Mar. 23, 2020
At present, there are two common connection methods for transformers: Y and D, and distribution transformers also use Z connection. Hermetically sealed transformers factory shares with you.
1. Advantages of the Y connection method: The most economical for high-voltage windings; midpoints can be used; allow direct grounding or grounding by impedance; allow to reduce the insulation level of the midpoint (ie, graded insulation); can be at the midpoint of each phase There are taps, and tap-changers can also be located at the midpoint; single-phase loads are allowed, and the midpoint can carry current.
2. Advantages of the D connection method: It is the most economical for high-current and low-voltage windings; it can reduce the zero-sequence impedance value when used in conjunction with the Y connection winding.
3. Advantages of Z connection method: Allows current-carrying load at the midpoint and has low zero-sequence impedance; Can be used as the connection of the grounding transformer to form an artificial midpoint; Can reduce the voltage imbalance in the system (three-phase load in the system) (Unbalanced); Can be used as a connection method for distribution transformers in mines.
The above are the advantages of a single connection method. Generally, a transformer has at least two windings, so the transformer has a combination of several connection methods.
(1) YNyn and OYN (YN self-coupling method) The zero-sequence current will switch between the windings, that is, the high-voltage and low-voltage windings have zero-sequence current, and they can be balanced to achieve a low zero-sequence impedance of the transformer. For transformers, a D-balanced winding must be used with this connection.
(2) YNy and Yyn have zero-sequence current in the winding drawn from the midpoint, but there is no such current in the winding drawn from the other without the midpoint, so the zero-sequence current cannot be balanced in turns, so for the core, there is an excitation Zero-sequence current, which is controlled by the zero-sequence excitation impedance. According to the design of the magnetic circuit, this zero-sequence excitation impedance can be large (such as three-phase three-column iron core) or particularly large (such as three-phase five-column iron core, three-phase shell type). core). The symmetry of the voltage to the ground will be affected, and the midpoint will be shifted. Therefore, this connection cannot be used for a three-phase five-column core, a single-phase three-phase group or a three-phase shell core.
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