详情描述
Design requirements for K-factor transformers (specifically for Ping'an, ICBC, and China Construction Bank data centers)
1. The K factor is a general measure of harmonic heating effect, particularly suitable for harmonics on transformers. It emphasizes not only the harmonic frequency but also the harmonic order, harmonic spectrum distribution, and spectrum ratio. Standard specifications for K factor transformers include K-4, K-13, K-20, K-30, and so on; K-13 is a common rated value for office loads and general machine room loads, while K-20 is geared towards specialized computer loads (precision air conditioning and precision motors) and power quality-sensitive PDU (Power Distribution Units).
2. The design of K-factor transformers is aimed at minimizing size and controlling harmonic thermal effects. K-factor transformers cannot completely eliminate harmonics (unless additional components like filters are added), but specially designed isolation transformers such as the Dzn0 isolation transformer can filter out triple-frequency harmonics. An isolation transformer with dual outputs and a phase difference of 30 degrees can filter out harmonics at frequencies of 5, 7, 17, and 19 times.
3. When selecting conductors for K-coefficient transformers, it is generally prohibited to use low-density insulation wires such as silk-wrapped wires. Instead, wire-wound copper wire or NOMAX paper-wrapped copper wire with a temperature rating above 180°C should be used to minimize the risk of local high temperatures in the wire due to skin effect caused by high-order harmonics, which can lead to insulation layer breakdown and transformer damage.
4. Design K-coefficient transformers to minimize thermal effects as much as possible, which can be achieved through optimized winding design, wire thickness-to-width ratio, and the number of winding parallel connections.
5. The winding design of the K-factor transformer's delta-connected input terminal also takes into consideration minimizing the thermal effect of the third harmonic.
6. The K coefficient transformer design must select an appropriate impedance value.
7. The magnetic flux density of the K factor transformer should be lower than the design value of a standard transformer.
8. Opt for low-loss silicon steel sheets for K-factor transformers whenever possible.
9. The design of K-factor transformers should enhance structural strength considerations.
10. Consider minimizing the thermal effect damage caused by the zero-sequence current of the transformer at the neutral point as much as possible.
11. The design of the K coefficient transformer coil must consider the thermal additional effect at high frequencies, with particular emphasis on the thermal additional effect of the transformer's output side winding.
Choose K-coefficient transformer example: Under rated fundamental frequency current of 50/60Hz and additional harmonics, the transformer should be able to operate safely within the required temperature rise range. For selecting which K-coefficient transformer is more suitable for application, refer to the following suggestions:
(A) For 50% non-linear load, it is recommended to use the K-4 transformer.
(B) For 75% non-linear load, it is recommended to use a K-9 transformer.
(When 95% of the load is non-linear, it is recommended to use the K-13 transformer.)
(D) For nonlinear loads up to 125%, it is recommended to use the K-20 transformer.
(E) For nonlinear loads up to 150%, it is recommended to use the K-30 transformer.
When the nonlinear load reaches 200%, it is recommended to use the K-50 transformer.
From a conservative standpoint, it may sometimes be necessary to opt for the higher-grade K-coefficient transformer as mentioned above.
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