Description
The cable monitoring device is intended for the monitoring of cable units to supply power to DC traction current systems with a nominal voltage of DC 2400V (other voltages available on request). The cable monitoring device is designed in accordance with the VDV papers 515, edition 4/93 and can be connected to all cables with a concentric shield or conductor and insulated outer sheath.
Plus polarity at the contact line.
The cable monitoring device allows the default insulation monitoring of “Conductor-shield” (I) and “Shield-earth” (E) insulation sections.
A zero-potential contact is provided for the train power failure message (also power supply fault). This contact is operated on the quiescent current principle so that the contact opens in the event of a power fault. A zero-potential make-type contact is provided for the “Shield-earth” (E) message. Two separate zero-potential contacts that also allow the switching of separate voltages are provided for signalling and switching off in the event of a “Conductor-shield” (I) fault. LEDs indicate if the system falls below the limiting values. The cable monitoring device is installed in a plastic housing (type of protection IP 50) and set up for installation on carrying rails and for fastening with screws.
The device has two test buttons for functional testing when in operation. The first one is for the “conductor-shield” insulation defect test. The second one is for the “Shield-earth” insulation defect test. The device has two potentiometers to set the limiting values. The test buttons and potentiometers are accessible from the front.
The type 8532 cable monitoring device complies with all the requirements today concerning such units and thus takes into consideration in particular the many years of experience of our company in making cable monitoring devices.
Function
The “Conductor-shield” and “Shield-earth” isolated section resistances that are to be monitored is switched in parallel to achieve the desired “low impedance state” (defined measuring voltage relationships, lack of sensitivity to charges and discharges and other forms of interference).
However, these resistances have a sufficiently high impedance to limit the the measuring current passing through the shield to less than 1 mA (in operating mode “Monitoring for shield interruption“) and the measuring voltage to approx. 40 V. The evaluation of the insulation states and their changes is done on the basis of the principle of voltage measurement against the earth (bridge principle). The voltage at the shield is taken as high impedance and passed on for evaluation by means of fibre optic light guides.
The evaluation itself is the classical evaluation that has been used for many years in the proven cable monitoring devices that our company has sold for many years now.
Notes
No dangerous contact voltages arise at the shield as a result of the actuation of the cable monitoring unit at the shield. The contact voltages are within the setting ranges required for voltages and times within VDE 0141.
However, and regardless of this, note that in the event of a “conductor-shield” insulation defect that the power limiting action of the cable monitoring unit can be bypassed under certain circumstances.
We therefore recommend using isolating terminals to protect the cable monitoring unit against excessively high voltages when testing the cables.
If the cable is switched off by the cable monitoring unit in the event of the latter actuating, any built-in section testing devices must be bridged.
