How to measure power supply quality 

By on

Fluke430PA
Fluke 430 Power Analyser
If your are ever called out to troubleshoot something on your electrical system, one of the first things consider is the supply voltage.  You want to ensure you have a good electrical supply before moving on to other possible problem causes. Here are a few things you can quickly measure to get an impression on the quality of supply:

  • Measure the supply voltage, current and frequency - you want to make sure all these are within expected limits.  If any of the readings are more than 10% out of range, this indicates a problem.
  • Check for phase unbalance - for three phase loads (i.e. motors), the system should be balanced; voltage unbalance of greater than 2% or current unbalance of greater than 6% would potentially indicate a problem.  You can expect some unbalance for single phase loads the phase, however if this is excessive it may still indicate problems.
  • Check for transients - these are more difficult to measure and will need some sort of recording instrument.  Look for transients 50 V and more above nominal.  You should measure for the duration in line with the observed symptoms.
  • Check for voltage dip - look for dips 50 V and more below nominal. Again measure for the duration in line with the observed symptoms.
  • Check the harmonics on the system - total harmonic distortion (THD) of greater than 6% could indicate problems.
  • Check the power factor - this should be inline with expectations.

The above should provide a fair indication that everything is ok with the supply.  If the supply looks good, you can then start investigating potential problems with the equipment itself.

In special cases, the power system parameters are more strictly defined (i.e. the CBEMA Information Technology Curve).  Where applicable, you should be looking to ensure the supply parameters are within the specification.

If you have any additional tips or suggestions on how to ensure the power supply is up to scratch, feel free to add them below.



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus



The ac resistance of conductors

In a previous article I looked at the dc resistance of conductors and in this article we turn our attention to ac resistance. If you have not read the...

Closed Doors

"I can live with doubt and uncertainty and not knowing. I think it is much more interesting to live not knowing than to have answers that might be wrong...

How to Size Current Transformers

The correct sizing of current transformers is required to ensure satisfactory operation of measuring instruments and protection relays. Several methods...

IEC 61439 - The Switchgear Standard

The new standard IEC 61439 replaces the old 60439. Compared to the old standard, the new 61439 is a more clearly defined and takes into account the assembly...

Lighting Design - An Introduction

From the earliest times, humans have found ways to create light. Pre-historic peoples used natural materials (moss, grass, etc.) soaked in animal fat and...

IEC 61439 Verification Methods

The (relatively new) switchgear and control gear standard, IEC 61439 'Low-voltage switchgear and controlgear assemblies' has three methods which can be...

IEC Document Designation

Often document control is dictated by project requirements, for example a particular organisation may have an existing numbering system. Existing company...

Harmonised Cable Codes and Colours

Within Europe the European Committee for Electrotechnical Standardization (CENELEC) has standardised the both the designation and colour of cables.   ...

Understanding Circuit Breaker Markings

IEC 60947 is the circuit breaker standard and covers the marking of breakers in detail. Any manufacturer following this standard should comply with the...

Dielectric loss in cables

Dielectrics (insulating materials for example) when subjected to a varying electric field, will have some energy loss.   The varying electric field causes...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note