference voltage is applied to the inverting input. With this circuit the output voltage (Eout) will remain at its maximum negative value as long as the input voltage is less positive than the reference voltage. Once Ein increases to a value even only slightly 10

11 more positive than the reference voltage, however the output will range to its maximum positive value. The circuit in (b) operates similarly, except that the polarity of the output voltage is reversed. Here the output voltage will be positive if Ein is less than reference voltage and will swing negative once Ein becomes more positive than the voltage on the non inverting terminal (Reference voltage). The above two comparators use one input voltage and a stable reference voltage. However the circuits can operate in the same manner with two separate, changing input voltages. In that case, one input is applied to the non-inverting input and the other to the inverting input. Except for the circuits will operate just file the above. OP amp is frequently operated from identical positive and negative voltages 12V When supply is provided this way its output voltage will swing between positive and negative values that are very close to the power supply voltages as explained above. Often however a comparator is operated with the negative supply terminal grounded in which case the output voltage can never become more negative than zero i.e. its output will be either zero (no output) or a positive voltage very close to the power supply voltage depending upon the input INTEGRATED CIRCUITS They consists of various components like transistors, diodes resistors etc. fabricated on a single chip. IC LM324 It consists of four independent high gain operational amplifiers, which were designed to operate from a single power supply over a wide range of voltage Pin configaration shown in the figure above. LM