ps lab manual_b.tech - final

POWER SYSTEM LABORATORY

MANUAL

Dr. Anil Swarnkar, Dr. KusumVerma

Assistant Professor, EED

(Lab In-charge)

Department of Electrical Engineering

MALAVIYA NATIONAL INSTITUTE OF TECHNOLOGY

JAIPUR

Prerequisites:

1. The knowledge of basic concepts of power system protection schemes.

2. The knowledge of the Electrical Power Transmission Systems.

3. The knowledge of modelling and performance of Transmission Lines.

List of Experiments:

Rotor 1

Expt. No. Title of the Experiment

1 To find out the dielectric strength of the transformer oil.

2 To study and plot the characteristic of fuse and Miniature Circuit Breaker

(MCB).

3 To study and evaluate the performance of small and medium (π and T

models) transmission lines.

4 To study the operation of inverse time overcurrent relay.

5 To study the operation of instantaneous under voltage relay.

Rotor 2

Expt. No. Title of the Experiment

1

To study and verify the operation of Inverse Definite Minimum Time

(IDMT) overcurrent relay for different current and Time Setting

Multiplier (TSM).

2 To observe the operation of overcurrent and earth fault relay for protection

of 3-phase feeder under (i) LG (ii) LL (iii) LLG (iv) LLL (v) LLLG faults.

3

(a) To study and evaluate the performance parameters of long

transmission lines (π and T models).

(b) To study the current in neutral conductor for different unbalanced

conditions and draw the phasor diagrams.

4 To study and verify the protection of a parallel feeder by using directional

overcurrent relay.

5 To observe and verify the current grading and time grading protection of

radial feeder.

Lab Guidelines and Instructions

Introduction:

The experiments in this laboratory course are designed to cover the theoretical

and analytical concepts of UG courses- Electrical Power Transmission

Systems(EET-212) &Power System Switchgear and Protection (EET-301). The

objective of the experiments is to enhance the students' understanding of important

analytical principles developed in these courses by engaging them in the real-world

application of these principles in the laboratory. In addition to further develop the

students' laboratory practice for experimentally testing and evaluating performance

of power systems employing different relays, switchgears and other protective

devices and to become familiar with modeling and analysis of power systems

under various operating conditions.

Instructions to Students:

Each lab session lasts two hours and starts promptly at the scheduled time. A

brief introduction and guide line for the experiments will be given by the instructor

at the beginning of the each lab section.

1. Preparing the lab is very important as it will save the time and allows the

student to work more efficiently. The pre-lab includes reading and

understanding each lab experiment in advance.

2. Review the material prior to coming to the lab; consult the textbook(s) if

required. Draw the connection diagram for the experiments, sketch anticipated

graphical results, and get an idea of the approximate range and scale of the

quantities you will be measuring.

3. Before coming to the lab, prepare an Issue Slip for conducting the experiment.

This should include the title of the experiment, list of equipments required and

circuit diagram. Write the names of the students performing the experiment. Get

the Issue Slip checked by the Faculty. The lab technician will issue the required

apparatus.

4. Each lab will be performed in the group of two/three students. The team

approach encourages interaction and helps with the debugging and data

collection. Each student required to have one lab notebook and is responsible

for recording the measurement data and any observations which will be helpful

for writing the lab report. Copying of data from other groups or submitting

artificial or altered information is in violation of the Code of Academic

Integrity and will result in a zero grade for the course. The lab report is an

individual effort and each student should present his or her own report.

5. Each lab notebook will be reviewed and signed and dated by the Lab

Technician or TA/ Faculty before leaving the lab.

6. Do not switch on the circuit/experiment until you get it checked once by

Technician/Instructor.

7. Leave your workplace at least as clean and tidy as you found it. Please put

everything back in its proper place before you leaving the Lab.

8. Be on time to the laboratory, late coming between 10 to 20 minutes will be

recorded and after 20 minutes you will be not allowed to start your lab and you

need to make an arrangement to come and makeup the lab with 25% penalty.

9. At the end of the class hour:

a. Clean up your table.

b. Switch off all equipment.

c. Hand in all components issued to you for the hour to the technician.

d. See that the instructor/Grad. Asst/lab technician has signed your data

sheet of the experiment done on that day.

e. Check what you have to do for your next experiment.

f. Get your table checked by the technician before you leave.

g. Put the stools, used by you to sit, back in the appropriate places.

10. Cell-phone ringing or use is not allowed in the lab.

Grading/Evaluation Policy:

Laboratory Component = 100 marks

Credits: 1 (0-0-2)

PRS: 60 Marks PRE: 40 Marks

Lab Work Makeup Policy:

All laboratory work has to be completed during the designated lab period.

Students who miss a lab session due to a documented emergency are expected to

schedule a makeup time with Lab Technician or TA/ Faculty to conduct the missed

lab work.

Guidelines for Writing Lab Reports:

Each student is required to maintain a laboratory notebook which is used to take

notes during the lab session, record, data, circuit analyses, calculations, graphs, etc.

The goal of the lab notebook is to keep complete and accurate records of your

work in the lab. The lab reports will be graded according to the experimental

procedure, clarity of presentation, neatness, data recording, analysis, calculation,

and discussion of the results. Reports are to be neatly hand written and should

contain the following information.

1. Write your names, student ID, date, Lab section, course title and code on the

front page.

2. Title of the experiment.

3. Object of the lab experiment.

4. List of Apparatus required.

5. Theory related to the experiment.

6. Experimental procedure.

7. Show the experiment measurement set-up (schematics); record the data with

proper units, sketches and observations.

8. Graphs must be in standard form with proper paper, label, title, and units.

Measured data points should be clearly visible even if a line has been

interpolated through the data points.

9. Tables must have column headings and units.

10. Compare the measured results with the expected ones. Explain any deviations

between the theoretical and experimental results.

11. Discussions and conclusions: This is an important part of the report. The

conclusion should contain the Summary of the results.

******

Rotor-1

EXPERIMENT NO.1

AIM: To find out the dielectric strength of the transformer oil.

Apparatus Required:

S.No. Name of Apparatus Quantity

1. Motorized oil testing set 1

2. Pure insulating oil 1

3. Insulating oil sample 1

Theory:

The fault free operation of power transformers is a factor of major economic

importance and safety in power supply utilities and industrial consumers of

electricity. In the current economic climate, industries/supply utilities tighten their

control on capital spending and make cutbacks in maintenance, an increased

awareness is placed on the reliability of the existing electric power supply. Down

time is at a premium. Often, the loading is increase on present units, as this will

defer purchasing additional plant capacity. Thus the stress on the transformer

increases. The net total effect of the thermal, electrical and mechanical stress

brought on by increased service needs to be monitored to ensure reliability.

Regular sampling and testing of insulation oil taken from transformers is a

valuable technique in a preventative maintenance program. If a proactive approach

is adopted based on the condition of the transformer oil, the life of the transformer

can be extended.

The dielectric strength: Dielectric strength of any insulating material indicates

the maximum applied electric field strength for which the insulation property

works fine. Imagine, you have a insulated wire and a voltage source. When you are

applying a huge voltage across the wire you will find that the wire is heated up and

after a certain point, the insulation coating is melted. Here, the voltage that causes

to demolish the insulation is referred as the dielectric strength of the insulating

material. Similarly for transformer, the insulating oil can withstand up to a certain

voltage level. After that, the insulation breakdown occurs. Generally, transformer

oil with minimum dielectric strength for 30 KV is used in power transformer and it

is the minimum safe level of insulating oil. So, before using, the oil is tested and

this procedure is termed as Transformer oil testing or Breakdown voltage testing of

transformer oil or simply the BDV test of transformer. High dielectric strength is a

desirable parameter of transformer insulating oil.

Dielectric dissipation factor: Suppose, you have a piece of insulated wire.

Whenever, you are applying some potential difference across the two terminals,

current starts flowing through the conductor. But you will also notice that, a little

amount of current is flowing through the insulation part also. This current is called

the leakage current. In ideal dielectric material, this leakage current leads the

applied voltage by the angle of 90°. This angle is termed as Delta and denoted by

δ. In case of transformer, the insulating oil is also a dielectric material. But, as it is

not a ideal one, so the angle δ in which the current leads the voltage is lesser than

90°. The tangent of this angle (tanδ) is termed as the Dielectric dissipation factor of

transformer oil. The current has two components; namely reactive component and

resistive component. High value of the resistive component indicates the high

strength of the insulator. Therefore, smaller dielectric dissipation factor is the

desirable parameter of transformer oil.

Resistivity: Resistivity means the effective resistance of the transformer oil.

Resistivity of any material is inversely proportional with the temperature.

Generally the temperature of a transformer is more or less same as the ambient

temperature. But, during full load condition or faulty condition, this temperature

goes to a very high value. So, there may be a chance of decreasing the effective

resistance of transformer oil and hence, this may leads to weaken the insulation.

Therefore, transformer oil with higher resistivity is always preferred. The

resistivity of transformer oil is measured in normal temperature as well as in high

temperature (90°) to ensure the safety for both normal and full load operation. The

minimum resistivity of Transformer Oil is 1500*1012

Ω – cm at 27 ° C and

35*1012

Ω – cm at 90 ° C. This is the standard for transformer oil resistivity.

Uses of transformer oil: There are two types of transformer oil namely Paraffin

based transformer oil and Naphtha based transformer oil. Naphtha based

transformer oil is more popular. The value of pour point and flash point is higher in

Paraffin based oil. The classical insulating oils are naphtha based but in modern

era, Paraffin based oils becoming more and more popular in India as well as in

foreign countries. Naphtha based oils are costly as compared to Paraffin based oils.

In large power transformers, Paraffin based oils is recommended for smoother

operation. The transformer oils mainly serve the following purposes:

Insulating: Being dielectric in nature, the transformer oil provide superior

insulation for the transformer core. It also protects the paper insulation which

ensures the safety of a transformer.

Arc quenching: Good transformer oil has a capability of suppressing the

spark generated. So, it is another safety measure which ensures the automatic

arc quenching in a transformer.

Cooling: During the full load operation, the temperature becomes very high.

This necessitates a sophisticated transformer cooling arrangement. In the full

load condition, the transformer oil flows throughout the transformer by

convection process and in this way, generated heat is absorbed by the oil. So,

transformer oil is used as the coolant.

Procedure:

1. Rinse the test chamber with pure insulating of oil two times to remove dirt,

carbon etc, from the walls of the cup.

2. Rinse the cup with the oil to be tested.

3. Fill the chamber with the oil to be tested. The oil level should be about 40

mm above the electrodes. Care should be taken that no bubbles are formed

while pouring of oil. If any bubbles are formed, remove them with the glass

rod provided.

4. Open the cover of the oil testing set and place the test chamber properly at

the required position.

5. Adjust the gap between electrodes 4mm by the metal rod provided. The rod

should pass between the electrodes a bit tightly.

6. Close the cover of the testing set properly. If the cover is not closed

properly, the micro-switch provided on the right hand side of the cover will

not operate and the H.T. will not be energized.

7. Switch of the supply of the unit by the circuit breaker provided on the

bottom left side of the unit. This will take LT ON/HT OFF indicator to

glow.

8. See the deflection on the voltmeter. If it is not zero, the H.T. will not be

energized. To make it zero, press REVERSED knob and keep it pressed till

the needle comes to zero. Now release the knob.

9. Press the HT on push button. The HT on indicator will glow while the HT

OFF indicator will turn off.

10. Press the FORWARD knob and keep it pressed till the reading on voltmeter

is 20 KV. Release the knob at this point and wait for one minute.

11. If the oil withstands this voltage, increase the voltage by pressing the

FORWARD knob in steps of 2 KV and wait at level for one minute

breakdown.

12. The dielectric strength of the oil is that highest voltage (in KV) which the

oil can withstand without breakdown for one minute.

13. The breakdown can be observed by flashover between the electrodes and

after which the H.T. trips by itself.

Observations and Results:

1. Once the flashover occurs, read the voltage on the voltmeter and the voltage

reading at this instant will be dielectric strength of test sample of oil.

2. Bring back the voltage to zero by pressing REVERSE knob. Press the HT

OFF switch. The indicators will changeover.

3. Switch off the L.T. supply. Open the cover of the unit and stir the oil by the

glass electrode. Check the gap between the electrodes by the metal rod.

4. Repeat the above procedure 5 times. The average of the different reading

will be the dielectric strength of the oil.

5. Determine the dielectric strength of test sample of oil in KV/cm.

6. Add 2-3 drops of water in the oil and repeat the test for same sample of oil.

7. Determine the dielectric strength of oil in KV/cm.

Discussions: Discuss the results obtained.

EXPERIMENT NO.2

AIM: To plot the characteristic of fuse and Miniature Circuit Breaker (MCB).

Apparatus Required:

S. No. Name of Apparatus Specification Quantity

1. Voltmeter (0-300)V 1

2. Ammeter (0-30)A 1

3. SPST(S/W) 30A 1

4. Fuse sample 5A 1

5. MCB 6A 1

6. Variable load 1 Φ, 15A 1

Theory:

The fuse is the cheapest and simplest form of automatic operating protectingdevice

andis used for protecting low voltage equipments against overloads and/or short

circuits. The fuse is designed to carry the normal working current safely without

overheating. During overload/short circuit conditions fuse gets heated up to

melting point rapidly and isolates the faulty device from the supply circuit.

Minimum fusing current is a value corresponding to operation in an arbitrary time

obtained under prescribed test conditions. The fuse rating is the value of current

which when flows through the element does not melt it. Fusing factor is a ratio of

minimum fusing current to the current rating of fusing element. Fusing factor is

always greater than unity. The prospective current is defined as the Root Mean

Square (RMS) value of current, which would flow in a circuit immediately

following the fuse when a short circuit occurs assuming that the fuse has been

replaced by a link of negligible resistance. The time taken from the instant the

current that causes a break in the fuse wire starts flowing to the instant the arc is

initiated is melting time or pre-arcing time. The time taken from the instant of arc

initiation to the instant of arc being extinguished is arcing time. The sum of pre-

arcing and arcing time is the total operating time of fuse.

The time current characteristics of fuse get deteriorated with time and hence are

not reliable for discrimination purposes. These fuses are mainly used for domestic

and lightning loads. The HRC (High Rupturing Capacity) cartridge fuses are used

to protect important and costly equipments operating at low voltages (up to 33

KV).

A miniature circuit breaker (MCB) is an automatically operated electrical switch

designed to protect an electrical circuit from damage caused due to excessive

current. Its basic function is to detect a fault and, by interrupting continuity to

immediately discontinue electrical flow. Unlike a fuse, which operates once and

then has to be replaced, a circuit breaker can be reset (either manually or

automatically) to resume normal operation. Circuit breakers are made in various

sizes, from small devices used to protect an individual household appliance up to

large switchgear designed to protect high voltage circuits to supply an entire city.

A MCB is a mechanical switching device which is capable of making, carrying for

a specified time and automatically breaking currents under specified abnormal

circuit conditions such as those of short circuit. In short, MCB is a device for

overload and short circuit protection. They are used in residential and commercial

areas.

Circuit Diagram:

Procedure:

1. Do the connections as per the circuit diagram.

2. Increase the load in small steps and set the rated current through fuse in

parallel with SPST switch.

3. Observe that the fuse does not blow off/MCB does not trip for the rated

current.

4. The current is increased in small steps above the rated value and the time

taken for the fuse to blow MCB/to trip is noted starting from opening of SPST

switch.

5. Readings are taken for different settings of current above rated value of

Fuse/MCB.

6. The experimental procedure is repeated for Fuse and MCB separate.


S. No. Voltage (V) Current(A) Time(sec)

1.

2.

3.

4.

5.


EXPERIMENT NO.3

AIM: To study and evaluate the performance of short and medium (π and T

models) transmission lines.

Apparatus Required:

S. No. Name of Apparatus Range Quantity

1. Ammeter (0-1)A 5

2. Voltmeter (0-250)V 3

3. Wattmeter (0-250)W 1

4. Rheostat 1.7A,300 Ω 1

5. Connecting Wires - -

Theory:

In this section we shall discuss the various models of the line. The line models are

classified by their length. These classifications are

• Short lines.

• Medium lines.

• Long lines (Discussed in rotor 2).

1. Short Transmission Line:

When the length of an overhead line is upto 80 km and line voltage is

comparatively low (<20 KV) it is usually considered as a short transmission line.

Due to smaller length and lower voltage the capacitance effect between ground and

conductor can be neglected. So, only inductance and resistance of line are taken

into account (as shown in figure 3.1). The sending end voltage and current for this

approximation are given by

Vs = VR + ZIR

Is = IR

Fig. 3.1 Short line model

2. Medium Transmission Line:

When the length of an overhead transmission line is about 80-200 km and the

line voltage is moderate high (>20 kV but less than 100 kV) it is considered as

medium transmission line. The capacitance effect is taken into account for

purpose of calculations. Medium transmission line can be studied by two

methods.

(i) Nominal-π model:

The capacitance is divided into two equal parts and in between them the total

inductance of line is placed. Let us define three currents I1, I2 and I3 as indicated

in Fig. 3.2. Applying KCL at nodes M and N we get

Is = I1 + I2 = I1 + IR + I3

=𝑌

2𝑉𝑠 +

𝑌

2𝑉𝑅 + 𝐼𝑅 and

Fig. 3.2 Medium T line model

(ii) Nominal-T model:

In this the capacitance is lumped at one place and the inductance of

transmission line is divided into two equal parts and placed on either sides of

the capacitor.

Circuit Diagrams:

Fig.1. Medium T line model

Fig.2. Medium π line model

Procedure:

2) Medium T Line:

1. Connect the circuit as shown in the figure 1. Connect an inductive load

across the line output terminals (13 and 14) and a wattmeter in the load

circuit.

2. Select position π on switch 1 and medium distance on switch 2.

3. Close MCB and adjust the load to provide a suitable load current and power

factor (e.g 0.8 -0.9).

4. Measure the voltage drop across the receiving end impedance Vd1 (terminals

4 and 5), and sending end impedance Vd2 (terminals 2 and 3). Record the

values of the listed reading as indicated in the table 1 below.

5. Calculate the receiving end power factor by using the reading from the

wattmeter and the receiving end voltage and current (e.g = W/IRVR).

6. Determine the line regulation and transmission efficiency.

3) Medium π Line:



circuit.

2. Select position π on switch 1 and medium distance on switch 2.


factor (e.g 0.8-0.9). Measure the voltage drop across the line impedance,

(terminal 2 and 5).Record the values of the sending end current I5 (terminal

11 and 12), receiving end capacitor current IC1 (terminals 19and 20),sending

end capacitor current IC2 (terminal 15 and 16), the line current IL(terminal 3

and 4) and the voltages VS and VR.

4. Record the values of the listed reading as indicated in the table 2 shown

below.


4) Short Line:



circuit.


factor (e.g 0.8-0.9). Measure the voltage drop across the line impedance,

(terminal 2 and 5) and the line current IL(terminal 3 and 4) and the voltages

VS and VR.

3. Record the values of the listed reading as indicated in the table 3 shown

below.



Table-1 Medium Transmission Line (Nominal T Model)

Readings Value

Receiving end impedance

Sending end impedance

Sending end current

Receiving end current

Capacitor current

Sending end voltage

Capacitor voltage

Receiving end voltage

Sending end power

Receiving end power

Sending end power factor

Receiving end power factor

Table-2 Medium Transmission Line (Nominal PI Model)

Readings Value

Line impedance

Sending end current


Receiving end capacitor current

Sending end capacitor current

Line current

Sending end voltage


Sending end power

Receiving end power



Table-3 Short Transmission Line

Readings Value

Line impedance

Sending end current


Line current

Sending end voltage


Sending end power

Receiving end power



Line regulation = 𝑉𝑠 – 𝑉𝑟

𝑉𝑟× 100

Transmission efficiency = 𝑉𝑟 𝐼𝑟 cos ∅𝑟

𝑉𝑠𝐼𝑠 cos ∅𝑠 ×100


EXPERIMENT NO.4

AIM: To study the operation of inverse time over current relay.

Apparatus Required:

S. No. Name of Apparatus Quantity

1. Voltmeter(0-300)V 1

2. Rheostat(300Ω, 1.7A) 1

3. Auto Transformer(220/0-270)V,50Hz , 1-Φ 1

4. Ammeter(0-10)A 1

5. Bulb(60W,220V) 1

6. Trip Coil -

Theory:

Over-current relay operates when the actuating quantity (current) exceeds a

predefined value. This is inherent electromagnetic relay due to saturation of the

magnetic circuit. So, by varying the point of saturation different characteristics are

obtained. The torque Equation of these Relay can be given as T α ϕ1 ϕ2 sinα.

The angle between ϕ1 and ϕ2 or I1 is directly proportional to if one of the

actuating quantities is Voltage. The current flowing in the voltage coils lags behind

voltage by approximately 90’.Assume this current to be I2 the load current I(say

I1) lags V by ϕ. Then the angle ϴ between I1 and I2 is equal to (90-ϕ).

T ∝ 𝐼1𝐼2𝐶𝑜𝑠Ѳ

Where,

I1=Current flowing in the potential coil of directional element.

I2=Current flowing in the C.T. of directional element.

Ѳ=Angle between I1 and I2.

I1∝ V

I2=Current in current coil = I(say)

T ∝ 𝑉𝐼𝐶𝑜𝑠Ѳ

A definite time Over-current relay in a definite time, when the current exceeds its

pick up value.Inverse definite minimum time (IDMT) relay gives an Inverse time

current characteristics of 10 min. values of the fault current for value of plug

setting multiplier (PSM) between 10 and 20 the characteristics tends to be a

straight line.

Current Setting:

The current above which an Over-current relay would operate can be set. Suppose

that relay current isset at 5A,then the relay will not operate.here are toppings on the

current coil.

Circuit Diagram:

Procedure:

1. Connect the circuit as shown in fig.

2. Close the key between 9 and 10 pin.

3. Apply rated voltage in the secondary circuit in which bulb & trip coil is

connected.

4. Set the PSM.

5. Now apply the current slightly greater PSM value.

6. As the key is opened, start the Stop watch.

7. As the graph become parallel to X-axis when the relay operates means trip

the circuit and the bulb is Enlighten.

8. When the bulb glows, stop the stopwatch.

9. Take the current and time reading and Plot the graph between these.


S.No. PSM Fault current(amp) Time(Sec)

1.

2.


Precautions:

1. After each fault, power supply must be turn OFF after taking reading.

2. Time reading should be taken precisely to reduce manual Error.

3. The two auto transformer should be connected to different phase as the need

to bring down the fault current.

EXPERIMENT NO.5

AIM: To study the operation of instantaneous under voltage relay.

Apparatus Required:


1. Voltmeter(0-300)V 1

2. Rheostat( 300Ω, 1.7A) 1

3. Auto Transformer (220V /0-270)V,50Hz , 1-Φ 1

4. Relay 1

5. Bulb(60W,220V) 1

Theory:

Under-voltage relay is one which operates when input voltage drops a predefined

(dropout) value. Under-voltage relays are usually instantaneous devices. Initiated

on instantaneous under-voltage, relays should complete their function every time

input voltage drops below the set point when setting on instantaneous under-

voltage relay. The drop out voltage needs to be specified and VI ratio needs to be

documented.

Circuit Diagram:

Procedure:

1. Make all connections according to the circuit diagram.

2. Connect phase at relay point 3 and neutral to the relay point 4 through a bulb.

3. Give a DC supply to the relay points 7& 8 positive and negative respectively.

4. Initially start from 200 volts and slightly decrease the voltage.

5. After a certain voltage, if the voltage is further decreased the bulb will glow.


Set tripping voltage of relay =.......

Experimentally observed voltage =.......

Calculated error =.......


Rotor-2

EXPERIMENT NO.1 AIM: To study and verify the operation of Inverse Definite Minimum Time

(IDMT) over current relay for different current and Time Setting Multiplier

(TSM).

Apparatus Required:


1. Relay test kit 1

2. Solid state over current relay 1

3. Timer circuit 1

4. Bulb 1

Theory:

Protective relay or relaying system detect abnormal or faulty condition in electrical

circuit and gives signal to operate automatic switchgear in order to isolate faulty

equipment from the system as quickly as possible. The protective relays are help in

protection of the system by avoiding the damage to the power system equipment

and also prevents from persisting the faults. In short circuit condition in power

systems are accompanied by large increase of the currents. The protective relays

which responds to rise in current flowing through the protected element over

predetermined values is called over current protection and the relay used for this

purpose is called over current relay. Earth fault protection can be provided with

normal over current relays with minimum earth fault current is sufficient in

magnitude to detect earth fault. The design of comprehensive protection in a power

system requires the detailed study of time current characteristics of the various

relays used in the scheme. Thus, it is necessary to obtain the operating time current

characteristics of these relays

Working principle and construction:-

The over current relay work on the induction principle. The moving system

consists of an aluminum disc fixed on vertical shaft and rotating on two jewel

bearing between the poles and an electromagnet and damping magnet. The

winding of electromagnet provided with generally seven tabs, which are brought

on to the front of panel, and the required tap is selected by a push in type plug. The

pickup current setting can thus be varied by the use of such plug set multiplier. The

pickup current values of earth fault relays are normally is quite low. The operating

time of all over current relays tends to become asymptotic to a definite minimum

value with increase in the value of current. This is an inherent property of the

electromagnetic relays due to magnetic saturation of magnetic circuit by varying

the point of magnetic saturation, the different characteristic can be obtain these are:

Characteristics of over current relay:-

1. Definite Time Over-Current Relay Characteristics.

2. Inverse Definite Minimum Time (IDMT) Characteristics.

The operating torque in over-current relay is proportional to ϕ1ϕ2sinα where

both flux are produced by the same quantity (single quantity relay).In the case of

current or voltage operated, the torque T is proportional to 12 or T KI^2, for coil

current below saturation, if the core is made to saturate at very early stages such

that with increase of I, K decreases so that time of operation remains the same over

the working range. The time current characteristics operand is known as definite

time characteristics.

If the core is made to saturate at a later stage, the characteristics obtained is known

as IDMT. The time current characteristics are inverse over some range and then

offer saturation assume the definite time form in order to ensure selectivity. It is

essential that the time of operation of the relay should be dependent on the severity

of the fault in such a way that more severe fault, the less is the time to operate, this

being called inverse time characteristic. This will also ensure that a relay shall not

operate under normal condition.

It is essential that there shall be definite minimum time of operation, which can be

adjusted to suite the requirement of the particular installation. At low values of

operating current the shape of the curve is determined by the effect of the

restraining force of the control spring, while at high values the effect of saturation

predominates. Different time settings can be obtained by moving a knurled

clamping screw along a calibrated scale graduated from 0.1 to 1.0 in steps of .05

this arrangement is called time multiplier setting and will vary the travel of the disc

required to close the contacts. This will shift the time current characteristics of the

relay parallel to itself. The delaying the saturation to a further point very inverse

and extremely inverse time current characteristics can be obtained.

Circuit Diagram:

Procedure:

1. Study the construction of the relay and identify the various parts.

2. Connect as shown in the circuit diagram.

3. Set the pickup value of the current marked 1A (100% full load current) by

inserting the plug in the groove.

4. Set the TSM initially at 1.0.

5. Adjust the load current to about 1.3 times of full load current by shorting the

switch K. Open the switch K to permit the adjustment current to flow through

the relay and record the time taken for this overload condition.

6. Vary the values of the load current in steps and record the time taken for the

operation of the relay in each case with the help of timer.

7. Repeat steps 5&6 for TMS of 0.2, 0.4 and 0.8.

8. Repeat the above experiment with different pick up current values using the

plug setting bridge.


Type of Relay:

Pick up current=……..Amps (PSM=Fault/pick upcurrent)

S. No. Fault current (Amp) PSM Operating time in sec. for

TMS of……

0.2 0.4 0.6 0.8 1.0


EXPERIMENT NO.2

AIM:To observe the operation of over current and earth fault relay for protection

of 3-phase feeder under

(i) Line to ground (LG) fault.

(ii) Line to Line(LL) fault.

(iii) Line-line to ground (LLG) fault.

(iv) Line-Line-Line (LLL) fault.

(v) Line-Line-Lineto ground (LLLG) faults.

Apparatus Required:


1. Induction Disc Type Overcurrent relay 2

2. Induction Disc Earth Fault relay 1

3. C.T. 3

4. Rheostat 9Ω, 12A 3

5. 3-phase Variac 1

6. Bulbs 60W, 230V 3

7. Ammeter (0-10)A 3

8. Ammeter (0-3)A 1

9. Key 4

Theory:

On a three phase system the breakdown of insulation between one of the phases

and ground is known as line to ground fault or a single phase earth fault. The

breakdown of insulation between either of two phases is known as line to line fault,

the breakdown of insulation between two phases and earth is known as double line

to ground fault and the breakdown of insulation between the three phases is known

as three phase fault.

Frequency of different types of faults occurring in our road lines is:

Type of fault % Occurrence

L-G 85

L-L 8

L-L-G 5

L-L-L 2or less

Line to ground fault occurs most commonly in practice. Two overcurrent and 1

earth fault relays are used for protection of 3 phase feeder under all types of fault.

An earth fault usually involves a partial breakdown of winding insulation to earth.

The resulting leakage current is considerably less than the short circuit current. An

earth fault relay is essentially an overcurrent relay of low setting and operates as

soon as an earth fault takes place. Whenever there is phase to phase to fault then

only overcurrent relay will operate and if there is a balanced earth fault means zero

current in neutral, than earth fault relay will not operate. We create fault by closing

k1 ,k2, k3 and k4.

Circuit Diagram:Rescan from manual

Procedure:

1. Make connections as shown in fig.

2. Adjust auto transformer wheel to obtain 60 V.

3. Earth fault is created by closing key k4 and line faults by closing keys k1 k2

and k3 for R,Y,B phase respectively.

4. To create phase to ground fault (RG) close k1 and k4 and observe the

operation of relays.

5. To create line to line fault (eg.RY) close k1 and k2observe the operation of

relays.

6. Similarly create other possible line and ground faults close their respective

key and observe operating relays.


S. No. Fault type K1 K2 K3 K4 O.C.

Relay

1

O.C.

Relay

2

Earth

Fault

Relay

1. L-G- RG

YG

BG

2. L-L- RY

YB

RB

3. L-L-G- RYG

YBG

RBG

4. L-L-L-RYB

5. L-L-L-G-RYBG

(balanced)

6. L-L-L-G-RYBG

(unbalanced)


EXPERIMENT NO.3 (a)

AIM: To study and evaluate the performance of long transmission lines (π and T

models)

Apparatus Required:

S. No. Name of Apparatus Ratings Quantity

1 Transmission line panel

2 Ammeter

3 Voltmeter

4 Wattmeter

5 Rheostat

6 Connecting wires

Circuit Diagram:

Theory: Theory related to the experiment.

Procedure:

1. Connect the circuit as shown in the figure, connect an inductive load across

the line output terminals (13 and 14) and a wattmeter in the load circuit.

2. Select position T on switch 1 and long distance on switch 2. Close MCB1 and

adjust the load to provide a suitable load current and power factor(e.g. 0.8-

0.9).end voltage V

3. Measure the voltage drop across the receiving end impedance Vd1 (terminals 8

and 11) and sending end impedance Vd2 (terminals 2 and 5).

4. Record the value of sending end current Is (terminals 11 and 12) capacitor

current Ic (terminals 17 and 18) ,sending end voltage Vs (indicated by

voltmeter Vi)capacitor voltage Vc(indicated by voltmeter V2)., and the

receiving end voltage VR (indicated by voltmeter V3)


Required readings Location Value

Line Impedance Terminal 15 and 19

Sending end current Is Terminal 1 and 2

Receiving End current Ir Terminal 11 and 12

Receiving end capacitor current Ic1 Terminal 19 and 20

Sending end Capacitor Current Ic2 Terminal 15 and 16

Line Current IL

Sending end voltage Vs Indicated by Voltmeter V1

Receiving End Voltage VR Indicated by Voltmeter V3

1. Calculate the receiving end power factor by using readings from the wattmeter

and the receiving end voltage current.

2. Construct the phasor diagram as described previously and determine the line

regulation and transmission efficiency.

Discussions: Discuss the result obtained.

EXPERIMENT NO.3 (b)

AIM: To study the current in neutral conductor for different unbalanced conditions

and draw the phasor diagrams.

Apparatus Required:


1 Transmission line panel

2 Ammeter

3 Voltmeter

4 Wattmeter

5 Rheostat

6 Connecting wires

Circuit Diagram:check the circuit diagram

Theory: Theory related to the experiment.

Procedure:

1. Connect the circuit as shown in the figure, connect an inductive load across the

line output terminals(13 and 14) and a wattmeter in the load circuit.

2. Select position Ton switch 1 and long distance on switch 2. Close MCB1 and

adjust the load to provide a suitable load current and power factor(e.g. 0.8-

0.9).end voltage V

3. Measure the voltage drop across the receiving end impedance Vd1 (terminals 8

and 11) and sending end impedance Vd2 (terminals 2 and 5).

4. Record the value of sending end current Is (terminals 11 and 12) capacitor

current Ic (terminals 17 and 18),sending end voltage Vs (indicated by voltmeter

Vi), capacitor voltageVc(indicated by voltmeter V2)and the receiving end

voltage VR (indicated by voltmeter V3)


Required readings Location Value

Receiving End impedance Vd1 Terminal 8 and 11

Sending end impedance Vd2 Terminal 2 and 5

sending end current Is Terminal 11 and 12

Capacitor Current Ic Terminal 17 and 18

Sending end voltage Vs Indicated by Voltmeter V1

Capacitor voltage Vc Indicated by Voltmeter V2

Receiving End Voltage VR Indicated by Voltmeter V3

1. Calculate the receiving end power factor by using readings from the wattmeter

and the receiving end voltage current.

2. Construct the phasor diagram as described previously and determine the line

regulation and transmission efficiency.


EXPERIMENT NO.4

AIM: To study and verify the protection of a parallel feeder by using directional

over current relays.

Apparatus Required:


1 Induction Disc Type Directional Over Current Relay 2

2 Induction Disc Type Over Current Relay 2

3 Rheostat (3Ω,18A) 1

4 Rheostat (9Ω,12A) 2

5 1Ф, Auto-transformer 1

6 Bulbs (60W, 230V) 4

7 Ammeter (0-10)A 2

Theory:

Under normal operating conditions, power flows in the normal direction in the

circuit protected by the relay. Therefore, directional overcurrent relay (upper

element) does not operate, thereby keeping the overcurrent element (lower

element) de-energized. However, when a fault or normal condition e.g. short

circuit occurs, there is a tendency for the current of power to flow in the reverse

direction. In this condition the current flows through relaying coil of the lower

element of the relay and the disc in the lower element rotates to bridge the fixed

contacts 1 and 2. This completes the circuit for overcurrent element i.e. upper

element. The disc in this element rotates and the moving contact attached to it

close the trip circuit. This gives command to operate the circuit breaker which

isolates the faulty section. The two relay elements are so arranged that final

tripping of the current controlled by them is not made till the following conditions

are satisfied.

Current flows in a direction such as to operate the directional element.

Current in the reverse direction exceeds the pre-set value.

Excessive current persist for a period corresponding to the time setting of

overcurrent element.

Construction: It consists of 2 relay elements mounted on a common case viz.

i. Directional element

ii. Non-directional element

Directional Element:

It is essentially a directional power relay which operates when power flows in a

specific direction. The potential coil of this element is connected through a

potential transformer (P.T.) to the system voltage. The current coil of the element

is energized through a C.T. by the circuit current. This winding is carried over the

upper magnet of the non-directional element. The trip contacts (1 and 2) of the

directional element are connected in series with the secondary circuit of the

overcurrent element. Therefore, the latter element cannot start to operate until its

secondary circuit is completed. In other words, the directional element must

operate first (i.e. contacts 1 and 2 should close) in order to operate the overcurrent

element.

Non-Directional Element:

It is an overcurrent element similar in all respects to a non-directional overcurrent

relay. The spindle of disc if this element carries a moving contact which closes the

fixed contacts (trip circuit contacts) after the operation of directional element. It

may be noted that Plug Setting Bridge is also provided in the relay for current

setting bus has been omitted in the figure for clarity and simplicity. The tapping is

provided on the upper magnet of overcurrent element and is connected to the

bridge.

Torque Equation:

In order to operate relay the Directional element of the relay operate first. Torque

developed in the directional element of the relay is given by equation:

T ∝ 𝐼1𝐼2𝐶𝑜𝑠Ѳ

Where,

I1=Current flowing in the potential coil of directional element.

I2=Current flowing in the C.T. of directional element.

Ѳ=Angle between I1 and I2.

I1∝ V

I2=Current in current coil = I(say)

T ∝ 𝑉𝐼𝐶𝑜𝑠Ѳ

Thus the torque is proportional to the power. The torque rotates the disc and closes

the contacts of directional element, which closes the circuit in overcurrent element

and the relay operate.

Circuit Diagram:

Procedure:


EXPERIMENT NO.5

AIM: To observe and verify the current grading and time grading protection of

radial feeder.

Apparatus Required:


1. Induction Disc Type Overcurrent Relay 3



4. 1ᴓ Autotransformer 1

5. Bulbs 60W,230V 3

6. Ammeter 1

Circuit Diagram:

Theory:

1) Time graded protection system for radial feeder:

The selectivity is achieved based on the time of operation of the relays. The relays

used are simple over current relays. The time of operation of the relays at various

locations is so adjusted that the relay farthest from the source will have minimum

time of operation and as it is approached towards the source the operating time

increases. This is the main drawback of grading the relays in this way because it is

required that the more severe a fault is, lesser should be the operating time of the

relays whereas in this scheme the operating time increases. The main application of

such a grading is done on systems where the fault current does not vary much with

the location of fault and hence the inverse characteristic is not used. For proper

coordination between various relays on a radial feeder the operating time of the

relay farthest from the source should be minimum and it should increase as we go

towards the source. If the time of operation of relay 1 is T1, then the time of

operation of relay 2 must be T2= T1+t where t is the time step between successive

relays and consists of the time of operation of C.B. at 1,over travel of relay at 2 and

factor of safety time.

2)Current grading protection system for radial feeder:

This type of grading is done on a system where the fault current varies appreciably

with the location of the fault. This means as we go towards the source the fault

current increases. With this if the relays are set to pick at a progressively higher

current towards the source, then the disadvantage of the long time delay that occurs

in case of time graded systems can be partially overcome. This is known as current

grading.

For proper coordination between various relays on a radial feeder the pickup of a

relay should be such that it will operate for all short circuits in its own line and

should provide backup protection for short circuits in immediately adjoining line.

According to Indian Standard Specifications the operating value should exceed 1.3

times the setting i.e. minimum short circuit current > 1.3*Isetting.

Procedure:

1) Time graded protection system for radial feeder:

1. Make the connections as per the circuit diagram.

2. The relays are set at a particular value of current.

3. The operating time of the relays for the fault for the particular time is

noted.

4. The time setting is changed and the procedure is repeated for different

values.

5. Plot the characteristics current vs time.

2) Current graded protection system for radial feeder:

1. Make the connections as per the circuit diagram.

2. The relays are set at a particular value of current.

3. The operating time of the relays for the fault for the particular time is

noted.

4. The time setting is changed and the procedure is repeated for different

values.


1) Time graded protection system for radial feeder

S. No. Time (sec) Current (A)

2) Current graded protection system for radial feeder

S. No. Time (sec) Current (A)


ps lab manual_b.tech - final

Documents

lab experiment

eed lab

lab session

lab guidelines

lab section

performance of power

operation of overcurrent

power system laboratory