Detection of loss of neutral

A method for detecting a break in connection of a neutral of a three-phase electricity network, the detection method being implemented at least partially in a processing unit of an item of electrical equipment connected to the electricity network, and comprising the steps, repeated regularly, of:

• acquiring, at a time T, a first phase voltage (V1) measured between a first phase of the three-phase electricity network and the neutral, a second phase voltage (V2) measured between a second phase and the neutral, and a third phase voltage (V3) measured between a third phase and the neutral, the first, second and third phase voltages being measured by voltage sensors of the item of electrical equipment;
• evaluating a first quantity representative of a ratio between a maximum phase voltage and a minimum phase voltage from the first, second and third phase voltages;
• and
• if the first quantity is greater than a predetermined threshold:
• evaluating, based on the first, second and third phase voltages, at least a second quantity representative of a current balance between said first, second and third phase voltages;
• and
• detecting a break in connection of the neutral at the time T when the at least one second quantity satisfies a predetermined reference criterion,
• wherein the at least one second quantity comprises a second quantity that is a function of an area of an actual triangle formed by the first, second and third phase voltages in the Fresnel diagram.

A method for detecting a break in connection of a neutral of a three-phase electricity network, the detection method being implemented at least partially in a processing unit of an item of electrical equipment connected to the electricity network, and comprising the steps, repeated regularly, of:

• acquiring, at a time T, a first phase voltage (V1) measured between a first phase of the three-phase electricity network and the neutral, a second phase voltage (V2) measured between a second phase and the neutral, and a third phase voltage (V3) measured between a third phase and the neutral, the first, second and third phase voltages being measured by voltage sensors of the item of electrical equipment;
• evaluating a first quantity representative of a ratio between a maximum phase voltage and a minimum phase voltage from the first, second and third phase voltages;
• and
• if the first quantity is greater than a predetermined threshold:
• evaluating, based on the first, second and third phase voltages, at least a second quantity representative of a current balance between said first, second and third phase voltages;
• and
• detecting a break in connection of the neutral at the time T when the at least one second quantity satisfies a predetermined reference criterion,
• wherein the at least one second quantity comprises second quantities which comprise a first line-to-line voltage U12 representative of a difference between the first phase voltage and the second phase voltage, a second line-to-line voltage U22 representative of a difference between the second phase voltage and the third phase voltage and a third line-to-line voltage U31 representative of a difference between the third phase voltage and the first phase voltage, the reference criterion then being that:
• Φ1−ε2≤U12Φ1+ε2 and
• Φ2−ε2≤U22≤Φ2+ε2 and
• Φ3−ε2≤U31≤Φ3+ε2,
• where ∠1, Φ2 and Φ3 are reference values of the first, second and third line-to-line voltages measured during operation at a reference time T0 preceding the time T and ε2 is a second predetermined measurement uncertainty.

A method for detecting a break in connection of a neutral of a three-phase electricity network, the detection method being implemented at least partially in a processing unit of an item of electrical equipment connected to the electricity network, and comprising the steps, repeated regularly, of:

• acquiring, at a time T, a first phase voltage (V1) measured between a first phase of the three-phase electricity network and the neutral, a second phase voltage (V2) measured between a second phase and the neutral, and a third phase voltage (V3) measured between a third phase and the neutral, the first, second and third phase voltages being measured by voltage sensors of the item of electrical equipment;
• evaluating a first quantity representative of a ratio between a maximum phase voltage and a minimum phase voltage from the first, second and third phase voltages;
• if the first quantity is greater than a predetermined threshold:
• evaluating, based on the first, second and third phase voltages, at least a second quantity representative of a current balance between said first, second and third phase voltages;
• and
• detecting a break in connection of the neutral at the time T when the at least one second quantity satisfies a predetermined reference criterion;
• and
• detecting whether:
• V1eff=Vnom and V2eff=Vnom and V3eff=Vnom,
• where Vnom is a nominal root mean square value of the phase voltage of the electricity network;
• if this condition is met, defining BorneInf and BorneSup as follows:
• BorneInf
• =
• V
• nom
• ⁢
• and
• ⁢
• BorneSup
• =
• 2
• ⁢
• 3
• +
• 1
• 4
• ⁢
• V
• nom
• ,
• wherein said second quantity G2 is equal to:
• G
• ⁢
• 2
• =
• 1
• 3
• ⁢
• (
• V
• 1
• ⁢
• eff
• ⁢
• V
• 2
• ⁢
• eff
• +
• V
• 2
• ⁢
• eff
• ⁢
• V
• 3
• ⁢
• eff
• +
• V
• 3
• ⁢
• eff
• ⁢
• V
• 1
• ⁢
• eff
• )
• ,
• where V1eff, V2eff and V3eff are respectively a root mean square value of the first phase voltage (V1), a root mean square value of the second phase voltage (V2) and a root mean square value of the third phase voltage (V3),
• wherein the predetermined reference criterion being that:
• BorneInf<G2<BorneSup;
• and
• wherein BorneInf is a lower limit and BorneSup is an upper limit, which limit the second quantity G2 when a break in connection of the neutral occurs, and
• wherein the at least one second quantity comprises a second quantity that is a function of a sum of pairwise products of root mean square values of the first, second and third phase voltages.