For the most part, testing electrical installations that include renewable energy sources covers familiar ground. There are, however, some specific requirements associated with these installations that are likely to be rather less familiar, as Simon Wood of Megger, UK explains.
Renewable energy installations take many forms. Small-scale hydro, solar thermal, hot water and ground source heat pumps are just a few examples, all of which have their own testing requirements. This article, however, deals principally with PV (photovoltaic) solar installations and, to some extent, small wind turbines, as these are without doubt the most popular options.
Let´s start with a potentially costly myth. Some suppliers say that it´s necessary to purchase expensive ´dedicated´test equipment for use on renewables installations, but that´s not true! Like all UK electrical installations, renewable energy installations are tested according to the 17th edition of the IET Wiring Regulations. It means that anyone who tests conventional installations will already have almost all of the test equipment they need for renewables.
So, why buy it again?
Note, however, that the last sentence said ´almost all´ of the test equipment needed. A small amount of additional test equipment is required, but buying this separately costs far less than buying a dedicated renewables test set.
What is this additional test equipment, and why is it needed?
Conventional domestic and commercial electrical installations are concerned only with AC voltages and currents, whereas PV panels produce a DC output. So for testing purposes, an instrument capable of reading DC voltage up to 600 V and DC current up to around 10 A is needed.
A good quality digital multimeter will easily meet these requirements. When choosing an instrument, however, look for one with a CAT IV 600 V safety rating. This means you are well protected against the potentially dangerous effects of voltage transients, whether from the renewable energy source or the supply network.
Those who work frequently on PV installations may also consider buying a clamp meter with AC and DC capabilities, as this will allow current measurements to be made without the need to break into the circuit. A clamp meter is, however, by no means essential.
For work on PV installations, the next additional instrument needed is an irradiance meter. Essentially, this is a special form of light meter that measures the amount of sunlight falling on its sensor, and it is used to ensure that the PV panels operate to the manufacturers published specification are fitted in the best possible location and are oriented to maximise their energy output.
Irradiance meters are not particularly expensive, but it is advantageous to select one that has the sensor built in to the instrument body. These meters are often used on a roof or at the top of a ladder, and juggling with a meter in one hand and a sensor in the other is neither convenient nor safe when working at height.
For similar reasons, a reading hold facility is also highly desirable, as it means the user doesn´t have to struggle to see the display while the actual reading is being taken. Instead, they can simply press the hold button and read the result later in a more convenient position!
Moving on now to wind turbine applications, it´s clear that the solar irradiance meter would need to be substituted for an anenometer, although the digital multimeter will still be very useful. Many wind turbine installations, however, have their own earthing electrode to ensure safe operation and some means will be needed of measuring the earth resistance of this electrode.
Electricians who have worked on installations for caravan parks and temporary outdoor installations may well have already met this requirement, and be in possession of the test equipment needed for earth resistance measurement. For those that don´t have this equipment, however, there are two options available.
The first is simply to buy a standalone earth resistance test set, and this is likely to be the right option for those who already have up-to-date instruments for testing standard electrical installations. Those who may be considering buying a complete set of new installation test equipment may, however, prefer to consider the second option - the purchase of a multifunction installation tester (MFT) with built-in facilities for earth resistance testing.
MFTs of this type have only recently appeared on the market and, for those purchasing new installation test equipment, they offer a considerable cost saving compared with buying a standard MFT plus a separate earth resistance test set. Testing renewable energy installations is nothing more than an extension of the testing work needed for conventional electrical installations. As we´ve seen, very little extra equipment is needed and, provided that equipment is chosen carefully, testing renewable installations conveniently and safely is a straightforward task for competent persons.
If you would like to know more about Megger´s range of test & measurement products, visit en.megger.com or mail at Pratyush.Sinha@megger.com.