Azuma Technical Equipment Arrangement

[ryan125hst]

As an Engineer, I was wondering about how the traction and auxiliary equipment is arranged throughout an Azuma (and other Class 80x) trains. I asked a question about the transformers on the Class 810 thread but I thought it deserves a thread of its own.

My understanding of the Class 80x trains (with the exception of the Class 810 which is different) is as follows:

DPTS – Driving Cab, Air Compressor, 25kV Transformer

MS - Traction Inverter, Auxiliary Converter, Generator Unit*

TS - No traction equipment, engine or auxiliary converter, so just air brake equipment, air conditioning equipment etc that the other coaches will also contain?

MC - Traction Inverter, Auxiliary Converter, Generator Unit*

MF - Traction Inverter, Auxiliary Converter, Generator Unit*

DPTF – Driving Cab, Air Compressor, 25kV Transformer

*Bi-Mode units only.

Electric trains contain one generator unit for the generation of hotel power (lights, toilets, heating, air conditioning, catering) in the event they are hauled by a locomotive or if the overhead wires are switched off. This engine can also move the train at low speed to clear the line.

My questions:

I saw a post while searching the forum for details about this the other day about how 9-coach Pendolinos are effectively 4-coach units with one pantograph feeding two transformers, with the transformer in the vehicle with the pantograph lowered fed by a 25kV bus on the top of the train. 11-coach Pendolinos have a third transformer to feed the two additional coaches.

Do Azumas use a similar method? Another poster suggested they don’t and only the transformer in the vehicle with the pantograph raised is in use. This would make sense on a 5-coach unit, however a lot of power would need to be delivered by a transformer small enough to fit under a passenger carriage for this to work on a 9-coach unit. Looking at photographs, it does appear as though a 25kV bus line exists, even on 5-coach units. Can anyone shed any light into how this works?

I presume both driving vehicles have a compressor as I listed above? If so, do they both run at the same time to speed up the time taken to raise air pressure?

400VAC – Am I correct that there is an Auxiliary Converter on each Motor vehicle? Do they all operate at the same time? Presumably there is a 400VAC cable running the length of the train that each converter feeds so if a Generator Unit is switched off, the power can still be provided to the other carriages.

110VDC – There is a PDF about the Super Express trains (as they were known as at the time) that said the Auxiliary Converters also provide 110DC, which will be for the batteries. Is there a battery per coach as with locomotive hauled carriages, or a distributed battery system as with London Underground trains?

I also wonder how similar the key points of the technical design is to other trains. For example, I presume the likes of Voyagers and Class 185’s have a 400VAC system that allows coaches to be powered when its engine is off, unlike a Class 158 that would have no power or air conditioning if its engine is off. Are the EMU's from other manufacturers such as Alstom and Stadler similar or very different? Do the new CAF DMU's have a facility to power adjacent coaches if an engine is off, or are they within coach only like their predecessors?


DPTS = Driving Pantograph Trailer Standard

MS = Motor Standard

TS = Trailer Standard

MC = Motor Composite (First and Standard Accommodation)

MF = Motor First

DPTF = Driving Pantograph Trailer First

Where 5 coach trains are formed DPTS-MS-MS-MC-DPTF and 9 coach trains are formed DPTS-MS-MS-TS-MS-TS-MC-MF-DPTF.

 

[marko2]

I suspect the Auxiliary converters are specifically providing 415VAC three-phase - a convenient supply for drives in HVAC and catering equipment - or in a star configuration, providing several 240v single-phase AC supplies. Looking at data sheets on Hitachi Energy's website, it seems like 1kV single-phase AC is the likely bus-line potential.

 

[driver9000]

If the vehicle has an engine (generator unit) then it is classified MeS or it certainly is on an 802.

 

[ryan125hst]

I suspect the Auxiliary converters are specifically providing 415VAC three-phase - a convenient supply for drives in HVAC and catering equipment - or in a star configuration, providing several 240v single-phase AC supplies. Looking at data sheets on Hitachi Energy's website, it seems like 1kV single-phase AC is the likely bus-line potential.

Yes that's my understanding too. I think the 110V DC power is for the batteries, although the Wikipedia article about the Class 185's suggests they have a 110 V DC auxiliary supply and a 24 V DC battery supply. I don't know if the Class 800's have this or if the batteries (presumably 12V cells) are wired to give 110V and this voltage is used in all control circuits.

If the vehicle has an engine (generator unit) then it is classified MeS or it certainly is on an 802.

I think that's right, the Wikipedia article I took the formation detail from omitted that information. Is there a reason why the presence of the accessible toilet and catering equipment isn't shown on the coach classification. Isn't the first class driving vehicle technically a DPTFKD - Driving Pantograph Trailer First Kitchen Disabled? What determines when a facility is shown in the code and when it isn't?

 

[driver9000]

I think that's right, the Wikipedia article I took the formation detail from omitted that information. Is there a reason why the presence of the accessible toilet and catering equipment isn't shown on the coach classification. Isn't the first class driving vehicle technically a DPTFKD - Driving Pantograph Trailer First Kitchen Disabled? What determines when a facility is shown in the code and when it isn't?

It would be L for Lavatory as there's no distinction made between standard or accessible toilet and D already refers to Driving cab. I don't know why Hitachi omit it.

 

[ryan125hst]

It would be L for Lavatory as there's no distinction made between standard or accessible toilet and D already refers to Driving cab. I don't know why Hitachi omit it.

Good point. I was thinking of TSO(D) which I believe is the designation for the Mark 4 standard class carriage with the accessible toilet and wheelchair space.

 

[hexagon789]

Good point. I was thinking of TSO(D) which I believe is the designation for the Mark 4 standard class carriage with the accessible toilet and wheelchair space.

TOD for the Mk4 Standard Class accessible vehicle.

The Azuma driving cars are just DPTF or DPTS I understand.

 

[ryan125hst]

I seem to have derailed my own thread with talk of carriage designations.

Has anyone got any answers to my questions regarding the technical equipment above?

 

[D365]

Yes that's my understanding too. I think the 110V DC power is for the batteries, although the Wikipedia article about the Class 185's suggests they have a 110 V DC auxiliary supply and a 24 V DC battery supply. I don't know if the Class 800's have this or if the batteries (presumably 12V cells) are wired to give 110V and this voltage is used in all control circuits.

I can’t imagine that the Class 185s have any 110V DC equipment; this would be highly atypical for a hydraulic or mechanical drive multiple unit. 24V DC is the defacto control voltage for all second generation DMUs (ex British Rail) and newer.

The vast majority of British EMUs and DEMUs/EDMUs (including Class 8xx) use a 110V DC control voltage.

 

[ryan125hst]

I can’t imagine that the Class 185s have any 110V DC equipment; this would be highly atypical for a hydraulic or mechanical drive multiple unit. 24V DC is the defacto control voltage for all second generation DMUs (ex British Rail) and newer.

The vast majority of British EMUs and DEMUs/EDMUs (including Class 8xx) use a 110V DC control voltage.

According to an archived document linked from their Wikipedia article, they have the following:

The hydrostatic powered generator supplies following voltages:

• 3 AC 400 V, 50 Hz
• 1 AC 230 V, 50 Hz

transformed from the 3 AC 400 V power supply:

• DC 110 V auxiliary
• DC 24 V battery circuit

Source: https://web.archive.org/web/20071107210309/http://www.siemenstransportation.co.uk//pdfs/185.pdf

I previously saw the information on Wikipedia but didn't spot the technical document. I wonder how similar this electrical arrangement is to other modern DMU and EMU trains (aside from the hydrostatic generation)?

 

[hwl]

According to an archived document linked from their Wikipedia article, they have the following:

The hydrostatic powered generator supplies following voltages:

• 3 AC 400 V, 50 Hz
• 1 AC 230 V, 50 Hz

transformed from the 3 AC 400 V power supply:

• DC 110 V auxiliary
• DC 24 V battery circuit

Source: https://web.archive.org/web/20071107210309/http://www.siemenstransportation.co.uk//pdfs/185.pdf

I previously saw the information on Wikipedia but didn't spot the technical document. I wonder how similar this electrical arrangement is to other modern DMU and EMU trains (aside from the hydrostatic generation)?

All the non electric-transmission DMUs have alternators driven from hydrostatic converters so 185 follows that practice.
As regards the rest the 185 are effectively an EMU (based on 350/450/444) with diesel added hence they are very different to other 1xx DMUs and have some unusual quirks for example not using waste heat from the engine for heating the passenger compartment (all electric) hence the size of the alternator is massive compared to any other 1xx DMUs.

 

[ac6000cw]

IIRC, the 185's have an 'eco' mode which can shut down engines when their power isn't needed for traction, so that may be another reason for having all-electric HVAC - as per the schematic diagram in the PDF (see below), the main 400V power bus has switchable links to the adjacent cars. I assume that means that a single alternator would have to be rated to support the HVAC load of two cars though, unless the system does load shedding in that situation.

 

[hwl]

IIRC, the 185's have an 'eco' mode which can shut down engines when their power isn't needed for traction, so that may be another reason for having all-electric HVAC - as per the schematic diagram in the PDF (see below), the main 400V power bus has switchable links to the adjacent cars. I assume that means that a single alternator would have to be rated to support the HVAC load of two cars though, unless the system does load shedding in that situation.

The alternator is a monster and can supports multi vehicles, the bus cabling is big enough to enable any combination of two vehicle to be able to supply the other ones so only 50% headroom per alternator is need to support half another vehicle rather than whole one.
One key reason for the hydrostatic converter (similar those on excavators and other vehicles that need to power hydraulic rams or electricity/gas company vehicles running power generators or air compressors from the vehicle engine) is that it dissociates the engine rpm from the alternator and other equipment speeds which can all be kept high and constant for maximum efficiency and be minimally sized (they would all have to be sized bigger to cope with lower rpm if they weren't fed from the hydrostatic converter). E.g. variable speed input fixed speed output.

 

[D365]

The alternator is a monster and can supports multi vehicles, the bus cabling is big enough to enable any combination of two vehicle to be able to supply the other ones so only 50% headroom per alternator is need to support half another vehicle rather than whole one.
One key reason for the hydrostatic converter (similar those on excavators and other vehicles that need to power hydraulic rams or electricity/gas company vehicles running power generators or air compressors from the vehicle engine) is that it dissociates the engine rpm from the alternator and other equipment speeds which can all be kept high and constant for maximum efficiency and be minimally sized (they would all have to be sized bigger to cope with lower rpm if they weren't fed from the hydrostatic converter). E.g. variable speed input fixed speed output.

Thanks for this additional detail. Electrically, I was expecting the 185 architecture to be similar to Class 17x and 19x, but it appears they are more akin to Class 22x.

 

[ryan125hst]

All the non electric-transmission DMUs have alternators driven from hydrostatic converters so 185 follows that practice.
As regards the rest the 185 are effectively an EMU (based on 350/450/444) with diesel added hence they are very different to other 1xx DMUs and have some unusual quirks for example not using waste heat from the engine for heating the passenger compartment (all electric) hence the size of the alternator is massive compared to any other 1xx DMUs.

Presumably the DEMU's such as the Class 220 and 221, 222 and Class 80x are similar in that their electrical design is closer to that of an EMU with the diesel engine added to produce the power. I wonder how the likes of the 175 and 180 are arranged, Are the new 195's and 197's closer to how the 158 is or more like the 185 from an auxiliary point of view?

IIRC, the 185's have an 'eco' mode which can shut down engines when their power isn't needed for traction, so that may be another reason for having all-electric HVAC - as per the schematic diagram in the PDF (see below), the main 400V power bus has switchable links to the adjacent cars. I assume that means that a single alternator would have to be rated to support the HVAC load of two cars though, unless the system does load shedding in that situation.

I presume this is fairly common on more modern trains. Back in 2017 I travelled on a Voyager from Birmingham to Sheffield that didn't have its engine running. The lighting remained on and I believe the air conditioning continued to function. The power must have been crossfed from the adjacent coach.

 

[D365]

Presumably the DEMU's such as the Class 220 and 221, 222 and Class 80x are similar in that their electrical design is closer to that of an EMU with the diesel engine added to produce the power. I wonder how the likes of the 175 and 180 are arranged, Are the new 195's and 197's closer to how the 158 is or more like the 185 from an auxiliary point of view?

Class 19x are more akin to Class 158* and their Class 16x/17x successors. Control voltage is 24V DC; all have separate auxiliary and starter batteries.

* I’m not 100% sure whether or not Class 158/159 has separate auxiliary and start batteries.

 

[hwl]

,Are the new 195's and 197's closer to how the 158 is or more like the 185 from an auxiliary point of view?

Closer to 158, the 185s are an anomaly.

I presume this is fairly common on more modern trains. Back in 2017 I travelled on a Voyager from Birmingham to Sheffield that didn't have its engine running. The lighting remained on and I believe the air conditioning continued to function. The power must have been crossfed from the adjacent coach.

220 and 221 have adjacent vehicle cross feed with 222 doing better than that.

== Doublepost prevention - post automatically merged: 22 Aug 2025 ==

Thanks for this additional detail. Electrically, I was expecting the 185 architecture to be similar to Class 17x and 19x, but it appears they are more akin to Class 22x.

Worth remembering that Siemens have very little history in DMU manufacturing as they always JV'd on rolling stock before about 25 years ago when they bought Kraus Maffei and then Duwag. They were also traditionally electric loco and EMU focused.

 

[ryan125hst]

Class 19x are more akin to Class 158* and their Class 16x/17x successors. Control voltage is 24V DC; all have separate auxiliary and starter batteries.

Closer to 158, the 185s are an anomaly.

I presume they have a 400VAC air conditioning system though rather than a compressor driven straight off the engine, which I think the Class 158 has if I'm remembering correctly?

Do the 19x's have any ability to crossfeed power?

 

[D365]

Continuing from the Class 810 discussion, but with respect to five car and nine car Class 80x units:

All transformers are used all of the time - on a 5 car both transformers (cars 1 and 5) and on a 9 car all three transformers (cars 1, 4 and 9)

The 25kV bus-bar runs along the roof linking the active pantograph to all transformers

Car 4 has the transformer. Of the 4 trailer cars, 1, 4 and 9 have transformers and 1, 6 and 9 have batteries.

Seems I misunderstood the arrangement of the VCBs on Class 80x - I was under the impression that each transformer could be switched in or out.

Having looked again, it appears that the capability of the HV system is sized in proportion with the number of traction packages that are fitted on a unit.

 

[Energy]

I saw a post while searching the forum for details about this the other day about how 9-coach Pendolinos are effectively 4-coach units with one pantograph feeding two transformers, with the transformer in the vehicle with the pantograph lowered fed by a 25kV bus on the top of the train. 11-coach Pendolinos have a third transformer to feed the two additional coaches.

Class 390s have two pantograph+transformer coaches. Both transformers are in use to supply nearby motor coaches; there is a 25kv bus linking the two transformers, so only one pantograph is in use at a time.

Image Description: Electrical diagram of a 9-car class 390. [Source - Unknown, sorry ]

For the 11-car extension, an additional transformer (though no pantograph) and a motor vehicle were added.



Image Description: Diagram of an 11-car class 390 train. [Source - Alstom via Internet Archive]


For the AT300s, this document from Hitachi may be useful.

 

[507 001]

185's have an 'eco' mode which can shut down engines when their power isn't needed for traction

They didn’t have that when they were first introduced though IIRC. I’m fairly certain it came about a year after introduction.

I presume this is fairly common on more modern trains. Back in 2017 I travelled on a Voyager from Birmingham to Sheffield that didn't have its engine running

I’m fairly certain voyagers don’t have the same engine shutdown capability as the 185s. My understanding is that if a voyager engine is shut down it’s usually just broken…

 

[DaveyJones]

They didn’t have that when they were first introduced though IIRC. I’m fairly certain it came about a year after introduction.



I’m fairly certain voyagers don’t have the same engine shutdown capability as the 185s. My understanding is that if a voyager engine is shut down it’s usually just broken…

Voyagers have a shut down capability, less of re-start capability. They tend to shutdown by themselves if left unattended. the incoming driver has to restart the engines i believe

 

[800301]

As an Engineer, I was wondering about how the traction and auxiliary equipment is arranged throughout an Azuma (and other Class 80x) trains. I asked a question about the transformers on the Class 810 thread but I thought it deserves a thread of its own.

My understanding of the Class 80x trains (with the exception of the Class 810 which is different) is as follows:

DPTS – Driving Cab, Air Compressor, 25kV Transformer

MS - Traction Inverter, Auxiliary Converter, Generator Unit*

TS - No traction equipment, engine or auxiliary converter, so just air brake equipment, air conditioning equipment etc that the other coaches will also contain?

MC - Traction Inverter, Auxiliary Converter, Generator Unit*

MF - Traction Inverter, Auxiliary Converter, Generator Unit*

DPTF – Driving Cab, Air Compressor, 25kV Transformer

*Bi-Mode units only.

Electric trains contain one generator unit for the generation of hotel power (lights, toilets, heating, air conditioning, catering) in the event they are hauled by a locomotive or if the overhead wires are switched off. This engine can also move the train at low speed to clear the line.

My questions:

I saw a post while searching the forum for details about this the other day about how 9-coach Pendolinos are effectively 4-coach units with one pantograph feeding two transformers, with the transformer in the vehicle with the pantograph lowered fed by a 25kV bus on the top of the train. 11-coach Pendolinos have a third transformer to feed the two additional coaches.

Do Azumas use a similar method? Another poster suggested they don’t and only the transformer in the vehicle with the pantograph raised is in use. This would make sense on a 5-coach unit, however a lot of power would need to be delivered by a transformer small enough to fit under a passenger carriage for this to work on a 9-coach unit. Looking at photographs, it does appear as though a 25kV bus line exists, even on 5-coach units. Can anyone shed any light into how this works?

I presume both driving vehicles have a compressor as I listed above? If so, do they both run at the same time to speed up the time taken to raise air pressure?

400VAC – Am I correct that there is an Auxiliary Converter on each Motor vehicle? Do they all operate at the same time? Presumably there is a 400VAC cable running the length of the train that each converter feeds so if a Generator Unit is switched off, the power can still be provided to the other carriages.

110VDC – There is a PDF about the Super Express trains (as they were known as at the time) that said the Auxiliary Converters also provide 110DC, which will be for the batteries. Is there a battery per coach as with locomotive hauled carriages, or a distributed battery system as with London Underground trains?

I also wonder how similar the key points of the technical design is to other trains. For example, I presume the likes of Voyagers and Class 185’s have a 400VAC system that allows coaches to be powered when its engine is off, unlike a Class 158 that would have no power or air conditioning if its engine is off. Are the EMU's from other manufacturers such as Alstom and Stadler similar or very different? Do the new CAF DMU's have a facility to power adjacent coaches if an engine is off, or are they within coach only like their predecessors?


DPTS = Driving Pantograph Trailer Standard

MS = Motor Standard

TS = Trailer Standard

MC = Motor Composite (First and Standard Accommodation)

MF = Motor First

DPTF = Driving Pantograph Trailer First

Where 5 coach trains are formed DPTS-MS-MS-MC-DPTF and 9 coach trains are formed DPTS-MS-MS-TS-MS-TS-MC-MF-DPTF.

I hope the diagram below helps you out


Auxiliary Power Supply (APS) units are fitted to each DPTx vehicle, and on 9-car units, the TpS and TS vehicles, they all run at same time around 398V, a 5 car can operate with 1 isolated and a 9 car is permitted in service to operate with 2 isolated but can run with 3 isolated ECS

If a TC is isolated/faulty the GU cannot provide power to other vehicles, As the APS powers the traction converters, the GU cannot be utilised in the event of a complete failure either

110V batteries are provided on the DPTx and TS vehicles. They are however very poor at there job and don’t last long, jump starting a dead 80X is a long process

 

[ryan125hst]

Class 390s have two pantograph+transformer coaches. Both transformers are in use to supply nearby motor coaches; there is a 25kv bus linking the two transformers, so only one pantograph is in use at a time.

Image Description: Electrical diagram of a 9-car class 390. [Source - Unknown, sorry ]

For the 11-car extension, an additional transformer (though no pantograph) and a motor vehicle were added.


View attachment 187502
Image Description: Diagram of an 11-car class 390 train. [Source - Alstom via Internet Archive]


For the AT300s, this document from Hitachi may be useful.

Thank you, that's a great schematic. It's interesting to see the feeds to the propulsion cases are labeled as single phase. I'd have thought the rectifier was in the transformer car, with a DC bus linking to the other carriages. Instead, the propulsion case must receive an AC input and both rectify to DC and contain the traction inverter.

I hope the diagram below helps you out


Auxiliary Power Supply (APS) units are fitted to each DPTx vehicle, and on 9-car units, the TpS and TS vehicles, they all run at same time around 398V, a 5 car can operate with 1 isolated and a 9 car is permitted in service to operate with 2 isolated but can run with 3 isolated ECS

If a TC is isolated/faulty the GU cannot provide power to other vehicles, As the APS powers the traction converters, the GU cannot be utilised in the event of a complete failure either

110V batteries are provided on the DPTx and TS vehicles. They are however very poor at there job and don’t last long, jump starting a dead 80X is a long process

Thank you, I didn't realise the 9 cars had three transformers until @littledude's post yesterday. It seems each transformer on the AT300 series can provide power for only one or two motor coaches.

I had seen the Hitachi document before and had thought the APS's were with the drive converters so thanks for clearing this up. It's odd they provide 398V rather than the standard 400V but I guess it's all within the tolerances of this.

Where is the supply for the 230V power sockets sourced? I know they cut out during neutral sections unlike on 225's, so I presume direct from the 398V three phase?

Where are the compressors? I'm assuming in the DPTx vehicles?

What voltage is output from the transformers? I presume there's a bus from them feeding the drive converters and APS units?

 

[507 001]

Voyagers have a shut down capability, less of re-start capability. They tend to shutdown by themselves if left unattended. the incoming driver has to restart the engines i believe

Yes, which is very different to the 185s which can shut down and restart engines (although only the centre car I think?) depending on demand.

 

[YorksLad12]

Yes, which is very different to the 185s which can shut down and restart engines (although only the centre car I think?) depending on demand.

I think it’s all of them. They cycle through the engines to even out the use. You need less power east of Leeds, which is one reason Eco Mode was introduced.

 

[SansHache]

Thank you, that's a great schematic. It's interesting to see the feeds to the propulsion cases are labeled as single phase. I'd have thought the rectifier was in the transformer car, with a DC bus linking to the other carriages. Instead, the propulsion case must receive an AC input and both rectify to DC and contain the traction inverter.

That is correct. The transformer vehicles mount the transformer and the associated switchgear that connect to each Traction Converter. The rectifiers are on the motor vehicles.
The Class 390 Propulsion Case contains two identical power modules, one is configured as the controlled rectifier and the other performs the Traction Inverter and Rheo Brake Chopper functions. A DC bus arrangement was considered but there were concerns that a short-circuit fault on an Inverter could also cause damage to the rectifier and therefore remove the supply to multiple Inverters. This concern appears to have been managed effectively on later Traction equipment supplied by other manufacturers. The key factor in the Class 390 Traction system design was to ensure that any component failure had minimal effect on the overall train performance.

 

[mernrith]

Hi,
As someone who had spent more time in east Asia (HK/Japan) than the UK, the design concept differences in multiple units across the continent surprises me (even the Azuma which I’d thought to be more Japanese-like) and I’d like to ask a few questions upon the design. (do forgive me if they sound too basic but I’m no expert in engineering).

From my understanding and observations on AC trains, such as JR 885s or E657s that are partially or completely built by Hitachi Katsudo, or MTR Rotems, IKK SP1900s and CRRCs, it seems that they are composed of 2 or more blocks, where each block gets their own pantograph, transformer, converter-inverter etc and can still propel the train even if one block is faulty, and in occasional cases blocks from different trains couple and work. There is no bus line across different blocks, unlike diagrams of Pendolinos or Azusa’s shown early in previous chats, which probably suggests that the English trains are basically one large block and cannot be separated in between. What could cause such differences, say regulation differences or preferences from DfT/TOCs?

Another interesting point I do found - it seems uncommon for EMUs to have their pantographs on the driving car in 3-car units or above, but why does the Azuma does so? Is it due to aerodynamics or other reasons?

Many thanks!

 

[ryan125hst]

That is correct. The transformer vehicles mount the transformer and the associated switchgear that connect to each Traction Converter. The rectifiers are on the motor vehicles.
The Class 390 Propulsion Case contains two identical power modules, one is configured as the controlled rectifier and the other performs the Traction Inverter and Rheo Brake Chopper functions. A DC bus arrangement was considered but there were concerns that a short-circuit fault on an Inverter could also cause damage to the rectifier and therefore remove the supply to multiple Inverters. This concern appears to have been managed effectively on later Traction equipment supplied by other manufacturers. The key factor in the Class 390 Traction system design was to ensure that any component failure had minimal effect on the overall train performance.

Do the auxiliary converters also contain rectifiers or do they take their supply from the output of the Propulsion Case rectifier? I understand there are two per half set, so four per train on a 9 car (and a fifth on an 11 car) so presumably they are located in some of the motor vehicles?

From my understanding and observations on AC trains, such as JR 885s or E657s that are partially or completely built by Hitachi Katsudo, or MTR Rotems, IKK SP1900s and CRRCs, it seems that they are composed of 2 or more blocks, where each block gets their own pantograph, transformer, converter-inverter etc and can still propel the train even if one block is faulty, and in occasional cases blocks from different trains couple and work. There is no bus line across different blocks, unlike diagrams of Pendolinos or Azusa’s shown early in previous chats, which probably suggests that the English trains are basically one large block and cannot be separated in between. What could cause such differences, say regulation differences or preferences from DfT/TOCs?

This is the case in some ways. The diagram of the Pendolino above shows it is effectively two 4 car trains joined together making an 8 car train, and then an additional unpowered vehicles added between the two (Pendolinos were originally delivered as 8 car units I believe but were quickly extended to 9 cars shortly after entering service). I think if one of the two halves had a fault, the other half could push or pull the other to clear the line. We don't tend to have blocks as small as two coaches though unless the train is only a couple of coaches long with a cab at each end, and I think the shortest train currently operating on overhead wires 25kV here is three coaches.

Another interesting point I do found - it seems uncommon for EMUs to have their pantographs on the driving car in 3-car units or above, but why does the Azuma does so? Is it due to aerodynamics or other reasons?

Many thanks!

You are right, most trains in the UK do seem to have their pantographs on an intermediate coach. I presume this is simply down to how the train is designed. With a 5 car Azuma, the three intermediate vehicles house the traction inverter and traction motors, and in the case of the bi-modes the diesel engine and fuel tank. This will take up all the space under the coach (as well as the brake equipment and bogies) and so the transformer, auxiliary converters, batteries and (I think?) compressors are in the driving vehicles. It's just how they designed a bi-mode train to meet the DfT spec and within our restricted loading gauge when compared to Europe and Japan.

It may have also been because of the need to work them in multiple at up to 125 mph. When operating as a 10 car, usually the front pantograph on the front unit is raised and the rear pantograph of the rear unit is raised. If the front both units is raised, or the rear pantograph of both units is raised, there is a speed restriction of 100mph. If the pantographs closest together are raised (so the rear of the front set, and front of the rear set) there is a speed restriction of 80mph. Moving the pantographs to the centre of the train on a 5 car unit would have probably prevented 125mph running when operating as a 10 car as there wouldn't have been enough distance between them.

The nine cars are simply a longer version of the 5 car train with a common design, having an additional motor vehicle and two extra trailer vehicles so they have their pantographs in the driving vehicles.