CLASS technology

The CLASS (Customer Load Active System Services) project installed a device called an autonomous substation controller (ASC) at 60 primary substations. This device linked to the control room management systems and the onsite automatic voltage control (AVC) relay. The AVC relay is a business as usual device which monitors voltage and operates the transformer on-load tap changers to maintain voltages within statutory limits.

The ASC is the onsite intelligence of the CLASS system which, once activated or enabled from the NMS (Network Management System) dashboard, via the remote terminal unit (RTU), makes decisions on what commands to send to the AVC and circuit breakers.

On a limited number of sites (ten) the ASC was also able to issue commands to trip one of the primary transformers to reduce demand very quickly, while keeping all customers supplied, by reducing voltage due to the increase in impedance as one of the pair of parallel transformers was taken out of service.

The changes in voltage and demand were measured by the primary monitors and sent via a standard resolution communications link, via the RTU, to the control room and planning tools.

The CLASS data was sent by a high resolution 3G (Envoy) communications link to a website (iHost) where information is stored by the second and to a resolution of one volt and one amp.

To make sure that customers did not experience any voltage outside of statutory limits the normal primary monitoring equipment was replaced by more accurate measurement equipment to monitor voltages on the low voltage and high voltage systems.