September 5th

Voltage Sag Source Location Based on Voltage Measurements Only

This paper introduces an alternative method for voltage sag source location based on voltage information only. The source is located considering the sag magnitude at the primary and secondary side of a transformer. A comprehensive review of previously proposed methods based on voltage and current measurements is presented. The performance of the proposed method is compared with the previous ones using PSCAD /EM TDC on a model of a regional network including transmission and sub-transmission levels.

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September 4th

Hybrid UPS Based on Supercapacitor Energy Storage and Adjustable Speed Generator

This paper presents a hybrid on-line UPS system (H-UPS). The system is based on an on-line (double conversion) UPS, consisting of two controlled energy storage systems. The first one is a static energy storage system based on supercapacitor bank. The second energy source is adjustable speed generating system supplying DC link voltage. A control concept of the UPS operation, according short and long failure of the supply utility voltage is developed. The 5 kW H-UPS is designed, built and tested.

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Sony City uses waste heat from sewage treatment plant

When talking about a heat pump, most people will think of a system taking heat at low temperature from the ground, the air, or a water reservoir. However, other configurations are possible. Sony City, the new Sony headquarters in Tokyo, receives heating and cooling from a heat pump connected to a nearby sewage water treatment plant.

By recycling the heat from the sewage plant, the system achieves a Coefficient of Performance (COP) of 5.19, which is exceptionally high. It means that the building receives 5.19 units of energy for each unit of primary energy that is consumed.

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September 3rd

Can LED lighting deliver?

Incandescent lamps are cheap but tend to have short lifetimes. The light emitted by incandescent sources is perceived as particularly pleasant because these hot radiators generate a continuous (or full) emission spectrum. But this very fact means that they waste much of the electrical energy supplied to them. Compact fluorescent lamps (CFLs) are actually the least compact of all the various lamps commercially available at present (Figure 1).

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Harmonic Domain Modelling of Transformer Core Nonlinearities Using the DIgSILENT PowerFactory Software

This paper demonstrates the results of implementation and verification of an already existing algorithm that allows for calculating saturation characteristics of singlephase power transformers. The algorithm was described for the first time in 1993. Now this algorithm has been implemented using the DIgSILENT Programming Language (DPL) as an external script in the harmonic domain calculations of a power system analysis tool PowerFactory [10]. The algorithm is verified by harmonic measurements on a single-phase power transformer.

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September 2nd

Exploitation of renewable power sources for local consumers reservation

Rapid growth of Latvian economy resulted in rapid growth of electricity demand in cities and rural regions. Consumers’ reliability requirements are increasing, but improvement of reliability is directly related to electricity supply reservation possibilities in case of one or more network components failure. This article describes conditions for independent operation of decentralized renewable power supply sources, evaluates its exploitation possibilities and feasibility for local consumers’ reservation.

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Interharmonics are voltages or currents with a frequency that is a non-integral multiple of the fundamental supply frequency, while each harmonic frequency is an integral multiple of the supply frequency.  Interharmonics, always present in the power system, have recently become of more importance since the widespread use of power electronic systems results in an increase of their magnitude.

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August 28th

Power Quality Monitoring System—Voltage Dips, Short Interruptions and Flicker

The Israel Electric corp. deployed a nationwide Power Quality Monitoring System (PQMS). The PQMS monitors the quality of supply of all of its high voltage costumers, as well as a sample of its medium voltage customers. The PQMS monitors both the voltages and the currents. The PQMS has been operational since October 2005. The paper presents preliminary measurement results obtained from the PQMS.

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Climate change: pay now or ask for credit?

If we continue business-as-usual, climate change — according to both the worst prognoses and the more optimistic ones — will confront humanity with serious consequences and a high price tag. However, the cost to society of mitigating climate change by reducing greenhouse gas emissions is also high. So inevitably, the question arises: what we should do? Pay today for mitigating climate change or pay later to deal with its consequences?

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August 22nd

Distributed Generation and Renewable Energy Sources in Poland

Nowadays, in many countries the increase of generating capacity takes place in small units of so-called distributed generation (DG), and among them in hybrid power (generating) systems (HPS). They use primary energy conventional sources as well as renewable energy sources (RES), and in many cases produce electricity and heat (CHP). It is very often that definition of distributed generation is connected with definition of renewable energy sources.

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