Circuit breaker control and signal circuits are generally divided into control and protection circuits, closing circuits, accident signal circuits, warning signal circuits, and disconnector and circuit breaker lockout circuits. The power supply for a circuit breaker's control and signal circuits depends on the type of operating mechanism and the control power supply. 3-35kV circuit breakers generally use electromagnetic or spring operating mechanisms (manual operating mechanisms were previously used for small-capacity, low-oil circuit breakers, but are no longer used). Spring operating mechanisms can operate with both AC and DC power supplies, while electromagnetic operating mechanisms can only operate with DC power. Circuit breaker control and signal circuit wiring can be configured with either light monitoring or audio monitoring. Circuit breakers can be closed and tripped manually using a control switch or automatically by automatic devices and relay protection.
The wiring requirements for the circuit breaker's control and signal circuits are as follows:
1. It must be able to monitor the integrity of the power supply protection devices (fuses and low-voltage circuit breakers) and the tripping and closing circuits (resistors must not be connected in parallel to the closing coil's audible signal or the closing contactor's coil).
2. It must be able to indicate the circuit breaker's closed and tripped positions, and automatic closing and automatic tripping must have clear signal indications.
3. It must have a locking device to prevent the circuit breaker from tripping.
4. The command pulse must be automatically released after closing or tripping. The circuit breaker's closing and tripping circuits are designed for short-term energization. After the operation is completed, the closing or tripping circuit must be automatically disconnected quickly to prevent burnout of the coil. To this end, the circuit breaker's auxiliary contacts should be connected to the corresponding circuit to ensure circuit disconnection and prepare for the next operation.
5. Wiring should be simple and reliable, using a minimum of cables.
When the circuit breaker control power supply utilizes a DC system with silicon rectifiers and capacitor energy storage, the following additional requirements apply to the circuit breaker's control and protection circuit:
1. To reduce excessive energy consumption in the energy storage capacitor during a fault, the positive terminals of normally connected loads, such as indicator lights, should be reconnected from the control power supply's positive busbar to a separate power supply circuit with a light indicator busbar.
2. For the reasons mentioned above, the control circuit's positive power supply should be monitored using alternative means, such as a closed position relay for critical circuits.
The circuit breaker's emergency trip signal circuit is wired using the principle of non-correspondence. When the circuit breaker is manually operated, the auxiliary contacts of the operating mechanism and the operating handle form a non-corresponding wiring. When the circuit breaker uses an electromagnetic and spring-operated mechanism, the control switch and the operating mechanism's auxiliary contacts form a non-corresponding wiring. The circuit breaker should have an emergency trip signal. This signal can cause the central control system to issue audible and visual signals to indicate a fault, and a signal relay can directly indicate the nature of the fault. The circuit breaker's control and signal circuits may incorporate flashing signal devices, as needed, to coordinate with the emergency signal and automatic devices to indicate emergency tripping and automatic switching. A flashing green light indicates automatic tripping of the circuit breaker, while a flashing red light indicates automatic closing (the red light is only included in the flashing function if an automatic switching device is present). The flashing signal can also serve as a countermeasure: the red light flashes when the transfer switch is in the "ready to trip" position and the green light flashes when in the "ready to close" position. For circuits and lines that may experience abnormalities, a backup signal should be provided. The preparatory signal should cause the central signaling device to emit sound and light signals, and use the signal relay to directly indicate the nature of the fault and the faulty line and circuit. Generally, the warning sound signal uses an electric bell, while the emergency sound signal uses an electric whistle to distinguish between the two.
