A liquid resistor is an electrical resistor in which the resistive element is a liquid. Fixed-value liquid resistors are typically used where very high power dissipation is required. They are used in the rotor circuits of large slip ring induction motors to control starting current, torque and to limit large electrical fault currents (while other protection systems operate to clear or isolate the fault). They typically have electrodes made of welded steel plate (galvanised to reduce corrosion), suspended by insulated connections in a conductive chemical solution held in a tank - which may be open or enclosed. The tank body is normally solidly grounded or earthed. A typical unit can be rated for continuous use, or for short periods when used for current limitation in protection systems.

Dynamic Braking Resistors (DBRs

When a motor is in an overhauling condition—that is, the load is moving faster than the designated motor speed—the motor acts as a generator and produces electrical energy from mechanical energy. This electrical energy, however, needs somewhere to go, and the most common way of dealing with its release is through dynamic braking.

With dynamic braking, the electrical energy generated during stopping is released as heat through a voltage regulated transistor and resistor. There are actually two versions of a dynamic braking circuit: a “chopper” and a “dynamic brake.” The dynamic brake circuit includes the switching device (an insulated-gate bipolar transistor, or IGBT), the control circuit, and the resistor.

A chopper, on the other hand, only includes the regulatory circuit and switching device, with the resistors being separate components. This allows the resistors to be appropriately sized and mounted remotely, which can be important, since the resistors generate a significant amount of heat. The combination of switching device and control circuit is generally referred to as the “chopper module,” while the resistor is referred to as a “dynamic brake resistor.” Dynamic brakes are typically rated for duty cycles in the 20 percent range, and choppers are often used in heavier-duty applications.

Switch

An electrical switch is any device used to interrupt the flow of electrons in a circuit.