Negative active power

[kasemu]

Hi,

We recently installed 2 smart meters as sub-meters in the basement of a building. We are monitoring in our platform several parameters such as active power, current, reactive power, voltage, power factor and energy consumption.

The strange thing is that we observe in our dashboard for one of the meters "negative active power" from time to time. This is strange as we do not have in the building any photovoltaics. What could be the reason for getting this negative active power?

Any help would be appreciated.

PS: We also observed for one of our meters a poor power factor (~0,2 sometimes)

 

[freddo]

What equipment is connected to these meters? 0.2 is very poor.

 

[kasemu]

Yes.
We connected 2 (3 phase) smart meters Meazon DinRail Advanced v4 NB wirelessly reports harmonics - https://meazon.com/meazon-products/meters-controllers-connectivity/dinrail-advanced-v4-nb/ for submetering to monitor electricity consumption to one Ferraris meter and a digital meter (those are the utility meters). We are only using 1 phase (even though they are 3 phase meters, but that should not be a problem). You can see the equipment highlighted with the arrows and ovals in the attached picture. Thanks.

 

[James]

Hi,

We recently installed 2 smart meters as sub-meters in the basement of a building. We are monitoring in our platform several parameters such as active power, current, reactive power, voltage, power factor and energy consumption.

The strange thing is that we observe in our dashboard for one of the meters "negative active power" from time to time. This is strange as we do not have in the building any photovoltaics. What could be the reason for getting this negative active power?

Any help would be appreciated.

PS: We also observed for one of our meters a poor power factor (~0,2 sometimes)

Negative active power, could be caused by motor breaking.

if it is a flat, maybe a washing machine? some of the more advanced energy saving models use regenerative breaking when slowing the drum from a fast spin.

if it is a landlord supply, what is attached to it?
again regen braking could play a part, especially if you have a lift in the building.

what timescale are you looking at, is the power factor of 0.2 sustained over a period of minutes or parts of a second?

a graph of the figures in question would help us out here.

 

[kasemu]

Negative active power, could be caused by motor breaking.

if it is a flat, maybe a washing machine? some of the more advanced energy saving models use regenerative breaking when slowing the drum from a fast spin.

if it is a landlord supply, what is attached to it?
again regen braking could play a part, especially if you have a lift in the building.

what timescale are you looking at, is the power factor of 0.2 sustained over a period of minutes or parts of a second?

a graph of the figures in question would help us out here.

Thanks for the feedback.
Yes, it is a flat. Each of the meters corresponds to a flat.

Sorry - I am not sure what do you mean by a landlord supply (I am not native english speaker). There is no lift in the building, but sure a washing machine.

Kindly see the attached pictures.

 

[James]

Just wanting a sanity check from another mentor but in the time being from my memory of active and reactive power.

at no point on the graph do I see a negative reactive power.
the reactive power is what you get billed for and therefore you are not generating any electricity.
however, a negative active power means you have a power factor over 1 (unity)
remember that when you are seeing negative active power, you are also seeing positive reactive power.
this would normally be due to a Highley capacitive load.

@Lucien Nunes
help me out here please, its been 20 years since i did power factor calculations and its a little fuzzy in my head!!

 

[pc1966]

I think "active power" is the billable value in domestic setups, but what the graphs appears to show is just short bursts of -ve energy flow of a couple of hundred watts, so regenerative washing machine, etc, could explain that. They also seem to coincide with high total demand, so a washing machine would make some sense.

A very poor power factor at low loads is not a big surprise, might be dominated by noise filter caps or inefficient switching power supplies, etc. However, it is hard from the posted screenshots to see what is going on. The minimum of around 250 VA reactive is too much to explain by filters to me!

 

[kasemu]

Agree- I understand active power is the power which is actually consumed and thus billable.

 

[Lucien Nunes]

The graphs are odd and do not seem to represent typical domestic appliance usage. They are suggestive of a metering error due to an internal fault or incorrect connection of the meter to the supply. Importantly, the active power rarely exceeds 500W but when it does, the reactive power exceeds 2kVAr. This implies that the heaviest loads have abnormally low power factor <0.25 whereas many heavy domestic loads have relatively high or unity power factor.

I would test the meter using one or more known loads, e.g. connect a 2kW heating appliance when the background load is low and check the meter for a corresponding 2kW active power reading with near unity pf.

 

[kasemu]

The graphs are odd and do not seem to represent typical domestic appliance usage. They are suggestive of a metering error due to an internal fault or incorrect connection of the meter to the supply. Importantly, the active power rarely exceeds 500W but when it does, the reactive power exceeds 2kVAr. This implies that the heaviest loads have abnormally low power factor <0.25 whereas many heavy domestic loads have relatively high or unity power factor.

I would test the meter using one or more known loads, e.g. connect a 2kW heating appliance when the background load is low and check the meter for a corresponding 2kW active power reading with near unity pf.

Hi Lucien,
Thanks for pointing out the inconsistent values in the dashboard. I also ended up suspecting there is something wrong with the installation. After revision, installation has changed as apparently the CT was attached to the wrong phase. Now we observe very good values for power factor and so far there is no negative active power. With regards to the value of active power I can only say that the apartment is quite small and there is only a single person living there. I attached the graphs after the changes on installation (that waws on August 26th around 14:00) - I highligthed with light blue that point in time.