What is the paralleling of generators
We use generators as a backup power supply in case of power failures so we can select a generator according to our need of backup power, in certain cases we may need more backup load so the generator output won’t be enough In that case, we can use paralleling generators, it is the process by which two or more generators connected together using special equipment to form a larger capacity power source
What are the requirements for the parallel operation of the Generators
Before connecting any two generators the oncoming terminal unit must have these features
• It must have the same magnitude as the running generator
• It must be in phase with the corresponding phases of the running unit
• Its phase sequence must be the same as the running generator
• It must have an equal frequency as the running generator
If the above requirements are not met then there will be circulating current between the generators which could be large enough to damage the machines
To check the above requirements the following method can be used
One “dark” two “bright” lamps method
In this method a lamp is connected across the a-phase of two generators and the second lamp is connected between the b-phase of the running generator to the c-phase of the oncoming generator, then the third lamp is connected between the c-phase of the running machine and the b-phase of the oncoming machine and by this arrangement the generators are paralleled when one lamp is dark and the other two is bright
Benefits of parallel power generation
In the early days, the parallel system wasn’t used because of its complexity, higher cost, and space. So many industries didn’t use it when they needed it because of these limitations. But now due to the arrival of sophisticated integrated digital control technologies, it is very easy to operate the parallel system and to benefits from its advantages
Reliability
By using parallel generator we could get more reliability than a single generator unit. we could get the desired load by using the parallel generator so we could get the required load by this and in a certain case, if one unit fails the load can be distributed to the other unit of the system in case of parallel generators but it is not possible in a single unit generator
Scalable
By using the parallel system one has the ability to expand to his needs. The required load could be received by this without overrunning the budget we can add generators according to the available space and generators can be detached according to our need
Easily serviceable
If one of the generators needs to be serviced it can be dismantled from the unit and serviced thus it won’t interrupt the function of the other loads.
Flexibility
We can use small generators for parallel system and thus we could get the required load and the generator system will fit in the desired space and by using small size generator we could use it in places were space is restricted
What is required to parallel generators
• Synchronizing
• Switching device
• Load sharing
• Protection
Synchronizing
• Same phase to phase voltage
• The same number of phases
• Same phase rotation
• Electronic governor- load sharing
• Electronic voltage regulator/ paralleling capability
• Identical internal alternator winding pitch
Switching
Switching can be done by using circuit breakers and integrated switching can be done with the utilizing contactor mounted on the generator Load sharing
Load sharing
Isochronous load sharing or speed drop
Reactive power
Reactive cross current or voltage drop
Protection
• Synchronizing process
25 sync check relay
• Real power system (governor & engine)
32 reverse power, frequency protection
• Reactive power system (Regulation & excitation)
Voltage protection
• Cabling and alternator
50/51 overcurrent