Sags

Sag is a reduction of AC Voltage at a given frequency for the duration of 0.5 cycles to 1 minute’s time.  Sags are usually caused by system faults, and are also often the result of switching loads with heavy start up current.

Sags account for the vast majority of power problems experienced by end users. They can be generated both internally and externally from an end users facility.

Common causes for sags include starting large loads, such as a large Air Conditioning Unit. Similarly, the starting of large motors inside an industrial facility can result in significant voltage sag.  A motor can draw more than 6 times its normal running current while starting.  Creating these large and sudden electrical loads will likely cause a significant voltage drop. 

Remote fault clearing performed by utility equipment is also very common.  Sags coming from the utility have a variety of causes including lightning, animal and human activity, and normal and abnormal utility equipment operation. Sags generated on the transmission or distribution system can travel hundreds of miles thereby affecting thousands of customers during a single event.

While many facilities deal with sags by adding a dedicated circuit for the large start-up loads this is not always effective, practical or economical, especially if the whole facility has a myriad of large start-up loads or the sags are externally generated.  Some of the same techniques used to address interruptions can be utilized to address sags including UPS equipment and motor generators but usually the most cost effective solution includes the use of Power Conditioners otherwise known as Voltage Regulators and system design techniques.  Our line of Power Conditioners and Voltage Regulators can be found here.

While still in its infant stage, some utilities now provide sag analysis of industrial processes as a value-added service to their customers.  A sag analysis can now be performed to determine at what sag levels equipment can properly function.  This data is being collected and analyzed by the equipment manufacturers, so they may improve the ride through characteristics of their equipment.

Undervoltage

Undervoltages are the result of long term problems that create sages.  The term ‘brownout’ has been commonly used to describe this problem, and has now been superseded by the term ‘undervoltage’.

Brownout was deemed ambiguous because it also refers to commercial power delivery during periods of high demand.  Undervoltage creates over heating in motors, and can lead to equipment failures. 

The solution to undervoltages is the same as sags however UPS units will likely require regular battery replacements and prove to be and extremely expensive long term solution.  Our line of Power Conditioners and Voltage Regulators would be more effective and can be found here.