Earth leakage protections are challenged, due to the continuing growth of complexity in electrical facilities and new regulations.
In this article a guest technical expert explains the new RGU-2 device, ready for these challenges, that increases productivity and saves in maintenance of facilities.
The majority of electrical installations nowadays increasingly include loads that incorporate electronics.
Loads with electronics influence the electrical installation in various ways:
- They generate harmonic distortion in the current they consume.
- They generate current leakages at the mains frequency, 50 Hz, and at higher frequencies under normal operating conditions.
- As soon as they are connected to the electrical power supply they generate a leakage current point.
- During an insulation fault, the leakage current might not be sinusoidal, but rather pulsating, for example.
Examples of units incorporating electronics:
Computers, low consumption light bulbs, ceramic hobs, washing machines, dishwashers, microwaves, mobile phone chargers, air conditioning units, electric vehicle chargers, dryers, machine tools, etc.
Under normal conditions all these receivers generate leakage current in the electrical installation which makes the earth leakage protection more prone to trip.
3.- RGU-2 Earth leakage
The new RGU-2 unit provides the following technical details that help us maintain a protected installation and at the same time avoid unwanted tripping of the earth leakage protection, therefore supply has more guarantee.
The manufacturing standard for earth leakage establishes that the trip range must be between 50% and 100% of the sensitivity, for example, an earth leakage of 30 mA should trip between 15 and 30 mA.
What happens if we have an earth leakage with a trip sensitivity at 16 mA and another at 25 mA?
- The two earth leakages comply with current legislation.
- The first one will trip before the second.
- If we also assert that there is always a leakage current in an installation without any malfunction, the first will always be much more prone to trip.
- If at the moment the power supply connection is made we have a transient leakage current, it is much more likely that the more sensitive one will trip sooner.
What the RGU-2 provides:
- It has a trip range of between 85% and 100% of its sensitivity.
- Therefore, it guarantees a greater, more robust and reliable supply.
|30||15 - 30||25 - 30|
|300||150 - 300||255 - 300|
|500||250 - 500||425 - 500|
|1000||500 - 1000||850 - 1000|
Earth leakage type:
The most commonly installed earth leakages are type AC, but they only detect 50 Hz alternating leakage currents. Therefore they are not suitable when there are loads with electronics.
These units are marked with the symbol:
The RGU-2 unit is capable of detecting pulsating and alternating leakage current, and it is classified as type A.
Type A units are marked with the following symbol:
Therefore, the RGU-2 provides our installation more security, and can detect both a pulsating and alternating leakage current.
Sensitivity with the frequency:
Another important detail is knowing how the earth leakage behaves with the frequency. Normal earth leakages are more sensitive to 50 Hz alternating current.
This would be enough if the facility did not have electronic loads.
The RGU-2, besides being sensitive to 50 Hz current, is less sensitive to higher frequency currents. Initially this might not appear as something good for electrical safety, but that is not entirely true.
We need to bear in mind that:
- receivers that incorporate electronics generate high frequency leakages.
- The human body is more sensitive to 50 Hz than 500 Hz. That means that the higher the frequency the more current is needed to produce the same effects.
International standard IEC 479-2 states the current values that a person can withstand depends on the current frequency. The RGU-2 earth leakage adjusts its sensitivity to the limits established by the safety standard.
Another important factor deduced from the response to high frequency is that it results in stronger immunity to inopportune trips. Plus, if it has less sensitivity at higher frequency, it means that in the end the earth leakage is more robust to any transient disturbances that could reach us through the electrical network itself.
Concept of Ultra-immunisation:
The RGU-2 is an ultra-immunised earth leakage!
But what does that mean and what does it add to our installation?
Ultra-immunised earth leakages protections are popularly known as ones that do not trip because of false alarms, or which are quite hard to trip inopportunely.
Where do these qualities come from? Well, basically from the data we have already described and which we summarise once more time:
- Trip range between 85% and 100% of the sensitivity.
- Frequency response, in particular reducing sensitivity when frequency increases.
- Higher immunity to network transients
Other features of the RGU-2:
The new RGU-2 provides the following features:
- Clear, simple display with a led bar graph or with an indicator of the exact leakage value on the LCD screen.
- Wide range of external toroidals.
- Sensitivity settings: 30, 100, 300, 500 mA, 1, 2, 3, 5 A.
- Adjustable trip time: Instantaneous, Selective, 0.1, 0.2, 0.3, 0.5, 1, 2, 3, 5 Seconds.
- 2 relay outputs for indicating pre-alarm and alarm.
All these features make possible to use the RGU-2 earth leakage relay for a wide range of applications, both for installation at the main panel, on sub-panels, and in the final load protection, as well as being valid for VT, TN-S and IT network regimes, including single-phase and three-phase with and without neutral.
Joan Romans Artigas
Francesc Fornieles Castells
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