G30 GENERATOR PROTECTION SYSTEM – INSTRUCTION MANUAL 9-1G30 Generator Protection SystemChapter 9: CommissioningCommissioning9.1 Testing9.1.1 Testing underfrequency and overfrequency elementsUnderfrequency and overfrequency protection requires techniques with subtle testing implications. Whereas mostprotection is designed to detect changes from normal to fault conditions that occur virtually instantaneously, powersystem inertia requires frequency protection to pick up while the frequency is changing slowly. Frequency measurement isinherently sensitive to noise, making high precision in combination with high speed challenging for both relays and testequipment.Injection to a particular G30 frequency element must be to its configured source and to the channels that the source usesfor frequency measurement. For frequency measurement, a source uses the first quantity configured in the followingorder:1. Phase voltages2. Auxiliary voltage3. Phase currents4. Ground currentFor example, if auxiliary voltage and phase currents are configured, the source uses the auxiliary voltage, not the phasevoltages or any of the currents.When phase voltages or phase currents are used, the source applies a filter that rejects the zero-sequence component. Assuch, the same signal must not be injected to all three phases, or the injected signal is completely filtered out. For anunderfrequency element using phase quantities, the phase A signal must be above the MIN VOLT/AMP setting value.Therefore, either inject into phase A only, or inject a balanced three-phase signal.
