Do leakage protection and grounding protection require external zero sequence transformers

Leakage protector（RCD）And grounding protector（GFPD）Usually, zero sequence current transformers are required（ZCT, Zero Current Transformer）To detect fault currents, but their application methods and detection logic are different.

1. Leakage protector（RCD）

Do you need a zero sequence transformer? need
Function: Detect phase lines（L）With the zero line（N）Current imbalance, determine whether there is leakage current (such as human electric shock or equipment shell leakage).

Working Principle:

Zero sequence transformer connects all phase lines（L1TheL2TheL3）And neutral wire（N）Pass through an iron core winding.

Under normal circumstances, the sum of all incoming and outgoing current vectors is zero (i.e∑I=0）.

If there is a leakage current, some of the current flows into the ground, causing an imbalance in the current. The zero sequence transformer detects the leakage current and triggers the protection action.

2. Grounding protector（GFPD）

Do you need a zero sequence transformer? Usually required, but sometimes ground faults can be detected through other means
Function: To detect whether there is a large grounding fault current in the electrical system and prevent equipment damage or fire.

Working Principle:

method 1: Use zero sequence transformer (similar toRCDBut the action current threshold is higher, usually300mAAnd above).

method 2Detecting grounding current (through specialized grounding current sensors or direct measurement of grounding conductor current).

method 3Detecting changes in grounding potential (used in high-voltage systems to determine if a grounding fault has occurred based on changes in grounding potential).

In short,RCD(Leakage protector): A zero sequence transformer is necessary to monitor leakage current and prevent electric shock.GFPD(Grounding protector): Zero sequence transformers are usually used, but in some industrial applications, other methods (such as ground current detection) can be used to determine grounding faults.

So for SchneiderEOCRSeveral core products in leakage protection products, such as:EOCR-3EZ/FEZ EOCR-3MZ/FMZ EOCR-I3MZ/IFMZ EOCR-3BZ/FBZ EOCR-PMZ/PFZ EOCR-MMEZ EOCR-ISEMZIn use, external zero sequence transformers are required, SchneiderEOCRThe specifications of zero sequence transformers are divided into ZCT-035 ZCT-080 ZCT-120Because SchneiderZCTThe transformation ratio is 200mA/1.5mAThis specification is basically not produced in China, so Schneider's dedicated zero sequence current transformer should be selected.