Companies, and particularly data centers, need a continuous supply of power from electrical supply networks. Losing power can be disastrous. Unfortunately, electrical supply networks do sometimes fail, so companies need a secure, alternative supply of power. The most practical alternative is to have standby or fully-redundant power supplies in place.
These back-up power supplies normally come in the form of batteries or generating-sets – usually a combination of the two. For example, in a bank, one would typically find a battery that can supply uninterruptible power, and that would instantly take over if the electricity supply from the grid failed. Once the battery had done the job of managing the immediate problem, a diesel generator would normally take over the medium-term supply of power. These generators can only run as long as they have fuel, so supplying enough fuel to run the generators for an extended period is a basic requirement.
Also, the generator itself needs to work properly. To ensure that it does, one should have the generator tested regularly. The price of doing so is trivial compared with the cost of the generator failing when it is needed. Unfortunately, many companies still do not conduct regular or effective testing.
This article explains why regular load bank testing, in particular, should be a crucial part of any company’s standby strategy. It also explains how load banks can be most effectively installed and used.
The Benefits of Routine Load Bank Testing
It is not sufficient to simply turn the motor on once a month to see if it works. Such infrequent use can create significant problems for a diesel generator. Diesel engines that are regularly run at very low loads – or no load at all – become increasingly unreliable and costly to maintain. They experience smoky exhausts, carbon build-up, fuel system problems and lubricating oil deterioration, all of which decrease reliability and add to running costs.
One can avoid these consequences by conducting routine testing, especially tests with a load bank. Routine testing doesn’t mean interrupting the power supply to a hospital, financial center or other critical application so that one can see if the generator set works. Rather, the test uses the load bank to bring the generator, with its engine, alternator, and radiator, up to its operating temperature. One can achieve that temperature by operating the generator set on a load of 20 to 40% of its rated power.
There are two benefits to this. One is that regular testing with a load bank offers a much higher degree of certainty that the set will perform as expected in a real power outage. The second is that costs are reduced. Many users, particularly telecommunications and utilities, recognize that it is cheaper to include a fixed load bank in the generator’s installation – or even to regularly hire a load bank – than it is to incur severe maintenance costs from not having one.
Sadly, there are still many standby generators going untested. We cannot be sure that they will work in a power outage. If power outages were more common, the industry might more clearly understand the value of a standby generator and load bank.
How To Install and Use Fixed Load Banks Most Effectively
Adding a fixed load bank to a generator at the time of installation is much less expensive than retrofitting one. The principal reason for this is that it provides the opportunity to fit the unit in the air inlet between the radiator and the acoustic splitter. This means you can use the inlet for cooling, which will reduce long-term fuel costs as well as initial capital expenditure.
A further benefit is that, if you install a load bank in front of the radiator it does not make any additional noise because there is no extra cooling. However, if you fit one externally, you will need to measure the noise emissions to make sure it doesn’t exceed the environmental demands.
However, in most retrofit projects there is not sufficient space in front of the radiator to do this. As a result, the most convenient location is often the plant room, but in applications where space is at a premium, the roof of the building can also be used.
Another way of reducing capital expenditure is to use a single load bank to test multiple generators, or multiple generators and a UPS, in sequence. Again, by considering testing at the planning stage, it’s easy to build this into the system.
In some cases, there is a further benefit in that the same load banks can be used as a ballast load during normal operation of the generating set. In those applications, where the connected load may vary over a wide range, either as a result of seasonal variations or the nature of the load itself, when the ‘real’ demand is small, it can be beneficial to add load to keep the engine operating at least at 20 to 40% of its capacity.
A third consideration for installing load banks is that if a load bank is incorporated into the set when it is built, the only addition needed to the control scheme is a load-sensing relay in the generator control panel. Load banks for fixed installations are designed as an installations stage bolt-on addition to the set, requiring a space of only 400 to 800 mm between the radiator and the acoustic splitters.
The grids are assembled in banks with ceramic insulation rated for 1kV operation. The load bank makes use of the radiator airflow for cooling, making the basic design simple, low-cost and adaptable to almost any engine. Most standard generating sets in the 50 to 1000kW range have radiators with a free pressure loss of at least 125Pa so that a load bank can be added without the need for modifications to the basic design or an increase in the rating or cost of the acoustic splitters.
Where power ratings of more than 50% of a set’s capacity are required, or where a single load bank is installed to serve multiple generating sets, other cooling arrangements can be used. You can arrange for cooling systems to be used to existing plant room fans and supplied many such loads for these applications, with power ratings ranging from 5kW up to 2MW. Customers include generating set builders, contractors, and end-users themselves.
The Recent Increase In Demand For Routine Load Tests
For many years it has been routine for all newly-installed generating sets to have a load test during the commissioning process to prove the performance of the set and all its ancillaries – the cooling system, exhaust system, switchgear, and protection scheme. When using mobile equipment, these tests have traditionally been performed by contractors who visit the site, bringing with them a portable load bank. Sadly, this was often the only time that equipment was adequately tested.
Encouragingly, however, we have recently seen instances of very high profile financial and telecoms firms investing in their portable load banks and in many cases still using the same contractors to test. This, in addition to those instances of fixed load banks for routine testing we have always seen, provides evidence that many high-profile companies have woken up to the importance of regular testing of standby power. This represents a big step forward.
Buying a generating set but not testing it, is like buying insurance but not making sure that your certificate is valid. It’s sad and ironic that many companies recognize the likelihood of failure in the electrical supply network, which is increasing as our sub-station and generation infrastructure ages but is undermining their preparations for it.