What’s the method that IR uses to couple together multiple locos? or, What’s ‘Locotrol’?

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What’s the method that IR uses to couple together multiple locos? or, What’s ‘Locotrol’?

June 20, 2019, 1:21 PM

Two to four or so locos can usually be coupled together to operate automatically, without any special provisions, with the crew manning only one of them. (This mode of operation is known as ‘Multiple Unit’ operation, or ‘MU’.)

Using more than about 4 or 5 locos together without some form of automatic control for them is problematic because couplings come under excessive strain and break. A system known as ‘Locotrol’ is used on IR, which couples 3 to 5 locos at the head of a train, and one or two somewhere in the middle of the train, and possibly another two or three at the rear. The locos at the middle and rear of the train are radio-controlled by the crew at the head of the train. This system is used in some places for heavy freight sections. It was introduced with WDM-2’s on the Kirandul-Kottavalasa line (near Vishakapatnam) in 1988 by SER. That line is now electrified and multiple WAM or WAG formations are used instead. Locotrol is (or was) also used on the Kulem-Londa section.

With multiple locos lashed up for MU operation, there are MU cables that pass between successive locos, which carry the control signals between the manned loco and the others. WDM-2 locos have a single MU cable, whereas the older WAG and WAM series use three MU cables, which also carry two connections for the tap-changers in the locos. The newer WAP-5 and WAG-9 locos use a single MU cable. The absence of this MU cable indicates manual coupling of locos — in this case, each loco is manned by crew, and they use horn or hand signals to communicate across the locos. Such non-automatic coupling can also be used for incompatible classes of locos, e.g. to couple a WDM-2 with a WAG loco in rare instances where the required electric loco wasn’t available. Even with some of the newer locos, coupling may not be possible for different classes of locos: e.g., a WAG-5 and a WAG-7 cannot be MU’d together and require separate crews for operation.

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In some cases the local loco sheds or workshops have carried out experimental modifications to locos to allow multiple unit operation even in cases where the locos were not designed for MU’ing originally. The Moula Ali shed of SCR, for instance, carried out an experiment in the 1990s to MU WDS-4 shunters to allow MU’d pairs of these to shunt long (24-coach) passenger rakes (SCR had an especially high number of 24-coach train services and not enough shunting power to match). Normally a single WDS-4 can only shunt up to about an 18-coach passenger rake. The experiment with MU’d WDS-4 did not work despite a lot of improvization and experimentation by Moula Ali and eventually this was dropped, as old WDM-2’s, and even WAM-4 or WAG-5 locos started being retired from mainline operations and becoming available for tasks like shunting.

IR never adopted the practice of designating locos as ‘A’ or ‘B’ units for coupling. All locos could be used as either a master or slave loco in coupled configurations. A few pairs of locos were sometimes kept in fixed-formation (mostly WDM-2 pairs); in such cases, both locos in the pair are usually oriented with their short hoods facing outwards (i.e., so that the short hood leads no matter which direction the locos travel in). (This is not universal practice, however, as lash-ups the other way around have been seen.)

Often, different locos may be seen coupled together, such as a WDG-2 with a WDM-2A.

Source – IFRCA.org

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