To accelerate the driver's controller's main handle with the positions "FP" - "RP", he selects the first position after starting the electric locomotive and the head cars, but not earlier than after3 seconds , adds a second position, waits time to set the entire train in motion.
After selecting the gaps in the automatic couplers, when the electric locomotive has traveled 7-10 m, and the train of increased length has reached 10-15 m, the ECG is added one position at a time, also with a delay ofless than 3 seconds , performs acceleration, while ensuring that the current of the traction motors does not exceed 1100-1200 A. The duration of operation of traction motors with a current of 1200 A is no more than 4 minutes.
If the train does not start moving, it is necessary to reset the positions (the TD windings should not be under current when the train is stationary for more than 15 s), compress the train at the rate of 1 m per 20-25 cars and again take the train from its place.
To prevent the electric locomotive from slipping, sand is periodically supplied under the wheel pairs, preventing the supply of sand at the switches.
In order to avoid breaking the train when starting from a stop after stopping with the use of auto brakes, it is allowed to set the electric locomotive in motion only after releasing all the auto brakes on the train. To do this, you need to wait the time from the moment of vacation until the electric locomotive is set in motion on freight trains with the air distributors turned on in flat mode:
o after the braking stage - at least 1.5 minutes;
o after full service braking - at least 2 minutes;
o after emergency braking in trains with a length of up to 100 axles - no less than 4 minutes, more than 100 axles - no less than 6 minutes.
In winterthe time from the moment the driver's crane handle is moved to the release position until the freight train is set in motion after it has stopped must be increased1.5 times .
II. Driving the train around the site
When driving a train along the site, the train is compressed (if braking was previously applied) or stretched (if the electric locomotive is in traction - in positions). To switch from the coasting (braking) mode to the traction mode, the driver manually selects several positions to stretch the train, then selects the required number of positions, otherwise there may be delays in the train. The holding time of the main handle in the “RP” position depends on the number of sections, two sections – 2 s, three sections – 3 s, with speed dial positions there may be desynchronization of the ECG shafts. Along the route, at speeds of 30 km/h and above, up to the 17th position (up to a current value in the TD of 300 A) can be dialed with the “AP” position, and then with the “FP” - “RP” positions, monitoring the voltage and current in the instruments. TD. On electric locomotives VL-80, the voltage should not exceed 950 V, and the current should not exceed 820A for continuous operation and 880A for hourly operation.
Long-term movement in traction mode should be carried out in the running positions of the controller (at the same time, green “0ХП” lamps are lit on the control panel of electric locomotives VL80 K, T, S); movement in the required positions is allowed for 3-5 minutes; they are designed for a smooth change in current and voltage on traction motors.
To switch from the traction (coasting) mode to the braking mode, it is necessary, when the load is removed, to pre-compress the train with the auxiliary brake of the electric locomotive so that there is no overrunning of the tail section. After applying the autobrake, the auxiliary brake of the electric locomotive must be released.
III. Driving the train when moving from the platform to the rise
When approaching a rise, it is desirable that the train reaches the maximum permissible speed, and the traction force of the electric locomotive should not be maximum, since only head part the train will begin to rise, its speed will slow down, and the cars at the rear will catch up with it. The tail section will run in, and large dynamic forces will arise in the train. To prevent this from happening. At the moment of starting the climb, it is necessary to gradually increase the traction force, moving to higher positions, or turn on the weakening of the TD field. If the climb is short, then the weakening of excitation is not removed before entering the pass, and if it is steep and protracted, then in order to avoid overheating of the TED, the weakening of excitation is gradually removed.
IV. Introduction of the train uphill
When following an incline, it is necessary to control the current in the traction motor (as the speed decreases, the current increases), preventing the wheelsets from slipping (at a speed of 45 km/h, the current in the traction motor of VL80 electric locomotives is no more than 880-900 A), which can lead to the shutdown of the hot water supply due to the activation of the RP in the TED. Boxing is determined by the unstable position of the kiloammeter needle (falls) and by the flashing of the “DB” signal lamp. To prevent gearbox failure, sand is fed into the box under the gearbox. However, with frequent (continuous) supply of sand, the resistance to movement increases. If the current in the electric motor approaches the maximum value, according to the conditions of adhesion of the wheel to the rail for a given speed, it is necessary to gradually reduce the current in the electric motor, turning off the weakening of the electric motor field or moving to lower positions; it is allowed to follow the controller in non-running positions for no more than 2-3 minutes. If there are short platforms when moving uphill, it is necessary to restore the maximum controller positions. According to the traction characteristics of the VL-80 electric locomotive, it is possible to reduce positions to the 5th position, but in this case the traction motor may overheat.
V. Driving a train from ascent to descent (platform)
When a train moves from an ascent to a descent (platform):
VI. Driving the train downhill
When the train moves along the descent, the speed of movement is controlled, not allowing the permissible speed to be exceeded. To regulate speed, step braking is used. The first stage of braking is performed by reducing the pressure in the UR in loaded trains by 0.6 - 0.7 kgf/cm2, in empty trains by 0.5-0.6 kgf/cm2, on steep long descents 0.7-0.9 kgf /cm 2 depending on the steepness of the descent. The second stage, if necessary, is performed after at least 5 seconds. after the release of air from the line through the driver's tap stops. If it is necessary to apply full service braking, as well as during regulatory braking when following a descent, the TM should not be discharged to a pressure below 3.8 kgf/cm 2 .
Repeated braking must be performed in a cycle consisting of braking and releasing when the required speed is reached. In order to prevent depletion of the auto brakes on the train when traveling along a descent on which repeated braking is performed, it is necessary to maintain a time of at least 1 minute between braking to recharge the train's brake network.
To fulfill this requirement, you should not do frequent braking and release the brakes at high speeds. The time of continuous movement of a train with a constant level of braking on a descent when the air distributors are switched on to the flat mode should, as a rule, not exceed 2.5 minutes. If longer braking is necessary, it is necessary to increase the TM discharge by 0.3-0.5 kgf/cm 2 and, after sufficiently reducing the speed, release the auto brakes.
When the train brakes are released, the auxiliary brake of the electric locomotive is activated to prevent the head of the train from jerking.
Braking of the electric locomotive and the train can be carried out by the electric brake of the electric locomotive (if available, which can be used to pre-braking the electric locomotive, automatically maintaining a constant speed on the descent, and stopping braking.
VII. Driving the train along the descent with a transition to the platform and again to the descent
Such sections of the track profile cause compression of the train when the train moves from the descent to the platform, and when moving from the platform to the descent, acceleration of the head part and reaction to rupture. The same reaction occurs when a train moves from a lower slope to a steeper slope.
When the train follows a descent with a transition to a platform and again to a descent or a steeper descent, an auxiliary brake of the electric locomotive is applied at the point of the profile bend and is released in stages after the entire train has reached the descent, depending on the speed of movement.
VIII. Driving a train during the transition from descent to ascent.
In such places on the site, wagons may be squeezed out, because at the point of transition from descent to ascent, the train is compressed, because the head part receives additional resistance to movement from the ascent and at the moment of entering the ascent it is necessary to significantly increase the traction force:
- when the train changes from starting to rising, it is necessary Towards the end of the descent, release the brakes in such a way that by the beginning of the ascent the train does not exceed the maximum permissible speed, taking into account the inclusion of traction;
- at the end of the descent manual dialing 9-13 positions stretch the train;
- further, when the head of the train enters the ascent, automatic dialing dial maximum amount positions;
- Further enable field weakening TD, in in this case It is important that the train travels along the incline in a stretched state.
IX. Driving a train along a broken profile
These places are characterized by the fact that the length of the descents and ascents is less than the length of the train, and the descents can prevail over the ascents.
Such places must be followed at an average speed, to the 17-21 positions of the controller using OP1-3 TED. When the head of the train is approaching an ascent, increase the traction force, and decrease it when descending. In such places, apply braking until the train stops.
X. Stop on the rise.
To stop on an incline:
XI. Starting procedure on an uphill climb.
1. If the train is held in place by the auxiliary brake of an electric locomotive , after releasing the brakes:
a) train stop in a stretched state;
b)start off after the brakes have been fully released ;
c) dial 1-2 positions when the TC of the electric locomotive is filled;
d)3rd with simultaneous release of the auxiliary brake .
2. If the train is not held in place by the electric locomotive's auxiliary brake , Then:
a) before stopping Squeeze the train and do not release the brakes;
b) it is necessary to know after what time, when released in the 2nd position of KM No. 395, the train starts moving backwards;
c) reduce this time by 5-10 seconds. And take the train from its place in a compressed state, while releasing the brakes in the 2nd position.
XII. Stop at a profile fracture. Starting order.
Stop the train, if possible, in a stretched state; in this case, at the moment of starting, a reaction to rupture does not occur.
Most dangerous case, when the main part of the train is on the descent and is compressed, and the smaller part is on the rise and is stretched. Release the auto brakes and, after waiting for the time for complete release, release the auxiliary brake in stages, while not allowing the head of the train to accelerate; complete release is only when the entire train is in motion.
XIII. Stop on the descent. Starting order.
In any case, when applying automatic brakes, the train is compressed.
If the train is held in place by the brake of an electric locomotivestart by waiting until the brakes are fully released and releasing the locomotive brake in stages to ensure that the entire train starts moving without allowing the head of the train to accelerate. If the train is not held in place by the electric locomotive brake, do not release the car brakes while in the parking lot. Before starting, release the auto brakes and, if possible, wait as long as possible. full pressure in the TC of the electric locomotive until the moment it starts moving, then feeding sand under the wheelsets, releasing the auxiliary brake in small steps to ensure that the entire train starts moving without allowing the head part to accelerate.
Measures to prevent train rupture
To avoid a train breakdown it is necessary:
- Realizesmooth starting of the train with slow movement of the operator controller handle to running positionstaking into account the length of the train and the track profile , while the traction force on the automatic coupler is:
when starting - 95 t;
when driving a train - 130 tons;
The maximum automatic coupler can withstand is 300 tons.
2. Move or pull a train it should only be connected to the established signalafter the brakes are fully released all carriages of the train.
3. Recovering the train from a place after a sharp compression by the locomotive of the head of the train when settlingnecessary, waiting for a possible delay the tail of the train.
4. Drive the train along the routetaking into account the features of the track profile fracture , in which it is possible for cars to run in and pull out on a train, using regime maps to help.
5. Brake correctly and release the brakes in a timely manner when the train stops at a station or on a stretch. When braking a train, as a result of the non-simultaneous action of the brakes in the initial period and the uneven braking forces of different cars, dynamic forces arise during the braking process.
During the development of the braking force of a train, four phases can be distinguished:
first phase - propagation of the wave of braking and compression of the train, since when the brakes of the tail cars begin to operate, the head cars are partially braked. Due to different gaps in automatic coupling devices and unequal braking forces during the compression process, groups of cars are formed that roll onto the already compressed group in front at high relative speeds. This leads to the emergence of shock forces acting in the direction of train movement;
second phase - uniform increase in pressure in the brake cylinders. The train remains compressed. A short but sharp blow and pull of the tail section occur. This phase is characterized by the greatest run-up of tail cars and reactions in the train;
third phase - pressure equalization occurs in the brake cylinders. Braking forces increase to maximum and uniform values throughout the train. The rush of the tail cars stops. Previously compressed shock-traction devices produce recoil, which causes a pull or twitching;
fourth phase - characterized by braking with maximum force. An excess of braking forces in the head part of the train compared to the tail causes compression of the shock-traction devices, and then, when the compression force in the head part is greater than the braking force in the tail part, the tail cars are pulled back. The gaps in the automatic coupling device allow the movement of coupled cars without compression of the absorbing devices. Therefore, at the moment of braking, the composition may be in an extended or compressed state. The smoothest braking occurs in a compressed train.
- Before braking begins (200-250 m), the train must be compressed . This is done using tap No. 254 until the pressure in the brake cylinders increases to 1.5-1.7 kgf/cm2.
- The driver must remember thatthe level of longitudinal dynamic reactions is influenced by the gap in the automatic coupling equipment . As a result of braking of compressed trains, small longitudinal forces appear; the presence of gaps in a stretched train before braking leads to an increase in longitudinal forces, especially during emergency braking.
Control of an electric locomotive under electric braking
To switch the VL-80S electric locomotive to electric braking mode, you must:
- put the main handle of the driver’s controller in position “0”, and the brake handle in position “P”;
- by the extinguishing of the control lamps “C1” and “C2”, we are convinced that the circuit has switched to the electric braking mode;
- you should move the brake handle to the “PT” position, while the braking force gradually (within 1-2 seconds) increases to 10 tons per axle.
- After waiting the time necessary to compress the train, move the brake handle to the “T” position, and the braking force increases from 20 to 50 tf. depending on the brake force adjuster;
- to move downhill at a constant speed, use the brake handle to set the required speed;
- it is necessary to control the armature current, which should not exceed 830 A, and the field current, which should not exceed 1100 A;
- the time the TD excitation windings are under a current of 1100A is no more than 7 minutes;
- If the braking force is insufficient to maintain a constant speed on the descent, you can brake the train using the driver's crane cond. No. 394 (395). It is impossible to use the auxiliary brake of an electric locomotive during electric braking, because at a pressure in the TC of 1.3-1.5, the electric brake is disassembled;
- To release the electric brake, the brake lever must be set to position “0”. To cool the braking resistors, do not move the circuit to the Pull position for 1 minute. with auxiliary switches on cars;
- To switch the circuit to the “Traction” mode, it is necessary to move the main handle of the KM to the “AB” position and monitor the extinguishing of the signal lamps on the driver’s console “C1” and “C2”.
Energy Saving Methods
Touching trains from place to produce only with fully released brakes trains (except for starting on an uphill slope).
Acceleration of heavy trains produce with the greatest traction forces, acceptable under the conditions of adhesion of wheels to rails, with rational use of sand.
Acceleration of trains of medium or light mass should be carried out with medium or low currents of traction motors, depending on the starting conditions, avoiding slipping if possible.
Modes weakening of excitation below the 21st position if possible do not apply.
In areas with rare changes in ascents and descents:
Ø on the climbs - withstand below average speed calculated;
Ø on the slopes – speed higher than average calculated
When approaching Towards the beginning of steep climbs, the train speed should be brought to the maximum permissible.
Do not use reduced excitation mode for short periods of time .
Transition from ascent to descent produce at a slightly reduced speed if there is no train delay.
When the train stops it is desirable that the entire composition or part of it stopped on the way down.
During surge lateness accelerate the train on slopes and flat sections and make extensive use of rheostatic or regenerative braking.
Safety measures when moving an electric locomotive along a stretch,
during shunting work
and movement of an electric locomotive by another electric locomotive
1. While driving locomotive is prohibited:
a)protrude from the side windows of the control cabin beyond the safety glass (paravan);
b)open external entrancedoors and lean out of them;
c)get up for an electric locomotiveand go down while driving;
d)short-circuit protective interlocks ;
e)the assistant driver must be in the engine room when setting (resetting) positions and when turning on (turning off) the train heating contactor. If it becomes necessary to reset the positions while the assistant driver is in the engine room, the driver must turn off the main switch;
f) open doors, curtains andenter the high voltage chamber , including with pantographs lowered;
g)manually turn on the main switch .
2. When an oncoming train moves the team must:
a)monitor his condition and in case of detection of sparking, overshooting or other damage to the oncoming train, immediately notify by radio the driver of the oncoming train and the attendant of the nearest station;
b)The driver's assistant must go to the driver's workplace ;
c) in the darkswitch the spotlight to position"Low light", so as not to blind the crew of the oncoming train;
d) after passing the head of the oncoming train, it is necessaryturn on the spotlight to the “Bright light” positionto inspect the carriages of an oncoming train .
3. If necessary, inspect the crew part When stopping an electric locomotive, the driver must:
a)brake the locomotive , make sure that he cannot move, and only after that the driver and assistant can get off the locomotive;
b)for inspection the crew is necessarystart onlyafter graduationrunning and pulling of cars trains;
c) brigadeIt is prohibited to inspect the carriage section when a train is passing along an adjacent track .
Requirements of safety regulations in the event of a forced stop, the occurrence of faults in the contact network and in the event of damage to the electric locomotive
When a train is forced to stop during a stretch, the driver is guided by clause 16.43 of the PTE and is obliged to:
1. stop the train if possible, on a platform and a straight section of the track, unless an emergency stop is required;
2. activate the train's automatic brakes Andauxiliary brake locomotive;
3. immediatelyannounce a stop via radio locomotive drivers traveling along the stretch, and duty officers at stations limiting the stretch;
4. if the stop is not due to the train being delayed at a traffic light with a prohibitory indication,to figure out its reasons andpossibility of further travel ;
5. if train traffic cannot be resumedwithin 20 mini more and there is no way to hold the train in place using auto brakes,apply the handbrake of the locomotive and give a signal to activate the existing ones in the compositionhand brakes . The assistant driver mustwill lay down b under the wheels of cars available on the locomotivebrake shoes , and if there is a shortage of them, in addition, apply the hand brakes of the cars in accordance with the Brake Operating Instructions; additionally inform the station duty officer (train dispatcher) via train radio about the reasons for the stop and necessary measures to eliminate any obstacles to traffic;
6. together with all employees servicing the train,take measures to eliminate the obstacle to traffic , and in necessary casesprovide train fencing and adjacent path.
7. in cases of activation of rolling stock derailment control devices when stopping a train due to a violation of the integrity of the brake line, identifying a derailment of rolling stock, and in all cases when stopping an oncoming train is required, the driver is obligedturn on the red lights at the buffer beam (if necessary, turn the spotlight on and off repeatedly). The red lights of the lamps at the buffer beam are a stop signal for the driver of an oncoming train. The driver of an oncoming train stops without passing the head of the stopped train, and after receiving information in person or via radio about the presence of a clearance, continues to move at a speed of no more than 20 km/h with special vigilance and readiness to stop if an obstacle to further movement is encountered;
Driving freight trains along various track profile elements. The order of stopping on a different route profile, starting from a place.
General provisions.
When moving, a freight train, consisting of a lead locomotive and a train of freight cars, is a complex mechanical system that is subject to many forces. The train itself is a set of rigid elements (cars) connected to each other by flexible connections (automatic couplers with absorbing devices). Load in cars, for example “liquid”, can move during movement and have an effect on the train. The track profile is heterogeneous, consisting of platforms and slopes (ascents, descents) of various lengths and steepness. The cars have different loadings and are located chaotically along the length of the train. There are speed limit points along the train route, which are located on an unfavorable track profile. To fulfill the schedule, the driver has to constantly change the train's movement modes. All of the listed factors during movement influence the occurrence of longitudinal dynamic reactions in the train, which can cause breakage of the automatic coupler, displacement of the cargo, and derailment of the cars.
When moving, as a rule, the train is in three states: compressed, semi-compressed, stretched. The basis for reducing longitudinal dynamic reactions is a smooth transition from one state to another. To do this, the driver, in accordance with the track profile, weight and length of the train, and the location of the loaded cars, sets and resets the controller positions accordingly, applies the auxiliary brake of the electric locomotive, and performs service braking. Due to constantly changing operational factors, each driver implements different modes of driving trains in his own way, guided by regime maps, experience, and intuition.
The main factors for the automatic transition of a train from one state to another are:
- The locomotive has a greater main resistance to movement in relation to the cars, therefore, after turning off the traction, the train on any track profile goes into a semi-compressed state.
- When using the auxiliary brake of a locomotive or using automatic brakes, the train is compressed, and a reaction occurs to the squeezing out of the cars.
- When the auxiliary brake or automatic brakes are released, due to the action of the compressed springs of the absorbing devices of the automatic couplers, the head or tail of the train receives acceleration and a reaction to the train breaking occurs.
- A sharp increase in traction force causes an increasing reaction along the train from head to tail to the train breaking, this is especially dangerous when parked if the time for releasing the brakes at the tail of the train is not met.
Along the route, it is prohibited to use an electric brake when following a prohibitory signal, which is auxiliary for regulating the speed and stopping the wheelsets from slipping.
Starting off and accelerating the train when leaving the station.
During the initial departure phase, the train is given a warning push. This measure is necessary in case there are station workers or other persons crossing the tracks under the carriages. The starting should be further accompanied by a stop of the train, while the tail cars should move by 1-2 m.
Having made sure that there are no people along the train, the driver sets the train in motion by dialing 1-2 positions (VL80s), then makes a pause to set the entire train in motion (5-10 m of electric locomotive movement). If the train does not start moving at the 2nd position of the controller, then before dialing the 3rd position, fill the TC of the electric locomotive, turn on the 3rd position and release the locomotive brake in stages.
All bodies are capable of deformation only to a certain limit. When this limit is reached, the body collapses. For example, a thread breaks when its elongation exceeds known value; the spring breaks when it is bent too much, etc.
Rice. 87. If you pull the bottom thread slowly, the top thread will break.
Rice. 88. By sharply pulling the bottom thread, you can break it, leaving the top thread intact
To explain why the destruction of a body occurred, it is necessary to consider the movement that preceded the destruction. Let us consider, for example, the reasons for breaking the thread in such an experiment (Fig. 87 and 88). A heavy load is suspended on a thread; a thread of the same strength is attached to the load below. If you pull the lower thread slowly, the upper thread on which the load hangs will break. If you pull the bottom thread sharply, it will be the bottom thread that breaks, not the top thread. The explanation for this experience is as follows. When the load is hanging, the upper thread has already been stretched to a certain length and its tension force balances the force of attraction of the load to the Earth. By slowly pulling the lower thread, we cause the load to move downward. Both threads are stretched, but the top thread is stretched more, since it has already been stretched. That's why it breaks earlier. If you sharply pull the lower thread, then as a result large mass load, even with a significant force acting from the thread, it will receive only a slight acceleration, and therefore for a short time jerk, the load will not have time to acquire a noticeable speed and move any noticeably. Almost the load will remain in place. Therefore, the upper thread will no longer lengthen and will remain intact; the lower thread will elongate beyond the permissible limit and break.
In a similar way, ruptures and destruction of moving bodies occur in other cases. To avoid ruptures and destruction when sudden change speed, you need to use clutches that can stretch significantly without breaking. Many types of couplings, such as steel cables, do not themselves have such properties. Therefore, in cranes, a special spring (“shock absorber”) is placed between the cable and the hook, which can significantly extend without breaking, and thus protects the cable from breaking. Hemp rope, which can withstand significant elongation, does not need a shock absorber.
They are also destroyed fragile bodies, such as glass objects, when dropped onto a hard floor. In this case, there is a sharp decrease in the speed of the part of the body that touched the floor, and deformation occurs in the body. If the elastic force caused by this deformation is not sufficient to immediately reduce the speed of the rest of the body to zero, then the deformation continues to increase. And since fragile bodies can withstand only small deformations without destruction, the object breaks.
63.1. Why does the coupling of the train cars sometimes break when an electric locomotive suddenly moves away? In which part of the train is the rupture most likely to occur?
63.2. Why are fragile items placed in shavings during transportation?
The theory of train movement is integral part applied science of train traction, studying issues of train movement and locomotive operation. For a clearer understanding of the operating process of an electric locomotive, it is necessary to know the basic provisions of this theory. First of all, let's consider the main forces acting on the train when moving - this is the traction force F, the resistance to movement W, the braking force B. The driver can change the traction force and braking force; the force of resistance to movement cannot be controlled.
How are these forces formed, what do they depend on? We have already said that each driving wheel pair of an electric locomotive has a separate traction motor, which is connected to it by a gear reducer (Fig. 3, a). The small gear wheel of the gearbox (gear) is mounted on the shaft of the traction motor, and the large one is mounted on the axis of the wheelset. Teeth ratio big wheel to the number of small teeth is called the gear ratio. If you start the traction motor, a torque is created on its shaft. The speed of rotation of the wheelset will be 1 time less than the speed of rotation of the engine shaft, but the torque is correspondingly 1 time greater (if you do not take into account the coefficient useful action gear transmission).
Let's consider the conditions necessary for an electric locomotive to start moving.
If the wheels of the electric locomotive did not touch the rails, then after starting the traction motors they would simply rotate, remaining in the same place. However, due to the fact that the wheels of the locomotive come into contact with the rails when torques M are transmitted to the axles of the wheel pairs, an adhesion force appears between the surfaces of the wheels and the rails.
In passing, we note that initially, when creating the first locomotives - steam locomotives, they generally doubted the possibility of their movement along a “smooth” rail track. Therefore, it was proposed to create gearing between the wheels of the locomotive and the rails (Blenkinson locomotive). A locomotive was also built (Brunton locomotive), which moved along the rails with the help of special devices that were alternately pushed off the track. Fortunately, these doubts were not justified.
The moment M (see Fig. 3) applied to the wheel forms a pair of forces with the shoulder R. The force FK is directed against the movement. It tends to move the reference point of the wheel relative to the rail in the direction opposite to the direction of movement. This is prevented by the reaction force of the rail, the so-called adhesion force Fcu, which arises under the action of pressing the wheel on the rail at the support point. According to Newton's third law, it is equal and opposite to the force FK. This force forces the wheel, and therefore the electric locomotive, to move along the rail.
At the point of contact of the wheel with the rail there are two points, one of which belongs to the bandage Ab, and the other to the rail Ar. For an electric locomotive standing still, these points merge into one. If, during the transfer of torque to the wheel, point Ab moves relative to point Lp, then in the next instant the points of the bandage will begin to alternately come into contact with point Lp. In this case, the locomotive does not start moving, and if it was already moving, then its speed sharply decreases, the wheel loses its support and begins to slip relative to the rail - slipping.
In the case when points Ap and Ab do not have a relative displacement, at each subsequent moment of time they leave contact, but at the same time the following points continuously come into contact: BB with Br, Wb with BP, etc.
The point of contact between the wheel and the rail represents the instantaneous center of rotation. Obviously, the speed with which the instantaneous center of rotation moves along the rails is equal to the speed of the forward motion of the locomotive.
To move an electric locomotive, it is necessary that the adhesion force at the point of contact between the wheel and the rail feu, equal but opposite in direction to the force FK, does not exceed a certain limit value. Until it reaches it, the force FC creates a reactive torque FCVLR, which, according to the condition of uniform motion, must be equal to the torque.
The sum of the adhesion forces at the points of contact of all wheels of the electric locomotive determines the total force, called the tangential traction force FK. It is not difficult to imagine that there is a certain maximum traction force, limited by adhesion forces, at which boxing does not yet occur.
The emergence of adhesion force can be somewhat simplified as follows. There are irregularities on the seemingly smooth surfaces of rails and wheels. Since the contact area (contact surface) of the wheel and rail is very small, and the load from the wheels on the rails is significant, large pressures arise at the point of contact. The irregularities of the wheel are pressed into the irregularities on the surface of the rails, resulting in the adhesion of the wheel to the rail.
It has been established that the adhesion force is directly proportional to the pressing force - the load from all moving wheels on the rails. This load is called the adhesion weight of the locomotive.
To calculate the maximum traction force that a locomotive can develop without exceeding the adhesion force, in addition to the adhesion weight, it is also necessary to know the adhesion coefficient. By multiplying the adhesion weight of the locomotive by this coefficient, the traction force is determined.
The work of many scientists and practitioners is devoted to the problem of maximizing the use of adhesion between wheels and rails. It has not yet been finally resolved.
What determines the value of the adhesion coefficient? First of all, it depends on the material and condition of the contacting surfaces, the shape of the bands and rails. With increasing hardness of tires of wheelsets and rails, the coefficient of adhesion increases. When the rail surface is wet and dirty, the coefficient of adhesion is lower than when it is dry and clean. The influence of the rail surface condition on the adhesion coefficient can be illustrated by the following example. In the Trud newspaper of December 13, 1973, in the article “Snails against the steam locomotive,” it was reported that one of the trains in Italy was forced to stop for several hours. The reason for the delay turned out to be great amount snails crawling across the railroad tracks. The driver tried to guide the train through this moving mass, but to no avail: the wheels were slipping and he could not budge. Only after the stream of snails thinned out was the train able to move.
The adhesion coefficient also depends on the design of the electric locomotive - the spring suspension device, the switching circuit of the traction motors, their location, the type of current, the state of the track (the more the rails are deformed or the ballast layer sags, the lower the realized adhesion coefficient) and other reasons. How these reasons influence the implementation of traction force will be discussed further in the relevant paragraphs of the book. The adhesion coefficient also depends on the speed of the train: at the moment the train starts to move, it is greater; with increasing speed, the realized adhesion coefficient first increases slightly, then falls. As is known, its value varies widely - from 0.06 to 0.5. Due to the fact that the adhesion coefficient depends on many factors, to determine maximum strength the traction that an electric locomotive can develop without slipping is used using the calculated adhesion coefficient. It represents the ratio of the greatest traction force, reliably realized under operating conditions, to the adhesion weight of the locomotive. The calculated coefficient of adhesion is determined using empirical formulas that depend on speed; they are based on numerous studies and experimental trips, taking into account the achievements of advanced machinists.
When starting from a standstill, i.e. when the speed is zero, the coefficient for direct current electric locomotives and dual power supply is 0.34 (0.33 for electric locomotives of the VL8 series) and 0.36 for alternating current electric locomotives. Thus, for a double-fed electric locomotive VL 82m, the adhesion weight of which is P = 1960 kN (200 tf), the tangential traction force Fk taking into account the design coefficient.
If the surface of the rails is dirty and the adhesion coefficient has decreased, say, to 0.2, then the traction force Pk will be 392 kN (40 tf). When sand is supplied, this coefficient can increase to the previous value and even exceed it. The use of sand is especially effective at low speeds: up to a speed of 10 km/h on wet rails, the adhesion coefficient increases by 70-75%. The effect of using sand decreases with increasing speed.
It is very important to ensure the highest coefficient of adhesion when starting and moving: the higher it is, the great strength The more traction an electric locomotive can achieve, the greater the mass the train can be driven.
Resistance to the movement of the train W arises due to friction of the wheels on the rails, friction in the axle boxes, track deformation, air resistance, resistance caused by descents and ascents, curved sections of the track, etc. The resultant of all resistance forces is usually directed against the movement and only on very steep descents coincides with the direction of movement.
Resistance to movement is divided into basic and additional. The main resistance acts constantly and occurs as soon as the train begins to move; additionally due to track slopes, curves, outside air temperature, strong wind, starting off.
It is very difficult to calculate the individual components of the main resistance to train movement. It is usually calculated for cars of each type and locomotives of different series using empirical formulas obtained based on the results of many studies and tests in different conditions. The main drag increases as the speed increases. At high speeds, air resistance predominates in it.
Taking into account the main resistance to the movement of the locomotive, in addition to the tangential traction force of the electric locomotive, the concept of traction force on the automatic coupler Fa is introduced (Fig. 4).
In the process of driving a train, brakes are used to reduce speed, stop, or maintain a constant speed on descents, creating a braking force B. The braking force is generated due to friction brake pads o wheel tires (mechanical braking) or when traction motors operate as generators. As a result of pressing the brake pad to the bandage with force K (see Fig. 3, b), a friction force arises on it.
friction. Due to this, an adhesion force B is formed on the bandage at the point of its contact with the rail, equal to the force T. Force B is braking: it prevents the movement of the train.
The maximum value of the braking force is determined by the same conditions as the traction force. To avoid skidding (sliding without rotation of the wheels on the rails) during braking, the condition of friction of the brake pads on the band must be met; it depends on the speed of movement, the specific pressure of the pads on the wheel and their material. This coefficient decreases with increasing speed and specific pressure due to an increase in the temperature of the rubbing surfaces. Therefore, apply bilateral pressure on the wheels when braking.
Depending on the forces applied to the train, three modes of train movement are distinguished: traction (movement under current), coasting (without current), braking.
At the moment of starting and during further movement under current, the train is subject to traction force Fк and resistance to the movement of the train K. The nature of the change in speed depending on time in the section of the OA curve (Fig. 5) is determined by the difference in forces. The greater this difference, the greater the acceleration of the train. Resistance to movement, as already noted, is a variable quantity that depends on speed. It increases with speed. Therefore, if the traction force remains constant, the accelerating traction force will decrease. After a certain point O, the traction force decreases. Then there comes a moment when Fк and the train under current moves at a constant speed (section of the AB curve).
Next, the driver can turn off the engines and continue moving on the coast (BV section) due to the kinetic energy of the train. In this case, the train is only affected by the force of resistance to movement, which reduces its speed if the train is not moving along a steep descent. When the driver turns on the brakes (from point B to point D), two forces act on the train - resistance to movement and braking force B. The speed of the train decreases. The sum of forces B represents the retarding force. It is also possible for a train to move down a steep slope and the driver uses braking force to maintain a constant permissible speed.
The use of electric locomotives is limited by: conditions of adhesion of wheels to rails; the power of traction motors (the highest voltage permissible for switching, and the current in combination with the time of its flow, which determine the heating of the engines), shutdown of the motor, by heating of the motor, by voltage in the motor, by heating the oil in the transformer. In addition to these main limitations, in some cases there may be others, for example, a limitation on the voltage in the contact network at the time of regeneration and on the ratio of the armature current and the excitation current of the motors in electric braking mode. When taking a train from a stop on a heavy climb on DC electric locomotives, one has to take into account the possible overheating of the starting resistors.
On AC electric locomotives, when the voltage in the contact network drops to 19-21 kV, failure of asynchronous motors of compressors, fans and pumps is possible, as well as overheating of the windings of individual phases, especially if the capacitors connected to them are insufficient. The operation of DC electric locomotives during a long-term decrease in voltage in the contact network can be affected by a decrease in the air supply to fans (overheating of traction motors) and compressors (insufficient air to control the brakes, sandbox and sound signals).
For electric locomotives, the weight per axle is 23-25 tons, and the smooth running of electric locomotives of some series is not sufficient, especially if the spring systems, body supports, shock absorbers are not properly maintained and with large lateral run-up of the wheel pairs. Therefore, in some areas with complex topsides way, the maximum speed of electric locomotives of one series or another is lower than their design speed specified by the manufacturer. For example, it is necessary to limit the maximum speed of VL8 electric locomotives that have not undergone modernization due to the increased rigidity of the spring system.
The maximum permissible speed of an electric locomotive is limited by the strength of the commutator and the fastening of the armature winding, and in some cases by the impact on the track.
In DC electric locomotives, when taking the train from a standstill on a rise, one has to take into account the heating limitation of the starting resistors (rheostats), when the driver, fearing slipping of the wheel pairs, does not move the main handle of the controller for a long time - to the non-rheostatic (running) position. A long delay of the controller handle at the rheostat positions leads to exceeding the permissible temperature (overheating) of the starting resistors. Resistors especially overheat when their normal ventilation is disrupted (blinds are closed, rotation speed is low), permissible temperature heating of resistors of all types 450 o C (except for resistors of the PEV type).
The traction force of an electric locomotive is limited by the adhesion of the gearbox to the rails, also due to; shutdown of the electric motor, by heating the electric motor, by voltage in the electric motor, by heating the oil in the transformer. When heated, the insulation quickly fails and breaks through. Temperature limits are determined by the insulation class (TED-135-150 °C, oil in the transformer 90-95 °C).
Amount of heat released
Q = r I 2 Δt, where;
r is the resistance of the TED windings,
I - current in TED,
Δt - amount of time.
The TED ventilation system prevents the entry of moisture, dust, etc. Turn on ventilation under load for cooling, without load for before cooling, when parked in a snowstorm to prevent snow from entering.
The load mode changes dramatically depending on the weight and profile of the track, so the concepts are used;
1. hourly current is the current at the rated voltage at which the electric motor operates for an hour, with ventilation without overheating the insulation.
2. Long-term current - engine operation for more than 6-8 hours with ventilation, without overheating of the insulation.
3. Maximum current - determined by the switching conditions and adhesion of the wheel to the rail, which can be supplied within 1-3 minutes.
4. Hourly (long-term) power - the product of the hourly (long-term) current and the maximum voltage in the electric motor.
Technical data of traction motors
Additional restrictions on the use of electric locomotives:
1. You cannot place more than two electric locomotives included in the traction at the head of the train. The traction force on the automatic coupler of a locomotive operating to stretch the train should not exceed 95 tf when starting from a stop, and 130 tf when accelerating and in motion (Instructions for organizing the circulation of freight trains of increased weight and length on railways RF TsD-TsT-851).
2. If there are two electric locomotives at the head of the train, included in the traction, then it is allowed to raise no more than three pantographs, two of them on the leading electric locomotive (Instruction TsT-TsE-844).
3. In winter (for northern roads from October 15, for southern roads - from November 1 to April 1) it is allowed to send electric locomotives in rafts to regulate the fleet in areas of their circulation at sub-zero outside temperatures in the following order and quantity:
VL80S, VL80R, VL80T, ChS8 (two-section) - up to five electric locomotives inclusive with raised rear pantographs on each in the direction of travel;
VL80S, VL80R (three-section) - up to three electric locomotives inclusive with raised rear (on the last section) pantographs in the direction of travel on each;
Rafts can include electric locomotives of different series of the same type of current.
Each electric locomotive not involved in traction is accompanied by a driver or assistant who has the right to drive the locomotive. On these electric locomotives, traction motor cooling fan motors must be turned on. When stationary and when starting off, the rafts on the leading locomotive are additionally raised to the front pantograph in the direction of travel. When the raft reaches a speed of 5-10 km/h, the first pantograph in the direction of travel on the leading electric locomotive is lowered - when the raft is sent from the side track of the station at a distance of at least 15-20 m from the nearest switch (Instruction TsT-TsE-844).
4. When passing neutral inserts in rafts with raised pantographs, the leading locomotive lowers the pantograph at a signal, the rest turn off the auxiliary machines.
5. In the summer, it is allowed to transport electric locomotives in rafts, accompanied by one locomotive crew. Forwarding electric locomotives to winter time at above-zero temperatures and absence of snow cover, it is allowed without being accompanied by a locomotive crew (Instruction TsT 310 “On the procedure for sending locomotives”).
6. There is a limitation on the heating of brake resistors on electric locomotives equipped with an electric (rheostatic) brake.
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