NOJA Power News

Issue 7

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Multi-Dropping Control Cubicles In A Substation Environment Using RS485

NOJA Power auto-reclosers are commonly used in substations to protect feeders. They are generally located outside in the switchyard with the control cubicles within 10 metres of the device. It is an increasingly common requirement for these reclosers to be controlled from inside the substation eliminating the need for personnel to enter high voltage locations.

One way of achieving this would be to extend the length of the control cables so the cubicle can be mounted remotely. This approach is undesirable because there is an increased danger of inducing damaging impulses into the control circuitry. For this reason NOJA Power recommends keeping the control cubicle adjacent to the device and keeping the standard length control cable.

The best approach to controlling NOJA Power reclosers remotely in a substation is to take advantage of the RS485 port built into the controller. When used with appropriate line isolation this method can allow safe operation of multiple reclosers on a single multi-dropped network.

Two communications protocols are available as standard - MODBUS and DNP3. Point mappings, Master/Slave IDs and physical port settings can all be accomplished using NOJA Power's recloser configuration software (TELUS). Input and output points can be controlled via these protocols making our reclosers ideal for sub-station automation.

The RS485 port is located inside the control cubicle as a set of WAGO cage clamp terminals. A twisted pair cable can be connected to these ports and looped to each recloser in the sub-station. If this medium is used it is absolutely essential to use opto or galvanic isolation where the cable enters the cubicle. Alternatively a fibre-optic modem can be connected eliminating the need for separate isolation.

Connecting sub-station reclosers back to a computer in the sub-station control room allows them to be controlled through a SCADA system. Another option is to use TELUS if a full SCADA system is not required. If NOJA Power's new TELUS Remote is used, engineers can connect to each recloser through a TCP-IP network without the need for a SCADA system.

These 15kV reclosers are all networked back to the substation control room using MODBUS over a multi-dropped RS485 network.

The RS485 connector is located inside the control cubicle. Both half-duplex and full-duplex communications are supported.

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