GENERATOR MAINTENANCE
Load bank testing The easiest way to avoid wet stacking during monthly exercise is to run the generator at the manufacturer’s recommended minimum load level (this will vary from engine to engine and manufacturer to manufacturer). Many of today’s infrastructure operators do not wish to ‘risk’ operational integrity by transferring the building load onto the generator at critical times. With many operations today being true 24/7 operations, time to undertake key preventive maintenance works is at an absolute premium, ensuring any generator testing is either off load or with a load bank. It is often the case that load bank testing is undertaken annually. In many operational environments – such as in a hospital, for example – monthly load testing might be mandatory. The use of a load-bank artificially
boosts the amount of load available to be placed on the generator itself, ideally ensuring that the engine reaches optimal temperature enabling it to burn any accumulated build up. Most generator operators recommend that load-bank testing be done at least annually for a minimum of 30 minutes runtime. Of course, needs will vary depending on overall hours run in the period; your generator maintainer will be happy to advise on this. In addition to running time, the
operator or maintenance company will need to consider the time it takes to setup the load bank. For a typical large hospital using between five and ten generators, that can add up to a significant time commitment by operations personnel – not to mention fuel consumption.
Latest diesel engine technology The push and pull of market forces, government legislation, and a growing environmental awareness have seen, over recent years, significant changes to the modern diesel engine. Modern engine designs now incorporate a number of new technologies that enhance operating efficiency, such as: l More precision engineering in cylinder blocks and heads which enable a reduction the gaps between pistons and rings that previously allowed lube oil from the sump to transit so easily into the combustion chamber or ‘blow-by’ which is when unburnt fuel escapes the cylinder.
l The introduction of high pressure common rail systems which allows better atomisation of fuel into the cylinder.
Common rail high-pressure fuel injection Figure 3. The KOHLER KD series diesel.
l More sophisticated engine management systems with ‘fuel mapping’ when combined with high pressure common rail systems can facilitate multiple fuel injections per cycle. This allows near real time management of the combustion process enabling it to be better tailored to the requirements of emissions and/or those all-important cylinder temperatures.
l The addition of charge air cooling allows more low temperature air to be delivered to the cylinder facilitating more complete combustion of the fuel permits fuel.
With the much finer tolerance now being achieved in the newer piston and piston ring assemblies over those of older engines, blow-by has been significantly reduced. Engines now burn fuel far more efficiently, mitigating some of the conditions that lead to wet stacking. A combination of:
l The use of higher cylinder pressures which increase cylinder temperature at lower loads.
l The addition of common rail systems and fuel mapping.
l Improved ring designs which better contain combustion gases and enable a shaped charge to be created (see Fig 3).
When all of these elements come together in one package, this enables the engine to run at much lower load levels when being testing on a regular basis.
Over time, wet stacking will lead to poor performance and reduced engine life
28
This combination of changes potentially permits generators to be safely run at loads as little as 30 per cent of the rated capacity or higher as little as once per year to maintain optimal performance and stay within emissions guidelines.
Revisiting load bank testing and maintenance procedures Many infrastructure operators/ maintenance organisations, where budgets permit, still undertake generator maintenance in the time-honoured way by conducting load bank testing in accordance with maintenance procedures drawn up many years ago and that have never been revisited. These procedures may not embrace many of the technological improvements that have been made and that can now simplify and reduce the monthly/quarterly/annual procedure. Many hours of testing and extensive
field experience suggests that ‘no load’ monthly exercise is allowable, providing the generator is load bank-tested annually, which is standard practice for many operators particularly in the healthcare sector.
Switch to annual load testing The financial and environmental savings available when switching from monthly to annual loaded testing are quite compelling. By way of an example, a KD4000/3120 kW set running at full load for 30 minutes each month will burn approximately 4,400 litres of diesel fuel per year.
If the same testing regime is used but with monthly no load tests and an annual full load test, approximately 1,160 litres less fuel per year is consumed and total pollutant emissions are reduced by 82
IFHE DIGEST 2025
Charge air cooling
Modern piston and ring assembly
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96
