Greybeard33
Established Member
It is perhaps worth quoting again what the Rail Engineer article last September had to say about the relative performance of the 769 and 150, according to Wabtec modelling:
The rated output of two diesel engines at 780kW is the maximum they can produce. By the time alternator efficiency, auxiliary supplies, and traction control efficiency are taken into account, the electrical input to the traction motors will be approximately 550kW, little more than half the maximum rated output of the traction motors.
[Wabtec and Porterbrook] are well aware of this deficit. They explained that simple headline figures do not tell the whole story and that the required performance on diesel was likely to be as good as, if not better than the Class 150. [Wabtec] described the modelling that had been carried out to gain confidence that the Class 769 trains will deliver this required performance. Wabtec had constructed its models from scratch and some worst-case routes had been selected to demonstrate the performance.
Modelling is only as good as the quality of the modelling algorithms, data and assumptions and Rail Engineer heard that a degree of conservatism has been built into the modelling, leading to confidence that the Class 769 will out-perform class 15X DMUs on the tough routes modelled.
Compared with a Class 150, the Class 769 has a higher tractive effort on starting, but the tractive effort falls away more steeply. This difference in tractive effort curves makes it difficult simply to predict performance on any particular route, illustrating the importance and value of modelling. Modelling has shown the gradient balancing speed on a flat gradient when powered by the diesel engines to be approximately 87mph and the trains will retain the 100mph capability when powered by electricity. The modelling has also shown that two 1000-litre fuel tanks should be ample for the expected duty.
The proof of the proverbial pudding will, of course, be in the eating... assuming the 769 dish at long last lands on the TOCs' tables!Whilst maintenance costs will inevitably rise compared with an electric-only Class 319, track access charges should be similar to the donor units. Compared with class 15X DMUs, overall fuel consumption – even on all-diesel routes – and routine maintenance costs will be lower, due to the use of a modern diesel engine requiring less maintenance.