Deutsch (DE) 
English (UK) 
Description
Why use short circuiters...
There is the danger of accidents caused by electric current when persons stay on the track of underground railways. The stay of these individuals may be planned, intended and admissible, but it may as well be unplanned, unintended and inadmissible. In both cases the danger of accidents needs to be reduced as fast and as effective as possible. Examples for a planned stay of individuals on a track:
- Fixation of billboards in underground stations
- Track inspection
- Collection of rubbish and cleaning works
- Repair and exchange works
Unfortunately there are also cases of unplanned and unpermitted stay of persons on the track, for instance:
- Accidents of individuals and rescue operations
- Vandalism
- Evacuation procedures
ARCUS Short Circuiters are suitable for use on de-energised current rails as well as live current rails, due to their design and contact principle. Either the short circuiters are stored in the trains, in the underground station or in the special cars of the firebrigade. Train drivers, clearance personnel on stations, and fire fighters are familiar with its usage and will know where the nearest short circuiter can be found.
Design
Design for power supply from top or bottom side …
As the design of both types of device is strongly differing, the main features are described as follows.
Design for power supply from top side
This short circuiter consists of a very compact housing made of several plastic plates, in between contacts and contact mechanism are arranged.The running rail contact consists of a springy stored copper block, which is held by a magnet on the running rail. As soon as the short circuiter is set onto the rails, a conductive electric connection exists towards the running rail.
The current rail contact as well is a copper block which is mounted to a pivoting compensator. This compensator is connected to the tension spring which is preloaded by an operating lever. At a certain lever position the preloaded force comes free and turns the compensator downwards as quick as a flash, until the contact block hits the surface of the current rail. The required counterforce is secured by a hook that grips underneath the head of the current rail.
Design for power supply from bottom side
This short circuiter is provided with a frame of glassfibre-reinforced synthetic tubes that are partly loosely joined and carry contacts and contact mechanism. The contact to the running rail consists of an aluminium shell into which aluminium contact rings are set. There is electric contact to the running rail at the moment when the device is placed onto it. Devices suitable for short circuit currents up to 30 kA are provided with a current rail contact made of one copper block which is linked to a movable arm, together with a slighty higher block of plastic material.This arm is connected to the tension spring which is preloaded by an operating lever. During operation, first the block of synthetic material makes contact on the surface of the current rail - the copper block is still without electric contact. While the tension spring gets increasingly preloaded, the synthetic block approaches the edge of the rail surface.
Then the synthetic block slips over the rail edge and makes way for the copper block to suddenly hit the surface of the current rail. The synthetic block remains on the lateral side of the rail head and forms a support for the contact force.
Short circuiters designed for short circuit currents up to max. 100 kA, consist of three silver-plated, loosely joined copper blocks. The synthetic blocks are hook-shaped. Thus they generate form-closure with the head of the current rail.
On both models those parts to take up voltage are either covered to a vast extent, or they are far enough at a distance of parts the user is to operate.
Function principle
Function principle:
Like all devices for earthing and short circuiting the short circuiter for underground railways also requires a reliable electric and mechanic connection between connection elements (copper blocks and aluminium rings) and the connection points (current and running rail).The reliable mechanic connection firstly is obtained by design and production of ARCUS Short Circuiters to the requirements of the installation. Secondly a rail connection is formed which to a certain extent is either form-fit or forcefit.
The reliable electric connection is obtained by choice of material and form of connection elements. The aluminium rings of the construction for power supply from the bottom side is shaped to suit all known running rail profiles in
Germany and many other countries (for instance UIC54, S49, S64 and others). The copper blocks of both designs are equipped with a spherical contact surface and are movably stored to have optimum contact to the rail surface, so to reach a large number of contact points. These contact points are permanently maintained by the force of the tension spring.
Yet it may happen, especially in case of emergency, that the short circuiter is placed on a rail section without optimum conditions. This may be a wavy, rough, soiled or corroded rail surface.At such points increased sparking and arcing, furthermore burnings on the rail, are possible. Thus it is recommended to briefly examine the rail section to which the short circuiter will be placed before each usage. As the case may be, a slight shifting of the device is sufficient to clearly improve the contact conditions.
In the moment of making contact with the current rail in any case sparking is to be expected (even the disconnected current rail carries residual voltages), so it is recommended to avert face and upper part of the body when contact is made. If possible, protective clothing and a suitable hearing protection against eventuel explosion-like bang have to be worn.
Standards and Tests
Standards and Tests:
Up to now there is no standard for devices for earthing and short circuiting in underground rail tracks. ARCUS Short Circuiter belong to the large group of portable devices for earthing and short circuiting.
Yet the applicable standard DIN VDE 0683 part 1, now DIN EN 61230 or IEC 61230, does not address the issue of characteristics of short circuiters. Neither the specific design of short circuiters, nor the fact that a short-circuit can be introduced by them, are considered. Consequently there is no standardised test installation and no test procedure for short circuiters.
To still be able to prove that the short circuiter is safe and short-circuit proof, one draws on a statement of the standard that tests are to represent the conditions under which the short circuiter usually is used. Furthermore the appreciably most disadvantageous conditions are to be considered in the test. Consequently this means that the proof of short-circuit strength is to be adduced on the track of the respective customer. Only these conditions correspond to the test principle. Consequently there is no certificate about the type test passed at an accredited test institute. Each customer is to verify by himself (on a sample) whether the short-circuit strength of the short circuiter is sufficient for his purposes. ARCUS as a manufacturer is not able to confirm values of short-circuit strength because these depend on the conditions of usage.
Depending on whether a short circuiter is close to a current feeder or at a distance, a short circuiter is used when current is switched onto it or to de-energise, or whether rails are bare and smooth or corroded and uneven, the values for short-circuit strength will be differing totally.
To still give an idea of the device's capacity, in the following we state the values of short-circuit tests carried out in 1973 at the Munich Underground for determination of track switch selectivity:
- Current rail 700 V DC
- Current switched onto installed device: max. 30.5 kA, 23 ms
- Installation of device when voltage is present: 28.5 kA, 23 ms
Latest tests were carried out in June 2006 at the IPH in Berlin. For this purpose a 1.4 m long rail model of Metro Taipei (Taiwan) was used. Tests were carried out by both switching onto the installed short circuiter and installation of the short circuiter with live current rail, with the following values:
- Current rail 750 V DC
- Short circuit current 100 kA / 35 ms
Under all other aspects the devices are designed to suit the requirements of the valid standard as far as possible, so that there is no increased risk for individuals and electric installations.
Additional Documents
Click here to download further information:
|
|
|
|
| Safety Equipment for Railway Systems | Short Circuiting Device for Underground Railways | Questionnaire |
