The document summarizes information about a main circuit breaker, including: - It is connected in series to switch on or off the catenary side circuit and protect it from short circuits, overloads, undervoltage, etc. - It has key electrical parameters like a rated voltage of 30kV, maximum continuous voltage of 31.5kV, and rated short-circuit switch-off current of 20kA. - It has three main parts: the upper high voltage circuit, intermediate isolation from earth, and lower electro-pneumatic mechanism and low voltage circuit. - Maintenance involves appearance inspection, checking tightening torques, and inspecting the pneumatic circuit.

1. Main Circuit breaker

2. Content

3. Main circuit breaker is connected in series in main loop to
switch on or off catenary side circuit and protect catenary side
circuit (short circuit, over load grounding, catenary under
voltage, etc.)
1.General
Main Circuit Breaker
type BVAC N99

4. Item Parameter Remark
Rated voltage 30 kV
Maximum allowable continuous
voltage
31.5 kV
Frequency 50 Hz
Rated thermal current 1000A
Rated short-circuit switch-off current 20 kA
Rated short-circuit impulse current
(peak value)
40 kA
Rated short-time current 25 kA 1 s
Maximum switch-off time 60 ms
2.Main Electrical parameters

5. (three main parts)

6. the upper part, which is the high voltage circuit.

7. The intermediate part, which ensures isolation from earth.
Vertical insulator

8. The lower part with the electro-pneumatic mechanism
and the low voltage circuit.
Where is the Pressure switch?

9. Main circuit breaker at off state
(1) Closing operation
Closer conditions???

10. At reset stage(open) Electro-valve opening Moving the main contact
Creating contact pressure Closed
Closing sequence

11. 2.Opening operation, BVAC closed
Opening the magnetic holding circuit Open
（2）Opening operation
Opening sequences

12. (3)Control of operation
Skeleton diagram of circuit breaker

13. Sequence diagram
ON/OFF: Control switch, closing/opening the circuit breaker. Order given by vehicle sequence diagram
HV: Main contact of vacuum switch tube; high voltage.
EV: Electro-magnet valve
Mm: Holding magnet coil.
Caux NO: Auxiliary contact NO(normlly open)
Caux NC: Auxiliary contact NO(normlly close)
ΔtC: closing time between ON/OFF switch closing and main contacts closing.
Δto: Open time from holding current is zero (IMm=0) to the separation of the main contacts.
ΔtNext C: Time until the next closing.
ΔtEV: Supply EV time.

14. (1)appearance inspection: Carry out a visual inspection of
the circuit breaker and, more specifically, of the state of the
insulator ceramics (A) (cracks or damage to enamel) and
connections (B) of BTE earthing switch.
General maintenance Process

15. (2) Checking tightening torque
A (High voltage connections): 67 Nm
A（高压接头）： 67 Nm
B (Earthing connections): 50 Nm
（接地接头）： 50 Nm
C (Circuit breaker fixing screws): 67 Nm
（断路器固定螺钉）： 67 Nm
General maintenance Process

16. (3)Inspection of pneumatic circuit
Draining the pressure regulator
Draining BVAC air tank
Checking seals
General maintenance Process

17. Test requirements
(1)The minimum and maximum voltages shall relate to the
nominal voltage as follow:
Minimum voltage: 0.7Uctrl n
Maximum voltage: 1.25Uctrl n
(2)The permissible pressure varition in vehicle supply pipe
es from: 450kPa～1000kPa
(3)measure insulation resistance
(4)Switch-off time

18. The BVAC circuit breaker does not close.
The BVAC circuit breaker does not remain closed.
electrical part
mechanical part
pneumatic circuit

19. Page 19
Thank you！