Functions, applications and testing breakers (load switches) in Smart Meters

Until the introduction of Smart Meters, the term ‘breaker test’ was used to describe the physical possibility of testing the breaker (also: disconnector or remote disconnection). Further functionalities have been added in the process of digitalisation. You can find out what these are and how they are related to the breaker in this article.

Definition

A breaker (or load switch) is a built‐in breaking relay or remote control device within an energy meter. With this type of disconnection, the customer can be disconnected from the power grid and, depending on legal requirements, reconnected to the grid. Modern Smart Meters offer additional functions for this purpose. Whether a breaker is available and may be used is the responsibility of the grid operator. In Germany, the specifications of the BSI (Federal Office for Information Security) for the Smart Meter Gateway do not allow a remote switching. Here, breakers are only used for prepaid meters.

Use with the Smart Meter

A breaker can be used with a Smart Meter, for example, to initiate remote switching operations. Remote operation, i.e. disconnection of the meter or customer from the power grid, is possible at the end of a contract or when a connection is cancelled. In some countries, the breaker is used for tariffing or power control. A defined maximum power is made available to the customer. If this power limit is exceeded, the breaker can be opened to interrupt the energy flow for a certain period or until the reconnection command is given.

In addition to the physical switching of the breaker, a Smart Meter can also transmit the status of the breaker. A type test should be carried out to ensure that this status corresponds to reality and that the meter does not transmit an invalid status (open/closed) by mistake. Otherwise, incorrect switching could accidentally occur.

The breaker is also used to fulfil prepaid functions. The customer pays a credit at the beginning, for which a certain amount of energy can be used. As soon as the amount or energy is used up, the breaker will be opened, and the energy supply will be stopped.

Breakers can also be triggered in the event of tampering. In this case, the meter sends an event or triggers an alarm if, for example, a strong magnetic field or the opening of the meter housing is detected. This action can lead to the customer being sanctioned and the need to proactively contact the energy supplier for reconnection.

Physical testing

In the past, the term ‘breaker test’ was used to describe the measurement of the resistance between the meter input and output. A defined current was sent through the meter to determine whether the breaker was open or closed. This possibility of physically testing the breaker still exists today. But modern Smart Meters make further tests possible.

Testing via remote switch-off

Modern Smart Meters can also be equipped with an built-in breaker function – the ‘remote switch-off’. For this purpose, the meter is addressed via the corresponding interface and used for remote switching operations, power control or Demand Side Management.

Example – Testing of a Smart Meter

A complete breaker test of a Smart Meter can be carried out as follows, for example.

  1. switch off the breaker in the meter with a direct switch-off command, via manipulation, due to excessive power consumption or via remote switch-off. (disconnect)
  2. measure the physical resistance at the meter (expected result: high resistance = breaker open/disconnected)
  3. query the breaker status at the meter or via MDMS (expected result: breaker open/disconnected)
  4. switch on the breaker; manual confirmation may be required directly at the meter (connect)
  5. measure the physical resistance at the meter (expected result: very low resistance = breaker closed/connected)
  6. summarising the individual results into a total result of the breaker test. As soon as a step is faulty, the total evaluation is negative.

Further steps can be added to the breaker test, e.g. to consider and evaluate event messages from the MDMS or the meter during switching operations.

Conclusion

The breaker is an element integrated into the energy meter that can be used to carry out switch-off procedures or remote queries. A distinction is made in the breaker test between the physical test, the remote switch-off and the status enquiry (including plausibility check). The use of the breaker in the Smart Meter varies from remotely querying the status of the meter to disconnecting the meter from the power grid. Status queries can be used for a wide range of functionalities. It is the responsibility of the grid operator to decide whether an installed meter has a breaker and whether and how it may be used. In Germany, remote switching is not permitted for Smart Meters.

Abbreviations:
BSI – Bundesamt für Sicherheit in der Informationstechnik (Federal Office for Information Security)
MDMS – Meter Data Management System