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Well Marconi is close enough that I have to give it to him. Yes, made by BTH, yes brushes are shorted together and run on a comm to create rotor repulsion, yes power is applied to stator only. However, repulsion is only used for starting - it's a Repulsion-Start, Induction-Run (RSIR or R/I) machine.

There are two ways to do this. Century and others in the USA, used a centrifugal mechanism like the starting switch of a split-phase induction, but instead of operating a switch, as the motor approaches full speed it does two things. It triggers a spring-loaded actuator that lifts the brushes off the comm (to save wear) and puts a shorting ring around all the commutator segments to convert the armature into the equivalent of a squirrel cage.

This BT-H (then part of AEI) avoids the centrifugal mechanism by having two windings on the rotor. The repulsion winding brought out to the commutator, and a separate squirrel cage. At a standstill, the high slip frequency puts the cage current out of phase due to its inductance (which is why inductions typically have poor starting torque.) But the repulsion winding takes over and accelerates the motor, at a speed and direction controlled as Marconi mentions, by the setting of the brush rocker. As the speed increases and the slip frequency reduces, the cage torque dominates and the relative placing of the windings in the slots causes the magnetic flux to bypass the repulsion winding, so the motor runs as an induction. Unlike the Century there is still brush wear, but it is low because the brushes are passing minimal current.

Why go to all this complication to start an induction motor? Simply because repulsion motors have excellent starting characteristics. Smooth and torquey, without the excessive line current required by other starting methods, despite being single-phase (which were always inferior to 3-phase at starting). RSIRs handle high inertia loads and starting against full torque, but once running they are not as efficient as inductions and lack the near-constant speed. Hence, to deal with difficult loads with only single-phase power available, start as induction for best torque and lowest overcurrent, then run as induction for best efficiency and stability.

I've no idea why Tel sees it heading to the skip. It's worked fine for 80 years and will probably be good for another 80. I'm sure skips will have been banned by then.

I don't even know which part of the photo we are looking at

The round thing bottom centre :)
 
LN is a master at framing his image. Why for example:

1. Is there a box with vents? (Which looks newer vintage to the motor.)
2. are there 3 lengths of vertical conduit?
3. are there 2 lengths of flexi conduit going under the box with vents?
4. do the connections to the motor (middle conduit) not directly connect to the vented box?
5. Where do the 3 vertical conduits end up?
6. Is the bottle a clue?
 
I think our posts crossed! If you know organ blowers, there are indeed lots of clues.

1. Transformer-rectifier for the 18V DC electric action. Yes it's newer.
2. To keep it off the floor, it's run across the ceiling.
3. No specific reason.
4. No, quite separate.
5. Motor supply from DOL starter, rectifier supply from contactor, rectifier output to DC busbars
6. Incidental. There are often old bottles of oil in organ blower rooms.

Organ clues include the Watkins & Watson shaft coupling, tantalising glimpse of flexible coupling top right, a similar hint of wind trunking, ancient masonry and age of plant. Organ blowers have a very high moment of inertia and have to start against heavier load that is usual for a fan or pump (because they are rated to work against backpressure and can overload the motor when filling the reservoirs). Hence the preference for an RSIR where there is no 3-phase supply.
 
LN is a master at framing his image. Why for example:

1. Is there a box with vents? (Which looks newer vintage to the motor.)
2. are there 3 lengths of vertical conduit?
3. are there 2 lengths of flexi conduit going under the box with vents?
4. do the connections to the motor (middle conduit) not directly connect to the vented box?
5. Where do the 3 vertical conduits end up?
6. Is the bottle a clue?

I think our posts crossed! If you know organ blowers, there are indeed lots of clues.

1. Transformer-rectifier for the 18V DC electric action. Yes it's newer.
2. To keep it off the floor, it's run across the ceiling.
3. No specific reason.
4. No, quite separate.
5. Motor supply from DOL starter, rectifier supply from contactor, rectifier output to DC busbars
6. Incidental. There are often old bottles of oil in organ blower rooms.

Organ clues include the Watkins & Watson shaft coupling, tantalising glimpse of flexible coupling top right, a similar hint of wind trunking, ancient masonry and age of plant. Organ blowers have a very high moment of inertia and have to start against heavier load that is usual for a fan or pump (because they are rated to work against backpressure and can overload the motor when filling the reservoirs). Hence the preference for an RSIR where there is no 3-phase supply.

It's great watching the two masters spar! It's like Bobby Fisher (Marconi) and Kasparov (LN)!
 
ps.. My apologies LN but I did not remove the CU containing the 45A mem fuse holder so I cannot send it to you. :(
 
Well Marconi is close enough that I have to give it to him. Yes, made by BTH, yes brushes are shorted together and run on a comm to create rotor repulsion, yes power is applied to stator only. However, repulsion is only used for starting - it's a Repulsion-Start, Induction-Run (RSIR or R/I) machine.

There are two ways to do this. Century and others in the USA, used a centrifugal mechanism like the starting switch of a split-phase induction, but instead of operating a switch, as the motor approaches full speed it does two things. It triggers a spring-loaded actuator that lifts the brushes off the comm (to save wear) and puts a shorting ring around all the commutator segments to convert the armature into the equivalent of a squirrel cage.

This BT-H (then part of AEI) avoids the centrifugal mechanism by having two windings on the rotor. The repulsion winding brought out to the commutator, and a separate squirrel cage. At a standstill, the high slip frequency puts the cage current out of phase due to its inductance (which is why inductions typically have poor starting torque.) But the repulsion winding takes over and accelerates the motor, at a speed and direction controlled as Marconi mentions, by the setting of the brush rocker. As the speed increases and the slip frequency reduces, the cage torque dominates and the relative placing of the windings in the slots causes the magnetic flux to bypass the repulsion winding, so the motor runs as an induction. Unlike the Century there is still brush wear, but it is low because the brushes are passing minimal current.

Why go to all this complication to start an induction motor? Simply because repulsion motors have excellent starting characteristics. Smooth and torquey, without the excessive line current required by other starting methods, despite being single-phase (which were always inferior to 3-phase at starting). RSIRs handle high inertia loads and starting against full torque, but once running they are not as efficient as inductions and lack the near-constant speed. Hence, to deal with difficult loads with only single-phase power available, start as induction for best torque and lowest overcurrent, then run as induction for best efficiency and stability.

I've no idea why Tel sees it heading to the skip. It's worked fine for 80 years and will probably be good for another 80. I'm sure skips will have been banned by then.



The round thing bottom centre :)

Clearer now Happyhippydad..?
 
I did not remove the CU containing the 45A mem fuse holder

No worries, people keep your eyes peeled for good examples of Wylex CUs with a 45A rewireable in. Especially the type with the separate 45A way the opposite side of the main switch. Also the E7 one with normal and off-peak in the same box.

Anyway, here's a pic of a 3hp BTH RSIR of my own and its plate. Not sure why I can't delete the duplicate pics, but I have a beer to drink so it will have to do.

What kind of motor is this? other 3hp RSIR plate - EletriciansForums.net

What kind of motor is this? other 3hp RSIR - EletriciansForums.net

View attachment 49710

View attachment 49711
 
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some cast iron control gear for vetilation equipment recently,

Any pics? Interested if 1930s or earlier, or unusual design etc.
 
Hmm, another duplicate post deleted, not sure why these are happening.
 
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It’s obviously steam powered, the wire is actually a pipe and there is a self contained boiler in the enclosure at the rear.
Neither Fleming’s Left or Right hand rules apply here.
 
Handy little motor, not sure why they weren't more popular over here. He describes it as a repulsion induction, but I think it's full-time repulsion as it always remains under the control of the brush rocker.
 
That motor is repulsive.
Needs a make over.
My late father used to tell a tale about a call to a factory where there was a long bench with lots of sewing machines driven off a line shaft - and with a motor at the end to drive it. He opened the lid of the enclosure expecting to find it solid with lint - but instead found it spotlessly clean.
One of the machinists explained that every Friday they had a cleanup session and always included inside the box with the motor - especially the bright brass bit. Yes, they were polishing the commutator on a running motor :eek:
 
That's not unheard of, Grinding and polishing a comm in the machine's own bearings as it runs, although usually by experienced sparks and 'dynamo attendants.' Normally though, it just needs the dust and carbon blowing out, no actual polishing is necessary, it just leads to excess wear, as the brown oxide coating that builds up is much tougher than the bare metal. Commutation is one of those things that is best experienced in operation, you can tell a lot about the adjustment and condition of the machine and suitability of the brush grade etc by seeing, hearing and feeling. The strapline at the bottom of the in-service maintenance pages of some popular plant used to be 'Use Your Fingers!'
 
Oh yes, machining etc of the comm in situ - great, and done with the power off ?
Untrained people cleaning and polishing the motor while it's powered and running, that's a different matter :eek:
 

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