Ans: The type of the construction of OHE to be used is primarily determined by the train speed. The effect of train speed on the current collection by the pantograph will be understood when the behavior of OHE under the passage of pantograph is followed.
1) The pan of pantograph along the overhead wire pushes it up by a certain amount of pushup.
2) The contact wire after the passage of pantograph, suddenly sags and starts vibrating vertically due to elasticity of the system.
3) When the collecting speed exceeds 120 kmph, a contact break phenomenon is likely to occur in the overhead wire system having simple catenary system.
In order to have satisfactory current collection at various speeds, various modifications in the construction of OHE are carried out.
i) For speeds up to 100 kmph: Simple Catenary construction (for employing regulation of mechanical tension)
ii) For speeds up to 120 kmph: Simple Catenary construction
iii) For speeds up to 160 kmph: Modified Y Simple Catenary construction
iv) For speeds beyond 160 kmph: Modified Y Compound Catenary construction