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However, the CRH3 changes you quoted upthrwad do not address the issue of "overspeed" on the entire range of CRH vehicles (including earlier CRH3), which applied from the 2007 timetable change resp. the 2008 opening of the Beijing-Tianjin line, that is, well before the modifications. On the other hand, that range of modifications, and operational data I found since, do indicate that engineers got more serious about making the vehicles suitable for the speeds permitted earlier, and the trains are operated more realistically.
On the issue of speed raises, let me first list the parts that are wear-and-tear-critical due to increased forces:
As for the testing side, to approve a vehicle for a certain speed, standard practice is to conduct a number of tests on a given amount of kilometres at 110% of that desired top speed, and braking tests, and a number of parameters (f.e., the mean of filtered lateral accelerations above the second bogie pivot) must stay below given limit values. Once that's achieved, standard practice is to paint the approved speed on the vehicle.
Now, the CRH1 (A, B, E), CRH2 (A, B, E) and CRH5 have been ordered for and designed for 200 km/h, and apparently type-approval-tested for the same, as you see that speed painted on them (examples: CRH1-064E, CRH2-136E [on the right], a CRH5). Yet, all of them are operated at up to 250 km/h since 2007.
The CRH2C (first batch), also called CRH2-300, nameplate speed 300 km/h, is operated up to 350 km/h since 2008, though it wasn't tested up to 385 km/h (CRH2-061C 22 April 2008 record: 370 km/h). What could be the consequences?
The CRH3 is a special case. The nameplate speed is 350 km/h for all vehicles (including the prototypes built in Germany, see f.e. CRH3-002A), which I guess had to do with the PR of the Beijing-Tianjin line opening.
Now, one might imagine that the Velaro design should be suitable for 350 km/h, given that the Spanish version is for that speed. However, Velaro CN is wider and thus heavier and with a larger wind resistance, but has the same maximum power. Still, one CRH3 reached 394.3 km/h in a test run, so maybe it made the full 350+10% tests? However, you'll find reports sourced to Siemens engineers on the German Wikipedia indicating an official top speed of 300 km/h in August 2008 (and operation to 340). Speed profiles I saw trawling hasea.com (can't find it again, but this thread has trip
report photos in line with that) showed 330 km/h max. in regular Beijing-Tianjin operation.
Of the modifications mentioned in your link, I would be most interested in a precise translation on those affecting power output. The 6% improvement in drag (apparently achieved mostly by changing protruding parts) means only a 2% improvement in speed at the same power (due to air resistance running at the second power of speed, and power being speed times force), that is, f.e. same power needed for 336.5 km/h instead of 330 km/h. However, the CH3 maximum of 8800 kW remained unchanged, so they must have improved continuous output, mybe with better cooling?
On the other hand, I tried to find WuGuang line speed profiles at hasea.com. Didn't find any, but I found photo-documented trip reports, which showed that 350 km/h is reached but not maintained continuously, and a thread where they say that timeplans were laid out for 330 km/h max. That sounds like a more realistic and equipment-friendly operation.
Finally, there are the new versions code-named CRH2-350 and CRH3-350. I was hard on these too, because 380 km/h max is planned, even though sources (f.e. Chinese Wikipedia) say that tests are planned only up to 400 km/h, not 418 km/h. On the other hand, if their planned operation is similar, that is 380 km/h is reached only in spurts, the wear & tear and other effects would be less.
One finds a detailed list of the planned modifications and research for the CRH2-350 and CRH3-350 here. It's pretty wide-ranging (including the modification of the CRH2 cross-shape), so there is a serious effort, which is reassuring. One critical component I will note though is the pantograph [which is based on a standard German design both on the CRH2 and CRH3, the Japanese pantograph was not imported]: this is the main source of noise at those speeds, and also of wear, but the list only seems to mention optimisation of the existing design, rather than a replacement with a single-arm pantograph with active-regulated pressure on the catenary. It might be noise-relevant that they don't plan to change the CRH3 nose shape.
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