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MTE Corporation Improving the Performance and Reliability of Power Electronic Systems 2
MTE solutions to Long lead dive applications Protection of motors drive cables and Variable frequency inverters 3
The opportunity IGBT devices are used in all modern switching inverter drives. These devices are pushed to operate at higher operating speeds to increase drive efficiency. Problems occur when higher switching speed and motor lead length are combined causing a dv/dt resonance that produces standing waves 4 X the bus voltage. Copper and wire cost are increasing consider protection of both the motor and cable as well. Not all motors are inverter drive compatible these motors need sine wave protection. It might be cheaper to buy a filter than to replace the motor and suffer down time. 4
System diagram 5
Motor cable The motor cable is really a complex transmission line made up of resistance inductance and capacitance. As the length increases so does the complexity it adds to the motor drive system. 6
Inconsistencies in cable 7
The complex motor winding 8
Drive output vs voltage at the motor Voltage At the motor Voltage from the VFD 9
Distance and rise time create over voltage at motor 10
Drive rated motor breakdown NEMA MG1 part 31 11
Switching related problems 12
More switching problems 13
Corona Discharge Physics explains: between current carrying conductors a electric field is established. Corona forms when voltage potential in wires reaches the inception voltage (CIV) which is a function of spacing, insulation type, surfaces, environmental conditions. If field strength is high enough air will breakdown or become ionized by the corona. Air ionizes if energy is high enough to change (02) into ozone (03). Highly reactive ozone working with oxygen breaks down and deteriorates wire insulation compounds Long term and short term effects can be catastrophic! 14
Switching an inductor Results in high energy arcing 15
First turn arc 16
Cable failure 17
Drive Manufactures suggest Minimize distance to motor Use inverter duty motors MG-1 section 31.4 with 1600 volt rating beyond 150 feet Use application specific drive motor cables Set switching frequency as low as possible without causing audible noise problems Use 3 phase reactor for 100 foot Use advanced filtering 300 to 1000 foot Call MTE 18
STANDARD MTE output protection products AC Line / Load Reactors (Single element filter) Series A dv/dt Filters (High order LRC filter) Series A 2-8 Khz Sine Wave filters (High order LRC filter) LC 5Khz sine wave filters (dual element L & C) 19
Standard RL Line/Load Reactors 1 2100 Amps 20
RL protection summary Low cost motor protection device Low cost long lead dv/dt filter up to 300ft MTE reactors can be used in both line and load applications the same one. Load reactors extend motor life (heat reduced) Load reactors decrease motor noise Helps protect motor cables as well Protects the drive by allowing the short circuit protection to work 21
Reactor performance Motor terminal voltage at 300 feet 2 khz switching 22
Standard DV/DT Filters 3 600 Amps 23
Highlights of series A dv/dt filters 1000 foot guarantee motor voltage will not exceed 1.5 X supply bus voltage Operates 900Hz-8 khz switch frequency. dc to 90 Hz drive fundamental Good operational results at 3000 feet. Reduces some motor noise Reduces some motor heating. NOT recommended multi motor applications 24
Series A dv/dt performance 22 Amp dv/dt Overall Performance 30hp 480 Vac Motor 1.80 1.60 Peak Voltage at Motor in K volts 1.40 1.20 1.00 0.80 0.60 0.40 Unfiltered With dv/dt 1.5 x Bus Drive Bus 0.20 0.00 100 FT 500 FT 1000 FT Cable Length 25
dv/dt visible performance 1000 foot shielded cable at 8kHz switching 26
Large dv/dt filter 27
Series A Sine Wave Filters 3 1200 Amps 28
Highlights of the series A sine wave filter Provide a 5% THVD sine-wave output voltage. Protect non drive rated motors. Ensure motor cable voltage doesn't exceed 900volts 2-8 KHz switching frequency range. Reduce electro-magnetic interference (EMI/RFI) Eliminate all the high dv/dt from long-lead runs Long lead protection 15,000 feet. Eliminate motor audible noise and heat attributed to PWM inverter drives. Step up transformers not required to be K rated Use one filter for many motors. Don t oversize filter to drive. 29
Series A sine wave performance 30
Custom Engineered Sine Wave Filters Feeding Motors and Transformers in open Panel, NEMA 1, 2, & 3R configurations up to 1500 amps 31
5 khz LC sine wave filter Classic dual element filter sine wave filter Inverter frequency not set below 5 KHz. Convert a PWM inverter output wave form into a 10% THVD sinusoidal wave form. Not recommended for new applications Restricted to 480 volts & >5kHz switching. 32
5 khz sine filter 33
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