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1. Automatic control (1) Close the air switch QF to turn on the three-phase power supply.
(2) Place the SA board in the automatic position and press the coil of the SB2 AC contactor KM1 to be energized and self-locked. The main contact is closed, and the three-phase power source of the motivation stator is started. (At this time, the frequency sensitive varistor is in series with the rotor circuit).
(3) At this time, the time relay KT is also energized and starts timing. After the set time, the normally closed contact of KT's time-delay closed is closed. The intermediate relay KA coil circuit is connected. The KA's normally open contact is closed, making the contactor KM2 coil. When the circuit is energized, the normally open contact of the KM2 is closed and the frequency-sensitive rheostat is short-circuited and the start-up process ends.
(4) The thermal relay for line overload protection is connected to the secondary side of the current transformer because of the large motor capacity. In order to increase the sensitivity and reliability of the thermal relay, it is connected to the secondary side of the current transformer.
(5) During the start-up period, the normally closed contact of the intermediate relay KA short-circuits the thermal element of the relay to prevent the thermal element from malfunctioning due to a large starting current. During the operation, the normally closed contact of KA is disconnected, and the thermal element is connected to the secondary circuit of the current transformer for overload protection.
2. Manual control (1) Close the air switch QF Turn on the three-phase power supply (2) Move the SA to the manual position (3) Press the start button SB2, the contactor KM1 coil is energized, suction and self-locking, main contacts Closed motor with frequency sensitive varistor start.
(4) When the speed is close to the rated speed or when the current meter is close to the rated current, press the button SB3 KA coil of the middle relay to be electrically sucked and self-locked. The normally open contact of KA is closed and the KM2 coil circuit is closed. The normally open contact of KM2 The short circuit of the frequency sensitive rheostat is cut off and the start-up process ends.
(5) The thermal relay for line overload protection is connected to the secondary side of the current transformer because of the large motor capacity. In order to increase the sensitivity and reliability of the thermal relay, it is connected to the secondary side of the current transformer.
(6) During the start-up period, the normally closed contact of the intermediate relay KA short-circuits the relay's thermal element in order to prevent the thermal element from malfunctioning due to a large starting current. During normal operation, the KA normally closed contact opens and the thermal element is connected to the secondary circuit of the current transformer for overload protection. 
The frequency sensitive rheostat starting process can be divided into automatic control and manual control by the switch SA.