I have an EV charge point that is a 3-phase 4 wire system that comprises of no neutral (L1/L2/L3/PE). As per the datasheet, the third harmonic content of the line current is rated as approx. 8% (THDi ≤8%).
Question: with no neutral, where does the current arising from the third harmonic content of the line current flow? My best guess would be through the protective conductor – which is not ideal as I’m trying to prevent unwanted tripping of the upstream 30mA RCD device.
thanks for the help.
Greetings all,
So the original question "with no neutral, where does the current arising from the third harmonic content of the line current flow? I’m trying to prevent unwanted tripping of the upstream 30mA RCD device."
The third harmonic content of the line current can create a residual current that may trip the device. However, if your EV charge point is a 3-phase 4-wire system that comprises of no neutral then the third harmonic current will not flow through the protective conductor (PE), but instead through the line conductors. This will create heat in the conductors due to the circulation of the third harmonic. The problem can be overcome with Third Harmonic Filter (THF) that eliminate up to 95% of third harmonics.
The third harmonic content of the line current can create a residual current that may trip the device. However, if your EV charge point is a 3-phase 4-wire system that comprises of no neutral then the third harmonic current will not flow through the protective conductor (PE), but instead through the line conductors. This will create heat in the conductors due to the circulation of the third harmonic. The problem can be overcome with Third Harmonic Filter (THF) that eliminate up to 95% of third harmonics.
The original question is perhaps a little mis-guided, in that it can't be a 4-wire system with no Neutral conductor. It would be a 3-phase 3-wire system by definition? There may be a neutral point in a 3-wire system but it doesn't have to be distributed, only earthed. That would be 3-phase 3-wire U0/U 230/400. The alternative is a 3-phase 3-wire (delta) with one line conductor earthed, which is U0/U 400/400
This is an important differentiation to answer the question you asked.
As Mike says in earlier posts, if it's 3-phase 3-wire 230/400 V, then some of the harmonics may travel back through PE, but some will still cause heating in the transformer.
However, if it's 3-phase 3-wire 400/400 V, then the harmonics pretty much all cause heating in the supply transformer.
Whichever, harmonics in general are bad for transformer efficiency and temperature, but triple-n harmonics cause additional problems for the neutral in 4-wire systems.
In the UK there are limits on harmonic distortion for equipment (EMC product standards) and installations as a whole (ENA EREC G5). Larger installations will require a harmonic study where equipment with power converters are used.
The third harmonic content of the line current can create a residual current that may trip the device. However, if your EV charge point is a 3-phase 4-wire system that comprises of no neutral then the third harmonic current will not flow through the protective conductor (PE), but instead through the line conductors. This will create heat in the conductors due to the circulation of the third harmonic. The problem can be overcome with Third Harmonic Filter (THF) that eliminate up to 95% of third harmonics.
The original question is perhaps a little mis-guided, in that it can't be a 4-wire system with no Neutral conductor. It would be a 3-phase 3-wire system by definition? There may be a neutral point in a 3-wire system but it doesn't have to be distributed, only earthed. That would be 3-phase 3-wire U0/U 230/400. The alternative is a 3-phase 3-wire (delta) with one line conductor earthed, which is U0/U 400/400
This is an important differentiation to answer the question you asked.
As Mike says in earlier posts, if it's 3-phase 3-wire 230/400 V, then some of the harmonics may travel back through PE, but some will still cause heating in the transformer.
However, if it's 3-phase 3-wire 400/400 V, then the harmonics pretty much all cause heating in the supply transformer.
Whichever, harmonics in general are bad for transformer efficiency and temperature, but triple-n harmonics cause additional problems for the neutral in 4-wire systems.
In the UK there are limits on harmonic distortion for equipment (EMC product standards) and installations as a whole (ENA EREC G5). Larger installations will require a harmonic study where equipment with power converters are used.
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