Previously, Insulect has written about a variety of individual power plant monitoring applications, including Fault and Disturbance, Power Quality and Dynamic Behaviour. In this article we take a look at a solution for monitoring and analysing all these aspects of a generation power system – as well as AEMO FCAS reporting – using a single device and one integrated software package.
Nearly all power plants today are supervised by Digital Control Systems (DCS) and most of these DCS provide some form of trend recording. Nearly all plants now have a Plant Information (PI) system too, either as an integrated part of their DCS or as a free standing unit. These trend recorders and PI systems can usually provide a fair picture of how a plant has behaved in normal slowly varying operation and through normal load change manoeuvres.
However it is still difficult to find good data on the dynamic behaviour of plants when they are disturbed by events on the grid. This suggests that the present standard monitoring elements in a power plant – the DCS and PI systems – are oriented to in-plant interests and are not well suited to the needs of the grid through which the plant delivers its product to market. Nor are these systems suited to supporting regulatory reporting commitments such as FCAS.
The primary focus of plant operations in a conventional generation plant is the condition of the boiler and turbine. Power production is controlled by changing fuel flow, but the operator is as concerned with the effect of changes of fuelling on temperatures and pressures in the boiler / turbine as with the effect on the transmission grid. The grid is regarded as maintaining steady conditions as it receives the power produced in the plant.
The thermodynamic processes of the boiler and turbine take place on a time scale of tens of seconds to many minutes.
By comparison, the grid control principles require each turbine generator to be controlled second-by-second, so as to balance the relationships between real power output and shaft speed, and reactive power output and terminal voltage.
These two relationships are enforced by the turbine governor and the generator voltage regulator, respectively. The responses of these controls are much quicker than the variations of temperature and pressure seen on the boiler / turbine side of the plant; key time constants range between 0.1 and 10 seconds.
The interest of the transmission grid is focused on the way the plant behaves in brief transient disturbances of the four key variables (real power output, reactive power output, shaft speed, terminal voltage). These transients:
- in many cases may not even be noticed by the plant operators
- in nearly all cases run their course so quickly that the plant operator could not do anything about them, even if he should see them
- cannot be 'captured' accurately, and can even be missed completely, by recording systems using sampling rates appropriate for the boiler-turbine side of the plant
Generators install power quality (PQ) monitors to ascertain their compliance with the Generation, Transmission and Distribution rules. In Australia and throughout the world, the focus on accurate, comparable PQ monitoring continues to increase as a result of the rapidly growing install base of renewable generation technologies – a trend that is expected to continue following the local introduction of the carbon tax and global efforts to curb greenhouse gas emissions.
A consequence of this growth is that distribution networks are faced with the connection of large distributed generation (DG) sources to their networks – which were not built for high DG penetration. A second problem is that distribution networks are not designed to accept large DG units, because their short circuit capacity is often close to the designed maximum value. A further complexity is the different types of generators in use, which each produce different PQ problems.
Meeting the requirements for interconnection of large scale DG will imply significant increase in infrastructure investments, so that all network operators can continue to meet their regulatory obligations to “not adversely affect the quality of supply for other network users” (AEMO, National Electricity Rules Version 51, Chapter 5 Network Connection).
There are three primary aspects to consider with regards to operation of distributed generation:
- Voltage quality of supply distribution network, impacting the generator performance
- Current quality of the generator, impacting the supply system and other connected customers
- System reliability and stability can be impacted when many sites trip offline simultaneously
The first point is well addressed by generator manufacturers through appropriate design and is not a significant issue today. The second aspect creates many concerns for DNSPs planning to connect DG to their grids, as they strive to ensure overall system power quality stays below the planning levels.
As a result of these factors, there is growing interest – from regulatory bodies and entities concerned with analysing grid behaviour – in the efficient response of power plant controls to sudden system disturbances. This rise in interest is due to the responsibility that regulatory bodies have in ensuring grid stability – a responsibility that must be shared by all sectors of the energy market.
Major grid events have demonstrated the importance of precise grid simulation to aid power analysts in forecasting, assessing and planning grid dependability. Furthermore, without access to the necessary post-event information, dispute resolution between suppliers, end-users and regulators becomes more costly and drawn out.
To address these disturbance challenges, the installation of permanent dynamic monitoring systems in generation plants is becoming the norm, motivated by the requirements of regulatory bodies to monitor plant compliance to dynamic performance standards.
Frequency control ancillary services
Hundreds of power stations and plants across the National Electricity Market (NEM) participate in Frequency Control Ancillary Services (FCAS) – a service that AEMO procures from participants to “maintain the frequency on the electrical system, at any point in time, close to fifty cycles per second as required by the NEM frequency standards” (Guide To Ancillary Services In The National Electricity Market, AEMO).
The power flow representing the amount of generation and the local frequency must be measured at or close to each of the relevant connection points. AEMO procures FCAS to ensure that when an event occurs on the power system (e.g. loss of the largest generator or loss of an inter-connector and subsequent islanding of a region) frequency is maintained within these standards.
For a generator to meet the FCAS reporting requirements, they require a monitoring device with a sampling rate of 20Hz minimum to meet the fast raise service and decimation application to meet the slow raise services.
Meeting the monitoring task
With these factors in mind, the Qualitrol IDM+ multifunctional power system monitor is ideally suited as a permanent monitoring system for power generation. The IDM+ reliably records issues pertaining to system disturbances through fault detection, isolation and resolution. Importantly, it allows a generating station to represent both mechanical and electrical parameters on the same time scale, relative to system events.
To meet a wide range of power system monitoring needs, IDM+ is built on a flexible, modular platform from which a variety of monitoring functions can be performed. This includes Digital Fault Recording (DFR) and Dynamic Disturbance Recording (DDR) with options for Class A Power Quality Monitoring (PQ) integrated into the same hardware platform. In addition to traditional PQ monitoring, modern equipment like the IDM+ can help to assess the performance of turbines, establish predictive maintenance criteria and analyse the response of the turbine during power system events like voltage dips.
IEC 61850 protocol is fully utilised in the IDM+ which is designed to meet both current and future-state substation automation architectures. And the IDM+ can be expanded in functionality as needs change.
Automation is the key
Automated real-time data and information processing of grid activity sourced through reliable, ongoing dynamic power supply monitoring can achieve dispute resolution between members of the electricity value chain; the grid operator, plant owner, customer and the regulatory body.
Through the identification of indicators of potential problems and facilitation of system forecast and maintenance planning, reliable power system monitoring is an integral factor of the smart grid concept. As outlined in the European Technology Platform for Electricity Networks for the Future, the smart grid model encompasses the incorporation of activities of all network suppliers and users to ensure efficient, sustainable, economic and secure electricity delivery.
iQ+ software can provide automated analysis of recorded data through customisable reporting, a high degree of personalisation, and automated alerts delivered via email and text message. It provides a system overview and health check, alerting the operator to problem areas and allowing them to drill down into the information.
Utilising DFR and DDR records time stamped down to 100nS, the IDM+ will provide the data as required by the regulator for FCAS reporting. Flexible sampling rates of up to 512 samples per second (25.6 kHz at 50Hz) meets both Fast Raise and Slow Raise services.
Autopoll software installed on a central server automatically downloads, stores and processes continuously recorded bulk data from IDM+ devices for compliance reporting.
Additionally iQ+ engineering software can provide further enhancements in post-event data processing to easily isolate the correct information to send to AEMO after a frequency event on the network. Data is readily exported to a CSV file and waveforms can similarly be transferred to spreadsheets.
Advanced power system monitoring for Generation – whether in a conventional power plant or renewable generation site – offers several benefits to plant operators and the wider energy network, including improved system stability, power quality, support more accurately predictive maintenance of turbines, and meet regulatory commitments.
As a single hardware/software platform for all these monitoring requirements, IDM+ and Autopoll provide a reliable and cost-effective dynamic monitoring solution to complement the standard DSC and PI system functions.
Find out more about IDM+ and Autopoll Software.