SELF

28

and S.B. Karavashkin

2. Experimental and theoretical study of process at the contacts opening inductive load

The main aim of experimental and theoretical study whose results we will state below was to yield and to process the experimental curves of breakdown voltage of contacts; the purpose was to create the stock of input data necessary for calculation and synthesis of circuits with the help of method to select the optimal parameters of spark-extinguish circuits.

The experimental device to yield oscillograms of unstable discharges (Fig. 6a) consisted of the circuit for contacts commutation 1, studied circuit 2, circuit for oscillograph starting 3, oscillograph 4 and block of regulated time delay 5. In Fig. 6b we show the photo of this device.

a)

b)

Fig. 6. The experimental device to obtain the oscillograms of unstable discharges (a) and photo of the device (b): 1 is the circuit of contact commutation, 2 is the studied circuit, 3 is the circuit of oscillograph starting, 4 is the oscillograph and 5 is the block of regulated time delay

The studied circuit as such consisted of the feeding source E₂  whose voltage varied in limits (13,6 - 80) V, of capacitance box which we could terminate in order to imitate large parasitic capacitance C_p (100 F - 0,1 F) ; in this way it was possible to scale to a definite extent the short arc processes. Furthermore, the studied circuit included the inductive L and active R_L  loads; for this purpose we used one either few sequentially connected windings of holding magnets of multiple coordinate connector; they had such parameters: L = 1,5 H, R_L = 1000 Ohm . As the studied contacts KS1 we used normally closed contacts of similar coordinate connector; the feeding to its starting winding was supplied from the source E₁ through the starting button SB that formed the driving circuit. The second pair of contacts KS2 of the studied coordinate connector was used to start the oscillograph which worked in triggered regime. When preparing the experiments, we selected these contacts from stipulation, contacts KS2 to come into action earlier than KS1. The signal to actuate the oscillograph was picked off the resistance R   and fed the X-input of oscillograph via the block of regulated time delay of starting, which allowed to register separate fragments of oscillograms of unstable discharges with a large resolution of horizontal sweep. The used oscillograph was the signal-storing oscillograph C 1-29 working with the higher screen brightness and with additional attenuation for the input Y to which the studied voltage from the contacts KS1 was supplied. General attenuation factor was varied with respect to task in limits (10³ - 10⁴). For feeding we used the universal feeding source UIP-2.