application note 3-line filters active common mode line ... · application note . preliminary data...

EPCOS AG 2014. Reproduction, publication and dissemination of this publication, enclosures hereto and the information contained therein without EPCOS’ prior express consent is prohibited.

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Application note Preliminary data

3-line filters

active common mode line filter LeaXield

207/360 to 305/530 V, 50/60 Hz, 50 °C Special features:

- Highest reduction of earth leakage current in compact package - Improves RCD compatibility - Add-on to reduce common mode conducted emissions Ordering code :

Date : 2015-02-11

Version: 01

P300193-F001

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DISTRIBUTED BY TEXIM EUROPE

mfi1

Texim Europe logo 4cm

3-line filters P300193-F001

active common mode line filter LeaXield Application note

Preliminary data

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Technical description

LeaXield works by actively cancelling common mode currents on the power line. The common mode current flowing on the load-side of LeaXield is measured using a current transformer. This signal controls an amplifier which generates the inverse of the measured line current. These currents are added at the line-side of LeaXield where they mutually cancel. This leaves a very small residual line-side common mode current.

Typical circuit diagram

PE

L3'

L2'

L1'

PE

L3

L2

L1

LOADLINE

AmplifierPSU

Functional principle of LeaXield – Intended point of installation

LeaXield should be inserted in the power line between the RCD and the line-side of the EMC filter as shown below.

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Preliminary data

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Typical applications

LeaXield is suitable for connection to a large range of power conversion systems. It is designed for use on three phase, 3 wire TN systems. Motor drives with carrier frequencies at or above 4 kHz and motor rotational frequency form 0 Hz up to 200 Hz. It is applicable for regenerative, as well as diode converter topologies (6 and 12 pulse). UPS systems, SMPSU and other switched power devices with carrier frequencies up to 40 kHz switching frequency are applicable. Higher frequencies must be investigated. Installation requirements

1) Line-side connection. LeaXield is designed for connection on the power line entry side of the power system.

2) Power line EMC filter. LeaXield is designed to be installed in conjunction with an

EMC line filter. LeaXield should be connected directly on the line-side of that filter.

3) Line – Load orientation. LeaXield must be connected with correct observance of

line and load orientation.

4) LeaXield performance system dependence. The performance of LeaXield is dependent on the operating parameters of the system and on the components used in the system. In particular the system carrier frequency, the power line filter insertion loss and the system earth capacitance all have an influence on the LeaXield performance. See system compatibility estimation and measurement in the following sections.

5) Phase Connections. LeaXield provides three on the line-side and three on the

load-side terminal blocks for the connection of three-phase cabling.

6) Grounding. LeaXield must be connected with its mounting plate electrically bonded to the earthed metal housing of the system (i.e. installation panel or cabinet), such that LeaXield and the drive have the same earth potential.

7) Mounting. LeaXield can be mounted in any physical orientation. A minimum

clearance of 10 mm should be observed between LeaXield and other devices.

8) Power line harmonics. The voltage harmonics of the system power line should comply with the limits given in EN 50160.

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Preliminary data

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System compatibility

For correct operation, it is important that LeaXield and the drive system are compatible. In particular the peak common mode current on the load-side of LeaXield must be no greater than 1 A. System compatibility can be checked by estimation or by measurement as described below. Estimation of system compatibility Use the following method to estimate the compatibility of the drive system.

1) Identify the lowest carrier frequency within the drive system.

Notes: a) In some cases carrier frequency is switched automatically to a lower rate at

slow motor speeds. To maintain a suitable carrier frequency it may be necessary to inhibit this function in the drive system.

b) For regenerative drives the carrier frequency of both converter and inverter must be checked.

c) For multi axis inverter systems carrier frequencies may vary from one axis to another.

2) From the published line filter insertion loss, find the 50R common mode insertion

loss, given in dB, at 10 kHz.

Note: If the 10 kHz insertion loss is not given, use the insertion loss given at 100 kHz and subtract 40 dB.

3) Estimate the total earth capacitance within the drive system.

Notes: a) For non-regenerative drives, use the total earth capacitance (stray and

intentional) on the inverter output only. b) For regenerative drives, use the total earth capacitance (stray and intentional)

on the dc link and the inverter output. c) For multi axis systems include the earth capacitance (stray and intentional)

from all axes. d) As a general guide only, a screened motor cable can typically have a stray

earth capacitance per unit length of between 0.5 nF and 1 nF per meter. e) As a general guide only, an induction motor can typically have a stray earth

capacitance of between 1*P2/3 nF to 2*P2/3 nF, where P is the nominal power of the motor in kW.

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Preliminary data

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4) Restriction zone

Note the restriction of system carrier frequency when using a line filter with 15dB, or less, 50R common mode insertion loss at 10 kHz. In this case the system carrier frequency must be increased in order to maintain compatibility.

5) Using the Maximum Earth Capacitance graph below:

a) Find the lowest drive carrier frequency on the horizontal axis. b) Find the line filter 50R common mode insertion loss at 10 kHz on the vertical

axis. c) At the point of intersection, find the maximum earth capacitance. d) The estimated system earth capacitance must be less than the maximum

capacitance identified in the graph.

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Preliminary data

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6) Example of system compatibility estimation a) Motor drive has lowest carrier frequency of 6 kHz. b) Line filter has 15 dB 50R common mode insertion loss at 10 kHz. c) From the Maximum Earth Capacitance graph above, the maximum capacitance

given is 150 nF. d) Therefore the actual system earth capacitance must be less than 150 nF.

Measurement of system compatibility

1) On the existing drive system, i.e. without LeaXield, measure the peak common mode line current.

2) The measurement instrumentation must have a bandwidth that includes the lowest drive carrier frequency. Suitable devices might be: Doepke DRCA1; RF current probe and oscilloscope with relevant correction factors; or other suitable.

3) The peak line common mode current measured without LeaXield must be no greater than 1 A.

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Preliminary data

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Typical measurement results LeaXield will typically provide insertion loss of system common mode and earth leakage currents as shown in the following plots.

Leakage current – time domain. No LeaXield. Peak residual current is 600 mA

Leakage current – time domain. With LeaXield. Peak residual current is < 20 mA. Sourced from power frequency harmonics.

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Preliminary data

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Leakage current – frequency domain. No LeaXield. Carrier frequency of 6 kHz is 250 mA exceeding the RCD trip limit.

Leakage current – frequency domain. With LeaXield. Carrier frequency of 6 kHz is 3 mA.

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EMC conducted emissions. No LeaXield. Emissions exceed C2 limit.

EMC conducted emissions. With LeaXield. Emissions comply with C2 limit.

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Preliminary data

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Exceptions

LeaXield provides only limited differential mode attenuation. LeaXield provides for extremely low earth leakage current on its line-side. Leakage on its load-side remains unchanged. If necessary the user must take measures to comply with any system related safety requirements. LeaXield does not support IT systems or corner earthed power systems. Fault analysis table

Fault Description Likely cause Corrective action

1.1

No attenuation

Line / load orientation not correct

Reconnect with correct line / load orientation

1.2 Power line harmonics exceed EN 50160

Improve power quality

1.3 No power line filter on load-side of LeaXield

Reconnect with suitable power line filter on load-side of LeaXield

1.4 Phase not connected Check that all phases are connected

2.1

Low attenuation

Earth capacitance too high for system carrier frequency

Increase system carrier frequency or use filter with higher insertion loss

2.2 Earth capacitance too high for power line filter installed

Increase system carrier frequency or use filter with higher insertion loss

3.1 EMC emissions high

Differential mode emission dominant

Apply line filter with improved differential mode insertion loss

4.1

RCD tripping

Switch-on inrush current Used RCD with lower sensitivity to in-rush

4.2 Earth leakage from power frequency harmonics too high

Check in particular fundamental and 3rd, 9th and 15th harmonics

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application note 3-line filters active common mode line ... · application note . preliminary data...

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