Precautions against stalling a loco
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On gradients, there is a danger of a train stalling and being unable to resume moving, especially with slippery track. The following are some precautions to be observed to avoid stalling.
1. Condition of the load
While taking over charge of the loco, the Brake Power Certificate should be examined and it should be ensured that the Brake Power Certificate (BPC) is valid. Moreover, continuity of the air pressure / vacuum from the engine to the load should be ascertained. While starting the train, two to three notches should be taken, and the train should start rolling with a traction motor current of about 400A. If the train does not move then, it indicates that the load is jammed. In such a case the crew of the train should examine the load and find the jammed vehicle and release the brake using the distributor valve / release valve manually. After it is verified that the load is fully released, the train should be started and it should move at 400A or less current.
If this check is not carried out, the train may depart with a jammed vehicle in the load. This will result in the train stalling on gradients because of the additional resistance from the jammed brake blocks. Therefore, it is very important to check the condition of load and ensure full release of brake blocks and continuity in the train.
2. Watch the traction motor current
It is always a good practice while driving to take notches gradually while keeping constant watch on the voltmeter ammeter readings of the traction motor. In no case should the current rating should be exceeded. Progression should be done notch by notch gradually so that tractive effort develops in the train smoothly without causing any wheel slipping. Quick notch transitions for accelerating the train may result in wheel slip causing auto-regression of the notches by the wheel slip relay. This will result in loss of tractive effort and this may become the cause of stalling on a gradient.
3. Picking up speed before gradient
Good road knowledge helps in taking proper action in driving. While working a fully loaded train, it is necessary to maintain a good momentum in the train before approaching an up gradient. The speed should be increased to the extent possible subject to the speed restriction in force. This will avoid stalling on the up gradient. It is for this reason that in working time tables, stopping goods trains at certain stations or signals situated on gradients is prohibited, to avoid stalling due to loss of momentum of the train.
4. Use of sanders and ZQWC
With a fully loaded train, it is essential that the sanders are working properly. The sanders must be used judiciously to the extent required. Excess use of sanders may lead to drop in main reservoir pressure causing DJ tripping of the locomotive. In addition to this, the sand may be exhausted early which may result in a situation where the sandbox is empty while negotiating an up gradient section. Therefore, while approaching a gradient the sanders should be operated from time to time to avoid any wheel slip of the locomotive, but not excessivley. Furthermore, the ZQWC if in working order should be switched on. This will help in adjusting the traction motor current and avoiding the wheel slip on the locomotive.
5. Negotiating caution order
If a caution order exists for a speed of 30km/h or less on an up gradient or on the spot approaching a up gradient, the chances of stalling increases. Therefore, such caution orders should be negotiated with great care. In such cases, it is very good driving practice to control the train well in advance of the spot of caution order by destroying the vacuum or air pressure by small amounts say 10 cm for vacuum-braked trains, or 0.2 to 0.5 kg/cm^2 for air-braked trains, according to the brake power of the train. This causes a gradual application of train brake. When the speed decreases to the desired level, the train brake handle should be kept in a released position. This will ensure the release of the brake. This should be done in such a way that the train passes through the site of the caution order with the train brakes in released condition. At this time the vacuum / air pressure level will be normal. Now, the driver has the advantage of taking notches as and when required, which will help in picking up speed just after the end of the caution order without any delay for releasing brakes.
6. Shunting notches
Whenever a gradient is negotiated by a fully loaded train, the maximum possible current is fed to the traction motor to achieve higher tractive effort. It is a good practice to increase the current by taking notches (or in other words by increasing the voltage). This will cause the increase in traction motor current in relation to speed of the train. However, if shunt notches are taken abruptly, they can cause a sudden increase of the tractive effort. This increase may cause wheel slip and auto-regression of notches. Therefore, as far as possible the use of shunt notches while approaching or negotiating the gradient should be avoided.