EPCOS has developed a new series of X2 capacitors featuring a low space requirement. Their technology places the company at the leading edge.

X and Y capacitors are vital to protection of people and equipment. The basic circuit for these components is shown in 1. Their main function is to suppress transients. These are overvoltages of brief duration which either affect the equipment along the power lines or are produced by the equipment itself. Transients may have various causes. They can be triggered by strong electromagnetic fields generated by lightning strikes close to power lines. But transients caused by the AC line and loads connected to it are much more frequent. Every line has a parasitic inductance, with typical values of 10 nH per meter. Long lines and switching of high currents can cause corresponding transients. Other causes may be nonlinear loads, such as power supplies or the commutator sparking of electric motors.

If these systems were not protected against transients, negative effects ranging from malfunctions and minor damage through injury to persons to total failure would result. Because transients are characterized by high dv/dt values as well as high voltages, they can be most effectively smoothed by capacitors. X capacitors are connected in parallel with the load and thus prevent common-mode interference. In single-phase systems, they are connected between the live and neutral conductors (240 V AC), in three-phase systems between the external conductors (400 V AC). In contrast, Y capacitors are connected between live and ground or between neutral and ground, and protect against differential-mode interference 1.

Both capacitor types are subdivided according to peak voltage 2 and 3.

EPCOS has specially developed a completely new and improved series for the X2 capacitor market targeted at general-purpose applications. Its major properties are:

• Capacitance from 10 nF to 10 µF
• Compact dimensions: from 4 × 9 × 13 mm
• Max. permissible operating temperature: 125 °C
• Rated temperature: 105 °C
• Max. operating voltage: 310 V AC
• Rated voltage: 305 V AC
• dv/dt values up to 550 V/µs
• DC voltages up to 760 V

Polypropylene is used as the dielectric material in these metalized film capacitors, thus ensuring very good selfhealing properties. The plastic case and epoxy resin encapsulation comply with UL94V-0. These components have been approved to all major national and international standards such as:

• ENEC (VDE), EN132400, JEC 60384-14, 2nd edition
• UL1414 (for C 1 µF, T 85 °C, V 250 V AC); pending C, D versions
• UL1283 (for C >1 µF, T >85 °C, V >250 V AC)
• c-UL (CSA 22.2 No. 1)
• c-UL (CSA 22.2 No. 8)
• CQC pending for C, D versions

As these capacitors are safety-relevant components, they must pass tough tests. Typically, an endurance test lasting 1000 hours is held at the maximum permissible temperature. The capacitor is then exposed to 1.25 times the normal operating voltage. Every hour, the test voltage is raised to 1000 V RMS at 50 Hz for 0.1 s 4. Flammability is another important criterion for these capacitors. It is tested by superimposing at intervals of 5 seconds a total of 20 pulses with a peak voltage of 2.5 kV on the rated voltage at 50 Hz 5. After the last discharge, the normal voltage is still applied for another 120 s. No selfignition of the component is allowed. These tests are conducted for specification of entire series.

In contrast, every single capacitor, apart from the types classified as X3 and Y3, must undergo a pulse voltage test to IEC 60384-14 and EN 132400. The voltage curve is shown in 7.

The pulse voltage V_P is a function of the capacitance of the X2 capacitor. At a capacitance up to 1 µF, a test voltage of 4 kV is applied in this test. At a capacitance above 1 µF, V_P is calculated from the ratio . The capacitance must be given in µF, and the pulse voltage is then obtained in kV.

An important criterion for evaluation of capacitors is their quality, which permits assessment of the parasitic coefficients of inductance and ohmic losses, i.e. impedance. Typical values for the new X2 generation are shown in 6. The capacitors of this new series have the ordering code B3292*.