In the test report of the on load tap changer, there is a parameter called "T0", which stands for three-phase synchronicity. Many engineers are not sure what this number represents and how much it exceeds, so they need to pay attention to it. Explain this parameter clearly today.
Definition of three-phase synchronicity
The on load tap changer of a three-phase transformer is usually three-phase linked - the switching action of A, B, and C phases is driven by the same transmission mechanism and theoretically should occur simultaneously. However, due to the presence of gaps in mechanical transmission and varying degrees of wear on the switching mechanisms of each phase, there may be slight differences in the actual timing of three-phase switching.
T0 is the time difference: taking the phase that completes the switching action earliest among the three phases as the time reference (T0=0), the time difference between the other two phases relative to this reference is the T0 value. HZYA-3Z provides T0 values for the other two phases based on the earliest detected switching phase.
What does T0 mean
The smaller T0, the more synchronous the three-phase switching action and the better the mechanical transmission state; An increase in T0 indicates a delay in the switching action of a certain phase compared to other phases, which may be due to issues such as increased clearance, insufficient lubrication, or local jamming in the transmission mechanism of that phase.
criteria for judgment
Different models of on load tap changers have different requirements for three-phase synchronicity, usually referring to the manufacturer's factory standards. Generally speaking, the three-phase synchronicity T0 is within the normal range within a few milliseconds; If T0 exceeds 10ms or even larger, it needs to be taken seriously and the status of the transmission mechanism checked.
Vertical comparison with previous test data is equally important: the T0 value of the same switch increases from 2ms in history to 8ms, even if the current absolute value does not exceed the limit. This trend change itself is a signal of mechanical degradation.
The difference between three-phase synchronicity and three-phase asynchrony
The large three-phase synchronicity T0 is only due to the time difference in switching moments, which belongs to the mechanical synchronization problem; If the waveform of a certain phase is completely abnormal (such as a phase that has not switched waveforms at all, or a very long transition time), it may be due to the phase switching mechanism refusing to move or contact failure, which is a more serious problem.
HZYA-3Z three-phase simultaneous sampling, synchronous recording of three-phase waveforms, automatic calculation and display of T0 values, no need to manually align waveform calculation time difference.