# Power Quality Impact and Its Assessment: A Review and a Survey of Lithuanian Industrial Companies
## 4 Results
After voltage sags, very often we cannot start the equipment without service assistance.\"
* \"The technological process is interrupted after each voltage sag, from four to eight technological lines are halted, grains remain in the devices and need to be removed. The restart takes up to several hours. Particularly sensitive equipment are 0.4 kV induction motors installed in the automated lines, grain dryers. We do not know the exact parameters of dangerous voltage sags, because we do not have PQ monitoring equipment and experience in PQ data analysis. However, when the technological line and electric drives stop, the company experiences large economic losses.\"
* \"The technological process is interrupted after each voltage sag, four production lines are interrupted, plastic solidifies in the devices and needs to be removed. The restart takes up to 4 h. Particularly sensitive equipment are 0.4 kV induction motors installed in the automated lines. In the near future, the company plans to install PQ monitoring and mitigation systems. We do not know exactly whether voltage sags are dangerous to 0.23 kV electric motors and mechanisms driven by them.\"
* \"We do not measure the residual voltage and duration [of voltage sags], thus the completed tables would be just an improvisation. If supply interruption is longer than 3 s, important equipment stops--steam generators, air compressors, wastewater treatment facilities, packing machines, conveyor systems, robots, autoclaves for sterilization, water pumps, etc. It takes up to 0.5-1 h to restore the work.\"
* \"We cannot fill the tables correctly, because we do not have the accurate data. The company has a lot of automatic technological equipment that are vulnerable to voltage sags. In most cases, the processes and the equipment stop when the voltage level is below 90%. The majority of the most sensitive equipment are protected with double-conversion uninterruptible power sources (UPS). The power of the installed UPS system is about 200 kW.\"
* \"When the phase-to-ground voltage of the 10 kV feeder No. 1 drops below 5 kV, undervoltage protection is triggered and the power supply is disconnected. Then, the automatic transfer switch restores the supply from the feeder No. 2. Phase sequence relays installed in railway stations, GSM-Railway base stations masts and some railway level crossings also protect the equipment from voltage sags by disconnecting it when phase-to-ground voltage level drops below 90% (207 V). In stations, crossings, and substations, where automatic protection from voltage sags is not installed, the biggest problem caused by either voltage sag or supply interruption is the distortion of railway signals before the train. LED lights, metal-halide lights, various bulbs, searchlights and spotlights, heating systems of railroad switches (heating elements, magnetic starters, isolation transformers), and controllers are not very sensitive to voltage sags. Voltage, current, and earthing transformers installed in 10 kV substations are vulnerable, as well as sensitive equipment is server rooms, supervisory control and data acquisition system, teleinformation collection and transmission equipment, remote terminal units, etc.\"
* \"In my opinion, the impact of voltage sag must be evaluated complexly. After voltage sag, the technological process is interrupted, the equipment is disturbed, and the company suffers losses. The restart takes up to 1-4 h if there is no electronic or mechanical failure. According to monitoring data, the critical depth of voltage sag for our company is 30% of nominal phase-to-ground voltage, and the critical duration--200 ms. In case of dependent voltage sags, i.e., when two or more voltage sags occur in an interval of several seconds, the devices practically have no possibility to continue working.\"
* \"The technological process is interrupted after each voltage sag. Four parquet production lines are halted. Any failure of any process chain irreversibly damages unprocessed material (product).