Switching Transient Problem with Loads
Download as PPTX, PDF•5 likes•3,393 views
This document discusses transient problems related to load switching that can cause nuisance tripping of adjustable speed drives (ASDs). It notes that ASDs use voltage source inverters with capacitors in the DC link, making them sensitive to overvoltage transients from utility capacitor switching or load switching. Such transients from load switching can generate high frequency impulses when energizing inductive loads like relays or contactors. Simultaneously energizing large transformers and capacitor banks can also cause dynamic overvoltage problems if system resonances occur. Protection methods include electrical separation of sensitive equipment, as well as using filters, isolation transformers, and shielding.
Switching Transient Problem with Loads
- 1. SWITCHING TRANSIENT PROBLEM WITH LOADS KKKL 4073 POWER QUALITY LECTURER: PROF. MADYA DR M.A HANNAN BY NORALINA ABDUL AZIZ A117805
- 2. TRANSIENT PROBLEM RELATED TO LOAD AND LOAD SWITCHING NUISANCE TRIPPING OF ASDs TRANSIENT FROM LOAD SWITCHING TRANSFORMER ENERGIZING
- 3. NUISANCE TRIPPING OF ASDs • Most adjustable speed drives use voltage source inverter VSI design with a capacitor in the dc link • But the control are sensitive to dc overvoltage and may trip the drive at the level as low as 117 percent • Since transient voltage due to utility capacitor switching exceed 130 percent, the probability of nuisance tripping of the drive is high
- 4. NUISANCE TRIPPING OF ASDs Effect of capacitor switching on adjustable speed drive ac current and dc voltage
- 5. TRANSIENT FROM LOAD SWITCHING • energizing inductive circuits with air-gap switches, such as relays and contactors, can generate bursts of high-frequency impulses. Fast transient can caused by deenergizing an inductive load
- 6. TRANSIENT FROM LOAD SWITCHING • From figure it shown cites representative 15ms burst composed of impulses having 5ns rise times and 50ns durations • There is very little energy in these type of energy due to short duration, but they can interfere with the operation of electronic loads.
- 7. EXAMPLE • electrical fast transient (EFT) activity, producing spikes up to 1 kV, is frequently due to cycling motors, such as air conditioners and elevators. • Transients as high as 3 kV can be caused by operation of arc welders and motor starters. • The duration of each impulse is short compared to the travel time of building wiring, thus the propagation of these impulses through the wiring can be analyzed with traveling wave theory. The impulses attenuate very quickly as they propagate through a building.
- 8. PROTECTION • Therefore, in most cases, the only protection needed is electrical separation. • Physical separation is also required because the high rate of rise allows these transients to couple into nearby sensitive equipment. • EFT suppression may be required with extremely sensitive equipment in close proximity to a disturbing load, such as a computer room. • High-frequency filters and isolation transformers can be used to protect against conduction of EFTs on power cables. • Shielding is required to prevent coupling into equipment and data lines.
- 9. TRANSFORMER ENERGIZING • Energizing a transformer produces inrush currents that are rich in harmonic components for a period lasting up to 1s. • If the system has a parallel resonance near one of the harmonic frequencies, a dynamic overvoltage condition results that can cause failure of arresters and problems with sensitive equipment. This problem can occur when large transformers are energized simultaneously with large power factor correction capacitor banks in industrial facilities. Energizing a capacitor and transformer simultaneously can lead to dynamic overvoltage
- 10. TRANSFORMER ENERGIZING • A dynamic overvoltage waveform caused by a third harmonic resonance in the circuit Dynamic overvoltage during transformer energizing
- 11. TRANSFORMER ENERGIZING • After the expected initial transient, the voltage again swells to nearly 150 percent for many cycles until the losses and load damp out the oscillations. • This can place severe stress on some arresters and has been known to significantly shorten the life of capacitors. • This form of dynamic overvoltage problem can often be eliminated simply by not energizing the capacitor and transformer together. • One plant solved the problem by energizing the transformer first and not energizing the capacitor until load was about to be connected to the transformer.
- 12. THANKS FOR THE TIME