G99 Commissioning & Testing
What is a G99?
It's all here
What is G99 Testing?
G99 Testing is only required when running two sources of supply in parallel, for example, a Mains source and a Generator Source. To clarify, in parallel, which means coupled to a common bus. When this is apparent, a G99 relay will need to be installed. Such will monitor the following to ensure the synchronisation is within the following tolerances:
1. Voltage Magnitudes
2. Frequency of Voltage
3. Phase Angle between Voltages
This is all and further explained here
Let's Focus?
Undertaking G99 testing on Mains & Generator(s) synchronous applications. The testing is actually quite straightforward and will take no more than two hours. Essentially, what is needed are the following personnel:
1) G99 Test Engineer
2) LV Panel Manufacturer Personnel
3) Generator Manufacturer Personnel
4) DNO Representative (Depends on your network, but 90% of the time they want to see)
It is wise to run through this before the big demonstration with the DNO, to make sure everything runs smoothly, as DNO are a law to no one and can be costly if you mess them around, that plus they are quite difficult to get hold of, but I must admit I have always had excellent service from all representatives.
Essentially undertaking a standard changeover where the mains and generator go into sync the G99 operative can do his tests, typically he requires three synchronisations to perform all tests to ensure the G99 relay is working and protecting, also likes to check that the parallel timer (5 minutes) for short term applications is present and works, once complete that's him done. The engineer is not bothered if the synchronous system works correctly otherwise, as long as the relay is working and protecting that their job is done and dusted.