Power System Laboratory - Tun Hussein Onn University of...
Transcript of 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
Edition 2
Revision No. 2
Effective Date filzlzaBAmendment Date w2l2at3
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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Revision No. 2
Effective Date 13l2l20t3Amendment Date 131212013
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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RevisionNo. 2
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Amendment Date n/ZDAB
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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Document TitleOVERIIEAD LINEMODEL
Edition 2
RevisionNo. 2
Effective Date t31212013
Amendment Date 131212013
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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Edition 2
RevisionNo. 2
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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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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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A:nenclment Date 131212013
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RevisionNo. 2
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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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Document TitleOVERHEAD LINEMODEL
Edition 2
RevisionNo. 2
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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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Document llitleOVERIIEAD LINEMODEL
Edition 2
Revision No. 2
Effective Date t3l2l20L3Amendment Date 13t2l20r3
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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:...