AC motor drivers (VFD-Variable Frequ-ency Drive) are electronic circuits that allow speed control in the motor by changing the voltage and frequency value at the ends of asynchronous motors. VFDs commonly used in industry; it is called by different names such as speed control device, frequency converter, inverter, inverter, AC drive. AC motor drives are used if the motor used in the system needs to be operated at a speed different from the speed indicated on its label or if the motor will be controlled according to certain variables. Drives are frequently used today, from small household appliances to huge motors used in industry. Drivers who have become an indispensable part of production;
• It protects the motor against overcurrent and voltage peaks.
• Allows soft switching.
• It minimizes the mechanical and electrical strains that may occur during stops and take-offs.
 • Enables energy saving by reducing the speed of the machine in applications where low capacity is required. • Helps to reduce the thermal and mechanical stress on the engine and belts during start-up.

Due to the advantages mentioned above, the use of drivers in the market is increasing day by day and drivers are becoming increasingly important. In order to get the desired performance from the system (motor + driver) and to avoid any problems that may cause malfunctions in the system, incorrect positioning and long wiring practices should be avoided during the installation of the drivers. Otherwise, depending on the capacitive reactance of the cable between the motor and the driver, the geometry, type and length of the cable, voltage rises and oscillations occur at the motor terminal at levels that will damage the motor insulation, as shown in Figure 3. While the driver output shown in red in the figure below is the shape of the voltage at the motor terminals due to the use of the long cable shown in blue. Due to the capacitive effect caused by the nature of the long cable used between the motor and the driver, the voltages that exceed the motor insulation resistance limit prepare the ground for the malfunction of the motor. For this reason, in applications where VFD is used, the length of the motor supply cable used with VFD should be considered as an important criterion and if it exceeds the dangerous limits given as catalog data by the VFD manufacturer, this high voltage effect should be eliminated by using the necessary VFD accessories. Among the accessories typically recommended by VFD manufacturers in this regard; - Socket coil (reactor) at VFD output - DV / dt filter - Sine wave output filter module - LC filter. VFD manufacturer catalogs specify from which cable types and lengths such accessories should be used. The maximum cable lengths that can be used may vary with the internal structure of VFDs (IGBTs, dU / dt trigger rate) and operating parameters (PWM frequency, modulation type, etc.). When the user manuals of the well-known brands and models, which are attached as an example, are examined, it is seen almost frequently that; At low powers (0.75kW and below), after 20 meters of cable lengths and at medium / high powers, after cable lengths such as 50 meters, high voltage oscillations occur at the motor terminals, as mentioned, that can damage the motor insulation. If shielded cables are used, these length values are further reduced. Motor windings are damaged if the voltage level exceeds the limit peak or limit rise time. In addition, the voltage oscillating at the motor terminal, When it exceeds the maximum allowable voltage level, the so called partial discharge or corona occurs. Accordingly, the air around the motor conductors becomes conductive by ionizing. This results in small voltage jumps between two conductors or conductors and ground. Although the cracks that will occur due to small voltage jumps in the winding insulation are microscopic, when these voltage jumps are repeated periodically, the insulation may rupture and cause the motor to burn. What can be done to reduce driver related failures in practice? Although the cracks that will occur due to small voltage jumps in the winding insulation are microscopic, when these voltage jumps are repeated periodically, the insulation may rupture and cause the motor to burn. What can be done to reduce driver related failures in practice? Although the cracks that will occur due to small voltage jumps in the winding insulation are microscopic, when these voltage jumps are repeated periodically, the insulation may rupture and cause the motor to burn. What can be done to reduce driver related failures in practice?