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ELECTRICAL ENGINEERING DEPARTMENT Bengal Engineering and Science University, Shibpur

POWER SYSTEM LABORATORY: (EE 651-new/EE 707-old) Sixth/Seventh Semester

Expt. No.: EE / PS - 1

Title: LOAD FLOW STUDY USING GAUSS-SEIDEL METHOD What is load-flow? Load-flow calculations provide voltages at different buses and power flows (active and reactive) through lines and transformers under specified bus conditions. Objective:

(a) learning to use a load-flow program for studying the behaviour of a transmission network for a set of specified bus conditions.

(b) to know how to accelerate the convergence of load-flow calculation process. (c) to study the effect of bus power (both active and reactive) variation on the bus voltage

magnitudes and angles. (d) to study the effect of line outage on the system behaviour.

Procedure: (a) The data format for load flow studies are as follows: [ value(data type)]

1. number of generator buses ( I ), no. of load buses ( I ) , no. of lines ( I ) 2. serial no.( I ), from bus no.( I ), to bus no.( I ), line impedance ( C ), half line charging

admittance ( C ), off-nominal ratio of transformer ( R ) * 3. serial no.( I ), voltage controlled bus no.( I ), Qmin ( R ), Qmax

4. acceleration factor ( R ), tolerance ( C ) ( R )

5. serial no. ( I ), initial bus voltage ( C ), generation ( C ), load ( C ) 6. number of shunt elements ( I )

** 7. serial no. ( I ), shunt element bus no.( I ), shunt element susceptance ( R ) Note:

i) * voltage controlled bus data is not to be fed if there is no generator bus. ii) ** shunt element data is not to be fed if there is no shunt element. iii) ( I ) - Integer data; ( R ) - Real data ; ( C ) - Complex data

b) Run 5-bus (Ref. Stagg and E1-Abiad) and 6 bus (Ref. Wood and Wollenberg) systems. Tabulate

bus voltage magnitudes and angles in one table(shown below) and line flow(active and reactive) in another table(prepare yourself).

BUS NO. Bus Voltage magnitude Bus Voltage Angle(deg.)

c) Vary the acceleration factor from 1.2 to 1. 8 the number of iterations for the networks. Make suitable table for your use.

in steps of 0.1 & note only

d) Vary the bus power (both active and reactive) alternatively at bus no.5 (say) for the networks and note the changes in bus voltage magnitudes and angles at different buses.

e) Trip out one line at a time and note its effect on the behaviour of the transmission systems. Note bus voltage magnitudes & angles and line flows in suitable tables.

Report : a) Make tables showing bus voltages, power flows and slack bus power. Do you think that the

results are acceptable? Justify your answer. b) Plot the no. of iterations vs. Acceleration factors for a particular value of tolerance. c) Plot variations of bus voltage angle vs. bus power and bus voltage magnitude vs. bus reactive

power.

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ELECTRICAL ENGINEERING DEPARTMENT Bengal Engineering and Science University, Shibpur

POWER SYSTEM LABORATORY: (EE 651-new/EE 707-old) Sixth/Seventh Semester

Expt. No.: EE / PS - 2

Title: STUDIES ON DC LOAD FLOW METHOD Objective: A) To run DC load flow program on a digital computer;

B) To be familiar with the application of DC load flow to contingency evaluation. Theory: DC load flow equation is P = B θ . . . . . . . (1) where P is the bus active power injection, B is the bus susceptance matrix, and θ is the bus voltage angles. For N bus system the dimensions of P, B and θ are (N-1)x1, (N-1)x(N-1), and (N-1)x1 respectively. Equation (1) is solved for θ by Gaussian Elimination technique and line flows are then computed by pij = bij (θ i - θ j) . . . . . . . (2) where pij is the MW flow through line i-j connected between buses i and j; bij is the primitive value of susceptance of the line i-j; and θ i , θ j are the ith bus and jth

bus voltage angles respectively.

Procedure: (a) The data format for DC load flow studies are as follows: [ value(data type)]

1. total no. of buses ( I ) , no. of lines ( I ) 2. serial no.( I ), from bus no.( I ), to bus no.( I ), line reactance ( R ), off-nominal ratio of

transformer ( R ) 3. serial no. ( I ), Active generation ( R ), Active load ( R )

Note: i) ( I ) - Integer data; ( R ) - Real data

b) Run 5-bus (Ref. Stagg and E1-Abiad) and 6 bus (Ref. Wood and Wollenberg) systems. Tabulate

bus voltage angles in one table(shown below) and line flow(active) in another table(prepare yourself).

BUS NO. Bus Voltage Angle(deg.)

c) Vary the MW load at all load buses for 80%, 90%, 110% & 120% of 5-bus & 6-bus systems. Run

DC load flow program and tabulate MW flows through all lines in each case. Contingency Analysis: It is primarily concerned with the outage of the transmission line, transformer, generator etc. to see the changes of MW flow through the remaining lines by running the same DC load flow program. The line flows may then be used to check the MW security of the system. Single line contingency will only be analysed here. d) Run DC load flow program for each line contingency of 5-bus & 6-bus systems. Tabulate the

MW flow through the remaining lines in each case. Report: i) Draw single line diagram of 5-bus & 6-bus systems. ii) Write data files for 5-bus and 6-bus systems. iii) What is the purpose of contingency analysis? What is multiple contingency analysis? iv) Compare angle and line flow with Gauss-Seidel method for standard data set using

%error in angle = 100 × (θ GSLF − θ DCLF) / θ GSLF

%error in line flow = 100 × (MW flow

GSLF − MW flow DCLF) / MW flow GSLF

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ELECTRICAL ENGINEERING DEPARTMENT Bengal Engineering and Science University, Shibpur

POWER SYSTEM LABORATORY: (EE 651-new/EE 707-old) Sixth/Seventh Semester Expt. No.: EE / PS - 3 Title: D.C. NETWORK ANALYSER - ITS USE IN FAULT STUDIES D.C. NETWORK ANALYSER: Maker - James H. - Starr La Grange, III. (General Radio Co.) Serial No. 105. Voltage (E) = 0.0 to 1.2 per unit; Impedance (Z) = 0.1 to 2.0 p.u.; Current (I) = 0.0 to 1.0 p.u., Battery voltage 24V. Procedure: The problem that is to be solved using a d.c. network analyser will be supplied to you. First of all choose the base voltage and the base KVA in such a way that most of the impedances lie in the range 2.0 to 0.1 pu. Convert the corresponding ohmic values to pu. Values. Draw the equivalent network as you do for ordinary fault calculation. The rest of the problem is to set up those reactances (resistances in this case) on the network analyser, connect them as per equivalent circuit and note down the total fault current and currents through different branches by turning the master switch to different positions. Voltage adjustment: The knob marked “Voltage adjustment” is used for the purpose. Rotation of the knob in a clockwise direction increases the voltage delivered to the calculator. Except in special cases, this knob should be adjusted until the voltmeter reads 1.0 per unit E during each rheostat adjustment or each current reading. Adjusting Table Rheostats: (1) Insert the three conductor plug at the free end of the multi-conductor cord into the jack corresponding to the table rheostat in question. (2) As a precaution, turn the rheostat knob fully counter clockwise to avoid excessive current. (3) Turn the master switch to the position “Adjust plus 0.1”. (4) Adjust the knob of the rheostat until the right hand instrument reads the desired

impedance plus 0.1 on the bottom scale, directly, keeping the voltmeter adjusted to 1.0 per unit E with the voltage adjustment knob.

(5) Turn the master switch to the position “Adjust plus 0.0”. (6) Adjust the knob of the rheostat until the right hand instrument, reads the desired

impedance on the bottom scale, directly, keeping the voltmeter adjusted to 1.0 per unit E with the voltage adjustment.

Precaution: The master switch should always be returned to the "OFF" position as soon as any reading or adjustment is completed. Never insert or withdraw any of the three conductor plugs except when the master switch is "OFF". Reference: W.D.Stevenson - Elements of Power System Analysis (Ch.-VIII). Report: (1) Calculate the total fault current using p.u. method.

(2) In tabular form show the total current (both experimental and theoretical) for comparison

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ELECTRICAL ENGINEERING DEPARTMENT Bengal Engineering and Science University, Shibpur

POWER SYSTEM LABORATORY: (EE 651-new/EE 707-old) Sixth/Seventh Semester Expt. No.: EE / PS - 4 Title: DETERMINATION OF ELECTRIC STRENGTH OF INSULATING OILS AND STUDY OF OIL TESTING SET. DESCRIPTION OF THE TEST SET

:

Oil Test Set is ideal for speedy and accurate testing of break down/withstand test of transformer and circuit breaker oil in accordance with IS 6792 : 1992, IEC 156. The test set is a compact unit and consisting of the following : H.T. transformer, Control circuit, Test cell with electrode and gauge. The H.T. transformers is specially designed to withstand frequent spark over or momentary short circuit conditions. The Control circuit consists of the following : Main ON/OFF switch, Lamp to indicate L.T. ON, Lamp to indicate H.T. ON, one continuously variable auto transformer for smooth variation of output voltage, variac zero position interlock , door interlock and memory device along with push button switch enables the volt meter to show the break down voltage after processing the memory switch even after the H.V. circuit is tripped OFF. The cell made of glass or rigid oil resistant plastic, shall be transparent. It shall have an effective volume 300 ml and 500 ml. It should be preferably be covered. For test with voltage in excess of 60 KV, RMS, special larger cell may be used. The copper, brass, bronze or stainless steel polished electrodes shall be either spherical (12.5 mm to 13 mm diameter) or spherical surfaced. The electrodes shall be mounted on a horizontal axis and shall be 2.5 mm

apart. The gap between then shall be set to an accuracy of + 0.01 mm by means of thick gauges. The axis of the electrodes is immersed to a depth of approximately 40 mm.

Preparation of the Cell : a) Between tests, the oil shall be poured away and the cell left in an inverted position to exclude dirt and moisture,

alternatively, the cell shall be filled with oil having high electric strength, and suitably covered. b) If the cell has not been used for sometime, it should be thoroughly cleaned; the electrodes shall be removed,

cleaned and finally rinsed with dry, clean new oil. Replacement of the electrodes should be carried out with the greatest care, avoiding all direct contact with the fingers.

c) Immediately before use, the cell shall be cleaned by rinsing with the test oil (at least twice) before proceeding to

the final filling with the conditioned sample oil. Preparation of Sample : (IS 6855 : 1973, IEC 475 : 1974) Whatever the test envisaged, a sample is always needed for the verification of a dielectric (B.D.V), and if it necessary to ensure that the sample is representative of the dielectric contained in the transformer. As per as possible, take a sample within three hours of the transformer/breaker being taken out of use, so as to obtain an average sample resulting from the agitation due to the circulation of the dielectric. The sample will then still be warm and less likely to be contaminated by condensation of the ambient moisture. Avoid any turbulance so as to minimise contact of the directive with the ambient air (formation of bubbles). Cleanliness is essential. It is advisable to fill the sample container by means of an tube and allow it to overflow by an amount equal to the volume of the container to rinse it out. Finally, care must be taken that the material of the sample. Container and any other apparatus used during sampling does not react with the dielectric. From this point of view, glass is the best material.

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Procedure : 1. The sample should be poured down into the test cell, slowly in order to avoid air forming (for example by means of a clean, dry glass rod). The operation should be carried out in a dry place free from dust.

2. Place the cell across the electrode. Close the door. 3. Ensure that the test set is properly earthed. This is most important. 4. Connect the chord to supply. Switch on the test set. Green lamp will glow. It not, check

connection, fuses on the front panel. 5. Bring the variac pointer gently at zero position. A clicking sound of the variac zero position

interlock pressure switch will confirm the zero position of the variac. 6. Press the greeen push button (ON). The Red lamp will glow.This indicates that the H.V. Ckt is

energised. Increase the voltage by rotating the variac (Clockwise) uniformly, at the mte. 2KV/Sec, starting from zero to the value producing break down.

7. After each break down the cell is gently stirred so as to keep away the carbon particles between the electrodes, avoiding as far as possible the production of air bubbles.

8. The test shall be carried out six times on the same cell filling. 9. For the subsequent five tests, the voltage is reapplied (follow step 5 and then step 6) one minute

after the disappearance of any air bubbles that may have been formed. If the observation of the disappearance of air bubbles is not possible, it is necessary to wait for five minutes before a new break down test is started.

10. The electric strength shall be the arithmetic mean of the six results which have been obtained. If there is a difference greater than 20 percent between one of the measurements and the average then it is considered prudent to carry out a further measurement to verify that the difference was not due to an error in carrying out the test.

Results : Break Down Voltage of Insulating Oil Gap length = mm.

No. of Observation BD Voltage in KV

Report :

1. Tabulate the result and give your conclusion. 2. Draw neatly

a) the front and side of the cell including electrodes. b) The Control Circuit

3. Answer the following questions.

a) Why oil testing is necessary ? b) How does air bubble and moisture would affect the insulation strength ? c) Why earthing of the oil testing set is a mandatory requirement ? d) What is the IS recommendation of the dielectric strength of oil ? e) What are the other properties of the oil ? State their acceptable limiting value. f) What type of oil you have tested ? g) Is it possible to test the dielectric strength of other liquid samples ?