Once upon a time, there was a great king called Vikramaditya - the WAM-4 - Shashank

Ideally, one power car is enough, but an EOG van is still needed for backup in case the HOG fails. And IR is modifying the existing EOG vans to be used as power cars for HOG, instead of building separate dedicated power cars. And there are restrictions on having passengers in the coaches containing diesel generators, as the noise and the danger of fire accidents are much higher in these coaches. So, even the under-slung generator coach that IR was testing, is only a Guard-cum-parcel van and not an SLR.
Another thing affecting the change is the lack of passenger-cum-guard LHB coaches. This was not required until now as all trains always had EOGs at the...
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end. But now, with one EOG removed, there is no provision to deploy a guard at the rear of the train.
To solve this problem, IR is now deploying EoTT devices ( End of train telemetry devices) on it's trains. These devices will monitor the rake continuously and directly let the driver know in case of rake-parting or any other mishap. This will remove the need to keep the guard in the last coach of the train and he/she can now be present in any coach in the train. And in case of HOG trains, there can be only one EOG van and the guard can monitor the rake even while sitting at the head of the train.
ICF CBC SLR's cannot be used for 2 reasons. First reason is their speed restriction to 110kmph, which obviously isn't sufficient for the high speed LHB trains with 130kmph clearance. The 2nd and more important reason is the difference in the electrical and brake connections for LHB and ICF coaches. Because of this, it is not safe to have a passenger-filled coach freely trailing behind the train as the ICF coach's brake pipe system would not be compatible with the LHB coach's system. Even a EOG style ICF coach can not be used in this case.