Home > Electricals Menu > The Oerlikon System

The Oerlikon System

Several interesting features are embodied in the Oerlikon system of train lighting, which has been devised by the Oerlikon Co., of Switzerland. The equipment comprises the usual dynamo, battery, and regulating apparatus. The latter device is different from other methods of voltage regulation, as although it introduced resistance into the field circuit of the dynamo, such introduction is of a periodic nature, and ensured by oscillating contacts. The dynamo is a standard four-pole shunt-wound machine, being suspended under the carriage, and driven by a belt in the usual manner, the weight of the dynamo giving the necessary belt tension. Sleeve bearings are provided, and these are fitted with extra large chambers containing sufficient lubricant for a long period.

Correct polarity, according to direction of rotation, is assured by the brush rocker moving the distance of a pole pitch, under the friction of the brushes, the rocker being fitted with ball bearings to assist rotation.

Dynamo

The battery, in the case of the Swiss Railways, is fitted in wooden boxes, placed in recesses arranged on the side of the carriages, the number of accumulators per set being divided into groups, so that one box containing a group can still be carried by two men.

When the train is at rest the current for lighting is supplied by the battery alone. As soon as the certain minimum speed is reached, say 15 miles per hour, the dynamo and battery are automatically connected in parallel, the dynamo pressure being brought to the correct value for parallel operation. While the train is in motion the current is supplied exclusively by the dynamo as long as the train exceeds minimum speed.

The dynamo then starts at the same time to charge the battery, whether the lighting is on or not. The charging takes place in such a way that, when the battery is entirely discharged, the maximum permis-sible charging current is supplied; the charging current then decreases as the charge increases and when a fixed end of charge pressure is reached, the dynamo is automatically reduced, with the result that the battery current becomes zero and the charging is interrupted.

Above the minimum speed, the dynamo voltage and the charging of battery remain independent of the speed and of the lighting current. In the event of the fuses of the battery blowing out, or in the case of a fault in the battery, the dynamo maintains the lighting while the train is running.

The Oerlikon Co. build their train lighting equipment for loads up to 1,600 watts.

The same size of regulator is used for all the above outputs ; the size of dynamo and battery on the other hand varies with the output required.

Dynamo

Regulator. The regulator is primarily intended to regulate the dynamo voltage which would otherwise vary with the speed, and to ensure that, on the one hand, the battery is charged, and when the train starts up, the dynamo energises itself, and owing to the above mentioned automatic change-over device, excitation takes place in either direction of running. As soon as the dynamo voltage reaches the necessary value for paralleling dynamo and battery (this occurs when the train reaches minimum speed), the automatic circuit breaker P is switched in through the action of the coil r of the paralleling switch (see diagram of connections) ; in this way dynamo and battery are connected in parallel. At the same time as the speed of the train increases, there is a rapid rise of the voltage of the dynamo, as the resistance W6 is at first cut out by the pair of contacts KI and Kg.  At a certain voltage, the magnetic force exerted by the coils is so great that it draws the moving armature and thus interrupts the pairs of contacts C1 and C2. These contacts serve to control the intermediate relay R, and the contacts K1 and K2 of this relay follow exactly the movements of C1 and C2. The contacts K1 and K2, therefore, open now and the resistance We is introduced in the excitation circuit of the dynamo. As a result, the voltage of the dynamo drops and the decrease in voltage is such that the coil S of the regulator releases the armature. The pairs of contacts C1 and C2 and K1, K2, close and the latter cut out the resistance We. The voltage of the dynamo thus increases again, after which the relay and contacts come rapidly into play again. In order to prevent excessive sparking, a condenser " C " is connected in parallel with the contacts K1 and K2. The coil z which is in parallel with the excitation circuit of the dynamo, serves to accelerate the rate of opening and closing of contacts, so as to prevent the flickering of lamps, due to the increase and decrease of voltage, from being visible.

The function of the coil i2 is to limit the charging current of the battery; when the maximum permissible charging rate is exceeded, this winding acts on the regulator in such a way that the dynamo voltage is somewhat reduced and the charging current decreases accordingly.

In order to prevent small charging current such as might damage the battery when fully charged, provision is made for a relay G, the operation of which is independent upon the voltage. This relay is fitted with a coil e which attracts the armature in the event of a limit charging voltage, and reduces the tension of the spring of the regulator s, through the intermediary of the fork a, so that the contacts  C1, C2, and K1, K2, open. The charging current then drops to zero again, and a slight discharge actually takes place temporarily until the battery can once more be charged.

The difference in value of the charge and discharge voltage of the battery would give rise to fluctuations in lighting. These fluctuations are prevented by means of the resistance 1 and through the action of the  coil 13, in the following way :—
   The series resistance 1 in the lighting circuit is so dimensioned that even in the event of different lighting loads the voltage can be kept constant within given limits. When the battery is nearly charged and the lighting system is switched on, the coil i3 brings the charge limiting relay G into play, with the result that the end of the charge voltage, which would have too high a value, is cut off from the lighting system.

When the coach comes to a standstill, the relay P is switched over automatically as a result of a reverse current, and the generator is disconnected from the battery. The lamps are now fed from the battery.