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.

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.

A voltage swell is a surge (increase) of voltage above 110 % of the rms magnitude in your power grid. The duration can be between ½ cycle and one minute. (EN 50160)
Note that not all smart meters have a power quality log. As us or your energy meter vendor.

• events below ½ cycle are transients (not recorded)
• events from ½ cycle to 30 cycles are instantaneous swells
• events from 30 cycles to 3 seconds are momentary swells
• events from 3 seconds to one minute are temporary swells
• above one minute it's over-voltage (different event)

The graphics shows a five cycle voltage swell, coming from a large load has been turned OFF.

What is the cause for voltage swells?

• sudden switching OFF of a big consumer (e.g. large electro-motor)
• a change in the ground reference in floating or unearthed phases

Voltage swell event logging

A voltage dip event consists of:

• event counter
• start date/time
• duration
• magnitude
  the maximum measured instantaneous voltage in any phase during voltage swell condition

The magnitude percentage (threshold) and the duration can be configured in the settings.
Energy meters have a typical interval time of 500 ms to retrieve the instantaneous voltage.
When the voltage magnitude is set to 110% rms, the power quality event log will be full too fast. So choose a higher value to get reasonable benefit from the event log.
If you don't mind to become annoyed from alert messages, you can also use an additional push event for voltage swell:)

The event starts when the instantaneous voltage rises above the threshold for the given duration.
The event ends when the voltage drops 2 % below the threshold. (We are operating with a 2% hysteresis).

Sometimes it's also referred to voltage sag (IEEE term). The meaning is the same. This article explains the power quality event logging inside of smart meters. For energy meter testing you can take a look at IEC 62053-11, chapter 7.1.2.

A voltage dip is a voltage drop between 90 % and 1 % of the rms magnitude in your power grid. The duration can be between ½ cycle and one minute. (EN 50160)
Note that not all smart meters have a power quality log. As us or your energy meter vendor.

• events below ½ cycle are transients (not recorded)
• events from ½ cycle to 30 cycles are instantaneous dips
• events from 30 cycles to 3 seconds are momentary dips
• events from 3 seconds to one minute are temporary dips
• above one minute it's under-voltage (different event)

The graphics shows a four cycle voltage dip, coming most likely from a strong electro motor.

What is the cause of voltage dips?

The dips can come from the power grid or from customer appliances. 

Possible power grid disturbances can be:

• overload
• short circuit
• lightening
• energizing of a transformer
• starting a machine
• animals
• overgrown vegetation

Dips generated at customer side coming from in-rush of high-current equipment, like:

• air condition
• motors
• micro-wave

What is the impact of voltage dips?

A end customer will feel flickering or dimming of the light. Electrical installations sensitive to voltage fluctuation might trip due to their internal protection.
Sensitive equipment can be protected with voltage stabilizers.

Voltage dip event logging

A voltage dip event consists of:

• event counter
• start date/time
• duration
• magnitude
  the minimum measured instantaneous voltage in any phase during voltage dip condition

The magnitude percentage (threshold) and the duration can be configured in the settings.
Energy meters have a typical interval time of 500 ms to retrieve the instantaneous voltage.
When the voltage magnitude is set to 90% rms, the power quality event log will be full too fast. So choose a lower value to get reasonable benefit from the event log.
If you don't mind to become annoyed from alert messages, you can also use an additional push event for voltage dip:)

The event starts when the instantaneous voltage drops below the threshold for the given duration.
The event ends when the voltage rises 2 % above the threshold. (We are operating with a 2% hysteresis).