External Drive Hardware

Transcription

1 US1086e_External Drive Hardware, 08/2010 External Drive Hardware Selection and Application Answers Answers to external hardware questions A soup to nuts list of questions with installation / application sensitive answers Do I need an inverter duty motor? Do I need a dv/dt filter? Do I need a sine filter? Do I need a common mode filter? Do I need a EMI filter? Can I use a circuit breaker to protect my drive? How can I avoid motor bearing current damage? Well, that all depends! Slide 2

2 What is an inverter duty motor? Basic standard NEMA MG1 Part 31, Definite-Purpose Inverter-Fed Polyphase Motors Speed-torque capability , Basis of Rating 4 characteristic points on speed vs. torque curve Peak voltage tolerance , Voltage Spikes V peak = 3.1 x V rated (minimum) (1550 V for 500 Vac motor) Rise time = 0.1 µs (minimum) Shaft voltage and bearing currents , Shaft Voltages and Bearing Insulation Information and recommendations (no requirements) Slide 3 Why consider using an inverter duty motor? Standard motors are designed for 60 Hz operation from a sinusoidal source Reduced frequency, reduced voltage torque capabilities are not explicitly defined Extended insulation capability is not provided In some drive installations / applications overheating or insulation failure could occur Inverter duty motors are designed for variable frequency operation from a PWM inverter source Reduced frequency, reduced voltage torque capabilities are explicitly defined Extended insulation capability is provided Installation / application overheating and insulation failure are avoided by motor design Increases motor reliability and life Slide 4

3 Do I need an inverter duty motor? ABB recommends inverter duty motors for all drives Inverter duty motors are especially important when motor lead lengths are long > 20 feet for 5 Hp or less > 50 feet for 25 Hp or less > 100 feet for all higher Hp drive voltage rise/fall times are rapid typically includes all IGBT drives constant torque applications which require well defined continuous low speed torque capability dv/dt filters and sine filters can provide an alternative when existing non-inverter duty motors are present filters address peak voltage and rise/fall time issues filters do not improve speed-torque capability Slide 5 What is a dv/dt filter? dv/dt rate of change of voltage per unit time (2000 to 6500 V/µs typical) dv/dt filter physical characteristics passive device installed between drive output and motor input includes inductive, capacitive, and resistive elements series inductors carry full rated motor current dv/dt filter functional characteristics designed to pass low frequency, filter out high frequency (i.e. a low pass filter) reduces dv/dt applied to motor reduces peak voltage applied to motor (addresses voltage reflection / voltage ringing) not designed to eliminate drive switching frequency not designed to provide common mode filtering Slide 6

4 Why consider using a dv/dt filter? Advantages of installing a dv/dt filter reduces peak voltage at motor terminals reduces dv/dt at motor terminals reduces peak cable charging current Disadvantages of installing a dv/dt filter Additional cost Additional space requirement Some additional voltage drop (approximately 1.5% at rated load) Additional losses (lowers efficiency) Imposes limits on maximum operating frequency limited to motor cable lengths of approximately 1500 feet or less Slide 7 Do I need a dv/dt filter? A dv/dt filter is not needed for motor insulation protection if: inverter duty motor(s) are installed and no secondary distribution point is involved and motor cable lengths are less than 1000 feet A dv/dt filter should be installed for motor insulation protection if: only standard duty motor(s) are installed or a secondary distribution point is included that is more than 20 feet from the drive or motor cable lengths are more than 1000 feet (significant double pulsing voltage peaks are likely) See Decision Flowchart for additional details and exceptions A dv/dt filter should be installed to reduce peak cable charging current if total motor cable length exceeds hardware manual limit and total motor cable length < 1.5 x hardware manual limit Slide 8

5 What is a sine filter? sine sinusoidal waveform output sine filter physical characteristics passive device installed between drive output and motor input includes inductive, resistive, and capacitive elements series elements carry full rated motor current sine filter functional characteristics designed to pass low frequency, filter out high frequency (i.e. a low pass filter) eliminates switching dv/dt at motor eliminates peak and ringing voltage at motor (no voltage reflection / no voltage ringing) designed to eliminate drive switching frequency not designed to provide common mode filtering Slide 9 Why consider using a sine filter? Advantages of installing a sine filter eliminates peak voltage at motor terminals eliminates dv/dt at motor terminals eliminates cable charging current peaks only positive solution for motor cable lengths beyond 1500 feet Disadvantages of installing a sine filter Significant additional cost Additional space requirement Significant additional voltage drop (approximately 5% at rated load) Often necessitates inclusion of a step-up transformer to insure sufficient motor voltage Transformation ratio may necessitate a larger drive due to increased current loading Additional losses (lowers efficiency) Drive must operate in scalar mode Imposes limits on maximum operating frequency Slide 10 Recommendation: Contact ABB Application Engineering

6 Do I need a sine filter? Install a sine filter if: a dv/dt filter can t provide sufficient motor insulation protection a dv/dt filter can t sufficiently limit cable charging current See Decision Review total voltage drops carefully Flowchart for Sine filter typically has 5% drop at rated load additional details Cables typically have 3% - 5% drop at 1500 feet A custom ratio step-up transformer is often needed Verify that motor voltage starvation won t occur (full speed / full load) Typical Sine Filter Circuit Slide 11 Recommendation: Contact ABB Application Engineering Decision Flowchart for Filter Inclusion Slide 12

7 What is a common mode filter? Common mode (CM) phenomenon voltage and current components three phases (referenced in common) to equipment ground present with inverters due to unsymmetrical output switching Common mode filter physical characteristics passive device installed between drive output and motor input appears as a lossy series inductive element Adds inductance with respect to ground (not between phases) Common mode filter functional characteristics attenuates CM current to ground reduces peak voltage to ground at motor (addresses common mode voltage reflection / voltage ringing) reduces dv/dt to ground at motor doesn t impact phase to phase voltage or current reduces inverter generated EMI (relatively slight impact) Slide 13 Why consider using a common mode filter? Advantages of installing a common mode filter reduces peak voltage to ground at motor terminals reduces dv/dt to ground at motor terminals reduces peak cable charging current to ground reduces drive generated EMI reduces peak shaft voltage (bearing current issue) Disadvantages of installing a common mode filter Additional cost Additional space requirement Additional losses (lowers efficiency) Often not readily available Slide 14

8 Do I need a common mode filter? Install a common mode filter if: Peak cable charging current is an issue even after installing a dv/dt filter (alternatively increase drive size) EMI is an issue even when all motor cable shielding recommendations have been followed (a dedicated EMI filter is more effective) Attenuation of motor bearing currents is desired (other methods provide more effective results) Slide 15 What is an EMI filter? EMI ElectroMagnetic Interference Conducted and/or radiated electrical noise alternatively referenced as EMC electromagnetic compatibility EMI filter physical characteristics passive device installed between the primary power source and the drive input includes series inductance (CM) and shunt capacitive elements series elements carry full rated drive current EMI filter functional characteristics block CM high frequencies from the line pass CM high frequencies from equipment ground to the drive input provide a path for high frequency CM currents to return to the inverter DC bus from which they originate 100 khz to 5 MHz bandpass Reduces EMI in the equipment grounding system Slide 16

9 Why consider using an EMI filter? Advantages of installing an EMI filter reduces EMI in sensitive external equipment provides a well defined high frequency CM ground return path Disadvantages of installing an EMI filter Additional cost Additional space requirement Slide 17 Do I need an EMI filter? Install an EMI filter if: The EMC Directive must be met (i.e. CE system compliance is required) EMI is an installation issue even though all motor cable shielding recommendations are in place Radio reception is a problem and line side cabling is suspected as the radiating source Slide 18

10 What protection does a circuit breaker provide? Circuit breakers can protect drive input cables (overload, short circuit, ground fault) serve as a drive disconnect Circuit breakers can not protect drive semiconductors (diodes, IGBTs) limit drive short circuit currents to a safe level limit drive I 2 t fault energy to a safe level guarantee that drive equipment will not rupture guarantee that a drive internal fault won t lead to a fire Slide 19 What protection do fuses provide? Fuses (as specified in ABB product manuals) can limit drive short circuit current to a safe level limit drive I 2 t fault energy to a safe level guarantee that drive equipment will not rupture guarantee that a drive internal fault won t lead to a fire protect drive input cables (overload, short circuit, ground fault) if properly coordinated by the installer Fuses (as specified in ABB product manuals) can not protect drive semiconductors (diodes, IGBTs) serve as a drive disconnect Slide 20

11 Can I use a circuit breaker to provide drive protection? In general circuit breakers can not be used to provide drive protection Exception: Drives installed on networks with low available short circuit current may be sufficiently protected by a fast acting circuit breaker However, confirming protection is complex and requires complete knowledge of both the network and the drive equipment ABB s recommendation is to provide drive protection utilizing the fuses as specified in our product literature Slide 21 What are high frequency motor bearing currents? High frequency motor bearing currents are PWM drive sourced, capacitively induced, discharge currents that may damage motor bearings if of sufficient magnitude These currents may occur due to three different circuit actions which can occur individually or in combination High Frequency Circulating (motor) High Frequency Capacitive Coupling (motor or driven load) High Frequency Frame Voltage (Shaft Grounding) (motor or driven load) Equivalent circuit diagrams follow Slide 22

12 High Frequency Circulating Inverter Motor Z C M Z CG M R MB R MB V ZS C SF C MB Z MBNL C MB Z MBNL Z MAG Normally only occurs in larger motors ( 100 hp) Slide 23 High Frequency Capacitive Coupling Inverter Motor Driven Machine Z C C SR R SFT Z CG M R MB R DMB V ZS C SF C RF C MB Z MBNL C DMB Z DMBNL Z MAG Z DMG Most prominent in smaller motors ( 20 hp) Slide 24

13 High Frequency Frame Voltage (Shaft Grounding) Inverter Motor Driven Machine Z C C SR R SFT Z CG M R MB R DMB V ZS C SF C RF C MB Z MBNL C DMB Z DMBNL Z MAG Z DMG Can only occur in applications where the motor shaft is grounded through the driven load. Slide 25 Do I need to provide motor bearing current protection? It is impractical to predict whether high frequency bearing currents will be a problem at a particular site due to the number of application variables involved motor size motor cable grounding driven load grounding motor bearing design motor air gap design motor magnetic symmetry bearing loading load speed variability If it is economically feasible to address high frequency bearing current issues proactively (i.e. insurance) utilize the two charts following to determine recommended actions Slide 26

14 Preventing Motor Bearing Currents Preventative Measure - Motor Bearing Current Type Grounding Brush Armored / Shielded Cable Single Insulated Bearing Double Insulated Bearing Common Mode Choke Insulated Drive Coupling A. High Frequency Circulating S S R B. High Frequency CapacitiveCoupling S S R C. High Frequency Frame Voltage (Shaft Grounding) S R S R S S = Solves R = Reduces Recommended Solution Slide 27 Note: Grounding brush and insulated bearing must be on opposite shaft ends. Preventing Driven Load Bearing Currents Preventative Measure - Driven Load Bearing Current Type Grounding Brush Armored / Shielded Cable Single Insulated Bearing Double Insulated Bearing Common Mode Choke Insulated Drive Coupling B. High Frequency CapacitiveCoupling R S C. High Frequency Frame Voltage (Shaft Grounding) R R S R S S = Solves R = Reduces Recommended Solution Slide 28

15 Grounding Device Effectiveness Before Grounding Device After Grounding Device Slide 29