Depending on the type of crane (overhead, tower, self-propelled jib, etc.) and the type of drive (electric, mechanical), the crane is equipped with a number of instruments and devices that ensure its safe operation. Such devices include:
a) limit switches designed to automatically stop the mechanisms of cranes with electric drive. On cranes with mechanically driven mechanisms, limit switches are not used. Requirements for equipping lifting machines with limit switches are set out in the Crane Rules;
b) blocking contacts used for electrically blocking the entrance door to the crane cabin from the landing platform, the hatch cover for the entrance to the bridge deck and other places;
c) lifting capacity limiters, designed to prevent crane accidents associated with lifting loads with a mass exceeding their lifting capacity (taking into account the hook reach). Installation of the device is mandatory on jib, tower and portal cranes. Overhead cranes must be equipped with a load limiter in cases where their overload cannot be excluded due to production technology. Requirements for installing the device are contained in the Crane Regulations;
d) skew limiters, designed to prevent dangerous skew of metal structures of gantry cranes and bridge loaders due to one of the supports being ahead of the other when the crane is moving. The need to install the device is determined by calculation during design;
e) a load capacity indicator installed on jib-type cranes, in which the load capacity changes with changes in the hook reach. The device automatically shows what the crane's lifting capacity is at the set reach, which helps prevent the crane from overloading;
e) tilt angle indicator for correct installation jib cranes, except those operating on rail tracks;
g) anemometer. Tower, portal and cable cranes should be equipped with such a device to automatically sound a sound signal at wind speeds dangerous for work;
h) anti-theft devices used on cranes operating on surface rail tracks to prevent them from being stolen by the wind. The requirements for these devices are set out in the Crane Regulations;
i) automatic dangerous voltage alarm (ASON), signaling the dangerous approach of the crane boom to live wires of the power line. The device is equipped with jib self-propelled cranes (with the exception of railway cranes);
j) supporting parts that are supplied to overhead cranes, mobile cantilever cranes, tower cranes, portal cranes, cable cranes, as well as cargo trolleys (except for electric hoists) to reduce dynamic loads on the metal structure in the event of breakdown of the axles of the running wheels;
k) stops installed at the ends of the rail track to prevent lifting machines from leaving them, as well as on jib cranes with variable boom reach to prevent it from tipping over;
m) beep nal device used on cranes controlled from the cabin or from a remote control (with remote control). On taps controlled from the floor, a signaling device is not installed.
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To prevent accidents and accidents, electric overhead cranes are installed the following devices and safety devices:
1. limit switches for automatic stopping of the lifting mechanism of the lifting body, the mechanism of movement of the crane and trolley;
2. buffer devices;
3. g/p limiter;
4. locking devices;
5. a device to prevent slings from falling out of the hook mouth;
6. sound and light alarm;
7. protective equipment against electric shock.
Limit switches used for automatic shutdown from the electric motor of the load lifting mechanism when the hook suspension approaches the main beams of the bridge (and the gap between the lifting body without a load and the stop must be at least 200 mm), as well as when approaching the end stops of the crane or cargo trolley.
The limit switch of the movement mechanism is installed so that the engine is turned off at a distance to the stop equal to at least half way of braking.
When installing mutual travel limiters for the movement mechanisms of cranes operating on the same track, this distance is taken to be at least 0.5 m.
Used in overhead electric cranes lever And spindle limit switches.
Lever switches are triggered by contact with some kind of stop, for example, a trip line, and usually serve to limit movement in one direction.
Spindle switches are used mainly to limit the lifting height of a lifting device and are designed to limit its movement up and down in both directions.
Hatch lock designed to automatically turn off the line contactor on the protective panel in the crane cabin when the hatch door exiting to the crane gallery is opened. In this case, the crane's bridge trolleys and electrical equipment installed on the crane's bridge are de-energized.
Cabin door the overhead crane must have an electronic lock (contact) that does not allow the crane to start moving when open door.
On overhead cranes, where the production technology does not exclude their overload, must be installed load limiters . The need for their installation must be indicated when ordering the faucet. The hydraulic limiter of an overhead crane can allow an overload of no more than 25%. The operator should adjust the limiter when operating the crane. is strictly prohibited .
Zero protection(electrical interlock) prevents spontaneous activation of the drive motors of the crane mechanisms when voltage is suddenly supplied to the external power supply network of the crane. This protection requires that the control handles be brought to the zero position, after which the engines can be started.
Buffer devices serve to soften impacts and jolts when crane bridges and load trolleys collide with end stops or when cranes collide. The buffer contains an elastic element that absorbs the kinetic energy of the progressively moving masses of the crane or trolley at the moment of impact and thereby increases the safety of the crane in the event of sudden failures of brakes or limit switches.
The elastic elements of the buffer are made of rubber, spring, spring-friction and hydraulic.
Cranes operating on open trestles supply anti-theft grips , excluding the movement of the crane along the crane tracks under the influence of wind load (inoperative state).
When the grips are in position, the pliers grip and clamp the heads of the crane track rails, holding the crane. The grips are applied by the driver when the wind increases to the limit state value.
Sound alarm on a crane is necessary to notify workers of the increased danger that arises when moving loads with cranes. Typically, for this purpose, electric bells, bells, and sirens are used, which are turned on using a button (on the control lever).
Light and sign signaling serves to inform the driver about possible malfunctions electrical equipment of the crane or hazardous areas his service.
The main trolleys of the crane have light alarm about the presence of voltage on the trolleys. Signal lamps are connected directly to the trolleys and installed on each phase. When using three-phase alternating current, the color of the lamps in this case red. When using direct current, two lamps are installed near the trolls white, connected in parallel.
The danger zone is also fenced off with safety signs and posters installed on the crane and in production premises.
The adopted system of signal colors is:
- red - prohibition – immediate danger, fire extinguishing agent;
- yellow - warning – possible danger;
Green - safety – prescription;
Blue - indication – information.
Installation of safety signs on crane equipment is mandatory!
Electric overhead cranes must be equipped with devices for automatically stopping the lifting mechanism and the movement mechanism of the bridge and trolley before approaching the stops, if their speed of movement can exceed 32 m/min. These devices are called limit switches or limit switches.
All limit switches can be divided according to the method of switching into main current switches, which open the main circuit of the motor, and control current switches, which open the circuit of the contactor coils. By design, limit switches are divided into lever (Fig. 2.53) and spindle (Fig. 2.54). When the lever switch lever deviates from the normal position, the contacts associated with it break the main current or control current circuit and the motor, lever switches of the KU series and spindle series VU. KU-700 switches allow any order of contact closure. KU-701 switches are used in control circuits to limit the linear movement of cranes with small run-outs, KU-703 switches are used to limit the stroke of lifting mechanisms. Switches KU-704 and KU-706 are used to limit the linear movement of mechanisms with any overrun.
The switch housing is made of cast aluminum alloy in a splash-proof design. When installing outdoors, it is recommended to protect the switches from exposure atmospheric precipitation. A drum with cam washers is fixed inside the housing; when rotated, the contacts of the block of cam elements are closed or opened.
Four fixed contacts and two levers with contact bridges are mounted on the insulating base of the cam element block. The contacts are made of silver. Springs keep the contacts closed. When the protrusion of the cam washer approaches the protrusion of the lever, the latter rotates and the contacts open.
A ratchet is installed on the shaft of switches KU-701, KU-704 and KU-706, which fixes the drive lever: in KU-701 - in the zero position, in KU-704 - in zero and two extreme positions, in KU-706 - in the extreme positions provisions. In the KU-703 switch, fixation is carried out by a weight suspended on the lever and a counterweight of the lever, which can be installed in different positions relative to the body. The limiting line acts as an influence on the KU-701 and KU-706 switches. In the KU-703 switch, the cam shaft rotates and returns to its original position when the counterweight is raised or lowered, which is raised or lowered by a shelf mounted on a hook clip. The cam drum of the KU-704 switch rotates when the pin acts on the plug.
Possible positions of the levers relative to the switch housings are shown in Fig. 2.55. The positions of the KU series switches are presented in table. 2.5.
Switches VU-150M and VU-250M are used as final switches in control circuits for the movement of cranes or to limit the travel of lifting mechanisms.
The switch at the end of the path can open or close contacts. To open the contacts, the washer rollers are installed in accordance with Fig. 2.56, A(when rotating the washers clockwise, viewed from the side of the contact washers) or fig. 2.56, b(when rotating the washers counterclockwise). The angle between the rollers is taken to be the smallest (32°). Corner A turning the paired washers until the contacts close or open is called the working angle. The working angle can be from 12 to 300°.
The entire path of the mechanism must correspond to the selected working angle. The operating angle (within the operating angle) for opening and closing contacts can be easily adjusted during installation. The angle of additional rotation of the washers caused by the mechanism running out after the switch is triggered should not exceed 300°. Switches of the VU series have a cast aluminum body, in which there is a shaft with closing and releasing washers, a lever with a contact bridge, a pawl and fixed contacts mounted on an insulating strip. The VU-150L1 switches have one circuit, and the VU-250M switches have two circuits, so the number of levers, fixed contacts, closing and breaking washers is doubled. Gearboxes with a gear ratio of 50:1 are built into the housings of the VU-150M and VU-250M switches (50 revolutions of the drive shaft correspond to one revolution of the shaft with washers).
When the roller of the closing washer runs against the protrusion of the lever, the latter slowly turns and closes two fixed contacts, being held in the closed position by the pawl. When the roller of the disconnecting washer runs against the protrusion of the pawl, the lever is released and, under the action of the spring, instantly rotates, opening the contacts.
The following requirements apply to the limit switches of the lifting mechanism: they must be installed so that after the load-handling device stops when lifting without load, the gap between lifting body and the stop was at least 200 mm, and for electric hoists - at least 50 mm.
In relation to grab cranes with a separate dual-motor drive of the grab winch, the switching circuit for the lifting limit switch must be designed so that the lifting mechanism motor and the grab closing motor are simultaneously switched off when the latter reaches the uppermost position. The limit switch of the travel mechanism must be installed in such a way that its motor is turned off at a distance to the stop equal to at least half the braking distance of the mechanism, and in gantry cranes - at least full path braking. If there are mutual travel limiters for the travel mechanisms of overhead cranes operating on the same track, the specified distance can be reduced to 0.5 m. The door for entering the control cabin of the overhead crane from the landing platform is equipped with an electrical lock that prevents movement when the door is open. The electrical circuit of magnetic cranes should be designed in such a way that the removal of voltage from the crane by the contacts of instruments and safety devices does not affect the voltage of the cargo electromagnet. For cranes with a three-phase electric drive, if any one phase breaks, the load lifting mechanism must be turned off. Contacts of devices and safety devices must operate to break the electrical circuit.
The electrical control circuit for the crane's electric motors must exclude: self-starting of the electric motors after the voltage in the network supplying the crane is restored; starting electric motors not according to a given acceleration pattern; starting electric motors with contacts of safety devices - contacts of limit switches and interlocking devices.
The input device of overhead cranes is equipped with an individual contact lock with a key, without which voltage cannot be supplied to the crane. All metal structures - housings of electric motors, apparatus, metal cable sheaths, protective pipes that are not included in electrical circuit, but may be energized due to insulation damage, must be grounded in accordance with the PUE.
To avoid damage to the crane equipment due to incorrect actions of the crane operator and to prevent accidents, block contacts are installed in the form of buttons with two break contacts and two make contacts. In general, the term “block contact” is applicable to any device that turns on and off control circuits. /On the cranes, block contacts enclosed in metal cases(Fig. 2.57). They are not used as limit switches on taps due to their small size, but they are quite acceptable for blocking. Their cases are tightly closed, do not allow dust and moisture to pass through, the permissible current is 6 A, the number of starts per hour is up to 300, wear occurs after 2 million starts. When closing the door, the block contact button is pressed and it closes the blocked section of the control circuit, thus preparing electrical diagram crane to work. Pressing the Start button will now turn on the main contactor of the safety panel.
The emergency shutdown “Stop” button is installed in a visible place in the control cabin. When it is pressed, the control circuit of the main contactor coil opens and all crane motors are turned off, the brakes stop the movement of all mechanisms.
After disconnecting the main contactor - both emergency and accidental - all controllers must be set to the zero position. The fastening of the block contact housing to metal structures must be reliable, and its operation must be trouble-free.
Occupational safety at urban construction and economic sites when using cranes and lifts.
Educational, methodological, practical and reference manual.
Authors: Roitman V.M., Umnyakova N.P., Chernysheva O.I.
Moscow 2005
1. OCCUPATIONAL HAZARDS WHEN USING CRANES AND LIFTS.
1.1. Concept of industrial hazard.
1.2. Danger zones on a construction site.
1.3. Examples of typical accidents and accidents associated with the use of cranes and hoists.
1.4. The main causes of accidents and accidents when using cranes and hoists.
2. GENERAL ISSUES OF ENSURING LABOR SAFETY WHEN USING CRANES AND LIFTS.
2.1. General condition for ensuring occupational safety.
2.2. Regulatory framework for ensuring occupational safety when using cranes and lifts.
2.3. The main tasks of ensuring occupational safety when using cranes and lifts.
3. ENSURING LABOR SAFETY WHEN USING CRANES AND LIFTS.
3.1. Selection of cranes and their safe binding.
3.1.1. Crane selection.
3.1.2. Transverse connection of cranes.
3.1.3. Longitudinal tie-down of tower cranes.
3.2. Determination of the boundaries of hazardous areas for the operation of cranes and lifts.
3.3. Ensuring labor safety in hazardous areas of cranes and lifts.
3.3.1. Instruments and safety devices installed on cranes.
3.3.2. Ensuring safety when installing cranes.
3.3.3. Protective grounding crane tracks.
3.3.4. Ensuring safety during joint operation of cranes.
3.3.5. Ensuring safety when using lifts.
3.4. Measures to limit the hazardous area of crane operation.
3.4.1. General provisions.
3.4.2. Forced limitation of the crane operating area.
3.4.3. Special measures to limit the hazardous area of crane operation.
3.5. Ensuring occupational safety when installing cranes near power lines.
3.6. Ensuring occupational safety when installing cranes near excavations.
3.7. Ensuring safety when storing materials, structures, products and equipment.
3.8. Ensuring safety during loading and unloading operations.
4. SOLUTIONS TO ENSURE LABOR SAFETY IN ORGANIZATIONAL AND TECHNOLOGICAL DOCUMENTATION (PPR, POS, etc.) WHEN USING CRANES AND HOISTS.
4.1.General provisions.
4.2. Stroygenplan.
4.3. Technological diagrams.
3.3. Ensuring labor safety in hazardous areas of cranes and lifts.
3.3.1. Instruments and safety devices installed on cranes.
Instruments and safety devices are designed to automatically shut down the units and mechanisms of the crane when any parameter characterizing the operating mode of the equipment deviates beyond the permissible values.
To the main instruments and safety devices installed on lifting cranes, include (Fig. 3.7):
- load capacity (load moment) limiters;
- boom extension limiters;
- limit switches;
- hook lift limiters;
- rotation limiters of the rotating part of the crane;
- anemometer;
- anti-theft devices, outriggers, brakes, fencing, galleries, platforms and stairs.
The crane's movement limiters must be installed in such a way that the motor of the movement mechanism is turned off at a distance not less than the braking distance to the dead-end stop.
To dampen the residual speed of the crane and prevent it from leaving the end sections of the crane runway in emergency situations, in case of failure of the travel limiter or the brakes of the crane movement mechanism, dead-end stops must be installed at the ends of the rail track (at a distance of at least 0.5 m) 12 (Fig. 3.7.).
The stops must be installed in such a way that the crane hits the stops simultaneously. When installing dead-end stops, it is necessary to take into account the distance from the ends of the track, the dimensions of the dead-end stops, the distance between paired dead-end stops for heavy cranes and the distance between the dead-end stops and the dimensions of the crane located at the extreme parking lot at the dead-end stop.
Boom extension limiters serve to automatically disable the mechanism that ensures the change in boom reach 5 (Fig. 3.7.) when the boom reaches its maximum or minimum working reach.
Hook lift height limiter 3 , 4 (Fig. 3.7.) serves to automatically disable the hook lifting mechanism when it approaches the upper extreme position. This limiter consists of a switch 4 and cargo 3 with two guide brackets into which the branches of the cargo rope are inserted. When the load suspension rests on the load 3 and lifts it, the switch lever is released from the load 4 , opens the electrical supply contacts of the hook lifting mechanism.
Turn limiter 7 (Fig. 3.7.) of the rotating part of the crane serves to prevent rotation of the rotating part of the crane in one direction more than twice, in order to prevent breakage of live wires when some ends of these wires are fixed on the running frame, and the other on the rotating part tap.
Anemometer 1 (Fig. 3.7.) is designed to automatically determine the wind speed at which work stops and emergency devices are activated. Anemometer 1 connected to the instrument panel in the crane operator's cabin. Light and sound alarm system 6 reacts to an increase in wind force to the maximum permissible value and to wind speed exceeding the permissible value.
Rice. 3.7. Instruments and devices providing safe work tower crane.
1
– anemometer; 2
- load limiter force sensor; 3
– hook lift limiter weight; 4
– hook lift height limiter switch; 5
– boom lift angle sensor; 6
– sound signal; 7
– limit switch of the turret rotation limiter; 8
– limiter alarm panel; 9
– load limiter relay unit; 10
– limit switch of the crane movement limiter; 11
– inventory track line; 12
– dead-end stop.
General conditions for protecting electrical equipment on cranes from emergency situations
According to its purpose, specificity of work and design features lifting cranes belong to the category of equipment that has increased danger, which is explained by the very process of operation of these mechanisms on sites and in rooms where people and valuable equipment are simultaneously located.
General requirements for the safety of operation of cranes and crane electrical equipment are formulated in accordance with the “Rules for Design and Safe Operation lifting cranes" and "Rules for electrical installations".
All electrical equipment located in crane control cabins is equipped with grounded metal casings or must be completely closed from the possibility of touching live parts. The control cabin must also contain a device that provides direct or remote shutdown of all power cable routes running along the crane, with the exception of input devices.
Access to crane platforms where electrical equipment and trolleys that are not protected by casings are located can only be achieved through doors and hatches that have a lock that turns off the power to all sources of electricity in the crane.
The section of the main trolleys, the main current collectors and current leads that remain energized when all intra-crane wiring is disconnected. must have reliable protection from accidental touching. This fence must have a lock with an individual key.
Repair and inspection of current leads can only be carried out when the power to the main trolleys or the general input device located outside the crane is turned off. The chains of several cranes are powered from general workshop trolleys, it is provided repair area, where the trolleys can be turned off without interrupting the power supply to the remaining cranes.
Cranes are moving installations and are subject to vibrations and shocks during movement, so the possibility of damage to cables and wires on cranes is relatively higher than with their stationary installation. In addition, on a number of cranes, current transfer to moving parts is carried out using flexible hose cables, the damage of which cannot be completely avoided. Taking this into account, the first task of protection is to protect electrical equipment on taps from short-circuit currents.
Short-circuit currents in individual circuits within the tap will be smaller, the smaller the cross-section of the installation wires of these circuits and smaller sizes various current junctions and current connectors. Maximum short-circuit currents in control circuits with a wire cross-section of 2.5 mm2 is 1200-2500 A. In this case, to protect the circuits it is possible to use fuses of the PR series for currents of 6-20 A or any types of automatic circuit breakers AP 50, AK 63, etc. Currents. h., A, in electric motor circuits can be approximately determined by the formula
Where I kzyuf - current short circuit in the supply phase, line after 0.04 s; s p - wire cross-section in the circuit under consideration, mm2.
Since the current k.e. should not, before turning it off, destroy the switching device located in this circuit, then when choosing devices and wire cross-sections, it is necessary to observe certain ratios that ensure the thermal resistance of the device. Assuming that the thermal resistance of most devices used in crane electric drives is 10I n for 1 s, then the relationship between the maximum permissible wire cross-section, mm2, and the rated current of the device should be as follows:
Where I n - rated current of the device, A.
The last relationship shows that at possible short-circuit currents. on a feeder of more than 8000 A, it is unacceptable to install 25 A devices due to thermal resistance. Devices for currents of 63 A can only be used with cable cross-sections of no more than 6 mm2, and devices for currents of 100 A - with cable cross-sections of no more than 16 mm2.
At possible short-circuit currents. 12,000 A (limit for cranes) devices with a current of 63 A can only be used with cable cross-sections of no more than 4 mm2, i.e., with rated currents up to 30 A. Devices with a current of 100 A can be used with cable cross-sections of no more than 10 mm2, i.e. at rated currents up to 60 A. Thus, for cranes receiving power from feeders of particularly high power, it is necessary either to install devices with currents of at least 100-160 A, or to limit the cross-section of wires to these devices in order to reduce possible currents k.z.
Protection of the crane cable network from short-circuit currents. is carried out using an instantaneous overcurrent relay, and, if necessary, can be carried out by automatic installation machines.
Protection of wires from short-circuit currents. is complicated by the large power range of the electric motors of the mechanisms within one crane. In accordance with the rules for electrical installations, protective devices must be designed for an operating current of no higher than 450% of the continuous current of the protected circuit. By the same rules, for wires and cables operating with intermittent loads, the permissible heating current is determined by the expression
Where I pv and I n - rated cable currents in intermittent and continuous operating modes.
At PV=40% I pv = 1.4 x I n. Thus, the multiple of the protection setting to the permissible current of the wire (cable) should not be higher than 450/1.4 = 320% of the current in the 40% duty cycle mode. Permissible loads on wires and cables within the crane at temperatures environment 45°C are given in the reference tables.
Crane electric drives have the following main types of protective devices:
Maximum protection for disconnecting the electric drive from the network when unacceptable currents occur in the protected circuit;
Zero protection to turn off the electric drive when the power supply from the electrical source is interrupted or interrupted. A type of zero protection is zero blocking, which prevents self-starting of the electric motor when power is restored to the supply line if the control is in the operating position
Ultimate protection to prevent movement of moving structures beyond certain permissible limits.
An important task of the protection system is to prevent unacceptable overloads for all types of electric drives of crane mechanisms associated with malfunction of control circuits, jamming of mechanisms, open brake circuits, etc. This is the difference between the requirements for overload protection of crane electric drives and overload protection for electric drives of continuous operation .
Due to the uncertainty of the load of crane mechanisms, changing heating rates of motors, and their operation under conditions of frequent starts and braking, it is not even possible to set the task of protecting electric drives from thermal overloads. The only condition for preventing thermal overloads of crane electrical equipment is its right choice taking into account any pre-calculated operating modes possible in operation.
Thus, overload protection comes down to monitoring the inrush current during step-by-step starting and protection against jamming squirrel cage motors or electric drives with current cut-off. With a properly organized start of the electric drive with stepwise acceleration, the starting current should not exceed 220-240% of the current corresponding to the calculated value.
Taking into account the necessary margin for the spread of both the starting current and the maximum relay setting, the latter should be designed to operate at a current of about 250% of the calculated one, which may be equal to or less than the electric motor current in duty cycle mode = 40%.
According to the above, the maximum current relay in the crane electric drive system has two functions:
1. protection against short-circuit currents. wires (cables) in each pole on direct current and in each phase on alternating current,
2. overload protection, to ensure which it is enough to turn on the relay in one of the poles or one of the phases.
In accordance with the rules, electric drives of cranes must have, i.e., when the power is interrupted, the electric drive must be turned off, and it can be turned on again only after the control has returned to the zero position. This requirement does not apply to floor push-button systems that have self-resetting pushbuttons.
The presence of zero blocking eliminates self-starting of electric drives of cranes, and also eliminates re-starting when various protections are triggered.
Phase loss protection is not used on taps. Analysis possible consequences phase failure outside the tap and an acceptable phase failure protection system showed that, on the one hand, there is currently no satisfactory technical solution for using a reliable, cheap and simple phase voltage monitoring device, and on the other hand, phase failure within the tap and outside it is unlikely due to the fact that the use of fuses in the main circuit is not currently practiced.
New dynamic braking systems, used instead of counter-switch braking, minimize the risk of a load falling due to phase failure.
Overload protection relay in electric crane drive
To protect crane electrical equipment circuits from overloads, an instantaneous electromagnetic relay type REO 401 is used. These relays can be used in both AC and DC circuits. The relay has two designs. In Fig. Figure 1 shows a general view of the REO 401 relay.
The relay consists of two main components: electromagnet 2 and opening auxiliary contact 1. The coil of the electromagnet 3 is located on the tube 4, in which the armature 5 moves freely. The position of the armature in the tube is adjustable in height and determines the value of the relay operating current. When the current in the coil increases above the operating current, the armature rises up and opens the contacts through the pusher of the contact assembly.
In the second version, relay electromagnets in the amount of two to four pieces are attached to a common base, which also has a common bracket that transmits the forces of any individual electromagnet armature to an auxiliary contact installed on the base. Thus, in this design several electromagnets act on one auxiliary contact.
After the current is turned off, the armature returns under the influence of its own weight. The relay has one normally open auxiliary contact. The auxiliary contact is rated for up to 10 A AC switching at 380 V and or 1 A DC switching at 220 V and L/R = 0.05
Rice. 1 . General view relay REO 401
Relay coils for currents above 40 A are made of bare copper. The terminals of these coils are located on a special insulating panel. Coils for currents up to 40 A are insulated. When choosing a relay to install in. complete devices should be guided by permissible load coils in PV mode = 40% and operating range taking into account the required shutdown settings.
REO 401 relays can perform their functions provided that the starting current of the electric drive is less than the current of the braked electric motor when it is turned on at the rated voltage, i.e., protection of short-circuited electric motors and electric drives with current cut-off using the REO 401 relay is impossible. Protection of such electric motors should be carried out using thermal series TRT.
TRT relays have five sizes in the current range from 1.75 to 550 A. Relays of all types are enclosed in a plastic casing and differ in the shape of the reacting thermal element, the presence of an additional heater and the size of the leads. The fifth size relay is mounted on a current transformer. Invarstal bimetal, flown by current and additionally heated by a heater, is used as a reacting thermal element of the relay. The relay has one normally open contact, rated for switching AC 10 A, 380 V at Cos φ = 0.4 and DC 0.5 A, 220 V at L/R = 0.05.
Technical data of the TRT relay are given in reference books. The timing characteristics of the TRT series relays are shown in Fig. 2. The relay does not operate at 110% of the rated current in continuous mode. At a current of 135% of the rated relay, it operates in 5-20 minutes. At a current of 600% of the rated relay, it operates in a time from 3 to 15 s. The regulator available on the relay allows you to adjust the rated current setting within ±15%. The relay contacts return to the on state 1-3 minutes after the current is turned off.
When choosing a relay, you should be guided by the following conditions:
1) the rms current of the protected circuit must not be higher than the rated current of the heater;
2) with three starts in a row, the relay should not operate;
3) the response time at the starting current should not be higher than the permissible time for the electric motor to remain under current in this mode.
When using the time characteristic of the operation of the TRT relay, it should be taken into account that the possible actual deviations of the operation current are about ±20% of the set current.
Protective panels
In accordance with the requirements, each crane must be equipped with a device designed to supply power to the electric drives of the mechanisms and turn it off, and turning it on, i.e., supplying power, can be carried out after unlocking the switching device using an individual brand key.
Rice. 2. Timing characteristics of TRT series relays.
In turn, the key cannot be removed without performing a shutdown operation. This locking makes it possible to ensure that the crane is brought into a usable state only by a person authorized to operate the crane.
On all types of electric cranes, except construction ones tower cranes, individual key brand is used in . For construction tower cranes, the specified key is used to lock the main switch (or circuit breaker) in the tower crane power cabinet to which the flexible power cable is connected.
Rice. 3. Diagram of control circuits of protective panels: a - when controlling cam controllers; b - when controlling magnetic controllers; 1P-ZP - fuses; KB - “return” button; CL - hatch contact; AB - emergency switch; L - linear contactor: MP1, MP2 - maximum relay contacts; KVV, KVN - limit switches; PP - test switch; K12 - zero contacts of controllers.
