Single Phase Capacitor Balance Unit – REFCL Project
On February 7, 2009, the Australian state of Victoria experienced more than 400 individual bushfires. The fire was spread over more than 4500 square kilometres of land, destroying more than 2000 homes and killing 173 people. The so-called “Black Saturday Bushfires” are often called the worst natural disaster in Australia’s history. The 2009 Victorian Bushfire Royal Commission was established on February 16, 2009, to investigate the causes and responses to these bushfires. The final report and its recommendations were published in July 2010. The major reason for the fire was a spark from a fallen powerline in scorching weather during a strong wind.
As a recommendation of the 2009 Victorian Bushfire Royal Commission, in 2011 Victorian Government invested in a powerline bushfire safety program to mitigate the bushfire risk originating from SWER and 22kV powerlines. As the outcome of this programme, REFCL – Rapid Earth Fault Current Limiters was introduced and proposed to install for Victoria regional areas’ electrical network, which are more vulnerable to bushfire incidents.
REFCL is an electricity network protection device which is designed to prevent fault current dissipated from phase-earth faults on 22kV network to reduce the fire risks associated with electricity network. Although there are various types of protection mechanisms falls under REFCL protection, here in Victoria we use Ground Fault Neutraliser (GFN), a technology introduced by Swedish Neutral.
REFCL device is installed in zone substations. This system can check the performance of all distribution powerlines to the further point. A REFCL operates when a single phase-to-earth fault occurs. Its operation causes the phase voltage of the faulted phase to be reduced to near-earth potential (zero volts), thereby working to eliminate the flow of fault current while simultaneously boosting the voltage of the two phases. So, during a fault condition the healthy phases remain energised, and customers can receive a continuous supply. The REFCL system is continuously monitoring the status of the fault and if the fault is temporary and fault is cleared then the power is restored in that line. If the fault is permanent, then power will be disconnected in the faulty phase.
REFCL system is made up of three main components.
- Arc Suppression Coil – also known as a large inductor, which compensates for the leakage current during an earth fault.
- Residual Current Compensator – also referred to as the inverter, which is located in the zone substation control building or switch room. It is used to reduce fault current by compensating for the active current during an earth fault
- Control Panels- which controls the equipment.
However, REFCL system requires more sub systems/ devices than the three components described above to ensure the safety and accuracy of operation. So, Distributed Networks Service Providers who are mainly engaged with REFCL installation have improved the network safety and reliability to support the REFCL system’s operational speed and sensitivity.
Network Balancing is one of the capital expenditures workstream associated with REFCL installation. In order to meet the performance standards in the regulations, the capacitive balance must be maintained because capacitive imbalance will negatively affect residual current and neutral voltage. In Victoria, long single-phase (two-wire) spurs teed off three-phase lines can create significant capacitive imbalance. So, one of the actions which has been taken to prevent capacitive imbalance is installing pole-mounted capacitor units along with the feeders.
Manufacturing of Single-Phase Capacitor Balance Unit:
The two main DNSP (Distributed Network Service Providers) engaged in REFCL installation are Powercor and Ausnet. I had an opportunity to engage with this project because I worked in a switchboard manufacturing company which is awarded with Single Phase Capacitive Balancing Unit supply contract.
As the pilot project we received an order for 200 units to deliver within three months. With the complexity of the product specification, it was a challenge to achieve the target within given timeline. DNSP has provided the electrical schematic of the design and estimated dimensions and mounting bracket details of the unit. Based on the given information, a 3D model of the product is generated to ensure that all the material can be integrated within the given dimensions. After finalising the mechanical design of the capacitor balance unit, an enclosure order was given to a third-party enclosure manufacturer to expedite the process at a minimum cost. We had resources to manufacture enclosures in-house. But with the project timeline and to cost optimisation, it was the best decision to outsource some of the items.
The design consists of several major components. Such are Capacitors, Current transformer, breakers, auxiliary contacts, UPS and a RTU (Remote Terminal Unit) and a 4G Router. The design has been done to remotely monitor some of the functions of the unit.
- The capacitor current – measured from a CT and signal is wired to RTU
- Breaker status – monitored whether it is tripped or not using auxiliary contacts wired to RTU
- UPS status – to make sure back power is available in a case of main power disruption.
RTU is processing all the function status of the unit and communicates to DNSP service depots via 4G router. If there is a fault of the unit, then we can send a service team to the exact location of the unit to rectify the issue based on the GIS details they have assigned to each unit.
In the manufacturing process, we took several decisions to optimise the resources and time. A separate team with more experience in control wiring is assigned to fit the wiring process. Then we reduce manual processes as much as possible. As an example, wire cutting, and crimping processes were done using machines. This saved us a lot of man-hours. All equipment was fitted and wired on a separate gear tray because it is more efficient compared to wiring and fitting inside an enclosure. Assembled gear tray was fitted into the enclosure at the last stage.
The final process was testing. Testing engineers conduct all required electrical testing and visual inspection. Visual inspection is a much more important step because a part of this inspection was checking the labels of units. Each of these units has been assigned a specific 22kV line feeder location, so it was our responsibility to ensure the correct number of capacitors has been fixed according to the feeder number. DNSP had provided us with all these details when they placed the order. The final step of the testing was doing a remote SCADA testing with service provider’s commissioning engineer. After we power up each unit, DNSP commissioning engineer checks the status of the unit remotely and ensure that all the functions are working well before we dispatch the units.
Finally, we pack and label each unit as per the guideline given by the service provider and dispatch it to relevant service depots.
We successfully completed the pilot project before the deadline and got the order for the 2nd batch as soon as we completed the first one. Until today, Service providers continuously place orders for more units as they complete each stage of the REFCL project. With the manufacturing process, we designed to run this order made this a more profitable project for the company and later, this was adapted for other similar projects the company did.