The FS E.636 is a class of Italian articulated electric locomotives. They were introduced in the course of the 1940s until the 1960s, and have been decommissioned since 2006. They have been one of the most numerous Italian locomotive groups, and have been widely employed during their long career, hauling every type of train, ranging from freight to long range passenger services. Their introduction also saw the employment of some revolutionary (for the time) design concepts, such as the articulated carbody and the three bogies scheme.
History
The E.636 was designed to overcome the problems shown in the 1930s by both the E.626 multi-purpose and E.326 high-speed locomotives, in order to better handle the increasing railway traffic in Italy.
The E.636 was the first Italian locomotive adopting the Bo-Bo-Bo configuration with chassis divided into two articulated parts pivoting on the central bogie, which is very well suited for the often tortuous lines of Italy and that would have been later repeated on the E.645/646 and E.656 classes. The presence of a great number of wheels was considered important due to the presence of a number of high-slope lines in the Italian railroad network as it increases the adhesion limit, meaning that the locomotive is less prone to wheel slips. The new engines weighted approximately . Engines were initially the same as E.626. The 32R used a 3 kV catenary but this was soon shown to be inadequate and so were updated and provided with a new hollow axle transmission system. Mainly two different gear ratios were installed: 21/65 for sloping lines or heavy freight trains (maximum speed of , elevated later to 110 km/h), and the longer 28/65, with a maximum speed of , suited for passenger services.
The locomotive was built in three different series: 1st series (001–108), from 1940 to 1942 2nd series (109–243), from 1952 to 1956 3rd series (244–469), from 1957 to 1962
The first unit entered service in May 1940. Six locomotives were destroyed during World War II. After the war the total number of locomotives was brought to 469, also thanks to the support from the Marshall Plan, and making it one of the most numerous groups of Italian locomotives. All the units were painted with an Auburn livery; this was changed in the 1990s to a white one with green stripes for most trains (XMPR livery).
By 2000s railway standards, E.636s were old and uncomfortable. The original design of the cockpits proved absolutely unfit to modern safety standards: this was shown in an accident in 1996 at Sulmona, where the engine driver died despite the low speed, without being able to leave the cockpit in time. 200 units were therefore rebuilt and stripped of all asbestos.
Starting from the 1990s, E.636s were used mainly for cargo services, save for the more rural Sicilian lines. Some units were lent to minor Italian railroads. The phasing out of the entire class was completed in May 2006.
Technical details
E.636 are very simple locomotives. Most functions of the main command circuit are accomplished through various relays and contactors. In case of failure the train driver could easily fix them to at least free the tracks; also, especially in the last years of their service, E.636s were the first locomotives that the new train drivers studied during their training courses, due to their simple working mechanics.
Motors and electrical description
As most older Italian locomotives, E.636 has a rheostat (formed by 16 cast iron resistors connected in series, for a total resistance of 29 ohms) that needs to be gradually, but as soon as possible, excluded on start-ups, which regulates the current to the six 32R-200 DC traction motors, two per bogie.
The motors can be connected in three combinations: series, series-parallel and parallel; each combination provides a progressively higher voltage to the motors, therefore increasing the current.
Their set-up is the following: Combination Motor set-up Voltage per motor Series All motors are connected in series 500 V Series-Parallel Two branches of three motors 1000 V Parallel Three branches of two motors 1500 V
The rheostat (connected in series to the traction motors) is necessary because the DC motor has the intrinsic characteristic of absorbing a current inversely proportional to its rotating speed; at high speeds, it absorbs less current. This means that on start the current would be very high, because the only resistance encountered would be only the one offered by motors and internal conductors, which is very low (a short circuit, in practice). The rheostat increases the overall resistance when starting the locomotive, lowering the current and allowing a smoother start.
In S-P and P combinations, the rheostat is divided in three branches connected in parallel; this lowers the overall rheostat equivalent resistance to about 3.5 ohm, while in S combination its elements are all connected in series.
Like almost every Italian locomotive with rheostatic regulation since E.626, traction is controlled via a lever (commonly referred to as maniglione) mounted on a support called roncola; this support has several notches, each representing a portion of the rheostat, plus three "end combination" notches and two "transition" positions (a bigger block between the notches). To accelerate, the driver rotates gradually counterclockwise the lever notch by notch, and in doing so the various rheostat contactors are closed, shunting the resistors and lowering the total rheostat resistance, also allowing more current to the motors; as speed builds up, the counter-electromotive force lowers this current, until the rheostat is no longer necessary: it is, then, totally excluded (obviously if in traction and in an "end combination" notch). This safely allows traction for an indefinite period of time, within certain limits.
When the end combination notches are reached, the driver can then insert the single shunt (one for each combination) or make a transition to the next combination, reintroducing the rheostat which has to be excluded again, for the following combinations until the end of the parallel combination is reached. The shunts increase the current into the motors by shunting some motor spires (through a contactor in parallel); this reduces the magnetic flux and, as said, increases the current (since the two are inversely proportional). There are various "shunt levels", depending on the locomotive, as is further explained; usually, there is one per combination. It is also important to remove the shunts before making a transition, in order to avoid flashes due to abnormally high currents.
Like some E.626s, E.636 locomotives are not provided with the "CEM" motor combiner (CEM stands for Combinatore Escluditore Motori), a device that, during transitions, rotates, combining the motors accordingly through various contactors.
On E.636, this is achieved through the uses of more delicate spires, so transitions (especially backward ones) need to be very slow and gradual. The optimal moment to pass to the following/preceding combination first/last notches is when the motor ammeter indicates 0 Ampères, which happens when passing over the transition position with the lever (the driver should briefly stop in the middle of the block and pay attention to the ammeter), meaning that the motor contactors are in optimal position and is safe to proceed. Failure in doing this may result in flashes that will damage the contactors.
An important parameter the driver has to consider, especially during rheostatic exclusion, is the current into the traction circuit.
In particular, if he is excluding too fast, a wheel slippage can occur (in this case the use of sanders and reducing throttle can help), and one or more maximum current relays can open when the maximum allowed current value is exceeded.
The locomotive is protected from overly high currents through different kinds of relays: General maximum current relay ("RMx"); Three motor branch () maximum current relays ("RMx 1-2, RMx 3-4, RMx 5-6"); REC (, is the electrical system used to provide the 3000 V coaches' electrical heating) maximum current relay ("RMx REC");
When they open, they also open the main breaker; that cuts the connection to the catenary.
Before the 1970s, the maximum currents for the relays were the following:
Relay Maximum Current allowed RMx 1050 A RMx 1–2 450 A RMx 2–3 350 A RMx 3–4 350 A RMx REC 500 A
Between 1970 and 1980, the previous values changed:
Relay Maximum Current allowed RMx 1200 A RMx 1–2 450 A RMx 2–3 400 A RMx 3–4 400 A RMx REC 500 A
As can be seen, the currents allowed in series are 450 A in both cases, while in Series-Parallel and Parallel combinations are 350 A and 450 A respectively.
As said, one level of field shunt (percentage of field weakening: 31%) is allowed in each combination; however, some units received 92-250 (used on FS Class E.424) and 32RT-200 type motors which allowed a maximum of 5 levels of field shunts (percentage of field weakening: 65%, 45% on the latters). These units were later made identical to standard ones again.
Motion transmission
Units from 001 to 243 mounted Negri-type transmission, except for units 195-198 and 176-183 which had a rubber tampons in place of coil packs and double hollow axle transmission and rubber tampons respectively.
All the following built units had the same transmission type of 176-183 but slightly different.
Different locomotives have received various gear ratios (see "Special Units" for more details):
Gear ratio Max speed Notes 21/65 Originally elevated to shortly after, then to in 1982 28/65 Eliminated in 1991 20/65 Units 044 and 089 only 24/74 Units 271-275 only
Auxiliary and pneumatic services
The motor cooling-fans were activated by two 4.5 kW 3,000 V dedicated motors until unit 201; later units had 1 kW motors identical to the ones used on FS Class E646. The motors were also used as dynamos to recharge the 24 V batteries (only if line voltage is greater than 1,500 V) and used to feed low tension devices (lights, locomotive heating systems, contactors etc.)
Locomotive brake air was provided by two C38 type compressors; later they were upgraded with the more reliable W242. However, on some units, only one compressor was replaced, leaving one of each type in use on a single locomotive: the C38 produced air until in main reservoir tanks was reached, while the W242 from . In fact, on these units, only the W242 was used on normal conditions; the other one only if pressure dropped below .
Main-tanks and the 24 V batteries supply air and current to several systems:
Braking system, which takes air from the main reservoir tanks and which is generally kept under a pressure of about (when brakes aren't unreleased). Main breaker (, IR), which is the "high voltage switch" that connects the 3 kV of the line to the locomotive. It can be closed only when pressure is greater than . Contactors. They are widely employed on Italian electro-mechanical locomotives, including E.636. They are used in various systems, mainly to insert/exclude the rheostat's resistors, can move only when pressure is greater than , and the IR must be closed. Horn and whistle (Tromba and Fischio). The locomotives have two horns and whistles, one above each driving cab. The former are activated by a solenoid valve and work only with battery power and when pressure is greater than , while the latter can reach their maximum intensity with pressures of about . Sand throwers (Sabbiere). As the name suggests, they throw sand on the track, in order to increase adhesion. They are to be manually activated by the driver in case of wheel-slip and work with pressure of about .