Motor Protection Functions under IEEE C37-2
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11/4/2019
sin-perfect-harmony-gh180-AMP-slides-en.pptx
Motor Protection Functions under IEEE C37-2
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11/4/2019
sin-perfect-harmony-gh180-AMP-slides-en.pptx
Motor protection for machines controlled by a drive ➢ Many protection functions become unnecessary in a Harmony drive because the drive output and motor are isolated from ground ▪ A ground fault affects the voltage distribution to ground but does not draw significant fault current ▪ Operation can continue in the presence of a ground fault as long as the occurrence of a second fault does not result in a hazardous condition due to the combination of ground resistance and fault current
➢ Ground isolation can only be exploited if a ground fault can be detected ▪ Zero sequence overvoltage (59G) (residual voltage detection) ▪ Insulation monitoring
➢ The necessity for ground fault protection is eliminated
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sin-perfect-harmony-gh180-AMP-slides-en.pptx
Advanced Motor Protection Functions – Built into the Drive ➢ The following functions are implemented in the Harmony Advanced Motor Protection functions: ▪ Overspeed (12) ▪ Underspeed (14) ▪ Machine Thermal Model (49T) ▪ Zero sequence overvoltage (59G) ▪ Inverse Time Overcurrent (51) ▪ Undercurrent (37) and Underpower (37P) ▪ Incomplete Sequence – maximum start time/ maximum stop time (48) ▪ Starts per hour (66) ▪ Mechanical Condition Monitoring (39) ▪ Current Unbalance, Negative Sequence (46-2) ▪ Power Factor (55) ▪ Over/Under Frequency (81) ▪ High Frequency Rate of Change (81) ▪ Over Temperature (49R) ▪ Bearing Over Temperature (38) ▪ Lockout relay (86)
This option includes the SIMATIC S7-1200, SM 1231 AI thermocouple 12 channel RTD unit. The AMP option is compatible with the most three-wire RTD types. Pt100 is a default setting and others are available on request. Siemens 2019 Unrestricted Page 4
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sin-perfect-harmony-gh180-AMP-slides-en.pptx
Many of the functions were developed based on a standard functional block
The complex standard block was developed and reused to implement different protection functions by changing the block inputs
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sin-perfect-harmony-gh180-AMP-slides-en.pptx
Machine thermal model for thermal protection (49T)
ieq ( t ) t H (t ) = Fa + H ( t − t ) + t kirated + t 2
• The thermal capacity used (H(t)) is calculated with a difference equation with effective stator current (ieq) as an input as well as Fa. • Fa is a factor that accounts for a difference between measured and rated ambient temperature. (Ambient temperature sensors are required to use this term) • The time constant (Tau) is a parameter of the equation that scales the rate at which the model heats up and cools down • The rated current (irated) is the rated current of the machine and is scaled by a k factor that reflects additional capacity 2 2
ieq = iavg + qi2
• The equivalent current (ieq) is equal to the sum of the average stator current plus a weighted amount of negative sequence current (i2) Siemens 2019 Unrestricted Page 6
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sin-perfect-harmony-gh180-AMP-slides-en.pptx
Thermal model – Adaptation for variable speed
ieq ( t ) H ( steadystate ) = Fa kirated 2
• Speed dependent parameters K and Tau have been added to the model to accommodate variable speed operation • K typically increases at lower speeds due to decreases in magnetic losses in the machine at lower frequencies in the stator although relatively constant frequencies in the rotor tend of offset the effect in induction machines • Time constants (Tau) increase with decreasing speed since the machine cooling tends to decrease • The thermal model can be “backed up” by stator temperature sensors • Other functions benefit from speed dependent pickup levels Siemens 2019 Unrestricted Page 7
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sin-perfect-harmony-gh180-AMP-slides-en.pptx
Differential protection • Intrawinding (turn to turn) faults and interwinding (winding to winding) faults are the only faults that do not involve a connection with ground • A winding to winding fault will be detected by differential protection of this type • A turn to turn fault will not be detected by differential protection since no current leaves the winding • A winding to winding fault will cause a substantial imbalance of stator currents (high negative sequence overcurrent)
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sin-perfect-harmony-gh180-AMP-slides-en.pptx
Shorted turn simulation
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Cross section of a 1000 HP induction machine
• A shorted turn results in very high currents in the shorted turn • A smaller (few percent) negative sequence current flows in the stator • Negative sequence currents are very small in drives due to a low negative sequence output voltage (dependent on machine quality) Siemens 2019 Unrestricted Page 9
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sin-perfect-harmony-gh180-AMP-slides-en.pptx
Summary ➢ The isolated output of a Harmony drive simplifies the protection problem ▪ Ground fault protection is not needed but ground fault detection is needed ➢ Variable speed operation complicates the protection problem ▪ Protections can be adapted using speed dependent parameters and trip settings ➢ The fault type protections offered by 6 current transformer differential protection can be obtained with a combination of zero sequence overvoltage protection and negative sequence overcurrent protection ➢ Negative sequence overcurrent protection can be used to detect turn to turn shorts in a phase winding if sufficiently sensitive
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11/4/2019
sin-perfect-harmony-gh180-AMP-slides-en.pptx