Application Of Surge Protector In Tt System
The TT power supply system refers to a protection system that directly grounds the metal shell of the electrical equipment, which is called a protective grounding system, also known as a TT system. The first symbol T represents the direct grounding of the neutral point of the power system. The second symbol T indicates that the exposed metal conductive part of the load equipment that is not connected to the live body is directly connected to the earth, and has nothing to do with the direct grounding of the system.
Surge protector (SPD), also known as surge protective device, is a lightning electromagnetic pulse protection device used on electronic signal equipment in low-voltage distribution systems. It is connected in parallel with the protected equipment to limit transient overvoltage and discharge surge current to protect the safety of circuits and equipment during lightning strikes and overvoltages. It is suitable for AC 50/60HZ, rated voltage 220V/380V power supply systems, and is suitable for surge protection device requirements in residential, tertiary and industrial fields.
The TT system has one point directly connected to the earth, and the exposed conductive part of the load-side electrical device is connected to an independent grounding device that is electrically unrelated to the grounding point of the power supply end, as shown in Figure 1-1. The TT system must have a direct grounding point, which is generally the neutral point of the distribution transformer or generator; if there is no neutral point, a phase line must be grounded. The exposed conductive parts of the electrical equipment must also be grounded. All exposed conductive parts of the electrical equipment protected by the same protective device are connected together with a protective wire and connected to their common grounding body; when several protectors are protected in stages, all exposed conductive parts protected by each protective device must also be grounded in this way.
In the TT system, the metal casing of the electrical equipment is grounded with a separate grounding body, and there is no electrical connection with the power supply in terms of grounding, so it is suitable for power supply of data processing equipment and precision electronic equipment that are sensitive to the equipment. The protective wires are also independent, and there will be no problem of ground fault propagation in the event of a fault.
The TT system is particularly suitable for electrical loads with smaller capacity, such as power supply to residential buildings. If the electrical load capacity is large, a residual current protector must be used, such as a leakage protector, to use the leakage current during a ground fault to cause the leakage protector to operate and cut off the power supply.
Surge protectors with a 3PN structure are often used in the protection of three-phase AC power TT systems. The wiring of surge protector in TT system, TT system is a system where the power system has one point of direct grounding. The grounding of the exposed conductive parts of the equipment is electrically unrelated to the grounding of the power system. Three-phase four-wire, the three L ports above are connected to the three phase wires (live wires), the N port is connected to the neutral wire, and the PE port is connected to the ground wire. The wiring method is shown in Figure 1-2.
For the wiring method of SPD in the low-voltage distribution system, the wiring form in the TT system should be correctly understood and used reasonably to avoid causing SPD failures or even fires, affecting the safe operation of the distribution system.
