Electrification of Taiwan main-line railway from Keelung to Kaohsiung

Electrification of Taiwan main-linerailway from Keelung to Kaohsiung

S.H. Case, B.Sc, C.Eng., M.I.E.E., A.M. Hayes, B.Sc, J.H. McNeil, B.Sc, R.E.Morrison, B.Sc, Ph.D., C.Eng., M.I.E.E., and E.E. Riches, M.Sc, C.Eng.,

F.I.E.E., M.lnst.P.

Indexing term: Railway electrification

Abstract: The paper discusses the electrification at 25 kV AC of a heavily used mixed-traffic railway in Taiwan.Descriptions are given of the thyristor-controlled electric locomotives and multiple passenger units, togetherwith the technical considerations used in the design of the power and communication equipments. Extensivetests of system performance are described, and results are summarised of power-system behaviour at fundamen-tal and harmonic frequencies, together with a statistical evaluation of interference into the telecommunicationcable system.

1 Introduction

1.1 BackgroundFrom the densely populated north of Taiwan island, a1067 mm gauge trunk railway line down the west coast(Fig. 1) is operated by the Taiwan Railway Administration

Keelung

(TRA). This railway carries an exceptionally high level ofboth passenger and freight traffic. It has been progressivelyupgraded and double tracked, leaving two mainly single-track sections taking different routes between Chunan andChanghua.

In the early 1970s, British consultants carried out aKeelung

Changhua

I Nanchang

coachyard track

Neili

Fukang neutral section

Hsinchu

Chunan

Houlung ' .

coastline

Chianan

mountainl ine

762mm gauge1067mm gaugedouble track

Fig. 1 Taiwan, showing railways and substations

Paper 2673B (P2), first received 1st March and in revised form 17th June, 1983Mr. Case is with Balfour Beatty Power Construction Ltd., PO Box 12, AcornfieldRd, Kirkby, Liverpool L33 7UG, England; Mr. Hayes is with GEC Transmissionand Distribution Projects Ltd., PO Box 132, Trafford Park, Manchester M60 1AF,England; Mr. McNeil is with GEC Traction Ltd., PO Box 134, Trafford Park,Manchester M60 1AH, England; Dr. Morrison is with GEC Transmission andDistribution Projects Ltd., PO Box 27, Lichfield Rd, Stafford ST17 4LN, England;and Mr. Riches is with GEC Transportation Projects Ltd., 45 Victoria St., St.Albans, Herts. AL1 3UG, England

Miaoli

Fengyuan

Changhua

Shiliu

Chiai

Shanhua

Kangshan

feasibility study which showed the operational need andeconomic advantages of electrifying, at 25 kV AC, the linesfrom Keelung, through the capital city Taipei to the portof Kaohsiung, a total route length of 406 km. Expresstrains were planned to operate on the single-track sectionvia Taichung, which traverses a fairly mountainous regionwith gradients up to 2.5% (Fig. 2).

IEE PROCEEDINGS, Vol. 130, Pt. B, No. 5, SEPTEMBER 1983 289

TRA accepted the advantages of electrification andcalled for tenders against outline specifications for mecha-nical and electrical equipments written by Deconsult, theconsulting organisation of Deutsches Bundesbahn. Themajor contract for equipment and project management

during peak periods. Interference with the public electricitysupply was calculated in terms of phase unbalance, powerfactor and harmonic distortion. Power-factor-correctionequipment requirements at substations were studied, partlyon a cost-benefit basis, and equipment was installed at

5 00

400

300

200

100distance from Keelung km

130 135 U0 U5 150 155 160 165 170 175 180 185Fengtu Nanshih Sani Taian Fengyuan

Tsaochiao ,. Tunglo ShenqhsingMiaoli 3 3 Houli

Fig. 2 Route profile, Chunan—Changhua

190 195 200 205 210 215Taichung Chenkung

Tantzu Wujih Changhua

was placed with British companies, to meet a 5-yeardesign, supply and installation programme.

The electrification system which then evolved is aninteresting combination of British and German practiceand differs in significant respects from the systems in use inboth the UK and in mainland Europe.

1.2 Basic systemThe original specification called for Bo-Bo locomotives of72 t to haul freight and the slower passenger trains, and ahigh-speed passenger service to be operated by luxury, air-conditioned 5-car multiple-unit train sets, in consists of upto 15 cars. In addition, contracts were placed with anothermanufacturer for Co-Co locomotives of 961. Allequipments were thyristor controlled, although there weredifferences in circuitry among the three types.

To supply the trains, 11 trackside substations, at 40 kmspacing, were proposed, fed from the public electricitynetwork.

The traffic density during peak periods gave a loadingof up to nine trains on a 20 km double-track feedingsection. Thus the system had to be designed to cope withhigh-density traffic, using two types of locomotive andmultiple-unit trains consisting of 5 to 15 cars.

The existing DC signalling system was retained, butwith added immunisation against AC interference, as wasthe CTC system. Operational control was, however,brought up to date by a new telecommunications systemusing lineside cables. The 25 kV overhead contact systemwas specified to meet typhoon conditions and a high inci-dence of lightning from tropical storms. Equipments gener-ally had to meet requirements for high temperatures andhumidity under tropical conditions.

Prior to detailed design and manufacture of the UKequipments described in the following Sections, studies ofthe total system were carried out to check the adequacy ofthe equipments to meet the operational requirements ofthe railway.

The total power-supply system was modelled on a com-puter; calculations were performed to ensure correct oper-ation of the various traction units and trains to the 1979graphic timetable, using techniques devised by GEC anddescribed in Reference 1. The calculations produced 25 kVtraction currents for each of the 23 feeder sections at10 min intervals throughout 24 h, and at 1 min intervals

290

substations after initial tests and operation of the system.The unbalance and harmonic distortion calculations

were required by the Taiwan power authority to confirmto them that the public electricity supply would not beadversely affected by operation of the railway, which had apossible maximum demand of 100 MVA. The publicnetwork was found to be strong enough to support therailway-system load without phase-balancing equipmentor harmonic filters.

The other area of detailed study was of interference intothe lineside telecommunication cable system, which wasrequired to operate with loaded audio circuits of up to90 km in length. In the mid 1970s, when the theoreticaldesign was being carried out, there was little practicalexperience of the noise interference from high-densitythyristor-controlled, high-powered traction units. Thestudy showed that psophometric current in the overheadsystem was likely to be at a high level, but that immunisa-tion of the cable system against induced noise would alsogive adequate protection against danger voltages. Thepublic telephone authority was separately concerned atpossible high levels of noise interference into telephonelines paralleling the railway. It decided to cable adjacentopen-wire lines and screen others, but only after it wasagreed with TRA that certain sections of the railway,where the interference was likely to be high, should incor-porate booster transformers. This booster-transformersystem could not be accurately engineered because of lackof information from the public telephone authority, parti-cularly on the length of circuits, to check train-in-sectioneffects, and the unusually high proportion of stations andsidings. A procedure was therefore agreed, in which adjac-ent feeder sections employed two spacings of boostertransformers at 2.5 and 3.75 km. Unfortunately, reliablestatistical information of interference into public telephonelines paralleling these sections has not yet been obtained,and it is not known whether the closer spacing gives lower,average or higher interference levels, although no problemshave been reported.

The railway has now been operating for more thanthree years without any major problems, and the systemwill soon be extended to lines in the south of the island.This paper outlines equipment systems supplied from theUK, giving particular attention to novel features; it sum-marises the results of system tests carried out on com-pletion of the project.

IEE PROCEEDINGS, Vol. 130, Pt. B, No. 5, SEPTEMBER 1983

2 Description of locomotives and EM Us

2.1 LocomotivesThe first of twenty 2100 kW thyristor-controlled, light-weight Bo-Bo locomotives was delivered to the TaiwanRailway Administration in late 1976. The locomotives(Fig. 3), with an overall weight of 72 t, haul freight trainsof 1250 t along the coastal route, with its ruling gradient of1%, and passenger trains of 525 t over the mountain line,

1 2 3 A

16 15 14

Fig. 3 General arrangement of 21001 Pantograph2 Vacuum circuit breaker3 Lightning arrester4 Potential divider5 Traction motor6 Interbogie coupling7 Traction-motor blower fan and ducting8 Bodyside filter panels9 Main compressor and motor

kW thyristor-controlled locomotive

10 Transformer oil pump and motor11 Traction-motor blower motor12 Traction-motor smoothing choke13 Driver's seat14 ATW-ATS control apparatus case15 Electronics control cubicle16 Transformer17 Rectifier/thyristor cubicles

with a ruling gradient of 2.7% (including 0.2% curveresistance). Locomotive performance is shown in Fig. 4.

Maximum use of the available adhesion is vital with alightweight locomotive, and so the locomotives have lowweight transfer bogies and thyristor control of the tractionmotors. The thyristor control gives smooth, notchlesscontrol of tractive effort and enables the locomotives to beworked at the peak of the notches which would be associ-ated with a tap-changer locomotive.

300 r

200 -

100 -

/125O t/ on level

on level

0 40 80

speed km / h

Fig. 4 Locomotive performance at 25 kV line voltage

120

CDT

to control

system

maintransformer

rrnto axle earthbrushes

Fig. 5 Schematic of locomotive power circuits


The traction-motor armatures are supplied by a pair ofhalf-controlled thyristor bridges connected in series, whichis an economical method of reducing the reactive kVA andlevel of harmonics generated due to retarded firing angle.

The traction motors are separately excited and eachfield is supplied from a transformer tertiary winding by itsown half-controlled thyristor bridge. Separate excitation ofthe motors allows for stepless control of field current, thusminimising the likelihood of wheelslip when operatingclose to the limit of adhesion. A schematic of the loco-motive power circuit is shown in Fig. 5.

The method of control of the locomotives providesthree main stages:

(a) Up to approximately 40 km/h (base speed), themotor field current demand is set at the continuous rating(this set demand is subsequently modified for each motorby the load share circuits), and the armature current iscontrolled to correspond to the setting of the driver's con-troller. The voltage applied to the traction motors isincreased by advancing the thyristor bridges in sequence.During this stage of operation, the setting of the driver'scontroller corresponds to a fixed level of tractive effort.

(b) Above base speed, the traction-motor field strengthis progressively weakened as the locomotive speedincreases until a limit is reached. During this stage, arma-ture voltage and current, and hence power, are maintainedat a constant level.

(c) Above the weak field limit, the ratio of field currentto armature current is maintained at a constant level andthe traction motor operates to a simulated series-motorcharacteristic.

At all speeds, traction-motor powers are maintainedequal by individual control of motor field strengths; thus,the tractive effort developed at every axle is the same,irrespective of variation in motor characteristics or wheeldiameters.

Probes mounted on the traction-motor gearcases con-stantly monitor traction-motor speed. Signals from theseprobes are used to operate the locomotive speedometers,the wheelslip correction system and deadman/vigilanceequipment. The wheelslip correction equipment protectsagainst different speeds between axles, excessive acceler-ation and overspeed. The traction motors are developedfrom motors used extensively on a fleet of DC locomotivesoverseas, where 4000 motors of this type are in service. The

major modifications necessary to the motor were to thefield windings to change the motor to separate excitation.

2.2 Electric multiple unitsThe 13, 5-car electric multiple units operate high-speedlimited-stop express trains between Taipei and Kaohsiung.The units, comprising a driving power car, motor car, twoplain trailers, and a driving trailer are fully air conditionedand provide a luxury passenger service. These were builtby British Rail Engineering Ltd., based on the Mark IIcoaches used in British Rail Inter-City trains. The bodywidth was increased to meet TRA requirements, and therewere other changes, such as larger double-glazed windowsand swivelling seats, rotated in pairs at the termini so thatall passengers face the direction of travel. An electric multi-ple unit can be seen, in service, in Fig. 6.

Air-conditioning equipment had to meet a high duty, asit maintains 20°C to 25°C at a relative humidity of 55%when the outside ambient temperature varies from 0°C to40°C, plus tropical sun temperatures, and relative humidityof up to 100%.

Primary suspension is by radius arm with rubberchevron springs; the secondary suspension consists of twoair springs per bogie with hydraulic and air damping. Thesuspension required careful adjustment to meet the difficultconditions imposed by the narrow gauge and tight curves.

Power equipment for the units is mounted on two cars,which are coupled together within the unit. The power carcollects current from the overhead system and contains thetransformer and thyristor convertors. Jumper cables trans-fer the power to the adjacent motor coach, which containsthe four traction motors and their associated contactorsand reversers.

The motors are series excited and are connected inparallel pairs, supplied by series-connected half-controlledthyristor bridges. Field weakening is achieved in a singlestage by a contactor on the tapped-motor field.

Series motors are used because the additional controlequipment for separate excitation is not justified with anEMU train. The accelerating tractive effort, however, is

120 r

5-car unit

up 2.7°/o

5-car un i tup 1.0 °/o

5 -ca r un i t

on level

120

Fig. 6 Electric multiple-unit train at Nanchang coachyard, headed by apower car

292

80

s p e e d , k m / h

Fig. 7 Multiple-unit performance, at 25 kV line voltage


tailored to match the comparatively low-adhesion levels(Fig. 7). Although the motors are thyristor controlled, themethod of control differs from that employed on the loco-motives. The driver sets the speed of the unit with themaster controller rather than setting the tractive effort; thethyristor bridges are then advanced separately until thedesired speed is reached. This set speed is then maintainedconstant until further action is taken by the driver.

Higher speeds are achieved by a single step of fieldweakening, with simultaneous reduction in voltage to givea jerk-free transition. The voltage is then graduallyincreased to maintain the tractive effort with the increasingspeed, until full voltage is reached in weak field.

If the speed of the unit increases beyond the set speed,due to, say, a gradient change, rheostatic braking of themotors is automatically applied, and should the brakingeffort available from the motors be insufficient, then threesteps of electropneumatic airbrake are progressivelybrought in on the power car and trailer cars to provide thenecessary amount of braking. The rheostatic brake is alsoactivated when the driver uses a reduction of set speed, toreduce train speed to match the many changes in speedrestrictions.

Prior to the manufacture of the electronic equipment, asimulator was constructed to prove the design. This simu-lator proved to be extremely useful, not only in ironing outmost of the preproduction problems with circuitry, butalso for demonstrating the method of operation to thecustomer, as well as to potential customers from otherrailway authorities. A particular problem demonstrated bythe simulator was concerned with ascending gradients inweak field. As the speed reduced, the electronic equipmentshould have returned the motor to full-field operation assoon as the continuous rating was reached. However, thetraction motor remained in the weak-field condition; asimple modification to the circuitry corrected it. This savedthe necessity for modification after production, whichwould have only been discovered by 'in service' running.

To provide for the auxiliaries, the units are fitted withtwo DC speed-controlled motors driving 3-phase alterna-tors, mounted in the power car and the driving trailer. Inthe unlikely event of failure of one of the motor alternatorsets it is possible to reconnect the auxiliary circuit toprovide essential supplies and a reduced air-conditioningservice to the whole train.

Transmission of control signals between adjacent unitsis accomplished using pulsewidth modulation techniques, asystem which is also employed on the locomotives. Thelocomotives and multiple units also incorporate the BritishRailways automatic power-control system which cuts offpower when the vehicle approaches a neutral section in theoverhead supply and automatically reapplies it afterwards.The track markers for this system are magnets locatedeach side of the neutral section; these operate one of a pairof transducer relays mounted low down on each side of thetraction units.

3 Description of substations and associatedequipment

The 11 trackside substations take power from 3-phase69 kV overhead lines connecting into the 60 Hz publicpower supply. Eight of the substations are each equippedwith two 69/25 kV 10 MVA transformers, and the remain-der, in the southern, more lightly-loaded section of therailway, use a single 10 MVA transformer.

The consultants to TRA recommended that Scott-connected transformers be provided to supply the traction

distribution system, on the basis that this would reduce theunbalance on the 3-phase supply network. This type oftransformer consists of two single-phase units with theprimary windings interconnected to form a 3-phaseprimary, such that the induced voltages on the secondarywindings are phased at 90°. This method of connectionnecessitates a complex winding arrangement with tappingsbrought out from the inner windings, resulting in an inher-ently bulky unit with a relatively low mechanical strength.

GEC proposed that Leblanc-connected transformers(Fig. 8) would be more appropriate for the application,

HV

Fig. 8 Phasor relationships, HV and LV windings

a Leblanc-connected transformersb Scott-connected transformersA, B, C: starting and ending of HV windingsa,b,c: starting and ending of LV windings

while providing an equivalent 3-phase to 2-phase trans-formation. Leblanc-connected transformers have the fol-lowing advantages over Scott type:

(a) lower iron loss(b) improved mechanical strength—an important con-

sideration for transformers used in traction power supplies(c) simplified HV lead arrangement—with potential

improvement in reliability(d) the less complicated primary winding results in

improved impulse strength and a more accurate predictionof impulse voltage distribution.

Leblanc-wound transformers were supplied, having split25 kV windings, giving two single-phase outputs, with 90°between phases.

The circuit breakers installed on the 69 kV incomingfeeders are reduced oil-volume breakers, which are wellproven and established.

The 25 kV supply is controlled by single-pole vacuumcircuit breakers located at the feeder substations (Fig. 9).The vacuum circuit breakers are rated 800 A continuousand are capable of breaking 12 kA (symmetrical) at 25 kV.

The transformer feeder and the track feeder are bothprotected by simple overcurrent relays, allowing faults tobe cleared in approximately 60 ms. The 25 kV protectionassociated with the track feeder circuit breakers incorpo-rates a single-shot autoreclose facility, so that the circuitbreaker is automatically reclosed about 2 s after trippingon a fault. If the fault persists, the breaker trips imme-diately for a second time, locking out. A checking pro-cedure must then be carried out before closing is againpossible, as this condition indicates a sustained fault whichmust be investigated and cleared. This autoreclose facility


was incorporated to avoid unnecessary disruption of traffic Power control of the electrification system was providedfrom the expected high level of faults caused by lightning at two control centres, one at Nanchang and the other atstrikes to overhead catenary equipment, causing fiashoverson the insulators.

3-phase HV supply

3-,to 2-phasetransformers

Changhua. Each has a mimic diagram of the distributionnetwork layout, providing remote control of circuit

motorised isolator-normally closed

motorised isolator-normally open

C"

vacuum circuit breaker

CT current transformer

—II— section insulation

—IhjHI— neutral section

single-core [25kV cables ' i

A

M-phase

midpointsection post

m

-H-j-HH

~ T-phase

Fig. 9 Substation sectioning/OCS feeding arrangements, double-track section

The substation sites are of conventional layout (Fig. 10),with the 25 kV switchgear and control equipment in brickbuildings adjacent to the track. Connection to the 25 kVoverhead equipment is made to both sides of the neutralsection. Underground power cable is used, run from asealing end inside the building. The track end of the cate-nary feeder cables are run up the catenary masts, adjacentto the substations, to sealing ends located on top, beforeconnection is made on to the contact wire via isolators (seeSection 4).

The continuously bonded traction rails on each trackare connected via return-current cables to a return-currentbusbar. The return-current busbar is directly connected toone pole of each secondary of the power transformer, alsoto the railway earthing system, and, at one point, to thesubstation earth mat. Current transformers monitor thevarious earth and neutral currents.

Fig. 10 Track-side substation

294

breakers and key isolators at the substations and mid-points, together with indications and alarms. The telemetryoutstations are interrogated by 600 baud audio FSK4-wire data links in the telecommunication cable. Theseloaded circuits are approximately 200 km in total lengthand were extensively studied to ensure that induced noisewould not interfere with the data stream. No problemshave been reported in several years of operation.

Under normal operation, at 2-transformer substationsboth transformers feed main (M) and teaser (T) busbars(Fig. 9), which are phased at 0° and 90°, respectively. Ingeneral, the scheme is arranged so that one busbar feedsthe section to the north of the station and the other feedsthe section to the south. The transformers at adjacent sub-stations are arranged so that the voltages on catenary sec-tions either side of the midpoint neutral sections are inphase. Under 'first emergency' conditions, or at singletransformer substations, one Leblanc transformer isrequired to supply both the M- and T-phases (Fig. 9) andis required to provide power to all the load, both northand south of the substation.

The system was also designed to operate in the 'secondemergency' condition, when power supply to one sub-station is lost and power is fed from adjacent substationsover double length feeding sections. The required configu-ration is achieved by connecting adjacent sections of theoverhead contact system by closing isolators across theneutral section at midpoints. Second emergency feedingrequires a reduction in traffic to avoid excessive voltagedrop on the feeders, but allows for a continuous limitedservice, even during substation outages, and enables anymaintenance or repairs to be carried out.

The design of the system, which ensured that sectionseither side of the midpoint neutral section were in phase,


allowed for the possibility of normal running with the mid-point neutral section isolator closed, with the objective ofreducing voltage drops. This effectively creates a double-end-fed system, but with the inherent disadvantage of cir-culating power current feeding from one part of the3-phase EHV network to another via the single-phaseoverhead contact system.

Problems of excessive voltage drop with heavy trafficwere encountered in practice between two substations and,to overcome these, catenary sections were interconnectedat the midpoint, and the traffic then operated normally.Circulating current between the two substations was foundto be small.

4 Description of overhead contact systemand associated equipment

4.1 General descriptionIn view of the requirement for a maximum train speed of120 km/h, a simple catenary construction, with a saggedcontact wire, was chosen as the basis for the overheadcontact system (OCS). The system consists of a 50 mm2

(7/3.0 mm) stranded, hard-drawn cadmium-copper cate-nary wire supporting a 107 mm2 hard-drawn coppercontact wire by means of droppers made from 3 mm diam-eter stainless-steel wire. The tension in the conductors ismaintained constant at approximately 10 kN throughoutthe operating temperature range, by means of concretebalance weights acting via a pulley system with a 3 :1ratio.

In open-route areas, the OCS is supported and regis-tered by single-track cantilever assemblies mounted on cir-cular, prestressed, reinforced concrete poles. A typicalexample is shown in Fig. 11. The cantilevers are attachedby means of long bolts passing through inserts cast intothe poles. This is a very economical arrangement, but it isnecessary that the poles be installed with considerable careto ensure that the holes are correctly positioned relative tothe track.

In multitrack areas, the OCS is supported by portalstructures. For spans of up to five tracks, the structure

consists of a fabricated lattice-type steel boom supportedon concrete poles. For spans of six to eight tracks, anall-steel construction is employed.

An important factor in the OCS design is the need tocater for relatively high wind loads. Although the trainsare withdrawn from service when the wind speed exceeds25 m/s, the OCS is designed to operate with winds up to26 m/s in normal areas and 29 m/s in the more exposedcoastal areas. The equipment is also required to withstand(as a nonoperating condition) typhoon winds of up to60 m/s. For straight track, the distance between poles islimited to 56 m and 50 m in normal and coastal areas,respectively.

4.2 InsulationElectrical clearances adopted were the same as those speci-fied for use in the UK by the Department of Transport in1977 [2]:

Normal ReducedStatic clearance, mm 270 200

Passing clearance, mm 200 150

Reduced clearances are generally only adopted at over-bridges and tunnels with restricted headroom, where itwould be uneconomic to undertake the civil engineeringrequired to obtain the normal clearances.

The various types of insulator are generally similar tothose used for the more recent electrification schemes inBritain [3, 4]. The route is divided into two categoriesdesignated 'normal' and 'endangered', depending on thelevel of pollution. Areas of heavy local industrial pollutionand coastal areas are considered to be endangered.Minimum creepage paths of 790 mm and 1070 mm wereadopted for the normal and endangered areas, respectively.In order to distinguish readily between solid-core insula-tors intended for normal and endangered areas, two differ-ent colours of glaze are used.

A particular problem encountered in tunnels, wherethere were space limitations despite lowering of tracks,meant that a new type of insulated support arm wasrequired. This is shown in Fig. 12.

galvanised steel tube

returnfeeders

Fig. 11 Typical single-track cantilever


4.3 Feeding and sectioningThe feeding and sectioning arrangements for two tracksare shown in Fig. 9. Connections between the substations

system, the faulty section of equipment can be locatedquickly, and appropriate action can then be taken.

The power feeding arrangement at a typical single-track

A80mm

butyl-rubber coveredglass-fibre insulatingarm

galvanised-steel arm

adjusting screw

Fig. 12 Typical tunnel support arm

and the OCS are made by means of single-core, paper-insulated, lead-sheathed cable with a 120 mm2 copper con-ductor. Two such cables are used in parallel for each of thefour connections to the OCS.

The substation at Miaoli supplies power to both themountain line and the coast line (Fig. 1). Connection tothe feeding point on the coast line is via a double-circuitoverhead line of approximately 7 km.

The OCS isolators at the substations and midpointsection posts are fitted with 125 V DC motorised oper-ating units. Power is supplied by a battery and charger,thus making it possible to continue operating the isolators,even after a failure of the local AC supply. The isolatorsare normally controlled from the remote control centres atNanchang and Changhua, but a local control panel is alsoprovided at each substation, and at the railway stationnearest to each midpoint section post.

Further sectioning facilities are provided at the railwaystations. The five motorised isolators at each railwaystation (Fig. 9) are controlled from a panel in the stationbuilding. This panel is not linked directly into the mainpower-control system. In this case, operation is by stationpersonnel in telephone contact with the power controller.One of the isolators connects the two main tracks in paral-lel via a current transformer with a ratio of 600 :1. Thesecondary of this current transformer is connected to analarm unit located in the isolator control panel in thestation. The alarm unit incorporates a horn and warninglight which operate whenever a current greater than 600 Aflows in the primary of the current transformer. In theevent of an OCS fault, a heavy current flows in the CTnearest to the fault. The warning unit then operates andthe power controller is ac' i by telephone. By this

contact wire

manually operated-°—»- isolator

—II—section insulation,

XX

\ bypass feeder

XXy

yFig. 13 Feeding arrangements, OCS supply, at station in single track

296

station is shown in Fig. 13. The bypass feeder allows theequipment in the station area to be switched off while stillmaintaining the supply to the equipment beyond thestation. The isolators are manually operated by stationpersonnel under the direction of the power controller.

4.4 EarthingFour essential criteria were considered in the design of theearthing system:

(a) touch and step body currents [6] should be as lowas possible, since the public have access to all parts of thetrack, where they could come into contact with rails,masts, equipment cases etc.

(b) the telecommunication cable sheath should havehigh leakance to earth, to fully utilise its good intrinsicscreening factor

(c) lightning strikes to the overhead equipment shouldhave low-impedance paths to earth, to minimise damage totrackside equipment and cables

(d) an earth resistivity ranging up to 100 Qm.

These constraints led to the adoption of a unifiedearthing system, proposed by the TRA consultants, for the25 kV traction supply, the signalling and telecommunica-tion equipments, and all metalwork on the railway. Thiscombined earthing depended on obtaining a high leakanceto earth of more than 1 S/m along the entire length of theelectrified railway. It was achieved by burying a bare earthwire in the ground above the telecommunication cable,bonded to the aerial earth wire and uninsulated tractionreturn rail at every fourth mast. The earth wire consists ofa 7/3.8 mm zinc-coated steel stranded conductor, with a1.5 mm thick lead sheath.

A buried earth wire has advantages over the conven-tional earth rod system in areas of medium to high earthresistivity, as it is more economical in terms of metalemployed, and is available to earth lineside equipment atevery location along the railway. It is particularly conve-nient for earthing telecommunication cable joints becauseof its close proximity to this cable.

The resulting low grounding impedances met therequirements of criteria (a) and (b) above in the highestearth resistivity areas. Additionally, the bonding togetherof all trackside metalwork eliminates the danger of aperson simultaneously contacting equipments at differentearth potentials.

4.5 Interference suppressionIn order to ensure that adjacent parallel electrical circuitsdo not suffer unacceptable induced voltages, two systems


of protection are used. In the first system, two 100 mm2

(7/4.39 mm) hard-drawn, aluminium return feeders aresupported on the OCS poles, as shown in Fig. 10. With thehigh degree of screening afforded by the telecommunica-tion cable sheath, and the buried earth wire, the twinreturn feeders give sufficient interference reduction for line-side circuits, and this system is used throughout most ofthe route.

In the areas where interference in remote telephone cir-cuits was considered to be a potential problem, a boostertransformer system is used. A 300 mm2 (37/3.23 mm) hard-drawn, aluminium return conductor, supported by insu-lated clamps, is used in place of the lower return feeder, theupper return feeder being retained. The return conductor isconnected in series with the secondary windings of thebooster transformers, which are installed on concrete foun-dations.

All non-live steelwork associated with each concretepole (including steel reinforcement in the pole andfoundation) is connected to the return feeder(s) using PVC-covered, stranded, galvanised iron wire. At every fourthpole (about every 200 m) the return feeder(s) are connectedto the buried earth wire and to the track. All metal partswithin 8 m of the track centre-line are bonded to the track.

The track circuits are protected against overvoltages byconnecting protection devices between the insulated andnoninsulated rails. These devices consist of a metal body,housing a replaceable spark-gap capsule, the gap beingdesigned to flash over at about 700 V. In the event of apower-follow current flowing, the spark gap would becomepermanently short-circuited, and the capsule would thenneed to be replaced.

5 Description of the telecommunicationssystem

The telecommunications transmission system is based onscreened lineside cables along the entire route. BetweenKeelung and Kaohsiung, via the mountain section, themain telecommunication cable consists of a core of four1.2/4.4 mm coaxial pairs for a duplicated line system withburied repeaters having a baseband capacity of 960 chan-nels. This coaxial core is surrounded by two layers of 0.9and 1.2 mm quads for audio and subscriber carrier cir-cuits. A proportion of the 1.27 mm audio quads are loadedfor long-distance voice frequency (VF) circuits. The cableon the coastal route between Chunan and Changhuaemploys only balanced carrier and audio quads, as a highcapacity is not required. Trackside maintenance telephonesspaced at 1 km intervals and other operational telephonesare connected via the VF-circuits system to signalling,power control, maintenance centres and to railway sta-tions. An existing CTC system, power-control circuits,local and central PABX systems and a small capacity VFtelegraph system also share the same cable system.

5.1 Telecommunication-cable screeningA combination of relatively high traction currents (up to1000 A on a double-tracked single-power-feed section) andhigh psophometric currents (7.7 A and 13.6 A for theBo-Bo and Co-Co locomotives respectively, and 15.3 A fora 15-car EMU) give induced field strengths at the track-side, requiring exceptionally efficient screening of the tele-communication cables and good side-to-earth balance ofthe audio pairs. Calculations, taking account of earthingpenalties [5], confirmed that a cable developed by BICCLtd., with aluminium sheath and high permeability steel-tape armour, would ensure longitudinal voltages less than

250 V in any continuous metallic circuits, and transverse(noise) voltage would not exceed 2.5 mV at the termina-tions of the longest VF circuit, both under normal oremergency operation. These show a relaxation on CCITTlimits for public-telephone networks based on internation-al connections, as these are unnecessarily onerous forapplication to this type of railway communicationsnetwork.

The intrinsic screening factors of the cable sheath weremeasured to be less than 0.0061 at 60 Hz (the fundamentalfrequency) and 75 V/km field strength, and 0.0009 at800 Hz with a superimposed 60 Hz sheath current of 25 A.Calculations did not take account of screening by thebooster transformers, as these were installed only in alimited number of sections. The combined screening of theaerial earth wires and the rails was, however, found to besignificant, being approximately 0.185 in double track and0.27 in single track for earth resistivity of 100 Qm.

The cable was buried directly in the ground at a depthof 1 m between the ballast and the inside of the masts.Great care was taken in continuously bonding the sheathat joints where it is also bonded to the buried earth wire.The plastics-insulated cable is air pressurised to exclude allmoisture. Special tests were carried out after installation,to check the integrity of the outer PVC sheath.

6 System performance and operational experience

The electrification programme of design, supply andinstallation of the equipments described in the precedingSections was completed ahead of schedule, and the electriclocomotives and multiple unit train sets were speedilybrought into operation. Not unexpectedly, there wereteething troubles which were corrected promptly. No sig-nificant changes have been made to the system as designed,which has now been in full operation for more than threeyears without difficulties occurring.

Absence of difficulties has in fact limited the automaticcollection of information on routine operation owing tolack of need for technical contacts with TRA. However,system tests during the early days of operation gave valu-able knowledge of actual performance, which has beencompared with that specified or estimated, as discussedbelow.

6.1 Organisation of commissioning testsThe commissioning tests took place on one electricalsection, which was double track, containing booster trans-formers. The physical layout and track profile are shownin Fig. 14. Commissioning trials took place with thebooster transformers either connected or shorted out, sothat their effect could be determined. The test track wasfed from the M-phase of Neili substation, and there weretwo 10 MVA transformers installed.

Puhsin station

200

150

Chungli station

Neili station

Yangmei station

Fukangneutral section

Neilisubstation

o> 100' •—' • • • ' • ' «-* 60 62.563.6 67.3 70 732 77.3 77.3 80 83.0

distance from Keelung

Fig. 14 Test track, Neili substation to Fukang neutral section


During the commissioning trials, only one electric loco-motive at a time was allowed on the test track. A load wasconnected to the locomotive to obtain realistic operation;the freight load was made as near as possible to 1250 t andthe passenger load consisted of a group of empty coachesweighing 550 t. These were normal design tonnages for thetwo types of train.

6.1.1 Test instrumentation: The test instrumentation wassituated mainly at the substation, although a limitedamount of equipment was placed on board a test carimmediately behind the locomotive. While the tests were inprogress, the following signals were recorded on a Philipsanalogue 714 FM instrumentation tape recorder:

(a) 25 kV voltage(b) 25 kV track feeder current(c) 69 kV voltage (all three phases)(d) 69 kV current (all three phases)(e) longitudinal voltage in a telecommunications cable(/) transverse voltage in a telecommunications cable.

The 25 kV and 69 kV voltage signals were obtaineddirectly from the busbar VTs, attenuators being connectedat the recorder to reduce the signal to the level required.The 25 kV current signal was obtained from a shunt con-nected to the secondary of the return current CT. The69 kV current signals were obtained from shunts con-nected to the secondaries of the HV feeder CTs. A second25 kV current signal was obtained from a wide bandwidthCT connected into the track feeder. The psophometric CTwas calibrated in Germany under the inspection of TRAconsultants and was stated to be accurate up to 10 kHz.All signal connections were made through twisted pairscreened cables with the screen earthed at the recorder; thebackground noise level was found to be less than 0.1 mVin all cases.

6.1.2. Commissioning test runs: The main object of thecommissioning trials was to ensure that all the equipmentwas operating within its specification. This was achievedby running a loaded locomotive along the test track fromNeili to Fukang, and measuring signals at various pointsin the electrical and communication systems. A normaldiesel service was operating during the tests, so the testlocomotive was forced to follow normal traffic constraints.Many tests were performed and two basic operating pat-terns were enforced:

(a) stop at all stations between Neili and Fukang(b) nonstop from Neili to Fukang.

During each test, a detailed log was kept by an observeron the test train and, in addition, a limited amount ofinformation was passed directly to the substation througha radio link.

6.1.3 Further test runs: About 18 months after the initialcommissioning tests, a further series of measurements tookplace when a near-normal railway service was in oper-ation. The recording procedure adopted was identical tothat used in the commissioning tests, although no attemptswere made to control the railway traffic during the record-ing periods.

6.2 Results of power-system measurements

6.2.1 Short-circuit tests: A series of short-circuit testswas carried out to prove that the protection relays wereoperating correctly and to derive the rise of earth potentialthat could be expected during faults.

298

Faults occurring at any position during normal 25 kVsystem feeding tripped the instantaneous element of thetrack feeder protection relay, clearing the fault within0.06 s. On second emergency system feeding, the faultsactivated the definite minimum time element of the relay,causing a trip in 1 s. The highest rise of earth potentialrecorded was less than 50 V between the substation earthmat and an isolated earth electrode 100 m from the sub-station.

6.2.2 Energy consumption and protection consider-ations: Energy consumption and power factor were mea-sured for all the commissioning tests with instrumentationat the substation. Specific energy-consumption values werederived from the results and average figures were producedto cover three types of train. These are shown in Table 1with power-factor values included.

Table 1: Specific energy consumption and power factor fordifferent train types

Type of train Specific energy consumption Power factor

Wh/t kmFreight 18Nonstop passenger 253-stops passenger 28

0.750.810.72

The slower freight and 3-stops passenger trains havelower power-factor values than the nonstop passengertrain, because they operate for longer periods with thethyristor bridges at partial conduction. Increased periodsof braking by the 3-stops passenger train are responsiblefor the high specific energy consumption for that type oftrain.

Measurements of track feeder current, when the near-normal railway service was operating, confirmed that allthe traction-power-supply components were operating wellwithin their rating. Although track feeder protection relaysare simple overcurrent relays, excessive load currents didnot cause unexpected tripping of the track feeder protec-tion. Even when the railway traffic grows, the frequency ofaccidental load current trips should be negligible andshould not affect normal railway operation.

6.2.3 25 kV system resonance: Voltage and currentwaveforms measured at the test track substation (Fig. 15),are of similar shape to those observed on British Railways[7]. System resonance is responsible for the ripple in boththe current and voltage waveforms, and, for the caseshown, the resonant frequency is between the 19th and21st harmonics. Overvoltages [8] caused by resonancewere minimal. During the system tests, the highest peakvoltages noted were 42 kV at the substation and 48 kV atthe locomotive pantograph. A further detailed computer

Fig. 15 Typical substation voltage and current waveforms


analysis [9] of the test tape recordings revealed that theprobability of exceeding 48 kV is less than 0.0008. Theundistorted crest voltage is 39 kV (27.5 x ^ k V ) , so, forpart of the time, an overvoltage exceeding 23% exists onthe system. No problems were noted with these levels ofovervoltage, with either the fixed equipment or the loco-motives.

Although in the case of the system in Taiwan, overvol-tages are not excessive, there are some railways wheregreater overvoltages would be generated. For instance, theuse of three or four locomotives in multiple, hauling heavymineral trains, would be expected to generate voltages inexcess of 70 kV [8]. It is recommended that an overvoltagestudy should be carried out in the design stage for any newrailway electrification scheme, employing thyristor-controlled traction units, to assess the need for overvoltagedamping equipment.

Other effects observed during the commissioning testsare worthy of note, as they, confirm previously noticedphenomena associated with traction-system resonance.The resonant frequency of a feeder section is practicallyindependent of locomotive position within the section,although different sections have different resonant fre-quencies. When the booster transformers were short-circuited, the resonant frequency decreased by a smallamount. Switching out one of the substation transformers,thereby doubling the effective reactance of the substation,reduced the resonant frequency by approximately •N/2.

Typical voltage and current spectra (measured at thesubstation) are reproduced in Fig. 16, and they both indi-cate that the 21st harmonic component is amplified. Har-monic components on either side of the 21st harmonichave also been amplified, since the circuit (Mactor is low.The results on the test track show a (Mactor of between 10and 20, the variation being caused because a psophometriccurrent filter is carried by the Co-Co locomotives.

6.2.4 HV system measurements: During the initial com-missioning test, only one phase of the 2-phase supply was

> 1 Or

2 0 . 5

13 15 17 19 21 23 25harmonic order

30

J 20

a

co£ 10

3 5 7 9 11 13 15 17 19 21 23 25b harmonic order

Fig. 16 Typical substation voltage and current spectraa Voltage b Current

in use and the unbalanced currents absorbed from thepublic electricity supply were therefore identical to thosethat would have been obtained from a single-phase trans-former. Both supply phases were in use for the tests carriedout with near-normal railway traffic, so the effect of the2-phase supply on unbalance could be monitored.

To illustrate the behaviour of the Leblanc transformer,three current/time graphs are presented (Fig. 17) whichcover the same time period:

(a) M-phase current(b) T-phase current(c) negative-phase sequence (NPS) current.

The negative-phase sequence current is proportional tothe difference between M- and T-phase currents [10], andthis is perceptible in the NPS current graph for the periodsof time when the current is steady in one 25 kV phase.

The graph of NPS current against time (Fig. 17) has alower peak than could be expected from single-phasetransformers, since the peak current in M-phase coincideswith a current of about 75 A in T-phase. This could bemisleading, since, on another occasion, the T-phase currentcould be zero with the M-phase current at its peak.Leblanc (or Scott)-connected transformers are unlikely toreduce the peak NPS current of one substation, but couldreduce the RMS NPS current over a period of about 5min. Since NPS voltages are responsible for overheating of

300

15

Fig. 17 Substation current/time graphs

a M-phase currentb T-phase currentc Negative-phase sequence current


3-phase induction motors, a better measure of the NPSvoltage distortion than the instaneous peak value is ashort-term RMS value which reflects the thermal time con-stant of the motor windings or the operating time of themotor phase unbalance relays. Given that Leblanc trans-formers are capable of reducing short-term RMS NPSvalues, they can be useful in alleviating unbalance, espe-cially for a single traction substation isolated within theHV system from other traction substations.

Most traction systems contain several substations con-nected to different phase pairs of a HV supply and the netunbalance voltage at any HV busbar is determined by thecurrent from all the traction substations. There is oftenconsiderable cancellation of unbalance within a HVsystem, even when single-phase transformers are used, andthere is no evidence to show that Leblanc transformerswould improve on this. To determine the true effect ofLeblanc transformers would require simultaneous mea-surement of the traction load at several substations, andthis was not carried out in the tests.

HV-system harmonic voltage distortion was measuredand the levels were found to be within those normallyacceptable; to the knowledge of the authors no customercomplaints have occurred. Although the primary voltage is69 kV, fault levels at most traction substation terminalsare of the order of 1000 MVA, a level considered to beacceptable for the type of railway traffic in Taiwan. Up tonine independent trains were operating on some feedersand the maximum harmonic distortion was considerablyless than nine times the distortion caused by one train; adetailed explanation of why this is so has been given [11].

6.3 Overhead contact systemAlthough current collection was generally satisfactory,unacceptable pantograph oscillations and sparking werefound to occur at speeds of around 75 km/h in certaintunnels. Two different types of pantograph were fitted to

the various locomotives and EMUs supplied to TRA, onetype incorporating frame damping, the other type beingwithout. The problem was confined to operations involv-ing the latter type.

A computer simulation of the dynamic interactionbetween the tunnel equipment and the undamped pan-tograph was undertaken, and this produced results whichindicated unacceptable current collection at a criticalspeed of 70 km/h (Fig. 18a). Further simulations werecarried out for the same pantograph with damping fitted,and these were found to give satisfactory results (Fig. ISb).Damping was therefore added to the previously undampedpantograph.

Strength of the overhead catenary system was provedsoon after completion of erection, when two typhoonsstruck Taiwan, severely damaging the overhead EHVpower lines. The catenary system withstood this battering,and also subsequent typhoons after the equipment hadbeen brought into normal service.

6.4 Telecommunication system interferenceThe measurement during system tests and analysis of inter-ference into the telecommunication cable has been report-ed in detail previously [12]. In brief, the traction currentsarising from normal operation, longitudinal voltages, andtransverse noise voltages were recorded by an instrumen-tation tape recorder on eight power-feeding sections. Therecordings were then analysed in the UK by fast-Fouriertransform analysis on a computer, followed by statisticalanalysis.

6.4.1 Results of tests: The interference into the 1.27 mmloaded pairs was analysed for each test section, togetherwith traction current at the feeding substation. A plot oftraction currents is given as a probability graph (Fig. 19).

In Table 2, the statistical results are summarised for theeight test sections. Traction currents are notably less thanthe maxima assumed in the design but this is because fewer

325

£

f-4.52.c

oQ4.42

'SOI75

143 156 169 182 195 2O8 221 234 247distance .m.

259 273 286 299 312

8143 156 169 182 195 2O8 221 234 247 259 273 286 299 312

b distance ,m

Fig. 18 Tunnel simulation at 70 km/h16 m spans with level contact wire. a Pantograph undamped b Pantograph damped

300 IEE PROCEEDINGS, Vol. 130, Pt. B, No. 5, SEPTEMBER 1983

Table 2: Summary of statistical results of interference into telecommunication cable

Test

123456789

10

Durationoftest.min

39603960608056606056

Measuredatsubstation

Neili (BT)Neili (BT)Neili (BT)Neili (BT)HsinchuHsinchuNanchang (BT)Nanchang (BT)Miaoli (BT)Miaoli

Traction current, A

0.5

95114140

93842436

1443636

Probability

0.9

186210240189204186

90252108

96

0.99

300420400315324288120400150144

Longitudinal induced

0.5

1.041.041.320.960.520.760.30.50.721.12

voltage, VProbability

0.9

1.91.52.01.681.001.440.460.681.841.64

0.99

2.662.42.62.141.682.320.761.042.522.24

Transverse psophometric

0.5

0.0580.0620.0500.0560.0280.0240.0420.0260.0380.026

voltage, mVProbability

0.9

0.0690.0740.0700.0660.0380.0320.0600.0340.0500.038

0.99

0.0800.0950.0840.0840.0500.0420.0760.0420.0620.046

Note, (a) Probability is that the value will not be exceeded, (b) BT indicates booster-transformer section.

10 20 30 A050607080 90 95 9899 99.8 999 99.99probability ,70

Fig. 19 Example of traction current, over 56 min (test 8), showing near-normal distribution

trains were being operated than in the design timetable.The maximum assessed values [13] (p = 0.99) of longitudi-nal and psophometric noise voltages are much lower thanthe design limits of 60 V RMS and 2.5 mV, respectively.The main reasons for the very low induced voltages are:

(a) low traction currents(b) the actual intrinsic longitudinal and noise screening

factors of the telecommunications cable (quoted above)were ten and three times better, respectively, than thevalues assumed for the design

(c) the actual earthing impedance was lower than speci-fied.

The test sections included sections with booster trans-formers at both spacings on double and single track, butthe results do not show any reduction of interferencewhere these are installed. It should be remembered,however, that these booster transformers are intended toreduce interference into distant public telephone linesrather than lineside cables.

These results are of particular interest to overseasrailway companies considering AC electrification, inshowing that interference in the railway telecommunica-tion system from thyristor-controlled traction units can be

held to very low levels by suitable design of cable screeningand earthing.

7 Acknowledgments

The authors wish to thank the Taiwan Railway Authorityand Deconsult for their co-operation and helpful advice;they also wish to thank the Directors of GEC and BalfourBeatty for their kind permission to publish the paper.

8 References

1 MORRISON, R.E., and SINGH, A.: GEC internal report PSD3273/10, Power Systems Department, GEC Stafford, Sept. 1982, pp.5-6

2 'Railway construction and operation requirements—structural andelectrical clearances' (Department of Transport, HMSO, London,1977)

3 GOLDRING, A.G., HARTSHORN, P.R, RICKETTS, C.E., andROBINSON, W.: 'Insulation for high-voltage ax. railway electrifica-tion in Great Britain', Proc. IEE, 1969,116, (8), pp. 1377-1386

4 GOLDRING, A.G., and SUDDARDS, A.D.: 'Development of over-head equipment for British Railways 50 Hz a.c. electrification sinceI960', ibid., 1971,118, (8), pp. 999-1011

5 ROSEN, A.: 'Interference in railway line-side telephone cable circuitsfrom 25 kV 50 c/s traction systems' ATE J., 1959,15, pp. 279-299

6 SVERAK, J.G., DICK, W.K., and HEPPE, R.H.: 'Safe substationgrounding—Part 1', IEEE Trans., 1981, PAS-100, pp. 4281-4287

7 HOWROYD, D.C.: 'Public-supply-system distortion and unbalancefrom single-phase a.c. traction', Proc. IEE, 1977, 124, (10), pp.853-859

8 MORRISON, R.E., and BARLOW, M.J.: 'Continuous overvoltageson a.c. traction systems'. IEEE PES meeting 1982 (82 SM 345-7)

9 MORRISON, R.E.: 'Computer harmonic analysis of distortedcurrent waveforms', IEE Conf. Publ. 210, 1982, pp. 189-192

10 CLARKE, E.: 'Circuit analysis of a.c. power systems—Vol. 1' (Wiley,1958), pp. 308-315

11 MORRISON, R.E.: 'Measurement, analysis and mathematical model-ling of harmonic currents in a.c. traction systems'. Ph.D. thesis, NorthStaffordshire Polytechnic, Aug. 1981

12 SOCHOR, J.R., and RICHES, E.E.: 'Measurement and statisticalanalysis of interference in a 25 kV a.c. railway, operating thyristor-controlled traction units', IEE Conf. Publ. 203, 1981, pp. 99-104

13 CORBYN, D.B.: 'This business of harmonics', Electron. & Power,1972, 18, (6), pp. 219-223


Documents

Electrification of Taiwan main-line railway from Keelung to Kaohsiung