Lab Manual

Electrical Power Distribution & Utilization Lab Manual HITEC University Taxila Cantt Department of Electrical Engineering

Lab Manual For Academic Session 2011

ELECTRICAL POWER DISTRIBUTION

&

UTILIZATION

EE-422

Department of Electrical Engineering

HITEC University Taxila Cantt


SAFETY RULES

1. Please don t touch any live parts.

2. Never use an electrical tool in a damp place.

3. Don t carry unnecessary belongings during performance of experiments (like

water bottle, bags etc).

4. Before connecting any leads/wires, make sure power is switched off.

5. In case of an emergency, push the nearby red color emergency switch of the

panel or immediately call for help.

6. In case of electric fire, never put water on it as it will further worsen the

condition; use the class C fire extinguisher.

Fire is a chemical reaction involving rapid oxidation

(combustion) of fuel. Three basic conditions when

met, fire takes place. These are fuel, oxygen & heat,

absence of any one of the component will extinguish

the fire.

If there is a small electrical fire, be sure to

use only a Class C or multipurpose (ABC)

fire extinguisher, otherwise you might make

the problem worsen.

The letters and symbols are explained in left

figure. Easy to remember words are also

shown.

Don t play with electricity, Treat electricity with respect, it deserves!


HITEC University

Heavy Industries Taxila Education City, Taxila Cantt

Department of Electrical Engineering

LIST OF EXPEREIMENTS

List of Experiments

1. Analysis of different types of cables.

2. Selection of appropriate size of cable for the given load.

3. Using measuring instruments measure the high level of voltage, current and resistance.

4. To study the operation and constructional features of a Distribution Transformer

5. To measure active, reactive and apparent power of a load

6. Power factor improvement with static capacitor.

7. Automatic Reactive Power Controller

8. Determine vector group of a three phase transformer.

9. No load performance of a distribution transformer

10. Load Performance of a distribution Transformer

11. Verifying the Inverse Square Law and compare the difference in output luminescence of

incandescent, fluorescent and compact fluorescent lamps.

12. Calculating the Total Cost in a Residential and Commercial or Industrial Bill.

13. To make connections in home electrical wiring from services main to different

distribution boards and electrical points for appliances in a room.

14. To measure Earthing Resistance and Soil resistivity.


EXPERIMENT 1

Power Cables

OBJECTIVE To dissect the power cable into it’s distinguished parts.

APPARATUS Dissected Cables

Vernier Calliper

Screw Gauge

THEORY A cable is defined as an assembly of conductors and insulators used for the transfer of power

in densely populated urban areas. Cables are mostly laid under the ground in order not to

disturb the land beauty and to avoid using the land for power transmission purposes.

Types of Cables

1. Single Core Cables

2. Double Core Cables

3. Three Core Cables

4. Four Core Cables


PARTS OF CABLE A cable is composed of the following parts;

Core All cables either have a central core (conductor) or a number of cores made of strands of

Copper or Aluminum conductors having highest conductivity. Conductors are stranded in

order to reduce the skin effect.

Insulation It is provided to insulate the conductors from each other and from the outside periphery. The

common insulating materials are Poly Vinyl Chloride (PVC) and Polyethylene.

Metallic Sheath Metallic Sheath protects the cable against the entry of moisture. It is made of lead, some alloy

of lead or Aluminum

Bedding In order to protect the metallic sheath from injury, bedding is wound over it. It consists of

paper tape compounded with a fibrous material.

Armoring It consists of one or two layers of galvanized steel wires or two layers of steel tape, to avoid

the mechanical injury. Armoring provides mechanical strength to the cable.


Serving A layer of fibrous material, used to protect the armoring.

Different constants for copper and aluminum conductors is given below.

EXERCISE: You are given three cables of unknown cross section: find out the following information

about each cable.

PROCEDURE Practical demonstration

RESULT Cables have been studied and their operation is understood.


EXPERIMENT 2

Select the Appropriate Cable Size

OBJECTIVE

Select the appropriate cable size for the given load.

APPARATUS Given Load

Cable Tables Book

THEORY The cable selection procedures set out in this LAB SESSION will give the basic guidelines to

be followed to determine the minimum size of cable required to satisfy a particular

installation condition.

The following three main factors influence the selection of a particular cable to satisfy the

circuit requirements:

(a) Current-carrying capacity dependent upon the method of installation and the presence

of external influences, such as thermal insulation, which restrict the operating temperature of

the cable.

(b) Voltage drop dependent upon the impedance of the cable, the magnitude of the load

current and the load power factor.

(c) Short-circuit temperature limit dependent upon energy produced during the short circuit

condition.

TASK: Determine the size of cable required & voltage drop in the cable.

SITUATION: A 150kW, three phase load is supplying from a 400V, 50Hz supply. The circuit is protected

using BSEN 60898 Type B circuit breaker and is situated 150m away from the distribution

board. It is run with two other power circuits and is buried in the ground at a depth of 0.8m.

There the soil resistivity is 1.2 ºC.m/W. The temperature within the installation can be

assumed to be 30 C. Calculate the size of cable required, assume armored Cu cable is used

here.

DB150 kW

Load

150 m


METHOD:

STEP #01 Determine the current requirements of the circuit. This current is known as Design current,

either specified by the manufacturer or can be calculated by the formulae.

Design Current (IN) = kilo Watt Power (For 1 phase)

Single Phase Voltage x power factor

Design Current (IN) = kilo Watt Power (For 3 phase)

3 x Line Voltage x power factor

If kVA power is given the above formula will change accordingly.

If motor power is given in hp then use the conversion 1hp=746 Watts.

Here,

Design Current (IN) = _______________________ = Amps

STEP #02 Determine the method of cable installation to be used.

Installation Conditions: The current-carrying capacity of a cable is dependent on the method of installation to maintain the

temperature of the cable within its operating limits. Different methods of installation vary the rate at

which the heat generated by the current flow is dissipated to the surrounding medium.

Specific conditions of installation are there like cables installed with or without wiring enclosures in

air, in the ground or embedded in building materials.

STEP #03

Determine the environmental conditions in the vicinity of the cable installation, where

applicable, like

(i) The ambient air or soil temperature

(ii) The depth of laying rating factor

(iii) The soil thermal resistivity rating factor

Use any cable s table book to find out the correction factor values.

Here, the correction factors from the tables:

Grouping Factor (Cg): _______

Ambient Temperature (Ca): _______

Soil Resistivity Factor (Cr): _______

Depth of laying factor (Cd): _______


STEP #04

Apply the correction factors to determine the current carrying capacity (Ic) of the cable by

using the formula.

Current carrying capacity of cable = Design current

Correction Factors

The above factors should be applied according to the design situation.

Current carrying capacity of cable = Design current

Cg x Ca x Cr x Cd

Here,

Current carrying capacity of cable = ________________________

Current carrying capacity of cable = ______________

Minimum cable size = _____________ mm2

Finding the Protective Device Size (IF).

The design current should be no greater than the fuse rating. The fuse rating must be no

greater than the current carrying capacity of the cable. The current carrying capacity of the

cable should not be greater than the tabulated capacity of the cable i.e.

IN ≤IF ≤ IC

The Worst-Case Scenario

A cable may experience various different environments along its route. For example it may start

at a switchboard, run through the switch room in a trench with a lid or steel flooring, pass

through a duct in a wall and under a roadway, run a long way directly buried and finish on a

ladder rack at the consumer. At each of these environments the thermal resistivity and ambient

temperature will be different. The environment that causes the most derating of the rated current

should be taken and used for the whole cable.

DETERMINATION OF VOLTAGE DROP FROM MILLI VOLTS PER AMP -

METRE

According to IEE Regulation 522-8 of the 15th edition, it is stipulated that: The voltage drop

within the installation does not exceed a value appropriate to the safe functioning of the

associated equipment in normal service. For final circuits protected by an over current protective

device having a normal current not exceeding 100A, this requirement is deemed to be satisfied if

the drop in voltage from the origin of the circuit to any other point in the circuit does not exceed

2.5 percent of the nominal voltage at the design current, disregarding staring conditions.

The voltage drop can be determine using the following formula 50 for applications where

only the route length and load current of balanced circuits are known.


Voltage Drop (Vd) = L x IN x Vc

1000

where

Vc = The millivolt drop per ampere-metre route length of circuit, as shown in the tables for

various conductors, in millivolts per ampere metre (mV/A.m)

Vd = Actual voltage drop, in volts

L = route length of circuit, in meters

IN = the current to be carried by the cable, in amperes.

Here,

L = 80m

IN = __________ Amps

Vc= __________ mV/A.m

Voltage Drop (Vd) = _________________

1000

Voltage Drop (Vd) = _______ i.e. % of 400V.

Hence the selected cable of mm2 is suitable for normal current of Amps & cable

length of 80m.

EXERCISE:

Repeat the above task

(i) With load 20kW at power factor 0.9.

(ii) With L = 130 m

(iii)Assume unarmored cable is used here installed in air.

Answer:

(i) mm2

(ii) mm2

(iii) mm2


EXPERIMENT 3

Measure the High Level Voltage, Current and Resistance

OBJECTIVE Using measuring instruments measure the high level of voltage, current and resistance.

APPARATUS Current Transformer

Potential Transformer

Megger

Clip on Ammeter

THEORY Current Transformers

Ammeters are employed for measurement of current in

circuits. In high voltage transmission lines, it is more feasible

to use Current Transformers for measurement of current owing

to its higher range of measurement. High values of currents

flowing in the transmission lines serve as the primary circuit of

a current transformer. The high current is stepped down to a

much lower value (normally not more than 5A) which is then

measured by an ordinary ammeter. This way, an ammeter is

not exposed to high currents and voltages.

Potential Transformers

For measurement of high voltages, potential transformers are

commonly used. Difference between the potential transformers and

current transformers is that Current Transformers are connected in

series whereas Potential Transformers are connected in parallel.

Among the available range of PTs and CTs, the selection is based on

the following factors

Insulation Class

Primary to Secondary ratio

Continuous thermal rating

Service conditions

Accuracy

Clip On Ammeter

Current is measured only when an ammeter is connected in a circuit in

series. What if the current in any wire connected to a load is required to

be measured. Using an ammeter, we shall first need to disconnect the

load from the source, insert an ammeter and then measure the current.

Instead of doing all this, a clip on ammeter allows current measurement

without disconnecting the line. It operates on the concept of

transformation, as in transformers where flux linkages produce voltages.


Megger

Megger is a name given to an instrument used to measure large

values of resistance. Measuring resistance of machines and

devices is very helpful in determining faults like short circuits

etc. Once a machine faces a fault, its internal resistance gets

changed. Machine resistance is regularly monitored in order to

detect any internal faults occurring in the machines and other

devices.

OBSERVATION Using Clip on Ammeter measure the current of a single phase load.

Sr. No Load Meter Reading Clip on Meter

Reading

Resistive Load 200 W

400W

Capacitive Load 20 µF

40 µF

60 µF

Inductive Load 0.75 H

1.5 H

3 H

Using CT (current Transformer) measure the current of a given load.

CT ratio: ________

Using Megger find the insulation Resistance of

1. A new cable _____________________ found to be___________________

2. An old cable______________________ found to be___________________

3. Across Burnt Motor Terminals______ found to be___________________

4. _________________________________ found to be___________________

RESULT Working of measuring instruments practically demonstrated.


EXPERIMENT 4

Distribution Transformer

OBJECTIVE To study the operation and constructional features of a Distribution Transformer

APPARATUS Distribution Transformer

THEORY Distribution transformer is used to convert electrical energy of higher voltage (usually 11-22-

33kV) to a lower voltage (250 or 433V) with frequency identical before and after the

transformation. Its main application is mainly within suburban areas, public supply authorities

and industrial customers. With given secondary voltage, distribution transformer is usually the

last in the chain of electrical energy supply to households and industrial enterprises.

CONSTRUCTION There are 3 main parts in the distribution transformer:

Coils/winding where incoming alternating current (through primary winding) generates

magnetic flux, which in turn induces a voltage in the secondary coil.

Magnetic core material allowing transfer of magnetic field generated by primary winding to

secondary winding by the principle of electromagnetic induction.

A transformer’s core and windings are called its Active Parts. This is because these two are

responsible for transformer s operation.

Tank serving as a mechanical package to protect active parts, as a holding vessel for

transformer oil used for cooling and insulation.

Transformer Accessories


Breather

Pressure relief device

Temperature Indicator

Tap Changer etc

SIGNIFICANCE OF VECTOR GROUPS

Three phase machines, such as transformers, are allotted symbols representing the type of phase

connection and the phase angle between the HV and LV terminals. The angle is described by a

clockface

hour figure. The HV vector is taken as 12 o clock, the reference, and the corresponding LV

vector is represented by the hour hand.

For example, a Dy11 represents;

D = HV winding is delta connected

y = LV winding is star connected

11 = clock-face reference indicating that the LV vector is at 11 o clock (30o lead)

with reference to the HV vector.

EXERCISE: Give the purposes of following parts of Distribution Transformer

1. Bushings

2. Conservator or expansion tank

3. Breather

4. Pressure relief device

5. Tap Changer (OFF Load)


EXPERIMENT 5

To measure active, reactive and apparent power of a load

Objective

To use voltmeter, ammeter, power factor meter and wattmeter to measure active, reactive and

apparent power of a load.

Apparatus

1. Wattmeter

2. Voltmeter

3. Ammeter

4. Load banks

5. Power factor meter

6. Connecting leads

Theory

In alternating current circuits, energy storage elements such as inductance and capacitance may

result in periodic reversals of the direction of energy flow. The portion of power flow that,

averaged over a complete cycle of the AC waveform, results in net transfer of energy in one

direction is known as real power (also referred to as active power). That portion of power flow

due to stored energy, that returns to the source in each cycle, is known as reactive power.

The relationship between real power, reactive power and apparent power can be expressed by

representing the quantities as vectors. Real power is represented as a horizontal vector and

reactive power is represented as a vertical vector. The apparent power vector is the hypotenuse of

a right triangle formed by connecting the real and reactive power vectors. This representation is

often called the power triangle. Using the Pythagorean Theorem, the relationship among real,

reactive and apparent power is:

http://en.wikipedia.org/wiki/AC_power

http://en.wikipedia.org/wiki/Inductance

http://en.wikipedia.org/wiki/Capacitance

http://en.wikipedia.org/wiki/Real_power

http://en.wikipedia.org/wiki/Reactive_power

http://en.wikipedia.org/wiki/Pythagorean_Theorem


(apparent power)2 = (real power)

2 + (reactive power)

2

Real and reactive powers can also be calculated directly from the apparent power, when the

current and voltage are both sinusoids with a known phase angle θ between them:

Real Power = VIcos(θ)

Reactive Power = VIsin(θ)

Power Factor = 𝑅𝑒𝑎𝑙 𝑃𝑜𝑤𝑒𝑟

𝐴𝑝𝑝𝑒𝑎𝑟𝑒𝑛𝑡 𝑃𝑜𝑤𝑒𝑟=

𝑉𝐼𝑐𝑜∅

𝑉𝐼

The ratio of real power to apparent power is called power factor and is a number always between

0 and 1. Where the currents and voltages have non-sinusoidal forms, power factor is generalized

to include the effects of distortion.

Procedure

Connect load and different measuring instruments as shown below.

Load

Power

Factor

Meter

Wattmeter

A

V

Measure supply voltage and load current by using voltmeter and ammeter respectively. Use

power factor meter to measure power factor of load. These measured values will be further used

in above mentioned formulas to calculate different type of powers taken by load.

Results

Sr. No. Load Power

Factor

cosɸ

Active

Power

VIcosɸ

(watts)

Reactive

Power

VIsinɸ

VAR

Apparent

Power

VI (VAs)

Wattmeter

Meter

Reading

(watts)

Resistive

Inductive

Capacitive

Conclusions

http://en.wikipedia.org/wiki/Sinusoid

http://en.wikipedia.org/wiki/Power_factor


EXPERIMENT 6

Power factor improvement with static capacitor

Objective

To improve the power factor of the power system by changing capacitance of capacitor banks

connected in parallel with distribution lines.

Apparatus Required

1. Squirrel cage motor (DL 1021)

2. Magnetic power brake (DL 1019P)

3. Magnetic brake control unit (DL 1054TT)

4. Three phase power supply unit (DL 2108TAL)

5. Switchable capacitor battery (DL 2108T20)

6. Wattmeter (DL 2109T26E)

7. Power Factor Meter (DL 2109T27)

8. Ammeter (DL 2108T2A5)

9. Connecting Leads

Theory

A power factor of one or "unity power factor" is the goal of any electric utility company since if

the power factor is less than one, they have to supply more current to the user for a given amount

of power use. In so doing, they incur more line losses. They also must have larger capacity

equipment in place than would be otherwise necessary. As a result, an industrial facility will be

charged a penalty if its power factor is much different from 1.

Industrial facilities tend to have a "lagging power factor", where the current lags the voltage (like

an inductor). This is primarily the result of having a lot of electric induction motors - the

windings of motors act as inductors as seen by the power supply. Capacitors have the opposite

effect and can compensate for the inductive motor windings. Some industrial sites will have

large banks of capacitors strictly for the purpose of correcting the power factor back toward one

to save on utility company charges.

For a DC circuit the power is P=VI, and this relationship also holds for the instantaneous

power in an AC circuit. However, the average power in an AC circuit expressed in terms of the

rms voltage and current is

where is the phase angle between the voltage and current. The additional term is called the

power factor

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/powfac.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/acind.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/accap.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/powerac.html#c2



http://hyperphysics.phy-astr.gsu.edu/hbase/electric/phase.html#c1


From the phasor diagram for AC impedance, it can be seen that the power factor is R/Z. For a

purely resistive AC circuit, R=Z and the power factor = 1.

Experiment Procedure

Assemble the circuit according to the following topographic diagram. Connect ammeter, power

factor meter and power meter in the same current path. Connect three phase induction motor in

star and set its load as zero by adjusting parameters of magnetic brake. Connect capacitor bank

as shown in schematic diagram. Run the system and check out power factor with out capacitor

bank activation. Step by step increase capacitance and check out its effect on reactive power and

power factor.

Circuit Diagram

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/phase.html#c2

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/imped.html#c1

http://hyperphysics.phy-astr.gsu.edu/hbase/electric/acres.html#c1


Results

1) No load operation

M = 0.2 Nm, f = 50 Hz, V = 380 V

Battery Level Qc (var) cosɸ Q (var) I (mains)

A

I Motor

A

1 0

1 90

1+2 270

1+2+3 630

1+2+3+4 1350

2+3+4 1260

3+4 1080

4 720

2) Load Operation

M = 2 Nm, f = 50 Hz, V = 380 V


A

I Motor

A

1 0

1 90

1+2 270

1+2+3 630

1+2+3+4 1350

2+3+4 1260

3+4 1080

4 720

3) Load Operation

M = 3 Nm, f = 50 Hz, V = 380 V


A

I Motor

A

1 0

1 90

1+2 270

1+2+3 630

1+2+3+4 1350

2+3+4 1260

3+4 1080

4 720


EXPERIMENT 7

Automatic Reactive Power Controller

Objective

Automatic operation on the control of reactive power at various inductive loads and at different

sensitivity.

Apparatus Required

1. Squirrel cage motor (DL 1021)

2. Magnetic power brake (DL 1019P)

3. Magnetic brake control unit (DL 1054TT)

4. Three phase power supply unit (DL 2108TAL)

5. Switchable capacitor battery (DL 2108T20)

6. Wattmeter (DL 2109T26E)

7. Power Factor Meter (DL 2109T27)

8. Ammeter (DL 2108T2A5)

9. Reactive Power Controller (DL 2108T19)

10. Connecting Leads

Procedure

Assemble the circuit according to the following topographic diagram. Connect ammeter, power

factor meter and power meter in the same current path. Connect three phase induction motor in

star and set its load as zero by adjusting parameters of magnetic brake. Set the reactive power

controller in automatic operation mode, three phase connection, 5A ammeter circuit, 15s lag of

batteries, 1-2-4-8 batteries sequence, 4 installed batteries. The power factor set point value of the

controller is set to 1 by mean of potentiometer.

At f=50 Hz, U=380V the current of first capacitor battery is;

23 3

U UIc fc

Xc = 0.14 A

So the sensitivity can be calculated as;

110

IcK

In = 0.28

Set this value on the controller by mean of K potentiometer, when it is positioned in manual

operation. The toggle switches of battery must be on left side position. Start the motor brake set

and don’t activate the brake exciter. The motor runs at no load. As expected the controller


executes automatically the calculation of wanting data and through the consequence the complete

summery, to adjust the installation power factor: the controller connects battery 4. Increasing the

load the compensation battery 4 remains always connected. Repeat the above testing for different

sensitivities and no load operation. Stop the motor and don’t forget the starter resistance that

must be completely inserted before any activation.

Set controller sensitivity K = 0.2; maximize K potentiometer in –ive direction. Start the motor

brake set and don’t activate the brake exciter. The motor runs at no load. The controller adjusts

the installation power factor automatically connecting the compensation batteries with a

determined sequence.

Now set controller sensitivity K = 1.2; maximize K potentiometer in +ive direction. Start the

motor brake set and don’t activate the brake exciter. The motor runs at no load. The controller

adjusts the installation power factor automatically connecting the compensation batteries with

another determined sequence (2/3/2 + 3/1 + 2 + 3/4).

Circuit Diagram


EXPERIMENT 8

Vector Group of a Distribution Transformer

Objective

Determine vector group of a three phase transformer.

Apparatus Required

1. Three phase power supply (DL 1013T1)

2. Three phase transformer (DL 1080TT)

3. Voltmeter (DL 2109T3PV)

Procedure

Initially assemble the circuit according to the following topographic diagram. Connect terminal

1U2 (capital A) with terminal 2U6 (lower case letter a), terminal 1V2 with capital B and 1W2

with capital C, terminal 2V6 with lower case letter b and 2W6 with lower case letter c.

Adjust the supply voltage in order to obtain a phase-to-neutral primary voltage of about 100 V.


In sequence measure the following voltages;

UCc = ………………….. (V)

UCb = ………………….. (V)

UBc = ………………….. (V)

UBb = ………………….. (V)

Compared the measured values in the following order;

UCc …………………….UCb

UCc……………………..UBc

UBb……………………..UCb

UBb……………………..UBc

UCb……………………...UBc

Use the group table and determine the vector group of its connection. Shut-off the supply voltage

and assemble a new connection according to the following topographic diagram, modify only the

secondary connections.

Connect terminal 1U2 (capital A) with terminal 2U1 (lower a). Now match terminal 2V1 with

lower case letter b and 2W1 with lower case letter c.

Repeat the above measurements:

UCc = ………………….. (V)

UCb = ………………….. (V)

UBc = ………………….. (V)

UBb = ………………….. (V)

Compared the measured values in the following order;

UCc …………………….UCb

UCc……………………..UBc

UBb……………………..UCb

UBb……………………..UBc


UCb……………………...UBc

Use the group table and determine the vector group of its connection.


EXPERIMENT 9

No load performance of a distribution transformer

Objective

To determine voltage transformation ratio and equivalent circuit quantities based on consumed

active and reactive power.

Apparatus Required



3. Power meter (DL 2109T26)

4. Ammeter (DL2109T1A)


Procedure

Assemble the circuit according to the following topographic diagram. Measurements are

conducted on one phase of transformer, don’t connect phases L2 and L3. Set primary side of

three phase transformer in star connection 380V, the secondary side in star connection and

tertiary side left open. Adjust the supply voltage in order to obtain the nominal voltage (phase-to-

neutral voltage 220V) at the primary side of three phase transformer. This value must be kept

constant for all the measurements. Measure the no load voltage U2 on the secondary side of three

phase transformer for every indicated tap. Enter the measured values in the following table and

calculate the transformation ratio;

n12 = U1/U2

U1 (V) 220 220 220 220 220

Tap

U2 (V)

n12

UN + 5% UN UN - 5% UN - 10% UN - 15%

The calculated value of transformation ratio reflects the approximate value of the winding turn

ratio w1/w2 of the winding taps used.

Without changing any of the relationship on the primary side use the voltmeter of the secondary

side to measure the voltage at the tertiary side (terminals 3U1 – 3U2).

Find out the transformation ratio n13 = U1/U3.


U1 (V) U3 (V) n13

220

Now remove the voltmeter on the secondary or tertiary side in order to refrain from distorting the

measurement results of no load current and active power consumed by the transformer.

Adjust again the supply voltage in order to obtain the nominal voltage at the primary side of

three phase transformer and measure the following quantities;

U1 (V) I10 (mA) P10 (W) Cos ɸ0

220

Calculate the power factor on primary side by using the following expression;

Cos ɸ0 = P10/(U1. I10)

At nominal voltage calculate the active and reactive components of the no-load current according

to the following expressions:

IFE = I10 .Cos ɸ0 =…………….. (mA)

Iµ = I10 .sin ɸ0 =………………..(mA)

Now calculate the iron resistance and magnetizing reactance by using following expressions:

RFE = U1/ IFE = ……………….(Ω)

Xh = U1/ Iµ = …………………(Ω)

Now also connect phases L2 and L3 and measure the transformation ratio at UN value on the

secondary side for a primary voltage supply of 380 V.

U1 = 220 V U2 = ………………..(V)

n12 = 220/U2 =……………


After disconnecting the voltmeter on the secondary side measure the no load current I10 and the

consumed active power P10.

I10 = …………(mA)

P10 =……………(W)

Circuit Diagram


EXPERIMENT 10

Load Performance of a distribution Transformer

Objective

Measuring the effect of load type and magnitude on the performance of secondary

voltage

Determining the efficiency of transformer

Apparatus required



3. Power meter (DL 2109T26)

4. Resistive load (DL 1017R)

5. Inductive load (DL 1017L)

6. Capacitive load (DL 1017C)

7. Ammeter (DL2109T1A)


Procedure

Assemble the circuit diagram in accordance with the following topographic diagram. Set the

primary side of transformer in star connection 380 V (phase voltage 220 V) and the secondary

side with Un = 220 V winding tap in star connection. First of all connect the resistive load in star

connection. Before starting the measurements the load is set to zero. Adjust the supply voltage in

order to obtain the nominal no load phase to neutral voltage U20 = 220 V.

Beginning from R1, reduce the value of resistive load in steps until R6 value. For each step

measure the load voltage U2 and current I2 as well as active power absorbed P1 at primary and

P2 at secondary side.


Enter the measured values in the following table and calculate the voltage drop on secondary

side after applying load and efficiency.

Load U20(V) U2(V) ΔU(V) I2(A) P1(W) P2(W) Ƞ (%)

R1

R2

R3

R4

R5

R6

220

220

220

220

220

220

Plot power vs. efficiency.

Now resistive load is first replaced with inductive and then with capacitive load. The above

measurements are repeated in the same fashion for the indicated three phase inductive and

capacitive loads.

The measurements of active power levels can be omitted here due to the fact that the inductive or

capacitive load consumes almost exclusively reactive power.

Enter the measured values in the following tables.

Inductive load

Load U20(V) U2(V) ΔU(V) I2(A)

L3

L4

L5

L6

L7

220

220

220

220

220

Capacitive Load

Load U20(V) U2(V) ΔU(V) I2(A)

C2

C3

C4

C5

C6

220

220

220

220

220

Results


EXPERIMENT 11

Luminescence

OBJECTIVE Verifying the Inverse Square Law and compare the difference in output luminescence of

incandescent, fluorescent and compact fluorescent lamps.

APPARATUS 1. A wooden board

2. Connecting wires

3. Fluorescent Light

4. Incandescent Light

5. LUX Meter

Theory INVERSE SQUARE LAW The inverse-square law, which states that the luminance at a point on a surface

perpendicular to the light ray is equal to the luminous intensity of the source at that point

divided by the square of the distance between the source and the point of calculation.

E = I/D2

Where:

E= Illuminance in footcandles

I = Luminous intensity in candles

D= Distance in feet between the source and the point of calculation

INCANDESCENT LIGHT BULBS

Incandescent light bulbs consist of a glass enclosure (the envelope, or bulb) which is filled with an

inert gas to reduce evaporation of the filament. Inside the bulb is a filament of tungsten wire, through


which an electric current is passed. The current heats the filament to an extremely high temperature

(typically 2000 K to 3300 K depending on the filament type, shape, size, and amount of current

passed through). The heated filament emits light that approximates a continuous spectrum. The

useful part of the emitted energy is visible light, but most energy is given off in the near-infrared

wavelengths.

FLOURESCENT TUBE LIGHT

A fluorescent lamp or fluorescent tube is a gas-discharge lamp that uses electricity to excite mercury

vapor. The excited mercury atoms produce short-wave ultraviolet light that then causes a phosphor to

fluoresce, producing visible light.

Compared with incandescent lamps, fluorescent lamps use less power for the same amount of light,

generally last longer, but are bulkier, more complex, and more expensive than a comparable

incandescent lamp.


A compact fluorescent lamp (CFL; also called compact fluorescent light, energy-saving light,

and compact fluorescent tube) is a fluorescent lampdesigned to replace an incandescent lamp; some

types fit into light fixtures formerly used for incandescent lamps.

Compared to general-service incandescent lamps giving the same amount of visible light, CFLs use

less power (typically one fifth) and have a longer rated life (six to ten times average). In most

countries, a CFL has a higher purchase price than an incandescent lamp, but can save over five times

its purchase price in electricity costs over the lamp's lifetime. Like all fluorescent lamps, CFLs

contain mercury, which complicates their disposal. In many countries, governments have established

recycling schemes for CFLs and glass generally.

CFLs radiate a light spectrum that is different from that of incandescent lamps.

Improved phosphor formulations have improved the perceived colour of the light emitted by CFLs,

such that some sources rate the best "soft white" CFLs as subjectively similar in colour to standard

incandescent lamps.

PROCDUERE & CALCULATIONS

Place different lamps on the wooden board & calculate the LUX level at different point (Approx

Results only due to some unavoidable problems).

Results

http://en.wikipedia.org/wiki/Fluorescent_lamp

http://en.wikipedia.org/wiki/Incandescent_light_bulb

http://en.wikipedia.org/wiki/Light_fixture

http://en.wikipedia.org/wiki/Luminous_flux

http://en.wikipedia.org/wiki/Mercury_(element)

http://en.wikipedia.org/wiki/Phosphor


EXPERIMENT 12

Calculating the Total Cost in a Residential and Commercial or Industrial Bill

OBJECTIVES You are given an Industrial or commercial Bill

Calculate the total energy cost of the utility bill.

Explain the terms used in the bill

Perform Exercise in the end of the Lab Session

Theory The rates of utility companies are based upon the following guidelines:

1. The amount of energy consumed [kWh]

2. The demand rate at which energy is consumed [kW]

3. The power factor of the load.

The amount of energy consumed is measured by Energy meter and the demand of the system

during the demand interval is measured by Demand meter.

What is The Difference Between Demand and Consumption? Demand is how much power you require at a single point in time, measured in

kilowatts (kW).

Consumption is how much energy you use over a period of time, measured in

kilowatt-hours (kWh).

Example: assume ten lights are turned on each with a 100-watt bulb. To accomplish

this, you must draw - or demand - 1,000 watts, or 1 kW of electricity from the power

grid. If you leave all ten lights on for two hours, you would consume 2 kWh of

electricity.

Demand Measurement Demand varies by customer and month. To record demand, a special meter tracks the

flow of electricity to a facility over a period of time, usually 30-minute intervals.

Over the course of a month, the 30-minute interval with the highest demand is

recorded and reflected on a monthly bill.

Minimum Charges means a charge to recover the costs for providing customer service to

consumers even if no energy is consumed during the month.

Fixed Charges means the part of sale rate in a two-part tariff to be recovered on the basis of

Billing Demand in kilowatt on monthly basis.

Variable Charge means the sale rate per kilowatt-hour (kWh) as a single rate or part of a

two-part tariff applicable to the actual kWh consumed by the consumer during a billing

period.

Maximum Demand where applicable , means the maximum of the demand obtained in any

month measured over successive periods each of 30 minutes duration.

Sanctioned Load where applicable means the installed load in kilowatt as applied for by the

consumer and allowed/authorized by the Company for usage by the consumer.

Power Factor shall be to the ratio of kWh to KVAh recorded during the month or the ratio of

kWh to the square root of sum of square of kWh and kVARh,.

Formulae to be used:


1. Energy Charges (Rs) = No. of Units x energy charges (Rs/kWh)

2. Fuel Adjustment Charges (Rs) = No. of Units x energy charges (Rs/kWh)

3. Fixed Charges (Rs)

If MXD>50% of connected load

then

Fix Charges (Rs) = Fix charges rates x MXD

If MXD<50% of connected load

then

Fix Charges (Rs) = Fix charges rates x 50% of connected load

4. Additional Surcharge

Additional Surcharge (Rs) = No. of Units x Additional surcharge (Rs/kWh)

5. Income Tax

Applicable on Taxable Amount

Taxable Amount = Energy Charges + Fuel Adjustment Charges + Additional Surcharge +

Fixed Charges + Electricty Duty + Meter Rent + P.f Penalty

6. Sales Tax

Sales Tax = some percent of Taxable amount (See Tarrifs)


EXPERIMENT 13

Home Electrical Wiring

OBJECTIVE To make connections in home electrical wiring from services main to different

distribution boards and electrical points for appliances in a room.

APPARATUS A large wooden board

Kilo Watt-hour Meter

Wires & Cables

Switches & Sockets

Bulbs& Fans

THEORY Designing the home electrical wiring needs careful consideration because of safety. For wiring in

residential buildings or industrial buildings, wiring layout should be first prepared on the drawing

board. The number of light and power points in a building is determined not only by its size, but is

also a matter of individual preference especially in the case of residential buildings and as such the

owner should be consulted for this. The number of outlets should be adequate to ensure convenient

hooking up of the various electric operated gadgets & appliances. Minimum four outlets one per wall

should be provided in each room. Lamps & motors should normally be wires on different circuits.

EXERCISE

Make connection of the three phase watt hour meter with the service main and

distribute the three-phase incoming service main & neural wire to different

distribution boards & electrical points (for appliances) in different rooms of

the house.

Select cables for them.

Measure the total energy.

Also draw the circuit diagram on AUTOCAD using the standard symbols of

switch fan bulb etc.


EXPERIMENT 14

Earthing

OBJECTIVE To measure Earthing Resistance and Soil resistivity.

APPARATUS Earth Resistance Tester

Hammer

Measuring Tape

THEORY Earthing provides protection to personnel and equipment by ensuring operation of protective

control gear and isolation of the faulted circuit in the following cases.

Insulation puncture or failure

Breakdown of insulation between primary & secondary windings of a transformer.

Lighting stroke

Ensuring low earth resistance is important in earthing

process. In case where protection against the faulted list is

provided by mean of fuse or a circuit breaker, the total

resistance of the earth path must be low enough to enable the

operation of the protective device.

The earth electrode resistance depends upon the electrical

resistivity of the soil in which the electrode is installed,

which in turn is determined by the following factors:

1. Nature of soil

2. Extent of moisture

3. Presence of suitable salts dissolved in moisture.

TYPES OF EARTH ELECTRODES

Rod & Pipe Electrodes

Plate Electrodes

Strip or Round Conductor Electrodes

Plate Electrodes: Plate electrodes consist of copper, cast iron or steel plate.

The minimum thickness of plate is recommended as

For cast iron - 12mm

For GI or steel - 6.3mm

For Copper - 3.15mm

And size not less than 600mm x 600mm.


The approximate resistance to ground in a uniform soil can be expressed by

4 2R

A

where p = resistivity of soil, considered uniform in m.

A= area of each side of the plate in m2

Rod & Pipe Electrodes: This type of earthing is more suited for a soil possessing high resistivity and the electrode is

required to be longer & driven deeper into the soil to obtain a lower resistance to ground.

The diameter, thickness and length of the pipe is recommended as follows:

Cast iron (CI) pipes - 100mm (internal diameter), 2.5 to 3 m (long), 13mm

thick.

MS pipes - 38 to 50mm (internal diameter), 2.5 to 3 m (long),

13mm thick

Copper -13,16 or 19mm diameter, 1.22 to 2.44m long.


In this case, the approximate resistance to ground in a uniform soil can be expressed by:

100 8ln 1

2* *

lR

l d

where

R= Resistance in

l = length of pipe in cm

d = internal diameter of pipe in cm

Resistivity of Soil:

Type of soil Average resistivity (Ω )

1. Wet organic soil 10

2. Moist Soil 100

3. Dry Soil 1000

4. Bed rock 10000

It has been found that the resistivity of the soil can be reduces by a chemical treatment with

the following salts.

Normal Salt (NaCl) and a mixture of salt & soft coke.

MgSO4

CuSO4

Lab Manual

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