Ordering instructions 1. System operation conditions 1.1. System nominal voltage 1.2. System frequency 1.3. Grounding mode of neutral of system 1.4. Capacitive current change range of power grid 2. Type of arc suppression coil and grounding transformer 2.1 Indirectly measure or estimate single phase grounding capacitive current of system. 2.2 According to measured or estimated value calculate the upper and lower limit of compensation. 2.3 Based on project actual situation to decide if Zigzag 3-ph grounding transformer is required or not and if used as station transformer.