We left off last time while checking the standby generator.  Specifically, is the engine block warm from the block heater?  These heaters often fail, and many diesel gensets have trouble starting if completely cold.


It’s always a good idea to exercise the generator periodically, and although it’s tempting to run it without its load (no interruptions and surges for the transmitter to cope with), that really doesn’t test much except the starter motor and battery unless the load is connected.  In fact, it is best if the generator is fully loaded up.


The best way to test, though possibly not the most convenient, is to turn off the main hydro breaker.  This after all is your best simulation of a complete hydro outage.  The generator should start up, the load should transfer, and the generator should fairly quickly settle at 60 Hz.  Don’t worry too much if the frequency is one or two Hz off frequency, but pay particular attention if the generator continues “seeking,” or changing speed.  In excessive cases the engine looks like it’s ready to leap off its motor mounts.  Problems of this nature may indicate adjustments to the governor are necessary.  Time to call in the generator specialists:  some of the newer electronic governors have as many as six or seven controls, all interdependent, for frequency, damping, response rate, sensitivity, etc., etc.  Proceed with caution! 


A good load test will run the generator for an hour or so.  Most of those I informally polled liked to see a load test every two to four weeks.



A three-phase system should have full three-phase failure sensing… while this seems like a no-brainer, it’s surprising what some genset suppliers will provide in lieu of the full-meal deal… usually one or two sensors.  If you think about it for a while, you’ll realize that you shouldn’t accept anything less than three sensors.  A single sensor, say between phase A and B, works unless phase C is lost.  A second sensor, between B and C, will sense the failure of C, but what if instead a tree, leaning against your power line, shorts lines A and C together, blowing the in-line fuse for C?  The two-sensor system will not detect this fault, and the genset will not start.  Been there, done that… best to check that you’re sensing voltages between all three legs of the line!


Delay on neutral is a deliberate hesitation of a few seconds, between hydro on load and generator on load.  Normally it’s an extra-cost option—it can become important if there are large motors, particularly single-phase units, on-site, and if the transfer switch operates quickly.  The still-rotating motor stores energy (mechanically—the “flywheel” effect) from before the transfer action—if the genset’s applied energy is out-of-phase with the stored energy, the resulting surge as the two power sources rush to synchronize may be large enough to intermittently pop circuit breakers or generator exciter diodes.  O joy!  Delay on neutral can be added to avoid this problem.  Some modern advanced transfer switches contain synchronizers, which add complexity but permit a very rapid (<100mS) hot transfer without requiring delay on neutral, and without these surges.


Unlike diesel fuel, gasoline spontaneously breaks down over time, with the more volatile components evapourating, and the heavier compounds depositing out, varnishing in the carburetor.  The gummy deposits ruin engine performance.  Gasoline generators should be exercised frequently to prevent this, and really stale gasoline should be replaced.  Diesel fuel will not break down this way, but fungus-like critters can actually live at the margin between the fuel and any water that’s gotten into the fuel tank.  They will plug up fuel injectors if they get past the fuel filters.  Recent practice has been to add extra, more efficient filters in the fuel line, and to occasionally have the fuel sampled and tested.  All that rust and crud that accumulates in outside tanks means it’s a good idea to refill once the tank’s half empty.  There’s less condensation in the tank that way, too.


Incidentally, if, ahem, your diesel generator ever runs out of fuel, it may take a surprising bit of effort to get it running smoothly again.  There’s often a little hand-pump located under the injectors—the correct procedure is to crack open the injectors, and pump the little manual plunger until fuel squirts from them.  Depending on the length of your fuel lines, this may take a while.  Then re-tighten the injectors and try to start without the load connected.  You may have to crack open the injectors again to bleed them while the engine coughs a bit.  Once you get the engine running smoothly, you can apply the load and you’re back in business!   We’ll leave the maintenance of belts, hoses, radiators, coolants, lubricants and batteries to your imagination.  Rest assured that, as with any mechanical device, something’s always ready to fail just as soon as you let down your guard!