LeaXield™ active leakage current filter

Aggregate earth leakage currents can often cause RCDs (residual current devices) to trip at their threshold. As a result, RCDs are either not usable or only with substantial additional outlay.

TDK presents the EPCOS LeaXield™ active leakage current filter, a novel electronic solution which facilitates a dramatic reduction of earth leakage currents. This enables the effective use of residual current devices (RCDs) and increases plant availability.

Usage

A complete drive system consists of an EMC input filter, the frequency converter and the motor. LeaXield is connected between the RCD and the EMC input filter, and feeds the leakage currents back to the source, preventing them from flowing through the RCD and tripping it unintentionally.

Thanks to its compact dimensions, LeaXield is also ideal for retrofitting into existing systems. Furthermore, as no external voltage supply is necessary for operation, the installation costs are low.

Function

LeaXield is effective over a broad frequency range from 150 Hz to 30 kHz. The unfiltered leakage currents (red) are dramatically attenuated (green) when LeaXield is used. It effectively filters both stationary leakage currents ranging from 150 Hz to 1 kHz and variable leakage currents, which are typically between 1 kHz and 16 kHz. The latter is determined by the frequency of the converter. The earth leakage currents filtered by LeaXield (green) are significantly below the RCD tripping threshold (blue), thereby preventing unintentional tripping of the RCD.

Applications

Converter-based variable-speed drives, including

• Pluggable devices
• Pumps
• Compressors
• Conveyance systems

Can LeaXield solve my problem?

What is the maximum permissible current?

The rated current of the LeaXield is 50 A at a rated temperature of 50 °C. A short-term overload of 75 A for up to 3 minutes per hour, or 125 A for up to 30 seconds per hour, is permissible.

What type of power system and what voltages is LeaXield suitable for?

LeaXield is suitable for use in a 3-wire TN system. It cannot be used in a 2-line system. Types for 4-line systems are available on request. The rated voltage is 305/530V AC (50 Hz). In addition, a minimum voltage of 208/360V AC (50 Hz) is required for operation. Types with higher rated currents are available on request.

Which RCD should be used?

The unintentional tripping of a universal RCD (Type B/Type B+) can be prevented with LeaXield. There are two distinct types which differ in their tripping characteristics, i.e. with regard to the tripping threshold dependent on the frequency and the time delay.
It should be noted that, in accordance with EN 50178 / VDE 0160, variable speed drive systems are only permissible if type B/B+ RCDs are used.

What is the maximum leakage current within the time range?

The maximum leakage current that can be reduced with the aid of the LeaXield is 1 A (peak value). Care should be taken not to exceed this value. Higher leakage currents can result in malfunctions or destruction of the device. To ensure that the maximum leakage current of 1 A is not exceeded, a leakage current measurement over time is first necessary.

The block diagram shows a typical drive system consisting of EMC filter, inverter and motor. For the analysis, the aggregate current via L1, L2 and L3 shall be measured with a current probe on the line side of the EMC filter. All three phases are to be conducted through the current probe (marked in green in the block diagram). A residual current measuring device should be used for the evaluation. Alternatively, an oscilloscope can also be used.

Important: The residual current must always be measured across all phases and not to ground.

The measurement example below shows the maximum leakage current that flows into the system/machine on the line side. The peak value is about 500 mA and is thus lower than the maximum permissible value of 1 A., In this case, it is possible to use the LeaXield.

How high is the leakage current depending on the frequency?

The analysis of the leakage current over the frequency range provides information on whether the frequencies to be attenuated lie within the operating range of LeaXield, which extends from 150 Hz to about 30 kHz. No significant attenuation is possible in these ranges beyond the operating range of LeaXield. The current probe as described in question 4 is to be used for this measurement. For the analysis, a differential current measuring device can again be used, or also the FFT mode of an oscilloscope.

Please note that the attenuation characteristic of LeaXield is frequency-dependent. As a rule, leakage currents with a frequency of >1 kHz exhibit higher amplitudes than at lower frequencies. Accordingly, the attenuation of LeaXield was also designed to be greater in the range above 1 kHz. The measurement example below shows the frequency spectrum of the leakage current. The frequency components that are problematical for the RCD, in this case, 150 Hz and 2 kHz, are within the operating range of the LeaXield (150 Hz – 30 kHz) where the use of LeaXield is possible.

Products

LeaXiled is available from stock at RS Components (185-3880)  

About TDK Corporation

TDK Corporation is a world leader in electronic solutions for the smart society based in Tokyo, Japan. Built on a foundation of material sciences mastery, TDK welcomes societal transformation by resolutely remaining at the forefront of technological evolution and deliberately “Attracting Tomorrow.” It was established in 1935 to commercialize ferrite, a key material in electronic and magnetic products. TDK's comprehensive, innovation-driven portfolio features passive components such as ceramic, aluminium electrolytic and film capacitors, as well as magnetics, high-frequency, and piezo and protection devices. The product spectrum also includes sensors and sensor systems such as temperature and pressure, magnetic, and MEMS sensors. In addition, TDK provides power supplies and energy devices, magnetic heads and more. These products are marketed under the product brands TDK, EPCOS, InvenSense, Micronas, Tronics and TDK-Lambda. TDK focuses on demanding markets in automotive, industrial and consumer electronics, and information and communication technology. The company has a network of design and manufacturing locations and sales offices in Asia, Europe, and in North and South America. In fiscal 2020, TDK posted total sales of USD 12.5 billion and employed about 107,000 people worldwide.