Marc Diaz-Aguiló

Experimental Determination of the ZIP Coefficients for Modern Residential, Commercial, and Industrial Loads

This paper presents the experimental determination of the ZIP coefficients model to represent (static) modern loads under varying voltage conditions. ZIP are the coefficients of a load model comprised of constant impedance Z, constant current I, and constant power P loads. A ZIP coefficient load model is used to represent power consumed by a load as a function of voltage. A series of surveys was performed on typical residential, commercial, and industrial customers in New York City. Household appliances and industrial equipment found in the different locations were tested in the laboratory by varying the voltage from 1.1-p.u. voltage to 0 and back to 1.1 pu in steps of 3 V to obtain the individual P- V, Q- V, and I- V characteristics. Customer load tables were built using seasonal factors and duty cycles to form weighted contributions for each device in every customer class. The loads found in several residential classes were assembled and tested in the lab. It was found that modern appliances behave quite differently than older appliances even from only 10 years back. Models of the different customer classes were validated against actual recordings of load variations under voltage reduction.

Field-Validated Load Model for the Analysis of CVR in Distribution Secondary Networks: Energy Conservation

This paper presents a field-validated load model for the calculation of the energy conservation gains due to conservation voltage reduction (CVR) in highly meshed secondary networks. Several networks in New York City are modeled in detail. A time resolution of one hour is used to compute the energy savings in a year. A total of 8760 power flow runs per year for voltage reductions of 0%, 2.25%, 4%, 6%, and 8% from the normal schedule are computed. An equivalent ZIP model is obtained for the network for active and reactive powers. The most important finding is that voltage reductions of up to 4% can be safely implemented in the majority of the New York City networks, without the need of investments in infrastructure. The networks under analysis show CVR factors between 0.5 and 1 for active power and between 1.2 and 2 for reactive power, leading to the conclusion that the implementation of CVR will provide energy and economic savings for the utility and the customer.

Combined Effect of CVR and DG Penetration in the Voltage Profile of Low-Voltage Secondary Distribution Networks

In this paper, the voltage profile of secondary networks under conservation voltage reduction and distributed-generation (DG) penetration is studied for the first time. Three networks in New York City, modeled in detail, are used as study cases. Interconnection of DG is proposed to eliminate localized low-voltage violations due to a voltage reduction of 4%, 6%, and 8% from the normal schedule. The selection of the type of DG is based on the requirements imposed by the various interconnection standards, most notably IEEE 1547, public service commission, and local utility regulations. It is found that a small percentage of DG penetration would alleviate voltage violations. The study shows that DGs installed in distributed networks improve voltage regulation, allowing utilities to use deeper voltage reductions during critical conditions. It is also shown that the network power factor is reduced when penetration of DG is high and, thus, the line drop compensation needs to be adjusted for the characteristics of the new power demand.

Ladder-Type Soil Model for Dynamic Thermal Rating of Underground Power Cables

This paper presents an optimal RC ladder-type equivalent circuit for the representation of the soil for dynamic thermal rating of underground cable installations. This is useful and necessary for their optimal and accurate real-time operation. The model stems from a nonuniform discretization of the soil into layers. The resistive and capacitive circuit elements are computed from the dimensions and physical parameters of the layers. The model is perfectly compatible with the International Electrotechnical Commission thermal–electric analog circuits for cables. The optimum model order is determined, for fast and slow thermal transients, from a comprehensive parametric study. It is shown that an exponential distribution of the soil layers leads to accurate results with differences of less than 0.5 °C with respect to transient finite-element simulations. An optimal model with only five layers that delivers accurate results for all practical installations and for all time scenarios is presented. The model of this paper is a simple-to-use and accurate tool to design and analyze transient operation of underground cables. It represents a relevant improvement to the available operation and monitoring tools. For illustration purposes, a step-by-step model construction example is given. The model has been validated against numerous dynamic finite-element simulations.

Energy and Economic Impacts of the Application of CVR in Heavily Meshed Secondary Distribution Networks

This paper presents an economic model, based on a field-validated load model, for the assessment of impact of conservation voltage reduction (CVR) implemented continuously during both on-peak and off-peak hours. The model evaluates the impact on individual customers and the utility, taking into account the different billing structures, including service class, monthly rates, and reactive power billing. The model considers as well the impact of the utilitys revenue decoupling mechanism. The hourly operation of three New York City networks of the Consolidated Edison Company of New York (ConEd) for an entire year has been simulated for the purpose of this study. The results presented for voltage reductions between 2.25% and 8% indicate that for individual customers, the larger the original bill, the greater the relative savings in percentage of the original bill. For the utility, the main advantages are the reduction in aggregated energy consumption and peak power demand with corresponding avoided investment and operating costs. The study and results presented are the first of their kind for a meshed power system. In addition, the economic model presented can be used for any utility system where distribution is separated from generation ownership.

Evaluation of DC Links on Dense-Load Urban Distribution Networks

This paper presents an investigation of utilizing dc links to merge heavily meshed urban distribution networks in dense-load areas to increase reliability and expand operational flexibility. It provides a cost-benefit evaluation of utilizing dc-link technology to interconnect three segments of New York City electric distribution networks with complex grid configurations. The outcome of this work highlights the advantages provided by dc links, such as increased reliability and power quality, improved voltage support, and demand relief for feeders at or above capacity limitations. Furthermore, the study shows that dc links may provide a better alternative to transformer installations, feeder upgrades, and/or capacitor additions, and offer the opportunity to postpone large capital investments for system upgrades (such as building a new substation) due to demand increase. The study was carried out with power-flow simulations using field-validated power-flow data.

Introducing Mutual Heating Effects in the Ladder-Type Soil Model for the Dynamic Thermal Rating of Underground Cables

The proper modeling of the transient thermal behavior of mutual heating effects between underground power cables is very important for the rating of transmission and distribution cables. The IEC standards proposed an accurate model based on exponential integrals that it can be difficult to implement in basic electrical software. The model is not consistent with the layered modeling of the cable thermal resistances. In this paper, a simple and easy-to-use alternative model is presented. It consists of injecting the correct current at the right position of the RC circuit representing the soil. The new model can accurately reproduce the full physics of the transient phenomenon and is consistent with the modeling of the cable used in the IEC standards themselves. The new model is tested and validated against numerous finite-element simulations for realistic cable installations.

Benefits of a Nonsynchronous Microgrid on Dense-Load LV Secondary Networks

This paper describes the advantages of using nonsynchronous microgrids in networked systems containing densely concentrated loads. The nonsynchronous bus arrangement, in addition to allowing for the integration of substantially larger distributed generation, completely isolates transient disturbances from and to the network and the microgrid. Significant is the fact that distributed generators installed in the microgrid do not contribute to the short-circuit current that needs to be interrupted by the substation breakers. The behavior of the grid and the microgrid is investigated by comparing: the occurrence of faults, voltage reduction, and losses, in the presence and absence of the microgrid. The benefits of the dc microgrid are made evident with steady-state and transient studies performed on a real distribution network in New York City.