Dynamic Braking Resistors are used with AC VFD’s to produce a braking torque in the motor during overhauling conditions. The dynamic braking resistor is connected across the DC bus and will see voltages as high as 800 volts. The drive manufacturer normally determines the power rating (watts) needed to prevent overheating during braking duty. The peak braking current is determined by the specified resistance value. Each drive manufacturer specifies a resistance range with a minimum to prevent overcurrent and damage to the drive and a maximum value to give adequate lower dissipation capability. A three-phase variable frequency drive (VFD) consists of three basic components – rectifier, DC line, and inverter – and a control system to manage these three components as illustrated. The rectifier converts the three-phase 60Hz AC input to a DC signal. Depending on the system, an inductor, a capacitor, or combination of these components smooths the DC signal (reduces voltage ripple) in the DC link part of the VFD. The inverter circuit converts the DC signal into a variable frequency AC voltage to control the speed of the induction motor. During braking, the VFD ramps the frequency to zero. The rotational energy of the motor and load are driven back through the inverter to the DC bus and the rotational energy is dissipated through the resistor.
Wire-wound Open Type Resistors
• Suitable for rugged applications.
• Two terminal extensions are fixed on both ends of a ceramic tube
• High temperature resistant, fireproof coating
Type 1 Brake resistors
• NEMA 1 Enclosure Design with Powder-coated, NEMA 3R and Stainless Steel options
• Thermal overloads
• Two Point terminal block
• Convenient Conduit Knockouts