Power System Effect on Breaker/Fuse Operations

Our entire power system has one purpose -- to provide power to loads. There are many ways to categorize loads, one of which is to recognize loads as either dependent or independent.

Dependent loads are those whose current directly follows the voltage. If the voltage decreases, the current decreases, and visa versa. Heaters and incandescent light bulbs are some examples.

Independent loads are those whose current indirectly follows the voltage. If the voltage decreases, the current increases, and visa versa. Transformers and motors are good examples of these types of loads.

If a business is dominated by dependent loads, then an overvoltage condition from the utility produces higher current in the system. The overvoltage may not be noticed, so the breaker trippage seems unexplainable.

If, on the other hand, independent loads dominate, then an undervoltage would create the overcurrent condition. Again, the undervoltage may not be noticed, but the breaker trippage will be.

There are two basic solutions to utility-based voltage problems, each based on a different philosophy. The first philosophy is to protect the facility from these disturbances at the expense of uptime. For example, if an overvoltage occurs, shut down the power. This is done through devices that sense the voltage level, and if they exceed a preset limit, they operate, opening the circuit.

The second philosophy is to protect the facility, or at least sensitive parts of it, at the expense of money. This approach maintains uptime while providing controlled voltage regulation. Voltage Regulators are employed to stabilize the voltage under an assortment of power disturbances.

Voltage regulators, or devices that incorporate voltage regulation, may be used at key distribution sites within the facility such as the service entrance, the main distribution panel, or the computer room panel. Typically, however, these devices are small, portable units used to protect one piece of equipment or one sensitive system.