mat lab 1

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EXPERIMENT NO: 01 NAME OF THE EXPERIMENT: REGULATION OF THE TRANSFORMER IN VARIOUS LOAD. OBJECTIVE: o To study the voltage regulation of the transformer with varying loads. o To study transformer regulation with inductive and capacitive loading. THEORY: A transformer has three basic elements: (i) a primary winding -the winding connected to the supply, (ii) a secondary winding- the output winding either connected to the load or otherwise left opened hence the name open circuit, and (iii) the core – which is a high-presence magnetic circuit made of thin lamination of steel sheets insulated from each other. The core links the primary winding to the secondary magnetically by providing a path for the magnetic flux of the primary to link the secondary windings The transformer secondary voltage will vary somewhat with the load and, because motors and incandescent lamps and heating devices are all quite sensitive to voltage changes, transformer regulation is of considerable importance. The secondary voltage is also dependent upon whether the power factor of the load is leading, lagging or unity. Therefore, it should be known how the transformer will behave when it is loaded with a capacitive, an inductive or a resistive load. If a transformer were perfect (ideal) its windings would have no resistance. Furthermore, it would require no reactive power (vars) to set up the magnetic field within it. Such a transformer would have perfect regulation under all load conditions and the secondary voltage would remain absolutely constant. But, practical transformers do have winding resistance and they do require reactive power to produce their magnetic fields. The primary and secondary winding possess, therefore, an overall resistance R and an overall reactance X. The equivalent circuit of a power transformer having a turn ratio of 1 to 1, can be approximated by the circuit shown in Figure-1. The actual transformer terminals are P 1 P 2 on the primary side and S 1 S 2 on the secondary. In between these terminals we have shown the transformer as being composed of a perfect (ideal) transformer in series with impedance consisting of R and X, which

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Page 1: MAT LAB 1

EXPERIMENT NO: 01

NAME OF THE EXPERIMENT: REGULATION OF THE TRANSFORMER IN VARIOUS LOAD.

OBJECTIVE:

o To study the voltage regulation of the transformer with varying loads.o To study transformer regulation with inductive and capacitive loading.

THEORY:

A transformer has three basic elements: (i) a primary winding -the winding connected to the supply, (ii) a secondary winding- the output winding either connected to the load or otherwise left opened hence the name open circuit, and (iii) the core – which is a high-presence magnetic circuit made of thin lamination of steel sheets insulated from each other. The core links the primary winding to the secondary magnetically by providing a path for the magnetic flux of the primary to link the secondary windings The transformer secondary voltage will vary somewhat with the load and, because motors and incandescent lamps and heating devices are all quite sensitive to voltage changes, transformer regulation is of considerable importance. The secondary voltage is also dependent upon whether the power factor of the load is leading, lagging or unity. Therefore, it should be known how the transformer will behave when it is loaded with a capacitive, an inductive or a resistive load. If a transformer were perfect (ideal) its windings would have no resistance. Furthermore, it would require no reactive power (vars) to set up the magnetic field within it. Such a transformer would have perfect regulation under all load conditions and the secondary voltage would remain absolutely constant. But, practical transformers do have winding resistance and they do require reactive power to produce their magnetic fields. The primary and secondary winding possess, therefore, an overall resistance R and an overall reactance X. The equivalent circuit of a power transformer having a turn ratio of 1 to 1, can be approximated by the circuit shown in Figure-1. The actual transformer terminals are P1 P2 on the primary side and S1 S2 on the secondary. In between these terminals we have shown the transformer as being composed of a perfect (ideal) transformer in series with impedance consisting of R and X, which represents its imperfections. It is clear that if the primary voltage is held constant, then the secondary voltage will vary with loading because of R and X. An interesting feature arises with a capacitive load, because partial resonance is set up between the capacitance and the reactance X so that the secondary voltage E2 may actually tend to rise as the capacitive load value increases. Ferromagnetic cores are subject to saturation and losses. Additionally, many factors affect the operation of transformers. The type of load has a significant effect on the transformer regulation.

The transformer regulation is determined as:

% Reg = x 100%

Page 2: MAT LAB 1

Equipment Required:

o A Single Phase Transformero Power Supply

o Resistive, Capacitive and Inductive Load

o AC Ammeter

o AC Voltmeter

o Wires

CIRCUIT DIAGRAM:

Page 3: MAT LAB 1

EXPERIMENTAL DATA:

I. FOR RESISTIVE LOAD

ZL

(ohms)

I2

(A ac)

E2

(V ac)

I1

(A ac)

Infinitive 0 99 0

4800 0.01 98 0.02

2400 0.03 96 0.04

1600 0.05 94 0.05

1200 0.07 93 0.07

960 0.09 91 0.09

II. FOR INDUCTIVE LOAD

ZL

(ohms)

I2

(A ac)

E2

(V ac)

I1

(A ac)

Infinitive 0 99 0

4800 0.01 97 0.02

2400 0.03 96 0.03

1600 0.04 93 0.05

1200 0.06 90 0.07

Page 4: MAT LAB 1

960 0.07 88 0.08

III. FOR CAPACITIVE LOAD

ZL

(ohms)

I2

(A ac)

E2

(V ac)

I1

(A ac)

Infinitive 0 99 0

4800 0.01 101 0.02

2400 0.03 106 0.03

1600 0.05 109 0.04

1200 0.07 115 0.07

960 0.11 116 0.10

CALCULATION:

I. FOR RESISTIVE LOAD

% Reg = x 100% (When load is 4800 ohms)

=1.01%

% Reg = x 100% (When load is 2400 ohms)

=3.03%

II. FOR INDUCTIVE LOAD

% Reg = x 100% (When load is 4800 ohms)

Page 5: MAT LAB 1

=2.02%

% Reg = x 100% (When load is 2400 ohms)

=3.03%

III. FOR CAPACITIVE LOAD

% Reg = x 100% (When load is 4800 ohms)

= - 2.02%

% Reg = x 100% (When load is 2400 ohms)

= - 7.07%

OVSERVATION :

In inductive circuit output voltage is less than input voltage. In capacitive circuit output voltage is greater than input voltage.

ANALYSIS:

For different value of load resistance, we can see the primary and secondary winding VA is not equal. For fixed value of E1 is 220 V ac and for decreasing load resistance, the primary winding current I1 increasing, the secondary winding current I2 increasing and voltage E2 decrease. For every value of load resistance, we can measure the primary winding VA always greater than the secondary winding VA.

Observe that the windings 1-2 and 5-6 are connected in series. After verification of correct wiring, apply an input voltage of approximately 250 V AC. The input voltage can be controlled by the PS voltmeter.

You will be working with voltages up to AC 250 V and currents up to 0. 25 A AC. These levels of voltages/currents are dangerous. To avoid electric shock, connecting circuits is permitted only after power has been disconnected. Circuits should be inspected by a demonstrator before they are powered on.

Do not connect any equipment on your bench to the power supply from an adjacent bench; this might connect the equipment to a different phase.

Note that power will be supplied to a circuit only if the variable voltage control (a big black knob in the center of the power supply panel; see Figure 1) is initially set to zero. This prevents the circuit from being accidentally operated at high voltage/current. Set this control to zero every time before you switch on the circuit.

Do not connect two or more short leads to make one long lead. Remove unused leads from the bench.

Page 6: MAT LAB 1

QUESTION AND ANSWER:

1. Explain why the output voltage increases when capacitive loading is used.

ANSWER: Capacitor is a medium of storing charge. Partial resonance is setup between the capacitance and resistance. That’s why output voltage increases when capacitive loading is used.

2. A transformer has very low impedance ( small R and X ):

a) What effect does this have on the regulation?

ANSWER: With the decrease in resistance the voltage regulation will increase. So a very low resistance transformer has high voltage regulation.

b) What effect does this have on short-circuit current?

ANSWER: With the decrease in impedance the short circuit current will increase. So a very low impedance transformer has high voltage regulation.

3. Very large transformer are sometimes designed not to have optimum regulation properties in order for the associated circuit breakers to be within reasonable size, Explain.

ANSWER: Very large transformer are sometimes designed not to have optimum regulation .Because it optimum regulation properties is higher than voltage pass through the circuit so more circuit breaker is used. That’s why optimum regulation properties kept low in very large transformer.

4. Will transformer heating be approximately the same for resistive, inductive or capacitive loads of the same VA rating? Explain. Yes/ NO

ANSWER: Yes, the transformer heating be approximately the same for loads of the same VA rating.

Page 7: MAT LAB 1

EXPERIMENT NO: - 01

NAME OF THE EXPERIMENT: - STUDY OF DIODE CHARACTERISTICS.

OBJECTIVE:-

o To study the I-V characteristics of silicon p-n junction diodes.

THEORY: -

A p-n junction is a two-terminal device that acts as a one-way conductor. When a diode is forward biased as shown in Figure1 (a), Current flows through the diode and current is given by

ID = IS (e Vo/nVT – 1) ------ (1)

When, n is the ideality factor and 1 ≥ n ≥ 2. IS is the reverse-saturation current and VT = KT/ q is the thermal voltage. VT is about 0.026V at room temperature.

When it is reverse biased as shown in Figure, ID = - IS. As it is generally in PA (Pico-Amp) range, in many applications this current is neglected and diode is considered open

ID = IS (e –VR

/VT - 1) = - IS for | V | >> VT ------- (2)

The material for p-n junction diode is silicon semiconductor. Semiconductors are a group of materials having electrical conductivity intermediate between metals and insulators. Metals: Al (Aluminum), Cu (Copper), Au (gold), Insulators: Ceramic, Wood, Rubber. Semiconductor: Si (Silicon), Ge (Germanium), Ga As (Gallium-Arsenide).

APPARATUSES: -

p-n junction diode (1N4003) ---- 1 Piece 5V Zener Diode ------------------- 1 Piece

Resistor (1K) ---------------------- 1 Piece

DC Power Supply ---------------- 1 Piece

Signal Generator ----------------- 1 Piece

Oscilloscope ---------------------- 1 Piece

Page 8: MAT LAB 1

Chords and Wire ----------------- Lot

CIRCUIT DIAGRAM:-

Page 9: MAT LAB 1
Page 10: MAT LAB 1

Resistance (R)

DC voltage

VDC (V)

Diode voltage VD (V)

Voltage across resistance VR

(V)

Current, ID= VR/R (mA)

0.1 0.08 0 0

0.2 0.20 0 0

0.3 0.24 0 0

0.4 0.33 0 0

0.5 0.42 0.06 0.05

0.6 0.44 0.11 0.09

1.16 0.7 0.47 0.21 0.18

1.0 0.51 0.41 0.35

5.0 0.62 4.37 3.77

9.0 0.65 8.20 7.07

15.0 0.67 14.21 12.25

21.0 0.70 20.2 17.41

22.0 0.70 21.2 18.28

EXPERIMENTAL DATA TABLE:-TABLE: 01

FOR FORWARD BIAS

Page 11: MAT LAB 1

TABLE: 02FOR REVERSE BIAS

Resistance (R)

DC voltage

VDC (V)

Diode voltage VD (V)

Voltage across

resistance VR

(V)

Current, ID= VR/R (mA)

0.5 0.4 0 01.0 0.9 0 01.5 1.5 0 02.0 1.9 0 02.5 2.4 0 03.0 2.9 0 0

1.16 5.0 4.5 0.4 0.348.0 4.9 2.9 2.58.5 5.0 3.4 2.939 5.0 3.9 3.36

10 5.0 4.9 4.22

GRAPH:-

Page 12: MAT LAB 1

CALCULATION:-

OVSERVATION:-

This model is easy to implement when analyzing circuits and it includes the important features of a real diode. This characteristic curve will be investigated as part of this lab. Two characteristics of the diode which will to be examined are reverse recovery time and reverse bias breakdown. The first, reverse recovery time, is a result of the fact that while the diode is forward biased, the depletion region is full of excess carriers. Immediately after the diode is switched to reverse bias, the depletion region is still full of carriers. Therefore, a large negative current will flow until all of the excess carriers are washed out. As the carriers are removed, the reverse current decays exponentially to approximately zero. The reverse recovery time is the time it takes for this to occur.

The other characteristic is reverse bias breakdown. In a normal diode, breakdown can result in damage to the diode. However, the Zener diode is designed to breakdown. In fact, the breakdown voltage is set to a desired point through the construction of the device. This effect can be exploited to perform voltage regulation in power supplies.

ANALYSIS:-

Plot both sets of results on the same graph, with IF going from 0 to 10mA, VF from 0 to 2V, IR

from 0 to -50µA and VR from 0 to –30V. (You may alter any of the dimensions if they don’t suit your results). Label your graph carefully and write each diode type next to its characteristic.

REPORT:-

Page 13: MAT LAB 1