To solve energy and environmental issue, Variable Renewable Energy (VRE) has been greatly promoted and power flow in transmission system becomes more uncertain due to VRE output fluctuation. N-1 criterion has been applied to determine secure generation dispatch or clearing point in the market so far, however, more strict risk management will be needed in the near future with more VRE integration. In this paper, a new market mechanism is proposed to determine clearing point considering overloading probability in addition to N-1 criterion. Supposing the clearing point can be given as a solution of optimal power flow calculation, congestion management is available with adjusting upper and lower limits of thermal capacity of transmission lines in the formulation. The effectiveness of the proposed method was verified through numerical simulation using modified IEEE New England 39 bus system model with taking into account bidding curves of both suppliers and customers.

Conductive objects insulated from the ground under DC transmission lines are electrified by the flow of ions supplied by corona discharge on the surface of the line conductor. The charge voltage of a human body as a result of the ion flow is an important factor in designing DC transmission lines. An insulated wire is also electrified at the outer surface by the ion flow even when the core conductor of the wire is grounded. There is concern whether an electric shock can occur when a grounded human body touches the outer surface of the insulated wire. In this study, we derived a new equation for predicting the charge voltage for an insulated wire with a grounded core conductor placed under a DC transmission line. The equation was derived from the relationship between electric field and charge voltage on the surface of the insulated wire. The equation allows us to assess the charge voltage of an insulated wire in the steady state by using input parameters such as electric field and ion current density at the ground level. To validate the equation, the charge voltage at the outer surface of the insulated wire was measured using a surface potential electrometer under bipolar-DC test lines energized at ±200kV. The predicted results of the charge voltage agreed well with the measured results, indicating that the newly derived equation is applicable to the prediction of the charge voltage of an insulated wire with a grounded core conductor placed under a DC transmission line.

A charging potential of a floating electrode modeled on vacuum interrupter was measured under unipolar AC voltage application using a surface potential meter. As a result, when a lower voltage was applied to the samples, only an induced potential depending on the electrostatic capacities of the sample and surrounding objects around the sample was measured from the floating electrode. However, in the case of high voltage application, not only induced voltage but also a positive charging potential was observed from the floating electrode which was enough to change the potential of the floating electrode. This is due to the field electron emission from the floating electrode itself.

This paper proposes a novel control method for the shunt capacitor equipped with a series inverter (ISC) in order to use with existing shunt capacitors in parallel. The proposed method controls the equivalent impedance of the ISC in the normal operation range to be equal to the conventional shunt capacitors equipped with a series inductor (LSC). The control increases the impedance to enhance its harmonic compatibility when the harmonic voltage increases beyond the normal operation range. Simulation results verify that the proposed ISC can compensate harmonic current together with the existing 6% LSC. In addition, the ISC can avoid its overcurrent even if it is used with the resonant condition by the existing shunt capacitor. This paper also investigates the circuit design for satisfying both harmonic compensation effect of the 6% LSC and the harmonic compatibility of the 13% LSC. The required dc voltage in the series inverter is 13% of the rated line-to-lime voltage. Thus, the capacity of the series inverter is much smaller than the total compensation capacity of the shunt capacitor.

Objects or human bodies under DC overhead transmission lines may be charged with ion flow due to corona discharge generated on the surface of charged conductors. Ion flow electrification is an important considerations in the construction and operation of DC overhead transmission lines, and the charged voltage due to ion flow is the item that determines the height of DC overhead transmission lines. In order to clarify the electrical environment around 200kV DC overhead transmission lines, ion flow verification tests were conducted using test lines at the Shiobara Testing Yard of CRIEPI. In this paper, the ion flow phenomenon of 200kV DC transmission line are clarified. The measurement results are shown of the current of corona discharge flowing in test lines, the ion flow charging voltage and of the surface ion current density under test lines.