High Stability Circulating Current Relay Block MCAG 34

Benefits :-
1. High stability with through faults
2. Tuned to rated frequency
3. Operates in 25ms at 5 times setting

APPLICATION :-
When circulating current protection schemes are subjected to heavy through faults, the sudden, and often asymmetrical growth in the system current can cause the protective current transformers to approach or even reach saturation level. This may result in a high unbalancing current due to the variations in the magnetising characteristics of the current transformers. To ensure stability under these conditions, it is common practice to use a high impedance relay, set to operate at a voltage slightly higher than that developed by the current transformers under maximum external fault
conditions.

This High Stability Circulating Current Relay block is easily insert in your schematic diagram and connect as you like way.

The relay is an attracted armature unit of simple and robust construction. The operating coil of this unit is connected in series with a small choke and capacitor, forming a series resonant circuit. These components are energized from an auto-transformer which is tapped to provide seven current settings. Due to the simple electro mechanical construction, the detection element and the output contacts are one and the same device. Operation is therefore fast and highly reliable. The relay circuit, tuned to the supply frequency, rejects the harmonics produced by current transformer saturation. The total impedance of the relay and series stabilizing resistor is usually low enough to prevent the current transformers developing voltages over 2 kV during maximum internal faults, but in some applications a non-linear resistor is required to limit this voltage. When circulating current protection schemes are subjected to heavy through faults, the sudden and often asymmetrical growth in the system current can cause the protective current transformers to approach or even reach saturation level. This may result in a high unbalancing current due to the variations in the magnetizing characteristics of the current transformers. To ensure stability under these conditions, it is common practice to use a high impedance relay, set to operate at a voltage slightly higher than that developed by the current transformers under maximum external fault conditions.