The first two Class 21 electric locomotives arrived by ship in Durban from China on the 11th December 2014. 21 001 & 21 002 were off loaded at Maydon Wharf and taken across to the Umbilo Electric Locomotive Depot. Their transfer to Pretoria was scheduled for departure at 2am on the morning of the 12th December 2014. Dead hauled by 18-636 and 18-748, I managed to catch them on the climb up from Frere to Chieveley in Northern KwaZulu Natal. Railways Africa reported recently as follows on the new Class 21: "On 16 September 2014, the first of the class 21E dual-voltage (3kV DC and 25kV) electric locomotives for Transnet Freight Rail was rolled out at the CSR Zhuzhou Electric Locomotive Company in China. Except for the first two units, the order is to be completed in South Africa.
The CSR Zhuzhou Electric Locomotive Company is a subsidiary of the China South Locomotive and Rolling Stock Corporation (CSR), a leading manufacturer. The first two locomotives are to be delivered for acceptance trials by 28 February 2015. According to the project plan, Transnet’s agreement with CSR includes the joint production of more electric locomotives, electric multiple units, suburban rail vehicles and rail transport equipment for South Africa and the African region.
The class 21E is virtually identical in visual appearance to the earlier class 20E locomotive which is described by the manufacturer as the “promotion version” of the class 21E. The new loco is in essence an upgraded version of the class 20E, based on customer requirements. It is a heavier locomotive with the axle load increased to 26,000kg, with improved tractive effort for service on the heavy-haul coal line to Richards Bay. It makes use of more advanced electronically controlled pneumatic (ECP) brake system technology to control the train’s air brakes through electric signals. This improves braking response time and results in improved safety and reliability. The four-axle locomotive is capable of an output of 3,000kW (4,023hp) and a speed of 100 km/h. A microcomputer network control system allows eight locomotives to work together in a multi-unit consist or in multiple with diesel-electric locomotives.
The only externally visible difference between the classes 20E and 21E is on the pilots. The class 20E has two cable sockets on each side of the coupler and a fifth socket in a cut-out on the sill, below the front door on the front pilot and in the same position on the rear pilot, near the right end of the sill. The class 21E has no cut-out in the sill and instead of two pairs of cable sockets, it has a rectangular box on each side of the coupler. These radio frequency distributed power (RFDP) connections are located behind the cowcatchers on the class 20E.
The locomotive body is a welded monocoque design, constructed of steel plates and profiled members, with a compressive strength of 4.45 meganewtons and a tensile strength of four meganewtons. The class 21E has a single cab and a gangway along the centre of the locomotive. It is equipped with a wireless data transmission system which can send the locomotive operation status, fault data and energy consumption data via GSM and Wi-Fi to a trackside station for analysis. It is equipped with an axle temperature alarm device, fire alarm system, closed-circuit television (CCTV), wheel flange lubricating device and, as personnel safety measure, high voltage protective interlocking. The AC traction motors are powered through insulated-gate bipolar transistor (IGBT) control.
As on the dual-voltage classes 19E and 20E, the main electric circuit is automatically selected in either AC or DC mode, based on the voltage of the overhead contact wire feeding the locomotive. To facilitate automatic trouble-free transition on the run, the locomotive is equipped with on-board voltage detectors, while the overhead wire is equipped with two wooden isolators and a three-metre length of neutral wire to separate the AC and DC feeds. The neutral section is connected to the rails, which serve as the return conductor on electrified lines.
The transition process requires that the locomotive be switched off automatically before it reaches the isolators and the unpowered overhead wire section, and automatically restarted after exiting from under the unpowered wire. This is done by a pair of track magnets, one on either side of the neutral overhead wire and spaced 45 metres apart. The two magnets are mounted with their polarities reversed in relation to each other and they activate a magnetic relay, located behind the cowcatcher of the locomotive, to effect the switching off and restarting."