“Electrical fire monitoring detector†is defined as “a detector that detects changes in electrical fire hazard parameters such as residual current, temperature, etc., in protected circuitsâ€.
Electrical fire monitoring detectors are distinguished by detection parameters: “residual current electrical fire monitoring detectors†and “thermostatic electrical fire monitoring detectorsâ€. There are independent detectors in the working mode (detection with monitoring alarm function. And non-independent detectors.
It can be seen that the residual current and temperature are considered to be the focus of technical fire prevention. In fact, grounding arc short circuits, excessive temperatures at the equipment or connection points are the main causes of electrical fires.
Based on the definition of electrical fire monitoring detectors, the task of residual current electrical fire monitoring detectors is to prevent electrical fires, and RCBO (residual current circuit breakers, ie "leakage switches") in the protection function, technical parameters, structural requirements, etc. There are big differences. RCBO focuses more on the protection of personal safety. Both should be used together, but they cannot be used interchangeably.
For the measurement monitoring and fault protection of current, voltage, and other power parameters, the existing electrical devices are very mature.
Several related concepts <br> <br> provided before discussing residual current electric fire detectors, it is necessary to clarify the following concepts:
"Residual current": The vector sum of the currents of the alternating current line (La, Lb, Lc) and the neutral line N. When no single-phase ground fault occurs, the theoretical value of this vector sum is zero (there is actually a normal leakage current between the line and the equipment) regardless of whether the three-phase load is balanced or not; when a ground fault occurs, the residual current is grounded The vector sum of fault current and normal leakage current.
"Zero-sequence current": The vector sum of the currents of the phases (La, Lb, Lc) of the AC supply line. When no ground fault occurs, the theoretical value of this vector sum is equal to the value of the neutral N current. When a ground fault occurs, the zero-sequence current is the vector sum of the phase line (La, Lb, Lc) currents, the ground fault current, and the normal leakage current; at this time, it is not equal to the neutral N current.
“Normal Leakage Currentâ€: The current flowing from the live parts of the device into the earth in the absence of an insulation fault. This current is often caused by non-pure resistive impedance, which is determined by the inherent operating characteristics of some devices and is allowed within a certain range.
"Ground fault current": current flowing into the earth due to an insulation fault or through an unexpected load. Popular habits are called "leakage currents." This current is generated by an arc short circuit to the ground. It is generally believed that in the non-flammable environment, less than 100mA does not constitute a fire hazard.
"The residual current transformer": The transformer that detects the residual current of the power supply line. Its primary circuit is the phase line (La, Lb, Lc) and the neutral line N. That is, the phase and neutral lines pass through the window at the same time and in the same direction. The main requirements of the residual current transformer are mA-level high accuracy and over 40A overload resistance.
"Zero-sequence current transformer": Transformer for detecting the zero-sequence current of the power supply line. Its primary circuit is the phase line (La, Lb, Lc). That is, all phase lines pass through the window at the same time and in the same direction. If used for single phase, the effect is the same as that of a normal current transformer (CT).
The task of the residual current type electrical fire monitoring detector is to correctly detect the ground fault current of the power supply line and equipment and issue an alarm in time. In fact, the residual current of the protected area is detected. Current residual current detectors basically use residual current transformers as detection elements.
Electrical fire monitoring detectors are distinguished by detection parameters: “residual current electrical fire monitoring detectors†and “thermostatic electrical fire monitoring detectorsâ€. There are independent detectors in the working mode (detection with monitoring alarm function. And non-independent detectors.
It can be seen that the residual current and temperature are considered to be the focus of technical fire prevention. In fact, grounding arc short circuits, excessive temperatures at the equipment or connection points are the main causes of electrical fires.
Based on the definition of electrical fire monitoring detectors, the task of residual current electrical fire monitoring detectors is to prevent electrical fires, and RCBO (residual current circuit breakers, ie "leakage switches") in the protection function, technical parameters, structural requirements, etc. There are big differences. RCBO focuses more on the protection of personal safety. Both should be used together, but they cannot be used interchangeably.
For the measurement monitoring and fault protection of current, voltage, and other power parameters, the existing electrical devices are very mature.
Several related concepts <br> <br> provided before discussing residual current electric fire detectors, it is necessary to clarify the following concepts:
"Residual current": The vector sum of the currents of the alternating current line (La, Lb, Lc) and the neutral line N. When no single-phase ground fault occurs, the theoretical value of this vector sum is zero (there is actually a normal leakage current between the line and the equipment) regardless of whether the three-phase load is balanced or not; when a ground fault occurs, the residual current is grounded The vector sum of fault current and normal leakage current.
"Zero-sequence current": The vector sum of the currents of the phases (La, Lb, Lc) of the AC supply line. When no ground fault occurs, the theoretical value of this vector sum is equal to the value of the neutral N current. When a ground fault occurs, the zero-sequence current is the vector sum of the phase line (La, Lb, Lc) currents, the ground fault current, and the normal leakage current; at this time, it is not equal to the neutral N current.
“Normal Leakage Currentâ€: The current flowing from the live parts of the device into the earth in the absence of an insulation fault. This current is often caused by non-pure resistive impedance, which is determined by the inherent operating characteristics of some devices and is allowed within a certain range.
"Ground fault current": current flowing into the earth due to an insulation fault or through an unexpected load. Popular habits are called "leakage currents." This current is generated by an arc short circuit to the ground. It is generally believed that in the non-flammable environment, less than 100mA does not constitute a fire hazard.
"The residual current transformer": The transformer that detects the residual current of the power supply line. Its primary circuit is the phase line (La, Lb, Lc) and the neutral line N. That is, the phase and neutral lines pass through the window at the same time and in the same direction. The main requirements of the residual current transformer are mA-level high accuracy and over 40A overload resistance.
"Zero-sequence current transformer": Transformer for detecting the zero-sequence current of the power supply line. Its primary circuit is the phase line (La, Lb, Lc). That is, all phase lines pass through the window at the same time and in the same direction. If used for single phase, the effect is the same as that of a normal current transformer (CT).
The task of the residual current type electrical fire monitoring detector is to correctly detect the ground fault current of the power supply line and equipment and issue an alarm in time. In fact, the residual current of the protected area is detected. Current residual current detectors basically use residual current transformers as detection elements.
Magnetostrictive level sensor is composed of three parts: probe rod, circuit unit and float. To measure, the circuit unit generates pulses of current that travel down the magnetostrictive line and generate a circular magnetic field. A float is arranged outside the probe rod, and the float moves up and down along the probe rod with the change of liquid level. The float generates a magnetic field at the same time because it is fitted with a set of permanent magnets. When the current magnetic field meets the float magnetic field, it produces a "twisting" or "return" pulse. The time difference between the "return" pulse and the current pulse is converted into pulse signals to calculate the actual position of the float and measure the liquid level.
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