power system laboratory - tun hussein onn university of...

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BEE20901 - Electronic Engineering Laboratory II

Instruction Sheet

Power System Laboratory

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UTHMUniverriti Tu* Hursein Ofin Malalsia

FACULTY OF ELECTRICAL AIYD ELECTROITICENGINEERING

E LECTRICAL POWEII ENGINEERING DIIPARTMEN'T

POWEII SI'S:TEM LABORATORY

LAtsORATORY TNSTRUCTI ON SHEET

SUBJECT COI}E AND NAME BEE 20901ELNCTRONIC EI{GINEERTNGLABORATORY II

EXPERIMEI{T CODE 2

EXPERIMENT 'I]ITLE OYERHEAD LINE MODEL

COURSfr CODE 2 BEE,

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Document TitieOVERI#AD LINEMODEL

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EXPERIMENT 2: OYERIIEAD LINE MODEL

AIM:

To apply the knowledge and understanding on theory and applications of transmission lines.

OBJECTTVES:

(1) To perfomr the measurement of the voltage and current relationships of an overhead line in no-load operation and matched-load operations.

(2) To understand the concept of operating capacitance.(3) To determine the line model with increased operating capacitance.(4) To interpret of the terms characteristic wave impedance, lagging and leading operation,

efficiency and transmission losses.(5) To perform fhe measurement of the current and voltage ratios of a transmission line with

mixed ohmic-inductive loads and mixed ohmic-capacitive loads.

THEORY:

For economic reasons, overhead power lines arc mainly used to transmit electrical energyfrom the power stations to the consumer, whereas in densely populated urban ares the power canonly be supplied via cables. Both means of transmission, overhead lines and cables, are included inthe general term "line".

As three-phase system show either inductive or capacitive performance, depending on theload, a reactive power compensation in the line is required for reasons of stability whentransmission line beyond a certain length are used.

When operating a transmission line with three-phase current, the leakage losses G and theinductive L and capacitive C properties offlre arrangement, as well as the resistance R of theconductor material must be taken into consideration. As these values are evenly distributed alongthe transmission line in the form of quantities per unit length, the Figure 1 equivalent circuitdiagram with concentrated circuit components applies only to short lines.

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Document TitleOVERHEAD LINEMODEL

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Figure l:Equivalent circuit diagram of a three-phase short line

The conductance value G refers to the leakage losses arising from the limited insulation

capacrty of cables or from leakage currents along the insulator and corona losses on the surfaces ofthe wire strands of the overhead transmission lines.

The line inductances L comprise the magnetic field which forms in a current flow at the

rated frequency.The inductive reactance are of the same order of magnitude for cables and overhead

lines, the values for overhead line are somewhat higher, due to the greater conductor spacing.

The line capacitance Cs and Cl describe the magnetic field created when s voltage oftherated frequency is applied. Some basic differences must be taken into consideration here, the

capacitance of cables are significanfly greater than those of overhead lines, due to the closer spacing

of conductors from each other, and due to insulation material.

In actual practice, an effort is made to construct overhead transmission lines syrnmetrical

with respect to the capacitances. When the three conductors are affanged in the form of an

equilateral triangle, the distances from each other me equal, but not distances from each conductor

to ground. A symmetry with respect to ground is achieved by cyclically exchanging the conductors

at certain intervals (twisting).

No load operation

This case exists when the nominal voltage is present at one end of the tansmission line,

while the other end is not under load.

Under certain circumstances, the voltage at the open transmission line end increases to

impermissible values due to the line capacitances. This phenomenon is called the Ferranti effect and

represent a dangerous state in grater line lengths, which must be compensated by the network

protection system. In a weakened form, the Ferranti effect also occurs when the network is subjected

to a weak load example at night.

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Document TitleOVERHEAD LtrNEMODEL

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EQUIPMENT LTSTS:

Experimenf 2.1 : No-load Performances

(1) N.l DL 2108TAL Three-phase supply

(2) N.l DL 2108T02 Power circuit breaker

(3) N.l DL 1080TT Three-phase transformer(4) N.1 DL 7901TT Overhead line model(5) N.2DL 2108T03 Line capacitor

(6) Three Phase Measurement Meter

Experimen t 2,2 z Ohmic-inductive Load

(l) N.l DL 2108TAL Three-phase supply

(2) N.1 DL 2108T02 Power circuit breaker

(3) N.1 DL 1080TT Three-phase transformer(4) N.1 DL 7901TT Overhead line model(5) N.1 DL l0lTRResistive load

(6) N.1 DL 1017L Inductive load

(7) Thrce Phase Measurement Meter

Experiment 2.3 : Ohmic-capacitive Load

(1) N.1 DL 2108TAL Tluee-phase supply(2) N.1 DL 2108T02 Power cilcuit breaker

(3) N.l DL 1080TT Three-phase transformer

(4) N.1 DL 7901TT Overhead line model(5) N.1 DL l0lTRResistive load

(6) N.1 DL 1017C Capacitive load

(7) Three Phase Measurement Meter

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PROCEDURES:

Experimen t 2.1 : No-load Performances

Experimen t 2.1 (a) : No-load Operation

(l) Assemble the circuit in accordance with the topographic diagram as shown in Figure 2'1(a)'

(2) Set primary-side of three-phase transformer in delta connection 380V and using bridging

plugs set the secondary to star -10%'

(3) Insert all bridging plugs connecting the capacitances to line model'

(4) Set the supply voltage to UN:380V

(5) Measure the voltage between the two outer conductors at the beginning and end of the line,

as well as the active and reactive power consumed by one of the phases:

U tl-r. :"""""""VIJ zt--t :...............VP :...............W

a :"""".'""'Var

(6) Compare the measured charging reactive power with that which it requires according to the

calculation:

Q* : wCs-U25 : 2n(50)'5x10-6'3802 : 227Y at

Note : The measured value is single-phase and thus must be multiplied by a factor of 3'In no-

load operation the transmission line requires a very small active power due to low current

flowing from the beginning to the end of the line and across half the operating capacitance'

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Experiment 2.1 (b) : Concept of Operating Capacitance

(1) Assemble the circuit in accordance withthe topographic diagram' as shown in

Figure 2.1 (b).(2) Set primary-side of the three-phase transformer in delta connection 380 V and using-

6tiAgiog plugs set the secondary-side to star UN - l0%'(3) R"],o; atl Uriaging plugs connecting the capacitP""t to line model.

(4) Connect tne artiftcilliini capacit*"J.-to the beginning and to the end of the line model'

(5) Set the supply voltage to Un = 380 V'(6) Measgre tft"

"oft"gI between the outer conductors at the beginning and end of each line

capacitance, as well as the reactive power consumed by one of the phases:

fJ rul :

IJ zr-t :........."""V

(7) Compare the results with those at Experiment 2.1 (a): a1 equivalgnt capacitance of the

operating "apacitaoce

cs performs in the same way as the individual capacitances cs and

Cr of the line.

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l)ocument TitleOVERHEAD LINEMODEL

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Effective Date t3l2l20l3Amendment Date L3/212073

Exp erimen t 2.t .(c) : Line with Increased operatin g c apacitance

(1) Assemble the circuit in accordance to the topographic diagram a1 shoyn in Figure 2.1(c).

iZi l" order to emphasize the difference between the performance of a cable and the' perfonnan"" ot* overhead transmission line in noJoad opgratjgn, reconnect all bridging

pt rgr connecting the capacitances to line model in the circuit of Experiment 2.1 (b),

iealizing thus the circuit of Experiment 2'1 (c).(:) nV conn?cti&iG two urtift.iA Hne-capacitances, the operating caq3gitgnces of the line is' '

doubled and ihe voltage-increase effect at the line end is thus amplified.

(4) Set the supply voltage to UN:380 V.(Si M"*".e the voltageietween two outer conductors at the beginning and end of each line

capacitor as well a-s the reactive power consumed by one of the phases:

{Jr :

Uz:

(6) Compare the results with those at Experiment -2.1(a).

The raised voltage effgct is much

more noticeaUte *irit" ihe charging is about twice-as great as in an overhead line without

additional capacitances.

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Experimen t 2.22 Ohmic-inductive Load

(l) Assemble the circuit in accordance withthe topographic diagram as shown inFigarc2'2'

(2) Set primary-side of the three-phase transformer in delta connection 380V and using

bridging plugs set the secondary-side to star UN +sY*

(3) Insert all bridging plWs connecting the capacitance to overhead line model'

(a) To end terminals of line, connect a three-phase balanced ohmic-inductive load: set 'the load

begin with resistance Rt:Ra:R::3 and inductance L1:L2:L3:4:1'27H'

(5) Measure the following quantities: voltage U1, current 11, active power Pr and reactive powel

Qr at the beginning of line, and voltage U2, current Iz and power factor cos92 at the line

end.

(6)Enterthemeasuredvaluesintothefollowingtable:

(7) Repeat the above measurements for inductive loads of 0-9H and 0'64H'

Inductive load: Lr:Lz:L::5:0.9H

Inductive load: Lr :L z:Lf 6:0 -64H

Note: In all measurements, the voltage at the line end is considerably lower than the voltage at the

line beginning and decreases as the current increases. A not true-to scale current voltage vector

diagramfor the case of a mixed ohmic-inductive load with power factor of 0'8 is illustrated in the

followingfigare (Ihe operating capacitance of the line is disregarded here)

Inductive load: L1:L z:Lf 4:1 -27H

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(8) Remove the connection to the resistive load and repeat the measurement for L1 :L2:Lt: 4: L.27H

UrCV) Ir(A) Pr(w) Qr(Var) Ur(V) Iz(A) cosQ2

Note: The inductive load also consume an active power due to ohmic resistance and iron losses ofthe inductor.

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Experiment 2.3: Ohmic-capacitive Load

(1) Assemble the circuit in accordance with the topographic diagram as shown in Figure 2.3.(2) Set primary-side of the three-phase transformer in delta connection 380V and using

bridglng plugs set the secondary-side to star U1q +5olo.

(3) Insert all bridging plugs connecting the capacitance to overhead line model.( ) To end terminals of line, connect a three-phase balanced ohmic-capacitive load: set the load

begin with resistance R1:R2:R3:3 and inductance C1:C2:C3:1:2pF.(5) Measure the following quantities: voltage U1, current It, active power Pr and reactive

power Q1 at the beginning of line, and voltage U2, curr€rlt 12 and power factor cosrp2 at the

line end.

(6) Enter the measured values into the following table:

(7) Repeat the above measurements for inductive loads of 3pF and 5pF.

Note: In all measurements, the voltage at the line end is considerably higher than the voltage atthe line beginning and decreases as the current increases. A not true-to scale current voltagevector diagramfor the case of a mixed ohmic-capacitive load with power factor of 0.8 is illuslratedin the followingfigure (Ihe operating capacitance of the transmission line is disregarded here)

Capacitive load: C r:C 2:C3:l:21tFRt:Rz:Rr Ur(V) Ir(A) Pr(w) Qrffar) Uzff) Ir(A) coStp2

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Capacitive load: C 1:C 2:C3:2:3 pF

Rt:Rz:Rr Ur[V) Ir(A) Pr(Ur) Qr(Var) Uz (V) Iz(A) CoSQz

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Capacitive load: C1:C2:C3:3:5 pF

Rt:R.z:Rl: Urff) Ir(A) Pr(w) Qr(Var) Uz(v) Ir(A) coS{p2

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(g) Remove the connection to the resistive load and repeat the measurement for : C1{2:Cl:3:5pF

Note: Capaertors demonstrate practically no losses so that here nearly no active power is

consumed.

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QUESTTON:

(1) What can be deduced from the results in Experiment 2.1(b) and2.l (c)? Why the Uz value(1) What can be deduced from the results in Experiment 2.1(b) arrdZ.L (c)'/ Why tho Uz varue

higher in experiment 2.1 (c)?

(2) How does the receiving end voltage (U2) of atransmission line vary with the quantity of the

connected resistive load?

(3) Explainthe performances of atansmission line in term of its receiving end voltage and

power factor in R-L and R-C load connections.

YERIT'ICATTON Of,' LABORATORY INSTRUCTOR:

Verified by: Signature:... .....

Name:.

Date:...

power system laboratory - tun hussein onn university of...

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