Purchase Specifications from the IEC
IEC 62055-41 :  ELECTRICITY METERING - PAYMENT SYSTEMS - Part 41: Standard transfer specification (STS) - Application layer protocol for one-way token carrier systems

IEC 62055-51 :  ELECTRICITY METERING - PAYMENT SYSTEMS - Part 51: Standard transfer specification (STS) - Physical layer protocol for one-way numeric and magnetic card token carriers

These standards have now been published by the IEC as international standards and are available from the IEC Webstore in Geneva