VISOR

What is project VISOR?

VISOR stands for Visualisation of System Dynamics Using Enhanced Monitoring, and the project demonstrates the first Wide-Area Monitoring System nationwide IT infrastructure in the GB, using state-of-the-art system monitoring at dozens of locations across England and Scotland. This revolutionises the real-time monitoring of the GB system by combining synchronised measurements from all three GB TOs to provide GB-wide real-time visibility of the dynamic system behaviour of the network.

Why do we need VISOR?

VISOR seeks to improve the understanding of two key areas of the power system – Real-Time System Dynamics and Sub-Synchronous Oscillation Monitoring, made possible by enhanced synchronised real-time measurements from across the whole GB system. Improving our understanding will allow us to get more from existing assets, and ensure the system remains reliable, as the network becomes more diverse.

What are the main problems VISOR is trying to address?

The two main target areas that VISOR seeks to improve are:

1. Real-Time System Dynamics (stability and security limits)
2. Sub-Synchronous Oscillation Monitoring.

There are a couple of ‘pinch-points’ in the GB system where constraints (forced reduction in generation) are frequent. The England-Scotland boundary is one such pinch-point, where wind generation in Scotland is often constrained off and replaced by generation elsewhere, coming at a cost to the GB customer and restricting the installation of further generation.

Furthermore, due to increasing diversity of generation, HVDC links, and other power electronic devices, the dynamic behaviour of the GB system is becoming increasingly complex. Such new technologies introduces the potential risk for new and dynamic modes of power oscillations – referred to as Sub-Synchronous Oscillations (SSO).

The accurate understanding of network dynamics enabled by VISOR, seeks to increase network resilience and optimise system stability limits, thereby effectively increasing network capacity using existing assets – maximising the generation capacity and alleviating generation constraints for generators.

Who are involved with the project?

The project is a collaboration project between the three mainland GB Transmission Owners (TOs), SPT, SHE and NGET, and the System Operator (SO), NGETSO.

Our project partners also include Alstom Grid UK and the University of Manchester as technology and research providers, respectively.

What is the duration of the project?

The project duration is 3 years, January 2014 – March 2017, and broadly comprises of two stages – and installation stage and an operational stage. The WAMS infrastructure is up and running and installation stage is due for completion in early 2016. The operational stage analyses uses the new insight to analyse the system and is underway.

What technology is VISOR using?

Traditional Existing PMU monitoring provides visibility only up to around 10Hz, due fundamental data sampling limitations and performance requirements. A new Waveform Measurement Unit device has therefore been developed, to provide visibility of SSO.

A new SSO Management Application has also been developed – to provide analysts with the information and toolset to characterise SSO behaviour in the GB system, and to provide operators with clear and actionable information to deal with any SSO issues that arise.

Where is VISOR being trialled?

The VISOR WAMS gathers data from a vast number of substations across the England, Scotland and Wales. The project studies the whole GB but with particular focus on the dynamic power flow across the boundary between Scotland and England, the “B6 boundary”.

The figure illustrates the VISOR WAMS system.

What does SSO mean?

SSO stands for Sub-Synchronous Oscillations, which are power oscillations below the synchronous frequency, 50Hz.

Power systems, at their basic consist of the exchange of energy between two elements of the power system. Ideally this exchange would solely consist of generators providing energy to the loads. However, at times two elements of the power system (e.g. two generators) will begin to exchange energy back and forth between them. This exchange of power can be observed as sinusoidal oscillations in the magnitude, frequency and phase angle of voltages, currents and powers. When these sinusoidal exchanges have frequencies below the synchronous frequency they are referred to as Sub-Synchronous Oscillations.

What are the benefits of VISOR?

Wide Area Monitoring can play a role in reducing uncertainty by providing synchronised monitoring and instantaneous operating points that can improve system models and operation. It has established a new infrastructure to ensure that potential threats are detected and the system remains secure. By improving our understanding of the dynamic behaviour, it will provide the System Operator with the means to optimise the full capacity and deliver further capacity release using existing assets. Deferred asset investment estimated in the order of £45m per 100MW capacity realised.

The deployment of phasor-based applications paves the way for the future use of phasor data for enhanced control and protection, all of which will allow operators to optimise existing assets without deteriorating reliability.

What applications is VISOR using?

The project introduces suite of new software applications to address three areas

1. Managing Risks: The project will demonstrate real‐time tools to monitor and locate the causes of oscillatory interactions and disturbances.
2. Maximising Assets: In order to maximise asset utilisation, the project will trial a new power‐angle constraint approach to power boundaries, and will deliver learning on optimal deployment of WAMS infrastructure
3. Reducing uncertainty: the benefits of synchronised phasor measurements will be explored for the line parameter estimation. The University of Manchester are also researching the use of phasor data in hybrid state estimation, the impact of uncertainty, and model validation.

How is the data being analysed?

The new phasor data gathered by PMUs and WMUs is fed through new data collector stations in each region and, in turn, transferred to a centralised data centre which analyses data and provides an instantaneous view of the whole system.

A new control room software module that will detect, monitor and visualise SSO information, enabling operators to observe & characterise SSO behaviour and respond effectively to issues that emerge in real‐time.

What do stability limits mean?

Security limits are an essential aspect of power system operation and are calculated by network models. They define the safe operating limits of the system to safeguard against network disturbances, ensuring the system does not breach Stability limits in the wake of changes to system operation.

Operating within the security limit appears easy if the limits and operating point are exactly known. However, this is not the case – the limits and operating point constantly change, and we must calculate these ourselves. Uncertainty in power system measurements and models prevent us from calculating this perfectly. Wide Area Monitoring can play a role in reducing uncertainty by providing synchronised monitoring and instantaneous operating points that can improve system models and operation.

What is the difference between SSO, SSR and SSTi etc?

The acronyms all refer to different types of sub-synchronous oscillation that typically occupy different frequency bands. Oscillations under 50Hz are grouped into modes by their frequency

• The lower modes (under 4Hz) stem from generators, their speed governors and controllers.
  • These are well known and monitored

• But we know less about the modes above 4Hz
  • Due to power electronic control systems, generator turbine shaft twisting, and power network resonances
  • Which are not very well monitored

All these modes are technically sub‐synchronous oscillations, but they tend to be categorised separately, as:

• VLF, very low frequency
• LF, low frequency
• And SSO, which is a key focus of VISOR

The new equipment installed through VISOR sheds new insight into the SSO range of oscillations.

What are the effects of power oscillations?

Oscillations pose a particular risk in the power system, and dangerous if not controlled. If oscillations occur, they can cause generators to trip, or even fail mechanically, and cause blackouts. The financial and societal impacts of blackouts, and partial blackouts, are huge.