How is a generator tested?

The term "test" defines a series of activities necessary to determine if a product is suitable for operation. Testing is often mistakenly misunderstood as the commissioning and the start-up of the product.

Let’s start by making a few clarifications: not all manufacturers of generators in the world have an equal and repeatable product testing process. Even those who adopt an ISO9001 quality management system do not have a standard test.

Some choose to carry out tests  on batches of products, while others choose to individually test each generator set, but with procedures that allow testing the functioning and not the performance of the generator. Then there are those who have chosen to adopt a complete test procedure that allows to test the functioning at 100% of the nominal power of the genset.

It is clear that the difference between these three test procedures affects the final result and the list price of the generating set.

With the sample test, usually chosen by large companies that produce large quantities of generator sets every day and in particular by all those companies that produce generators of small power, the risk of defective product is not insignificant. In fact, if the average incidence of the non-conforming product is 1%, in a company that has adopted this testing system it cannot be ruled out that this incidence is concentrated entirely in a few lots or even in the same lot.

Those who choose to test 100% of the production, but are limited to a functional test, can "guarantee" the conformity of the product in functional terms, but cannot guarantee the performance. For example, a 10kVA generator set is tested with a switch to the main parameters, but it is not subjected to an electrical load that can simulate the generator's behaviour in all its functions, so you cannot know if it will actually deliver the 10kVA for which it is sold on the market, nor can you be sure that when reaching the maximum power there are no technical problems.

In the end there are the manufacturers who choose instead to carry out a scrupulous test, which allows to verify the operation and performance of the generator, subjecting it to an electrical load to simulate the operation in the most severe condition of the generator.

The latter type of testing is indeed the most appropriate. the term "test" comes from the Latin cum-laude which means "work of art". So testing is definitely something that serves to establish if a product has been done well, to the letter.


Is it better to test the generator set directly at the installation site?

Some, explicitly ask for the factory test, while others take for granted that the test is performed at the site where the generator is installed. The testing is the responsibility of the manufacturer, who after a positive test issues a declaration of conformity. The ideal testing conditions can be reproduced only with suitable instruments present in the testing rooms and in particular with instruments equipped with calibration, however, even if  these equipment are available at the installation site, the operating conditions are hardly ideal for testing, especially the electric load connected to the generator.

A professional manufacturer, sets up the generator and tests it with a standardized and repeatable procedure. Here's how (synthetically) a general test is performed in a few steps:

• Check electrical connections, hydraulic connections and tightening.

• Starting with blank test.

• Try loading steps. (x% of nominal power up to 100% divided into different and increasing load ramps).

• 100% power test.

• 110% power test.

• Alarm simulation, instrument reading test, emergency stops ... etc.

During a test, the behaviour of the user, i.e. the dummy load used to simulate the user to feed, (usually a resistive load) is not comparable to a system with different loads and subject to anomalous voltages, unbalanced absorption, eddy currents, and so on and so forth.

From the point of view of the end user, there is no difference between factory testing and on-site testing, but in light of what is written above and considering the fact that the constructor of the generating set is not responsible for what is connected to the generator, the difference exists and is relevant.

Factory testing is a protection for the manufacturer and for the customer. If the generating set reaches the nominal power in the factory, while it presents anomalies of operation at the site of installation, it is possible to make evaluations to compare between the measurements taken during testing and those measured in service to the user.

Many companies allow to assist the testing of the generator, others are available to add specific test sequences required by the customer.

The test report must be requested during the signing of the supply contract, when ordering. In fact, many companies have a digital system for archiving tests and do not issue a paper certificate if it is not explicitly requested.


Testing is not just for the new generators.

I have a generator for a few years, which has been repaired, how can I be sure that it works like before...?"

The test is not exclusive for the "new" ones, in fact any generator can be tested with the same procedures adopted for a new generator. It is the only way to be sure of the functioning of a generator.

Let's take an example: Two years ago, I assisted as a counterpart, at the Expertise of  a Technical Consultant for the court. The engineer was in charge of determining whether a disputed Generating Set was in default or functioning normally.

Being also a Consultant for the Court of Cagliari, I immediately had doubts about the procedure adopted to determine if the generator set was working, in fact, the engineer with the help of an assistant, started the generator engine and seeing it turned on, he related to the judge that the generator was tested and was well functioning.

Now, to make a comparison, it is as if to check the functioning of a car for which you are complaining of a fault, you limit yourself to turning the starter key and turning on the engine to say that it works. A minimally qualified technician will take care of a test run and test the greatest possible number of instruments and accessories, reaching the maximum speed allowed to evaluate the effective efficiency.