ACTM Volume-II (Part- I) II CHAPTER XI RECENT DEVELOPMENTS

CHAPTER XI RECENT DEVELOPMENTS 21100 2x25 kV Auto-Transformer Feed System 1. Incoming Power Supply The incoming power supply scheme is similar to 25 W simple feed system. Power supply for ac traction is obtained from the nearest grid sub-station of the Power Supply Authority. For this purpose duplicate feeders, generally at 132 kV or 220kV, comprising only two phases are provided from the grid sub-station to traction substation. The loads, however, are 2-3 times higher compared to.25 kV system and therefore Wood-bridge/V-connected transformers are provided in the traction substations to bring down the unbalance within acceptable limits. It is possible to absorb such unbalances without exceeding the permissible limits if the grid system capacity is adequate. 2. Power Receiving Arrangement. Traction Sub-station The incoming extra high voltage power is stepped down to 2x25 kV by the main traction power transformer. The 2x25 kV supply is then fed to an auto-transformer. One terminal of the auto-transformer is connected to the overhead catenary wires and the other terminal to a feeder wire which runs parallel to overhead contact/catenary wire all along the section and is usually supported from super masts fixed on the OHE structures. The mid point of the auto-transformer is connected to the rail, thus providing a 25 kV supply, with reference to the rail potential, for traction. The capacity of the auto-transformers and their spacing is decided based on the traffic pattern in the section. The general arrangement of the scheme for 2x25 kV auto-transformer feeding system is indicated at Fig. 11.01. This is for a Scott connected transformer substation. 3. Distribution of Traction Power Supply Feeding Post (FP) The arrangement at the feeding post is generally similar to that at the 25 kV conventional system feeding post. Sectioning and Paralleling Post (SP) A short neutral section is provided in the OHE opposite the feeding post as well as mid-way between two adjacent traction substations. The feeder wire is also provided with a neutral section by means of two cut-in insulators coincidental in space with the ends of the neutral section. Sub-sectioning and Paralleling Post (SSP) The arrangement at the SSP is generally similar to that at the 25kV conventional SSP system. Auto-Transformer Post These are provided adjacent to the track through-out the length of the section. The spacing and capacity of the auto-transformers is decided as a part of system design based on specific requirements and traffic pattern. Typically the spacing is 15 km and capacity 2 MVA. Distribution of current in AT system is shown in Fig. 11.02.   4. Overhead Equipment: The OHE system is generally similar to that for the 25 kV conventional system except that an additional conductor, called feeder wire is also run parallel to OHE, all along the length of the track. This feeder wire is insulated at 25 kV from the steel structure and at 2x25 kV from the traction OHE. 5. Protective system .• In addition to the relays and protection devices for the transformer protection, a set of following relays are provided at the traction sub-stations specially for 2x25 kV AT feed system. — Distance relay — ac failure detection device — Over-current relay 21101 OHE Recording-cum-Tcst Car 1. For satisfactory current collection, the geometry of the overhead equipment is required to be maintained within very stringent limits. Presently monitoring of various parameters of overhead equipment like height, stagger, wear of contact wire, condition at the cross-overs and overlaps, is being done manually which could introduce errors in measurement due to individual's judgment. Moreover, it is time consuming. For the very high reliability of operation expected of electric traction system, mechanized monitoring of various parameters is essential. 2. Due to increasing demand for freight and passenger traffic, trailing loads and speed of trains are being increased gradually. Heavier freight trains hauled by one or two consists of locomotives will draw heavy currents from the substation. For meeting the requirement of increasing passenger traffic, trains with higher speeds are being introduced. In view of these developments, it is necessary to ascertain potential of the existing OHE and pantograph contact system for effecting requisite improvement and developing newer designs to achieve satisfactory current collection at higher speeds and heavier loads. 3. For achieving these objectives, efforts are on to develop an Overhead Equipment Recording cum Test Car. This car will be used to measure and record various parameters of OHE and pantograph both under static and dynamic conditions. The proposed car will be of trailer type, suitable for running at speeds of 160 km/h with potential to run up to 200 km/h. The car shall be hauled by locomotive or attached to a train. The car will be provided with on-board computer based data acquisition and processing system. The facility for video recording of arcs generated due to interruption in current drawn by locomotive as a result of loss of contact between pantograph and the OHE is also proposed to be provided. 4. The various parameters proposed to be monitored are: Measurements on pantograph: a) aero-dynamic upward force of the pantograph; b) contact force between pantograph and contact wire; c) vertical and horizontal movement of pantograph; d) quality of current collection- loss of contact; Measurements on OHE: a) height of contact wire; b) stagger of the contact wire; c) gradient of the contact wire; d) detection of hard spots; e) checking of cross-overs and turn-outs; f) body vertical acceleration; g) body lateral acceleration; h) quality of current collection loss of contact. 21102 Rail-cum Road Vehicle Such a vehicle is suitable for propulsion both on the road as well as on the track. Two sets of wheels are provided for this purpose. This vehicle is provided with an extendible swivelling platform. The vehicle can be driven on road to the level crossing nearest to the work site and taken there on the track. 21103 Transportable Self Propelled Trolley This is a self propelled trolley which can be transported by a truck to a point accessible through road, close to the work site, for carrying out work on OHE. The trolley is provided with extendible swivelling platform. 21104 Dry Type Booster Transformer and Auxiliary Transformers Conventional oil filled transformers require lot of care and attention for maintaining the characteristic of oil within the permissible limits to avoid failure of insulation. Dry type cast resin transformer is a relatively new technology. The chief advantage of this type of transformer over the oil filled ones is that they are practically maintenance free. The copper in the windings cannot be retrieved from the cast resin and so the risk of theft is eliminated. There being no oil risk of fire and explosion are also absent. Dry cast resin transformers are currently under evaluation for their service performance. 21105 Static Distance Protection Relay for Protection of OHE 1. For the distance protection of the overhead equipment, the relay which is in use is the electro-mechanical type. This relay has a Mho characteristic as illustrated in Fig. 11.03. The relay is prone to trip on normal overloads because of its inadequate discrimination between load current and the fault current when the fault is at the farther end causing undesirable tripping of the feeder circuit breaker. This problem will be more acute in the future due to the further increase in traffic anticipated and the increase in the traction power transformer capacity at TSS. 2. To over-come the above problem RDSO has developed a static type distance protection relay. This relay is a three zone relay, the first two zones having Mho characteristic and the third zone having a lenticular characteristic with adjustable aspect ratio. The relay characteristic is illustrated in Fig. 11.04. While the first zone operation is instantaneous, the second and third zones have adjustable time settings (zero to Is). The first zone can be set to cover about 80% of the OHE from TSS to SP, the second zone to cover a distance which is slightly shorter than the distance to the adjacent TSS and the third zone may cover the adjacent TSS. By providing a time delay of about 0.4s to 0.5s in the second zone/third zone of the relay, adequate discrimination between faults from TSS to SP and SP to the adjacent TSS can be achieved - the under voltage relay at the SP acting as primary protection and the second/third zones of the distance relay at TSS acting as back up protection for faults beyond SP in case of feed extension. The settings of the various zones of the relay should be based on the RDSO's guidelines in this regard. 3. As an alternative to the static distance relay described above, the static relay with parallelogram characteristic as illustrated in Fig. 11.05 can also be used. At present these relays have to be imported. However, efforts to develop these relays indigenously are on. The advantages of this relay as compared with the electro-mechanical relay with Mho characteristic are similar to those of the static relay described above. The rtlay settings for this relay also should be based on the RDSO's guidelines in this regard. 21106 Composite Insulators The conventional porcelain insulators have poor impact withstand capability. The sheds of such insulators are easily broken during handling and also due to acts of vandalism. The glazed surface of porcelain also does not have good hydro-phobic property. These limitations can be overcome to a great extent with the use of composite insulators. The composite insulator comprises a porcelain (alumino) or a resin bonded glass fibre core and moulded sheds of elastomeric/plastic material e.g., silcone elastomer or poly-tetra-fluoro-ethylene (PTFE). The interface between the core and the sheds is sealed with special compound to prevent ingress of moisture and direct tracking along the length of the core. The end fittings are usually crimped to the core. Such insulators have exhibited excellent performance in simulated pollution tests. They also have excellent impact withstand capability. Efforts are on in RDSO to introduce such insulators.

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