P.S. Bodger

Three Phase Transmisssion System Modelling for Harmonic Penetration Studies

Three phase modelling of an a.c. transmission system is presented for harmonic penetration studies. Circuit coupling and impedance unbalance are incorporated in a simulation programme which models an 86 bus equivalent of the New Zealand South Island system. A comparison of measured and simulated results at the current injection busbar is used to select system component models; then results of impedances and sequence voltages are presented for selected busbars when the system is subjected to current unbalance and circuit configuration changes.

Logistic and energy substitution models for electricity forecasting: A comparison using New Zealand consumption data

Abstract The potential of using simple logistic curves for forecasting electricity consumption is investigated with reference to New Zealand sectoral data. In Part A of the paper, fitting of logistic trend curves to historical consumption data uses a Fibonacci search technique to establish optimal asymptotes. The results obtained indicate that current electricity consumptions are approaching saturation. In Part B, a description of an Energy Substitution Model and its assumptions is given. Generally, the Energy Substitution Model is capable of modeling the substitution process among various secondary energy forms, namely, coal, oil, electricity, and gas. The Energy Substitution Model predicts a decline of electricity consumption in New Zealand, a future different from that predicted by the Logistic Model of Part A. This is seen as being due to the unstable penetration rate of natural gas causing significant uncertainties in the results of the former.

Potential impacts from tephra fall to electric power systems: a review and mitigation strategies

Modern society is highly dependent on a reliable electricity supply. During explosive volcanic eruptions, tephra contamination of power networks (systems) can compromise the reliability of supply. Outages can have significant cascading impacts for other critical infrastructure sectors and for society as a whole. This paper summarises known impacts to power systems following tephra falls since 1980. The main impacts are (1) supply outages from insulator flashover caused by tephra contamination, (2) disruption of generation facilities, (3) controlled outages during tephra cleaning, (4) abrasion and corrosion of exposed equipment and (5) line (conductor) breakage due to tephra loading. Of these impacts, insulator flashover is the most common disruption. The review highlights multiple instances of electric power systems exhibiting tolerance to tephra falls, suggesting that failure thresholds exist and should be identified to avoid future unplanned interruptions. To address this need, we have produced a fragility function that quantifies the likelihood of insulator flashover at different thicknesses of tephra. Finally, based on our review of case studies, potential mitigation strategies are summarised. Specifically, avoiding tephra-induced insulator flashover by cleaning key facilities such as generation sites and transmission and distribution substations is of critical importance in maintaining the integrity of an electric power system.

An s-domain model of an HVDC converter

This paper describes a technique to model an HVDC power converter installation in the s-domain. A system equivalent is developed, utilising a frequency-domain model, allowing the closed loop frequency response to be expressed. A rational function approximation of the closed loop frequency response is found by writing an overdetermined equation set, solved directly using singular value decomposition. System poles and zeros in the s-domain are extracted through the solution of the rational function roots. Validation of the model at two power converter operating points is obtained via time-domain simulation and step response techniques for an inverter voltage perturbation.

Controlling harmonic instability of HDVC links connected to weak AC systems

The effectiveness of providing positive damping of harmonic oscillations by either modifying the AC-system filter characteristics or adding to the rectifier control circuitry are examined. Two alternative measures of controlling harmonic instability are investigated: the use of C-type AC filters, and a simple addition of a harmonic damping circuit in the rectifier converter control. The design of a C-type filter is presented and its effectiveness described. Harmonic damping by controls consists of taking the output from a fast-response DC current transducer, passing it through a filter and a gain, and adding the output to the firing-angle order. Both methods result in stable recovery from faults at both rectifier and inverter terminal busbars for a DC system inherently harmonically unstable. >

Reverse as-built transformer design method

A reverse approach to designing as-built transformers is presented in this paper. The physical characteristics and dimensions of the windings and core are the specifications. By manipulating the amount and type of material actually to be used in the construction of the transformer, its performance can be determined. Such an approach is essentially the opposite of the conventional transformer design method. The method is applied to two sample high voltage transformers. The measured performance of the transformers verifies the usefulness of using this reverse design approach.

National Energy Policies and the electricity sector in Malaysia

Since its independence in 1957, Malaysia has gone a long way in developing its economy and infrastructures. As one of the fast growing developing nations, its world renowned infrastructures include the Petronas Twin Tower, SMART tunnel and Bakun hydro dam. A key component that enables this growth is its secure, affordable and reliable electricity sector. Eventhough the initial electricity facilities here was constructed by the British during colonization, Malaysia then continue to nurture its development and reliability through her national policies to ensure that it continues to support her growth and prowess. The main national policy involving the electricity sector in Malaysia is the National Energy Policy. It was formulated in 1979 to ensure efficient, secure and environmentally sustainable supplies of energy including electricity. Later other policies were also formulated to address the arising issues and concerns on the energy sector. Among them are the National Depletion Policy, the Four Fuel Diversification Policy and the Fifth Fuel Policy. This paper reviews and discusses their implementation and various impacts on the electricity sector in Malaysia.

HTS Transformer: Construction Details, Test Results, and Noted Failure Mechanisms

An experimental high temperature superconducting transformer has been designed and built using Bi2223 HTS tape. The transformer is unique in that the magnetic circuit is comprised of air and a silicon steel partial core. Electrical tests were performed on the transformer and it was found to be 98.6% efficient at full load. The transformer failed during a full load endurance run and an investigation was carried out to determine the cause of the failure. The cause was believed to be from operating the HTS windings close to critical conditions. Presentation of the failure details will be of use to other researchers who are building HTS transformers.

Harmonic Resposnse Tests on Voltage Transducers for the New Zealand Power System

This paper presents the results of harmonic response tests carried out on capacitive voltage transformers, as used on the New Zealand 220 kV a.c. network. It is shown that the harmonic response measured using low voltage test equipment is considerably different from that obtained at high voltage. The latter is highly non-linear and is affected by the specific magnetization characteristic of the CVT tested. It is concluded that for field measurement of harmonics at rated voltage, the transformer of a CVT unit should be disconnected and the CVT used as a purely capacitive or resistor-capacitor divider.

A resonant transformer for high voltage testing of generator stators

Abstract A partial core transformer has been designed such that its magnetising reactance has been matched to a generator stator insulation capacitance. The reactive current drawn by the stator insulation is provided by the transformer magnetisation This means that the supply only has to provide the real power losses of the transformer and in practice any mismatch between the magnetisation current and the stator capacitance. A high voltage inductor was designed and used in the testing of a generator at a New Zealand power station. It supplied 115kVAr of reactive power compensation at 23kV. The inductor was turned into a resonant transformer by the addition of a low voltage primary. A laboratory test showed that the required high voltage of 23kV could be obtained from energising the primary at 285V at 60A or at a rating of about 1/7th the load. A further resonant transformer was then designed for a 334kVAr capacitor load to test generator stators at 31.5kV. This transformer was supplied from a nominal 400V supply and gave a gain in kVA of 16. The transformer has a finished weight of approximately 300kg.