Switchgear is an assembly of switching devices, associated with regulation, protection & metering of electrical power systems. In the event of a fault occurrence, the switchgear immediately responds and disconnects the electrical power system causing the fault. Traditionally, switchgears used to be an assembly of circuit breaker, current transformer, voltage transformer, measurement equipment, etc. with minimal onboard intelligence. As the world of embedded systems is becoming more advanced, there is an increasing trend to make every device smarter. The smartness of any device is typically characterized by
Ability to make informed decisions
- Software defined personalities
- Extensive network capabilities
- Distributed & centralized computing
The power of these smart devices is greatly enhanced when they are networked together. Needless to say, the latest trends of switchgears/circuit breakers are evolving towards making them smart and networked.
Embedded Systems for Electrical Power systems
This section discusses the technologies & benefits offered by National Instruments' Embedded Platforms for embedding smartness into the next generation switchgear systems. Embedded systems for Electrical power systems include Synchrophasor units, Smart metering units, Power Quality Analyzers, Reclosers etc. Traditional embedded systems have different hardware & software for each of the above units, i.e. to upgrade an existing Power quality analyzer to a Synchrophasor unit, it may be necessary to change the entire embedded hardware. Many of these systems are installed in remote locations making cost of upgrade very high. Embedded systems for electrical power systems typically require high quality & synchronized measurements, expandable functionality, field upgradeability, deterministic control, rugged hardware and 24x7 operation.
National Instruments addresses this with the Graphical System Design approach of bringing Commercially off the shelf hardware that is powerful, modular, rugged and reconfigurable with powerful software like LabVIEW. The architecture of the CompactRIO product series fits best for this requirement.
As shown in figure 1, a Real-time processor that runs a very deterministic real-time operating system connected to an FPGA( Field Programmable Gate Array) that can do concurrent high speed operations defined in Software, finally connected to the I/Os that can connect to the CT/PTs to measure current and voltages precisely at high speeds. The modular nature of this platform enables addition of the GPS Time stamping module as well.
The CompactRIO system is programmed using NI LabVIEW Graphical System Design platform, and it can be customized as well as upgraded in the field. With minimal/no addition to the hardware, it can be programmed to behave as a number of different “personalities”, such as PMU, Power Quality Analyzer, Smart Switch, Recloser, etc. Also with readily available software support for DNP3, IEC 60870, IEC 61850 protocols, the developers can implement these protocols on CompactRIO at an abstracted level with minimum effort. Due to the modular nature of the hardware & remotely upgradeable software, NI CompactRIO is the ideal approach for smart grid applications that demand evolving functionality and requirements.
Owing to the above mentioned benefits, National Instruments, in collaboration with Siemens, has developed an 'Advanced Smart Distribution Switch'. It uses an NI CompactRIO with current and voltage input modules, digital output modules & GPS module along with Siemens' high voltage switches. The FPGA present on the CompactRIO implements deterministic control algorithms for the Siemens' high voltage switch. Also, the system can be upgraded/changed into a smart recloser, power quality analyzer, synchrophasor or any combination of these by configuring the software.
Testing switchgears for performance & reliability
As discussed earlier, switchgears are deployed in various remote locations on power distribution networks. Also, they play a crucial role in protecting the electrical system from faults. Hence, reliability & lifetime of switchgears is extremely important and they need to be tested for the same. Switchgears need to be tested in different aspects like mechanical endurance & lifetime, contact resistance, thermal endurance, isolation, response time etc. National Instruments has long been established in the fields of Automated Test & Data Acquisition. NI offers wide range of hardware for implementing these tests.
Some of these tests like the mechanical endurance testing require extended periods of stimulus generation and recording of data. This requires automation of tests in a test rig. Some other tests like response time test require accurate timing measurement between the injection of fault and the response of the switchgear. This requires synchronized measurements between the fault injection and contact resistance measurement. With a powerful industry standard test platform like PXI, (See Figure 2) NI offers wide range of I/O cards to perform these tests on the switchgear systems. The most important benefit is that, the same Graphical System Design software - LabVIEW, can be used for the development of these test rigs also.(Raviteja Chivukula is a Technical Marketing Engineer with National Instruments. A graduate in Electrical Engineering from IIT Madras, he has worked with NI in various roles and has been actively involved in supporting customers from the fields of power measurement & power electronics.)