5p20 is a general purpose protection classification which defined by IEC.
PS is a general termination for 'Protection Special'. This class of CT's are used
for special protection such as differential protection (class X), distance protection (TPY), sensitive earth leakage protection (core balance current transformer) etc. They are fabricated using supreme quality raw materials for maximum durability, toughness and long service life.
PS CTs are of low reactance and usually specified by:
• Turn ratio (error less than _+0.25%)
• Minimum knee point voltage (Vk)
• Maximum exciting current at Vk or at its fraction.
• Maximum resistance of secondary winding.
• In case Vk is not known, following information may be given;
• Tech. specs of the relay to be used and relay set current.
• Scheme of protection where CTs are to be used.
• Maximum fault current of the system at CT point.