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. Ask 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:
- short circuit
- energizing of a transformer
- starting a machine
- overgrown vegetation
Dips generated at customer side coming from in-rush of high-current equipment, like:
- air condition
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
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).
Thank you for reading and stay safe!
Editor's note: This article was originally published in January 2020 and has been updated for comprehensiveness.