First, do not confuse the "radiation" produced by high tension power transmission lines (高壓電覽) with the types of ionizing radiation, like x-rays or gamma rays, that people usually refer to.
High tension power transmission lines only produce time varying electric and magnetic fields (時變電場及磁場) at its vicinity. There is completely no "radiation" at all.
Up to date, there is no scientific evidence, as reported by the World Health Organization (世界衛生組織) that electric field produced by high tension cable causes adverse health effect. Although there are reports that the magentic field produced by these cables causes childhood leukemia (兒童白血病), further evidence is still needed to establish a confirm result.
In Hong Kong, any erection of high tension transmission cable must need to comply with the guidelines specified in the Hong Kong Planning Guide (香港規劃標準與準則) issued by the Planning Department (香港規劃署). The Guide requrests that the electric and magnetic field strength at places where there are human occupation shall not exceed the reference levels recommended by the International Commission on Non-ionizing Protection (國際非電離輻射防護委員會), i.e. 5 kV/m and 100 uT respectively for electric and magnetic fields. You may refer to the following web-page for the Planning Guide (Chinese version):
http://www.pland.gov.hk/pland_tc/tech_doc/hkpsg/full/ch7/ch7_text.htm#2
Please read section 2.3.10 on Health Consideration (健康方面的考慮)
You could also refer to my answer given previously to a similar question in this forum:
http://hk.knowledge.yahoo.com/question/question?qid=7010122901860
More information on the health effect of electric and magnetic field produced by power transmission vables can also be found from the following web-page:
http://www.greenfacts.org/en/power-lines/index.htm#il1
Hope the above information could settle your worries.