title: Permeance based modelling, design and optimization of supercapacitor assisted surge absorber (SCASA)

authors: Silva Thotabaddadurage, Sadeeshvara Udayanga

subjects: Surge protection

abstract: Supercapacitor assisted (SCA) techniques are a unique set of circuit topologies designed to fulfil power conversion and protection tasks by circumventing the energy losses normally associated with RC based circuits. With million times larger capacitance compared to electrolytic type, supercapacitors (SCs) have shown a remarkable surge endurance as discovered by the University of Waikato (UoW) power electronics group. This thesis examines a patented SCA surge protector based on the novel use of SCs' surge withstanding capability, and investigates ways to optimize the present design based on the improvements made to circuit's magnetic components.

The supercapacitor assisted surge absorber (SCASA) developed at UoW incorporates a coupled-inductor wound to a specially selected magnetic material—powdered-iron—that absorbs transients. Despite its high performance, the circuit generates a secondary effect of a negative voltage-peak due to inductive energy release by the core. One aim of our study is to eliminate this undesirable voltage spike using air-gapped ferrite cores. We first identified coupled-inductor transformer action under contrasting voltage conditions. In predicting the SCASA operation under both 50 Hz AC and transient conditions, a permeance based model is used. Our model highlights non-ideal characteristics of the coupled-inductor such as leakage and magnetizing inductances, and provides theoretical predictions based on the permeance coefficients extracted from manufacturer specifications. Inductance measurements are taken over a range of kilohertz frequencies to confirm the accuracy of modelling work.

During initial investigations, we inserted air gaps to ferrite toroids to enhance surge energy storage capability and fringing losses associated with the core. Single- and double-gapped core approach we tested yielded positive test results showing a reduction in negative-surge effect. This encouraged us to develop circuit prototypes using commercially available (Magnetics Inc.) gapped cores of EER type which has an effective permeance comparable to original powdered-iron toroid. This new core configuration indicated improved performance under transient conditions while continually facilitating the passage of AC mains power. In particular, air-gapped cores resulted in optimizing SCASA performance by showing:
•	95% depletion of the negative-surge effect associated with the coupled-inductor
•	~10% reduction of MOV clamping improving the load-side voltage characteristics
•	improved surge endurance as per UL-1449 test standards
•	minimized inductance tolerance and reduced manufacturing cost
To comprehend SCASA surge propagation, we applied a Laplace transform analysis to predict primary and secondary transient currents in the coupled-inductor. Compared to ideal transformer action, we quantify how the primary:secondary current ratio deviates from the turns ratio due to magnetic reluctance of powdered-iron. LTSpice numerical simulations further confirm our analytical predictions.

All experimental procedures presented in this thesis are compliant with IEEE C62.41/IEC 61000-4-5 standards, and generated using a lightning surge simulator (Noiseken LSS-6230) coupled to 230 V, 50 Hz utility mains. Test results generated under these conditions were all within 10% of the predictions showing good consistency with the theorized models.

text: Permeance based modelling, design and optimization of supercapacitor assisted surge absorber (SCASA) Supercapacitor assisted (SCA) techniques are a unique set of circuit topologies designed to fulfil power conversion and protection tasks by circumventing the energy losses normally associated with RC based circuits. With million times larger capacitance compared to electrolytic type, supercapacitors (SCs) have shown a remarkable surge endurance as discovered by the University of Waikato (UoW) power electronics group. This thesis examines a patented SCA surge protector based on the novel use of SCs' surge withstanding capability, and investigates ways to optimize the present design based on the improvements made to circuit's magnetic components.

The supercapacitor assisted surge absorber (SCASA) developed at UoW incorporates a coupled-inductor wound to a specially selected magnetic material—powdered-iron—that absorbs transients. Despite its high performance, the circuit generates a secondary effect of a negative voltage-peak due to inductive energy release by the core. One aim of our study is to eliminate this undesirable voltage spike using air-gapped ferrite cores. We first identified coupled-inductor transformer action under contrasting voltage conditions. In predicting the SCASA operation under both 50 Hz AC and transient conditions, a permeance based model is used. Our model highlights non-ideal characteristics of the coupled-inductor such as leakage and magnetizing inductances, and provides theoretical predictions based on the permeance coefficients extracted from manufacturer specifications. Inductance measurements are taken over a range of kilohertz frequencies to confirm the accuracy of modelling work.

During initial investigations, we inserted air gaps to ferrite toroids to enhance surge energy storage capability and fringing losses associated with the core. Single- and double-gapped core approach we tested yielded positive test results showing a reduction in negative-surge effect. This encouraged us to develop circuit prototypes using commercially available (Magnetics Inc.) gapped cores of EER type which has an effective permeance comparable to original powdered-iron toroid. This new core configuration indicated improved performance under transient conditions while continually facilitating the passage of AC mains power. In particular, air-gapped cores resulted in optimizing SCASA performance by showing:
•	95% depletion of the negative-surge effect associated with the coupled-inductor
•	~10% reduction of MOV clamping improving the load-side voltage characteristics
•	improved surge endurance as per UL-1449 test standards
•	minimized inductance tolerance and reduced manufacturing cost
To comprehend SCASA surge propagation, we applied a Laplace transform analysis to predict primary and secondary transient currents in the coupled-inductor. Compared to ideal transformer action, we quantify how the primary:secondary current ratio deviates from the turns ratio due to magnetic reluctance of powdered-iron. LTSpice numerical simulations further confirm our analytical predictions.

All experimental procedures presented in this thesis are compliant with IEEE C62.41/IEC 61000-4-5 standards, and generated using a lightning surge simulator (Noiseken LSS-6230) coupled to 230 V, 50 Hz utility mains. Test results generated under these conditions were all within 10% of the predictions showing good consistency with the theorized models.

year: 2021

title: Geoscientific reconnaisance of Perry Aggregates quarry, River Road, Horotiu

authors: Nelson, Campbell S.

abstract: At the request of David Jennings, Opus International Consul tan ts Ltd, Hamil ton, we visited the Perry Aggregates quarry on River Road, Horotiu, on the morning of Wednesday 23 April 1997 to comment on the geoscientific context of the quarry. Our specific remarks relate only to observations made at the pit face at the present northwestern extremity of the quarry, which nevertheless are probably appropriate for the quarry as a whole. The quarry area inspected lies on a low terrace about 8 m above present-day river level (about 15 m a.s.l.) immediately adjacent to the Waikato River and covers an area of about 180 x 250 m centred on approximate grid reference S14 029885 (1:50 000 topographic map series NZMS 260).

text: Geoscientific reconnaisance of Perry Aggregates quarry, River Road, Horotiu At the request of David Jennings, Opus International Consul tan ts Ltd, Hamil ton, we visited the Perry Aggregates quarry on River Road, Horotiu, on the morning of Wednesday 23 April 1997 to comment on the geoscientific context of the quarry. Our specific remarks relate only to observations made at the pit face at the present northwestern extremity of the quarry, which nevertheless are probably appropriate for the quarry as a whole. The quarry area inspected lies on a low terrace about 8 m above present-day river level (about 15 m a.s.l.) immediately adjacent to the Waikato River and covers an area of about 180 x 250 m centred on approximate grid reference S14 029885 (1:50 000 topographic map series NZMS 260).

year: 1997

title: The recruitment dynamics of post-settlement juvenile toheroa and the potential applications for aquaculture

authors: van der Lee, Marieka

subjects: Toheroa

abstract: Managing the recovery of threatened species due to anthropogenic disturbance is one of the most challenging problems in ecological monitoring. Researching species ecology is vital to help us improve ecosystem health and subsequently develop better management strategies in the environment. Humanity is entirely reliant on ecosystem services for food security. With the world population expected to reach ten billion by 2050, there is a growing need for more sustainable food sources. With the exploitation of many environmental resources worldwide, aquaculture has been championed as a sustainable option for future seafood production. In New Zealand, the toheroa (Paphies ventricosa) has been identified as a potentially valuable asset to the aquaculture industry and for possible conservation strategies via the implementation of reseeding populations with hatchery-reared spat.

Toheroa faced inadequate resource management and exploitation in the 1900s which ultimately led to the closure of an important recreational, cultural and commercial fishery. However, toheroa populations have failed to recover despite over 40 years of protection. It has been proposed that the continued decline of toheroa populations is not due to a lack of juvenile recruitment. Very little is known about juvenile toheroa recruitment, and there is no available information that could facilitate restoration management or determine the appropriate action to take for monitoring juvenile populations. From both a conservation and an aquaculture perspective, understanding the underlying ecology will be pivotal for future endeavours.

My thesis aimed to investigate the distribution dynamics of post-settlement juvenile toheroa on Ripiro Beach and the potential applications for aquaculture. Population surveys were conducted on Ripiro Beach in February and May to establish a sampling methodology that accurately captures the juvenile population both spatially and temporally. Surveys on vertical substrate stratification significantly affected both density and shell size with increasing sediment depth. Additionally, in contrast to the hypothesis formed on the basis of traditional knowledge that juvenile distribution is limited to the dunes and upper intertidal, spat appeared to have far more varied littoral distributions than previously theorised. The data from these surveys were used to make estimates of the total juvenile population on Ripiro Beach with attention to changes spatially (habitat type), temporally (seasonally), and by size cohorts (mm). My results indicated that toheroa populations are not recruit-limited. Estimates for the total February population ranged between 580 (±190) million and 650 (±200) million. By May, large abundance losses (> 90%) dropped the estimated population to between 30 (±15) million and 37 (±17) million, indicating significant bottleneck mortality during the early growth stages. However, the high abundances of small spat (< 5 mm) indicate that toheroa aquaculture is potentially viable. In aid of future aquaculture applications, I investigated how handling, harvesting, and different transportation methods could impact toheroa health, survival, or performance. This experiment aimed to mimic real-world applications wherein juvenile spat would be harvested and ongrown in hatcheries. To do this, I utilised the burrowing behaviour of juvenile toheroa as a quantitative indicator of stress. I found that if appropriate storage methods were implemented, initial handling and harvesting had a greater impact than actual transportation.

The research in this thesis demonstrated that populations do not appear to be recruit-limited. Furthermore, the findings indicate that aquaculture built on the foundation of wild-harvested juveniles is potentially viable. However, further research is required in order to quantify potential annual recruitment variation both spatially and temporally. Additionally, in order to establish a conservation approach, we must first define the niche requirements of toheroa to determine the obstacle (or obstacles) inhibiting recovery.

text: The recruitment dynamics of post-settlement juvenile toheroa and the potential applications for aquaculture Managing the recovery of threatened species due to anthropogenic disturbance is one of the most challenging problems in ecological monitoring. Researching species ecology is vital to help us improve ecosystem health and subsequently develop better management strategies in the environment. Humanity is entirely reliant on ecosystem services for food security. With the world population expected to reach ten billion by 2050, there is a growing need for more sustainable food sources. With the exploitation of many environmental resources worldwide, aquaculture has been championed as a sustainable option for future seafood production. In New Zealand, the toheroa (Paphies ventricosa) has been identified as a potentially valuable asset to the aquaculture industry and for possible conservation strategies via the implementation of reseeding populations with hatchery-reared spat.

Toheroa faced inadequate resource management and exploitation in the 1900s which ultimately led to the closure of an important recreational, cultural and commercial fishery. However, toheroa populations have failed to recover despite over 40 years of protection. It has been proposed that the continued decline of toheroa populations is not due to a lack of juvenile recruitment. Very little is known about juvenile toheroa recruitment, and there is no available information that could facilitate restoration management or determine the appropriate action to take for monitoring juvenile populations. From both a conservation and an aquaculture perspective, understanding the underlying ecology will be pivotal for future endeavours.

My thesis aimed to investigate the distribution dynamics of post-settlement juvenile toheroa on Ripiro Beach and the potential applications for aquaculture. Population surveys were conducted on Ripiro Beach in February and May to establish a sampling methodology that accurately captures the juvenile population both spatially and temporally. Surveys on vertical substrate stratification significantly affected both density and shell size with increasing sediment depth. Additionally, in contrast to the hypothesis formed on the basis of traditional knowledge that juvenile distribution is limited to the dunes and upper intertidal, spat appeared to have far more varied littoral distributions than previously theorised. The data from these surveys were used to make estimates of the total juvenile population on Ripiro Beach with attention to changes spatially (habitat type), temporally (seasonally), and by size cohorts (mm). My results indicated that toheroa populations are not recruit-limited. Estimates for the total February population ranged between 580 (±190) million and 650 (±200) million. By May, large abundance losses (> 90%) dropped the estimated population to between 30 (±15) million and 37 (±17) million, indicating significant bottleneck mortality during the early growth stages. However, the high abundances of small spat (< 5 mm) indicate that toheroa aquaculture is potentially viable. In aid of future aquaculture applications, I investigated how handling, harvesting, and different transportation methods could impact toheroa health, survival, or performance. This experiment aimed to mimic real-world applications wherein juvenile spat would be harvested and ongrown in hatcheries. To do this, I utilised the burrowing behaviour of juvenile toheroa as a quantitative indicator of stress. I found that if appropriate storage methods were implemented, initial handling and harvesting had a greater impact than actual transportation.

The research in this thesis demonstrated that populations do not appear to be recruit-limited. Furthermore, the findings indicate that aquaculture built on the foundation of wild-harvested juveniles is potentially viable. However, further research is required in order to quantify potential annual recruitment variation both spatially and temporally. Additionally, in order to establish a conservation approach, we must first define the niche requirements of toheroa to determine the obstacle (or obstacles) inhibiting recovery.

year: 2022