Description
The differential DC current relay is designed to monitor IT systems for insulation deterioration. The DDCA is able to selectively indicate faults in branched systems. In addition to this it shows if the fault is related to the positive or the negative wire for easy maintenance. Used with only one wire through the sensing core, it can monitor a circuit for connectivity and function. If the DC current drops below the set value, the relay will trip. This is another key feature as the DDCA allows, up to the cable capacity, AC and DC Amps to flow under normal conditions without having the usual voltage drop and heat from a shunt resistor.
Operation
Set the DIP switches (123) to the requested sensitivity, latching relay (5) to On or Off and the relay (6) to Normal (fail safe) or Inverse function. When the power is connected to A1 and A2, and with no differential current through the sensing coil, the green LEDs for Differential and Relay ON (normal function) will be on. When a differential current above the set limit is detected, one of the red Differential LED’s will be switched on, showing the polarity of the cable leaking to ground. (For leak currents above 15A both red Differential LEDs will be switched on indicating that the DDCA is saturated and cannot detect which cable is leaking). When high current is detected, the OFF delay starts to elapse, indicated by a green LED, and the relay will drop out when the set time has expired. If the latch function is selected the relay will stay de-energized (normal function) and the red Latch LED will be on until the Reset button is activated. If the latch function is not active and the differential current drops below the set level, the green Differential LED will be switched on and the ON delay starts to elapse, indicated by a green LED. The relay will pull in (normal function) when the set time has expired.
Test and Reset function
The Test switch activates a real functional test as it conducts a DC current through a separate winding on the sensing core. The Reset switch will while activated release the latch function.
Application
Selective DC earth leakage detection in single and branched systems. The DDCA is the solution for pure DC installations used in UPS and control systems for chemical, petrochemical, mining industry as well as seagoing vessels. The DDCA is also ideal in AC installations including loads with rectifiers e.g. in variable speed drives, causing the AC monitors to malfunction.
