The basic circuit of relay-contactor automatic control and the basic rules of drawing electrical schematic diagram

1. The composition of the relay-contactor automatic control circuit

Basic rules for drawing schematics: 7 points

1) In order to distinguish between the main circuit and the control circuit, the main circuit is represented by a thick line while the control circuit is represented by a thin line when drawing the circuit diagram. It is customary to place the main circuit on the left side of the circuit diagram and the control circuit on the right (or lower part).

2) In the schematic diagram, the power lines in the control circuit are arranged on two sides, and the control circuits are basically drawn in parallel from top to bottom according to the action sequence of the electrical components.

3) In the schematic diagram, each electrical appliance is not drawn on the line according to its actual layout. Instead, the parts of the same electrical appliance are drawn separately where they complete their functions.

(4) In order to distinguish the types and functions of the electrical appliances in the control circuit, each electrical appliance and its components are represented by a certain graphic symbol, and each electrical appliance has a text symbol, and each component belonging to the same electrical appliance uses the same Text symbol representation. The appliances with the same function are all indicated by a certain number.

5) It is stipulated that the contacts of all electrical appliances indicate the normal position, that is, the position of various electrical appliances when the coil is not energized or the machinery is not yet operating.

6) In order to check the line convenience. In the schematic diagram, the electrical connection of more than two wires should be marked with a dot, and each contact should be marked with a number. The numbering principle is: the power line close to the left is marked with a single number, and the power line close to the right is marked with a double number Label.

7) For the mechanism with cyclic motion, a working cycle diagram should be given.

2. The basic circuit of relay-contactor automatic control

Take AC asynchronous motor as the control object to study its starting, forward and reverse rotation, jog, chain control and other lines.

1. Start control circuit and protection device

1) Start the control circuit

Direct start

The contact of the AC contactor keeps its coil energized, so that the circuit link that ensures long-term work is called the self-locking link. This kind of contact is called a self-locking contact.

The basic circuit of relay-contactor automatic control and the basic rules of drawing electrical schematic diagram