Check frequency and voltage difference vs the running bus before closing breaker - the classic paralleling window per IEC 60092-301 / IEEE 45.
Formula
$$ |\Delta f| \leq 0.3,\text{Hz}, \ |\Delta U| \leq 5%, \ |\Delta\varphi| \leq 10° $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\Delta f$ | Frequency difference | Hz | synchroscope |
| $\Delta U$ | Voltage difference | V | dual-voltmeter |
| $\Delta\varphi$ | Phase angle difference | ° | synchroscope |
Sources
- IEC 60092-301.
- IEEE 45.1.