Depending on the load requirements, the implementation of a reliable back up supply of electrical power can be critical to the electrical design of an installation.
The role of automatic transfer switch equipment (ATSE) is to provide a dependable power transfer between the main source and the emergency source to essential or critical loads.
When the main source fails, the transfer switch detects the event with certainty, starts the standby generator and transfers the load to the emergency generator when it is ready.
When the main source comes back, again, the ATSE detects the event and transfers back to the mains (sometimes under conditional criteria), provides a cool down period to the diesel generator (DG) if any, then stops it.
When the emergency source is a transformer, the DG start and stop sequences are not implemented.
The contribution of ATSE to the reliability of an installation is as important as the transformer, DG or protection devices. The choice of the architecture of ATSE and the selection of its components is, as a consequence, a major responsibility of the designer.
As with any design, a set of goals needs to be outlined. The design goals for an ATS, in order of importance, are:
- To safely automatically transfer between incoming supplies
- To ensure isolation of supplies from one another
- To maintain electrical protection offered by switch-gear in the installation
- To be capable of safe and straightforward manual operation by operators in emergency/shutdown situations
- To provide end users with a cost effective solution with minimal maintenance.
The consequences of failure if the ATSE design does not meet these goals are:
- Danger to operators
- Damage to installation
- Damage to switchgear
- Loss of supply to load.
In the Australian and New Zealand market the majority of ATSE historically installed utilised circuit breakers.
However, more recently there has been a push through the electrical industry towards load break based ATSE systems as they provide the best results when judged by the above criteria.
Load break switch based ATSE
A load breaker switch ATSE architecture such as the Socomec ATyS is one functional unit that has all incoming and outgoing connection terminals, mechanical interlocking, electrical wiring, logic controller and switching mechanisms built into the switch.
The switching mechanisms comprises of two interlocked load break switches mounted to a controller and logic unit.
It is designed specifically in accordance with AS/NZS 60947.6.1, which refers directly to transfer switch requirements, therefore ensuring the safe automatic transfer between incoming supplies.
Upstream circuit breakers are still required in a load break ATSE implementation to provide short circuit and overload cable protection.
Separating the transfer function and the protection function frees up the circuit breakers for maintenance in installations, without compromising the operation or installation of the ATS.
Furthermore without the circuit breaker motor operator and interlocking requirement, the circuit breakers can be a basic, economical type that are easy to test and be replaced as needed.
It is worth noting that load break switch based ATS devices do not have any effect on the protection in terms of protection selectivity/coordination, avoiding issues of potentially complying with AS3000 protection grading requirements.
During an emergency or shut down situation, manual switching by operators is required. To facilitate this, a load breaker switch ATS has an easily accessible, front mounted selector switch for manual operation.
Simple handle for manual operation is important to provide a single point of operation.
Finally, a load break switch based ATS provides an end user cost effective solution, with reductions in installation labour for the switchboard builder and with minimal maintenance for the end user.
Socomec ATS solutions from NHP
NHP offers a wide range of open transition load break based transfer switches from Socomec (ATyS) that guarantee both the continuity of the power supply and the safety of operators. All devices comply with IEC609473 and AS/NZS 60947.6.1.
The complete ATyS range is user friendly, with a quick and easy installation process, catering for applications from 40 to 3200A.
Its stable positions allow energy consumption to be minimised whilst ensuring maximum immunity to electrical network disturbances, making this a truly robust and reliable solution.
This partner content is brought to you by NHP. For more information on this range, please visit nhp.com.au/more/water.