Basic theoretical information. Switching equipment is an integral part of the system of transferring and distribution of electric energy on an aircraft

Switching equipment is an integral part of the system of transferring and distribution of electric energy on an aircraft. Switching equipment (SE) is devices by which the electrical circuits are switched on, switched off and shunted. Its function is divided into hardware direct action (buttons, switches, limit switches) devices and remote actions (relays, etc.). The use of a particular type of equipment is determined by the current in switching circuits.

Switchgear (controlgear). The controlgear, in addition to the basic requirements, has the following ones:

- turn on and off of contacts should occur almost instantaneously;

- continuous operation at rated load and at tenfold overload must be provided within a specified time;

- resistance between conductive parts and the cabin of devices must be at least 2 Ohm;

- specified number of switching on have to be practiced.

- Contactors and relays are installed in the vicinity of managed objects and limit switches are installed directly on frameworks of these objects.

Buttons in electrical networks are embedded with the necessity to lock or to unlock circuits briefly (Fig. 1.1).

On the aircraft the buttons of the types 5K, 204K, 205K and their modifications are the most commonly used, they close circuits with the time not more than 1 min.

In Fig.1.1 there are circuit diagrams of aviation buttons with normally opened contacts (a, b); with normally closed contacts (b); buttons that switch electrical circuits (g).

Fig.1

Button 5K made as double- contact and allows value of current up to 5 A. Buttons 204K and 205K are triple-contact and are designed for current that reaches 20 A. These buttons are used on AC with power systems of direct and alternating currents.

Any button (Fig. 1.2) includes the cap 6, frame 5, 3 button head, 1 moving and fixed contacts 7, return spring 4 and other small parts. Slider 1 mounted on the rod head 2, and stationary contact on the cap. When you press the button head Fig.2. 2, the return spring is closed 4 and slider 1, which has a conical surface, combines with the stationary contacts

7. To create the necessary contact pressure the fixed contacts have spring properties.

Circuit breakers and switches are aimed for prolonged closure and disconnection of electrical circuits. There are the following devices: push-button switch, throw-over switch and at flick of switch. Electrical circuit breakers and switches are shown in Fig. 1.3, where а - single-pole switch B-45; б - double pole switch 2B-45; в -unipolar throw-over switch PP-45; г - the single pole push-button switch with neutral attitude of handle PN-45; д - brush switch.

Circuit breakers and switches with switching arms are called unipolar, bipolar etc. Unlike conventional push button throw-over switch or switches after stopping pressing the switching arm back to its original position. Rotary switches and switch circuits commute only when you turn the handle control. This metal brush (brushes) moves from one fixed contact to another, making switching circuits (Figure 1.3, etc.). Fig. 1.3

Fig. 1 .3

The simplest design is in a circuit breaker of the type B-45 and switch of the type PP-45 (Fig. 1.4). Switch PE-45 consists of a brass casing 8, a metal lid 6, textolite base 2, the fixed contacts 1, 7 contact rocker, metal handle with spring 5, 4 pin of insulating material 3. Switches perform the same function as the circuit breakers, but in the process of commutation, one switching circle (or several) Fig. 1.4

is closed and the other one is opened.

In the switch PP-45, unlike the circuit breaker B-45, on the third textolite panel extreme terminal 1 is located. When you press the switch arm 5 the pin 3 begins to slide on the rocker 7 and the spring 4 is compressed, and the stored energy of the spring facilitates rapid and reliable circuit electrical contacts closing. Along with the closure of one contact the opening of another contact takes place.

In a multipolar circuit breakers (switches) there are several contact rockers 7 pins 3 and springs 4 that run simultaneously. This plastic pins with springs are inserted into the brake shoe.

Limit switches. Limit switches and circuit breakers are widespread on aircraft, they switch on and off under the influence of air moving parts of mechanisms in accordance with a given program. These devices are designed for different automatic control mechanisms, (landing gear, landing speed brakes, etc.), for community alarms, for blocking various electrical circuits and etc. Limit switches can have both large and small movement of rod. Limit switches МВШ-2T are the most spread among limit switches with a large movement of rod. Switches with a slow speed rod are miniature circuit breakers of series ВК-140, КВ-6, КВ-9 and КВ-20, which are classified as instantaneously acting devices.

Circuit breakers of the series ВК-140, depending on the scheme contacting performance of the system, are divided into switches, circuit breakers and closing switches. Switches have the designation number 140, circuit breakers have 141, and closing switches have 142. The colors of cap are black, white and red colors relatively. Depending on the method of wires joining to the output clamps, numbers 1 and 2 are used to indicate these circuit breakers. So, if solder is there, number 1 is used, and if joining screw is the, we use number 2. In addition, depending on the design of the button device and case letters or letters with numbers can be used in designation. For example, the designation ВК-1-140В means that this switch has solder clamps, with constructive execution " B".

Contact system (Fig. 1.5) and some details of the circuit breaker ВК-140 are collected in plastic casing 8, covered with a cap 2, on which the weighted lever 3 is located.

Two stationary contacts, 10 the three-clutch contact pressure spring from beryllium copper 9, the push button 4 with plastic pins 5, screws 6 and cramp 7 are mounted directly inside.

Fig. 1.5

At the end of the three-clutch pressure contact spring the two-way moved contact 1 is located, that is pressed to the upper stationary contact 10 when the button 4 is not pressed.

On the fig. 1.6 the contact scheme of the limit switch ВК-140 is represented: 1 - strap; 2 - contact spring; 3 - contact; 4 - fixed contact; 5 - button.

Before pressing the upper button 5, the contacts of the circle breaker are closed due to the elastic forces of extreme petals of the contact spring 2. Fig. 1.6

When you press the button, vertical power Р_к appears, acting in accordance with the vertical force component from the effects of secondary petals Р_л. Average petal of the contact spring is in strained state due to deformed outer petals.

At a certain deformation of the the middle lobe of the contact springs, total value of the vertical components of middle petals' and button's forces become more vertical component of the outer petals Р_КЛ:

Р_К + Р_Л > Р_КЛ.

The result is a transfer of a movable contact to lower position. Reverse switch of contacts is made when the pressure is removed from the button. Push button switches ВК are designed for continuous operation at load current up to 15 A.

Microcircuit breakers of series КВ-6 differ only in a performance of terminals and in the contact scheme. These differences are fixed in the definitions of circuit breakers. The following symbols mean: letters KB - limit switch; figure 6 - the switch; combination of numbers 6-1 and 6-2 circuit breaker and closing switch respectively; A letter means that the limit switches КВ-6А, КВ-6-1А, КВ-6-2А-clamps are carried by the side wall of the case.

Contact system of the circuit breaker КВ-6 is collected in plastic case. Thus all contacts 4 (Fig. 1.7) are located both on the contact plastic 7, made of beryllium copper, and on the housing. Two-clutch pressure contact spring has a fixing antennae. In the plastic button elastic nail there are fixed lyre-shaped spring 3 and guide plate 6, Fig. 1.7 on which return spring 5 is located.

If the button 2 is not pressed, then under the action of the elastic force of the contact plate 1 lower fixed contacts are closed. When you press the button 7 petals fall down and lyre-shaped spring is deformed. When petals 7 are combined with the area of the contact plate there is an unstable state. With further movement of petals spring the contact spring is quickly bent in the opposite direction and squeeze the lyro- shaped spring petals 7 down vigorously. Returning of the pressure button and contact spring in the initial position is carried under the action of the return cylindrical spring 5. Most circuit breakers of the series КВ-6 are designed for the load current of 10 A.

Circle breakers МВШ-2Т with great movement of rod are constructed using microcircuit breaker КВ-9 (fig.1.8), which with the pressing device is placed in a metal case 2. Fig. 1.8 Pressing device consists of a movable rod 11, which twists with the adjusting screw 10. At the rod 11 the textolite ring 7 is placed, and inside the rod return spring 6 is situated. To protect the device against moisture the felt stuffing box 9 is located on the rod. Immediately the impact on the button 5 of the microcircuit breaker 4 is carried with the steel lever 13, which is pressed to ring 7 with a spring 12. When the rod 11 is pressed, the ring 7, through the lever 13, presses the button of circuit breaker 4 and commutation of electrical circuits is switching. Bushing 8 runs the rod 11. Connector block is closed with the cap 1 with the pipe connection for the coupling nut. To the connector block the wires 3 are connected.

Relays and contactors are designed for remote control of electrical capacities, help automatization of many processes on an aircraft. According to the principle of operation the electrical relays are divided into electromagnetic, permanent magnet, electronic and thyratron ones. On the aircraft electromagnetic relays and contactors are the most commonly used, mainly due to their reliability and versatility. There is no principal difference between relays and contactors. Relays commute with a current range up to 10 A, and with the usage of contactors they manage large currents in electric circuits.

Relays and contactors can be retractable (armor) and valve (rotary) type. On the fig. 1.9 there are sketches of magnetic systems of relays and contactors: a - the magnetic system of valve type; B - magnetic system of armor type; 1 - anchor; 2 - winding; 3 - magnetic path; d - air gap.

Contactors of series КМ, КП, К are widely used in AC. In addition, there is large widespread of the type of contactors ТКД, ТКС and ТКТ and relay ТКЕ, THE and others. Relays and contactors are designated with letters

and numbers. Fig. 1.9

Table 1.1 shows some technical information on relays and contactors and their designations.

For the contactors of the following types К, КМ, КП the letter K means " contactor". On the second place there may be the letter M or П, which means words " miniature" or " switching". The numbers 50, 100, 200 and so on represent the rated current of the circuit contactor. The letters that stand at the end of signs point to the factory modification.

Contactors and relays of the type ТКД, ТКЕ, ТНЕ, ТКС contain indexes in the designations that determine their structural and technical data. In the first place, the letter indicates the tension in the circle of coil control, such as Д – ten, П - fifteen, Т - thirty, C - hundred. The second letter indicates the purpose of the device, for example: K - switching relay or contactor, H - voltage relay, B - relay with time delay, T - current relay, П - relay AC, Д - detector relay. In the third and the fourth places there are the letters and numbers that indicate the nominal current value in the circle of contacts, and the letter means the rate (E - unit Д - dozens C - hundreds), and the number indicates the number of units of the given rate.

Table 1.1