(1) Rated voltage (nominal voltage): refers to the rated voltage of a certain level of system in which the circuit breaker works. In the three-phase system, it refers to the line voltage, and in the single-phase system, it is the phase voltage. It shows the insulation level of the circuit breaker and its arc extinguishing capability.
It is a parameter that characterizes the insulation strength of a circuit breaker and is the standard voltage for long-term operation of a circuit breaker. In order to meet the requirements of the power system work, the circuit breaker also specifies the highest working voltage corresponding to the rated voltage of each stage. For the 3-220KV level, the maximum working voltage is about 15% higher than the rated voltage; for 330KV and above, the highest working voltage is about 10% higher than the rated voltage. The circuit breaker should be able to operate reliably for a long time at the highest operating voltage.
(2) Rated current: refers to the maximum working current that the circuit breaker can pass for a long period of time under the voltage of the amount. At this time, the temperature rise of the conductor part cannot exceed the specified allowable value. It is a parameter that characterizes the ability of a circuit breaker to pass long-term current, that is, the maximum current that the circuit breaker allows for continuous long-term passage.
(3) Rated breaking current: It is a parameter that characterizes the breaking capacity of the circuit breaker. Under the rated voltage, the maximum current that the circuit breaker can ensure reliable breaking is called the rated breaking current, and its unit is expressed by the kiloamperes of the effective value of the short-circuit current period component of the breaker contact separation. When the circuit breaker is operated in a grid below its rated voltage, its breaking current can be increased. However, due to the limitation of the mechanical strength of the arc extinguishing chamber, the breaking current has a maximum value, which is called the limit breaking current.
(4) Dynamic steady current: It is a parameter that characterizes the ability of the circuit breaker to pass short-time current, reflecting the ability of the circuit breaker to withstand the short-circuit current electrodynamic effect. The maximum peak value of the current allowed to pass through the circuit breaker in the closed state or closed, called the electric steady current, also known as the limit through current. When the circuit breaker passes the steady current, it cannot be damaged by the action of electric power.
(5) Closing current: Because the circuit breaker may be pre-volted with a short-circuit fault when the circuit is turned on, the circuit breaker will close a large short-circuit current. Thus, on the one hand, the electric power of the short-circuit current weakens the operating force of the closing, and on the other hand, the arc is generated due to the breakdown before the contact has not been contacted, which may cause the contact to be welded, thereby causing damage to the circuit breaker. The maximum peak value of the current that the circuit breaker can reliably close is called the rated closing current. The rated closing current and the dynamic stabilizing current are equal in value, both equal to 2.55 times the rated breaking current.
(6) Duration of thermal stable current and thermal stable current: The steady current is also a parameter that characterizes the ability of the circuit breaker to pass short-time current, but it reflects the ability of the circuit breaker to withstand the thermal effects of short-circuit current. The thermal stable current refers to the effective value of the maximum period component of the allowed current through the circuit breaker in the closed state for a certain duration. At this time, the circuit breaker should not be damaged by short-time heating. The national standard stipulates that the rated thermal stability current of the circuit breaker is equal to the rated breaking current. The rated thermal stability current is 2S. When it is greater than 2S, 4S is recommended.
(7) Closing time and opening time: This is a parameter that characterizes the operating performance of the circuit breaker. Different types of circuit breakers have different opening and closing times, but they all require quick action. The closing time refers to the time from the closing of the closing mechanism of the circuit breaker operating mechanism to the contact of the main contact. The opening time of the circuit breaker includes two parts: the inherent opening time and the arc extinguishing time. The inherent opening time is the time from when the operating mechanism opens the coil to when the contacts are separated. The arc extinction time is the time from the separation of the contacts to the extinguishment of the arcs of the phases. Therefore, the opening time is also called the full opening time.
(8) Operating cycle: This is also an indicator of the operational performance of the circuit breaker. The short-circuit fault of the overhead line is mostly temporary, and the fault disappears quickly after the short-circuit current is cut off. Therefore, in order to improve the reliability of the power supply and the stability of the system operation, the circuit breaker should be able to withstand the action of opening or closing immediately after opening, closing, or closing. Such an operation of dividing and closing a plurality of times at a certain time interval is called an operation cycle. The rated operating cycle of circuit breakers in China is as follows:
Automatic reclosing operation cycle: points - t' - combined points - t - points
Non-automatic reclosing operation cycle: points - t - combined points - t - combined points
The minute is - indicating the opening action;
Combined score - indicates the action of opening immediately after closing;
t'——No current interval time, that is, the time when the circuit breaker is disconnected from the fault circuit, from the time when the arc is extinguished to the time when the circuit is automatically turned on again, the standard time is 0.3S or 0.5S, that is, the reclosing action time.
t——Power transmission time for the operating personnel, the standard time is 180S
Isolation switch selection
The isolating switch is arranged on the main wiring to ensure that the line and equipment are obviously isolated and isolated from the live part. Since the isolating switch has no arc extinguishing device and low breaking capacity, the operation sequence of the switch must be observed when operating the isolating switch. That is, when power is supplied, first close the busbar side isolating switch, secondly close the line side isolating switch, and finally close the circuit breaker, and the power failure is reversed.
1. Provide an electrical interval during the inspection of electrical equipment and is a clearly visible disconnect point to ensure the personal safety of maintenance personnel.
2, the isolating switch can not be loaded with operation: can not be operated with rated load or large load, but the arc extinguishing chamber can be operated with small load and no-load line.
3. For normal power transmission operation: first isolate switch, rear switch breaker or load switch;
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