Practical Power Plant Engineering

3Switching Equipment

CHAPTER MENU

• 3.1 MV Switchgear
  • 3.1.1 Breaker Ratings
  • 3.1.2 Switchgear “Constant MVA” or “Constant kA” Interrupting
  • 3.1.3 Breaker Status Contacts
  • 3.1.4 Switchgear Arc Flash Design
• 3.2 Circuit Breakers
• 3.3 MV MCC Motor Controllers
  • 3.3.1 4.16 kV MCC Assembly
  • 3.3.2 Motor Controllers
  • 3.3.3 Key Interlocks
• 3.4 LV Unit Substations
  • 3.4.1 LV Distribution
  • 3.4.2 Unit Substation, Equipment Features
  • 3.4.3 LV Switchgear
• 3.5 Motor Control Centers (MCCs)
  • 3.5.1 Assembly
  • 3.5.2 Motor Starters
  • 3.5.3 Branch Circuit Breakers for Feeders
  • 3.5.4 Branch Circuit Breakers for Motors
  • 3.5.5 MCC Interrupting Capacity
  • 3.5.6 MCC Breaker Characteristics
  • 3.5.7 Motor Starter Selection
  • 3.5.8 Breaker and Contactor Operation
  • 3.5.9 Arc Flash Modern MCC Design
• References

3.1 MV Switchgear

Electrical switchgear (Figure 3.1) is one of the principal elements of the plant distribution system. It houses the switching devices, controls, metering, and protection. The main components of the switchgear are the medium voltage (MV) circuit breakers employed to distribute power to the major plant load centers. The MV switchgear [1] is built to 4.16, 6.6, 11, 13.8, 27.6, and 33 kV voltages. A 2.4 kV voltage can still be found, but it is presently on a way out.

Figure 3.1 (a) MV switchgear and (b) circuit breaker.

For higher voltages up to 750 kV, gas insulated switchgear (GIS) is employed. GIS is several ...