Comparison of Waveform Relaxation with Traditional Real Time Digital Simulation for Closed Loop Performance Testing of Protective Relays

摘要

Real time Hardware-in-the-Loop (HIL) simulation tools are widely used in testing and tuning power system protection, monitoring and control design. Commercially available real time simulators (rts) today utilize multiple high performing processors in order to simulate power system models, to which the Hardware Under Test (HUT) will be connected. The number of processors needed to simulate a computer model of a typical power system is directly related to the size and complexity of the model. Protective relays are critical security elements of any power grid, particularly in case of transmission lines. Real time closed loop tests that rely on comprehensive system models are valuable tools for protection engineers, for example, to analyse performance of new protection schemes in real world models. To date, access to the test equipment that makes real time closed loop testing possible has been limited to those utilities and institutions that can afford them. While relatively less informative, an alternate approach to rts equipment, particularly for testing protection relay hardware, is to use an off-line electromagnetic transient (EMT) simulation program to simulate the power network, and playback the simulation results in real-time but open loop to the relay hardware under test. While a limited number of contact outputs from the HUT could be fed back, such as a breaker operation, these simply trigger a new simulation. Depending on the system model, number of protective relays under test and the dependency on one another, results range from inaccurate to simply inadequate when compared to comprehensive closed loop testing. This paper demonstrates the practical application of waveform relaxation techniques to provide real time closed loop results that mirror those of traditional closed loop real time simulators. The relatively lower processing requirements, and therefore potential for lower cost, of waveform relaxation techniques proposes the potential for a much broader adoption of real time closed loop testing which can lead to improved overall power system performance and innovation. A cost effective method for closed loop testing of protective relays with real time results is offered in this paper by combining PSCAD models and low cost processing technology with a Real Time Player/Recorder (RTPR) interface. A HIL simulation is performed with a protective relay using two methods, the first is the proposed low cost processing technology using PSCAD and the second is the RTDS using RSCAD. The simulation results prove successful both methods provide identical real time results.