Brownout (electricity)

A brownout is a drop in the magnitude of voltage in an electrical power system. Unintentional brownouts can be caused by excessive electricity demand, severe weather events, or a malfunction or error affecting electrical grid control or monitoring systems. Intentional brownouts are used for load reduction in an emergency, or to prevent a total grid power outage due to high demand. The term brownout comes from the dimming of incandescent lighting when voltage reduces. In some countries, the term brownout refers not to a drop in voltage but to an intentional or unintentional power outage (or blackout). Different types of electrical apparatus will react in different ways to a voltage reduction. Some devices will be severely affected, while others may not be affected at all. The heat output of any resistive device, such as an electric space heater, is equal to the power consumption, which is directly proportional to the square of the applied voltage if the resistance stays constant. Therefore, a significant reduction of heat output will occur with a relatively small reduction in voltage. An incandescent lamp will dim due to lower heat creation in the filament, as well as lower conversion of heat to light. Generally speaking, no damage will occur but functionality will be impaired. Commutated electric motors, such as universal motors, will run at reduced speed or reduced torque. Depending on the motor design, no harm may occur. However, under load, the motor may draw more current due to the reduced back-EMF developed at the lower armature speed. Unless the motor has ample cooling capacity, it may eventually overheat and burn out. An induction motor will draw more current to compensate for the decreased voltage, which may lead to overheating and burnout. If a substantial part of a grid's load is electric motors, reducing voltage may not actually reduce load and can result in damage to customers' equipment. An unregulated DC supply will produce a lower output voltage. The output voltage ripple will decrease in line with the usually reduced load current.