Each unit is equipped with 6 IGBT modules and replaced the old cam controller in the same space. The controller was designed specially for SEPTA and the B-IV cars and was not purchased off the shelf. So far 75 B-IV cars have been equipped. The buzz was an unintended side effect of the chopped DC current being fed through the dynamic brake resistor grids. I can post some pictures later along with a video of a B-IV cam controller being sequenced.
There were two people demoing the controller units. One was the chief tech guy in charge of the new AC stuff, the other was a maintainer for the PA Systems and destination boards who was so interested in the cam controller packages that he did the leg work to set up the demo even tho it wasn't his craft (Call the Union!!)
The cam controller packages are overhauled and rebuilt at the Woodland Depot and trucked back to Fern Rock. This mirrors the MBTA practice of rebuilding the cam controllers for its 1500-1700 fleet at the Everett Shops which haven't even had a rail hookup in 20 years. Also 10 of the B-IV propulsion units were given to the RRD to help keep the Silverliner IV's running as their cam control equipment shares components with what is found on the B-IV cars. Additional controllers are being thrown in the trash if anybody wants one.
This display was special for my gust because his father worked at GE Erie during the late 70's and early 80's and helped design components such as those. Today he works for NASA.
BTW the Fern Rock maintenance personnel were unaware that the BSS was the fastest "classic" subway system in the country and were quite pleased with the positive reputation.
Ok, here are two photos of the original cam controller. If you are wondering what a cam controller is, it is a type of motor controller that uses a camshaft to make and break electrical contacts in response to the movement of the motorman's control handle. In a DC-DC propulsion system, motor rotational speed is a function of voltage. The maximum amount of voltage that can be applied in this system is the 650 that comes straight from the third rail. Just like you would never try to run your car with the engine directly linked to the wheels the motor controller gradually switches in more resistance (remember V=IR) so the train accelerates smoothly. In addition the controller handles the transitions between the three major "gears" of a train, series, parallel and shunt. Series means that the motors are connected in a daisy chain, one after another so each sees 650/4 volts. If you want to go faster parallel increases the voltage to the full 650. Shut weakens the counteracting electric field in the motor to increase balancing speed at the expense of torque.
The camshaft is turned by what is called a "pilot motor" driven by the low voltage current that flows through the motorman's control and the train line. Here we see the pilot motor and the lobed camshaft which push up the high voltage electrical contacts. Behind the contact gaps are arc chutes that break any arcs that might form under load. This is truly analogue electronics at its finest. When you watch old sci-fi movies and the characters keep talking about "circuits", this is the sort of stuff they mean. No bits and bytes, just physical stuff touching eachother.
Here is the cam controller sequencer, which is a fancy name for the electronics that control the electro-mechanical cam components via the pilot motor. This is the place you finally find some printed circuit boards, but again, its probably all analogue electronics so no microprocessors. For an idea of what troubleshooting these types of systems are like here is a little video on how to service an Ampex Quad video recorder. This whole unit dates from 1983/84 and while young compared to the stuff from the 1970's that is still running around some places I believe that GE is aggressively telling transit agencies that they will no longer support their old cam propulsion systems.
Here is the replacement IGBT unit from Vossloh. Sorry, but I don't think my flash went off for that one.Unlike the camshaft or the later chopper controls this uses processors and software to rapidly turn electric currents on and off via high energy semi-conductors. The more on the higher the voltage. Simple as that. The controller takes the same inputs from the motorman's control and simulates the output of the old cam control unit. The match was perfect and the upgraded cars could run in multiple with the original cars without any problems.
Moving onto the video segment the first shows someone placing the controller into Parallel and the second with me running through the control points on the test rig in order. I believe they are Coast, Coast ?, Switching, Series, Parallel and Brake. Sorry about the sound, the background roar drowned out the cam noises.