from redundant stock for fitting into the vehicles, Acton Works have had to convert them from 630 V operation to work on 320 V. The lead-acid batteries are usually recharged inside a depot, although the 1985 batch of locomotives could recharge their batteries from the power rails while moving. Protection All battery locomotives are fitted with tripcocks which are operated by trackside equipment if the train passes a signal at danger. Eighteen (L15–L21 and L44–L54) are also fitted with Central line Automatic Train Protection (ATP). When they were built, locomotives L25 to L32 were fitted with Automatic Train Operation (ATO) equipment, which allowed them to work on the Victoria line. The tripcock could be isolated, and a trip valve performed a similar function, except that it was operated by the ATO controller. A special setting was provided that allowed the vehicles to move if they were not receiving safety track signals, but the maximum speed in these circumstances was limited to . By the mid-1980s, this equipment had ceased to be used, as works trains were only run on the Victoria line when engineers had possession of the whole line. Subsequently, some locomotives (L27–L32) have been fitted with a new type of Victoria line ATP equipment which was designed by Metronet on behalf of Transplant, the operator of the fleet. This system was installed during 2007 at Ruislip Depot. It is compatible with the new Distance-to-Go Radio (DTG-R) ATP system which has been implemented on the Victoria line by Westinghouse Rail Systems. Ownership The locomotives are, since the start of London Underground's PPP scheme, in the ownership of TransPlant. The locomotives are all based at Ruislip Depot. Use The traditional use of these locomotives has been to haul trains using power from the rails until they reach the area where work is to be undertaken, where they switch to battery operation if the traction supply has been isolated. They are also used for transporting diesel powered equipment such as track tamping machines through tunnel sections. Normally one locomotive is marshalled at each end of the train, allowing the train to be reversed easily. The connections between different Underground lines often require reversals on route. Early locomotives were not allowed to operate on their own as they only had a single air compressor, but twin compressors were fitted to vehicles built from 1964 onwards, to allow single operation. With the building