ТЕХНИЧЕСКИЕ НАУКИ/ 6.Электротехника и радиоэлектроника

C.t.s. Hovhannisyan A.T., D.t.s Grigoryan A.Kh.,

Sargsyan V.G., Khachatryan V.H.

STATE ENGINEERING UNIVERSITY OF ARMENIA (POLYTECHNIC)

The Applications of the trapezoid control coil in electromechanics

The control coils of the electromechanical systems, as a rule, have a rectangular section. However, in some particular cases, especially in electromagnets for optical researches, in order to obtain a powerful electromagnetic field a coil with a trapezoidal section is used [1]:

In order to increase the sensitivity of electromechanical systems with open magnetic circuits, to improve dynamic characteristics, to increase the distance of the possible movement of the moving body (anchor, core) and, ultimately, in order to decrease the sizes and the weight of the system we have made an attempt to replace the rectangular coil by the one with a trapezoidal section [2...4].

Below we will discuss the application features of the mentioned above coils in two different electromechanical systems.

1. Linear solenoid electromagnet

By use of linear electromechanical systems various transmitters are being created which are being used in several industrial fields, especially in control and monitoring processes.

The observed solenoid electromagnet which ensures the linear movement consists of (1) control coil, and (2) ferromagnetic core (pic.1). In the first, traditional, case (pic.1, a) the coil has a rectangular section and symmetrically distributed over longitudinal axis. In the next two pictures (pic.1. b, c) are our proposed systems with trapezoidal section coil.

We will introduce below the research results of solenoid electromagnets, which ensures linear movement, with rectangular and trapezoidal section control coils, where the coils had the following parameters: the number of the windings – 3500, the diameter of the wire – 0.17 mm, the active impedance – 154 Ohms, the length – 58 mm, the internal diameter – 11.2 mm.

a) b) c)

Pic.1. The studied linear electromagnets

a) with rectangular section coil, b) with trapezoidal section coil, the core is set at the smaller base of trapezoidal, c) with trapezoidal section coil, the core is set at the longer base of trapezoidal

Experimentally and theoretically, through calculations, the distribution of magnetic induction over longitudinal axis of two types coils (without presence of core) for magnetomotive force value of 350A. The graphical images of the obtained results are shown in Pic.2.

Pic. 2. Magnetic field induction distribution by coil longitudinal axis

As shown in the graph, the maximum value of the magnetic induction inside rectangular symmetrical coil turns out at the center of the coil, while in case of trapezoidal one the coordinate of the maximum value shifted from the center to longer base side. Thereby, in rectangular coil at X=29 mm coordinate the induction value is B_max=7,52×10^-3 Tl, but in trapezoidal case at coordinate X=50 mm the induction is B_max=10,2×10^-3 Tl. This means that in coil with trapezoidal section the maximum value of the induction is 1,35 times higher than in rectangular one. Moreover, the magnetic field changes over the length unit have a greater change.

The influence of the external magnet wire of the coil on the magnetic field distribution nature and values is also studied (in the Pic.1 the external magnet wire doesn’t exist). The research results showed that in the two different coils systems the proportion between maximum values of magnetic induction and coordinates of maximum induction remain the same toward the systems without an external magnet wire.

The influence of the electromagnetic attractive force on the core was studied when in the coils the ferromagnetic core was placed at the different positions. There were two cores with the same diameters d=8 mm but with different lengths; the length of the core 1 - l₁=23 mm, core 2 - l₁=42 mm. The measurement of the electromagnetic attractive force performed by the developed and manufactured by us scientific-experimental device which have provided the necessary accuracy and application usability.

The graphical dependencies of attractive force from core position coordinates for systems with and without external magnetic wire are brought in Pic. 3. Moreover in trapezoidal coil system the ferromagnetic core is located at smaller base of the trapezoid.

a) b)

Նկ. 3. The dependencies of attractive force from core position coordinates

a) rectangular coil, b) trapezoidal coil

1,2- core 1, 3,4- core 2, 1,3- system without magnetic wire, 2,4- system with magnetic wire

Research results show that, regardless of type of coil, the value of the derived force is higher in case of core 2. Thus, in case of core 1 in rectangular coil the maximum power were 9 g at X=41 mm, and in trapezoidal coil 10 g at X=9 mm. In case of core 2 the power was as follow: in rectangular coil 24 g at X=31 mm, and in trapezoidal coil 32 g at X=9 mm. The presented data of force show that in trapezoidal coil (10 g, 32 g) it is higher than values obtained in rectangular coil (9 g, 24 g). It was also studied in electromagnets with both types of coils the ferromagnetic core DX movement size, where symmetry axes of the above cores were matched: for rectangular coil with the edge of the coil (Pic. 1, a), and for trapezoidal coil with the smaller base. It was turned out that the core movement size in the trapezoidal section coil (from smaller base) exceeds the core movement in rectangular coil system, thus in case of core 1 in rectangular coil system that movement is DX=12 mm, and in trapezoidal coil system DX=39 mm. Beside that the movement of the same core in trapezoidal section coil from the longer base is DX=21 mm.

For the research purpose as an example of linear electromagnet application with trapezoidal coil the having of various uses electromagnetic valve were chosen. In such valves the closing clapper is moving due to linear electromagnet, which coil powered from alternating or direct voltage source. The coils of these type electromagnets are usually being with a rectangular section. During our experiment the rectangular coil were replaced with the same length of trapezoidal section coil. The researches results one more time revealed the features and advantages of the trapezoidal coil which were discovered during the researches represented above. Moreover, due to these advantages, by replacing of the rectangular coil with trapezoidal one and by maintaining the characteristics of the electromagnetic valve, it became possible, by preserving the characteristics of electromagnet, to reduce the cooper weight of the control coil from 150 g to 83 g, means to cut down for about 45%; and the valve clapper, due to increasing of movement size, to extend for nearly 15 mm (Pic. 4).

Pic. 4. Electromagnetic valve with trapezoidal section control coil

2. Asymmetric reed relay

As is well known, the asymmetric red relays are consisting from asymmetric reed switch and control coil which placed on the glass tube of the reed (equally distributed over the tube length) and have a rectangular cross section. In case of direct current passing through the control coil the magnetomotive force occures which created magnetic flux passes through reed’s contact gap and creates electromagnetic attractive force. If the value of magnetomotive force is enough the reed’s contacts are closing with influence of attractive force – the relay is operating. The power starting value of the coil determines the sensitivity of the relay.

The disadvantage of such system comparing to symmetric reed relay (where the contact gap symmetry axe matches with the coil symmetry axe) is that the relay has a smaller sensitivity, means higher starting power. This is due to the deviation of the reed’s contact gap from the zone of maximum magnetic field created by coil.

During our researches the rectangular coil was replaced by trapezoidal coil, and the asymmetric reed was placed in the coil in a way that the reed’s contact gap to be near to the longer base, means in the zone of the maximum value of magnetic field induction (Pic. 5). In the Pic. 5 1 is a reed, 2 is a control coil, and 3 is a coil frame.

Pic. 5. Asymmetric reed relay with trapezoidal coil

The experimental studies of asymmetric reed relay were accomplished on reed’s phisical model. The control of the same reed were performed with both rectungular and trapezoidal sections coils. The following results are obtained: the current and the power of the relay’s coil at the starting point in rectungular section coil were accordingly 27,4 mA and 88 mWatt, and releasing parameters are 22,6 mA and 60 mWatt. The same parameters of the reed relay with trapezoidal coil were 20,4 mA and 66 mWatt at starting point; and 17,2 mA with 47 mWatt at releasing point. From the obtained results is following that when replacing the rectangular coil with trapezoidal one the relay’s starting and releasing functional parameters are decreasing for about 22% – 25 %, due to which the relay acquires comparatively high sensitivity and requires comparatively small control power.

Conclusion

1. In trapezoidal section coil the coordinate of the magnetic field induction maxumum value can be changed, by changing the nature of windings distribution over the coil’s length (the ratio of the smaller and longer bases of the trapezoid).

2. Comparing with rectangular coil the linear electromagmet with trapezoidal coil is two-coordinate system, since it provides the bigger movement of the core from the smaller base side and short movement from the longer base side of trapezoid; on the other hand, provides comparatively longer movement of the core, bigger electromagnetic attractive force; and due to rapid changes of the value of magnetic field coordinate it provides the stability of the core position against external vibration factors.

3. The trapezoidal section coil can be used to control the reed as observed the above, as well as the toggle type symmetric reeds, and to simultaneous control of multiple asymmetric reeds.

4. The use of trapezoidal section control coil in open magnetic circuit electromechanical systems creates opportunities to increase the sensitivity of the system and to decrease the sizes and the weight.

Literature

1. Карасик В.Р. Физика и техника сильных магнитных полей. Наука, М.: – 1964 – 347 с.

2. Patent of RA 2349A, Reed Relay: / A.T. Hovhannisyan, A.Kh. Grigoryan, V.G Sargsyan, 25.01.2010.

3. Patent of RA 2572A. The Linear Electromagnet / A.T. Hovhannisyan, 25.11.2011.

4. Patent of RA 2609A. Electromagnet / A.T. Hovhannisyan, 2012.

5. Patent of RA 2708. The Electromagnetic Linear Accelerator. / A.T. Hovhannisyan, 2013.

This work was supported by State Committee of Science MES RA, in scope of the research project № SCS 13-2B059.

Hovhannisyan Andranik - Candidat of technical sciences, SEUA associate professor, Armenia, Erevan-0017, Sari Tax, Rue 6, Flat 36.

Tel.: (+37410) 57-77-27, (+37493) 32-12-60. E-mail: andranik.hovhannisyan@yandex.ru

Grigoryan Areg Khachiki - Doctor of technical sciences, professor.

Tel.: (+37410) 52-17-92, E-mail: Grigoryan@seua.am

Sargsyan V.G. – Engineer, valeri@sas-se com

Khachatryan V.H. - Engineer, (+37493) 69-37-09, vaharpa@mail.ru