On Determining Train Composition Size in Underground Electric Locomotive Transport
Abstract Generated abstract
The paper examines calculation procedures for selecting train consist weight in underground electric locomotive haulage, focusing on the braking-distance condition used alongside adhesion, motor heating, and battery capacity constraints. It argues that deriving braking deceleration from a prescribed 40 m stopping distance and the locomotive’s continuous speed is unreliable because it ignores the maximum braking force available from wheel-rail adhesion and may use a speed that differs from actual operating speed. Using a 10 KR locomotive example, the author shows that the calculated consist weight would require a braking force greater than the locomotive can provide and would not satisfy the stopping-distance limit after traction calculation. The paper recommends omitting this preliminary braking-based limit, choosing the consist from the other constraints, and then verifying braking performance after detailed traction calculations.
Full Text
ON THE ISSUE OF DETERMINING THE TRAIN CONSIST SIZE IN UNDERGROUND ELECTRIC LOCOMOTIVE TRANSPORT
V. A. TIMOFEEV
(Presented by the scientific seminar of the Department of Mining Mechanics)
The weight of the train consist in underground electric-locomotive transport is determined [1] on the basis of the conditions of adhesion of the electric locomotive wheels to the rails, heating of the traction motors, capacity of the electric-locomotive battery, and the permissible length of the braking distance. In this, the braking deceleration is found from the condition of braking a loaded consist over a track length of 40 m, as specified by safety regulations, and the speed at the beginning of braking is taken equal to the continuous speed of the electric locomotive, i.e.
\[ j_t=\frac{V_{\mathrm{dl}}^{2}}{2\cdot l_t}, \tag{1} \]
where \(j_t\) is the braking deceleration, m/sec\(^2\);
\(V_{\mathrm{dl}}\) is the continuous permissible speed of the electric locomotive, m/sec;
\(l_t\) is the maximum permissible length of the braking distance, m.
After determining the size of the consist, a traction calculation is performed; refined speeds of motion are found, and the selected consist is again checked according to the braking condition. This method is not entirely correct and leads to significant errors in determining the maximum weight of the consist permissible according to the technical data of the electric locomotive. In fact, formula (1) determines what the deceleration must be in order to stop the consist over a track length of 40 m, but it does not at all take into account whether the electric locomotive, with its own braking means, can provide the indicated deceleration. The magnitude of the braking force must not exceed the adhesion force and, consequently, for a given type of electric locomotive it is impossible to obtain a braking force above a certain value. In addition, the actually established speed of a loaded consist usually differs considerably from the continuous speed. Let us clarify what has been said with an example.
Example: electric locomotive—10 KR; mine cars of 3-ton capacity with roller bearings; running resistance of a loaded mine car—7 kg/t, and track gradient 3‰.
According to the condition of braking a loaded consist on the prevailing gradient and with a braking distance of 40 m, by the indicated method it was ob-
a train consist weighing 89 tons was obtained. In this case, the required braking deceleration was \(0.24\ \text{m/sec}^2\). To obtain such a deceleration with the given train-consist weight, it is necessary to create a specific braking force of \(22.4\ \text{kg/t}\), or a total braking force of \(2000\ \text{kg}\). However, for this type of electric locomotive, with the recommended values of the coefficient of friction between the wheel rim and the brake shoe of 0.2 and the coefficient of pressing of the brake shoes of \(0.8\)—\(0.85\), the maximum braking force, according to the adhesion condition, should not exceed \(1600\)—\(1700\ \text{kg}\). If the adopted train consist is checked by the length of the braking distance, it will turn out that its value exceeds 40 m. This is explained by the fact that the actual running speed proved to be higher than the long-term speed adopted as the initial value in determining the train-consist weight. Therefore, in the existing calculation procedure, the item concerning the determination of the maximum permissible value of the loaded train consist according to the braking condition should be removed, especially since the results obtained cannot subsequently be used in determining the size of the train consist for either contact or storage-battery electric locomotives. It seems to us sufficient to retain only the first three conditions and, after choosing the value of the loaded train consist from the smallest of the results obtained, to check the train-consist weight according to the braking condition after the traction calculations have been performed. After this, the required size of the train consist should be finally adopted and the necessary measures should be provided to ensure the reliability and safety of traffic.
REFERENCES
- Volotkovskii S. A. Mine Electric-Locomotive Traction, Ugletekhizdat, 1955.