Title: Validation of KESTREL EMT for Industrial Capacitor Switching Transient Studies
ArXiv ID: 2602.17118
Date: 2026-02-19
Authors: - S. Ramharack (Corresponding Author, sramharack@ieee.org) - ※ 논문에 명시된 다른 저자 정보가 없으므로, 저자 목록은 현재 확인된 저자만 포함합니다.
📝 Abstract
Electromagnetic transient (EMT) simulation is essential for analyzing sub-cycle switching phenomena in industrial power systems; however, commercial EMT platforms present significant cost barriers for smaller utilities, consultancies, and academic institutions, particularly in developing regions. This paper validates KESTREL EMT, a free and open-source electromagnetic transient solver with Python integration, through three progressive case studies involving industrial capacitor switching transients. This work investigates energization, switching resonance and VFD interactions with capacitor banks. The results demonstrate that KESTREL, when supported by appropriate circuit modeling techniques, produces EMT responses consistent with analytical predictions and established IEEE benchmarks. This work establishes a validated and reproducible methodology for conducting industrial EMT studies using freely available, open-source tools.
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The proliferation of power electronic loads in industrial facilities has fundamentally changed power quality challenges. Variable frequency drives (VFDs) and other converterinterfaced loads exhibit complex interactions with grid disturbances that phasor-domain analysis cannot capture [1], [2]. Electromagnetic transient (EMT) simulation is required for analyzing sub-cycle switching transients, nonlinear device behavior, and resonance conditions [3].
Submitted to IEEE CaribCon 2026. Code and data: https://github.com/
shanks847/xxxxx. Correspondence: sramharack@ieee.org Capacitor switching transients represent one of the most common and consequential EMT phenomena. Greenwood [3] established the foundational analytical framework. Hensley et al. [1], [2] documented voltage magnification at low-voltage buses and VFD nuisance tripping due to DC bus overvoltage. Abedini et al. [4] demonstrated EMT modeling for industrial capacitor bank transients validated against IEEE 1036. Shipp et al. [5] documented transformer failures attributable to switching transients.
Commercial EMT platforms (PSCAD/EMTDC, EMTP-RV, ETAP eMT) carry annual licensing costs of $10,000-$50,000 per seat, creating barriers for smaller consultancies, academic institutions in developing regions, and independent researchers [6]. Open-source initiatives including ParaEMT [6] and Pow-erSimulationsDynamics.jl [7] address this gap primarily for transmission-level studies.
KESTREL EMT [8] is a free EMT solver implementing Dommel’s nodal analysis with trapezoidal integration [9], providing standard circuit elements, switching devices, nonlinear elements, and Python code block integration for custom control models at each simulation timestep.
This paper validates KESTREL through three progressive case studies: (1) single capacitor bank energization validated against analytical solutions, (2) voltage magnification through a Dyn transformer, and (3) 6-pulse VFD interaction with a utility capacitor bank during energization.
The system under study represents a typical mediumvoltage industrial facility supplied from a utility substation with switched capacitor banks. Fig. 1 shows the single-line diagram. Key parameters are summarized in Table I.
The 500 MVA short-circuit capacity represents a moderately stiff utility connection. The 10 Mvar capacitor bank is standard for this voltage class. The 500 kvar facility capacitor bank, at approximately 20% of transformer rating, creates the voltage
Given the X/R = 10, the source inductance and resistance are:
The utility capacitor bank capacitance per phase is:
Energization of an initially uncharged capacitor bank from an inductive utility source produces a series RLC transient [3]. The natural oscillation frequency is:
Under worst-case conditions (switch closure at voltage peak, zero initial charge), the theoretical peak transient voltage approaches 2.0 p.u. [3], [10]. The peak inrush current is:
The damping ratio ζ = (R s /2) C 1 /L s = 0.051 confirms a highly underdamped system.
The KESTREL model comprises a three-phase cosine voltage source (13.8 kV line-to-line RMS), series inductance (1.005 mH/phase), series resistance (37.9 mΩ/phase), a timecontrolled switch closing at t = 4.167 ms (Phase A voltage peak), and a wye-connected capacitor bank (139.3 µF/phase). Simulation parameters were set to a 2 µs timestep over 200 ms duration. Table II summarizes the quantitative validation. The oscillation frequency measured via FFT analysis agrees within 1.2% of the analytical prediction. Peak voltage shows 3.9% deviation from the theoretical 2.0 p.u. maximum, attributable to finite damping. Peak inrush current agrees within 8.7%, well within typical engineering tolerances.
The FFT spectrum (Fig. 3) confirms both the 60 Hz fundamental and 420 Hz transient oscillation, closely matching the analytical prediction. The 1.2% frequency error validates correct LC resonance implementation. Peak voltage below 2.0 p.u. is consistent with finite damping (ζ = 0.051), and 8.7% current overshoot reflects sensitivity to the precise switching instant [4].
Voltage magnification occurs when a transient oscillation from utility capacitor switching couples through a distribution transformer and excites resonance at a facility’s LV bus [11], [12]. When the facility has PFC capacitors, the transformer leakage inductance and facility capacitance form a resonant circuit. Maximum magnification (up to 4×) occurs when the tuning ratio f utility /f f acility approaches unity [13].
From Case 1, f utility = 425 Hz. The facility-side resonant frequency is:
The tuning ratio of 0.76 indicates frequencies sufficiently close for significant voltage magnification. However, the Dyn transformer configuration provides inherent attenuation by trapping zero-sequence transient components in the delta primary winding.
Table III summarizes the voltage magnification results. Fig. 4 shows the MV and LV bus voltage waveforms, and Fig. 5 presents the per