MEDIUM VOLTAGE CAPACITOR SWITCHING DEVICE SELECTION TUTORIALS

Capacitance switching constitutes severe operating duty for a circuit breaker. At the time the breaker opens at near current zero the capacitor is fully charged. After interruption, when the alternating voltage on the source side of the breaker reaches its opposite maximum, the voltage that appears across the contacts of the open circuited breaker is at least twice the normal line-to-neutral voltage of the circuit.

Due to the circuit constants on the supply side of the breaker the voltage across the open contact can reach three times the normal line-to-neutral. If a breakdown occurs across the open contact the arc is reestablished. After it is interrupted and with subsequent alternation of the supply side voltage, the voltage across the open contact is even higher.

ANSI Standard C37.06 (indoor oilless circuit breakers). The application guide ANSI/IEEE Standard C37.012 covers the method of calculation of the quantities covered by C37.06 Standard.

Note that the definitions in C37.04 make the switching of two capacitors banks in close proximity to the switchgear bus a back-to back mode of switching. This classification requires a definite purpose circuit breaker (breakers specifically designed for capacitance switching).

A breaker specified for capacitor switching should include as applicable.
1. Rated maximum voltage.
2. Rated frequency.
3. Rated open wire line charging switching current.
4. Rated isolated cable charging and shunt capacitor switching current.
5. Rated back-to-back cable charging and back-to-back capacitor switching current.
6. Rated transient overvoltage factor.
7. Rated transient inrush current and its frequency.
8. Rated interrupting time.
9. Rated capacitive current switching life.
10.Grounding of system and capacitor bank.

Loadbreak interrupter switches are permitted by ANSI/IEEE Standard C37.30 to switch capacitance but they must have tested ratings for the purpose.

Related post



No comments:

PREVIOUS ARTICLES