Preservation Report Summer 2002

The most recent articles have tended to concentrate on the body work of power car 11187. This car is of course an electric loco as well as a railway carriage, and it is the electrical equipment that this article will concentrate on. Figures 1 and 2 show the general layout of the equipment underneath the coach. Most of this equipment has been mentioned in earlier articles. Most of the auxiliaries are now in a working state. Since we have made up a three phase rectifier which provides about 550 volts DC, we have been able to power up the motor generator (MG). This device is an electric motor (running off the rectifier) coupled to a low voltage generator which generates 70 volts to drive the lighting and control circuits. The MG requires a resistance in series in order to start otherwise the starting current would be too high, this resistance is situated on the opposite side to the MG. The MG has been cleaned off and repainted, but otherwise has required very little attention. The starting resistor case has required some repair work, the perforated metal sheet having rusted somewhat.

Once the 70 volts from the MG was available the compressor could then be run, the starting relay for the compressor requires 70 volts to turn on the main input from the rectifier to the compressor. The compressor you may remember was hauled into position after being cleaned and repainted off the coach. The MG has remained in place all the time.

The compressor charges up the main train air reservoir to 100 psi. This pressure is necessary to operate the brakes, but a regulator situated close to the compressor reduces this to 70 psi to drive the pneumatic controls to the traction motor circuits. This regulator initially leaked slightly but after some cleaning is now quite air tight. The smaller carriage brake reservoir is charged from the main one via the triple valve in the standard Westinghouse arrangement. This is shown in Figure 3. The main air line runs the length of the train.

When the air line is sealed i.e. no brake application is being made, the triple valve connects the main reservoir to the carriage brake reservoir. However if this line is opened to atmosphere either partly by a brake application or fully if part of the train was to break away, the pressure on this line will fall below that in the brake reservoir. The triple valve will then flip over to connect the brake reservoir to the brake cylinder and hence apply the brakes.

The problem of part of the train breaking away was not unknown in Cor days, one disadvantage of Westinghouse brakes is that it takes quite a long time for the pressure to equalise throughout the length of the train, thus when the brakes are released the cars at the back of say a 12 car set will still have the brakes firmly on for several seconds. If power is then applied, the front can pull away from the back. It became a standing instruction to drivers to wait 10 seconds after releasing the brakes before applying power. The regulator, which is required to maintain the pressure at 100 psi and is fitted inside the cab worked perfectly once the compressor was running.

The brake blocks have been refitted to the power bogie which we overhauled four or five years ago now. These blocks have now been adjusted correctly, they are made of steel, whereas those fitted on trailer bogies are composition. presumably there must be greater braking force applied to the power bogies. Some brake linkage, which was also removed during the bogie overhaul, has now been replaced and the brakes have been tested - all work perfectly. Both reservoirs therefore hold pressure and the triple valve and the brake cylinder are also in good order. It seems that there may be an opportunity some time not too far in the future to do a running brake test outside the shed at St Leonards, with the power car propelled by a diesel shunter, which will also charge the air braking system.

So well and good for the auxiliaries, the part remaining to look at is of course is the traction system. The main contactor is the on/off for the motors complete with an overload relay designed to trip if the traction current is excessive this relay has recently been overhauled. This main contactor is operated by a mechanical linkage from the cab, bevelled gearing being used to make the control shaft rotate to operate the contactor as the on/off handle, fitted behind the drivers seat is turned. This linkage had seized solid over the years without use, but repeated soaking with paraffin eventually cleared it.

It is probably necessary to explain the basic operation of the motor controls before describing the equipment in more detail. Figure 4 shows a simplified circuit diagram for the motors. The motors are series wound. This type of motor is well suited to traction because as it runs faster, it weakens its own field as its back emf builds up, and thus enables it to run faster still. Back emf is the voltage which the motor generates by virtue of its own rotation to oppose the applied voltage. If the motor was to run without any load it would keep on running faster and faster until it flew apart, but on load it will run faster or slower as the gradient dictates. A shunt motor by comparison has a fixed field, and will tend to run at a fixed speed therefore. The motor half of the MG on the Cor would almost certainly be such a motor. In more modern trains which use shunt motors for traction the field has to be weakened by the control circuitry to allow them to run faster.

Even with this self regulating property the motor does need some control to get started. This is done by switching resistors in series with the motors, crude perhaps, but effective. The resistance is reduced by resistive elements being shorted out, by the contactors inside the main equipment case as the speed increases. The contactors are operated pneumatically, the control to the pneumatic actuators coming from the 70 volt system. Each contactor as it switches over also operates some switches on the 70 volt control system inside the equipment case. These switches are the "interlocks" which obviously must also play a part in the contactor switching sequence.

We have acquired new copper tips for the contactors, other than this they are in good order. Also the interlocks have all been replaced by newer ones, the 70 volt control connections carefully being removed and replaced one at a time to avoid getting them in the wrong place. This low voltage wiring certainly appears to be in a perfectly reasonable condition. In order for the motors to run in either direction it is necessary to reverse the current flow in the field winding, this has to be done for both motors in the bogie, only one is shown in the figure. This function is performed by the reverser. This device consists of a shaft with a pattern of conducting segments on it, it is forced by electro pneumatic actuators, to rotate into one of two positions. This then makes suitable connections on the fixed contacts around it. It is a complicated looking thing for doing what you would think was a fairly simple job. We have fitted a new shaft to the reverser on our power car, the old one having rather pitted contacts.

Apparently it is quite possible to connect up the motor windings in the wrong polarity so that the wheels will rotate in the wrong direction. There is a story that once a set was leaving the depot after overhaul when it was noticed that wheels on one bogie were spinning like Catherine wheels in the wrong direction as the train pulled away. The mistake was soon rectified without any serious damage however. This brings me to the last major component in the traction system, the load resistors which are run in series with the motors. these obviously have to carry a very large current and a good deal of heat is generated. The older types of resistance consists of cast iron bars, we have some of these at St Leonards which we took from the Brighton Belle car at Stewarts lane. The newer type which is fitted to 11187 has resistance elements formed of sheet metal (stainless steel). This metal is OK but the steel shafts and mica washers that hold it in place do not look as good. We have not as yet made any attempt to overhaul these, but these look to be the main obstacle to the car running at present.

One more item that has been completed is running new control cables through conduit from the controller in the cab to the junction box on the other end of the car. This is the same gauge as the lighting cable, 12 individual lines.

Just to round off, the body work is now completely painted grey and a start has been made on the green top coat. We are keen to get this done during the summer. All the doors have now been refitted, and my shed seems very empty without one propped up in the middle. Finally I would like to thank M J Blunden for the thoughts on the windscreen wiper and tail lamp in LR 186, it is always nice to receive comments concerning our work on the Cor.

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