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

  • Thread starter Thread starter cnf9115
  • Start date Start date
  • Tags Tags
    Phase
Click For Summary

Discussion Overview

The discussion revolves around the behavior of kilowatt-hour (kWh) meters when connected to single-phase 415V loads in a three-phase installation. Participants explore why one meter may turn in reverse while others function normally, considering various electrical configurations and potential causes.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that when a single-phase 415V load is connected, one kWh meter turns in reverse while others operate correctly, regardless of the type of load (welder, flood light, inductive heater).
  • Another participant questions whether the "Line" and "Load" connections are correctly oriented, suggesting that current sensors might be reversed.
  • A participant clarifies that all meters are connected correctly and describes a scenario where one meter reverses when a specific load is applied, speculating that power factor correcting capacitors might be involved.
  • There is a suggestion to create a detailed diagram to confirm connections and polarity, indicating that misconnection might be a factor.
  • One participant asks if the reversing meter's reading is the negative of the other meter's reading over time, implying a relationship between the two meters' measurements.
  • Another participant raises the possibility of a two wattmeter connection and questions if the unbalance from a single-phase load could cause one meter to legitimately turn backward, suggesting that true power might be the sum of the two meters' readings.
  • A request for clarification on phasor notation is made, indicating a need for deeper technical understanding.
  • One participant expresses hope for a response from the original poster to further the explanation.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the cause of the reversing meter, with multiple competing views and hypotheses presented regarding connections, configurations, and the impact of load types.

Contextual Notes

Participants acknowledge the complexity of the electrical setup, including the potential for miswiring and the influence of power factor correction, but do not resolve the underlying issues or assumptions regarding the system's behavior.

cnf9115
Messages
2
Reaction score
0
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?
 
Engineering news on Phys.org
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.
 

Similar threads

Understand AC Transformer Polarity for Three-Phase Connections
  • · Replies 18 ·
Replies
18
Views
5K
Trying to determine true power of household devices
  • · Replies 3 ·
Replies
3
Views
4K
Why does voltage drop as circuits are energized
  • · Replies 17 ·
Replies
17
Views
12K
Graduate Starring Gravity, Co-Starring Magnetism
  • · Replies 7 ·
Replies
7
Views
4K
Mathematica This Week's Finds in Mathematical Physics (Week 228)
  • · Replies 2 ·
Replies
2
Views
3K
Mathematica This Week's Finds in Mathematical Physics (Week 228)
  • · Replies 2 ·
Replies
2
Views
4K