Dynamic braking with self excitation

This braking is easily realized. The capacitor is connected into stator circuit as per below scheme. This braking is also called as capacitor braking. Such braking is mainly applied for AD with short-circuited rotor.

Figure 3.48 – Scheme of dynamic braking with self excitation.

For realization of capacitor braking in accordance with scheme it is enough to deenergize the linear contactor KM. Machine operates as induction generator with self excitation. Emf induced in stator windings due to rotor rotation produces self excitation (under the action of accumulated potential or kinetic energy of mechanism), that has insignificant emf of residual magnetizing. Insignificant emf of residual processes applied to capacitor furnishes low current of stator circuit. This current creates insignificant rotational field that increase stator emf. As a result capacitor voltage, current, braking moment grow. Further this process becomes intensive and lasts until the voltage on motor and capacitor terminals becomes equal.

Mechanical characteristic of dynamic braking with self excitation are shown for the three capacitor values. With decrease in capacity braking moment maximum is shifted into zone of higher speeds and its absolute value increases.

Figure 3.49 – Mechanical characteristics of dynamic braking with self excitation.

Drawbacks of such braking is presence of so-called dead zone where breaking moment doesn`t build up. With capacitor decreasing critical speed is significantly higher and reaches somewhere.

Besides for decreasing of non-sensitivity zone it is necessary to increase capacity that is not efficient.

Advantage of dynamic braking with self excitation is the absence of power source at braking.

Дата добавления: 2014-01-05