2024 EMTP® User Conference

The EMTP® development team is introduced, along with the program schedule and a brief history on EMTP® . Also, attendees will have the chance to learn about upcoming software developments, provide feedback to developers, request updated modules, features, and discuss EMTP-related issues.

This presentation shows the acceptance tests performed on a wind power plant modeled using the WECC model. The plant cosistes of 121 turbines, each with a capacity of 0.85 MW, operating at 60 Hz. These turbines are connected to the 34.5 kV medium voltage collector system via 121 step-up transformers. The wind power plant is linked to the 320 kV network through a 230/34.5 kV 125 MVA main facility transformer. Other network components, such as collector cables and wind turbine step-up transformers, have also been represented by their equivalents. The model was developed and validated using two commercial tools - EMTP® and PSS®E. Simulations and analysis were performed to validate a group of acceptance tests required by the local utility. This presentation will focus on the modelling process, analysis and results obtained using EMTP®. The results obtained from the EMTP® and PSS®E are compared and discussed.

Shunt compensation reactors, deployed in long AC transmission lines, serve to mitigate overvoltages induced by capacitive charging under light load conditions. However, these reactors can introduce operational challenges, notably sustained overvoltages due to zero sequence resonance. Such resonance occurs in unbalanced conditions, often stemming from circuit breaker malfunctions that result in one- or two-phase disconnections. The zero-sequence resonance is triggered between shunt reactors and phase capacitance in disconnected phases. The overvoltage caused by this resonance can lead to equipment damage.                            
The presentation will cover:

• Zero Sequence Resonance: Background on the phenomenon and resulting sustained overvoltages.
• Case Study: A practical example from a large US wind project.
• EMTP Simulations: Investigating zero sequence resonance in shunt compensated lines using EMTP® software.
• Mitigation Measures: Strategies to address the issue, including neutral grounding reactors and specialized protection schemes.

The increasing integration of distributed energy resources (DERs), such as photovoltaic (PV) systems, in electrical power distribution systems (EPDS) represents a promisor path towards sustainable development. This integration can be beneficial because the closer the energy resources are from the consuming point, the less power is lost along its transmission. On the other hand, DER integration can lead to bidirectional power flows in the system, for which the EPDS protection system is not prepared, causing miscoordination of protection elements, problems in the detection of faults in the system, and changes in the operation time of protection elements, compromising the protection system’s reliability. In the context of protection systems for EPDS with DERs, previous works have investigated the DER integration impacts on the protection system. The study [1] evaluates the performance of the protection system of a distribution network by considering two locations to connect a PV system, which has its rated output power gradually increased until it reaches the distribution feeder peak load. However, only solid-phase-to-ground (SPG) faults were considered. In [2], DERs are connected to a test case distribution system to evaluate the reduction in the fault current seen by the feeder relay considering four penetration levels and increasing the fault impedance up to 2 Ω. Additionally, both studies only consider a three-phase connection topology for the DER. In [3], the authors analyzed the impact on the relay protection settings in a microgrid with high penetration of DERs under fault conditions using a Hardware-in-the-loop setup. The paper considered the grid-connected and islanded modes of operation, and the simulated events were successfully validated using a commercial protection relay. However, it is worth noting that while the authors assume the microgrid and its loads are three-phase and balanced, real-world low-voltage distribution networks are typically unbalanced due to factors such as single-phase loads and untransposed feeder impedances [4]. The novelty of this paper stands in how the high penetration of DERs is considered for evaluating the impacts on the protection system. Instead of concentrating the overall rated power of DERs into specific nodes of the system, DERs of different rated powers are distributed along the whole unbalanced feeder by connecting single-phase and three-phase PV systems to the grid. Additionally, the study examines various types of faults, both with 40 Ω impedance and without it, further enhancing its comprehensiveness. The potential deterioration of the overcurrent protection was evaluated using data from the IEEE 34-node test feeder [5], and the simulations were carried out using the EMTP-RV software [6]. Three scenarios of operation were analyzed: (i) without DERs, (ii) 50% of DER penetration with the protection setting defined according to the feeder’s rated load, and (iii) 50% of DER penetration with the protection setting defined according to the conductor’s capacity. Three-phase (TP), phase-to-phase (PP), and phase-to-ground (PG) faults were applied to three locations. Three-phase and single-phase PV systems were modelled based on data from the PVSyst tool considering the location of Surrey in British Columbia and based on the EMTP-RV default parameters, respectively. When comparing scenarios with and without DERs, the results showed a slight reduction in the feeder relay currents for TP and PP faults and significant decreases in the faulty-phase and neutral currents of the feeder relay for PG with impedance faults. These effects caused relay blindness and delays in the operation time of protection elements. These findings potentially offer valuable insights for utilities by supporting decision-making and the planning of EPDS protection systems considering DERs.

The Chile Power Grid is an extremely long and narrow system, and it is surpassing 70% instant power in participation from renewable inverter-based resources regularly during the daytime when photovoltaic power plants are at their zenith. This scenario results in typical values of 30 GVAs of inertia and local Short Circuit Ratios (SCR) below 1.5, in a system where these values were usually above 60 GVAs and 6, respectively. A weaker system is prone to wider, less damped voltage and frequency oscillations that arise from high-frequency modelling of components, which is neglected by Phasor Domain Transient solvers, also known as RMS simulations. Chile ISO is addressing this challenge by modeling, or integrate models, in EMTP every existing facility (OEM and standard), new more friendly Grid Following inverters, Grid Forming inverters, FACTS and HVDC projects.

Initially, the EMTP databases were built manually without little tracking of what was done and ongoing developments of the grid. Currently, the team is working on an automated version of database building. This reduces the time-consuming task on setting up operation points and minimizes human error while increasing the range of results. Additionally, it will be the main tool to migrate online variables from real-time measures like a SCADA system, allowing us to update the operation point of the EMTP database at regular intervals, e.g., every 15 min, so we are able to assess the system's reliability automatically and in real-time. This is what we call the digital twin.

The latest intervention involes discussions to update the National Grid Code regarding inverter-based resources, including requirements to increase transient stability reliability and tests that need to be passed by the EMTP models handed over to the ISO. To this end, we have been working closely with PGSTech to demonstrate the expected responses from standardized Grid Forming models. A by-product of these models will be to test Chile Power Grid to its limits: increasing renewable participation percentage and displacing synchronous conventional generation, thus reducing conventional inertia and SCR.

This paper proposes a time-domain-based protection scheme for radial and loop microgrid systems with inverter-based resources (IBRs), such as solar photovoltaic (PV) systems and type-4 wind turbines. The protection scheme is designed to function during both grid-interconnected and grid-isolated modes. The proposed scheme provides an ultra-high-speed sub-cycle directional element aided with low bandwidth communication between relays. Like directional comparison schemes, relays identify whether faults are in-zone or out-zone. The directional element is based on time-domain superimposed quantities and Park's transformation algorithms. Specifically, the element calculates the superimposed positive-sequence direct component of transient energy during faults. Superimposed voltage and current quantities are calculated using delta filters and decoupled double synchronous reference frame (DDSRF) filters. The proposed filtering method improves the reliability of the superimposed directional element when IBRs are the main source of fault current. The protection scheme is evaluated on a modified IEEE 34-bus distribution system simulated using an electromagnetic transients program (EMTP).

More information will be coming soon.