This article describes how to model a three-phase equivalent source in SPLITS and HIFREQ, based only on data from a standard phase-to-ground short-circuit study, using a Y-Δ power transformer. This model works very well for all types of faults when the system replaced by the source has similar negative and positive sequence impedances, and performs reasonably well for single-phase-to-ground faults, when these impedances differ. A Microsoft Excel spreadsheet accompanies this article to spare you the need to calculate the transformer impedances by hand. A future “asymmetrical” transformer will make it possible to specify different zero, negative and positive sequence impedances and, indeed, generalized n-port networks in HIFREQ.

Modelling an auto-star-delta or star-star-delta transformer can be a trying experience, especially when you need it to reproduce the transformer behavior in a short-circuit study of which it is a part. This article shows how to use short-circuit study data from ground faults at the high and low voltage busses of such a transformer to derive a suitable equivalent for HIFREQ and SPLITS models, dispensing with the need for transformer test data sheets, which are often incomplete, unavailable or require that you choose from an array of tap settings. A Microsoft Excel spreadsheet accompanies this article to spare you the complex number arithmetic that would otherwise be required to determine the transformer impedances.

Many grounding systems, especially the larger ones, have complex impedances. Due to the non-negligible longitudinal or shunt reactance of long conductors, parts of a system can be out-of-phase with other parts. This can lead to surprising effects, which are nonetheless genuine. We present five anomalous or counterintuitive scientific results in simulations carried out using MultiGround (MALT computation module), MultiGroundZ (MALZ computation module), MultiFields (HIFREQ computation module), and Right-Of-Way (ROW application). The practical examples used to showcase these intriguing results consist of two connected grounding grids, a long counterpoise wire, a buried pipeline, an aerial transmission line, and a pipeline coating. We present the theory along the results for each example, and, finally, we use a simplified circuit model consisting of two complex impedances to derive mathematical conditions for the appearance of some counterintuitive behaviors in grounding systems.

HVDC electrodes discharge stray currents in the soil due to slight bipolar current unbalance during normal conditions. This stray current can cause serious corrosion concerns to nearby metallic structures such as pipelines. This article provides useful guidelines on how to conduct a HVDC corrosion interference analysis using SES Software packages, particularly CorrCAD. It discusses some common concerns users had in the past years such as: which modules to use; what important considerations need to be addressed for an appropriate HVDC corrosion study; what mitigation methods to use and how to effectively model them; etc. Practical examples and solutions are included for demonstration purpose on each specific item.

The complete articles are available in the 2023 User Group Conference Proceedings.

In order for providing a safe, reliable, accurate and cost-effective transmission stations grounding design, ground fault current distribution computations have a key role. Accuracy and cost effectiveness of substation grounding design depends on how accurately ground fault current distribution computations are performed. The effects of accuracy of ground fault current distribution are important regardless of footprint of station. In this paper, the effects of accuracy of ground fault current distribution computation have been shown to be significant when CDEGS MultiField HIFREQ program is used versus FCDIST. In order to show that a case study of 115/14.2 kV substation connected to four 115 kV underground cable circuits modeled in Multifield HIFREQ has been presented which analyzes 3-phase, single line-to-ground and double line-to-ground faults at central substation buses and outside central substation at cable joint boxes. Additionally, another case study has also been briefly described where ground fault current computations were initially conducted by using FCDIST which concluded the substation not meeting safety thresholds and required upgrading substation grounding. When Multifield HIFREQ was used for modeling ground fault current distribution computations to the same case; it resulted in improving accuracy of fault current computations such that the substation grounding was found to be adequate for meeting safety thresholds not only for an existing fault scenario rather for the case of future growth of fault current. This eventually resulted in saving costs of installing unnecessary additional grounding i.e. cost of materials, labor, project management, and time required for installing additional grounding. Moreover, ground fault current distribution computations conducted using Multifield HIFREQ were also found in close agreement with field measurements which increased confidence in using HIFREQ.

Manapōuri Power Station is unique in many aspects; New Zealand’s largest hydro station, New Zealand’s first underground power station, and is located in the World Heritage area of the Fiordland National Park. There is no road access to Manapōuri power station. Therefore, access to the power station is primarily by a 45-minute boat ride on a ferry (either a Meridian owned ferry or a tourist ferry).

Manapōuri has an extensive earthing system, consisting of several discrete but connected earth grids. These include the switchyard, below ground powerhouse, and 11 kV installations around the wider site such as the workshops, visitor centre, jetty, and the staff hostel.

During installation of a new distribution board at the jetty a defective earthing system was identified at the jetty transformer. When inspected it appeared that the designed segregated HV/LV system had been poorly implemented and there was a small standing potential difference between the two earths. This was remedied via combining the HV and LV earths. As an unintended consequence, the standing voltage propagated to the LV earthing system and all metallic items bonded to it, including the jetty itself. Staff noticed small electric shocks when stepping on and off the ferry and when working on the underside of the jetty. An investigation discovered a permanent earth current flowing into the earthing system, leading to a permanent earth grid voltage rise (EGVR).

An electromagnetic transient model of the earthing and transmission systems showed an imbalance in the magnetic coupling between phases and earth wires of the connected transmission lines which leads to an induced earth current returning to the grid step-up transformer neutrals.

In this paper we detail the history of the earthing system designs and testing performed at Manapōuri, the investigation work leading up to this find, and the proposed mitigation methods.

In late 2019 helicopter training was being conducted near two Transpower owned 220 kV single circuit, flat top transmission lines. Personnel standing on the ground received a very painful micro-shock from a steel winch cable connected to the helicopter. The micro-shock was caused by capacitive coupling (also known as electrostatic induction), from the nearby high voltage lines onto the helicopter. A modelling study, using specialist software, CDEGS, was conducted to calculate the capacitive coupling issues. The initial aim of this modelling was to model the helicopter winching scenario experienced by the operators. Additional parameters (such as Helicopter size, helicopter height, separation, line voltage, line configuration and phasing etc) were modelled, to better understand the separation distances required between transmission lines and helicopters, and ensure future micro-shock incidents are minimised as far as practically possible.

In this paper:

1. The concept of electric fields (EF), capacitive coupling, and EF sources are explained.
2. The effects of capacitive coupling are explained.
3. Typical perception and discomfort limits are given in context with New Zealand and Internationally.
4. The capacitively coupled voltages, currents, and energy onto a simulated helicopter are assessed.

The complete articles are available in the 2023 User Group Conference Proceedings.