The Class E.656 is an Italian articulated rheostatic-type electric locomotive built from 1975 to 1989. An evolution of the E.646, they are all-purpose locomotives, and have been used on every kind of train, ranging from freight to intercity passenger transport.
The E.656 is nicknamed "Caimano" (Caiman).
The hull is divided in two parts, each one with its own twin axle bogie, plus a central bogie in the middle. Each bogie mounts four DC motors, each providing 400 kW (540 hp), for a total of 12.
The initial project speed was 160 km/h (99 mph), but later it was reduced to 150 due to stability problems; further, the heavy mass of the locomotive did not allow the use of rheostatic braking.
Recently, many E.656s have been transferred to the Cargo Division of Trenitalia to haul freight trains. The gear ratio has been reduced from 28/61 to 23/66, and the speed limit to 120 km/h (75 mph). The modified units form the Class E.655.
The E.656 class is officially subdivided by FS into three series:
The differences between series regard electrical and mechanical equipment.
The 3rd series locomotives have four field weakening shunts in parallel and super-parallel motor combinations (where the other series have three), and the 78-wire cable to remote control the locomotive from a control car (Carrozza semipilota) or another Delfina-fitted locomotive.
Differences between locomotives can also be summed up as follows:
|1st||001 - 104||Motoalternators|
|2nd||201-251||Single static converter|
|4th||159-200||Single Static converters (except unit 200)|
|5th||401-550||2 ARSA static converters|
|6th||551-608||2 ARSA static converters and Delfina control unit, for remote command.|
The locomotive has twelve 82/400 motors, with class B insulation, four per bogie.
They can be connected in the same combinations used on E.646:
Like their predecessors, E.656s have a rheostat (31 resistors subdivided in 21 packs, for a total resistance of 17,015 ohm) that, by varying its resistance, gradually regulates the current to the motors on starts, and on each time a transition to the next combination is made; however, differently from older Italian types, rheostatic exclusion is not controlled manually, by default.
The driver selects the desired combination, which is automatically accomplished by a system which, through a particular array of logic gates and other components (capacitors, resistors, etc.), called "RAE" (Relè Accelerazione Elettronico), controls a rotating device (called avviatore automatico). The driver selects the maximum exclusion current through a potentiometer on his desk, and the system, when the c.e.m.f. present in the motors brings the current (which is read by transducers) to a value lower than the set current, makes the avviatore advance, closing the rheostat contactors (thus shunting the relative resistors) as speed builds up, until it is totally excluded; similarly it may go backwards, when the current reaches high levels in relation to speed.
The different connections of the motors in the various combinations are accomplished by closing various contactors; their set-ups during transitions are handled by a device called "CEM" (Commutatore Escluditore Motori").
If rheostatic exclusion is needed to be controlled finely (e.g. on coupling maneuvers, or in case of a heavy train or poor adherence situations), the driver can use the "PAC" (Pomello Avanzamento Comandato), a small lever that makes the "avviatore automatico" advance or go backwards step by step (for "Series" combination only).
On Third series locomotives (official classification), many functions such as the ones of RAE, Avviatore Automatico, CEM, etc., are assumed by an electronic control unit (called Delfina) derived from the ones employed on FS Class E.444.
The rheostat is robust and designed to stand high currents, however it cannot for an excessive period of time, as there is the risk of overheating; the driver has to keep this in mind when driving. When the temperature is too high (greater than 200 °C or 392 °F), the "VR" (Ventilazione Reostato, Rheostat Fans) light starts to blink on the driver's console to warn him.
The following components form the auxiliary systems:
They are fed in various ways, depending on the series:
Motor cooling fans are automatically activated when the reverser is in non-neutral position, while rheostat fans activate when the temperature into the rheostat's resistors reaches 65 °C or they are manually activated by the driver via an apposite button.
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