Question: I understand the working principle, but what determines when the energy is too high for the bus, in other words how many trains can get resupplied by another train 's regen braking before it gets consumed by the braking resistor?
Voltage of the DC bus at substation determines the activation of AARU which eventually dissipates the energy in form of heat. This voltage level is set based on voltage limits prescribed by en50163. It is up to the operation time table that how many trains are accelerating in section when other has to brake. In case two train are in section and both brake then all will go to resistor, however if one accelerates it will take the regenerative energy.
Typically if aaru is not present then we have the similar device (braking resistor) on train (RST). However, if hypothetically nothing is present, it will lead to overvoltage as energy across capacitor will keeping on increasing. Eventually, DC HSCBs will trip on overvoltage cutting of the supply.
Hi sir, in traction system 3rd rail 750V DC or 25kV AC . which is advanced system? i mean AC or DC which is more advanced. Thanks in advance for the reply.
Hi Vignesh, both are good. 750Vdc (3rd rail) is used mostly worldwide compared to 25kV mainly because 25kVac is aesthetically not good and modern cities don't prefer wires hanging around. Also, nowadays in India we have mainly 750Vdc coming in most of the newly launched projects like Agra, Indore, Bhopal since Bangalore and Kochi metro have been successful.
