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



Sony Pocket eBook Reader

For the past few years I have reading eBooks on my HTC touch phone. On and off I have debated buying an eReader and recently purchased a Sony PRS-300 ...

How to refer fault levels across a transformer

Over the past year or so I've been involved in on going discussions related to referring fault levels from the secondary of a transformer to the primary...

1,000 kV UHV First for China

At the beginning of the year China put the world's first 1,000 kV UHV transmission system into operation. Transmitting power at over a million volts is...

Induction Motor Calculator

Just added a page to the tools, which will allow you to calculate the synchronous speed, slip and rated torque for an induction motor. Not a particularly...

Cable Trumps

Bored at work and would rather be playing trump card game with you son. The next best thing (or not) maybe the online cable trump card game from AEI Cables...

Voltage Levels – Confused?

I was having a conversation the other day about voltage levels.  While everyone was in agreement that low voltage was 1000 V and less, there was more confusion...

Mobile Phones (Brick to Implant)

The mobile phone was born in 1973. They were the size of a brick and weighed a couple of kg, making them difficult to fit into your pocket. At a few thousand...

Paths of Flight

GE have put together a time-lapse video shown flight take-off and landings at some airports. An interesting view:

Getting Started with Patents

If you have a great idea or invent something the last thing you want is someone to steal the idea. One of the things you can do is protect the intellectual...

Generator Sizing & Operation Limits

When selecting a generator, there are inherent limits on the active and reactive power which can be delivered. Generators are normally sized for a certain...

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