Electric Arc Furnace Voltage Sag:
- The electric arc furnace with its high thermal efficiency is suitable for melting down scrap.
- The electric arc furnace uses about 30% less energy for the same process that the blast furnace and the basic oxygen steelmaking plant.
- Electric Arc when operated, requires a large amount of current and produces voltage harmonics which affects the voltage supply.
- This disturbance in the voltage creates a voltage sag.
Fault clearing Voltage Sag:
- During a fault on a parallel feeder or a fault on transmission system, the customer will experience voltage sag during the period that the fault is actually on the system.
- As soon as breaker open to clear the fault or close after clearing fault, normal voltage will be restored at customer.
- Breaker usually requires about 5 to 6 cycle to operate and during this time, voltage sag occurs.
Area of Vulnerability:
- An area of vulnerability is determined by the total circuit miles of exposure to faults that can cause voltage magnitudes at an end-user facility to drop below the equipment minimum voltage sag ride-through capability.
- Minimum Voltage Ride through capability: It is the minimum voltage-magnitude, a piece of equipment can withstand or tolerate without miss-operation or fault. It is also called as the Equipment voltage sag immunity or substantiality limit.
Estimating Voltage-Sag Performance:
It is important to estimate voltage sag performance so that facilities can be designed and equipment specifications developed to assure the optimum operation of production facilities.
For the estimation of voltage sag performance, the following procedure is considered:
1. Determine the number and characteristics of voltage sags that result from transmission system faults.
2. Determine the number and characteristics of voltage sags that result from distribution system faults (for facilities that are supplied from distribution systems).
3. Determine the equipment sensitivity to voltage sags. (This will determine the actual performance of the production process based on voltage sag performance calculated in steps 1 and 2).
4. Evaluate the economics of different solutions that could improve the performance, either on the supply system (fewer voltage sags) or within the customer facility (better immunity).
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