What are Transient Voltages?

This post deals only with the aspects related to energy metering.

Transient voltages are short time surges in the a.c. power supply. They typically last a few milliseconds and the voltage can reach several thousand volt. A transient is by definition shorter than half cycle.

transient voltage
voltage transient

Causes for transients

There are two major groups of transient voltages.

Power system switching transients

Power system switching transients can be separated into transients associated with:

  • major power system switching disturbances, like capacitor bank switching
  • minor local switching activity or load changes in the power distribution system
  • resonating thyristors circuits
  • short circuits
  • arcing faults to the grounding system

Lightning transients

  • direct lightning stroke
  • induction due to an indirect lightning stroke
  • nearby lightning-to-earth discharge

Energy meters can not detect a voltage transient. The event is too short. Most power quality analyzers are designed to capture surges in voltage.
The energy meters are protected to surge effects according to IEC61000-4-5.
For certain regions additional external arresters can be added during meter installation.

2 Replies to “What are Transient Voltages?”

  1. Dear LaoRren, I have started reading some of your blog entries, and I find them very helpful and well written. On the subject of transient voltages, there are also surges that are frequently applied to meters in EMC testing, e.g. 6kV at 50┬Ás. In the case of a poly-phase meter, is the surge voltage typically applied to all three phases, or just one at a time? It is very difficult to find an answer on the web. Knowing the test method helps understanding how transformers and other components on the grid side of the meter have to be isolated.

    1. Wolf, thanks for your comment. The surge immunity test is described in IEC 61000-4-5. A polyphase meter is connected with all phases, but the surge applies only to one phase at time. Take a look at the wiring schematics in figure 10 of the IEC.

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