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Single and Parallel Generator Operation

Standby generators, particularly diesel generators, have an extremely highMTBF (meantime between failure) and are very reliable if correctly operated. If not, however, problems can occur which may lessen their dependability. In generator operation, one of the most common causes of failure to start is a flat starter battery, which can be easily avoided if the correct checks and operational procedures are applied at all times. So, how do you operate a generator (or generators) correctly?

Firstly, the location of the generator should allow it to be well ventilated and kept free from dust, dirt and moisture. All standby generators should be run, in earnest, at least once a month to lubricate the engine, pass fresh fuel through the carburettor and recharge the battery.

Single Generator Operation

  • Check the starter battery regularly and ensure it is maintained at full charge.
  • Check the fuel level before starting the generator.
  • Never use stale of contaminated fuel and avoid getting dirt and water in the fuel tank.
  • Never refuel when the generator is on or still hot after operation. Always refuel when cold and off, and wipe up fuel spills immediately (a generator produces enough heat and static electricity to ignite spilled fuel or fuel vapours).
  • Check the oil level and air filter before starting the generator and after each refuelling.
  • Check the oil for quality as well as quantity.
  • Do not overload by exceeding the stated capacity of the generator.

Parallel Generator Operation

Parallel generator operation increases reliability in mission-critical applications, where a single generator may represent a potential single point of failure. Alongside reliability, it makes load expansion easier, simplifies maintenance and service, can be cost-effective and enhances quality of performance.

Operating generators in parallel entails connecting them with parallel switchgear to achieve maximum output during peak requirements (and the desired minimum output). The usual operating schematic for parallel generator operation offers two methods of system function: 1) the first set to reach full power assumes the load and 2) both sets are allowed to power up, achieve output synchronisation with each other and then equally share the load.

The first solution has a faster response, but it makes the generator vulnerable to overload, whereas the second options takes a little longer but negates the problem of overload. If the generators are being used in a power protection system alongside UPS, installing sufficient UPS batteries to maintain loads during the time the generators takes to reach full power will alleviate the issue of longer start up.

There are a few things that should be considered in terms of installation and operation, however, and parallel generator operation should only to carried out by suitably qualified and experienced electrical technicians:

Speed control – when generators are coupled together, their engine speeds are locked into the overall speed of the entire system.

Load balance – the load shared by each generator determines the speed of its engine. The load is shared by all generators in parallel systems.

Synchronisation – the phase of each generator must be synchronised to that of the overall system.

Voltage regulation – the voltage regulators of each generator must be interconnected in a reactive cross current system. This regulates the voltage site points of individual generators.


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