Question
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TION (11 marks)
A distribution transformer for a polytechnic is specified as
MVA, ONAN, DYN11.
(i) Explain the term DYN11.
(ii) State two (2) physical differences between this transformer and an
ANAF transformer.

Ask by Pope Ford. in Singapore
Dec 09,2024

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Answer

(i) Explanation of the term DYN11

DYN11 is a transformer vector group that indicates winding configuration and phase displacement. It means Delta primary, Star secondary with neutral, and a 30-degree phase shift.

(ii) Two physical differences between this transformer and an ANAF transformer

  1. Cooling Method: DYN11 (ONAN) uses natural oil and air cooling, while ANAF uses natural air cooling with forced air.
  2. Winding Configuration: DYN11 has Delta/Star configuration for phase shifting and grounding, while ANAF may have different configurations without phase shifting.

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Extra Insights

The designation DYN11 in a transformer indicates its vector group. “D” stands for a delta-connected winding on the primary side, while “Y” indicates a star (or wye) connection on the secondary side. The “N” denotes that the neutral point is accessible, and the “11” refers to the phase displacement of 30 degrees (or 11 times 30 degrees) between the primary and secondary voltages, with the secondary leading the primary. This configuration is often used to allow for effective grounding and to manage phase shifts in three-phase systems.
Compared to an ANAF transformer, which is an air-cooled transformer with both high and low voltage sides in an open delta configuration, the distribution transformer specified operates with a closed delta (as indicated by “D”). This leads to one of the visible differences: the ANAF transformer typically has a smaller footprint due to its open design, while the DYN11 transformer often features more robust insulation and cooling systems. Additionally, the DYN11’s capability for neutral grounding provides a method for managing fault currents, which is not a characteristic of the ANAF transformer.

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