G99 Protection Relay
What is G99?
G99 is the regulation that surrounds connection any generating device in parallel with the mains electricity supply, IE the mains distribution grid network or the national grid
What is G99 Used for?
When a generator is to be paralleled with the Supply Utility Grid the voltage from both the Mains & Generator (both supplies) must be synchronised.
To achieve this synchronisation of the Mains & Generator voltages, three different parameters of the generator set voltage across the open paralleling circuit breaker must be controlled:
• The voltage magnitudes
• The frequency of the voltage
• The phase angle between the voltages
Voltage Magnitude maximum voltage differentiate of 0.5%
Frequency - A maximum frequency differentiate of 0.1Hz
Vector / Phase Angle maximum phase angle differentiate of 10°
Fundamentals of G99?
Think of the above like a rowing boat. The left-hand side is the national grid (mains) and the right-hand side the generator Supply. If one side is working at a larger magnitude, a larger frequency and/or towards a different angle it's quite safe to say it's going to be a disaster. Think of this in regards of electricity with a very narrow channel, of which if you step outside the boundaries, well it quite frankly blows up.
This is why generators are controlled and used to synchronise to the mains, they are therefore controlled to be within the boundaries detailed above of the mains supply. For obvious reasons, you synchronise your generator to the mains supply rather than the other way round, simply because the size of the generator is typically a mere atom compared to the humongous national mains grid network, which won't shift trust me.
Basically, you need:
1) Mains Supply
2) Generator Supply
3) Switchboard of some form/coupling arrangement
4) Control / Automation
5) G99 Relay Protection
So far 1-3 Check, 4 is detailed further herein the Automation Section but I would advise DeepSea Controllers every time, there are also ComAp Controllers and hundreds of others but DeepSea are by far the best (in my opinion) because they are quite frankly the simplest solution for a complicated operation which is a godsend trust me, as I always say simple is best, again in my opinion.
So What about No.5?
G99 Protection Relay
Again sorry a shameless DeepSea plug but to be honest there are lots out there and they are all very similar and I have no preference here.
G99 Relays, firstly can I clarify THEY DO NOT CONTROL ANY CHANGEOVER. I am going to say that again THEY DO NOT CONTROL, THEY DO NOT CONTROL THE CHANGEOVER.
They do one and one this along, protect. Simples.
The three elements we spoke of earlier Voltage Magnitude, Frequency & Vector, remember those? Well, this device monitors these aspects of the mains supply and if the supply falls out of the scope of any of these detailed scenarios it drops your unstable supply. The Mains.
So this relay only functions when in sync and it just monitors the supply, if it falls out of the tolerances it ditches it. No more no less, it can only open breakers. It's a typical protection relay.
This is pretty much the low down of G99, if you need to know more drop us a message or check out the Automation Link to understand the control aspect.