Negative Phase Current

Electronic energy meters can have various additional useful functions for tamper protection, event logging or billing. The screenshot below was taken from our four-quadrant simulation. Other names used in literature are Reversed Phase Current or Reversed Power Flow.

Principle for negative phase current detection

negative-phase-current
negative-phase-current
example

The electronic energy meter monitors constantly the direction of current flowing through each phase. When a specific phase current is detected to be flowing reverse, a event for negative phase current is set for each phase individually.

negative-power-waveform
negative-power-waveform
example

Default logic

When the current direction in one phase is different from current direction of two other phases and all currents are above the current threshold parameter, meter starts a timer. If such condition stays for a time period longer than Reverse power flow time threshold, the meter triggers a reverse power flow condition.

When later all currents start flowing in same direction or at least one of the currents falls below threshold, meters starts a timer again. If same condition stays for a time period longer than Reverse power flow time threshold, the meter detects normal phase sequence condition.
Reverse power flow condition is registered via dedicated events in tamper log book and tamper alarm on display is set.

This function can be disabled.
Disabling the function is necessary when the customer is feeding-back power to the grid, e.g. in case of solar installations.

The logic behind the negative phase current detection can be customized.


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8 Replies to “Negative Phase Current”

  1. Hi, we have a similar issue as Saeed Ullah, on 3 phase meters we find that one or more phases have reverse current at some times. What might be the reason for that? I have even noticed that one meter had a reverse current continously for over than 6 hours. We have checked the connection for all phases and it is was okay. Always the reverse current is small in value.

    1. Thanks for your question, Andro.
      I saw such cases in Middle-East. The reason behind was a poor grounding.
      The utility was using a three-phase connection from the transformer and building-up Neutral from Earth.
      Take a look at the TT-System for better understanding.
      Either the grounding pole wasn’t deep enough or the soil temporary too dry, it was leading to an impedance in neutral.
      As long as the load is balanced in all 3 phases, the current in Neutral is zero. If you have asymmetric load conditions, the current can’t be returned via Neutral in full. Then, the phases with lower load will return the current particular to the grid.
      If you have portable meter test equipment, you can do an easy check. Under the above unbalanced conditions, you can find asymmetric voltages and the phase angles between the voltages are different from 120°.
      See also our article about resistance in the neutral current circuit.

  2. If the load supply switching off then how showing reverse in PQA L1- 0.00 kW , L2 -0.00 kW , L3 o.1 kw if there is no load it should not show reverse flow accordingly

    1. If you switch off the load, your analyser can’t measure current. Power analysers need a certain minimum current to indicate power. So, -0.00 kW can also be +0.00 kW. I assume that the analyser is connected to phase L3 and has a consumption of 100 W. Check the specifications of your instrument for minimum current and switch-on one consumer to meet the minimum currents in all 3 phases.

  3. Dear sir i already checked to use power quality analyzer the flow is showing reverse on two phases L1 L2 and some time in all please can you tell me the reason.
    The connection of meter checked and verified its proper nothing found wrong with connection

    1. It’s hard to say without having more details. Sounds like magic, you are delivering power to the grid. If you have the possibility, check the export registers of the meter, only to avoid that the power quality analyser delivers false information.
      If you have heavy rotating masses like huge electro motors, you have a temporary reversed current until the motor stops rotating after switching off.
      I suggest monitoring all consumers individually to narrow the problem.
      Keep us informed, it’s interesting.

  4. Why the smart meter is showing reverse flow while connected properly and there is no solar panels etc

    1. The meter detects the flow direction of the current. Seems that your meter has inverted connections. That doesn’t harm the functionality, but better inform your energy provider. They have tools to check the flow.

Clou Symbol55

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