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Pterra Conducts Interconnection Assessment for New York Great Lakes Wind Energy Feasibility Study

In December 2022, the New York State Energy Research and Development Authority (NYSERDA) published a report on the Great Lakes Wind (GLW) energy feasibility based on a study conducted by the National Renewable Energy Laboratory (NREL), Advisian Worley Group, Brattle Group and Pterra Consulting.  This study (link to the full report) was intended to complement the options for renewable resources such as land-based wind, solar, hydro and offshore wind that would help meet New York’s renewable energy portfolio and decarbonization goals under the New York State Climate Act.

New York State is bounded by two of the Great Lakes, Lake Erie to the west and Lake Ontario to the north. The potential for developing fixed and floating wind turbines on the lakes using both existing and emerging technologies was the focus of the feasibility study. The study examined myriad issues, including environmental, maritime, economic, and social implications of wind energy areas in these bodies of freshwater and the potential contributions of offshore GLW projects.

Pterra’s role in the study (link to interconnection report) was to conduct a feasibility assessment for potential interconnections of GLW generation with the New York Bulk Power System (NYBPS). To perform the assessment, Pterra developed power flow models to represent the NYBPS in 2030 with an assumed renewable generation buildout.

To provide a measure of interconnection capacity, the capacity headroom definition and calculation method described in recent New York State Public Service Commission orders were selected. Potential points of interconnection (POIs) on the existing NYBPS substations located within 20 miles of either the Lake Erie or Lake Ontario shoreline were initially selected for analysis. These were filtered down to a few representative POIs for more detailed analysis. (Headroom represents the potential capability for GLW to interconnect; however, it also represents the capacity that is available to any other generation resource that may want to interconnect at the same POI. The nature of the NYISO market for any new generation is competitive and GLW is expected to compete with other resource development modeling analyses to utilize the available headroom.)

Lake Erie abuts the New York counties of Erie in the north and Chautauqua in the south. For Lake Erie GLW, the available POIs showed combined capacity headroom of 270 megawatts (MW) without transmission upgrades. Applying a set of simple transmission upgrades costing some $68.8 million can increase the Lake Erie total headroom capacity by 60 MW to 330 MW.

New York State has a longer shoreline along Lake Ontario compared to Lake Erie. Several New York State counties border the lake, including Niagara, Orleans, Monroe, Wayne, Cayuga, Oswego and Jefferson. For Lake Ontario GLW, several POIs in Monroe and Oswego counties showed solo headroom capacity in the range of 850 to 1100 MW without the need for transmission upgrades. At most, there is a total headroom capacity of up to 1140 MW for the Lake Ontario POIs. The total headroom capacity may be increased by 140 MW by implementing simple upgrades costing some $236.6m. In Jefferson County, the studied POIs showed no solo headroom capacity. Simple transmission upgrades costing at least $164.5 million may open about 50 MW of headroom capacity.

Pterra’s interconnection assessment found that there is some headroom capacity on the NYBPS for which GLW can compete for the delivery of energy to the grid. In order to access the POIs with headroom, other reliability issues relating to transient voltage, stability, short circuit, deliverability, transfer capability and higher-level contingencies would also need to be considered.

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Auxiliary Metering for BESS+PV Installations: Are They Necessary? By Pterra Consulting

For hybrid solar photovoltaic and battery energy storage systems (PV+BESS), a seemingly innocuous question during interconnection is: “Are two meters that much better than one meter?” This is a question that relates to both technical accuracy and economics. The economics is fairly easy to understand, adding a second meter can be expensive and may spell the difference between a viable PV+BESS project and a failed one. The accuracy aspect is not so simple and requires some explanation.

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Initial Power Grid Study to Achieve New York’s Renewable Energy Targets

Pterra is supporting New York State’s actions to meet its renewable energy targets. In the recent Power Grid Study (co-authored by Pterra’s Ric Austria and Ketut Dartawan) Pterra helped review bulk transmission, local transmission (or sub-transmission) and distribution needs and solutions, as well as the necessary infrastructure for the offshore wind build-out, and provided recommendations for improving methodologies and processes for transmission planning.

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System Impact Study for a Proposed Transmission Interconnection Project in New York

By R. Tapia, M. Gutierrez and M. Infantado


Independent System Operators (ISO) constantly face the challenge of assessing the impact of facility additions to the power grid. They normally require a system impact study for any proposed interconnection of a large generating plant or transmission project. The purpose of this analytical study is to determine the potential adverse impacts of the interconnection of transmission facilities to a power system and whether it would cause any of the following:

  • Post-contingency thermal overloading on transmission lines and transformers,
  • Voltage criteria violations on substations,
  • Negative impact on the dynamic response of power system facilities,
  • Degradation on the transfer limit of transmission interfaces,
  • Increase in substation short circuit current that could possibly exceed the fault duty of existing circuit breakers.

The system impact study determines the impact of the proposed project by comparing simulation results of the case with the project in service against the case without the project. If adverse impacts were to be found, appropriate solutions to mitigate the violations would be required, except for the extreme contingency assessment which is performed for information purposes on issues such as avoidance of widespread load interruptions, uncontrolled cascading, and system blackouts among others.

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Development of Dynamic Models for Submission to Regional System Operator

Client: Pacificorp

Pterra was contracted by PacifiCorp to compile, document and check system dynamic model data for submission to the Western Electricity Coordinating Council (“WECC”). In coordination with PacifiCorp Transmission Planning, Pterra reviewed existing data provided to PacifiCorp by generator owners and compiled appropriate synchronous generator model data. Synchronous generator, exciter, governor/turbine and power system stabilizer model data were developed consistent with NERC MOD-012 requirements.

PacifiCorp compiled dynamics data for the western control area power plants. For the generators owned by PacifiCorp, the data comprised of generator test reports from various engineering test firms. Model parameters for each generation unit were taken from the corresponding test reports. Data were adjusted as required for tuning or software compatibility purposes. For other power plants, the data available ranged from fairly complete data to little more than nameplate values.

Pterra conducted several tests of the models for each generating unit. These tests included comparison of typical range of values, step response tests on the excitation system and governor/turbine models, and disturbance response tests on a sample system. Pterra adjusted the model parameters to represent field conditions and to improve the numerical performance. A total 59 generating units were evaluated.

Pacificorp submitted to the models to the WECC.

Figure: Block diagram for an IEEE excitation system.

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Load Rejection Overvoltage Issues on Distributed Generation Projects

Client: Confidential

Increased penetration of solar photovoltaic (“PV”) generation in distribution circuits raises a potential issue with load rejection overvoltages. The condition occurs with the lightly loaded feeders. If the feeder load is much smaller than the total isolated generation then the load rejection overvoltage could pose a threat of damage to equipment insulation and surge arresters. In addition, the inverter characteristics used for PV installations present their own unique impacts. Different inverter designs respond differently to the phenomenon. Pterra used a time domain simulation tool to quantify the impact of load rejection on several different circuit configurations and several different types of inverters.

The study system is shown in Figure 1.

Figure 1.

The maximum magnitude of transient overvoltage (“TOV”) could reach 240% of the nominal voltage if the generation is 6 times the load on the islanded feeder. For a criterion setting, 120% of minimum load as the limit for PV penetration is conservative. In some utilities, this criterion is set at 150%. However, when in doubt, it is always preferable to run a simulation using the feeder and load electrical characteristics and the manufacturer model for their inverters.

Mitigation options to allow for increased PV penetration include implementation of a direct transfer-trip scheme, usually an expensive and complicated choice.

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Distributed Generation Impacts on the Island of Lanai in Hawaii

Client: National Renewable Energy Laboratory

National Renewable Energy Laboratory (“NREL”) contracted Pterra to conduct an island-wide system-level integration study to determine the impact of additional photovoltaic (“PV”) systems of varying size and locations being installed on Lanai over the next few years.

Pterra conducted several technical studies including power flow, short circuit, protection coordination, angular and voltage stability, frequency regulation, system operation and limitations, harmonics and power quality, transient overvoltage and ground-fault overvoltage. Each of these studies provided a unique look at the levels of PV penetration that may lead to undesirable reliability impacts and costly system reinforcements.

The key finding of the study is the critical impact on frequency response of new PV generation. The study system is shown in Figure 1. The existing electrical supply comes from: L7, L8 and CHP – conventional diesel units, and LSRPV – PV units. The existing PV includes a battery to provide support during low-frequency conditions. The generators provide power to a peak load of about 4,200 kilo-watts, with a day-time minimum of 2,300 kilo-watts. An additional 800 kilo-watts of new PV was considered for the study.

Figure 1. Existing Generator Locations

With the new PV in service, the option to operate with fewer diesel units is available. However, this dispatch mode results in a reduced spinning reserve. The study simulations show that the system voltages collapse after applying a contingency. The voltage plot is shown in Figure 2.

The result of the analysis is an operating requirement to continue to operate an extra diesel unit for spinning reserve purposes. This had an immediate consequence on the economic benefit of the new PV, as the non-power related costs of the extra diesel unit offset the savings from use of solar energy.

The other technical tests did not identify any other constraints on the 800 kilo-watts of new PV.

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