Northern Plains Power Technologies | Traditional EMT Studies
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Traditional EMT Studies

NPPT has a long history with electromagnetic transient (EMT)simulations, studies and analyses of power systems, power electronics, and power quality, and provides an array of related services for power system operators and project developers. Examples include:

  • Harmonics and circuit resonance studies, including characterization of inverters or other harmonic-producing loads or DG and their system impacts.
  • Transient overvoltage studies, including:
    • Lightning transient study and protection
    • Transient recovery voltage (TRV)
    • Transformer inrush
    • Load rejection overvoltage(LROV)
    • Ground-fault overvoltage(GFOV)
    • Ferroresonance
  • Studies of the performance of weak, high-impedance, or “problem” sections of the system
  • Arrester and grounding transformer/reactor specification and verification
  • Distributed generation interconnection studies, in particular risk-of-islanding studies
  • Studies of specific field events or situations

NPPT provides these services with an exceptional level of skill, professionalism, responsiveness, and creative but practical thinking. If you have a need that does not appear on this list, please contact us.

Example projects


A brief listing of a few relevant recent projects includes the following.

Risk of islanding study for a multi-DER circuit. This particular study involved over seven hundred inverters, rotating generation, energy storage, and VSD loads on a highly branched distribution circuit with sparse loading. Specific duties:
  • Construction of a detailed transient model of the affected circuits
  • Direct collaboration with equipment manufacturers to produce or obtain reliable, validated models of inverters and controllers
  • Parametric sweeps, so that the study is not simply a “snapshot” of a single condition
  • Conclusion: no island persisted for more than 2 s and no mitigation was necessary.
Ground fault overvoltage (GFOV) and load rejection overvoltage (LROV) This study quantified LROV downstream and GFOV upstream from a substation.Specific duties:
  • Construction of a detailed transient model of the affected portion of the system
  • Direct collaboration with equipment manufacturers to produce or obtain reliable, validated models of inverters and controllers
  • Quantification of GFOV and LROV levels as a function of DER status and load level
  • Determination of mitigation need and recommendations for viable mitigation strategies
Harmonics study. This study involved the identification of the source of, and mitigation strategies for, a harmonic distortion issue on a pair of distribution circuits that was leading to tripping of sensitive industrial loads.Specific duties:
  • Construction of a detailed transient model of the circuits suitable for harmonic propagation (i.e., high-frequency model)
  • Construction of harmonic models for the inverters on the circuits
  • Harmonic propagation simulations under different loading and circuit configurations
  • Identification of the source of the problem and a suitable mitigation strategy
Capacitor switching This study involved sizing of a transmission-level capacitor bank; identification of whether a DVC offers sufficient advantages in this application to justify its cost; determining whether independent-pole switching of the fixed capacitors was needed; and determination of whether the new capacitor bank’s switching needed to be coordinated with that of a nearby capacitor bank. Specific duties:
  • Construction of a detailed system and DVC model
  • Study of various capacitor switching scenarios, with and without the DVC
  • Conclusions:
    • Independent-pole switching was needed
    • Coordination was highly desirable, but could be avoided if certain operational procedures were put in place
    • The DVC provided a great deal of benefit but was probably not absolutely necessary if the above recommendations were implemented