Positive sequence pilot impedance protection of AC tie line based on MMC-HVDC system

MMC-HVDC has the characteristics of limited amplitude, controlled phase angle and unequal positive and negative sequence impedance. Therefore, the fault characteristics of flexible direct system and AC power grid tie line are quite different from traditional synchronous power supply, which may affect the performance of AC power grid sudden variable protection. Therefore, a new AC protection method based on positive sequence current sudden variable impedance is proposed. The results show that when an in zone fault occurs, the direction of current sudden changes at both ends is the same, and the positive sequence impedance may approach the line impedance; When an out of area fault occurs, the current abrupt variables at both ends have opposite directions and equal sizes, and the positive sequence impedance is much greater than the line impedance. Based on the above characteristics, the criteria of fault start up and fault type are constructed. The simulation results show that the protection method can realize fault discrimination quickly and reliably.

Corrosion Behavior of VM12-SHC Steel in Contact with Solar Salt and Ternary Molten Salt in Accelerated Fluid Conditions

Ternary low melting point mixtures with the addition of LiNO3 and Ca(NO3)2 have been presented as direct system candidates for CSP technologies due to having better physical and chemical properties than those of Solar Salt. In this study, thermal, physical and chemical properties are measured as is the corrosive behavior of stainless alloy VM12 (Cr 12%) when in contact with Solar Salt, 60% NaNO3-40% KNO3 (wt.%) and ternary 46% NaNO3-19% Ca(NO3)2-35% LiNO3 (wt.%). Gravimetric weight change measurements were performed on the test specimens, which were tested under accelerated fluid conditions (0.2 m s−1) at 500 °C for 2000 h. This research confirms the potential of this novel formulation as a thermal storage medium and validates the suitability of ferritic VM12-SHC stainless steel as a structural material for CSP technology with Solar Salt. Meanwhile, the results obtained by scanning electron microscopy and X-ray diffraction indicate a reduction in the protective character of the oxide layer formed on this alloy when the medium contains calcium and lithium components.

Utilization of the Alumni Site of SMA Negeri 1 Kelam Permai

<p>One who has an important role in school development is alumni, but regarding alumni, many schools have not utilized alumni in school contributions, one of which is SMA Negeri 1 Kelam Permai. So far, the alumni data collection at SMA Negeri 1 Kelam Permai has not been carried out in a structured and online manner. In collecting data on alumni, it is still done by recording in written documents which results in data management cannot be done quickly and errors often occur, and it is difficult to update information about alumni. In carrying out this service, the author uses the lecture method and direct system demonstration to participants. The lecture method is used because it is efficient to interact directly with the participants. While the demonstration method is used to teach participants how to use the system. The purpose of this service is to teach participants how to use a website that can help schools quickly and accurately in the process of collecting data and managing alumni data in obtaining information about alumni.</p>

Numerical Study of Hydrocarbon Charge Reduction Methods in HVAC Heat Exchangers

Required refrigerant charge in heat pump systems with propane is analyzed. Two systems are compared: the first a direct heat pump, with fin-and-tube heat exchangers, and the second an indirect system, with plate heat exchangers with an additional brine-to-air heat exchanger. Each system was considered to be able to work reversibly, with 5~kW design cooling capacity in summer and 8~kW design heating capacity in winter. Two separately developed simulation codes were used to calculate the required refrigerant charge and the efficiency of each of the systems. The charge was reduced by the use of microfinned tubes up to 22% in direct system reduced using microfinned tubes compared to the smooth tube. For the indirect system using specially designed plate heat exchangers with the minimum internal volume, their charge was reduced by up to 66% compared to normal plate heat exchangers.

Validation of the Growth Direct System for Microbial Environmental Monitoring and Define Optimal Incubation Conditions

The validation of the Growth Direct system is described for the automated incubation and enumeration of microbial colonies on TSA LP80 and TSA LP80HT media plates. The analytical validation strategy and data generated are given to demonstrate the technology is validatable following the requirements of USP <1223> for microbial recovery. Single and serial temperature incubations were evaluated to optimize microbial detection. Data is provided to demonstrate equivalence to the current compendia test method for environmental monitoring.