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2.3. Direct current supply and trolleybus overhead



The trolleybus network and current supplies were renewed at an expenditure of 3,6 millions DM in the years 1990-1997.

The trolleybus operates with a rated voltage of 600 V direct current.

Direct current supply

Electric rectifier substation centre (GUW Mitte)

Three electric rectifier substations make the current supply from the public network. The electric rectifier substations are equipped with 3 1000 KVA transformers and 3 silicium electric rectifiers.


Trolleybus overhead network

Into the trolleybus network are inserted 5 switches, 4 intake switches, 7 crossings, 19 disconnecting places (places without voltage), several crosswise clutches and 11 supplies of direct current.

The trolleybus network is approx. 44,6 km long and structured after the so-called Lombard system. Thus two contact wires run parallel to each other. Going in the driving direction the left contact wire is plus-polarized; accordingly the right contact wire is minus-polarized. The contact wire consists of solid copper wire 12 mm in diameter. The trolleybus overhead network is installed at a height of 5,5 m over the roadway. In some places, e.g. in the proximity of traffic lights, the trolleybus overhead network was lowered on 5,3 m over the roadway.

Here is a picture of the turnaround loop of the trolleybus network at the final stop Ostend:

Turnaround loop of the trolleybus network at the final stops Ostend
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Switches

The electronic switches are of the type U-88 of the Kummler+Matter company Zürich/Switzerland. The mechanical structure consists of two modules, the switch module and the drive module.

The switch module carries only the connecting pieces and the tongue of the switch. When worn these are easily removed and replaced. By an easy adjustment the position of the connecting pieces and the tongue of the switch can be moved to the left, right or centered.

The drive module carries the necessary sections for drive and the monitoring units.
The drive magnet has two switching modes. Thus the switch can be used with or without resetting of the tongue.

In the trolleybus network of Eberswalde the switches are used with automatic resetting of the tongue. A monitoring unit at the drive magnet inductively sends the position of the tongue of the switch. For the automatic resetting of the tongue the necessary signal comes from a non-contact inductive sender.

In the drive module is integrated a control unit. This receives the switching impulses from the trolleybuses.
The switches have an electronic direction signal, which displays the position of the switch to the trolleybuses drivers.

The manufacturer claims that one can drive on the switches at high speeds (50-60 km/h). However there were bad experiences in Eberswalde. After several heavy damages it was determined that the safe rate for driving on the switches to be 15-20 km/h. The true reasons for the several heavy damages are unknown.

The switches of the trolleybus network are controlled by the driver of the trolleybus. A switching contact rail is added to the trolleybus network before each switch. If the driver of the trolleybus wants to switch the trolleybus network switch, he operates a switch, which briefly switches on the trolleybus's heating system (a large power consumer). Current must be drawn when driving on the switching contact rail. If the driver of the trolleybus does not want to switch the trolleybus network switch, he operates another switch that switches off the high voltage system of the trolleybus. Thus no current is drawn when driving on the switching contact rail, and the trolleybus network switch does not switch.

Picture: Switch at the branch to the depot Nordend

Switch at the branch to the depot in Nordend, Neue Straße


To switch the trolleybus network switch or not requires a little practice. The correct switch must operate at the right time in the correct place with approx. 10-20 km/h (considering other traffic). If it does not operate correctly the driver must take work gloves and go to the rear of the trolleybus to put the current collectors (trolleys) onto the correct wires by hand.
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Intake switches

Intake switches are switches of the trolleybus network, which are mechanically switched by the end pieces of the current collectors (trolleys). This takes place without action by the driver of the trolleybus.

Picture: Intake switch in Nordend, Poratzstraße

Intake switch in Nordend, Poratzstraße
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Crossings

Crossings are crossings of the contact wires. In order to avoid short-circuit, insulating material is used, which leads the end pieces of the current collectors (trolley's). When driving on crossings the accelerator may not be operated and the maximum speed must not be exceed by 15-20 km/h.

Picture: Crossing at the depot Eberswalde/Nordend

Crossing at the depot Eberswalde/Nordend
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Disconnecting places

Disconnecting places are dead places (places without voltage) in the trolleybus network, which serve to separate the supply of direct current of the different sections.

The planners and designer of the trolleybus network made some serious mistakes with these dead places. Some of the disconnecting places are in the area before crossings with traffic lights, directly on road crossings and in places in which one actually needs full current when starting. Sometimes it is a feat not to be stopped on a disconnecting place. Also the driver of a trolleybus must concentrate on the traffic. There are times when one must stop on a disconnecting place. Try to explain to another motorist that the driver of the trolleybus leaves a gap in the traffic for the necessary momentum for getting through the disconnecting place. The other motorists think the driver of the trolleybus is "asleep" and drive their cars into the gap, and the driver of the trolleybus must brake.

With a trolleybus of the Hungarian type Ikarus 280.93 the driver of the trolleybus then has a problem. This problem might be solved by pushing the trolleybuses, with muscle power, about 5-10 cm forward or backwards . In this case the driver of a trolleybus of the Austrian type ÖAF-Gräf & Stift NGE 152 M17 switchs on the emergency power generator.

The accelerator may not be operated when driving on disconnecting places.

Picture: Disconnecting places in the Spechthausener Straße

Disconnecting places in the Spechthausener Straße
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Crosswise clutches

Crosswise clutches are electrical connections of the respective minus or plus contact wires of the trolleybus network of the "there and back" directions. A crosswise clutch serves to balance the different electrical loads of the trolleybus network between " there and back" directions.
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Direct current connections

Direct current connection in Nordend, Neue Straße

Direct current connections are places in the contact wires, into which is fed the 600 V direct current to the trolleybus network that was produced in the electric rectifier substations. In order to compensate for load, resistance and voltage fluctuations in the trolleybus network, it is fed at several direct current connections, which are approximately 1-1.5 km apart. The direct current connections receive the current over ground cables from the electric rectifier substations. The ground cables have a total length of 54 km.

The picture at the left shows the direct current connection in Nordend, Neue Straße.
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