English Electric 12CSVT Mk2 and Mk3 traction motor amps surging

[aussiesteve]

G'day,
I have a technical question about English Electric 12 CSVT Mk 2 and Mk 3 units.
My only footplate exposure to EEs was during my three year exile in Tasmania.
These units, dubbed the Z and ZA class regularly surged in traction motor amps when under full load.
I was told that this was normal.
I am wondering if this surging was due to the load regulator associated with the governor.
These units were air throttle and with Davies Metcalfe M9A brake system.
Yes, these units were built in Australia, but I am attempting to obtain a comparison with UK built units.
Alco and EMD motive power that I was familiar with here in NSW would only surge in motor amps due to wheel-slip etc.
I did enjoy the Tassie EEs once becoming familiar with their idiosyncrasies.
Though, the metal head control jumper cable was a bit of a pain.
Much the same as the trio of control jumper cables necessary on our NSWR 46 class Metro Vickers units.
Hopefully, somebody can enlighten me as to the reason for the traction motor amp surging.
Thanks,
Steve.

[Master Cutler]

Hi Steve, what an interesting post.
I only have very limited knowledge from preservation Diesel interests, but, from past discussions with ex-engine men,I'm assuming this surging is to do with the slow response between engine Govenor and Govenor switches acting on the load regulator when calling for full power.
At all speeds the load regulator controls the excitation on the generator but at full load the response to changing track elevations and conditions will not be as quick to react causing over excitation and excessive power to be generated.
I believe this situation could also lead to flash over between generator and ground.
I'm sure there are more knowledgeable participants on the forum, so hopefully someone can enlighten you further.

[aussiesteve]

G'day Master Cutler,
Thanks for you response.
The units mentioned were built in 1972 and 1973, so were aged by the time I got to play with them.
Yes, this effect was most noticeable when climbing the various 1 in 40 grades on the Tassie South Line.
The occasional flash-over (ground relay as I am familiar with) would occur.
I don't know what the balancing speed was for these units.
But, would assume that it would be around 18 kph.
The ZA class were originally 2350 hp, but downrated to 1800 hp to match the Z class.
The ZA class were not Driver Only Operation, so were multiple unit with DOO Z class.
The chant of four or more such beasties in multiple was magic even though not my beloved Aussie Alcos.
Steve.