Weter, on 08 June 2020 - 12:46 PM, said:
As I understand, the position of throttle handle more likely gives POWER reference for Diesel set, not rpm, when reverser isn't at 0 position.
Because there's complex Power-regulating system between Engineer`s controller and high pressure fuel-injecting pump in powerful locos.
So, when load rapidly rises, the RPM drops, but at the same time the exaltation of Main Generator is increased by the systrm, so DG-set gives more current (mean-more power) to traction motors. And opposite, when load drops, exaltation lowers automaticaly, but rpm rises a little, and then fuel quantity is reduced by regulator, trying to maintain defined rotation speed.
Making black clouds, when rising up calls "Loko Gived a bear" among staff in some countries.
It probably depends on the manufacturer. On EMD units the throttle commands four relays which create a binary signal for the governor to interpret. The governor solely controls engine RPM, but, as it is mechanical, it will always lag to some degree. Its operation is discussed in detail
here. This lag is the reason why the engine on an EMD locomotive will tend to briefly overspeed a little bit when the load is dumped by the wheelslip control, and this lag is also why it will tend to overspeed when changing throttle positions, especially when large changes are commanded. This is something that I wish OR would model - with greater RPM acceleration values and larger commands in engine speed, the sim should have the engine speed exceed the commanded RPM briefly.
This often gives people the false impression that, under normal operating conditions, varying load changes the fuel consumption or that the governor operates on a fuel flow schedule rather than an RPM schedule. Neither is true. The governor commands engine RPM, and the power is a constant in any given throttle setting unless the wheelslip system is dumping the load (giggle). How that juice makes it to the motors without frying the whole works is, of course, why locomotives transition. There's a good explanation of that
here. There's also a detailed explanation of how the governor and load regulator work together to keep both engine RPM and the generator's power output constant between pages 7-30 and 7-32 of the
GP38-2 service manual.
So the main takeaways are this:
1. The governor sets engine RPM
2. Being a mechanical device, the governor lags somewhat
3. The power sent to the traction motors, and thus load on the engine, in any given throttle setting is a constant, maintained by a feedback loop between the governor and load regulator
4. During either wheelslip or transition, the load will be removed from the engine. Because the governor lags slightly during large power changes, the engine will momentarily overspeed under these conditions.