HomeInternationalThe Standard Transfer Specification: An update

The Standard Transfer Specification: An update

The Standard Transfer Specification (STS) has become recognised as the only globally accepted standard for prepayment systems, ensuring inter-operability between system components from different manufacturers of these systems. The application of the technology is licensed through the STS Association, thus ensuring that the appropriate encryption key management practices are applied to protect the security of the prepayment transactions of utilities operating STS systems. It has become established as a de facto standard for transfer of electricity prepayment tokens since its introduction in South Africa in 1993.

The STS has found widespread application, first in South Africa and subsequently in many developed and developing countries, as well as in other utility prepayment applications such as water and PV systems. Its strength lies in that it is: 

  • An open standard, allowing STS-compliant equipment from any number of suppliers to be integrated into an electricity sales system.
  • A secure standard – the encryption technology used has proved to be extremely robust.
  • Supported by complementary specifications and standards, for prepayment meters and vending systems.
  • Simple for customers to use.

The extent of worldwide use of STS systems is now such that plans need to be established for ensuring that the support infrastructure is maintained, and that the STS is developed to meet new needs.


In 2002, the STS Association established formal liaison with the IEC, and a proposal for the STS to be published by the IEC as a publicly available specification (IEC PAS) is currently being formalised. A new work item, IEC NWIP 13/1298, was issued in March 2003 with the proposed title ‘Electricity metering – Payment metering – Part 41: standard transfer specification.’ The plan is to fast track this work item to establish the current version of STS as a recognised IEC standard within the shortest practicable time frame. Responsibility for the project management of this activity will rest with the STS Association, in liaison with working group 15 of IEC TC13.

STS systems continue to be deployed around the world, with systems now in use in some 28 countries, including 17 on and around the African continent.


As a consequence of the increased global application of STS systems, the implications of changes to the encryption key management to include distributed key management using multiple key management centres worldwide is being investigated. A working group of the STS Association is currently studying a report prepared by the Council for Scientific and Industrial Research (CSIR) on this subject.

A further working group was established in 2002 to prepare specifications that would lead to the roll-out of ‘STS 2’ – an enhanced version of STS that will provide considerably increased functionality, opening up the application of STS to more complex prepayment requirements, such as those required, for example, by the water prepayment metering industry. This work is already far advanced.

As the South African industry is now poised for major restructuring, the STS Association will focus on ensuring that support services are available into the future, given that certain functions such as type testing of STS equipment and the key management centre (KMC) are currently resourced from Eskom, the national utility in South Africa.