Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coils

Abstract

The turn-to-turn contact resistance (characteristic resistance) is a very important factor to a no-insulation (NI) (RE)Ba2Cu3Oy (REBCO) pancake coil. It characterizes the stability and charging delay of NI REBCO pancake coils. However, the ordinary sudden-discharging method cannot measure the turn-to-turn contact resistance under different conditions, such as an operating current, a temperature, and an external magnetic field. Although the turn-to-turn contact condition is strongly affected by the pressure inside of the NI REBCO coils, the feature of the contact resistance must be clarified to estimate the stability of NI REBCO coils.In this paper, we have proposed a new method to measure the turn-to-turn contact resistance applying AC current. The theory and the measurement results are also shown. The measured turn-to-turn contact resistance is reasonable, compared with that measured by the ordinary sudden-discharging method. In near future, we will measure the turn-to-turn contact resistance under different conditions by means of the proposed method.Index Terms-No-insulation winding technique, REBCO pancake coil, turn-to-turn contact resistance measurement.

Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coil: External Field Dependence

“…On this method, applying a low-frequency-AC current to an NI pancake coil, the AC impedance, which corresponds to the contact resistance, is measured. The validity of the proposed method was confirmed [10].…”

“…We have previously proposed a low-frequency-AC current method to measure the turn-to-turn contact resistance of NI REBCO pancake coil [10], [11]. In the proposed LFAC method, by applying a low-frequency AC current to an NI REBCO pancake coil or superimposing on a DC transport current, the coil impedance is measured.…”

“…In the proposed LFAC method, by applying a low-frequency AC current to an NI REBCO pancake coil or superimposing on a DC transport current, the coil impedance is measured. When the following condition is held, the coil impedance Z is the turn-to-turn contact resistance Rct (Z = Rct) [10]:…”

“…In our previous paper [10], a low-frequency-AC current (LFAC) method was proposed to measure the contact resistance. On this method, applying a low-frequency-AC current to an NI pancake coil, the AC impedance, which corresponds to the contact resistance, is measured.…”

Turn-to-Turn Contact Resistance Measurement of No-Insulation REBCO Pancake Coil at DC Current Operation

“…That is, since an electromagnetic force working for NI pancake coil varies with the change of transport current and magnetic field, the contact resistance would also vary due to the change of the contact condition between REBCO tapes or metals. Therefore, we have previously proposed a low-frequency-AC-current (LFAC) contact resistance measurement method [7]. The proposed LFAC method can measure the turn-toturn contact resistance of REBCO NI pancake coils under various conditions.…”