Switched intelligent grid networking systems

Switched Intelligent Grid Networking Systems (SIGNS) is the result of research, analysis and development of an alternative process for controlling end-user electrical power quality, as well as transients on the incoming electricity supply grid. In the past power quality issues associated with the grid network were usually generated by the connected loads. This has changed in today’s grid system with embedded intermittent renewable energy being included on the energy profile. The research demonstrated that it is possible to control end-user electrical power quality through the addition of battery storage at the user end of the grid and a switching device, forming an intelligent buffer between the electrical grid supply and the load. The function of the device is to select the most appropriate energy source to effectively absorb a proportion of any surges and transients, whilst offering a path for augmented alternative energy

Condition monitoring in New Zealand power transformers

Transpower owns and operates New Zealand’s high voltage electricity grid which includes approximately 725 in service power transformers [1]. Presently, condition monitoring of these units is routinely carried out by oil testing (moisture, acidity and dielectric breakdown) and using dissolved gas analysis (DGA), (every year), and winding resistance, insulation resistance, and bushing power factor tests (every four years). However, since the average age of a power transformer in New Zealand is nearly 40 years [1], it is considered that online condition monitoring of important transformers or transformers that have known issues is carried out to identify any incipient faults. The online condition monitoring in existing power transformers is hoped to minimize the risk of sudden failures and thereby prolong the in service life. It is equally important to decide on what to monitor in a power transformer and how to monitor, and these are also governed by the budgetary constraints. Transpower is in the process of acquiring online condition monitoring units for some of the new large power transformers it plans to purchase and will also retrofit such units to some old transformers as required. This paper presents the condition monitoring techniques currently used by Transpower on power transformers, and the online condition monitoring techniques for new and existing power transformers

Corrosion detection in steel reinforced aluminium conductor cables

Aluminum Conductor Steel Reinforced (ACSR) cables, as part of transmission lines, are used in severe environments in coastal areas and industrial zones for many years. These cables are affected by galvanic corrosion in the interface between the aluminum and steel strands. This paper investigates the existing methods of corrosion detection used in ACSR cables of overhead transmission lines, and estimates the location of corrosion through simulation in a computer program. The paper also analyses two promising methods of corrosion detection, namely “electromagnetic induction” and “time domain reflectometry (TDR)”, and explains in detail their principle of operation and efficiency. The paper then thoroughly investigates the time domain reflectometry techniques by implementing it in a computer program, and the simulation results are discussed

An intelligent approach of achieving demand response by fuzzy logic based domestic load management

Demand response is an important demand-side resource that allows consumers to consume less electricity when the system is under stress. Existing demand response mechanism reduces power consumption by forcefully shutting down the consumers’ loads or punishing the consumers with high consumption prices during high peak hours without considering their comfort level. This paper presents a methodology to design a model for domestic load management based on fuzzy logic techniques where three optimization parameters – comfort, cost and demand response are taken into account. Furthermore a comparative analysis for the power consumption and cost saving performance is carried out to show the benefit of using renewable energy sources along with a fuzzy logic based load controller. Simulation results show that the proposed controller successfully limits the power consumption during the peak hours and concurrently maximizes the savings of energy consumption cost without violating consumers’ comfort level

Estimating transformer parameters for partial discharge location

Partial discharge (PD) location in power transformers using electrical methods require transformer parameters to estimate the PD location. Previous research using a lumped parameter model of a transformer consisting of inductance (L), series capacitance (K) and shunt capacitance (C) has shown an algorithm for PD location. This algorithm does not require L, K and C values for the transformer in their explicit form. Rather, the products LC and LK are required. This paper presents three methods of estimating LC and LK values for a power transformer, which could then be used for PD location. The paper shows that all three methods give identical results confirming that either of these methods could be used for estimating LC and LK values. Results based on impedance measurements from two transformer windings are also presented

Investigation of propagation of partial discharges in power transformers and techniques for locating the discharge

The location of partial discharges in a power transformer can be determined based on the characteristics of the transfer function from the discharge source to the measuring terminal. Previous studies partially validated the technique using computer simulation and practical experiments based on a PD calibrator to represent a discharge signal. 'Real' discharges produced by insulation defect models were used to study how discharges propagate in an 11 kV plain-disc-type transformer winding: A corona model and a 'floating objects in oil' model produced discharge signals with different durations at various locations along the winding. Measurements were taken at the tap of the bushing capacitance through a conventional discharge detector. The signals were filtered, amplified and fed into a digital storage oscilloscope. The frequency spectra of the measured signals showed significant similarities irrespective of the type of discharge source. The characteristic of the transfer functions, i.e. the crests and troughs in the spectra, could be used for locating the source of the discharge. Energising the transformer increased the level of electric noise, which did affect the low frequency end of the spectra, but did not have any impact on the characteristics used for location

Generalized Analysis Framework for SPAMM, HARP and DENSE

A number of MR imaging techniques are used to measure deformation in the heart including SPAtial Modulation of Magnetization (SPAMM), HARmonic Phase (HARP) and Displacement ENcoding using Stimulated Echoes (DENSE). In SPAMM, a line or grid tag pattern is created magnetically in the tissue and displacement is measured from this reference by tracking the tags. In HARP, position information is encoded into the phase of a filtered image and this is used to calculate displacement. In DENSE, displacements are directly encoded into the phase of the image

A measurements-based discharge location algorithm for plain disc winding power transformers

A measurements-based electrical method for locating partial discharges (PD) in transformers is described in the paper. This location method relies on the series resonance frequencies of the signals produced at the transformer terminals by a discharge on the winding. Based on the equivalent circuit of plain disc type winding which consists of series inductance (L), series capacitance (K) and shunt capacitance to earth (C) of the winding, an analytical location algorithm is derived which gives the relationship between the location of a discharge and its terminal response's series resonance frequencies. LKC parameters of the equivalent circuit can be estimated using the series resonance frequencies of a calibration signal measured at the bushing tap during PD calibration. The PD location algorithm was tested on 11 kV transformer winding using signals produced by a discharge simulator and real discharges, and the results confirm its validity with a location accuracy of better than 10% of the winding length. However, blind area where this location algorithm is not applicable does exist near the neutral of the winding and far away from the measuring terminal. Since this location algorithm uses the series resonance frequencies below 500 kHz, it can be implemented with conventional PD measuring circuitry and instruments to detect and locate discharges in power transformers

Experimental investigation into the propagation of partial discharge pulses in transformers

An experimental investigation into the propagation behaviour of partial discharge (PD) pulses in a continuous disc type 6.6kV transformer winding is described in this paper. PD pulses were injected into the winding using a calibrator and the resulting current signals at the line and neutral end terminals measured using wide band current transformers. The location of the troughs (or zeros) in the frequency spectra of the measured signals change in accordance with the position of the injected pulse. The crests (or poles) in the spectra convey information about the resonance frequencies of the winding and are not affected by the position of the injected pulse. The measured spectra are compared with the spectra generated by a simulation model and although differences exist the overall shape and location of the poles and zeros are similar