IPASJ International Journal of Mechanical Engineering (IIJME)
Web Site: http://www.ipasj.org/IIJME/IIJME.htm
Email: editoriijme@ipasj.org
ISSN 2321-6441
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Volume 3, Issue 12, December 2015
DESIGN AND ANALYSIS OF PREINSERTION RESISTOR MECHANISM
Bhavik Bhesaniya1, Nilesh J Parekh 2 , Sanket Khatri3
1
Student, Mechanical Engineering, Nirma University, Ahmedabad
2
Assistant Professor, Mechanical Engineering, Hasmukh Goswami College of Engineering, Ahmedabad
3
Student, Mechanical Engineering, Nirma University, Ahmedabad
ABSTRACT
In electrical system, circuit breaker is used to make or break current for different power system equipments like transformers,
reactors, transmission lines, capacitor banks etc. in normal as well as abnormal (short circuits, over voltages and many more)
conditions. These conditions create switching over voltages. This can be substantially damped by inserting pre-insertion resistor
in circuit. The existing electrically parallel pre-insertion resistor is to be converted in to a new simple and easily controllable
electrically series pre insertion resistor mechanism with mechanical feasibility. The mechanism is comprised of two electrical
contacts and certain means for controlling the motion of the electrical contact. The motion of two electrical contacts should be
controlled to insert the resistor for 10 ms as soon as the circuit breaker is closed and bypass the resistor while opening the
circuit breaker. Five different concepts are developed from scratch to insert resistor. Dynamic motion analyses of concepts are
carried out in MSC ADAMS for various control parameters. Stress analysis of critical components of final concept which
fulfills the requirement of insertion is carried out and subsequent shape modification is followed by final dynamic analysis
which aligns with the requirement.
Keywords: Pre-Insertion Resistor, Circuit Breaker, Dynamic Analysis
1 INTRODUCTION
A circuit breaker (CB) is an apparatus in electrical a system that has the capability to, in the shortest possible time,
switch from being an ideal conductor to an ideal insulator and vice-versa. The most important task of a drive operated
circuit breaker is to interrupt fault currents and thus protect electric and electronic equipment [1]. The interruption and
the
Fig 1: Schematic of circuit showing the process of inserting resistor (R) in series with main contacts
Subsequent reconnection is called opening and closing respectively. Switching operations create transient voltages
which can be damped by inserting a particular value of resistor for certain duration in the circuit during connection [1].
Many switch like mechanisms which insert resistor in series during closing are used in industries. Fig 1 shows
completely open position initially. In open position, PIR contacts ‘1’ and main circuit breaker contacts ‘2’ are open. For
inserting resistor ‘R’ in circuit, main breaker contacts ‘2’ are closed first, whereas PIR contact ‘1’ remains open.
Resistor ‘R’ is bypassed after closing PIR contacts ‘1’.
Freeman, Froelich and Johnson [2] developed a switch like mechanism (‘1’ in Fig. 1) using a linearly moving roller.
The roller engages a crank arm that is pivotally connected to movable pre-insertion resistor (PIR) contact of switch
mechanism. Variable mechanical advantage obtained from angle between roller and crank causes the PIR contacts to
close at high speed just after main circuit breaker contacts (‘2’ in Fig. 1) to insert resistor during closing. A piston
cylinder coupling establishing rectilinear connection between main circuit breaker contacts and PIR contacts was
devised by Muller and Talir [3]. Coupling was designed to provide closing and opening delay of PIR contacts to insert
resistor and bypass resistor respectively. Michel Perret [4] invented a ‘switch like’ mechanism with both PIR contacts
movable. Initial pressure suction is used to maintain gap between PIR contacts. This initial maintenance of gap
provides closing delay of PIR contacts to insert resistor. Opening delay is provided by resistance provided to motion of
Volume 3, Issue 12, December 2015
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IPASJ International Journal of Mechanical Engineering (IIJME)
A Publisher for Research Motivation........
Volume 3, Issue 12, December 2015
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Email: editoriijme@ipasj.org
ISSN 2321-6441
PIR contact via separate spring damper system. Considering the inventions, there is a need to develop a mechanism
which can be controlled easily for insertion time.
The present work focuses on development of an easy to control mechanism for closing and opening where insertion
time can be controlled easily. The specifications to insert a resistor in series for 10 milliseconds (ms) are as under
1. Gap of at least 35 mm should be maintained between PIR contacts until main circuit breaker contacts close; 2.
2. PIR contacts should close at 65.9 ms i.e. after 10 ms of main circuit breaker closing as shown in Fig. 2;
3. PIR contacts should open at 469.2 ms i.e. after 300 ms of main circuit breaker opening as shown in Fig. 2
Fig 2: Input motion curve shows instants of closing and opening of main circuit breaker and PIR switch
2. METHODOLOGY
The concepts for new switch mechanisms are developed based on three central ideas which are as under.
1. Only one contact of mechanism is movable, the other is fixed.
2. Both the contacts moving, where motion of one contact is controlled by input motion and the other is controlled
by spring.
3. Both the contacts moving, where motion of one contact is controlled partially by input motion and partially by
spring damper, the other is controlled by spring.
2.1 Generation of concepts based on first idea
2.1.1 Concept 1
The concept simplifies and replaces the spring with that of damper of the switch mechanism invented by Muller &
Talir and patented as US5814782 [3]. As shown in Fig. 3, piston – cylinder is used to couple main circuit breaker
contacts to PIR contacts. The gap between piston–cylinder walls d1 will delay motion of PIR contacts during opening
and closing. Spring used in patented mechanism will only aid to control the closing but the same spring will not control
the motion of movable contact during opening. The damper used in concept 1 will control the motion of movable
contact while opening and closing both.
Fig3: Open and closed position of concept 1
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A Publisher for Research Motivation........
Volume 3, Issue 12, December 2015
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2.1.2 Concept 2
Fig 4: Open and closed position of concept 2
Input from main circuit breaker is provided to a crank which consists of radial slot connected to movable contact (free
slider) via connecting rod as shown in Fig. 4. Fixed contact is not shown in Fig. 4. In the closing process, the movable
contact does not move until the crank rotates angle θ1 (as shown in Fig. 4) and strikes connecting rod to transfer
motion. The angle θ1 is control parameter which delays the motion of PIR contact thus providing delayed closing.
The same method is followed in opening which provides opening delay of PIR contacts.
2.2 Generation of concepts based on second idea
Fig 5 depicts general working of PIR switch based on second idea, where input motion is provided to front contact and
the same motion is transmitted by certain means to back contact also. In the closing process, initially both the contacts
move in closing direction without much affecting the gap between them. After some time the back contact is released
from the input motion and as shown in Fig.5, the compressed spring will make back contact to return to its original
position; mean while the front contact (slider) is moving in closing direction thus closes the switch. In opening, the
motion is not transmitted to the back contact so it will remain at its position and only front contact will move and opens
the switch. Overlap between contacts will give opening delay.
Fig 5: Schematic showing operation of second idea
Concept 3 and concept 4 are developed based on second idea
2.2.1 Concept 3
Fig 6 shows the working of concept 3. A crank, push fitted on shaft is connected to front contact and a disc, free on
shaft is connected to back contact (contacts are not shown in Fig. 6). Main circuit breaker input drives the crank and
also the disc, due to the pin inserted in the disc is extended to the crank as shown in Fig 6. Initially as per idea both the
contacts move in same direction maintaining gap even if the motion is transferred. As soon as the pin is lifted off by
cam ( as shown in Fig 6), back contact is no longer driven by input and compressed spring makes back contact and thus
disc to return to original position. As crank and thus front contact are still in motion the closing occurs. To control
insertion time the control parameters are crank and disc radius, the position of cam and stiffness of spring attached to
back contact.
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Volume 3, Issue 12, December 2015
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ISSN 2321-6441
Fig 6: Working of concept 3
2.2.2 Concept 4
Fig.7 Working of Concept 4
Fig.8 General schematic of concept 4
Fig 7 shows working of concept 4. The input motion is provided to front contact and same motion is transferred to back
contact via collapsible link as shown in Fig 8. Back contact is equipped with a cam profile and is held by back spring
and damper. As per the idea, front contact travels in closing direction and the motion is also transferred to collapsible
link. When collapsible link strikes to cam of back contact, back contact also starts travelling in closing direction. After
sufficient angular travel of collapsible link, back contact is no longer controlled by input motion and is only
controllable by back spring. Initial travel of both contacts in closing direction aid to maintain gap between two contacts
and closing of PIR contacts is thus delayed.
In opening, the motion transferred to the front contact is also transferred to the collapsible link, but design of
collapsible link is such that it collapses on cam and regains its shape due to spring. Thus, the back contact does not
move in opening. Overlap between two contacts in closed position is kept higher than overlap of main circuit breaker
contacts to get opening delay. Control parameters of switch for closing are crank radius of collapsible link, back spring
stiffness which holds back contact, horizontal distance between onset of cam and hinge of collapsible link and for
opening delay overlap of two contacts.
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IPASJ International Journal of Mechanical Engineering (IIJME)
A Publisher for Research Motivation........
Volume 3, Issue 12, December 2015
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Email: editoriijme@ipasj.org
ISSN 2321-6441
2.3 General Concepts based on third idea
Fig.9 Schematic showing operation of third idea
As shown in Fig. 9, 'F' is front contact and 'Back' is back contact. Initially front contact is held by a spring damper
system. Back contact is also held by a spring. Input motion is provided to a slider and the same motion is transmitted by
some means to back contact. In closing, front contact follows the same input motion only after the slider strikes the
front contact stretching the spring attached to it. Due to motion transmitted to the back contact, it moves in closing
direction initially and increases or maintains the gap between two contacts. Sometime later, back contact is released
from the input motion and due to spring force it travels in opening direction as shown in closing mode. The front
contact still moves in closing direction and closing takes place. In the opening process, due to the motion provided to
slider it travels in the direction as shown in opening mode. The back contact is held by spring so it will not move from
the position. The front contact is acted upon by a spring force and damper as soon as the slider leaves contact with
'front contact' and the motion of the front contact is then controlled by stiffness and damping co-efficient of spring
damper system.
2.3.1 Concept 5
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Fig.10 Closing and Opening of Concept 5
Fig 10 shows concept 5 which is based on third idea, where a separate slider is used to take the motion from main
circuit breaker during closing and same is transferred to collapsible link. As shown Fig 10(2) front contact does not
move until the separate slider strikes front contact, meanwhile the motion transferred to collapsible link strikes ‘back
contact’ and it travels in closing direction too. The rest is followed as per concept 4. Initial travel of both the contacts in
closing direction maintains the gap between them and provides delayed closing of PIR contacts. In opening, due to the
motion provided to separate slider it moves in opening direction but front contact cannot follow the same velocity as it
is controlled by spring and piston cylinder dashpot (The idea here of using the piston cylinder for damping in opening
is taken from US patent 6239399 [4], however different damper instead of piston cylinder can be used.). Back contact
does not move in opening same as in concept 4. Thus, delayed opening is achieved by setting proper damping.
Control parameters of switch for closing are crank radius of collapsible link, back spring stiffness which holds ‘back
contact’, horizontal distance between onset of cam and hinge of collapsible link(striking distance) and initial gap
between separate slider and front contact. For opening delay stiffness of opening spring attached to front contact and
damping coefficient are control parameters.
3 RESULT AND DISCUSSION
From primary analysis of concepts, it is found that concept 2 requires more space and is complex to control whereas
concept 3 involves more parts subjected to wear which creates suspended metal particles in electrical system. Thus
concept 2 and concept 3 are dropped here. Dynamic analysis of concept 1, 4 and 5 are as follow.
3.1 Dynamic analysis of concept 1in MSC ADAMS
For d1= 48 mm, initial gap between contacts = 70 mm, overlap =12 mm, damping co-efficient = 0.5 Ns/mm, Adams
contact stiffness = 100000 N/mm, exponent = 2.2, maximum contact damping = 10 Ns/mm and for Aluminum material
of all the moving parts, Insertion time of 10 ms and opening delay of 3.65 ms is obtained as shown in Fig 11. For
any combination of parameters, the gap between PIR contacts at the instant of closing of main circuit breaker cannot be
obtained more than 14 mm. This gap should be at least 35 mm. Thus, concept 1 fails to fulfill the gap requirement and
hence it is dropped.
Fig.11 Gap between PRI contacts and main circuit’s breaker contacts v/s time superimposed
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Volume 3, Issue 12, December 2015
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3.2 Dynamic Analysis of Contact 4
Fig 12: Gap between PIR contacts and main circuit breaker contacts v/s time superimposed
As shown in Fig 12 insertion time of 7.7 ms and opening delay of 3 ms is obtained for crank radius of 90.5 mm, back
spring stiffness and damping of 2 N/mm and 0.050 Ns/mm respectively, horizontal distance between onset of cam and
hinge of collapsible link (striking distance) of – 2 mm and overlap of 37 mm. All the moving parts are assumed of
Aluminum material. Adams contact parameters are taken as of concept 1 for analysis. Insertion time of 10 ms can be
obtained by setting back spring stiffness but maximum opening delay obtainable here is 15.6 ms. It is difficult to
achieve opening delay of 300 ms, hence concept 4 is dropped here.
3.3 Dynamic Analysis of Contact 5
Parameters like back spring stiffness, crank radius and striking distance (horizontal distance between onset of cam and
hinge of collapsible link) are critical parameters to control insertion time. These parameters are varied to understand
their effect on travel of back contact.
Fig 13: Effect of stiffness on travel of back contact
As seen from Fig 13, as the spring stiffness increases travel of back contact decreases as well as it returns to initial
position more quickly. As seen from Fig 14, as the crank radius increases, the linear velocity of striking and hence the
velocity of back contact decreases. Higher crank radius will generate less impact forces on back contact. As seen from
Fig 15, as the striking distance increases striking instance is delayed. However at zero striking distance, the force will
be only horizontal thus no vertical reactions will have to be borne by system.
To reduce contact forces, bottom collapsible link is assumed to be covered with PU foam (Young’s Modulus of 0.5GPa
and Poison’s ratio of 0.5). ADAMS contact stiffness of 5000 N/mm and maximum contact damping of 100N ms/mm is
obtained from Lankarani and Nikravesh [6] model of contact stiffness.
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Volume 3, Issue 12, December 2015
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From above results, for least impact, maximum possible crank radius considering space is 75 mm. To avoid vertical
reaction force in system, appropriate striking distance is 0mm. For analysis, crank radius of 75 mm and striking
Fig.14 Effect of crank radius on travel of back contact
distance of 0 mm is taken. Setting these two parameters, whole system depends on back contact spring stiffness.
Fig.15 Effect of striking distance on travel of back contact
To get 10 ms insertion time of resistor, spring stiffness of 6.9 N/mm is obtained from dynamic analysis. Thus stiffness
can be varied to obtain variety of insertion time. Opening delay can be easily controlled by opening spring stiffness and
damping. As the requirement of insertion time and opening delay can be fulfilled in concept 5, it is selected for further
design and analysis.
3.4 Design of Mechanism based on Concept 5
To design the mechanism various forces acting on joints as well as inertia forces are obtained from analysis of concept
5.
Fig 16 shows loads on connecting link (as shown in Fig 10) from which stresses at various sections are obtained. The
link needs to be non-conducting for electrical feasibility.
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Fig. 16: Loads on connecting link
Max. Compressive stress at mid section with area of 5×12 mm2 is 29.57 MPa and tensile stress at joint cross section
with area of 5×6 mm2 is 52.48 MPa. For stresses produced, glass fiber reinforced plastic material is proposed.
Fig. 17 Loads on top and bottom collapsible link
Fig 17 shows loads on top and bottom collapsible links.
Boundary Condition: X-Y displacements made zero at hinge point. Inertia loads and moments are applied at CG of the
link. However, inertia force in top collapsible link is neglected due to minimal value.
Shapes are modified after pre-stress analysis and final shape is analyzed as shown in Fig 18. For prevailing stresses,
alloy steel equivalent to 40NiCr1Mo15 having yield strength of 580Mpa [7] is proposed.
Fig. 18 stresses in top and bottom collapsible link
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Volume 3, Issue 12, December 2015
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3.4.1 Final analysis of concept 5
Using the dimensions and proposed material, final dynamic analysis is carried out for crank radius of 75 mm, striking
distance of 0mm, back spring stiffness of 7.05 N/mm, opening spring stiffness of 1N/mm and gas damping coefficient
of 0.985 Ns/mm. Fig 19 shows that concept 5 gives insertion time of 10 ms, opening delay of 300 ms and gap of 51
mm is maintained between PIR contacts until the main circuit breaker contacts are closed.
Fig.19 Gap between PIR contacts and main circuit breaker contacts v/s time superimposed
4. Conclusion
Five concepts are developed for inserting resistor in series. Two concepts are dropped due to mechanical and electrical
feasibility. Dynamic analyses of three concepts are carried out in MSC ADAMS. Two more concepts are dropped as
they cannot fulfill specific requirement. Concept 5 is selected for final design of mechanism after analysis. After
modifying shapes according to stresses and using the material proposed final dynamic analysis is carried out. Final
dynamic analysis gives insertion time of 10 ms, opening delay of 300 ms and maintains gap of 51 mm between PIR
contacts until the main contacts are closed. Thus, mechanism based on concept 5 can be used to insert resistor in series.
Moreover in concept 5, variety of insertion time can be obtained by just adjusting back spring stiffness. Thus, Concept 5
is very easy to control mechanism.
References
[1] http://www.abb.com/global/scot/scot245.nsf/veritydisplay/_le/buyers guide hv live tank circuit breaker sed5en.pdf
accessed on 29th, April, 2013.
[2] W. B. Freeman, K. Froelich, D. S. Johnson, Modular Closing Resistor, US5245145, 1993.
[3] R. Muller, J. Talir, Rower circuit breaker having closing resistor, US5814782, 1998.
[4] M. Perret, Interrupter with resistor insertion system having long insertion time, US6239399, 2001.
[5] W. Daniel, Contact Modeling, Benelux ADAMS User Meeting, 2012.
[6] C. Pereira, A. Ramalho, J. Ambrsio, a Critical Overview of Internal and External Cylinder Contact Force Models.
[7] V. Bhandari, Design of Machine Elements, 2004.
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