Power Disturbances: Normal (Common) Mode Impulses and Ringing Transients

“Transients”, a term used for simplicity, are “Transient Voltages” or more commonly referred to as “surges” or “spikes”. Transients are momentary changes in voltage or current that occur over a short period of time.

In the context of power supplies, noise is any undesirable voltage impulse which appears at the output. Common-mode noise is present on both the active and neutral wires and is measured with respect to ground. The term "common" refers to the fact that identical noise appears on both the active and neutral wires.

In electronics, ringing is the oscillation of a signal, particularly in the step response to a sudden change in input. Ringing is often undesirable, but not always, as in the case of resonant inductive coupling. (Inductive coupling is electrical coupling in which the influence is that of mutual induction, usually between two coils close together, or wound on a common core. In electrical engineering, two conductors are said to be inductively coupled or magnetically coupled when they are configured such that a change in current through one wire induces a voltage across the ends of the other wire through electromagnetic induction.) It is sometimes described as a “ringing transient”. This type of transients is characterized by swings above and below the normal line voltage.

This interval is usually described as approximately 1/16 of a voltage cycle (about 1/60th of a second) or about 1 millisecond. Voltage transients normally last only about 50 microseconds. Current transients last typically 20 microseconds which is the standard for transients in facilities operating under 600 Volts. 

Key Points

• Transient activity is believed to account for 80% of all electrically-related downtime.

• Effective transient voltage suppression equipment can double or triple the life of electrical and electronic equipment.

• Transient Voltage Surge Suppression is the most immediately apparent, and the most cost-effective means of improving power quality.

You may also refer to the following Power Management video for additional overview information about power.