Indian Railways AC Traction Manual PDF

CHAPTER I GENERAL 30100 Evolution of Electrical Rolling Stock 1 Electrical Concept 1.1 The development of mercury arc rectifier for rolling stock application, wherein the dc motor could be used for traction became a single major factor for...

CHAPTER I GENERAL 30100 Evolution of Electrical Rolling Stock 1 Electrical Concept 1.1 The development of mercury arc rectifier for rolling stock application, wherein the dc motor could be used for traction became a single major factor for large scale application of single phase 50Hz 25kV for mainline electrification. Hitherto the performance of ac traction motor in locomotive had always been considered inferior to its dc counterpart and dc traction was only a compromise solution to save on the cost of OHE. The use of rectifier on the locomotive on the other hand offered an alternative of a superior locomotive to a dc locomotive. Initially water cooled mercury arc rectifiers known as ignitions, (ignited internally through an ignitting electrode) were used. Indian Railway purchased two types of locomotives of this type (WAM-1 from Europe &WAM -2 from Japan). But they gave way to neater and more reliable solution of externally fired air cooled rectifiers i.e. excitrons. Excitrons had the additional advantage of reversibility i.e converting dc back to ac and could be utilized for regeneration to a limited extent. Indian Railways imported a few locomoitive of this design from Europe (WAG-1) and a sizable fleet was assembled and manufactured at CLW as well. A few Japanese locomotives using silicon retifier were also imported (WAG-2) 1.2 With the development of High Power Silicon Diode Devices the entire technological development of ac traction stock took a new turn and more powerful units of ac locomotives were conceived. The silicon diode is simple to maintain and is extremely reliable. At present bulk of the fleet of Indian Railways consists of such locomotives. 1.3 Both with mercury arc and silicon rectifiers, the voltage control is achieved by an electro- pneumatically operated tap changer. In the locomotives the high tension tap changer has been utilized. Typical power circuit diagrams of WAG-5and WCAM-1 type locomotives are given in Fig. 1.01and Fig.1.02. On some of the WAG-1 and WAM-2 locomotives, silicon rectifier with tap changer control has been replaced by the phase angle controlled thyristor convertor. 1.4 MG locomotives: These locomotives of YAM-1class (Japanese design) are in use in a single isolated section viz. MAS-Villupuram section. They employ silicon rectifiers for conversion. Salient data on electrtic locomotives is given in Annexure 1.01./A. 1.5 EMU (Electrical Multiple Units) both on MG and BG employ silicon rectifiers for conversion and LT tap changers are used for voltage control. Salient features of EMU are given in Annexure 1.01./B. A typical power circuit diagram of EMU type WAU-4 is also given in Fig.1.03. Phase angle controlled thyristor convertor has also been deployed on a few 25kVac MG EMUs in place of silicon rectifier and LT tap changer on Southern Railway. 2.0 Sources of Electric Locos 2.1 Indian Railways imported 100 WAM-1 Bo-Bo locomotives from Europe, and 36 WAM-2 and 2 WAM-3 Bo-Bo locomotive from Japan. Subsequent to this, 42B-B high adhesion(mono motor bogies)locomotives designated as WAG-1 were imported from Europe and 45designated as WAG-2 from Japan. Ten WAG-3 locomotive of B-B design of higher rating were imported from Europe Manufacture of WAG-1type of locomotive was taken up in Chittaranjan :locomotive Works (CLW) and later on CLW switched over to the manufacture of WAG-4 type of locomotives. After completion of 186 WAG-4 locomotives, Indian Railways switched over to 6 axle locomotive of indigenous design and CLW have manufactured a series of WAM-4 and WAG-5 locomotives. INDIAN RAILWAYS—AC TRACTION MANUAL—VOLUME III (3) With a view to improving the performance of the locomotive, WAG-5 locomotives with minor variations to suit specific application were also manufactured and designated as WAG-5 with different suffixes. 2.2 Eighteen prototype 6000 HP thyristor control locomotives of 3 type designated as WAG -6A, B&C were imported, six from ASEA and twelve from Hitachi in 1988. A prototype locomotive of 5000 HP capacity with high adhesion bogies, designated as WAG -7 has been designed and manufactured by Chittaranjan Locomotive Works. A new prototype control is under development. 2.3.To meet the specific requirements of higher speeds for passenger services,CLW manufactured WAP type locomotive using Co-Co flexi -coil bogies to work upto a speed of 130km/h designated as WAP-1. This loco has been further upgraded for speed potential of 140km/h by providing improved version of indigenously designed bogies. This loco is designated as WAP-3. A few WAM-2 locomotives were fitted with modified drive and designated as WAP-2 locomotive. 2.4 A chart exhibiting the salient features of ac electric locomotive is enclosed as Annexure 1.01/B sheet No.1&2. Major dimensions of the various locos are shown in Annexure 1.02. Load table for various locomotives are available at Annexure 1.03. Starting tractive effert is limited to 37.5t due to limitation of bridges on Indian Railways. Brief write ups on 6000HP microprocessor controlled thyristor locomotives are given in Annexure 1.04 and 1.05. Functional description of main circuit of thyristor EMU is given in Annexure 1.06. 3.0. Mechanical concepts. 3.1 Four axle locomotives had the following types of drives: i) WAM1 : cordon shaft drive ii) WAM2 and WAM 3 : WN coupled gear drive iii) WAG(1,3and4) : coupled gear drive through cordon shaft monomotor bogie European design and also built at CLW. iv) WAG2 : Monomotor bogie with flexible rubber couplings (quill drive ) arrangement (Japanese Design) 3.2 The monomotor bogie locomotives had a starting tractive effort of just under 32 tonne with motor power of 790HP per axle. Except for a few WAG 1, WAG 2and WAG 3 class locomotives the bulk to the series of WAG1 and WAG4 class were manufactured at Chittranjan Locomotive Works till early seventies. The performance of these locomotives was also not found to be adequate for meeting increased operating requirements. 3.3 WAM4 andWAG5 locomotives which were indigenously manufactured used Co-Co , trimount bogies of ALCO design with axle hung nose-suspended traction motors. Same design of bogie was also used in dual voltage locomotives (WCAM-I). In WAG-6A & B locomotives, with a view to have a high tractive efforts and high speeds (beyond 160 Km/h), 6-axle locomotive having Bo-Bo-Bo arrangement was adopted. WAG -6A locomotives utilises ASEA hollow shaft drive system whereas WAG-6B locomotive uses WN coupling. In WAG-6 locomotives high adhesion Co-Co bogies using unidirectional motor and secondary suspension arrangement was adopted. Indigenous bogies similar to those of WAG -6C locomotives will be used in the prototype WAG-7 & 8 locomotives. 3.4 In WAP-1 locomotives, flexicoil bogie modifying the existing WDM-1 (General Motor Design) has been used. WAP3 loco utilises an improved version of this bogie. INDIAN RAILWAYS AC TRACTION MANUAL VOLUME III  ANNEXURE 1.03 WAP 1 SHEET – 1/13 HAULAGE CAPACITY (WITH OUT 5% ACCELERATION RESERVE) ------------------------------------------------------------------------------------------------------------------------------------- -------------------| | SERVICE | GRADE | TONNES AT km / h (TANGENT TRACK) | | | | | |---------------|-------------|------------------------------------------------------------------------------------------------------ --------------------| | | 20 | 40 | 60 | 70 | 80 | 90 | 100 | 110 | 120 | 130 | START* | | | | | |-------------------------------------------------------------------------------------------------------- ------------------| | | LEVEL | ABOVE 1500 | 1235 | 4340 | | | | ------------------------------------------------------------------------------------------------------------------- -------------------| | | 1/500 | ABOVE 1500 | 1350 | 1100 | 835 | 3070 | | |----------|------------------------------------------------------------------------- | | | | | | PASSANGER | 1/200 | ABOVE 1500 | 1460 | 1215 | 1010 | 860 | 715 | 545 | 2115 | | | | | | | | | | | | | | | | | | | | | | | | SERVICE | 1/150 | ABOVE 1500| 1415| 1360 | 1185 | 990 | 830 | 710 | 590 | 450 | 1790 | | | | | | | | | | | | | | | | | | | | | | | | | | | | ICF | 1/100| 1120 | 1060| 1000| 965 | 850 | 715 | 600 | 515 | 425 | | 1370 | | | | | | | | | | | | | | | | COACHING | 1/50 | 540 | 520 | 500 | 490| 430 | | | | | | 775 | | | | | | | | | | | | | | | | STOCK | | | | | | | | | | | | | |------------------------------------------------------------------------------------------------------------------------------------ -------------------| MAXIMUM STARTING T.E. -= 25.0 t INDIAN RAILWAYS – AC TRACTION MANUAL – VOLUME III  Annexure 1.04 Functional description of main circuit of WAG-6A 1. General Outline Fig. 1 shows a simplified diagram of the main circuit. The current is taken from the 25 KV 50 Hz overhead line by pantograph and passes through the main circuit breaker to the primary winding of the main transformer, and then through the grounding transformer (GT) to the car body. The purpose of the GT is to ensure that the current going through the car body finally finds its way through the wheels and is then earth via the rails. In addition to the four traction windings, secondary windings are connected to the auxiliary power system, hotel load and motor field circuit respectively. As can be seen in Fig. 1, the main circuit is divided in two parts, called traction motor modules. These are controlled individually, depending on adhesion conditions. 2. Traction motor modules Fig. 2 shows the armature circuit for one motor module. In the convertors, which are built up from thyristors and diodes, the 50 Hz supply voltage is rectified and fed to the traction motors. To smooth the current from the convertors smoothing reactor is connected in series with each motor. Connected parallel to each traction winding, the power factor control has the form of three tuned LC- links. Between the transformer and the convertors, automatically operated module disconnectors (MD) are connected (Fig.2) which also disconnect the field circuit of the module (Fig. 3) 3. The Convertors. The convertors consist of thyristors and diode to allow a path for the free wheeling current when the thyristors are not fired. During acceleration, one bridge only is being fired until shortly before it is fully advanced. Then the two bridges are both fired until the first one is fully advanced, after which the second is further advanced, until it too is fully fired. This procedure is called “overlapping control”. Phase angle control of the thyristors will introduce harmonics and because of this, both power factor and psophometric current will vary considerably at different speeds. In order to minimize the influence on the supply network, Power Factor Control equipment (PFC) is used. 4. The Motors The traction motors are separately excited, bogie suspended dc motors. Each motor is individually fed from a convertor, consisting of two rectifying bridges. 4.1 The Field Circuit The field circuit (Fig 3) feeds the motor field windings, each of which is individually controlled. During acceleration from stand still, the field current is kept approximately constant until maximum motor voltage (or maximum available voltage) is reached. In order to further increase the speed, field weakening must take place, which leads to lower tractive effort. At over speed i.e. when slip tends to occur on one axle, the field is weakened, tractive effort of the motor concerned thus lowered, thereby, lowering its armature current and subsequently decreasing the over speed. INDIAN RAILWAYS – AC TRACTION MANUAL – VOLUME III 4.2 The PFC System Parallel to each of the four of traction windings of the main transformer, Power Factor Control equipment (PFC) is connected and this has the form of three tuned LC-1 links, switched in and out by two anti-parallel thyristors as shown in Fig.4. The PFC has two purposes. One is to be a capacitive compensation for the otherwise inductive traction circuit, thus raising the power factor. The other is to filter the harmonics out from the transformer windings, thus further increasing the power factor and, at the same time, the decreasing the psophometric current. The two purposes are fulfilled by using tuned LC-links,in this case three links showing best filtering performance at 3rd,5th and 7th harmonics respectively. The demand for capacitive compensation and filtering performance varies strongly with the speed and with the tractive effort i.e. with the firing angle of the main thyristors and the current through these. The PFC is controlled so that each locomotive will appear as an inductive or a resistive load, seen from the overhead line at the pantograph. When the ac current to the locomotive tends to go capacitive, one or more the PFC modules are cut to avoid over compensation. 4.3 Safety monitoring and fault detection For safety and monitoring purposes, current transformers and breakers are used (Fig.5). To curb over voltage, a lightning arrestor (LA) is used, limiting the maximum voltage over the main transformer. The current in all windings of the main transformers and all motor fields (Fig.3) is monitored continuously, through the use of current transformer (CT). Should an over current occur on any of the monitoring transformers, the main circuit breaker (MCB) will open immediately. The potential transformer (PT) is used for monitoring the supply voltage. When the supply is too high or too low, the MCB is opened. To enable the driver to immediately discover any faults in the locomotive and, if possible, reset from the cab, a computerized fault indicating system (FIS) has been incorporated. This system consists of a microprocessor which supervises all running conditions. Together with a display panel in each driver’s cab this gives the driver all the necessary information during fault conditions and also provides possibility to reset most of the faults from the driver’s cab through a push button. Indian Railways – AC Traction Manual – volume III  Annexure 1.05 Functional description of main circuit of WAG-6B/WAG-6C 1. General Outline Fig.1 shows a simplified diagram of the main circuit. The current is taken from 25 Kv 50Hz overhead line by pantograph and passes through the main circuit breaker to the primary winding of the main transformer and then through the ground brushes to wheels and is then to earth via the rails. In addition to the four traction windings, secondary windings for auxiliary power system, hotel load & motor field circuit have been provided. 2. Traction Motor Groups Traction motor armature circuit is divided into two groups of three traction motors each. The output from convertor is fed to the traction motors through smoothing reactors in series with each traction motor. Power factor correction LC banks are connected across the traction windings. 3. The Convertors The convertors consist of thyristors and diodes to allow path for the free wheeling current when the thyristors are not fired. During acceleration, one bridge only is initially fired untill shortly before it is fully advanced. Then the second bridge is also fired. This procedure is called ‘overlapping control’. Phase angle control of the thyristors will introduce harmonics and because of this, power factor and psophometric current will vary considerably at different speeds. In order to minimise the influence on the supply net work , power factor control equipment (PFC) is used. 4. Traction Motors The traction motors are compound wound motors having a ratio of approximately 60:40 for the separate field strength to series field strength. Motors are fully suspended in WAG-6B and axle hung, nose-suspended in WAG-6C. Three motors in parallel are fed from a convertor consisting of two sequence control bridges shown in Fig,1 5. The Field Circuit The field circuit arrangement is shown in Fig.2. There is one field convertor for each of the traction motor groups i.e., three traction motors are fed by one field convertor. During acceleration, the field current is kept proportional to the armature current until maximum motor voltage reference is reached. After this the field current is reduced to get a constant power characteristic till the weakest field strength is reached The field convertor also performs the required field current control during rheostatic breaking to get the desired breaking characteristics. 6. Power Factor Correction System Each traction group has a power factor correction equipment which consists of two independent LC- links which can be switched on/off through thyristors. The arrangement in shown in Fig.3. When the primary current of the traction transformer reaches about 100A, the switching thyristors switch on the PFC unit No.1 of both traction groups to improve the power factor. If the current increases to about 150A, the 2nd PFC unit is switched on. INDIAN RAILWAYS – AC TRACTION MANUAL – VOLUME III 7. Safety Monitoring and Fault Detection For safety and monitoring purposes, current transformers and breakers are used (Fig.4). To curb over voltage, a lightning arrestor (LA) is used, limiting the maximum voltage over the main transformer.The current in all windinds of the main transformer & all motor fields is monitored continuously, through the use of current transformer (CT). Should an over current occur on any of the monitoring transformers, the main circuit breaker (MCB) will open immediately. The potential transformer (PT) is used for monitoring the supply voltage. When the supply is too high or too low, the MCB is opened. To enable the driver to immediately discover any faults in the locomotive and, if possible, the reset from the cab, a computerized fault indicating system (FIS) has been incorporated. This system consists of a microprocessor which supervises all running conditions. Together with a display panel in each driver’s cab this gives the driver all the necessary information during fault conditions and also provides possibility to reset most of the faults from the drivers cab through a push button. Annexure 1.06 Functional description of the main circuit of Thyristor EMU 1. Power Circuits 2. The power circuits are shown in Fig.1.The symbols appearing in it are listed below together with the location of the equipment. III. Symbol Description Location ABB Air-Blast circuit –breaker Roof AF1-3 Auxiliary fuses Main transformer CMD1-2 Current-monitoring device Contactor case D1-4 Main diodes Rectifier case DX1-2 Di/Dt inductors Rectifier case EAS Earthing switch Roof EFR Earth fault relay Contactor case ERF Electronic reference fuse Rectifier case FRS Forward and reverse switch Contactor case HFSK1-4 High-frequency surge-suppression capacitors. Rectifier case LA Lighting arrestor Roof M1-4 Traction motors Bogies MC1-4 Motor contactors Contactor case MOR1-2 Motor overload relays Contactor case MT Main Transformer Underframe P Pantograph Roof POCT Primary-overload current transformer Roof Indian Railways – AC Traction Manual – volume III POR Primary-overload relay Contactor case SOCT Secondary-overload current transformer Rectifier case SOR Secondary-overload relay Contactor case SSF1-4 Surge-suppression fuses Rectifier case SSK1-4 Surge-suppression capacitor Rectifier case SSR1-2 Surge-suppression relays Rectifier case SST1-2 Surge-suppression transformer Rectifier case SSZ1-4 Surge-suppression resistors Rectifier case SX1-4 Smoothing inductor Underframe T1-4 Thyristors Rectifier case WSR1-2 Wheel slip relays Contactor case WSZ1-4 Wheel slip resistor Contactor case 3. Description of Circuit The supply current is taken from the overhead conductor by the pantograph P, through the air-blast circuit-breaker ABB and the H.T. bushing and cable, to the primary winding of the main transformer MT. The return circuit to the running rails is via an insulated earth cable to the axle earth-brushes fitted on each traction-motor axle-suspension. Also connected to the high-voltage end of the transformer primary winding are a two pole earthing switch EAS and a lightning arrestor LA. A primary-overload relay POR with its associated current transformer POCT protect the main transformer. The main transformer has two equal secondary winding supplying two half controlled asymmetrical bridges T1, T2, D1, D2 and T3, T4, D3, D4 the dc outputs of which are connected in series. The rectifier bridges supply the four traction motors M1-M4 which are permanently connected in series parallel configuration, with their fields and compoles arranged in the centre (virtual earth position). The main smoothing inductor SX is divided into four sections, so that in the event of a motor fault, a high impedance is in circuit and motor cut-out is simplified. The output voltage of the rectifier is controlled to maintain a constant current in the armatures during acceleration, the current being measured by current monitoring devices CMD1-2. Overload protection is provided by the two current-monitoring devices and two motor-over load relays MOR1- 2. A single twin-circuit linear reversing switch FRS is used. Motor isolation is provided by the motor contactors MC1-4 and the motors can be cut out in pairs. Wheel slip detection is provided by voltage-sensitive circuits comprising resistors WSZ1-4 and wheel slip relays WSR1-2. The power circuit includes four surge-suppression circuits: 1. High frequency surge-suppression capacitors HFSK1-4 connected between each secondary terminal and earth. 2. Resistor/capacitor snubber-circuits connected across each power device in the main bridges. 3. Limiting inductors DX1-2 for rate-of-rise of current. 4. Main surge suppression networks SSF1-4, SSZ1-4,SSK1-4. These networks are connected in pairs across each secondary winding; a failure of any component in these energizes one of the surge-suppression relays SSR1-2 The main rectifier bridges are protected from overload by the secondary-overload-relay circuits SOR, SOCT1-2 INDIAN RAILWAYS – AC TRACTION MANUAL – VOLUME III