低压TT配电系统在大型石化企业应用的探讨

Application of low-voltage TT power distribution system for large petrochemical projects

随着石油化工企业加工能力和装置规模越来越大型化,变电所与装置距离越来越远,当0.38/0.22 kV系统供电距离超过200 m时,单相接地短路保护已小于规范要求,接地线电化学腐蚀严重、电缆投资较大。在大型石化配电系统中,TN系统的缺点难以克服。选取0.38/0.22 kV系统中常用的变压器、电缆和负荷,作为典型的算例,通过计算得到TN系统短路保护的极限距离为200~230 m。通过比较TN和TT系统在超过230 m供电距离时的保护设置,得到TT系统在远距离供电上的优势。在大型石化企业供配电系统中,随着供电距离的加大,传统的低压配电系统接地方式,应当适当改变。石油化工企业供电规范,也应依据理论和实践经验,及时修订。

With the petrochemical plants becoming increasingly larger,the distance between the substation and process units becomes increasingly longer. When the distance of 0. 38/0. 22 kV substation is longer than 200 m,the electric current of Line-Grounding short circuit is lower than that required for protection,the electro-chemical corrosion to the underground wiring lines is severe,and the cost of low-voltage cable is great.In power distribution system of large petrochemical projects,it is very difficult to overcome the shortcomings of TN system. In the case studies,the transformer,cables and load in the 0. 38/0. 22 kV system as well as typical case studies have been selected. The calculation concludes that the limit distance of short-circuit protection of TN system is 200 ~ 230 m. By the comparison of protection design for 230 m power supply distance for TN and TT system,the advantages of TT system in long-distance power supply have been obtained. In the large power distribution systems of large petrochemical,the conventional low-voltage power supply and grounding system should be changed when the power supply distance becomes increasingly longer. The applicable codes and standards for petrochemical projects should be timely revised based upon the theory and practice experience.