IEC 61921

Design of reactive power compensation panel is much different and not that simple like standard distribution panel. When dealing with such panels, there are dozens of parameters to specify and other things to take care of. MODUTEC could collaborate with you to empower this Type Testing together.

IEC 61921: (Power Capacitors- Low voltage power factor correction banks) is the international standard applicable for Low Voltage Power Factor Correction Banks and Automatic Power Factor Correction (APFC) equipments intended to be used for power factor correction purposes, equipped with built in switch gears and control gears. The guidelines for design, installation, operation and safety of APFC panels are followed based on this international standard.The standard describes the general requirements for the capacitor bank. The most important of them are listed below:

  • Access to the particular elements within the capacitor bank should be easy, so that there is no problem to replace an element in case of failure
  • Index of protection depends of the place of the installation of a capacitor bank. If the capacitor bank is to be placed in the same place as the main switchgear or utility room next to it, IP 20 is enough.
  • Section construction – in a device for reactive power compensation particular sections can be determined, placing them in separate partitions or within the same cubicle.
  • Marking – each capacitor bank has to have nameplate, which contains information about: manufacturer, identification number, date of manufacture, rated power in [kVar], rated voltage in [V], min and max ambient temperature, index of protection, short circuit strength in [A]

Such capacitor banks, otherwise known as power factor correction panels (PFC panels), are used to avoid inefficiencies in power distribution networks associated with large electrical motors similar loads with a low power factor. Testing these products require specific knowledge, expertise and facilities.

Although most of the international standards for this equipment (IEC 61921) refers to the IEC 61439-2 standard, there are also some critical differences with respect to temperature rise testing. MODUTEC can support you in testing these panels. The major differences are described below.

Increasing the load current

One major difference is that temperature rise testing should be performed at increased load current. Several options for increasing the load current in the circuits of the PFC panel are described in IEC 61921 - in clause 7.2.1 You can: a)increase the voltage, b)increase the frequency, c) increase the capacitance, and/or d) superimpose harmonics.

At MODUTEC, we can perform testing according to several of the above options. In most cases, we will discuss the preferred method with the manufacturer. We think that a very realistic way of testing would be a combination of increasing the frequency and increasing the voltage. A higher test frequency (from 50 Hz to 60 Hz) can be used to deliver part of the load current (1.2 times) and increasing the test voltage can be used to achieve the final load current if required. Only increasing the voltage may overstress the control circuits. A disadvantage of only increasing the capacitance may be that this does not reflect the worst-case scenario, as the capacitors are not loaded up to the current as specified. We think that a combination of increasing the frequency and increasing the voltage is most realistic without the need to change the test object (capacitors and/or control circuits) and/or to use more costly components.

To make testing as realistic as possible, an inductive load bank is used. For manufacturers this is an advantage because there is no need to adapt the test sample to control the capacitor banks. This can be easily controlled, using the standard functionality of the control circuit of the PFC panel.

Full line voltage

Another major difference is the fact that temperature rise testing should be performed at nominal line voltage. Testing to IEC 61439-2 is normally done at low voltages. However, for PFC panels the standard requires testing at nominal line voltage. Safety conditions during testing are, of course, a critical element. MODUTEC will coordinate to ensure that the test laboratories are fully equipped to make the appropriate measurement and to ensure that these tests are done safely.

Testing at higher ambient temperatures

In areas with a hot climate, e.g. in the Middle East, additional testing at higher ambient temperatures than those specified in the international standards is required. To meet this demand MODUTECwill enable testing in a climate-controlled test laboratory, where we can test equipment at 15 - 60°C. This automatically controlled climate chamber assures that the elevated ambient temperature of e.g. 50 or 52°C is kept stable during the complete test. This is of course important for manufacturers and end-users to witness these tests as fluctuations during testing may lead to discussions on the outcome. Temperature rise testing of a PFC panel is one of the critical tests as the lifetime of capacitors reduces drastically at higher temperatures. Accurate measuring and stable conditions during testing is in that respect, of vital importance.

We trust that the above information will help you prepare for testing a PFC panel. At MODUTEC we have the right people, the right knowledge and the right expertise to support you. Our experienced engineers are familiar with the requirements for specific markets and ensure that your equipment will be tested quickly and efficiently.

For different manufacturers, the APFC Panel dimensions could differ. This would also depend on whether the Panel is with Reactors, Thyristors or Contactors and type of switchgear. A sample standard to give you an idea is depicted in the table above.