Reliable Rate-of-Change-of-Frequency Measurements: Use Cases and Test Conditions

Abstract

Based on user expectations and requirements, this article discusses three use cases (UCs) for measurements of power system frequency and rate-of-change-of-frequency (ROCOF) measurements, specifying accuracy and latency requirement for each UC. Furthermore, a set of realistic test conditions are proposed, extending those of the present IEC/IEEE 60255-118-1 standard, to ensure ROCOF measuring instruments are adequately tested on their suitability for reliable ROCOF measurements in power systems. Target worst case ROCOF errors (RFEs) are given for each test waveform and UC. Several published ROCOF algorithms are tested using the proposed test conditions. A selection of the test results is reported and compared against the target RFEs. The results show that the defined tests are indeed helpful in evaluating the ROCOF algorithms, and furthermore that the algorithms can be designed to meet all the requirements on RFEs for the tests proposed in this article.

Contribution of Wind Farms to the Stability of Power Systems with High Penetration of Renewables

“…However, measuring ROCOF, as any derivative magnitude, is prone to error and noise. Intensive filtering is therefore applied, which causes a significant latency period [22]. Estimating the derivative of the frequency requires measures over long time windows, typically 200-500 ms [22][23][24], leading to measurement latencies and response delays around 100-250 ms. During a frequency event, response time is of paramount importance when trying to limit ROCOF and frequency nadir, and therefore a significant difference compared to SG and VSG performance can be expected.…”

“…There is a lack of a standard for the requirements on ROCOF maximum latency and error for Fast Frequency Response applications. In [22], an enquiry among utilities yielded that an ideal target would be a latency of 100 ms and a peak error of 0.02 Hz/s for this application. However, taking into account the state-of-the-art in ROCOF measurements, it is challenging to achieve such performance, although it seems possible in most situations.…”

“…Unlike other renewable technologies, wind generation does have a real kinetic energy buffer because of the rotating parts of the wind turbine. However, that energy is limited and care should be taken when extracting energy from the rotor by slowing it down, as there is a limit to the power that can be extracted before the turbine stability is compromised [20][21][22][23]. Here, a detailed analysis on the impact on the wind turbine speed is carried out.…”

Calibration of a Digital Current Transformer Measuring Bridge: Metrological Challenges and Uncertainty Contributions

“…In order to address such challenges, also the measurement infrastructure needs to undergo a significant renovation, both in terms of instrumentation and control strategies [7]. In particular, the transition from traditional to digital electrical substations paves the way to more sophisticated and optimized approaches for the collection and aggregation of the quantities of interest, e.g., voltage and current levels at the transformer secondary windings [8].…”

Phasor Measurement Unit and Sampled Values: Measurement and Implementation Challenges

“…Modern power systems are characterized by an everincreasing penetration of distributed generation and renewable energy sources [1], [2]. Due to their inherent volatility and lack of rotating inertia, such resources are likely to produce faster dynamics and high distortion levels, that might interfere with the traditional monitoring and control schemes [3]- [5].…”