The Australian Energy Market Commission made the Generator technical performance standards rule (the GTPS rule) on 27 September 2018. It covers a range of technical performance standards for generators and represents a major reform.
The rules were made following extensive consultation with key stakeholders who informed the Commission’s decision making, along with expert technical advice. Now that the rule has been made, the responsible parties – being generators, network businesses and the system operator are working through the implementation of the new rules. Consistent with our practice, we are monitoring the implementation so issues can be addressed as they arise.
The GTPS rule achieves the right trade-off between lowest cost solutions for consumers and keeping the system safe and secure.
Generators play a fundamental role, not just in supplying energy but also in helping AEMO and network businesses keep the lights on. Their role in keeping the power system secure comes from their technical capability to control their voltage and frequency, and their ability to stay connected even when there is a major disturbance to the power system.
The GTPS rule was requested by AEMO and provides a foundation for a secure, least cost transition as new generators, often with different technical characteristics, seek to connect to the national electricity grid. The change tightens some standards where needed and sets clearer roles and responsibilities so all parties – generators, networks and the market operator, know what they have to do when negotiating the required standards for a new connection in a particular location.
The access standards, and the framework for the negotiation of performance standards, minimises barriers to entry by allowing for the specific technical capabilities of different generation technologies.
Multiple fault ride through
The GTPS rule introduced new requirements for generators to stay connected following multiple faults on the power system. These changes are intended to reduce the likelihood of cascading generator tripping following non-credible contingencies.
The likelihood of multiple fault events happening in the system has not changed. But their depth and severity may increase in parts of the power system with low system strength. The GTPS rule consequently explicitly defines requirements for generators to build-in the capacity to survive these kinds of multiple fault events.
Different generation technologies have different capabilities to withstand multiple faults. In particular, some generating systems may not be able to withstand multiple severe faults within a tight timeframe.
The GTPS rule includes a wide range of capability between the minimum access standard and the automatic access standard. Connecting generators will be able to negotiate a level of capability between the automatic and minimum, considering factors including technical and commercial feasibility of providing different levels of capability, how best to protect their generating plant, and the needs of the power system.
The minimum access standard for multiple fault ride through recognises the potential technical and safety limitations of synchronous generators and type three asynchronous wind farms. It limits the number of rapid succession faults a generating system has to withstand, to no more than three disturbances within a 30 second period, and no more than six disturbances within a five minute period. This is designed to address the risk of internal oscillatory instabilities and potential damage to generating units.
Overvoltage ride through requirements
The GTPS rule introduced new requirements for generators to stay connected following over-voltage events on the power system.
Prolonged periods of over-voltage can reduce the lifespan of power system equipment and can lead to immediate damage. The National Electricity Rules therefore establish system standards that require network service providers to contain the level of over-voltage for normal operation and following credible contingencies. The GTPS rule does not change these system standards for voltage control.
Generators also need to remain connected to the system following non-credible contingencies that can result in severe, temporary over voltages on the power system. These over-voltage disturbances may get worse in future, as the generation mix changes and levels of system strength decline.
The GTPS rule therefore expanded the existing requirements for generators to remain connected during over-voltages caused by more severe, non-credible contingencies. Generators that remain connected during these disturbances can help to manage over-voltages, by absorbing reactive power. Conversely, if these generators tripped, the removal of this reactive absorption means that nearby generators may experience more extreme over-voltages, potentially triggering cascading outages and a major supply disruption.
Allowance for generators to trip
The GTPS rule made no changes to existing arrangements that allow generators to trip in order to prevent damage to their equipment. In regards to multiple fault ride through, protection settings including those that activate in anticipation of pole slip, will exempt generating systems from the requirement to stay connected for multiple faults where staying connected would cause damage to the generator or the power system .
The GTPS rule also allows generators to trip for over-voltages, under a number of circumstances. For instance, once over-voltages on the system have exceeded the levels and timeframes set out in the National Electricity Rules, the generator can trip. The GTPS rule also made no changes to the provisions in the rules that allow generators to trip where the over voltage is caused by mal-operation within the generating system. Under these circumstances, protection mechanisms will trip the generator to avoid it being damaged .
Application to existing generators
The GTPS rule introduced new arrangements for the renegotiation of GPS, which allow a generator to use its previously agreed performance standards as the starting point of new negotiations.
This arrangement allows for amendments to the GPS that reflect technical capabilities and safety limitations of the generating unit, where a generator wants to make an alteration to its equipment. It will also allow for the identification of the most cost efficient solution, balancing commercial feasibility against the needs of the system.
Conclusions
The GTPS rule has been carefully designed to maintain power system security, at the lowest overall cost to consumers.
The National Electricity Rules still retain a number of protections that allow generators to trip to avoid damage.
Different generation technologies will have different capabilities to meet the new requirements. We expect that through the process of negotiation, generators will develop performance standards that are technically and commercially feasible, and which are consistent with protecting their plant from damage.
Media: Prudence Anderson, Communication Director, 0404 821 935 or (02) 8296 7817