GB2328663A - Electric current supply; sectioned conductor rail - Google Patents

Abstract

In an electrical supply system where current is taken from an exposed live conductor, the conductor is supplied from an insulated, auxiliary conductor only when required. As described, the live third rail for supplying electrical current to electric locomotives is divided into sections with insulating breaks 8 and an isolated auxiliary cable 9 parallel to the live rail supplies current thereto via contact switches 7 only while the locomotive is on that section of track. The switch may be activated by pressure of the locomotive on the tracks e.g. with thyristor control, pressure of the collector shoe on the live rail, or by a signal from the locomotive e.g. radio, ultrasonic, optic or electromagnetic. Since the track sections would only be live when necessary, accidental electrocutions would be prevented. Multiple voltage and current levels may also be allowed on the same live line for power, signalling or data transmission purposes.

Description

PICA system This invention relates to a Parallel Isolated Connection Auxiliary PICA The PICA system can be used to isolate an electrical system where a line is normally kept at a set voltage potential. The reasons using the PICA system for isolation are: i) isolating an exposed live voltage line where a safety or other hazard is present.

ii) changing the voltage potential so multiple voltages or currents can be derived from a single line.

Although the PICA system has many safety applications one of simplest examples is the use of the PICA system to isolate live electrified third rail tracks as used by underground and electrified commuter rail networks. The voltage levels in these networks are between 600V and 750V in the U.K. although higher voltages are used in some European networks. Unlike the overhead power cables used on inter-city routes, the power is supplied through a third rail (4 in Fig. 1) laid parallel to the two conventional tracks (3 in Fig. 1). The power supplied by this third rail is d.c. (direct current) and the rail remains live at all times. The electric locomotive takes electric current from the third rail for its motors and returns the current via the two conventional rails. The two conventional rails are kept at earth potential and on their own pose no electrocution hazard. Accidental electrocution requires two electrical contacts the live rail and usually the nearest conventional rail, although electrocution can also occur if contact is made with the live rail and any earth contact.

In its simplest form the engine for the locomotive is an electric motor requiring connection to two electrical terminals, a 'positive' and a 'negative'. The third rail acts as the positive terminal the conventional rail acts as the negative terminal. Contact between the live third rail and the locomotive electrical motor system is achieved using a 'shoe' (5 in Fig. 2), an electrical contact on the locomotive. The current returns through the conventional tracks by the electrical contact between locomotive's metal 'wheels and the track.

In the U.K. the third rail is raised above the level of the two conventional rails on supports and consists of lengths of rail welded together to produce continuous unbroken rail except at stations and other junction points where breaks in the third rail are connected together by cable for electrical continuity. The reason for the continuous welded third track is to produce good electrical continuity along the whole length and to avoid unnecessary jolting 'which might otherwise cause problems with the connecting 'shoe'.

The PICA system proposes the use of an isolated auxiliary cable (9 in Fig. 3) running parallel to the live rail. The auxiliary cable would be totally insulated with no exposed live contacts. Although the 'P' in PICA stands for parallel this may also be used in the electrical meaning of parallel where the auxiliary line may not have to run physically parallel to the existing lines.

The PICA system uses short sections of third rail each length of which is electrically isolated from the next length by a short insulating section, 8 in Fig. 3 (and Fig. 4 the side view). When the locomotive passes over the PICA section a contact switch (7 in Fig. 3) operates, connecting the live auxiliary line to the third rail, Drovidina electrical Dower onlv while the locomotive is on that section of track. Once the locomotive has moved on to the next third rail section the switch moves to the off position again, so the only time any section of the third rail is live is when the locomotive is actually on that section of track. Additional switching may be needed to earth the third rail while not in use to ensure any electric charge built up during the contact stage is quickly dissipated to earth.

PICA switching There are numerous ways the switching can be effected using proprietary switchgear, some examples are listed below.

i) Mechanical of hydraulic pressure using switches strategically placed between the rail tracks activated when the mass of the locomotive is acting on the rails ('track bending and deflection'). Since the rail deflection is of the order of 2 mm some mechanical or hydraulic amplification 'would be needed to produce the necessary switch clearance. The switching mechanism could be achieved by building it into a modified 'tie plate'.

ii) Switching from the pressure of the 'shoe' on the live rail.

iii) Operation by transponderltranducer action in response to a radio, ultra-sonic, optic or electromagnetic signal from the locomotive. These methods would probably need a 12 volt d.c. line to operate the relay switch connecting the auxiliary line to the third rail.

iv) Operation by mechanical switching described in (i) linked to a low voltage d.c.

line used to pulse a thyristor to the ON state, connecting the auxiliary to the third rail. A thyristor is a semiconductor 'solid state' device (no moving parts) which is triggered by a low voltage signal typically about 5 volts which causes the high voltage terminals to switch on.

unlike a mechanically operated switch such as an ordinary light switch which requires mechanical movement, the thyristor has an extra low voltage electrical terminal, when a low voltage pulse of approximately 5V is applied to this terminal the thyristor switches on the two high voltage terminals without any mechanical movement.

Given that exposed track sections may operate between -2OOC and 500C the 'solid state' electrical switching would prove to be the most reliable. This method has two additional advantages; (a) no additional hardware needs to be fitted to the locomotive, (b) the thyristors automatically switch OFF when the locomotive moves to a new section of track.

Fig. 5 shows PICA sections introduced with the existing third rail.

10 and 12 in Fig. 5 indicate the PICA isolated sections, 11 in Fig. 5 is a standard unmodified live section, when the PICA sections are not in use the electric current flows through the auxiliary line but still maintains current in the unmodified live sections. No current flows through PICA third rail sections 10 and 12 when no locomotive is on that section of track.

Advantanes of the PICA system i) The PICA systems connected with fail-safe switching system virtually eliminates the chance of accidental electrocution.

ii) The PICA system can be introduced piecemeal into existing 'third rail' networks, a single section at a time without interruption to the rest of the power line. The most obvious choice for introducing PICA sections would be where public access is greatest e.g. at the railway stations or where there is a high incidence of accidental electrocutions. The stations have the additional advantage that they already have existing breaks in the third rail which can be utilised without the addition of insulating blocks.

iii) If the risk factors of the ordinary third rail system are eliminated, the new PICA system can be used to carry much higher voltages without the inherent risks associated with the normal third rail system. Higher voltages can produce savings from power losses associated with low voltage, high current systems. Reducing the current to a half reduces power losses to a quarter, reducing to a quarter of current reduces power losses to a sixteenth.

iv) A key switching mechanism fitted at appropriate points along the auxiliary line would allow railway maintenance to be carried out without interruption of the supply by switching the power between the auxiliary and the third rail v) The PICA system can be used in conjunction with multiple auxiliary (9 and 13 in Fig. 6) lines to produce a multi-voltage system, allowing locomotives with different voltages systems to use the same track.

vi) The multi-voltage switching system via PICA auxiliary lines may also be used in non-railway applications such as power delivery and signal transmission.

Claims (4)

1. A Parallel Isolated Connecting Auxiliary (PICA) system used for isolating or insulating power to any system requiring electrical current or voltage (alternating current or direct current) where a danger or hazard is present through a live line.

2. The use of the PICA system or any system based on the PICA principles outlined in claim 1 for any isolation, insulation or separation purposes.

3. The use of the PICA system or any system based on the PICA principles outlined in claim 1 for supplying or connecting multiple voltage or current systems for power, signalling or data transmission.

4. The use of the PICA system or any system based on the principles outlined in claim 1 for reducing interference or degradation to any form of signal or data transfer or transmission.