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The ZJJ series DC ground fault detector can monitor the insulation condition of the DC bus and the grounding resistance of the positive and negative buses online in real-time. When the busbar-to-ground insulation drops to a certain value, the relay sends a warning signal. This ground fault monitoring device uses a fully static circuit, including a highly sensitive ground resistance monitoring and display circuit. When the insulation monitor falls below the set value, the ground fault monitoring relay sends a warning signal. This ground fault monitoring system features panel mount or DIN rail insulation monitoring relays.

This ground fault detector is used in DC or AC main circuits, UPS systems, battery systems, IT systems with high leakage capacitance, and DC charging stations for electric vehicles.

This ZJJ series insulation monitoring relay utilizes a complete hardware divider operation circuit for the direct display of grounding resistance values. The alarm threshold is easily adjusted, set, and displayed on the panel. The ZJJ series includes ZJJ-4SC and ZJJ-4SA.

ZJJ-4SC DC Ground fault relay, with a compact size of 115X90X40, is installed on a din rail and features a dry contact alarm output for convenient installation and use. It can monitor voltage values within a wide range of 48-1500v, unaffected by measured voltage fluctuations, making it applicable in various fields such as DC speed motors and solar power generation.

ZJJ-4SA ground fault insulation monitoring relay adopts an instrument junction with the panel for specialized applications.

Working Principle of the ZJJ Series DC ground fault detector
The ZJJ series DC ground fault detector relay employs the high-resistance bridge balancing method to measure single-side ground resistance, depicted in the figure below. +KM and -KM mark the positive and negative busbars under measurement, with R1 and R2 as balancing resistors achieving voltage division at point A. R3 increases impedance between the bridge and the earth to mitigate the measurement circuit’s impact on the bus. RL serves as the sampling resistor for current measurement. In the event of a single-sided insulation drop (RX or RY), ground current flows through R3, creating a voltage drop Vo on RL. The magnitude and direction of this voltage drop are measured and summed. Applying Ohm’s law: V-/I=(R3+RY), the resistance value of RY is obtained through the hardware divider operation circuit. Similarly, with a positive bus grounding resistance RX, the analysis yields: V+/I=(R3+RX). An alarm is triggered if any resistance value exceeds the limit.

Feature of ZJJ Series DC Ground Fault Detector

• Max measuring Resistance is 199.9KΩ( ZJJ-4SA) or 1999KΩ( ZJJ-4SC)
• Bridge balance method for resistance measurement.
• Smaller short-circuit grounding current for safe operation.
• Alarm resistance threshold online display and direct setting.
• Terminals are pl able for easy maintenance and replacement.
• Monitoring the DC circuit bus bar’s RF-to-earth insulation resistance.
• Direct LCD busbar grounding resistance values, positive and negative.
• Reinforced shell, modular structure, high reliability.
• Wide monitoring voltage, 48-1000V, working voltage 24-220V can be customized, adjustable response value ranges of 0-100kΩ.