In recent years, energy consumption in the commercial sector is increasing and this trend is expected to continue in the future. This paper proposes a comprehensive model to examine potential energy savings and CO2 emission reduction in commercial buildings from architectural and facility improvements. We use the dynamic cooling and heating demand calculation model to estimate thermal energy consumption and the effect of energy saving technologies such as insulating and efficient lighting system. Thermal energy and electric supply system model is also developed for the analysis of electric power and gas requirement by various systems in commercial buildings. Finally CO2 emission reduction by the energy saving technologies is calculated using the estimated energy consumption and the CO2 emission intensity of electricity obtained by a power generation best mix model. We evaluate the economic efficiency and potential CO2 emission reduction by energy saving technologies in the commercial buildings in Tokyo with this approach.
In order to determine the upper limit value of charging currents on overhead transmission lines, the transition of conductor temperature by charging currents, i.e. conductor thermal hysteresis should be evaluated correctly at first. This paper shows that the conductor thermal hysteresis can be evaluated more correctlythan the accepted manner, by means of long-term tracing the conductor temperature in the constant charging currents based on the data by meteorological observatory. In other wards, the conductor thermal htsteresis based on the data by meteorological observatory is evaluated excessively than the actual thermal htsteresis. However accumulated conductor thermal htsteresis based on the meteorologicaldata during past 30 years is a little, and it shows that the value of conductor deterioration is drastically less than the present supposed value. (40% of present supposed value) Accordingly if the long-term evaluation of conductor thermal hysteresis based on the data by meteorological observatory is applied, the upperlimit value of charging currents can be increased sufficiently from point of view of conductor deterioration.
By treating a power system as balanced, it becomes easy to do load flow calculation, transient stability calculation and nominal rating calculation of power system apparatus. So, most of conventional analysis and apparatus design have been done on the premise that the power system is balanced. Recent years, however, the long heavily loaded untransposed transmission lines and large unbalanced loads have led to an increase in the unbalanced components of a power system. Hence, the influence of negative sequence components on different power system apparatus caused by the unbalance is of concern to power utility. The authors investigate a mechanism of unbalance current flow and voltage distribution in a trunk power system by converting unbalance components caused in a transmission line to zero sequence component and negative sequence component. This paper also shows a verification using a model power system.
This work presents the application of generalized switching functions to the modeling of Thyristor Controlled Reactors (TCRs). The development of detailed nonlinear and linear analytical models of TCRs are presented. These models allow for the precise analysis of the TCR transient phenomena for a frequency range of up to some tens of Hz. Validation of the models was done by comparing simulated results obtained with the proposed models with those obtained with a traditional electromagnetic transients program (EMTP). The nonlinear model for the TCR was developed using generalized switching functions. Based on this model, a detailed linear model was derived. This linear model allows for the analysis and precise understanding of the behavior of a TCR under small disturbances both in the time and frequency domain. Interactions between voltage controllers of two SVCs in the subsynchronous frequency range were analyzed for a specific example. It was shown that the analytical linear model is a very precise and powerful tool to evaluate such interactions. The model predicts system instabilities, which could not be predicted at all by traditional models. With the proposed model it is possible to design the controllers of SVCs in an integrated form so that the risk of instabilities can be avoided.
This paper proposes a design method of damping controllers of two facts devices, namely Synchronous Voltage Source when it is used only for reactive shunt compensation, i. e. ‘Advanced Static Var Compensator’ (ASVC) and Static Var compensator (SVC). The applications of ASVC and SVC for damping control are demonstrated and the comparison is made about the damping control capabilities paying attention to the difference in the design philosophy and detailed dynamic performances. An important issue in designing this kind of controllers is to suppress overvoltage that appears under large disturbance. This overvoltage problem sometimes appears in the existing SVC system. To cope with this overvoltage problem, it is proposed to use the control sensitivity function to regulate indirectly the controller output so that the overvoltage problem is treated in the design step. Another important issue is that we point out the zero problem tends to appear inherent in a typical ASVC system making the controller design difficult. To design robust controllers under this condition, we suggest to use the bilinear transform to design a robust H∞-optimal controller. It is shown that the proposed controller provides more robust stability and better performance for additional damping for power system oscillations while suppressing overvoltages. Performance comparison is also made between ASVC and SVC cases.
A new technique to numerically analyze transient phenomena of magnetic nonlinear circuit is presented in this paper. The technique is based on representing the magnetic nonlinear characteristics by relations between the coil currents and differential inductance, and applying the measured multiple characteristics separately by current range and by current history to the differential equations which describe the circuit operation. This paper reports about the measured results of actual behaviors of transient magnetizing currents of no-load transformer which has initially demagnetized core, and also reports the numerical analyzed results of the transient phenomena computed by the technique.
This paper presents the development of a general surge analysis program named VSTL (Virtual Surge Test Lab.) based on the FDTD (finite-difference time-domain) method. The FDTD method divides the space of interest into cubic cells and directly calculates the electric and magnetic fields of the cells by discretizing the Maxwell Equations of electromagnetic fields, where the derivatives with respect to time and space are replaced by a numerical difference. By use of the FDTD method, the developed program is inherently able to take into account the geometrical features of a simulated structure, unlike EMTP-type circuit-based transient programs. Thus, the program is advantageous to solve problems: (i) surge propagation on a three-dimensional skeleton structure, and (ii) surge propagation insideathree-dimensional imperfectly conducting medium such as earth soil. The method of moments (MoM) also numerically solves the Maxwell Equations, and NEC-2 is awell-known program based on MoM. Although MoM efficiently solves the problem (i), it cannot solve the problem (ii) except very simple cases, because it cannot deal with three-dimensional current distribution in the imperfectly conducting medium. On the other hand, FDTD is able to solve both the problems. One weak pointof FDTD is the treatment of a thin wire. Thus, a field correction method to accurately treat the radius of the thin wire is proposed in this paper. Starting from the description of VSTL's solution method, benchmark simulations and comparisons with experimental results are presented in this paper.
This paper describes the experimental results on the arc quenching properties under plastic-plates surrounded condition found in low-voltage circuit breakers. The alternating current used is from 500 to 1, 100A(rms. ) with 60-Hz frequency. The plastic material investigated here are polymethylpentene(-C3H5-), polymethylmethacrylate(-C5H8O2-), polybutyleneterephthalate(C12H14O4-), polycarbonate(-C16H18O3-) and PTFE(-C2F4-). In conjunction with the usual arc current and voltage measurements, two images of spectrum intensity of 511 and 522nm emitted from copper electrode vapor are detected simultaneously by using two band pass-filters. A high speed digital video technique (4, 500 frames per second) is used for analyzing the transient space movement of copper vapor. The arc voltage is strongly influenced by the plastic materials rather than the arc current. Especially, in the case of-C3H5-, the magnitude of arc current was strongly limited by its high arc voltage. On the other hand, in the case of-C2F4-, the arc can't beinterrupted and the arc voltage is the lowest value of all. The arcing period isalso much influenced by the sort of plastic materials (most shortest and longestwere-C3H5-and-C2F4-, respectively), while it shows almost no change with amplitude of arc current. The spectroscopic images of copper vapor obtained by high speed video for transparent plastics of-C5H8O2-and-C16H18O3-showed that the vapor expanding speed of the former is considerably faster than that of the latter. The results indicate strongly that the arc quenching property is affectedby the ablation and blast speed of arc-surrounding plastic materials.
A series Voltage Source Inverter based voltage sag correcting device has been developed and tested in this paper. A control system is designed using the derived mathematical model of the sag correcting device. Voltage tracking capabilities for inner controllers and good performance characteristics for load voltage regulation and reactive power loops are demonstrated for steady state and transient conditions. Also, additional loops for unbalanced sag conditions are designed decomposing the voltages and currents into positive and negative sequence components. Verification of the designed system has done by both simulation and experimental studies.
High temperature superconducting (HTS) wires are expected to be applicable to electric power apparatuses such as transmission cables and transformers operating at liquid nitrogen temperature. Reduction of AC losses at power frequency is one of the most important and critical issues for these AC apparatuses to be feasible. The AC losses of the HTS wires are caused by the transport current and external magnetic fields. The former one, the AC losses from the current power supply to the wire, is usually called as the AC transport current losses. Many works have been done to measure the AC transport current losses of HTS tapes with no external field or with DC external field. Usually, the AC transport current losses of HTS tapes are measured by measuring voltage across the voltage taps attached on the tape. It has been pointed out that the voltage measurement loop should include the magnetic flux over a distance much larger than the tape width to correctly measure the AC losses of the tape. However, this wide voltage loop needs wide space and the linkage flux of the voltage leads loop may include loss components caused by other parts of the tapes than the part between the voltage taps when multiple tapes are assembled. In our previous work, we have proposed a new measurement method to properly measure AC transport current losses of HTS tapes which are subjected to external magnetic field generated by adjacent tapes in a conductor assembled from multiple tapes or generated by a winding of a coil. In our measurement arrangement, the leads from voltage taps on the tape are wound on a cylindrical surface enclosing the tape. This method can save space for voltage leads and avoid spurious loss component caused by the magnetic field of the other tape. The basic principle of our method has been presented and verified. In the paper, the previously presented results on the measurement method using the spiral voltage lead loop are summarized. The additional experimental and numerical data are completed to examine the problems of application to the practical loss measurement. The validity and effectiveness of the spiral lead loop arrangement are systematically demonstrated.
Insulators in coastal substation are polluted due to salty wind blowing from seaside. Hazardous level of pollution deposit causes higher leakage current under damp condition, resulting in system blackout and dam-age to substation due to flashover. To avoid those accidents, the insulators are frequently washed using much amount of pure water. This research developed a computer system for automatic decision washing timing of polluted insulators in substations with easy operation. In the computer system, newly proposed prediction method of pollution in coastal insulators called multi-event matching prediction is used to make accurate decision of timing for insulator washing.
Counterpoise is mainly used to reduce the grounding resistance as a part of a substation grounding and a tower footing. However, surge propagation, frequency-and current-dependent characteristics have not been cleared enough to be applied to the lightning protection design. Measurement data are required to develop a calculation model for the accurate analysis. Thus, the authors measured surge characteristics of the ground grids and straight conductor for low currents with steep wave front and high currents with a few microseconds rise time. This paper presents the measured data, and a grounding resistance model.
We investigated propagation properties of acoustic waves in the frequency range from 10 kHz to 200 kHz using two acoustic emission (AE) sensors to diagnose the insulation performance of GIS. From the experimental results, we estimated that attenuation and velocity of the acoustic waves propagating in SF6, gas and GIS tank wall. Taking these results into consideration, we tried to identify the location of partial discharge (PD) source in the model GIS tank using the difference in the measured time between the PD occurrence and the first wave arrival at two different frequency components of the acoustic signal by utilizing the dispersive property of the velocity of the waves. Consequently, we could identify the location of PD with high accuracy.