Abstract: A measurement method is disclosed for measuring the resistance component leakage current. The signal waveform of at least one AC cycle is sampled in the resistance component leakage current measurement, and the resistance component leakage current is measured. A zero-cross detecting circuit for detecting a voltage zero-crossing point of the target measurement circuit and outputting a sampling start signal is provided, voltage digital data of the sine wave form whose effective value is 1 and the output signal of the zero-phase current transformer are sampled, and the products of multiplication are averaged by synchronizing the sampled output signal value and the voltage digital data to obtain an active leakage component current of leakage currents.

Abstract: A measurement method is disclosed for measuring the resistance component leakage current included in the leakage current and the resistance value that is an insulation resistance to monitor the insulation state of a distribution system. The signal waveform of at least one AC cycle is sampled in the resistance component leakage current measurement from the leakage current signal and the voltage signal of a current transformer of target measurement circuit, and the resistance component leakage current is measured by dividing the average of integrated value of the instantaneous leakage current values and the instantaneous voltage values by the square root of average of squared instantaneous voltage values.

Abstract: A molten steel, which may optionally contain boron to increase hardenability is poured into ingot molds, bloomed and primary hot worked to a mother tube of intermediate cross-section. Before being cooled down to below about 800.degree. C, the mother tube is reheated to about 930.degree. C, scale from the outside surface thereof is removed, and it is secondary hot worked to a pipe of final dimensions with a reduction, measured in terms of equivalent strain as expressed by the following formula, of not less than .epsilon. = 0.02 for the removal of scale from the inside surface of the pipe. It is then directly quenched to produce a finished seamless steel pipe having far better shape at a higher heat efficiency than in the conventional process. Better toughness is effected when the degree of secondary hot work is not smaller than .epsilon. = 0.20..epsilon. = .sqroot.2/3 .sqroot.(.epsilon..sub.1 - .epsilon..sub.2).sup.2 + (.epsilon..sub.2 - .epsilon..sub.3).sup.2 + (.epsilon..sub.3 - .epsilon..sub.1).sup.