WHERE DO TRANSIENTS COME FROM?

    Transients are inserted into electrical systems from external and internal sources.  They travel through your electrical system through common wiring.

EXTERNAL SOURCES OF TRANSIENT VOLTAGES

    External sources of transients account for between 5% to 15% of transient activity
SEE ARTICLE

    This type of transient tends to create the most damage in the shortest period of time.  The larger the customer, the lower this percentage will be.  The most common external sources are (in order of volume, from highest to lowest):

Neighboring Businesses:

    Smaller business and homes may share a transformer. Because all of the facilities on the customer side of the transformer are connected by common wiring, transient activity produced by any of the businesses will be seen in neighboring businesses.  An example of where this can cause problems is a small business park where a copy facility or an automotive facility shares a power source with offices or retail customers.  While neighboring businesses account for the highest volume of transient activity from external sources, they are the least damaging and seldom result in dramatic failures.

Lightning:

    The most well-known source of lightning is the most obviously destructive.  Fortunately, lightning does not "travel" well on electrical systems.   What most people don't realize is that even equipment that doesn't fail immediately is damaged severely and remaining life is greatly shortened.

Electrical Utility Sources:

    While utility load switching can account for as much as 5% of all transient activity, some of the effect of this switching is damped in the customer's transformer (which is usually owned by the utility).  It usually isn't a problem unless the customer is very close to a substation, or very far away from the utility and has a large number of switching stations between it and the main utility source.  Another utility source is from short outages.  For example, when a utility lightning arrester "works", it results in a complete loss of power to customers for a very brief period (usually a second or two).  When power is reapplied, the utility "sees" a much larger load than when the power was shut off.  As the system compensates for this increased demand, the demand suddenly drops (starting loads change to running loads) and a large voltage increase is suddenly seen.

Accidents:

    A variety of accidents regularly occur resulting in over voltages. Many electrical lines run overhead and can be damaged. Higher voltage lines can be dropped onto lower voltage lines.  Animals can damage wiring or transformers. Vehicular accidents involving utility lines can cause short area outages.

   For more information on external transient sources go:    

 

INTERNAL SOURCES OF TRANSIENT ACTIVITY

 

    Internal sources of transients account for between 85% to 95% of transient activity and are the least understood.

    They can be generated by many different types of loads and be presented in many different ways.  These sources can be best broken up into three groups:

Inductive Loads:

    Any load that is magnetically driven, such as motors and transformers, produce very large transients upon startup.  These transients can easily exceed 2,000 volts in common electrical systems SEE ARTICLE.  While transformers generally only produce a transient when the device is powered, motors can produce transients every time they start, stop, or even change loads.

    Some motors approaching failure can even produce a continuous stream of transient activity.  Examples of these types of loads are Motors, Welders, Magnetic Lighting Ballasts, Solenoids, Relays, Motor Starters, and devices which limit current flow such as the operation of fuses or circu it breakers.

Power Supplies:

    Common power supplies such as those found in computers, printers, and copiers, can produce very large transients.  Unlike those transients produced by inductive loads, transient activity produced from power supplies is continuous and is a double-edged sword

    Besides producing transient voltage surges, these devices are also susceptible to damage by them.  Motor speed controllers also fall into this category.  This is not limited to variable-speed drives... but also includes "soft-start" motor starters.

Switching Equipment:

    Powering of resistive loads, either on startup or during normal operation, generally do not produce much of a transient effect.  An exception to this generalization is resistive loads that are controlled by electronic switching devices.

    Many temperature controllers, although controlling a resistive load, control this load by quickly turning on and off the device.  This can produce significant transient activity.  In fact, one of the largest instances of transient activity recorded was on a dimming panel controlling a section of a small lecture hall.
SEE ARTICLE.

    Comprehensive surge suppression results in numerous benefits.  While most people immediately think "lightning" when considering whether they need transient voltage surge suppression,  a Florida Utility  indicates that all sources of externally produced transient activity account for less than 15% of total transient activity.  Lightning is only one of those sources.
SEE ARTICLE.

  For more information on internal transient sources go:  

   For more information on common sources of transient surges go: 

Even this amount is referring to a relatively inactive environment (like a home or a smaller business) in an area with a very high incidence of lightning.

Stedi-Power, Inc
5044 B U Bowman Drive #102
Buford, Georgia 30518
PHONE: (678) 546-6780

Last Updated: 07 Jun 2004
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