Grid Connection: Meeting the new AEMO requirements for simulation model

On February 18 2020, the Australian Energy Market Operator (AEMO) published a new guidance document that imposes important new obligations for energy project developers in the National Electricity Market (NEM).

This AEMO document, applicable to all utility-scale generation, codifies the acceptance test requirements for simulation models in PSCAD software. Over the last five years, these ‘electromagnetic transient’ models in PSCAD have been increasingly relied upon for detailed studies of the technical performance of grid connection, creating a new compliance challenge and focus on risk for the industry.

Prior to 2016, a PSCAD study for a grid connection was a bespoke exercise, required in unusual circumstances where modelling in the more straightforward PSS/E software did not suffice. Fast forward two years, and by 2018 PSCAD simulation models became required from all project developers, which was cemented by the release of updated Power System Model Guidelines by AEMO in July 2018.

This was seen as a necessary step given instances of new connections where PSCAD modelling had revealed technical compliance issues that the simpler PSS/E models failed to detect.

The South Australia blackout of 2016, whilst it was not caused by any factor linked to the technical difference between PSCAD and PSS/E models, assuredly also played a role in the increased level of vigilance applied to the technical performance of grid connections.

While PSCAD models have been required for all projects since, the pre-qualification requirements on these models have been less explicit, limited to informal checks against the AEMO Guidelines and partial benchmarking against hardware tests or PSS/E model results.

Until recently, there was not a formal acceptance test specification similar to that which had existed for PSS/E models since 2013. On February 18 however, that gap was closed.

The new model

The new Dynamic Model Acceptance Test Guideline (DMAG) specifies that new test requirements are to be satisfied for pre-qualification of electrical plant models in PSCAD as well as PSS/E before connection studies are undertaken. This further extends the time and effort required at the due diligence and planning stage of all new projects.

The acceptance tests required by the DMAG will involve over 400 simulation cases in the PSCAD software for a single generator model. For BESS technologies, these tests must be repeated for charge and discharge scenarios. Where a project is a hybrid of multiple technologies, the full suite of tests will need to be performed for each model individually, and then again for the combined system. This will result in hundreds, if not thousands, of tests for a new connection. For example, a wind farm with battery storage requires over 2,000 PSCAD tests to be performed – a significant undertaking.

Furthermore, the requirement for PSCAD test results to be benchmarked against PSS/E results has been extended to include all balanced fault scenarios, and all changes in control system setpoints for voltage, reactive power, active power and frequency.

As project developers will appreciate, this number of PSCAD test scenarios will require substantial time and effort to complete and document.

Vysus Group has been anticipating these requirements and as a result has developed a fully automated PSCAD test suite, which is expected to be capable of handling all the tests within the DMAG as published.

Carrying out the required tests in a timely manner will demand speed and accuracy from the simulation tools, ideally automated to achieve 24-hour execution, and with automatic visual presentation of results that will nonetheless require an ongoing review by engineers to assure data quality.

Parallel processing within the PSCAD architecture can be optimised to cut back on simulation time. The required benchmarking of PSCAD results against equivalent results in the PSS/E software can also be fully automated.

Despite the abundance of expertise, technology and tools at our fingertips, the required testing effort under the DMAG will still greatly challenge industry participants who aim to bring new energy sources online in a timely manner. This is due to the extensive time and effort it will take to carry out the sheer number of PSCAD runs required.

The stringency of these new requirements brings into sharper focus the value industry can reap were bodies such as AEMO and the major transmission operators to make a stronger, more explicit technical case for the level of modelling detail now required. This would help set out in clearer fashion the actual purpose driving this technical effort.

Such technical cases are routinely produced when changes are made in most other elements of the NEM governing framework. A change to the market rules or to the technical standards for generators, for example, triggers a formal rule change process run by the Australian Energy Market Commission (AEMC). This includes the consideration of public submissions, a two-stage drafting process, and a published determination that sets out the reasons for the rule as made.

It has been suggested that future changes to the due diligence requirements for simulation models also, could benefit from a process of this nature. This would mean when successfully run, it serves not to delay necessary changes, but to ensure that participants reach a degree of understanding (if not consensus) that changes that go forward are justified and draw on the broadest practicable range of expertise.

Looking ahead, we expect new requirements to arise in the challenging Australian electricity market and welcome the industry consultations that are now underpinning these developments. Understanding the undertaking of the new PSCAD model acceptance procedures is the first step for developers in achieving greater certainty for their projects when it comes to compliance.

Author: Tony Morton, Global Technical Head for Power Systems, Vysus Group