Overview of voltage sag mitigation techniques

Transcription

1 Overview of voltage sag mitigation techniques Ambra Sannino Department of Electrical Engineering University of Palermo, Italy Michelle Ghans Miller, Math H.J.Bollen Department of Electric Power Engineering Chalmers University of Technology Gothenburg, Sweden

2 2 outline need for voltage sag mitigation mitigation through system improvement increasing equipment immunity installation of additional equipment conclusions

3 today s scenario the need for power quality improvement 3 Factory sensitive equipment production lines Automated factories use sensitive equipment power electronics (AC and DC drives) process-control electronics (computers, PLCs) Faults in the power system can cause process interruptions with associated costs due to loss of production, damaged product and equipment, and other factors

4 different faults cause different sags 4 100% 80% Voltage 50% fuses remote MV networks transmission network local MV network motor starting 0% 0.1 s 1 s Duration interruptions

5 from system faults to process interruptions 5 Faults in the utility power system: three-phase single-phase-to-ground phase-to-phase Consequences at the PCC: voltage sags interruptions Consequences on the process: equipment trip process interruption

6 improving power quality for sensitive customers 6 system improvement mitigation equipment improvement of equipment immunity

7 mitigation through system improvement 7 critical factors: improvements: frequency of events reducing the number of faults sag duration reducing the duration of faults sag magnitude changing power system layout

8 equipment sensitivity (1) 8 ~ SINGLE-PHASE DIODE RECTIFIER DC-DC CONVERTER POWER SYSTEM ~ DIODE RECTIFIER ~ INVERTER AC MOTOR low-power electronics AC drive POWER SYSTEM ~ CONTROLLED RECTIFIER ~ FIELD WINDING + - DC MOTOR ARMATURE WINDING SINGLE-PHASE DIODE RECTIFIER DC drive

9 equipment sensitivity (2) 9 sag 70% magnitude, 100 ms duration voltage [V] time [s] effect of a sag on a single-phase rectifier

10 equipment sensitivity (3) sag 70% magnitude, 100 ms duration on phase C 200 voltage [V] time [s] effect of an unbalanced sag on a three-phase rectifier

11 improving equipment immunity 11 low-power electronics: adding capacitance, improving the dc/dc converter AC drives : adding capacitance, reducing the setting for the dc bus protection DC drives: implementing proper control algorithms for adjusting the firing angle of the devices according to changes in the input voltage. Adding capacitance is not a viable option

12 mitigation devices 12 motor-generator set ferroresonance transformer electronic tap changer uninterruptible power supply static transfer switch series-connected voltage source converter shunt-connected back-up source

13 different sags require different solutions % 80% Voltage 50% fuses transmission network remote MV networks equipment improvement local MV network motor starting 0% system improvement 0.1 s 1 s Duration interruptions

14 14 conclusions mitigation of voltage sags requires careful inspection of the characteristics of the process and of the nature and origin of sag events the installation of mitigation devices (normally the only choice for the customer) can be seen as a short-term solution. The mitigation capability of these devices is mainly limited by the energy storage capacity only improvement of system performance (for long, deep sags) and of equipment tolerance (for short, shallow sags) can solve the problem in the long term