Frequency-sensitive rheostat starting control principle is analyzed

Frequency-sensitive rheostat is actually a special core for three-phase reactor, it has an iron core, three pillars on each column, there is a winding three-phase winding generally pick up into a star. Frequency-sensitive rheostat impedance as the change of frequency of current changes in high current frequency, the impedance value is high, the current low frequency, the impedance value is low. The frequency characteristics of frequency-sensitive rheostat is very suitable for control of asynchronous motor starting process. The largest startup, the rotor current frequency of fz. Rf and Xd, largest motor can get bigger starting torque. Starts, gradually reduce with the increase of rotational speed rotor current frequency, the Rf and the Xf is automatically reduced, so the motor can be approximately constant torque characteristics, and realize the stepless motor startup. After the start, frequency-sensitive rheostat should be short circuit.

one, automatic control,

to close the air switch QF three-phase power supply is connected.

in lien will SA board to the automatic position, press KM1 SB2 ac contactor coil electricity and self-locking, the main contact closure, motivation of the stator access to start three-phase power. （ The frequency-sensitive rheostat string into the rotor circuit) 。

timing starts to time relay KT electricity and at this time, reached after the setting time of KT delay closed closed normally open contacts, switches on intermediate relay KA coil circuit, KA its normally open contacts closed, the contactor KM2 coil electric circuit, KM2 normally open contact closure, the frequency-sensitive rheostat short-circuit resection, end of the boot process.

looking lines thermal relay overload protection in current transformer secondary side, this is because the motor capacity is big. In order to improve the thermal sensitive degree and reliability of the relay, so the access to the current transformer secondary side.

and the other during startup, intermediate relay KA normally closed contacts will relay sub heat element, is to prevent large starting current misoperation caused by hot components. KA during into operation normally closed contacts disconnect, thermal element access current transformer secondary circuit overload protection.

2, manual control

to close the air switch QF on three-phase power supply

in lien moving SA to manually position

to press the launch button SB2, contactor KM1 coil electricity, absorption merger self-locking, main contactor closing start motor with frequency sensitive rheostat.

looking for speed close to the rated speed or observing current meter close to the rated current, press the button SB3 intermediate relay KA coil electric absorption merger self-locking, KA on the normally open contact closure KM2 coil circuit, KM2 will normally open contact closure of frequency-sensitive rheostat short-circuit resection.

and KA the normally closed contact of disconnection, the thermal element access current transformer secondary circuit overload protection.