18-12-2011, 03:39 PM
Thank you for your interest. This is encouraging.
I don't want to turn this into a 'train-spotting' thread, nor make it too complex and boring.
Today, I will try to describe the basic design of the power circuits on the locomotive.
When running as an electric locomotive, 73140 takes power from a conductor rail through collector shoes. The voltage varies, but is usually around 850V and the current can be 2000A when starting with a heavy load. A 110V supply for the control equipment is supplied from a motor-generator set which is simply a machine comprising of 850V motor and 110V generator wound on the same armature, but with separate commutators at each end.
When running as a diesel-electric locomotive, the collector shoes are retracted and a diesel engine drives a pair of generators. A 'main generator' supplies current for the traction motors and an 'auxiliary generator' provides 110V DC for the control equipment. This assembly is called the power unit.
73140 has the power unit at one end of the locomotive and the electrical control equipment at the other for two reasons. The first is to keep high voltage equipment away from anyone servicing the diesel engine and the other is to prevent dirt and oil contamination of the electrical equipment.
73140 has four wheelsets (a wheelset is an axle with a wheel at each end). There are two wheelsets under each bogie and a bogie under each end of the locomotive. All the axles carry a traction motor between the wheels (normally hidden from view). The two motors under each bogie are permanently connected in parallel.
Under electric operation, the traction motors are initially connected as two series groups of two motors in parallel. As the locomotive speed increases, the motors are connected in parallel. The voltage across the motors is increased by short-circuiting sections of the main starting resistors under the control of an electrically-driven camshaft. Once maximum speed has been attained, a further increase in motor speed is obtained by four stages of weak field diversion under the control on another electrically-driven camshaft. Inductive shunts are connected in series with the field divert resistors to prevent damage caused by motor flashovers.
Under diesel operation, current for the traction motors is obtained from the main generator (driven directly from the engine crankshaft). The generator output is varied by a combination of engine speed and control of generator field excitation by a electrically-driven load regulator. The starting resistors are therefore not required under diesel operation until the motors are re-grouped from series to parallel. Weak field diversion operates using the camshaft, but this time under the control of the diesel engine load regulator.
All power circuits are connected using electro-pneumatic line breakers rated at 2000A DC current at 1000V.
(no, you definitely do not want to stand near them or look at them when they operate under full load).
That is probably enough said about the power circuits for now.
It may be easier to consider the operation of the power circuits in a more familiar form......
Take four (say 12V) DC motors and connect them permanently as two parallel pairs.
Then connect the two parallel pairs in series.
Put some resistance in series with the motors and apply 12V.
Progressively short out the resistance in stages until it is zero and the motors are running at half speed (6V across each pair of motors).
Reconnect the two parallel pairs in parallel.
Put the resistance back in and reconnect 12V.
Progressively short out the resistance in stages until it is zero and the motors are running at full speed (12V across each pair of motors).
The motors cannot run any faster as it stands.
Now divert some of the field current by putting some resistance across the field of each motor i.e. weak fielding the motors.
The motors will now run faster.
Now further weaken the field by putting additonal resistances across the field of each motor until four stages of weak field have been applied.
The motors are now running at maximum speed in full weak field, and the locomotive will be running at maximum speed.
Perhaps the attached power schematic will help too....
The line breakers to connect the motors close in sequence L1, L3, JR, ISC and L2 under electric operation and L7, L5, L6, ISC, J and L2 under diesel operation.
Some clever interlocking prevents faulty operation such as connecting the output of the main generator to the live rail! Ouch.
OL1, OL2 are overload relays, CBR is the current balance relay to ensure the current though M1+M2 = the current through M2+M4, and WSR are wheelslip relays to prevent wheel spinning. All to be explained next time.
Logically, when moving in a forward direction, the front (or leading) half of the locomotive will be moving forwards, but the rear (or trailing) half will be travelling in reverse. This is a bit confusing until you understand the concept. The direction of travel is changed by reversing the field current on all four traction motors (while the locomotive is stationary of course!).
I shall try and describe some of the control equipment next time; sufficient to say that this has to be complex by it's very nature.
I don't want to turn this into a 'train-spotting' thread, nor make it too complex and boring.
Today, I will try to describe the basic design of the power circuits on the locomotive.
When running as an electric locomotive, 73140 takes power from a conductor rail through collector shoes. The voltage varies, but is usually around 850V and the current can be 2000A when starting with a heavy load. A 110V supply for the control equipment is supplied from a motor-generator set which is simply a machine comprising of 850V motor and 110V generator wound on the same armature, but with separate commutators at each end.
When running as a diesel-electric locomotive, the collector shoes are retracted and a diesel engine drives a pair of generators. A 'main generator' supplies current for the traction motors and an 'auxiliary generator' provides 110V DC for the control equipment. This assembly is called the power unit.
73140 has the power unit at one end of the locomotive and the electrical control equipment at the other for two reasons. The first is to keep high voltage equipment away from anyone servicing the diesel engine and the other is to prevent dirt and oil contamination of the electrical equipment.
73140 has four wheelsets (a wheelset is an axle with a wheel at each end). There are two wheelsets under each bogie and a bogie under each end of the locomotive. All the axles carry a traction motor between the wheels (normally hidden from view). The two motors under each bogie are permanently connected in parallel.
Under electric operation, the traction motors are initially connected as two series groups of two motors in parallel. As the locomotive speed increases, the motors are connected in parallel. The voltage across the motors is increased by short-circuiting sections of the main starting resistors under the control of an electrically-driven camshaft. Once maximum speed has been attained, a further increase in motor speed is obtained by four stages of weak field diversion under the control on another electrically-driven camshaft. Inductive shunts are connected in series with the field divert resistors to prevent damage caused by motor flashovers.
Under diesel operation, current for the traction motors is obtained from the main generator (driven directly from the engine crankshaft). The generator output is varied by a combination of engine speed and control of generator field excitation by a electrically-driven load regulator. The starting resistors are therefore not required under diesel operation until the motors are re-grouped from series to parallel. Weak field diversion operates using the camshaft, but this time under the control of the diesel engine load regulator.
All power circuits are connected using electro-pneumatic line breakers rated at 2000A DC current at 1000V.
(no, you definitely do not want to stand near them or look at them when they operate under full load).
That is probably enough said about the power circuits for now.
It may be easier to consider the operation of the power circuits in a more familiar form......
Take four (say 12V) DC motors and connect them permanently as two parallel pairs.
Then connect the two parallel pairs in series.
Put some resistance in series with the motors and apply 12V.
Progressively short out the resistance in stages until it is zero and the motors are running at half speed (6V across each pair of motors).
Reconnect the two parallel pairs in parallel.
Put the resistance back in and reconnect 12V.
Progressively short out the resistance in stages until it is zero and the motors are running at full speed (12V across each pair of motors).
The motors cannot run any faster as it stands.
Now divert some of the field current by putting some resistance across the field of each motor i.e. weak fielding the motors.
The motors will now run faster.
Now further weaken the field by putting additonal resistances across the field of each motor until four stages of weak field have been applied.
The motors are now running at maximum speed in full weak field, and the locomotive will be running at maximum speed.
Perhaps the attached power schematic will help too....
The line breakers to connect the motors close in sequence L1, L3, JR, ISC and L2 under electric operation and L7, L5, L6, ISC, J and L2 under diesel operation.
Some clever interlocking prevents faulty operation such as connecting the output of the main generator to the live rail! Ouch.
OL1, OL2 are overload relays, CBR is the current balance relay to ensure the current though M1+M2 = the current through M2+M4, and WSR are wheelslip relays to prevent wheel spinning. All to be explained next time.
Logically, when moving in a forward direction, the front (or leading) half of the locomotive will be moving forwards, but the rear (or trailing) half will be travelling in reverse. This is a bit confusing until you understand the concept. The direction of travel is changed by reversing the field current on all four traction motors (while the locomotive is stationary of course!).
I shall try and describe some of the control equipment next time; sufficient to say that this has to be complex by it's very nature.
