Electrical appliance refers to an electrical device that can manually or automatically turn on or off a circuit according to externally applied signals or requirements, intermittently or continuously change circuit parameters, and switch, control, protect, detect, and regulate electrical or non-electrical objects. Or equipment. Low-voltage electrical appliances usually refer to appliances that work in circuits with rated AC voltages up to 1200V or DC voltages up to 1500V.
Low-voltage electrical appliances are generally divided into electrical appliances and control appliances according to their basic purposes. Distribution electrical appliances mainly include combination switches, low-voltage circuit breakers, fuses, and transformers. Control electrical appliances mainly include contactors, relays, and main control devices (including buttons, limit switches, and transfer switches).
Low-voltage electrical classification methods are: According to the operating mode is divided into automatic appliances and manual electrical appliances; according to the principle of operation is divided into electromagnetic appliances and non-electricity control electrical appliances; according to whether the contact is divided into contact electrical appliances, non-contact appliances and mixed Electrical appliances; According to the electrical configuration is divided into a single electrical and complete sets of electrical appliances; According to use occasions are divided into general industrial electrical appliances, chemical electrical appliances, mining electrical appliances, traction electrical appliances, aviation electrical appliances, marine appliances and so on.

The combination switch is often used as a transfer switch, but it is also used as an isolation switch in an electrical control circuit to act as an infrequent switch on and off the electrical control circuit.

1. Combined switch structure

The shape and structure of the combination switch are shown in Fig. 1. The combination switch is installed with three-layer switch components from the bottom to the top of the shaft 4. Each layer has a movable contact 8, a pair of static contacts 9 and a pair of terminals 1. Each layer controls the opening and closing of a branch, forming a three-pole combination switch. When the handle 3 is rotated through a certain angle, the three movable contacts in the three-layer switch assembly fixed on the rotary shaft are simultaneously turned to a new position, and are respectively connected or disconnected with the static contacts of each layer in the new position. open.
According to the different functions of the combination switch in the circuit, there are two types of combination switch patterns and text symbols. When used as isolating switch in the circuit, its picture symbol is shown in Fig. 2, its character label is QS, there are unipolar, bipolar and tripolar distinction, the electrical circuit of the machine tool generally adopts the three-pole combination switch.

Fig.1 Graphical text symbol when combination switch is used as isolating switch
a) Unipolar b) Bipolar c) Tripolar

Figure 3 shows the combination of switches for the use of the switch when the graphical symbols, the figure is a three-pole combination switch, I and II in the figure respectively represents the combination switch handle rotation of the two operating positions, I position line on the three empty Points on the right draw three black dots, indicating that when the handle is rotated to the I position, the L1, L2, and L3 branches are connected to the U, V, and W branches, respectively; and the three empty points on the II position line are not to the right. Corresponding black dots indicate that when the handle is rotated to position II, the L1, L2, and L3 tributaries and the U, V, and W tributaries are in a disconnected state. The textual indicator is SA.

Figure 3 Graphical text symbols when combination switch is used as switch

The commonly used combination switch series specifications in the electrical control circuit include HZ5, HZ10, HZ15, and 3LB.
1) HZ5 series HZ5 series is suitable for AC 50HZ (or 60HZ), voltage 380V and below, current to 60A electrical control circuit, as a power induction switch or asynchronous motor control switch. HZ5 series model marking type is:
HZ 5 - /
1 2 3 4 5 6
1 HZ is the combination switch group code;
25 is the design code;
3 Rated current value (A);
4 switch control motor power (KW);
5 positioning feature code (L - single-phase clockwise 60 °, M - two-way 60 °);
6 switch structure number (01 - bipolar switch, 02 - three-pole switch, 03 - four-pole switch, 04 - two voltage bipolar switch, 05 - induction motor reverse switch, 06 - two voltage three-pole switch, 07 —Star Delta Starter, 08—Two-Speed ​​Motor Switch).
2) The HZ10 series HZ10 series is used to switch on or off the electrical control circuit infrequently. Its model callout type is:
HZ 10 D - /
1 2 3 4 5 6
1 HZ is the combination switch group code;
2 10 is the design code;
3 D is a modified code;
4 Rated current (10A, 25A, 63A and 100A);
5 switch type (P - two kinds of circuit conversion, S - three types of circuit conversion, G - four kinds of circuit conversion);
6 poles.
3) HZ15 series HZ15 series is a modified product on the basis of HZ10 series, its model callout type is:
HZ 15 - /
1 2 3 4
1 Rated current value;
2 poles;
3 Codes for open and closed positions (0 - open circuit, 1 - open circuit limit, 2 - no open circuit);
4 conversion circuit number.
4) The 3LB series 3LB series is a product manufactured with the introduction of German Siemens technology and is mainly used for three-phase asynchronous motor load start and variable speed commutation. The 3LB series model marking type is:
3LB - /
1 2 3 4 5 6
1 3LB is the combination switch code;
2 basic specification code;
3 Two-digit switch type code type;
4 number of contact elements;
5 Two-digit line symbols;
6 handle type code (00 - no handle, 01 - ordinary black handle, 02 - normal red handle, 03 - long black handle, 04 - long red handle, 51 - round black handle, 52 - round red handle) .

According to the combination switch model, you can find more technical parameters, and the main technical parameters that characterize the performance of the combination switch are:
1) Rated voltage Rated voltage refers to the highest voltage that the switch can withstand in long-term operation under the specified conditions.
2) Rated current Rated current refers to the maximum operating current allowed to pass for a long time at the closing position under the specified conditions.
3) On-off capability The on-off capability refers to the maximum current value that can be reliably turned on and off at rated voltage under specified conditions.
4) Mechanical life refers to the number of no-load operations that can be tolerated before needing to repair or replace mechanical parts.
5) The electrical life refers to the number of times that the load operation is performed under the specified normal working conditions without repair or replacement of parts.

When the combination switch is used as an isolating switch, its rated current should be lower than the sum of the load currents in the isolated circuit; when used to control the motor, its rated current is generally 1.5 to 2.5 times the rated current of the motor.
According to the actual needs of the electrical control circuit, determine the combination of switch wiring, and correctly select the specifications of the combination switch that meets the wiring requirements.

Low-voltage circuit breakers, also known as automatic switches and air switches, can be used not only to switch on and off the circuit frequently during normal conditions, but also to automatically cut off the fault circuit when an overload, short circuit or loss of voltage occurs in the circuit. It protects the electrical equipment connected in series, so it is widely used in electrical control circuits.

Figure 4 Low Voltage Circuit Breaker
1-Main contact 2 - Free tripping mechanism 3 - Overcurrent release 4 - Shunt release 5 - Thermal release 6 - Lossless release 7 - Button

Figure 4 is a schematic diagram of a low-voltage circuit breaker. The main contact 1 is manually or electrically closed by the operating mechanism. In the closing position, the free tripping mechanism 2 locks the main contact in the closed state. When the electrical control circuit works normally, the suction force generated by the coil of the over-current release 3 cannot pull the upper swing rod, and the short circuit fault occurs in the electrical control circuit. The short-circuit over-current increases the coil attraction force of the over-current release, and above the coil The pendulum-type armature pulls in and rotates counterclockwise around the fulcrum, the free tripping mechanism rises and releases the main contact, and the main contact is moved to the left to break the circuit under the action of the extension spring.

In the case of an overload fault in the electrical control circuit, the coil of the thermal release 5 heats the upper bimetal due to heat, since the coefficient of linear expansion of the lower metal material of the bimetal is larger than that of the upper layer, and the bimetal generates an upward warp after heating. , Push the free tripping mechanism up and the main contact trips the breaking circuit.
When the voltage loss occurs in the electrical control circuit, the suction force of the coil of the voltage loss tripping device 6 decreases, and the upper armature cannot be pulled in, so that the armature rises, causing the free tripping mechanism to rise, and the main contact trips to break the circuit.
The shunt release 4 is used as a remote control breaking circuit and is controlled by the button 7 and closes the remote button. Then, the shunt release coil pulls up the swing-type armature above the free trip mechanism to make the main Contact breaking circuit.
The graphic symbol of the low-voltage circuit breaker in the electrical schematic is shown in Figure 5. (Should it be normally closed?)

Figure 5 Low-voltage circuit breaker graphic text symbol

The series of low voltage circuit breakers commonly used in electrical control circuits include the DZ15, DZ20, T, H, 3VE, and C45 series.
1) DZ15 series DZ15 series circuit breakers have obvious quick-separation and quick-closing functions for the overload protection and short-circuit protection of electrical distribution, motor and lighting circuits in the electrical control circuit of operating machinery.
2) DZ20 series DZ20 series not only has the ability of rapid closing and disconnection, but also has alarm contacts, which are used for power distribution in the electrical control circuit. DZ series model marking type is:
DZ - /
1 2 3 4 5 6 7 8 9
1 DZ is the code of the circuit breaker, which means a plastic shell circuit breaker;
2 design code;
3 Rated breaking capacity code (Y - general type, J - higher type, G - highest type, C - economic type);
4 shell rated current (A);
5 derived code (P - electric operation, L - leakage operation);
6 poles;
7 release code (0 - no release, 1 - thermal release, 2 - electromagnetic release, 3 - double release);
8 Accessory code (0—without accessories, 2—shunt release, 3—undervoltage release, 4—shunt release auxiliary contacts, 5—shunt undervoltage release, 6—two Group auxiliary contacts, 7-auxiliary contacts for undervoltage release);
9 accessory auxiliary code (0 - no alarm contacts, 8 - alarm contacts).
3) T series T series is a product introduced from the introduction of Japan Teratech Electric Corporation. T series has a variety of TO standard type, TG high breaking capacity type, and the domestic code name is DZ949. It is applicable to infrequent closing in electrical control circuit. On and off occasions, this series of circuit breakers have overload and short circuit protection.
4) The H series H series is a product produced by the introduction of American Westinghouse technology and is suitable for the distribution of electrical control circuits. Normal operating conditions can be used for infrequent conversion.
5) The 3VE series 3VE series is a product manufactured with the introduction of German Siemens technology. The domestic code name is DZ108. In the electrical control circuit is often used for motor overload protection, short circuit protection, plus accessories can also carry out remote control and protection. The 3VE series model marking type is:
3V
1 2 3 4 5
1 3V is the breaker code;
2 Use category code (E—motor protection type, N—short circuit protection only, A—only overload protection, T—distribution protection type);
3 Basic specification codes (1-20A, 3-32A, 4-63A);
â‘£ 3-digit code of the auxiliary contacts (005-3VE1 no auxiliary contacts, 015-3VE1 auxiliary contacts, a normally open a normally closed, 025-3VE1 auxiliary contacts, two normally open, 035-3VE1 auxiliary contact , two normally closed, 000-3VE3 without auxiliary contacts, 200-3VE4 without auxiliary contacts);
5 Release current setting range code (Example 2BU-3VE1, trip current setting range is 0.1~0.16A, 2MA-3VE3, trip current setting range is 10~16A, CL-3VE4, trip current setting The range is 6.3~10A, etc.)
6) The C45 series C45 series is a product manufactured with the introduction of French Merlin Gerin Technology. The domestic model is DZ47. As the lighting distribution system, motor power distribution system and electrical control circuit overload protection and short circuit protection.

1) The rated voltage refers to the working voltage that the circuit breaker can withstand under long-term operation under the specified conditions, generally it is the line voltage. Commonly used in the exchange of 220V, 380V, 500V, 660V and so on.
2) Rated current <br> Refers to the current that the circuit breaker can pass for a long time under the specified conditions, also called the rated current of the release.
3) Short circuit breaker means <br> making capacity under specified conditions rated frequency and power factor, can be short-circuit current making capacity, expressed as the maximum expected peak current.
4) rated short-circuit breaking capacity under a predetermined condition refers <br> rated frequency and power factor, etc., the maximum short-circuit current of the circuit breaker capable of breaking.
5) Rated short-time withstand current <br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br><br>
6) Operation time <br> Refers to the time from the short circuit moment of the electric control circuit to the time when the contact is separated, the arc is extinguished and the circuit is completely broken. It is also called the full breaking time, which is generally 30~60ms.
7) Service life <br> Including electrical life and mechanical life. Refers to the operation in a predetermined normal load conditions the number of operations without having to replace parts, electrical life is typically 0.2 to 1.2 million times, the mechanical life of 0.2 to 20,000 times.

The rated current and rated voltage of the low-voltage circuit-breaker shall not be lower than the normal working current and operating voltage of the equipment in the electrical control circuit. The limit-switching capacity shall not be less than the maximum short-circuit current of the circuit. The rated voltage of the under-voltage release shall be equal to the electrical The rated voltage of the control circuit, the rated current of the overcurrent release shall not be less than the maximum load current of the electrical control circuit.

Three tasks

According to the combination switch and the appearance and model of the low-voltage circuit breaker, identify, consult the electrical parameters, and write the electrical parameter report. (guided grammar)

Information: Summarize the decision of relevant lecture notes: make judgment based on the appearance and labeling specifications

Plan: 1. Check the appliance manual according to the specifications and models. Record electrical parameters 3. Design report format implementation: Completion of assignments after school hours: Comparison with physical or photographs Assessment: Subgroup evaluation

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