Chichibu RR 7800 Type having trouble

[ToniBabelony]

It seems that the Chichibu RR made some miscalculations when letting Tōkyū Sharyō modifying this new 7800 Type (an ex-8090 from Tōkyū) for the Chichibu Railway.

 

This new train type can't handle a mere 2% grade when accelerating. The other type, the 7500 Type, can cope with this, since two of three cars are powered (66,6%), whereas the 7800 has only one of two cars powered (50%). 

 

 

Good job Chichibu...

[Densha]

Lol! That is a very simple calculation isn't it? Just take in account the weight of the train, the power output and the grade. How can (professional?) engineers mess this up?

In the end he had to reverse and go full power and try it again. It must be very funny to be in that train as a passenger.

[miyakoji]

A real bummer, I'm sure Chichibu doesn't need this! Do traction motors have hard limits on incoming power, or could they "warm up" the electrical system to provide a little more power? What were the modifications? Was overall power reduced, weight increased, or both?

[Nick_Burman]

Gents,

 

I think the problem here is more likely to be Autumn foliage than lack of tractive effort...

 

Cheers NB

[ToniBabelony]

I think the problem here is more likely to be Autumn foliage than lack of tractive effort...

 

March isn't in autumn though ;) It's really a miscalculation on the Chichibu Railway's behalf. Then again, it's not so strange this has happened, since this is one of the first 2-car EMU to run on this network for a very long time! There must be something wrong with the gears I think, since the motors are powerful enough (130kW) to pull a measly 2-car train up this 2% grade.

[Davo Dentetsu]

At least there were no bright spark rail side engineers who would try the natural reaction to grab it this time... :D

[KenS]

The Japanese wikipedia page (for the 7500, but contains comments on the 7800) ascribes the problems to the body being too light, coupled with the chopper control having a low output, assuming Google didn't mangle the translation.

 

However, the original 8090 page says that these had 130 kW motors (so one motor car is 260 kw or 174 hp, presuming both trucks are powered) and an acceleration of 4.5 km/h/s which is fairly high (numbers in the 3's are more common), with a gear ratio of 5.31:1 (the same as the original Chichibu sets). That's a fairly low ratio: the E231, by contrast, uses a 7.07:1 ratio with 95 kW motors on both trucks. And the JR West 125 series, which presumably has to deal with grades, uses a 6.53:1 ratio with 220 kW motors, albeit with only one truck powered per car.

 

So the 7800 would appear to be undergeared compared to other trains, designed more for speed than power. Perhaps because its light weight allow it to accelerate well without extra power on level ground. Although the original 8090 had a weight of 58t across two cars, so it's not really that light by modern Japanese standards. It's likely light only in comparison to JNR-era steel cars.

 

The gear ratio suggests that this would translate to low power for accelerating up a hill, as Toni suggested.

[bill937ca]

However, the original 8090 page says that these had 130 kW motors (so one motor car is 260 kw or 174 hp, presuming both trucks are powered) and an acceleration of 4.5 km/h/s which is fairly high (numbers in the 3's are more common), with a gear ratio of 5.31:1 (the same as the original Chichibu sets). 

 

Usual practice with electric traction motors is one motor per axle. Two motor cars are troublesome.  Four motor cars can cut out two motors when there is a problem and limp along to the depot.

[bill937ca]

March isn't in autumn though ;)

 

It could be black rail. You can't see it, but you can't stop and you can't get traction.

[westfalen]

Doesn't sound like he's slipping and the last thing I'd do on black rail is reverse back at that speed, bad enough not being able to stop if you can't see where you're going. Seemed more like lack of power to me, I had a six car train this morning with two of sixteen traction motors cut out and could barely get up to 60kph going up hill.

 

I wonder if there was a fault on the train on the day because surely the Chichibu would have run test and training runs before placing the trains in service and performance like that is something that wouldn't go unoticed.

Edited May 27, 2013 by westfalen