Why Do Some Kw/h Meters Reverse Direction with 415V Single Phase Loads?

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SUMMARY

The discussion centers on the behavior of kilowatt-hour (kWh) meters when connected to single-phase 415V or 480V loads in a three-phase installation. It is established that one kWh meter may reverse direction while another operates normally, likely due to incorrect phase connections or the influence of power factor correction capacitors. The participants suggest verifying the connections and polarity to ensure accurate readings and consider the implications of unbalanced loads on meter behavior. The "Meterman's Handbook" is recommended as a key resource for understanding these phenomena.

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  • Understanding of three-phase electrical systems
  • Knowledge of kilowatt-hour (kWh) meters and their operation
  • Familiarity with power factor correction techniques
  • Basic principles of electrical phase connections
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  • Study the "Meterman's Handbook" for in-depth knowledge on meter operation
  • Learn about power factor correction capacitors and their effects on electrical loads
  • Research the principles of unbalanced loads in three-phase systems
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Electrical engineers, electricians, and technicians involved in the installation and maintenance of three-phase electrical systems, particularly those working with kWh meters and load balancing.

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When a single phase 415 / 480 volt load is connected, one Kw/h meter will turn in the right direction whilst the other will turn in the reverse direction. This is the case whether the load is a welder or flood light or inductive heater. Can anybody please explain the reason why?
 
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Are the "Line" and "Load" connections the same, or if a current sensor is used, they are probably reversed. Otherwise you have provided very little info.
 
Hi Windadct, thanks for your reply. The situation is like this. We have a normal 3 phase installation with 3 single phase Kwh meters. All are connected correctly IE line and load tails are correctly oriented at the meter connections. The meters all turn in the correct direction when normal single phase or 3 phase loads are connected. However, when a single phase 415 volt load is connected (supplied by 2 of the 3 meters) one of the meters will stop and turn in reverse until that particular load is switched off at which time, the reversing meter will resume turning in the right direction. I was wondering if the cause might be due to the power factor correcting capacitor across the 2 phases perhaps. NB this also occurs with single phase 480volt loads where power is supplied by a single phase (centre tap) transformer where the output is 2 actives and one neutral.
I hope that this makes it a little clearer.
 
Hello Again - best bet will be to develop a detailed diagram of the connections, and visually confirm each connection and polarity. e.g. not how you think or believe it is connected, but how you know it is. I am thinking there is a connection on the wrong phase, etc.
 
cnf9115 said:
when a single phase 415 volt load is connected (supplied by 2 of the 3 meters) one of the meters will stop and turn in reverse
Does that reversing meter gives a reading which is the same as the reading of the other meter, though negative, over a set period of time?
 
Does that amount to a two wattmeter connection?

Is it possible that with unbalance due to single phase load, one meter legitimately turns backward? And true power is the sum of the two?

Anybody fresh on phasor notation ?

It's not clear to me whether you are describing a system with intermediate voltage taps.
"Meterman's Handbook" is the Bible on this subject - see
http://books.google.com/books?id=ZE...e&q=two wattmeter meterman's handbook&f=false
 
I'm hoping the OP answers my question here, so I can then finish the explanation.
 

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