The monopolar groundcircuit operation mode of DC transmission system gives rise to excessive vibration and noise of some transformers in the power grid, which impacts the safety of equipment.
直流输电系统单极大地回路运行方式导致电网部分变压器振动加剧，噪声增大，影响了设备安全。
2
Because you need both a voltage source and a ground in order to create a complete circuit, you need to have a sourcing input or output connected to a sinking output or input.
因为在一个完整的电路中必须有一对电源和地。
3
Scope ground may be connected to other DC level in the circuit other than ground provided the circuit under test is floating.