1000Vac distribution system for Signalling System applications

Transcription

1 1000Vac distribution system for Signalling System applications

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3 System for Transforming, Carrying and Distributing 1000Vac electric energy for technological equipment and devices along the railway line. This system allows to implement a distribution system that can be supplied from either ends (without distinction), but with sources which can never be paralleled. The main components of the distribution system being dealt with are the following: Station A 400Vac/1000Vac step-up transformer; Station B 400Vac/1000Vac step-up transformer; Three-core cable for 1000Vac distribution backbones; 1000Vac/400Vac step-down transformers for serving IS/ Aut/TLC lineside systems with input-output configuration present in peripheral locations. Each step-up transformer in the stations is supplied by the essential switchboards set after the UPS unit (SIAP IS 732D or pre-existing power supply system). Below is shown a synoptic single line diagram of the 1000Vac distribution line between two generic stations A and B in the assumption that (for instance) between the two stations there exist N peripheral locations. The need for running the system with at least one sectioning point open results from the fact that it must not be possible to parallel the essential distributions (UPS) of the two stations (A and B) in which are fitted the step-up transformers. The input-output configuration on the step-down transformer allows to supply the transformer from either side (right or left). 1000Vac line reconfiguration after a failure can be performed via manual commands or via automatic procedures which restore the system by making use of the backup energy provided by the system auxiliary services. Such operations can be managed locally, as well as remotely in manual mode by personnel qualified to remote control. If load arrangement reconfiguration on the 1000Vac line can be planned and is not linked to the effects of automatic reconfigurations after a failure, then it will be possible to manage the shutdown (via terminal block contacts), on those pieces of equipment which require this operation before the powering off and restarting (bootstrap) procedures. 3

4 1000V distribution in Italian Signalling Systems (SS) 1000V distribution in SS systems in Italy has historically been managed via (not distributed) neutral connected to the ground. Based on overhead line electrification characteristics, the two cases described below there result. 1000Vac distribution with 3kVdc overhead line electrification In railway lines electrified with direct current (3kVdc), distribution is of TT type; consequently: step-up transformer secondary winding star centre is connected to station grounding system; step-down transformer ground points are connected to the centre of the inductive connections which are connected to rails; the screen of the distribution cable between two 1000V transformers (step-up - step-down transformer or stepdown - step-down transformer) is connected to ground from one end only in order to prevent current circulation inside transformers and most of all in the screen of the 1000Vac cable. In first earth fault conditions (on either the cable or transformers): voltage on ground points has a value which is very close to the nominal value of ground system voltage (1000Vac/1,73 = 580Vac) whereas fault currents feature an extremely low value that can only be identified by using a differential relay. 1000Vac distribution with 25kVdc overhead line electrification In railway lines electrified with alternate current (25kVac), distribution is of TN-S type; consequently: step-up transformer secondary winding star centre is connected to station grounding system which is connected to the buried linear ground plate laid along railway line; step-down transformer ground points are connected to the linear ground plate which is connected to the track via inductive connections; the screen of the distribution cable between two 1000V transformers (step-up - step-down transformer or stepdown - step-down transformer) is connected to ground at both ends. In first earth fault conditions (on either the cable or transformers): voltage on ground points has a value which is equal to a fraction of the ground system voltage whereas fault currents feature a high value which - although not sufficient to trigger the over-current relay of the circuit-breaker protecting the 1000Vac line - is however more than sufficient for safe triggering of a differential relay. 4

5 Characteristics of the proposed system: IT distribution system and 1000Vac transformers in Class II In conventional systems the use of differential relays leads to risks of untimely releases due to indirect overvoltages mainly from atmosphere; such overvoltages may generate unbalanced pulse capacitive currents; these cases are rather frequent when the line is geographically wide. Proposed solution redefines the neutral point connection and the protection system against indirect contacts: in particular, this solution removes the problems in the best way by means of distribution systems with insulated neutral (IT) for managing the 1000Vac cable line and provides also step-up and step-down transformers in Class II with SELV type auxiliaries. An IT system provides for: transformer secondary winding star centre to be insulated from the ground; no ground point for step-up or step-down transformer as defined for Class II; screen of the distribution cable between two 1000V transformers (step-up - step-down transformer or step-down - step-down transformer) to be connected to ground from one end in 3 kvdc environment, or at both ends if in 25 kvac environment. In first earth fault conditions (on the cable), armor voltage has a value which is extremely low due to the extent of both the stray capacities of ground wires and the ground resistance at the screen ground connection point. Apart from system coordination, the first earth fault can persist with no time limit since power supply cut off is not required. Timely fault removal is however recommended in order to prevent that the occurrence of a second fault will cause power supply cut off. As concerns safety, this system does not therefore require that differential relays are used; consequently, the hazard of untimely releases is totally removed. This solution, consisting of QD400/1000 station Step-up Transformers and corresponding QD1000/400 line Step-down transformers, is used to supply line peripheral locations dedicated to manage individual devices and/or equipment like BA, RSC, Bca/M, PLL and RTB/RTR; this choice allows to confirm in advance that results expected in terms of reliability and consequently of working continuity will be high; these results will be more significant in line sections geographically characterized in unfavourable electrical conditions. In connection with the technical specifications in force at the present date, and in connection with improvements requested by the various circular letters, a power supply system has been implemented for 1000Vac lines with insulated neutral point connection (IT) and Class II transformers suitable to implement, among other things, an adequate partitioning barrier suitable to supply the electrical loads set downstream under Protection by Electrical Separation. Particularly remarkable is the 1000Vac energy distribution system managed with insulated neutral point connection and Tx and Rx transformer, since it results to be extremely immune to any line overvoltages, thereby improving considerably required service stability, safety and continuity. Further, as it is easily understood, immunity to noise caused by the proximity to the overhead line electrification system results to be decisive for the quality of service performed by electronic equipment. Line management with TT system and/or 380Vac line management: the right module within a common structure solution It could be required to supply the technological lineside loads with ground and neutral point connection different from the standard IT one (described above), for instance: with TT system. A TT system provides for: transformer secondary winding star centre to be freeearthing connected. differential relay provided on step-up transformer output circuit breaker. screen of the distribution cable between two 1000V transformers (step-up - step-down transformer or step-down - step-down transformer) to be connected to ground from one end in 3 kvdc environment, or at both ends if in 25 kvac environment. In this case, implementing an electrical protection system, suitable for operating under the abovementioned wires and grounds operating conditions, will provide for the following: Circuit breaker module fitted with differential relay; Transformer module electrical connection between stepup transformer secondary winding star centre and earth These interventions are minimal and do not involve changes to the fixed transformer structure which has been designed for all of the case histories known at present, thereby enabling friendly upgrades on site. Should it be required to carry out interventions on obsolete operating lines characterised by non-high nominal voltage due to the limited geographical extension of the line then, it will be possible to manage line 380/400Vac voltage by simply providing a proper transformer module with a different ratio of transformation, with no intervention on the fixed transformer structure. Main components V circuit breakers for step-up transformer outlets; V circuit breakers for step-down transformers; 3. Low voltage / low voltage transformers; 4. Parameters for setting 1000 [Vac] lines protections (like for instance short circuit current at end of line, 1kV transformers connection data to line section switchgear, neutral point connection, etc.). 5

6 400/1000 Vac step-up transformer It is the transformer which is generally installed at the station; its task is to raise the voltage dedicated to the line. Step-up transformer is a unit: in Class II as to 400 Vac low voltage circuits; in Class II as to 1000 Vac low voltage circuits; in Class III as to 24 Vdc safety extra-low voltage (SELV) circuits. This allows to create a suitable separation barrier between electrical systems managed with different neutral point connections (before and after the transformer) and to safely supply the equipment (transformer input circuits) in IT, or with Electrical Separation if required. Therefore, implementing Class II for some transformer circuits in the presence of metal structural work, implies: that double or reinforced insulation is not assigned to an insulating chassis; that parts inside the transformer have solid insulation, in air and of reinforced surface type towards metal structural work and that consequently metal structural work does not result to be classified as a ground point; that interior parts are provided with suitable mechanical protections aimed at not thwarting, during time, above indicated increased insulation. General characteristics Product name : 400/1000 step-up transformer Power supply Nominal input voltage: 400Vac, three-phase Nominal output voltage: 1.000Vac, three-phase Output voltage regulation steps: Nominal sizes [kva]: 1, Impulse voltage: 400Vac side: kv, 1000Vac side: 20 kv Mechanical characteristics Dimensions [l, h, d] [mm]: 900, 2.170, 785 Materials used: aluzinc steel Environmental and climatic characteristics IP rating: 21 Working temperature [C] : Storage temperature [ C] : Height: max 2,000m above sea level Relative humidity: 90% without condensate Diagnostics PLC Standards Complying with: EN1439, EN0950, EN0529. Availability, reliability and maintainability Maximum MTTR [h]: 30 Safety SIL level : 0 Single line diagram

7 Vdc auxiliary circuit-breaker module 2. Diagnostic (PLC), control and HMI module Vac circuit-breaker (after transformer) Vac circuit-breaker (at transformer input) 5. Ground switch disconnector. Voltage transformer and polling contactor /1000Vac three-phase step-up transformer 8. Terminal block compartment for line cable connection 7

8 1000/400 Vac step-down transformer It is the transformer which is generally installed on the line; its task is to adapt voltage coming from the line to industrial use parameters (230/400Vac, three-phase). Step-down transformer is a unit: in Class II as to 400 Vac low voltage circuits; in Class II as to 1000 Vac low voltage circuits; in Class III as to 24 Vdc safety extra-low voltage (SELV) circuits. This allows to create a suitable separation barrier between electrical systems managed with different neutral point connections (before and after the transformer) and to safely supply the equipment located after the transformer in Electrical Separation. Therefore, implementing Class II for the transformer circuits in the presence of metal structural work, implies: that double or reinforced insulation is not assigned to an insulating chassis; that parts inside the transformer have solid insulation, in air and of reinforced surface type towards metal structural work and that consequently metal structural work does not result to be classified as a ground point; that interior parts are provided with suitable mechanical protections aimed at not thwarting, during time, above indicated increased insulation. General characteristics Product name : 1000/400 Vac step-down transformer Power supply Nominal input voltage: 1000Vac, three-phase Nominal output voltage: 400Vac, three-phase Output voltage regulation steps: Nominal sizes [kva]: 1, Impulse voltage: 400Vac side: kv, 1000Vac side: 20 kv Mechanical characteristics Dimensions [l, h, d] [mm]: 900, 2.170, 785 Materials used: aluzinc steel Environmental and climatic characteristics IP rating: 21 Working temperature [C] : Storage temperature [ C] : Height: max 2,000m above sea level Relative humidity: 90% without condensate Diagnostics PLC Standards Complying with: EN1439, EN0950, EN0529. Availability, reliability and maintainability Maximum MTTR [h]: 30 Safety SIL level : 0 Single line diagram

9 Vdc auxiliary circuit-breaker module 2. Diagnostic (PLC) and control module Vac circuit-breaker (before transformer) Vac circuit-breaker (input/output) Vac circuit-breaker (output/input). Ground switch disconnector module 7. Battery charger module /400Vac three-phase step-down transformer 9. Terminal block compartment for line cable and battery connections 9

10 1000Vac line drive and control system The implemented 1000Vac line drive and control technological system is a real added value for this system of electrical energy distribution to technological lineside equipment and devices. The PLC installed in step-down transformers acts as concentrator of the relevant diagnostic info and data and controls the local logic functions. The same function is run also by the PLCs installed in step-up transformers which in addition are charged with the following roles: line manager, data concentrator of all the relevant transformers, diagnostic front-end to remote supervision system (Scada D&M). Communication architecture between PLCs provides TCP-IP (Modbus) network connection to be implemented in optical fibre(preferably) according to overvoltage protection matters issued by the latest RFI directions. The drive and control system implements several functions among which the main ones are the following: displaying the 1000Vac line energization state and diagnostic details of each transformer connected to it, on the HMI terminal provided on step-up transformers; executing single remote commands; managing insulation control between active wires and ground of the 1000Vac line (if the line is managed with neutral point connection and IT type grounds); option to run troubleshooting on 1000Vac line via remote control manual procedure or, via automatic procedure managed autonomously by the step-up transformer PLC which will identify the line section in failure and will provide to run automatic line reconfiguration isolating the failing section and supplying the step-down tran- sformers from line sections not involved in the failure. The identification procedure of the section in failure and the consequent reconfiguration of the circuit will be performed after Operator s confirmation if the 1000Vac line is managed with neutral point connection and IT type grounds or, immediately after the failure which has caused its powering-off in case the line is managed with neutral point connection and TT type grounds; automatic line reconfiguration when a live step-up transformer is powered off by its power supply system (set upstream) in order to allow prompt supplying to the technological lineside equipment and devices by the other step-up transformer, thereby restoring all the relevant functions; smart line management suitable to avoid unrequired circuit closing via interlocks on motorized commands and preventing undue manual commands directly on circuit breakers in order to safeguard power supply continuity; Integrated Energy Management (GEI) of line loads suitable to control supplying of non priority electrical loads (like for instance HVAC) in time-sharing thereby reducing the electrical load over the line in case of need; management of the power-off control of those technological equipment and devices that allow for this possibility for a correct shut-down before the intentional reconfiguration of the line, and management of the power-on control of the abovementioned equipment and devices once the reconfiguration procedure is over; management of the insulation control after the stepdown transformer, also in discontinuous control mode, and monitoring of main electrical parameters if choosing power supply of downstream loads with wires and grounds in Electrical Separation operation. 10

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