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


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.


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.

Thank you for taking a look.
You can leave a comment below.

Editor's note: This article was originally published in March 2020 and has been updated for comprehensiveness.

12 Replies to “Negative Phase Current”
  1. Prezado senhor.
    Preciso de instalar um grupo gerador para alimentar um pequeno condomínio de 10 casas. A questão é que cada casa vai ter um medidor pré-pago independente, porém com o gerador deve ser possível alimentar as cargas das casas sem passar pelos medidores. Uma das ideias é fazer uma ligação de tal forma que a tensão do gerador vai directo aos bornes de saídas dos medidores. A questão é: enquanto o gerador estiver em funcionamento, os bornes de saída do medidor estarão permanentemente em tensão do gerador, pese embora não haverá circulação de corrente no medidor por conta do ATS que estará aberto do lado do transformador. Qual é a inconveniência de ter tensão (reversa) nos bornes do medidor?

    1. Caro Abudo Assane,
      Obrigado pela sua pergunta. Se você ligar o gerador e alimentar a energia nos terminais de saída, pode encontrar alguns problemas. A carga desequilibrada no lado secundário do transformador pode causar corrente reversa em alguns medidores, levando à detecção de violação e cobranças adicionais. Também pode resultar em perda significativa de energia do gerador. Para evitar essas inconveniências e garantir a segurança, é recomendável instalar contatores que desconectem os terminais de saída do medidor quando o gerador estiver em uso. É fundamental contar com um eletricista qualificado para lidar com essa instalação.

    1. You can see a "raised hand" symbol on the display, together with an arrow, showing to the left. Your power company can read out more details from the internal log-file.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

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