A Consideration of Medium Voltage Substation Primary Applications


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Copyright AIST Reprinted with Permission. Presented at the 2013 Iron and Steel Technology Conference and Exposition (AISTech 2013). Unit substations have long served as the method for reducing voltage from higher distribution levels to lower, locally usable voltages. One of the main considerations affecting the design of the substation and the electrical protection and distribution system as a whole is the primary switching device of a substation. By comparing the abilities and options inherited with both types of primary switching devices, an informed decision can be made for specific system designs.

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A Consideration of Medium Voltage Substation Primary Applications

  1. 1. Joe Richard Senior Marketing Specialist Schneider Electric A Consideration of Medium Voltage Substation Primary Applications Insert your LOGO here James Stacy Manager, Strategy and Innovation Schneider Electric
  2. 2. Substation Design Medium Voltage 4160 V Low Voltage 480 V
  3. 3. Substation Design TransformerPrimary Secondary Power Flow
  4. 4. Choosing a Primary Protection Cost Application
  5. 5. Protection Transformer Inrush Current to the left of the Fuse Curve Primary Fuse and Secondary Breaker Overlap at High Overcurrent Transformer Damage Curve and Fuse Curve Overlap.
  6. 6. Protection Transformer Differential (ANSI 87): • Phase Currents are summed on the Source and Load sides to see if there is any ground current leakage. • Effective at detecting low-level ground faults that damage equipment over time.
  7. 7. Cost Budget Example MV Fused Switch MV Circuit Breaker 5kV Switch Section $10,500 $28,000 5kV Breaker Section 5kV Fuses $1,800 $4,000 Protection Relay Installation $2,500 $1,500 Relay Commissioning $2,500 Installation Total $14,800 $36,000 Total
  8. 8. Application Virtual main: • Use a Protection Relay at the Secondary Terminal to detect faults and overcurrent on the secondary side of the transformer. • Relay signals Primary Circuit Breaker to trip in the event of a fault. • Normally includes a switch to increase instantaneous trip current during maintenance to lower arc flash incident energy. • Particularly useful in retrofit applications
  9. 9. Application Primary Loop System: • Application allows for primary source selection at the unit substation. • Resistant to cable failures within the loop as the system can be self- healing. • Prime example of Medium Voltage Circuit Breaker application.
  10. 10. Application Secondary Selective System: • Source selection is in the secondary switchgear. • No automation in the primary switching device of the substation • Example of Fused Switch Application
  11. 11. Metal-Enclosed Fused Switches Benefits: • Lower Capitol Cost • Simple Protection Application • Smaller Footprint • Fast High-level Fault Protection Disadvantages: • Stock of Fuses • Less Customizable Protection • Higher Arc Flash Energy in Transformers above 750kVA •Low Lifetime Operations
  12. 12. Metal-Clad Circuit Breakers Benefits: • Customizable Protection • Higher Lifetime Operations • Broader Applications (Automated Transfer, Virtual Main, Higher Primary Amperages, Differential Protection, etc.) • Better Coordination Disadvantages: • Increased Capitol Cost • Relay Commissioning • Larger Footprint
  13. 13. Thank You Joe Richard Senior Marketing Specialist Schneider Electric James Stacy Manager, Strategy and Innovation Schneider Electric