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Small Signal Stability
Sub-synchronous Resonance (SSR) occurs when an electrical network exchanges energy with a source at a frequency lower than the system’s synchronous frequency. This energy exchange induces torsional stress on generator shafts, posing a risk of damage or fracture.
Traditional power grids are designed to mitigate disturbances, however the increasing integration of renewables and electronic equipment has intensified and complicated grid oscillations.
These grid oscillations are typically between 5-25 Hz, and cannot be seen by SCADA. With no visibility grid operators such as Australia’s AEMO and the UK’s NGESO can only preemptively constrain or direct.
The maximum theoretical detectable oscillation frequency of standard PMU‘s is <25Hz (in 50Hz grids due to the Nyquist limitation) for P-class devices – the detectable oscillation frequency is even lower for M-Class devices.
Real-world PMU based oscillation measurement at frequencies >10Hz is often challenging due to bandwidth and accuracy limitations. However – oscillation frequencies present in modern highly penetrated IBR networks are often higher than 25Hz.
The VECTO 3 uses a small signal stability algorithm that was developed to address grid oscillation detection and monitoring. It detects and calculates the frequency, amplitude and phase angle of a dominant oscillation phasor within a specified frequency range. VECTO’s small signal stability algorithm concurrently identifies three ranges of dominant oscillation phasors between 0.1Hz to 43Hz, representing low, medium and high frequency ranges.
The VECTO oscillatory stability monitor meets all the functional elements for Australia’s NER S5.2.5.10, proposed in AEMO‘s review of technical requirements for connection in the Australian NEM. As operators in other regions with high penetration of IBR‘s start firming up their grid rules related to oscillations, the VECTO oPMU can be configured to meet these requirements for detection, event monitoring, SSCI relay control signals and compliance reporting.
VECTO includes unique phasor measurement capabilities that delivers the experience of an Oscillation Phasor Measurement Unit (oPMU). The system captures GPS time synchronised data through a fleet of wave synchronised edge-computers installed throughout the grid, continuously recording and streaming oscillation phasor data using the established IEEE C37-118 protocol. Oscillation phasors captured at different locations is similar to synchrophasor data, allowing for interaction with all existing Phasor Measurement Units (PMU‘s) currently on the market.
VECTO concurrently identifies up to three dominant oscillation phasors within the range of 0.1Hz to 43Hz.
The algorithm’s low-frequency range, spanning from 0.1Hz to 1Hz, is designed to identify inter-area oscillations. These oscillations typically arise from the interaction of significant energy sources that are geographically distant. This type of oscillation is commonly observed within the frequency range of 0.2Hz to 0.8Hz.
The algorithm’s mid-frequency range, ranging from 1Hz to 10Hz, is tailored to identify local-area oscillations. These oscillations typically emerge from the interaction among energy sources situated in closer proximity. A common cause is the phenomenon known as “hunting” among a group of generators.
The algorithm’s high-frequency range, spanning from 10Hz to 43Hz, is designed to pinpoint oscillations arising from control loop instability among different Inverter-Based Resources (IBR) energy sources.
High precision oscillation phasor estimation
The VECTO 3 is a rugged, multifunction, wave-synchronised, Class-A power quality measurement device, now in its fourth generation. The device is permanently GPS or PTP time synchronised to within <100ns from absolute time, and offers high accuracy and high-bandwidth programmable gain analog inputs in a flexible arrangement.
VECTO’s synchro-waveform technology delivers an interactive experience that has to be seen to be appreciated. Designed by engineers for engineers, VECTO GridOS is flexible, user friendly and open source, precluding the need for expensive third party software.
