Variable ratio selection of 0 sequence micro current transformer

- Mar 15, 2018-

0 Sequence Micro current transformer in the use of this ratio, refers to the rated primary current and the ratio of the rated two times current. For the application of 0 sequential miniature current transformers, a smaller variable ratio is generally chosen, which is often used to include 50/5, 75/5, 100/5, 150/5, 200/5, 20/1, 50/1, 100/1, 150/1, 200/1, etc., because only one grounding failure occurs, the 0 sequence current transformer has output. When used, as far as we are concerned, it is generally not allowed to make the grounding current very large to make the protection action (do not consider dodging the load current). However, because a winding is a power cable, only one turn, so that 50/5 of the 0 sequence micro-current transformer two rated turns, only 10 turns, so 50/5 of the 0 sequence current transformer load characteristics are poor, the actual load impedance and 0 sequence current transformer capacity is inconsistent when there is bound to be a large error,

However, the error will increase when below the rated current, so try to choose a larger variable ratio if allowed. The time-varying ratio selection of the existing protection tuning value on the 0 sequence micro current transformer is selected. As far as this is concerned, we should note that for existing protection values, it will be easier to choose.

For example, for a fixed value is a one-time current 80A protection action, when the GB will choose 100/5 or 100/1.

0 Sequence Micro current transformer on the selection of Resistance grounding system, first of all, on the resistance grounding system connection point current is in fact, there will be two components, one is capacitance current, the other is neutral resistance current, the difference between the two 90o. Therefore, in the use of 0 sequence micro-current transformer, that is, will take into account the fault loop when the 0 sequence current is equal to the connection point current and the line grounding capacitance current vector difference, in this case, to a large extent, will be equal to all non-fault line grounding capacitance current and resistive current vector and negative value.