What is a contact solution. Parameters of switching contacts of electrical devices
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The gap (contact gap) is the distance between the working surfaces of the contacts in their off position.
The failure (lapping) is the distance traveled by the moving contact from the moment the contacts come into contact with the auxiliary surfaces until they are completely closed by the working surfaces. Produced by a lapping spring.
The initial contact pressure (pressure) is generated by the lapping spring. Depending on the type of apparatus, it is in the range of 3.5 - 9 kg.
The final contact pressure (pressure) is created by an electro-pneumatic or electromagnetic drive, depending on the type of apparatus, it must be less than 14 - 27 kg.
Figure 4. Template for measuring contact gap
a) contactors of the PK MK 310 (MK 010) MK 015 (MK 009) type and group switches, b) cam switches and contact break of the MKP 23 type contactor
Contact line must be at least 80% of the total contact area.
The contact gap is determined by the smallest distance between the contacts in the open position. It is measured with an angular template graduated in millimeters (Figure 4 a and b).
The failure of contacts in each of the devices is measured depending on the design of the contact system. Thus, the measurement of the failure of contacts for contactors of the PK type and contactor elements of group switches is carried out with the device turned on with angular templates of 12 and 14 degrees. mm
The failure of the contacts of the cam elements of the cam switches is determined in the closed position of the contacts by the distance A(Figure 5, b). Distance " A » 7-10 mm corresponds to a dip of 10-14 mm
Figure 5. Definition of contact failure.
a) determination of the failure of contacts of contactors of the PK type and contactor elements of group switches b) - determination of the failure of contacts of cam elements to cam devices
The initial contact pressure is determined by the compression force of the lapping spring. The final pressure of the contacts is measured with a dynamometer with closed contacts, which is measured at the moment when it is possible to pull out a strip of paper sandwiched between the contacts with a compressed air pressure of 5 kg / cm 2 in an electro-pneumatic drive. With an electromagnetic drive, the voltage on the closing coil must be 50V. In this case, the dynamometer must be fixed to the movable contact so that the force applied to it crosses the line of contact of the contacts and coincides with the direction of movement of the contact at the moment of separation.
For knife disconnectors, the contact quality is checked by the force on the handle when turned on, it must be at least 2.1-2.5 kg / cm 2, and when turned off - 1.3-1.6 kg / cm 2.
The contact line of contacts must be at least 80% for all devices, except for devices specified in the technical specifications. Determined by the print on carbon paper when the machine is turned on
It is customary to call the failure of the contact the distance by which the place of contact of the movable contact with the fixed one can shift from the position of full closure if the fixed contact is removed. Since it is practically difficult to determine the size of the wire, they are limited to checking the gap formed between the plate on which the fixed contact is fixed and the contact holder bracket when the contacts are closed.
The initial pressing is the force created by the contact spring at the point of initial contact with the contacts. If the value of the initial pressure is insufficient, welding of the contacts may occur, and if the required value of the initial pressure is exceeded, the clarity of the contactor operation is disturbed. Checking the initial pressing is performed as follows.
Previously, a contact line is drawn on the moving contact. When changing the initial pressure, the contacts must be in the open state.
A strip of thin paper is clamped between the moving contact and the plate on which the moving contact is mounted. A dynamometer hook is threaded through the opening of the moving contact, which is pulled back until the paper can be freely moved by pulling it out by hand. The dynamometer reading at this moment gives the value of the initial pressure.
The end pressure is the force generated by the contact spring.
The check of the final pressing is carried out with the contactor fully turned on, similarly to the measurement, only the paper in this case is laid between the movable and fixed contact.
The adjustment of the amount of pressing of the contacts is made by changing the position of the bracket of the holders of the movable contacts by tightening or loosening the nuts.
Operating principle:
The contactor works as follows. When voltage is applied to the target of the coil, the core attracts an armature that presses the moving contacts against the fixed ones. The core rests on shock-absorbing springs, softening the blows of the armature on the core at the moment the contactor is turned on. With the help of a spring, the armature returns to the off position. The path of movement of the armature rotating on the axis is limited by the stop. When the armature is attracted to the core, the moving contacts are pressed against the fixed contacts and close the auxiliary contacts, which bypass the “Start” button so that after starting the motor it can be released.
The principle of operation of the switching device:
To prevent vibration of the contacts, the contact spring creates a pre-pressure equal to half the final pressing force. The rigidity of the fixing of the fixed contact and the resistance to vibrations of the entire contact as a whole have a great influence on the vibration. In this regard, the design of the KPV-600 series is very successful. the fixed contact is rigidly attached to the bracket. One end of the arc chute is attached to the same bracket. The second end of the coil, together with the output, is securely fastened to an insulating plastic base. The latter is attached to a strong steel bracket, which is the base of the apparatus. The moving contact is made in the form of a thick plate. The lower end of the plate has the ability to rotate relative to the fulcrum. Due to this, the plate can roll over the cracker of the fixed contact. The output is connected to the moving contact using a flexible conductor (connection). Contact pressure is created by a spring.
When the contacts are worn, the cracker is replaced with a new one, and the movable contact plate is rotated 180 ° and its undamaged side is used in operation.
To reduce the melting of the main contacts by an arc at currents of more than 50 A, the contactor has arcing contacts - horns. Under the action of the magnetic field of the arc quenching device, the reference points of the arc quickly move to the bracket connected to the fixed contact and to the protective horn of the movable contact. The anchor is returned to its initial position by a spring.
The main contact parameter is rated current, which defines the dimensions of the contactor.
The KPV contact series is designed with a break contact. Closing is due to the action of the spring, and opening - due to the force developed by the electromagnet.
The rated current of the contactor is the current of intermittent-continuous operation. In this mode, the contactor is in the on state for no more than 8 hours. After this period, the device must be switched on and off several times (to clean the contacts from copper oxide). After that, the device turns on again.
Type KTPV-500, has an electromagnet direct current, the moving contacts are isolated from the housing, which makes it safer to operate the machine.
The movable contact with a spring is mounted on an insulating lever connected to the contactor shaft. Due to easier arc extinguishing alternating current the contact solution can be taken small. Reducing the opening makes it possible to approach the axis of rotation. The small distance of the contact point from the axis of rotation makes it possible to reduce the strength of the electromagnet required to turn on the contact, which makes it possible to reduce the size and power consumption of the magnet.
The movable contact and the armature of the electromagnet are interconnected through the contactor shaft. Unlike DC contactors, the movable contact in the KPV-600 contactor does not have rolling. The device is switched off under the action of contact springs and the weight forces of the moving parts.
The principle of operation of the extinguishing device.
In DC contactors, devices with electromagnetic blast are most widely used. When the magnetic field interacts with the arc, an electrodynamic force arises that moves the arc at high speed. To improve the cooling of the arc, it is driven into a slot made of arc-resistant material with high thermal conductivity.
When the contacts diverge, an arc occurs between them. The arc can be considered as a current-carrying conductor. The coil creates a C.D.S., under the action of which a current arises. This flow passes through the core of the coil, the pole pieces and the air gap in which the arc burns.
To ensure the conditions for extinguishing the arc, it is necessary to raise the current with increasing volt-ampere characteristic arcs.
In the region of low currents, with increasing current, the contact gap required for quenching increases. At a given speed of their movement, more time is required to reach the required solution. In the region of high currents, the quenching process is determined by electrodynamic forces. The greater the rate of stretching of the arc by dynamic forces, the shorter the time required for the arc to reach the critical length.
In high-frequency installations, to ensure normal operating conditions for generators, cos φ circuits tend to be closer to unity.
For reliable and fast arc extinguishing in the area of low currents, small current contactors with replaceable magnetic blowing coils are used. These coils have a nominal current of 1.5 - 40 A. With a low breaking current, a coil with a large number of turns is installed, due to which the necessary magnetic field is created to extinguish the arc in a short time.
ELECTROSPETS
ELECTROSPETS
AC contactors, contact adjustment.
The main parameters of the contact device are the contact gap, the failure of the contacts, and the pressure on the contacts of the contactors, so they are subject to mandatory periodic checks and adjustments in accordance with the data in Table. 1.
|
Contactor type |
Contact gap, mm |
Gap controlling dip, mm |
Initial pressing. kg (N) |
Final pressure kg (N) |
|
Table 1. Contactors series KT6000, KT7000 and KTP6000 |
||||
|
|
||||
|
KT6012, KT6022, |
2,2-2,4 |
2,5-2,9 |
||
|
KT5013, KT6023, |
1,5-1,6 |
1,8-2,2 |
||
|
KT6014, KT6024, KT7014, KT7024 |
1,1-1,2 |
1,4-1,7 |
||
|
KT7015, KT7025 |
0,85-0,95 |
1.1-1,4 |
||
|
KT6032, KTP6032, KTP6033, KTP6033 |
2,0-2,2 |
3,7-4,5 |
||
|
1,4-1,56 |
3-3,4 |
|||
|
1.1-1,2 |
2,6-3 |
|||
|
5,3-5,5 |
7,32-8,43 |
|||
|
13,1-16,6 |
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|
7,32-8,43 |
||||
|
13,1-16,6 |
||||
|
4-4,2 |
6,12-7,13 |
|||
|
3,2-3,3 |
5,34-5,23 |
|||
Continuation of table 1.
|
Contactor type |
Contact gap, mm |
Gap controlling dip, mm |
Initial pressing, kg (N) |
Final pressing, kg (N) |
|
KT6052, KTP6052. KT6053, KTP6053 |
10 - 12,5 |
3,7 - 4 |
9,6-10,0 |
18
-
21 |
|
KT6054 |
6,5-6,8 |
12,5-15 |
||
|
KT6055 |
4,8-5 |
10,5-13 |
||
| Contactors series KT6000/2 | ||||
|
KT6022/2 |
7,5-8,5 |
1,7-2 |
2.2,-2,4 |
2,5-2,9 |
|
KT6023/2 |
1,5-1,6 |
1,8-2,2 |
||
|
KT6032/2, KT6033/2 |
3,3-3,5 |
2,0-2,2 |
3,7-4,5 |
|
|
KT6042/2, KT6052/2, KT6043/2, KT6053/2 |
10-12,5 |
3,7-4 |
9,6-10,0 |
18-21 |
Rice. 2. Positions (on, off) of contacts for adjusting solutions, dips, pressings and simultaneous touching of contacts of contactors of series KTP6000, KTP6000, KT7000 and KT6000/2. a - contactors KT6032/2, KT6033/2; b, c - contactors of the KTP6000, KTP6000, KTP7000 series; 1 - the place of laying the paper tape when measuring the initial pressure on the contact; 2 - gap controlling contact failure; 3 - contact line of contacts; 4 - the place of laying the paper tape when measuring the final pressure on the contact; 5 - contact solution; 6 - direction of application of force when measuring the final pressure on the contacts; 7-directional application of force when measuring the initial pressure on the contacts; 8 - adjustment of pressure on the contact; 9 - adjustment of the dip and simultaneity of touching the Contacts.
Checking for contact failures. Since it is practically impossible to measure the magnitude of the dip, the gap that controls the dip is checked, i.e. the gap formed when the main contacts are completely closed, between the contact holder and the adjusting screws of the lever that carries the moving contact (Fig. 2). Control the failure of the main contacts in the closed position of the magnetic system of the contactor. With the full value of the contact dip, a complete final pressing on the contact is ensured. As the contacts wear, the dip decreases, therefore, the final pressure on the contact also decreases, which can lead to overheating of the contact. It is not allowed that the value of the gap that controls the failure is less than 1/2 of its initial value, indicated in Table. 1.In contactors of the KT6000/2 series, the failure of the main contacts is set by turning one adjusting screw in contactors for 160 A currents or two adjusting screws in contactors for currents of 250, 400 and 630 A. The design of the contact system of contactors of the KTP6000, KTP6000 and KTP7000 series allows double dip recovery, which is performed by turning the adjusting screw (in 100 and 160 A contactors), bushing (in 400 A contactors) and adjusting screws (in 250 and 630 A contactors).
The gap that controls the dip is measured with a feeler gauge. It is desirable that the contact dips be as large as possible. Having set the required gap and making sure that there is no skew of the moving contact, the adjusting screws must be tightened, and the bushings must be fixed with the petals of the plate.
Checking the simultaneity of contacts touching. The non-simultaneity of the contact of the main contacts is checked with a probe that controls the gap between the contacts when the other contacts touch each other. It is convenient to control the simultaneous touching of contacts using light bulb voltage 3-6 V, connected in series to the circuit of contacts, but within the limits specified in Table. 1. Non-simultaneity of touching new contacts is allowed up to 0.3 mm. It should be borne in mind that the more precisely the dips are adjusted, the less the non-simultaneity of contact contact.
Checking contact solutions. Contact solutions are checked by caliber and must correspond to the dimensions indicated in Table. 1. If the solution is not normal, then by turning the eccentric bar “the time of the anchor around the axis, they are brought back to normal (KT6000/2 series contactors). In contactors of the KTP6000, KTP6000, KTP7000 series (except for KTP6050), the contact gap is adjusted by turning the stop around the axis by 90°. These contactors have several stop positions that determine the degree of adjustment of the solution.
Checking contact pressure. The pressing of the main contacts is determined by the elasticity of the contact springs. Pressing contacts is regulated by the largest values indicated in Table. 1, so that after wear of the contacts it does not decrease below the permissible values. The degree of wear of the contacts (crackers) is determined by the magnitude of the dip. If, as a result of the wear of crackers, the dip turns out to be less than the minimum values \u200b\u200bspecified in Table 1, the contacts should be replaced with new ones. When measuring pressure, it is necessary to ensure that the tension line is approximately perpendicular to the plane of contact of the contacts.
Initial pressing- this is the force created by the contact spring at the point of initial contact of the contacts. Insufficient initial pressure leads to melting or welding of contacts, and an increased initial pressure can lead to fuzzy switching on of the contactor or its sticking in intermediate positions.
Initial Press Check produced with open contacts (no current in the coil). In practice, the control of the initial pressing of the contacts is carried out not on the contact line of the contacts, but between the movable contact and the lever using a dynamometer, a strip of thin paper and a loop (for example, made of steel wire or keeper tape). The loop is superimposed on the movable contact, and a thin paper tape is inserted between the shaft protrusion and the adjusting screw - for 100 and 160 A contactors (Fig. 2, c), between the holder and the adjusting sleeve - for 400 A contactors (Fig. 2, b ), between the holder and two adjusting screws - for contactors for 250, 400 and 630 A (Fig. 2, a). Then the tension of the dynamometer is determined by the force at which the strip of paper is easily pulled out. This force must correspond to the initial contact force indicated in Table. 1. In fig. 2, the arrow indicates the direction of tension of the dynamometer. If the tension does not correspond to the table, it is necessary to change the tightening of the contact spring by turning the adjusting screws, nuts and bushings. After setting the required pressure, the adjusting devices must be firmly fixed so that the setting is not disturbed.
End push. The final pressing characterizes the pressure of the contacts when the contactor is on. Compliance of end presses with tabular ones is possible only for new contacts. As the contacts wear, the amount of final pressure will decrease. To measure the final pressure, it is necessary to fully switch on the contacts, for which the armature of the magnetic system is pressed against the core and wedged or the pull-in coil is connected to full voltage. A strip of fire paper is clamped between the contacts. A loop is put on the moving contact (as when measuring the initial tension). The loop is pulled with a dynamometer hook until the contacts are so far apart that the paper can be moved. In this case, the dynamometer readings give the value of the final pressure on the contacts. The end pressure is not adjustable, but controlled. If the final pressing does not correspond to that indicated in the table. 1, it is necessary to replace the contact spring and carry out the entire adjustment process from the beginning.
electromagnetic relays
The most important element of all electromagnetic relays is the contact
system. Provide the same conditions at the point of electrical contact
the passage of current, which a solid conductor has, is almost impossible,
as a result, contact connections are the weakest point of any
electrical apparatus and require special attention during operation.
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| |
|
The value of the transition resistance of the contact is influenced by the series
reasons: it depends on the material of the contact connection, on the pressure,
tested
contact
elements,
quantities
surfaces
contact and its condition and on the contact temperature. Electricity,
released during the passage of current through the contact elements, partially
turns into heat, heating these elements in the course of their work and
scattering into environment. Excessive heating of the contacts often
leads to their oxidation, and the oxide films of most metals do not
electrical wiring and increase the value of the transition resistance.
Reliability of relay operation largely depends on the quality
adjustment of the contact system and the state of the contacts. If the relay contacts
vibrate, then during operation they burn and collapse, and sometimes
are welded.
The operation of the relay contacts is characterized by the values of the solution between
movable and fixed contacts, failure and pressing force of contacts.
Each metal is characterized by a certain optimal value
providing
limiting
pressure,
whom
magnitude
transitional
resistance
practically
changes
further
an increase in contact force.
contacts
least
distance
contact
surfaces of fully open relay contacts.
The failure of contacts is the distance over which the movable
contact system of the relay after touching the contacts (distance over which
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the contact system moves if the fixed contact system
mentally remove). Contact failure [mm] is a passport technical value,
providing pressing force. During operation, the contact wears out
(friction, burnout of part of the contact due to an electric arc) and contact
pressure decreases, which means that the contact resistance increases and increases
danger of welding. Therefore, the failure of contacts during operation
controlled.
The gap and failure of the relay contacts are determined using a measuring
tool. Measured values of openings, dips and pressures for each
much
differ
relevant
given in the data sheets of the relay. Allowable dip reduction
contacts by 50% of the initial value given in the factory documentation
manufacturer.
Clear and reliable operation of relay contacts without sparking, welding,
flashing and jumping depends both on their mechanical adjustment and on
electrical adjustment of the relay as a whole. Therefore, finally contacts
govern
underflow
settings
electrical
parameters
having previously performed mechanical adjustment of the contacts.
Before adjustment, dirty burnt contacts are washed with alcohol.
or cleaned with a velvet file and polished. Wash them with gasoline
ammonia or other detergent composition is not recommended.
Contact relays are adjusted so that there is no vibration and
jumping of moving contacts to fixed ones, and when editing
fixed contacts with tweezers to avoid breaking the contact springs. Deflection
springs of fixed contacts depends on their elasticity, meeting angle and
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joint course of contacts, as well as from their pre-tensioning
created by limit stops and anti-vibration plates.
Cause
unacceptable
vibration
contacts
mechanical malfunctions of the relay that do not appear at low currents. Usually
cause
vibration
is
wrong
position
relative to the armature or skew of the armature axis relative to the axis of the magnetic flux due to
for misalignment of the holes for thrust bearings. In the first case, remove
large longitudinal and transverse gaps, replace the return spring
contact bridge, eliminate distortions of the axis of the contact bridge or magnetic
relay systems. In other cases, mechanical adjustment is also carried out
contacts.
Automotive relays
Electromagnetic relays on relay exchanges
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It's also an electromagnetic relay.
Under the failure of contacts the value of the displacement of the movable contact at the level of the point of contact with the fixed contact in case the fixed one is removed.
The failure of the contacts provides a reliable circuit closure when the thickness of the contacts decreases due to the burnout of their material under the action of an electric arc. The value of the dip determines the supply of contact material for wear during the operation of the contactor.
After the contacts come into contact, the movable contact rolls over the fixed one. The contact spring creates a certain pressure in the contacts, therefore, when rolling, the destruction of oxide films and other chemical compounds that may appear on the surface of the contacts occurs. The touch points of the contacts during rolling move to new places of the contact surface that were not exposed to the arc and are therefore more “clean”. All this reduces the contact resistance of the contacts and improves their working conditions. At the same time, rolling increases the mechanical wear of the contacts (contacts wear out).
contact solution is the distance between the moving and fixed contacts in the off state of the contactor. The contact spacing usually ranges from 1 to 20 mm. The lower the contact gap, the shorter the stroke of the armature of the drive electromagnet. This leads to a decrease in the working air gap in the electromagnet, magnetic resistance, magnetizing force, power of the electromagnet coil and its dimensions. The minimum value of the contact gap is determined by: technological and operational conditions, the possibility of forming a metal bridge between the contacts when the current circuit is broken, the conditions for eliminating the possibility of closing the contacts when the moving system rebounds from the stop when the device is turned off. The contact gap must also be sufficient to provide conditions for reliable arc quenching at low currents.