Purpose/Aim
During the switching test of on-load tap-changer(OLTC), it is found that the switching process of odd-even, even-odd taps and the value of the damping resistance affect the degree of distortion of the switching current and the assessment of the breaking current and recovery voltage of the contact. In order to reasonably assess the ability of the tap changer contacts and reduce the degree of distortion of the switching current, this paper studies the effects of different switching processes and damping resistances on the switching current.
Experimental/Modeling methods
In this paper, the switching sequence model of OLTC and the switching test loop model of resonance method are built in ATP-EMTP. And the influence of different damping resistances and different switching processes of odd-even and even-odd taps on the distortion current is simulated and analyzed. Besides, the mathematical model of optimum damping resistance is proposed.
Results/discussion
When the tap changer is switched from the odd to the even gears, the sudden change of the circuit state causes a small amplitude distortion of the test phase current. When switching from the even to the odd gears, the long-arm damping resistor consumes the energy stored in the capacitor bank and the reactor bank, and the energy consumption is faster when the damping resistor has a larger resistance value.
Conclusions
(1) The switching current distortion is small when switching from odd to even gears; the switching current distortion is large when switching from even to odd gears.
(2) During the switching process, the long-arm damping resistance on the secondary side of the tap changer test transformer plays the role of consuming the energy stored in the capacitor bank and the reactor bank. The larger the damping resistance, the smaller the switching current distortion rate.
(3) An optimum damping resistance selection method is established with the current distortion rate as the objective function. When the test parameters and transition resistance values change, the same method can still be used to select the damping resistance.
 

OLTC,switching test,damping resistance