FORM 2
THE PATENT ACT 1970
&
The Patents Rules, 2003
PROVISIONAL SPECIFICATION (See section 10 and rule 13)
1. TITLE OF THE INVENTION:
"System for Life Test of Contactors for AC3 Duty"
2. APPLICANT:
(a) NAME: Larsen & Toubro Limited
(b) NATIONALITY: Indian Company registered under the
provisions of the Companies Act-1956.
(c) ADDRESS: Larsen & Toubro Limited
Electrical & Automation North Wing, Gate 7, Level 0, Powai Campus, Saki Vihar Road, Mumbai 400 072, INDIA
3. PREAMBLE TO THE DESCRIPTION:
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

System for Life Test of Contactors for AC3 Duty
Field of invention
The present invention relates to power and control contactors testing, and more particularly, to a system for life test of contactors for AC3 duty.
Background of the invention
As per IEC/IS 60947-4-1, for verification of number of on-load operating cycles for contactors for AC3 utilization category, the unit under test has to make at 6Ie and break at Ie. The breaking at 6Ie has to be taken care by some other devices which by conventional way were carried out using some back up contactor.
Implementing abovementioned back up contactor is not advisable from the economical point of view as there is a frequent need of its replacement because of heavy corrosion or contact weld situations. Moreover, the time involved in arranging, mounting and rewiring of this back up was leading to a delay in the actual duration of this particular test.
Earlier conventional ways of doing these particular 'Verification of the number of on-load operating cycles' test is to have a back up device obviously nothing else than a contactor as it has to operate million number of times that too of higher current rating as it has to break the 6k current. This breaking at 6Ie used to call for heavy corrosion of contacts of back up resulting into immediate replacement of the same after few thousand operations. Continuing this test for claimed millions of operations is not beneficial from economical as well as human efforts point of view.
Object of present invention

Object of the invention is to reduce testing time, cost, human efforts and to bring more precise results in verification of the number of on-load operating cycles test.
Summary of the invention
Accordingly, the present invention provides a system for life test of contactors for AC3 duty using a hybrid circuitry, for breaking the 6 times of the rated current. The system comprises at least two thyristors. The thyristors are connected only in R and B phase with Y phase permanently short circuited. Further, the system includes at least two snabbers to take care of over voltages and transients during switching ON and OFF, a control card having a triggering circuit for the plurality of thyristors, at least one centre tap control transformer for generating two voltage levels, a rectifier provided in the trigeering circuit to drive a transistor Tl and IC555, and a zener provided in the in the trigeering circuit for driving a transisitor T2, T3, T4 and pulse transformer respectively. Wherein an output of transistor Tl and IC555 are used to trigger transistor T2, T3 and T4 which in turn gives pulse output based on the mode of the 555 TIMER through the pulse transformer to the gate Gl, G2, G3 and G4 and the transients and the over voltages created at the time of thyristor switching is taken care by the snubber circuit connected.
Brief description of the drawings of present invention
Figure 1, 2 and 2a shows a consolidated view if the hybrid circuitry;
Figure 3, 4, 3a and 4a shows a trigger circuit for hybrid contactor (control card); and
Fig. 5 showing flowchart for checking the functionality of the trigger circuit.
Detailed description of present invention

The foregoing objects of the present invention are accomplished and the problems and shortcomings associated with the prior art, techniques and approaches are overcome by the present invention as described below in the preferred embodiments.
The present invention provides an improved system for breaking the 6 times of the rated current which has to be accomplished using back up contactor or any other device which will take care of the breaking current. The following description will elaborate the functioning of the power circuit along with the control card which is used to drive the thyristor and snubber circuit.
Referring to figure 1 and 2, there is shown a consolidated view of a hybrid circuitry (100) for breaking the 6 times of the rated current. The hybrid circuitry (100) includes a plurality of thyristors (10) and a plurality of snubbers (20) to take care of over voltages and transients during switching on and off with basic control card (30).
As shown in figure 1 that the hybrid concept is being incorporated in only the breaking of two phases as after opening of any of the above said the current is going to be zero as the load output is star connected. Figure 2 shows the plurality of thyristors (10) are connected only in R and B phase with Y phase permanently short circuited.
Referring to figure 3 and 4, there is shown a a triggering circuit (200) used for thyristors (10) which also becomes a major part of the control card (30) driving the entire hybrid concept. Figure 3 shows that one centre tap control transformer is being used for generating the two voltage levels i.e. 15V & 30V AC after accepting the regular 240V AC supply at the input. After that using a rectifier and zener in circuit, the 10V and 15 V DC levels have been generated to drive the transistor II & IC555 and next for driving the T2, T3, T4 and pulse transformer respectively.

Now the output of transistor Tl and IC555 i..e ]1 & 12 are being used to trigger transistor T2, T3 and T4 which in turn will give pulse output based on the mode of the 555 TIMER through pulse transformer to the gate G1, G2, G3 and G4. The transients and the over voltages created at the time of thyristor (10) switching is taken care by the snubber circuit connected.
The details of the components are attached in timing diagram shown in figure 5 for functioning of the circuit. The timing diagram shows that the SCRs will be given a triggering signal exactly synchronized with the 6Ie contactor drop off instant. Sufficient time gap of 150msec is kept between the SCR circuit to clear the 6Ie current and back up contactor drop off instant which helps the back up to open almost at no load increasing the life of the same.
The flowchart for the trouble shooting in case if the circuit is not working as per the expected output is already provided for the ready use of an user.
For verification of number of on load operating cycles for AC3 utilization category as per 1EC/IS 60947-4-1, following technical criteria should meet:

Utilization category Value of the rated
operational
current Make Break

I/Ie U/Ue Cosф Ic/Ie Ur/Ue Cosф
AC-3 Ie<=17A 6 1 0.65 1 0.17 0.65
Ie>17A 6 I 0.35 1 0.17 0.35
Where,
Ie = rated operational current U = applied voltage
Ue = rated operational voltage Ur = power frequency voltage
I = Current made 1c = current broken

As explained above and from the table, the contactor under test has to only make the 6Ie current and it should break on 1 le. Since breaking 6Ie current calls for heavy contact corrosion or sometimes contact weld situations introducing a back up contactor was not feasible.
COMPONENT LIST FOR ELECTRONIC CONTROL CIRCUIT
Component Component value Qty
Designation
RESISTORS (Tolerance - 5%)
Rl , R2 33Ω ,10 W 2 Nos.
R3,R13 220Ω1/2W 2
R4, R6 56KΩ ,1/4 W 2
R5 22KΩ, 1/4 W 2
R7 12KΩ, 1/4W 1
R8 2KΩ ,1/4W 1
R9,R]0
R12.R15 lOKΩ,l/4W 4
Rll 47KΩ, 1/4W 3
R14 27Ω , 1/4W 1
CAPACITORS
C1,C2 O.5μf,2000v 2NO S.
C3 100μf,25V (Electrolytic) 1
C4 2000μf, 25V 1
C5 25μf, 25V 1

C6,C8,C9 0.01μf,400V 3
C7 0.47μf, 100 V 1
C10 47Kpf, 30V 1
C11 22μf,63V (Electrolytic) 1
Component Component Value Qty
Designation
DIODES
D1 ,D2,D3 IN4004 3 NOS.
D4 to D8 SD40 5
D9 IN4002 1
ZD1 FN10A 1
ZD2 IZ15A 1
TRANSISTORS
Tl ,T2 BC107A 2 NOS.
T3 CP 100/ZN 2905 1
T4 2N 3054 1
ICs
1C1 IC 555 (Metal Can) 1
Advantages of the present invention

1. Present invention reduces testing time, cost, and human efforts that bring more precise results.
2. Saves carbon foot print and contribute towards green earth.
The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed. and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.

We Claim:
1. A system for life test of contactors for AC3 duty using a hybrid circuitry, for breaking the 6 times of the rated current, the system comprising:
at least two thyristors, the thyristors connected only in R and B phase with Y phase permanently short circuited;
at least two snabbers to take care of over voltages and transients during switching ON and OFF;
a control card having a triggering circuit for the thyristors;
at least one centre tap control transformer for generating two voltage levels;
a rectifier provided in the trigeering circuit to drive a transistor Tl and IC555;and
a zener provided in the in the trigeering circuit for driving a transisitor T2. T3, T4 and pulse transformer respectively;
wherein an output of transistor Tl and IC555 are used to trigger transistor T2, T3 and T4 which in turn gives pulse output based on the mode of the 555 TIMER through the pulse transformer to the gate Gl, G2, G3 and G4 and the transients and the over voltages created at the time of thyristor switching is taken care by the snubber circuit connected.