## 1 Introduction  
Currently, electric vehicles (EVs) are regarded as good candidates for decreasing environmental pollution by reducing the use of fossil fuels [1; 2; 3; 4; 5; 6; 7]. Accordingly, there has been rapid progress in the creation of electric vehicles. An EV, also known as an electric vehicle, is a type of transportation which uses electric motors for propulsion in place of a conventional propulsion system, such as an internal combustion engine (ICE). EVs can include electric cars, electric buses, electric trucks, electric trains, electric aircraft, electric scooters and even electric ships. Motion in EVs can be provided by wheels or propellers driven by traction motors, or in the case of railway vehicles, by linear motors. Two types of electric motors are commonly used for vehicle applications: The induction motor (IM), and the permanent magnet synchronous motor (PMSM), and it is generally known that IMs have lower rated torque and efficiency levels compared to PMSMs. In general, PMSMs are more efficient, and for this reason electric vehicles commonly use these types of electric motors. However, because a PMSM uses constant magnetic flux generated by PMs, the flux can only be regulated by means of an armature reaction flux control by a converter. This decreases the machine efficiency, because it significantly increases the winding losses. While PMSMs have employed innovative technologies, it is not easy to increase the electric motor output power any further. As an advanced technology for electric motors, researchers have made progress on the development of high-temperature superconducting rotating machines. Because superconducting wires can handle high-density current flows well, compared to copper wire, it is possible to manufacture a coil capable of generating a very high magnetic field, even with a low number of windings using superconducting wires. Therefore, by applying superconducting coils to electrical machines such as a motor and generator, it is possible to develop electrical machines with high efficiency and high output power levels. Accordingly, many researchers have attempted to apply superconducting motors to EVs, and the applicability of superconducting motors has been largely verified [8; 9; 10; 11; 12; 13; 14; 15]. However, for the practical application of superconducting motors to EVs, the operating stability and reliability must be improved. Superconductors can exhibit superconductivity only under critical environmental conditions, such as those with a critical current, critical temperature and critical magnetic field, and superconductivity is lost when this condition deviates for any reason. If this phenomenon, called quenching, occurs, superconductors gain electrical resistance, which can lead to Joule heating and damage. In particular, such damage can be a serious problem in high-temperature superconducting (HTS) wires, given their relatively slow normal zone propagation velocities. Therefore, in order to apply superconducting coils wound with HTS wiring to electrical machines, it is very important to protect the HTS coils from the quenching phenomenon. The approach known as the no-insulation (NI) winding technique is a viable quench-protection method for HTS coils [16; 17; 18; 19; 20; 21; 22; 23; 24; 25]. The NI winding technique involves the fabrication of coils without insulation materials between the turns. Figure 1 shows the quench-protection mechanism of the NI winding technique. In this figure, \(I_{op}\) is the operating current flowing through the coil. For an HTS coil with turn-to-turn insulation, even if a hot spot occurs due to a partial quench, the current flows continuously through the hot spot, meaning that Joule heat is continuously generated. On the other hand, an NI coil without turn-to-turn insulation has a self-protection mechanism, in that it bypasses the current to the adjacent turns automatically when the HTS coil is partially quenched.