Danfoss FC 300, FC 200, FC 100 Design guide

MAKING MODERN LIVING POSSIBLE

Output Filters Design Guide

VLT® AutomationDrive FC 300

VLT® AQUA Drive FC 200

VLT® HVAC Drive FC 100

Contents	Output Filters Design Guide

Contents

1 How to Read this Design Guide	3
1.1.2 Abbreviations	3
2 Safety and Conformity	4
2.1 Safety Precautions	4
2.1.1 CE Conformity and Labelling	4
3 Introduction to Output Filters	5
3.1 Why use Output Filters	5
3.2 Protection of Motor Insulation	5
3.2.1 The Output Voltage	5
3.3 Reduction of Motor Acoustic Noise	7
3.4 Reduction of High Frequency Electromagnetic Noise in the Motor Cable	8
3.5 What are Bearing Currents and Shaft Voltages?	9
3.5.1 Mitigation of Premature Bearing Wear-Out	9
3.5.2 Measuring Electric Discharges in the Motor Bearings	10
3.6 Which Filter for which Purpose	12
3.6.1 dU/dt Filters	12
3.6.2 Sine-wave Filters	14
3.6.3 High-Frequency Common-Mode Core Kits	16
4 Selection of Output Filters	17
4.1 How to Select the Correct Output Filter	17
4.1.1 Product Overview	17
4.1.2 HF-CM Selection	19
4.2 Electrical Data - dU/dt Filters	20
4.3 Electrical Data - Sine-wave Filters	22
4.3.1 Spare Parts/Accessories	27
4.3.2 Cable Glands for Floor Standing Filters	27
4.3.3 Terminal Kits	28
4.4 Sine-Wave Filters	29
4.4.1 dU/dt Filters	30
4.4.2 Sine-Wave Foot Print Filter	31
5 How to Install	32
5.1 Mechanical Mounting	32
5.1.1 Safety Requirements for Mechanical Installation	32
5.1.2 Mounting	32
5.1.3 Mechanical Installation of HF-CM	32
5.1.4 Earthing of Sine-wave and dU/dt Filters	33

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Contents	Output Filters Design Guide

5.1.5 Screening	33
5.2 Mechanical Dimensions	34
5.2.1 Sketches	34

6 How to Programme the Frequency Converter	43
6.1.1 Parameter Settings for Operation with Sine-wave Filter	43
Index	44

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How to Read this Design Gui... Output Filters Design Guide

1 How to Read this Design Guide	1	1

This Design Guide will introduce all aspects of output filters for your frequency converter; from choosing the right output filter for the application to instructions about how to install it and how to program the frequency converter.

Danfoss technical literature is also available online at www.danfoss.com/BusinessAreas/DrivesSolutions/Documentations/Technical+Documentation.

1.1.1 Symbols

Symbols used in this manual

NOTE

Indicates something to be noted by the reader.

CAUTION

Indicates a general warning.

WARNING

Indicates a high-voltage warning.

Indicates default setting

1.1.2 Abbreviations

Alternating current	AC
American wire gauge	AWG
Ampere/AMP	A
Automatic Motor Adaptation	AMA
Current limit	ILIM
Degrees Celsius	°C
Direct current	DC
Drive Dependent	D-TYPE
Electro Magnetic Compatibility	EMC
Electronic Thermal Relay	ETR
Drive	FC
Gram	g
Hertz	Hz
Kilohertz	kHz
Local Control Panel	LCP
Meter	m
Millihenry Inductance	mH
Milliampere	mA
Millisecond	ms
Minute	min
Motion Control Tool	MCT
Nanofarad	nF
Newton Meters	Nm
Nominal motor current	IM,N
Nominal motor frequency	fM,N
Nominal motor power	PM,N
Nominal motor voltage	UM,N
Parameter	par.
Protective Extra Low Voltage	PELV
Rated Inverter Output Current	IINV
Revolutions Per Minute	RPM
Second	sec.
Synchronous Motor Speed	ns
Torque limit	TLIM
Volts	V
IVLT,MAX	The maximum output current.
IVLT,N	The rated output current
	supplied by the frequency
	converter.

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Safety and Conformity	Output Filters Design Guide

2 Safety and Conformity

2 2

2.1 Safety Precautions

Equipment containing electrical components may not be disposed of together with domestic waste.

It must be separately collected with electrical and electronic waste according to local and currently valid legislation.

MCC 101/102

Design Guide

2.1.1 CE Conformity and Labelling

What is CE Conformity and Labelling?

The purpose of CE labelling is to avoid technical trade obstacles within EFTA and the EU. The EU has introduced the CE label as a simple way of showing whether a product complies with the relevant EU directives. The CE label says nothing about the specifications or quality of the product. The low-voltage directive (73/23/EEC)

Frequency converters must be CE labelled in accordance with the low-voltage directive of January 1, 1997. The directive applies to all electrical equipment and appliances used in the 50 - 1000V AC and the 75 - 1500V DC voltage ranges. Danfoss CE-labels in accordance with the directive and issues a declaration of conformity upon request.

Warnings

NOTE

Never attempt to repair a defect filter.

NOTE

The filters presented in this design guide are specially designed and tested for Danfoss frequency converters (FC 102/202/301 and 302). Danfoss takes no resposibility for the use of third party output filters.

NOTE

The phased out LC-filters that were developed for the VLT5000 series and are not compatible with the VLT FC 100/200/300.

However, the new filters are compatible with both FC-series and VLT 5000-series

NOTE

690V applications:

For motors not specially designed for frequency converter operation or without double insulation, Danfoss highly recommend the use of either dU/dt or Sine-Wave filters.

NOTE

Sine-wave filters can be used at switching frequencies higher than the nominal switching frequency, but should never be used at switching frequencies with less than 20% lower than the nominal switching frequency.

NOTE

dU/dt filters, unlike Sine-wave filters, can be used at lower switching frequency than the nominal switching frequency, but higher switching frequency will cause overheating of the filter and should be avoided.

CAUTION

When in use the filter surface temperature rises. DO NOT touch the filter during operation.

WARNING

Never work on a filter in operation. Touching the electrical parts may be fatal - even after the equipment has been disconnected from the frequency converter or motor.

WARNING

Before servicing the filter, wait at least the voltage discharge time stated in the Design Guide for the corresponding frequency converter to avoid electrical shock hazard.

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Introduction to Output Filt...	Output Filters Design Guide

3 Introduction to Output Filters

3.1 Why use Output Filters

This chapter describes why and when to use Output Filters with Danfoss frequency converters. It is divided into 4 sections:

•Protection of Motor Insulation

•Reduction of Motor Acoustic Noise

•Reduction of High Frequency Electromagnetic Noise in Motor Cable

•Bearing currents and shaft voltage

3.2Protection of Motor Insulation

3.2.1 The Output Voltage

The output voltage of the frequency converter is a series of trapezoidal pulses with a variable width (pulse width modulation) characterized by a pulse rise-time tr.

When a transistor in the inverter switches, the voltage across the motor terminal increases by a dU/dt ratio that depends on:

•

3 3

the motor cable (type, cross-section, length, screened or unscreened, inductance and capacitance)

•the high frequency surge impendance of the motor

Because of the impedance mismatch between the cable characteristic impedance and the motor surge impedance a wave reflection occurs, causing a ringing voltage overshoot at the motor terminals - see Illustration 3.1. The motor surge impedance decreases with the increase of motor size resulting in reduced mismatch with the cable impedance. The lower reflection coefficient (Γ) reduces the wave reflection and thereby the voltage overshoot. Typical values are given in Table 3.1.

In the case of parallel cables the cable characteristic impedance is reduced, resulting in a higher reflection coefficient higher overshoot. For more information please see IEC 61800-8.

Illustration 3.1 Example of Converter Output Voltage (dotted line) and Motor Terminal Voltage After 200m of Cable (solid line)

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Introduction to Output Filt...	Output Filters Design Guide

Typical values for the rise time and peak voltage UPEAK are measured on the motor terminals between two phases.

Two different definitions for the risetime tr are used in practice. The international IEC standards define the rise-time

3 3 as the time between 10% to 90% of the peak voltage Upeak. The US National Electrical Manufacturers Association (NEMA) defines the rise-time as the time between 10% and 90% of the final, settled voltage, that is equal to the DC link voltage UDC. See Illustration 3.2 and Illustration 3.3.

To obtain approximate values for cable lengths and voltages not mentioned below, use the following rules of thumb:

1.Rise time increases with cable length.

2.UPEAK = DC link voltage x (1+Γ); Γ represents the reflection coefficient and typical values can be found in table below

(DC link voltage = Mains voltage x 1.35).

3.	dU/dt =	0.8	× UPEAK		(IEC)
			tr
	dU/dt =	0.8	× UDC	(NEMA)
		tr(NEMA )

(For dU/dt, rise time, Upeak values at different cable lengths please consult the drive Design Guide)

Motor power [kW]	Zm [Ω]	Γ
<3.7	2000 - 5000	0.95
90	800	0.82
355	400	0.6

Table 3.1 Typical Values for Reflection Coefficients (IEC 61800-8).

The IEC and NEMA Definitions of Risetime tr

Illustration 3.2 IEC

Illustration 3.3 NEMA

Various standards and technical specifications present limits of the admissible Upeak and tr for different motor types. Some of the most used limit lines are shown in Illustration 3.4

•IEC 60034-17 – limit line for general purpose motors when fed by frequency converters, 500V motors.

•IEC 60034-25 – limit for converter rated motors: curve A is for 500V motors and curve B is for 690V motors.

•NEMA MG1 – Definite purpose Inverter Fed Motors.

If, in your application, the resulting Upeak and tr exceed the limits that apply for the motor used, an output filter should be used for protecting the motor insulation.

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Introduction to Output Filt...	Output Filters Design Guide

3 3

Illustration 3.4 Limit Lines for Upeak and Risetime tr.

3.3 Reduction of Motor Acoustic Noise

The acoustic noise generated by motors has three main sources.

1.The magnetic noise produced by the motor core, through magnetostriction

2.The noise produced by the motor bearings

3.The noise produced by the motor ventilation

When a motor is fed by a frequency converter, the pulsewidth modulated (PWM) voltage applied to the motor causes additional magnetic noise at the switching frequency and harmonics of the switching frequency (mainly the double of the switching frequency). In some applications this is not acceptable. In order to eliminate this additional switching noise, a sine-wave filter should be used. This will filter the pulse shaped voltage from the frequency converter and provide a sinusoidal phase-to-phase voltage at the motor terminals.

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Introduction to Output Filt... Output Filters Design Guide

3.4 Reduction of High Frequency Electromagnetic Noise in the Motor Cable

		When no filters are used, the ringing voltage overshoot that occurs at the motor terminals is the main high-frequency noise
		source. Illustration 3.5 shows the correlation between the frequency of the voltage ringing at the motor terminals and the
		spectrum of the high-frequency conducted interference in the motor cable.
3	3	Besides this noise component, there are also other noise components such as:

•The common-mode voltage between phases and ground at the switching frequency and its harmonics - high amplitude but low frequency.

•High-frequency noise (above 10MHz) caused by the switching of semiconductors - high frequency but low amplitude.

Illustration 3.5 Correlation Between the Frequency of the Ringing Voltage Overshoot and the Spectrum of Noise Emissions.

When an output filter is installed following effect is achieved:

•In the case of dU/dt filters the frequency of the ringing oscillation is reduced below 150kHz.

•In the case of sine-wave filters the ringing oscillation is completely eliminated and the motor is fed by a sinusoidal phase-to-phase voltage.

Remember, that the other two noise components are still present. This is illustrated in the conducted emission measurements shown in Illustration 3.7 and Illustration 3.8. The use of unshielded motor cables is possible, but the layout of the installation should prevent noise coupling between the unshielded motor cable and the mains line or other sensitive cables (sensors, communication, etc.). This can be achieved by cable segregation and placement of the motor cable in a separate, continuous and grounded cable tray.

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Introduction to Output Filt...	Output Filters Design Guide

3.5What are Bearing Currents and Shaft Voltages?

Fast switching transistors in the frequency converter combined with an inherent common-mode voltage (voltage between phases and ground) generate high-frequency bearing currents and shaft voltages. While bearing currents and shaft voltages can also occur in direct-on-line motors, these phenomena are accentuated when the motor is fed from a frequency converter. The majority of bearing damages in motors fed by frequency converters are because of vibrations, misalignment, excessive axial or radial loading, improper lubrication, impurities in the grease. In some cases, bearing damages are caused by bearing currents and shaft voltages. The mechanism that causes bearing currents and shaft voltages is quite intricate and beyond the scope of this Design Guide. Basically, two main mechanisms can be identified:

•Capacitive coupling: the voltage across the bearing is generated by parasitic capacitances in the motor.

•Inductive coupling: caused by circulating currents in the motor.

The grease film of a running bearing behaves like isolation. The voltage across the bearing can cause a breakdown of the grease film and produce a small electric discharge (a spark) between the bearing balls and the running track. This discharge produces a microscopic melting of the bearing ball and running track metal and in time it causes the premature wear-out of the bearing. This mechanism is called Electrical Discharge Machining or EDM.

Measures that isolate the motor shaft from the load
•	Use isolated bearings (or at least one isolated
	bearing at the non-driving end NDE).
•	Prevent shaft ground current by using isolated
	couplings.	3	3
Mechanical measures

•Make sure that the motor and load are properly aligned.

•Make sure the loading of the bearing (axial and radial) is within the specifications.

•Check the vibration level in the bearing.

•Check the grease in the bearing and make sure the bearing is correctly lubricated for the given operating conditions.

One of the mitigation measures is to use filters. This can be used in combination with other measures, such as those presented above. High-frequency common-mode (HF-CM) filters (core kits) are specially designed for reducing bearing stress. Sine-wave filters also have a good effect. dU/dt filters have less effect and it is recommended to use them in combination with HF-CM cores.

3.5.1Mitigation of Premature Bearing WearOut

There are a number of measures that can be taken for preventing premature wearing and damage of the bearings (not all of them are applicable in all cases – combinations can be used). These measures aim either to provide a lowimpedance return path to the high-frequency currents or to electrically isolate the motor shaft for preventing currents through the bearings. Besides, there are also mechanical related measures.

Measures to provide a low-impedance return path

•Follow EMC installation rules strictly. A good highfrequency return path should be provided between motor and frequency converter, for example by using shielded cables.

•Make sure that the motor is properly grounded and the grounding has a low-impedance for highfrequency currents.

•

•

Provide a good high-frequency ground connection between motor chassis and load.

Use shaft grounding brushes.

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Introduction to Output Filt...	Output Filters Design Guide

3.5.2Measuring Electric Discharges in the Motor Bearings

The occurrence of electric discharges in the motor bearings can be measured using an oscilloscope and a brush to pick

3 3 up the shaft voltage. This method is difficult and the interpretation of the measured waveforms requires a deep understanding of the bearing current phenomena. An easy alternative is to use an electrical discharge detector (130B8000), as shown in Illustration 3.6. Such a device consists of a loop antenna that receives signals in the frequency range of 50MHz – 200MHz and a counter. Each electric discharge produces an electromagnetic wave that is detected by the instrument and the counter is incremented. If the counter displays a high number of discharges it means that there are many discharges occurring in the bearing and mitigation measures have to be taken to prevent the early wear out of the bearing. This instrument can be used for experimentally determining the exact number of cores needed to reduce bearing currents. Start with a set of 2 cores. If the discharges are not eliminated, or drastically reduced, add more cores. The number of cores presented in the table above is a guiding value that should cover most applications with a generous safety margin. If the cores are installed on the drive terminals and you experiment core saturation because of long motor cables (the cores have no effect on bearing currents), check the correctness of the installation. If cores keep saturating after the installation is made according to EMC best practice, consider moving the cores to the motor terminals.

<![if ! IE]>

<![endif]>130BB729.10

129

50 - 200 MHz

130B8000

Illustration 3.6 Electrical Discharge Detector

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Introduction to Output Filt...

Output Filters Design Guide

<![if ! IE]>

<![endif]>Level in dBµV

Frequency in Hz

Illustration 3.7 Mains Line Conducted Noise, No Filter

Illustration 3.8 Mains Line Conducted Noise, Sine-wave Filter

<![if ! IE]>

<![endif]>130BT119.10

3 3

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Introduction to Output Filt...	Output Filters Design Guide

3.6 Which Filter for which Purpose

Table 3.2 shows a comparison of dU/dt, Sine-wave filter, and HF-CMperformance. It can be used to determine which filter to use with your application.

3		3		Performance criteria	dU/dt filters	Sine-wave filters		High-frequency common-mode filters
				Motor insulation	Up to 150m cable (screened/	Provides a sinusoidal phase-to-phase		Does not reduce motor insulation stress
				stress	unscreened) complies with the	motor terminal voltage. Complies with
					requirements of IEC 60034-171	IEC 60034-17 1 and NEMA-MG1
					(general purpose motors). Above	requirements for general purpose
					this cable length the risk of “double	motors with cables up to 500m (1km for
					pulsing” (two time mains network	VLT frame size D and above).
					voltage) increases.
				Motor bearing stress	Slightly reduced, only in high-	Reduces bearing currents caused by		Reduces bearing stress by limiting
					power motors.	circulating currents. Does not reduce		common-mode high-frequency
						common-mode currents (shaft		currents
						currents).
				EMC performance	Eliminates motor cable ringing.	Eliminates motor cable ringing. Does		Reduces high-frequency emissions
					Does not change the emission class.	not change the emission class. Does not		(above 1MHz). Does not change the
					Does not allow longer motor cables	allow longer motor cables as specified		emission class of the RFI filter. Does not
					as specified for the frequency	for the frequency converter’s built-in		allow longer motor cables as specified
					converter’s built-in RFI filter.	RFI filter.		for the frequency converter.
				Max. motor cable	100m ... 150m	With guaranteed EMC performance:		150m screened (frame size A, B, C), 300
				length	With guaranteed EMC performance:	150m screened and 300m unscreened.		m screened (frame size D, E, F), 300 m
					150m screened.	Without guaranteed EMC performance:		unscreened
					Without guaranteed EMC	up to 500m (1km for VLT frame size D
					performance: 150m unscreened.	and above)
				Acoustic motor	Does not eliminate acoustic	Eliminates acoustic switching noise		Does not eliminate acoustic switching
				switching noise	switching noise.	from the motor caused by magneto-		noise.
						striction.
				Relative size	15-50% (depending on power size)	100%		5 - 15%
				Voltage drop	0.5%	4-10%		none
				Table 3.2 Comparison of dU/dt and Sine-wave Filters
				1) Not 690V.		Advantages
				2) See general specification for formula.
				3.6.1 dU/dt Filters		•	Protects the motor against high dU/dt values and
							voltage peaks, hence prolongs the lifetime of the

motor

The dU/dt filters consist of inductors and capacitors in a low pass filter arrangement and their cut off frequency is above the nominal switching frequency of the frequency converter. The inductance (L) and capacitance (C) values are shown in the tables in 4.2 Electrical Data - dU/dt Filters. Compared to Sine-wave filters they have lower L and C values, thus they are cheaper and smaller. With a dU/dt filter the voltage wave form is still pulse shaped but the current is sinusoidal - see following illustrations.

Features and benefits

dU/dt filters reduce the voltage peaks and dU/dt of the pulses at the motor terminals. The dU/dt filters reduce dU/dt to approx. 500V/μs.

•Allows the use of motors which are not specifically designed for converter operation, for example in retrofit applications

Application areas

Danfoss recommends the use of dU/dt filters in the following applications:

•Applications with frequent regenerative braking

•Motors that are not rated for frequency converter operation and not complying with IEC 600034-25

•Motors placed in aggressive environments or running at high temperatures

•Applications with risk of flash over

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•Installations using old motors (retrofit) or general purpose motors not complying with IEC 600034-17

•	Applications with short motor cables (less than			<![if ! IE]> <![endif]>130BB113.11
	15m)
•	690V applications			3	3
Voltage and current with and without dU/dt filter:		<![if ! IE]> <![endif]>[kV]
		<![if ! IE]> <![endif]>Upeak	50M DV/DT FILTER
				150M DV/DT FILTER
			15M DV/DT FILTER
			rise time [µs]
		Illustration 3.11 Measured dU/dt values (rise time and peak
		voltages) with and without dU/dt filter using 15m, 50m and 150m
		cable lengths on a 400V, 37kW induction motor.

		The dU/dt value decreases with the motor cable length
		whereas the peak voltage increases (see Illustration 3.11). The
		Upeak value depends on the Udc from the frequency converter
		and as Udc increases during motor braking (generative) Upeak
		can increase to values above the limits of IEC 60034-17 and
Illustration 3.9 Without Filter		thereby stress the motor insulation. Danfoss therefore
		recommends dU/dt filters in applications with frequent
		braking. Furthermore the illustration above shows how the
		Upeak increases with the cable length. As the cable length
		increases, the cable capacitance rises and the cable behaves
		like a low-pass filter. That means longer rise-time tr for longer
		cables. Therefore it is recommended to use dU/dt filters only
		in applications with cable lengths up to 150m. Above 150m
		dU/dt filters have no effect. If further reduction is needed,
		use a sine-wave filter.
		Filter features

•

•

•

•

IP00 and IP20/23/54 enclosure in the entire power range

Side by side mounting with the drive

Reduced size, weight and price compared to the sine-wave filters

Possibility of connecting screened cables with included decoupling plate

Illustration 3.10 With dU/dt Filter	•	Compatible with all control principles including
		flux and VVCPLUS
	•	Filters wall mounted up to 177A and floor mounted
		above that size

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Introduction to Output Filt...	Output Filters Design Guide

3 3

Illustration 3.12 525V - With and Without dU/dt Filter

Illustration 3.13 690V - With and Without dU/dt Filter

Source: Test of 690V 30kW VLT FC 302 with MCC 102 dU/dt filter

Illustration 3.12 and Illustration 3.13 show how Upeak and rise time behaves as a function of the motor cable length. In installations with short motor cables (below 5-10m) the rise time is short which causes high dU/dt values. The high dU/dt can cause a damaging high potential difference between the windings in the motor which can lead to breakdown of the insulation and flash-over. Danfoss therefore recommends dU/dt filters in applications with motor cable lengths shorter than 15m.

3.6.2 Sine-wave Filters

Sine-wave filters are designed to let only low frequencies pass. High frequencies are consequently shunted away which results in a sinusoidal phase to phase voltage waveform and sinusoidal current waveforms. With the sinusoidal waveforms the use of special frequency converter motors with reinforced insulation is no longer needed. The acoustic noise from the motor is also damped as a consequence of the sinusoidal wave condition. The sinewave filter also reduces insulation stress and bearing currents in the motor, thus leading to prolonged motor lifetime and longer periods between services. Sine-wave filters enable use of longer motor cables in applications where the motor is installed far from the frequency converter. As the filter does not act between motor phases and ground, it does not reduce leakage currents in the cables. Therefore the motor cable length is limited - see

Table 3.2.

The Danfoss Sine-wave filters are designed to operate with the VLT® FC 100/200/300. They replace the LC-filter product range and are backwards compatible with the VLT 5000-8000 Series Drives. They consist of inductors and capacitors in a low-pass filter arrangement. The inductance

(L) and capacitance (C) values are shown in tables in

4.3 Electrical Data - Sine-wave Filters.

Features and benefits

As described above, Sine-wave filters reduce motor insulation stress and eliminate switching acoustic noise from the motor. The motor losses are reduced because the motor is fed with a sinusoidal voltage, as shown in Illustration 3.12. Moreover, the filter eliminates the pulse reflections in the motor cable thus reducing the losses in the frequency converter.

Advantages

•Protects the motor against voltage peaks hence prolongs the lifetime

•Reduces the losses in the motor

•Eliminates acoustic switching noise from the motor

•Reduces semiconductor losses in the drive with long motor cables

•Decreases electromagnetic emissions from motor cables by eliminating high frequency ringing in the cable

•Reduces electromagnetic interference from unscreened motor cables

•Reduces the bearing current thus prolonging the lifetime of the motor

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