In order to protect the utility revenue it’s essential to do regular on-site tests on meter installations. If you are suffering huge losses you should focus on transformer operated meters first.
Those meter installations can be faulty at different points:
- the instrument transformer ratio does not match with the meter
typical mistake is a wrong programmed meter
the fault can be figured out by checking the meter accuracy on the primary side
- the burden of the instrument transformer does not match with the installation
typical mistakes are:
– wiring is too long or wrong cross section
– a backup meter is installed and overburdens the installation
the fault can be figured out by doing a burden measurement
- the instrument transformers have a ratio- or phase displacement error
the fault can be figured out by doing a instrument transformer test
- The meter accuracy is out of range
Old electromechanical meters (ferraris meters) have worn-out uper and lower bearings. If you hear a scratching sound coming from the rotating disc it’s likely possible that the meter is running too slow.
- wrong installation (tamper or mistake of the installer)
This is the part I saw most often. Let’s take a closer look on this.
The screenshots below are taken from our wiring simulator. This simulator is part of the portable test equipment RS350.
In our example we have a three-phase four wire CT-operated meter 2500/5 A, like it’s installed in shopping malls and for small industry. We assume that the consumption is equal to the nominal load.
The wiring looks like this:
What happens when by mistake an instrument transformer for one phase is reversed?
We see that this simple mistake is causing a loss of 66%. Or in terms of money 165,600US$ per month. (20ct/kWh)
In Germany the utilities are inspecting CT installations every 6 months. CT/PT installations are inspected every 3 months.
The real loss reduction does mainly comes mainly from good maintenance of the transformer operated metering installations.
What is your experience with on-site test of energy meters? Leave us a comment below or use our contact form. Thank you for reading.
Editor's note: This article was originally published in October 2019 and has been updated for comprehensiveness.