Difference comparison and selection of transformer wiring Dyn11 and Yyn0

At present, power transformers are mainly divided into two categories: dry-type transformers and oil-immersed transformers. One of the specifications of the transformer is called the connection group number (connection main type). That is the wiring method we usually talk about. Generally, there are two types: Dyn11 and Yyn0, whether it is the dry transformer mentioned above, or an S11 transformer.

(1) Dyn11 wiring: It has the characteristics of high output voltage quality, no drift of neutral point, and good lightning protection performance. When the three-phase load on the low-voltage side of the box-type transformer is unbalanced, since the zero-sequence current and third-harmonic current can flow in the closed loop of the high-voltage winding, the total zero-sequence magnetic potential and third harmonic magnetic potential on each core column are almost Equal to zero, so the low-voltage neutral point potential does not drift, and the voltage quality is high; similarly, because lightning current can also flow in the closed loop of the high-voltage winding, the total magnetic potential of the lightning current on each core column is almost equal to zero, eliminating Forward and reverse conversion overvoltage, so the lightning protection performance is good. However, there is a problem of non-full-phase operation, and an undervoltage protection device can be installed on the low-voltage main switch.

(2) Yyn0 wiring: When one phase of the high-voltage fuse is blown, the voltage of one phase will be zero, and the voltage of the other two phases will not change, which can reduce the power outage range to 1/3. This situation will not have an impact on the low-voltage side -9*3 lighting load with single-phase power supply. If the low-voltage side is a power load with three-phase power supply, it is generally equipped with phase loss protection, so the power load will not be burned due to phase loss operation.

Generally speaking: the zero sequence impedance of the Dyn11 connection transformer is much smaller than that of the Yyn0 connection transformer, which is beneficial to the removal of low-voltage single-phase grounding short-circuit faults. Dyn11 wiring transformers allow neutral current to reach more than 75% of phase current.

Therefore, in the selection of transformer wiring, it is necessary to choose Dyn11 connection transformer. Since the insulation strength requirements of the high-voltage winding of the Yyn0 connection transformer are slightly lower than those of the Dyn11 connection transformer, it is not suitable to change the Yyn0 connection transformer to the Dyn11 connection.