Deceleration of the series excitation DCT
Anti-vibration braking (generator operation in series with the network).
There are two possible ways:
1. Change in polarity U at the anchor while maintaining the current direction in the field winding. It is accompanied by a transition from characteristic 1 (point a) to characteristic 2 (point b). Fig. 4.44 shows the mechanical characteristics of the DCT of series excitation (1) and the actuator L/c. At all - the braking mode is opposing.
2. If the DFT operates in the propulsion mode according to characteristic 1 at the point a, , when the armature A is introduced into the chain, it will work on characteristic 3. Since in this case < strong> M., & lt; , then the engine will start to decelerate, and then accelerate in the opposite direction to the point d. when N = N/c. This mode also applies to the braking mode by opposing.
Dynamic deceleration of sequential excitation DCT
Two schemes of inclusion are possible: independent excitation (Figure 4.45, a) and self-excitation (Figure 4.45, b).
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Figure . 4.45
In the first case, the mechanical characteristics shown in Fig. 4.46, correspond to the characteristics of the DCT of independent excitation. When the DCT is dynamically braked in series with 4.45, b with self-excitation, it is necessary that the residual magnetic flux Ф1К | coincided with the excitation flux Ф ", and the speed со * 0. In Fig. 4.47 shows the mechanical characteristics of the DCT of series excitation in the self-excitation mode.
Each resistance value R, corresponds to its own critical speed & quot; u, .. For small values of r0, if A <& lt; L ", self-excitation does not occur.
This mode of braking DPT of series excitation is used for intensive braking in electric drives of transport and load-lifting mechanisms.
Features of mixed excitation DCT
The scheme of inclusion of the mixed excitation DPT is shown in Fig. 4.48.
The motor has two excitation windings: serial (ORP) and independent (OR), which can be switched on as a parallel to a single voltage source U.
The magnetic flux of the motor Ф is created by two components: Ф0 "" - independent of the load current and Ф "" "proportional to the load current I, as shown in Fig. 4.49.
When/= - /, the magnetic flux Φ = 0, the magnetic system is demagnetized. Equations of electromechanical and mechanical characteristics have the form
The electromechanical and mechanical characteristics are shown in Fig. 4.50 and Fig. 4.51. An analysis of the characteristics shows that when t = -f, Φ = 0 and the velocity tends to w.
With o) = a>
The mixed excitation DMT combines the properties of the DCT of independent and sequential excitation, works in all previously considered modes: idling, short circuit, motor, generator, sequentially, in parallel with the network and regardless of the network. Regulation is carried out by all considered methods: change of Ф, anchor current, voltage. The low technical and economic indicators of mixed excitation DPT (high mass, cost, dimensions) lead to the fact that it is rarely used in electric drives.
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