Most owners of standby sets ensure that they are completely and regularly maintained. There are, however, other operators who ignore maintenance and when there is a power shutdown, the set does not always start. In most of these instances, faulty starting and control systems are blamed, but over the years, the real villain is neglect of regular preventive maintenance.
This neglect can be expensive and can endanger life.
Preventive maintenance is the easiest and most inexpensive form of maintenance since it permits staff to carry out the work at convenient times. It starts with a well prepared schedule. This should be established according to the duties expected of the generating set, since while most sets are only used for short periods, “in anger”, there are others used for load shedding, which have higher working periods.
Regular checking
Generally, a standby set should be checked weekly and run for a short period, preferably on load, to exercise both the engine/alternator and its control panel. All information and readings should be logged. The suggested schedule check sheet may be used as a guide to establish a maintenance programme to fit any specific operation. It is assumed that the set has been commissioned and that the initial running in instructions have been carried out by a properly trained maintenance Dept, who should supplement these with any other particular operation that may be listed in the generating sets engine manual. The time between checks could vary depending upon site conditions, e.g. high dust laden atmosphere, which the maintenance schedule should take into account.
At some installations, there may be no properly trained maintenance staff to carry out this work in which case it is advisable to enter into a regular maintenance contract with the supplier.
A maintenance contract can take the form of a simple signed agreement between the owners of the generating set and the set manufacturer or its representative. The owner being referred to as the “user”, the manufacturer as “The contractor”. It would be expected that the maintenance contract would include clauses covering:
1. That the user only utilises experienced and trained operators.
2. An agreed time between visits.
3. Exact details of work to be carried out.
4. The contractor to replace any parts recommended by the user not covered by the guarantee or maintenance schedule within a reasonable period of time.
5. The contractor to undertake arrangements for major engine overhauls that may be needed from time to time.
6. An agreed period for work laid down in the maintenance schedule (it is usual to add the cost of parts used during the execution of the schedule).
7. The user to provide all necessary facilities to enable the contractor to carry out the execution of the schedule during normal workday hours.
8. Indemnification of the contractor against loss or damage to property or injury to personnel arising directly or indirectly in the performance of the service.
9. Notice of termination of the contract by either party. To avoid any contention that may arise as a result of any misunderstanding or obligation it is advisable to have a formal, legalised agreement drawn up.
The basic maintenance schedule normally covers the following services:
(a) Check condition of air cleaners, fuel oil filter elements and lubricating oil filter elements, change if necessary.
(b) Check coolant level, leaks, anti-freeze strength and DCA content where applicable.
(c) Check lubricating oil level and leaks and top up or change if necessary.
(d) Check fuel oil levels and leaks.
(e) Check fuel injectors (visual only).
(f) Check fan belt condition and tension correct if necessary.
(g) Check starter battery condition, voltage and specific gravity of electrolyte and level.
(h) Check alternator brushes if applicable, replace as necessary.
(i) Check condition of switchboard lamps, fuses, meter, contactors and other switches.
(j) Check output of battery charger if applicable.
(k) Check for loose electrical and mechanical connections, tighten as necessary.
(l) Check regulation of alternator voltage and frequency.
(m) Simulate “mains failure” operation if applicable.
(n) Submit report to customer on condition and state of plant. the most common cause of an engine failing to start is badly charged batteries. Since most installations incorporate lead-acid batteries, care has to be taken as to their method of charging.
G E N E R A L M A I N T E N A N C E P R O C E D U R E S Section E
Batteries
Invariably batteries are either under-charged or over-charged, the latter being more common and causing a deterioration in the battery’s life.
It is essential that special attention is given to batteries to ensure that they are always in a near fully charged condition at possible and regular readings are taken of their specific gravity. The misuse of battery chargers is normally found to be the cause of over-charging.
Nickel-cadmium batteries do not suffer with this problem and therefore require less maintenance, but of course they do cost considerably more than an equivalent lead-acid battery.
Nicads must have a condition discharge-recharge, recommend this twice per year.
It is not generally appreciated by the user of a diesel generating set that during the starting cycle of an engine the voltage of the battery drops to its lowest value and the current drawn is at its highest level directly the starting switch is operated.
Immediately the motor turns or “breaks away” the current falls off with the voltage rising. It is at the initial critical moment of operating the starting switch that essential components such as fuel cut off solenoids and relays are required to operate. Although some manufacturers arrange their circuits to avoid this situation, by slightly delaying the operation of the starter motor, there are many sets where these two operations are carried out simultaneously. It is therefore absolutely vital that the battery is in peak condition.
Light Loads
A fault that occurs quite frequently even when maintenance is carried out regularly, is the engine injectors fouling due to excessive light load running. As will be seen from the typical maintenance schedule, a figure of 50 per cent loading is mentioned. The load factor should be considered as a minimum and a full load factor would be more desirable, followed by 110 per cent load for a short period.
With this load factor it does ensure that the engine does not suffer from injectors being “clogged with carbon deposits due to unburnt fuel. Also, running on a light load could in time dilute the engine lubricating oil. Obviously there are many causes of a set failing to start or failing to provide volts when started, preventive or planned maintenance is not a panacea for malfunctioning, but it will go a long way to avoid the non-starting of the set when it is most needed.