DCB preparing for UK implementation
Brian Cheung, ABB Principal Technology Engineer gives an update on the potential for implementing the Disconnecting Circuit Breaker (DCB) in the UK.
When ABB introduced the DCB in 2000, it was a revolutionary concept for high-voltage air-insulated switchgear (AIS). By integrating the function of disconnector and circuit breaker into a single unit, the DCB opened up the potential to use a single piece of switchgear in place of three.
Then in 2013, we introduced the Fibre Optic Current Sensor (FOCS) to the DCB for current measurement that is accurate to 0.1 percent. This enabled the removal of current transformers from a switchgear bay.
Combined, the DCB-FOCS has the potential to reduce the overall physical footprint of a substation by 60 percent compared with a conventional arrangement. And because the FOCS is equipped with a digital interface, it is compatible with the IEC 61850 standard.
The DCB is now a well-proven concept elsewhere in the world, and particularly Sweden, where installations have been in operation since 2000.
As part of their drive towards innovation, operators in the UK are now considering how they can use the equipment. ABB is preparing for the DCB to undergo review by the ENA (Energy Networks Association). Once approved, operators across the UK will be able to adopt the switchgear for substations rated at up to 400 kV.
What is the DCB?
The DCB is based on ABB’s well known LTB and HPL circuit breakers. Its basic functions are exactly the same as a conventional circuit breaker with the additional feature that the circuit breaker contacts also provide the disconnecting function. This means that once the breaker is open, the DCB uses the open breaker contact set as the disconnector and the isolation gap fulfils the IEC disconnector requirements.
To ensure the circuit is securely isolated for maintenance, the DCB is equipped with a mechanical blocking device which operates directly on the shaft that moves the circuit breaker main contacts. When the mechanical block is engaged and padlocked, it is impossible to close the breaker hence providing a secure point of isolation as a disconnector. An integrated earthing switch is also included as standard for DCB rated 245 kV or below which provides another means of visual indication that the circuit is safe to work on.
Optical current measurement
FOCS is a type of sensor that measures DC current by viewing the changes made to a beam of light when it passes through the magnetic field generated by the current. It can measure currents of up to 600 kA (kiloamperes), providing readings that are accurate to 0.1 percent and it is equipped with a digital interface that is compatible with IEC 61850.
Because it measures changes to the physical properties of light, it does not require the regular re-calibration needed by a conventional current transformer, meaning that it is not just compact but also requires little maintenance.
Performance and savings
As a single piece of switchgear that replaces three, the DCB can deliver greater availability and grid performance as well as save 60 percent of the overall physical footprint of a substation compared to conventional technology, and enables significant cost savings for civil engineering and capital costs.
For new installations, a more compact footprint leads to reduced cost for land acquisition as well as civil works and installation costs and time. Indirect cost savings come from reduced energy losses and lower costs from outages and maintenance. And because the line has greater availability, the DCB can also protect revenues.
Designed for low maintenance, it can be delivered on a standalone basis or as a component part of a complete switchgear bay. It is also more environmentally friendly than its predecessor in terms of CO2 emissions and material used for production and insulation.
Try out the DCB on-screen
ABB has developed a website where visitors can select the design parameters of a substation and compare a number of layouts.
The tool allows users to input voltage, busbar arrangement, number of lines, number of transformers and the estimated cost of an outage. It then gives options for minimum space, extendability and maximum availability.