what is it system

The IT system is one of the three different types of grounding systems distinguished by the international standard IEC60364; the IT system is not directly connected to the earth, and the exposed conductive parts of the electrical device are connected to the grounding electrode through a protective grounding wire. In the IT system, the live conductor of the electrical device is insulated from the ground, or the neutral point of the power supply is grounded through high impedance; all exposed conductive parts and conductive parts outside the device are grounded through the ground electrode of the electrical device.

The operating environment of this tutorial: Windows 7 system, Dell G3 computer.

IT system is one of the three different types of grounding systems distinguished by the international standard IEC60364, using two letter codes to represent TN, TT and IT. The first letter indicates the relationship between the power supply end and the ground: T means that one point of the power supply end is directly grounded; I means that all live parts of the power supply end are not grounded or have one point that is grounded through impedance. The second letter indicates the relationship between the exposed conductive part of the electrical installation and the ground: T indicates that the exposed conductive part of the electrical installation is directly connected to the ground, and this grounding point is electrically independent from the grounding point at the power supply end; N indicates that the exposed conductive part of the electrical installation Some have a direct electrical connection to power terminal ground.

System Introduction

The IT system is not directly connected to the earth. The exposed conductive parts of the electrical device are connected to the ground electrode through the protective ground wire.

In the IT system:

• The live conductor of the electrical device is insulated from the ground, or the neutral point of the power supply is grounded through high impedance;

• All exposed conductive parts and conductive parts outside the installation are grounded through the grounding electrode of the electrical installation.

Since the fault current is small when the system fails for the first time, the metal shell of the electrical equipment will not produce dangerous contact voltage, so the power supply can not be cut off and the electrical equipment can continue to operate. And faults can be eliminated through alarm devices and inspections.

The power supply should be automatically cut off when a second fault occurs in the IT system: When a second fault occurs on another phase line or neutral line, the fault must be removed quickly.

IT system characteristics (no neutral wire leads out)

• #-When the first ground fault occurs, the ground fault current is only non-fault The capacitive current relative to the ground has a very small value, and the voltage of the exposed conductive part to the ground does not exceed 50V. There is no need to cut off the fault circuit immediately to ensure the continuity of the power supply;

• - A ground fault occurs When , the voltage to ground increases by 1.73 times;

• -220V load needs to be equipped with a step-down transformer, or be supplied exclusively by a power supply outside the system;

• －Install insulation monitor. Place of use: Power supply continuity requirements are high, such as emergency power supply, hospital operating room, etc.

IT mode power supply system I means that the power supply side has no working ground, or is grounded through high impedance. The second letter T indicates that the load-side electrical equipment is grounded for protection.

IT mode power supply system has high power supply reliability and good safety when the power supply distance is not very long. It is generally used in places where power outages are not allowed, or where continuous power supply is strictly required, such as electric steelmaking, operating rooms in large hospitals, underground mines, etc. The power supply conditions in underground mines are relatively poor, and cables are susceptible to moisture.

Using the IT mode power supply system, even if the neutral point of the power supply is not grounded, once the equipment leaks, the single-phase ground leakage current will still be small and will not destroy the balance of the power supply voltage, so it is safer than a system with a grounded neutral point of the power supply. . However, if it is used in a long power supply distance, the distributed capacitance of the power supply line to the earth cannot be ignored.

When a short-circuit fault occurs in the load or current leakage causes the equipment shell to be electrified, the leakage current forms a circuit through the earth, and the protective equipment may not necessarily operate, which is dangerous. It is safer only if the power supply distance is not too long. This method of power supply is rare on construction sites.

Scope of application

Its application is limited due to the unfavorable factors of the IT system. In our country, due to the lack of understanding of IT systems, except for the use of IT systems in mines, metallurgical enterprises and some local areas, IT systems are almost not used in the distribution of electrical equipment in buildings.

• Surgical equipment in the hospital and equipment that maintains the patient's life

Some electrical medical equipment that maintains the patient's life, such as cardiopulmonary system extracorporeal circulation equipment , if the power supply is interrupted, the patient's life will be in danger soon. An IT system with high reliability of uninterrupted power supply can avoid this risk.

• Safety lighting in certain gathering places

This can be divided into two situations: one is a gathering place with a large number of people. When there is a power outage, an IT system should be used for evacuation lighting to ensure the safe evacuation of people; the other is an important gathering place with significant political influence, where interruption of power supply will cause serious political impact. Such places include lighting power distribution The system should all adopt IT systems. [4]

• mine

Whether it is a coal mine or a metal mine, it is a special place with high electrical hazards. There is groundwater underground in the mine, and the power supply to the water pump must be ensured to prevent people underground from being flooded. The exhaust fans underground in coal mines must also be powered to discharge gas. In addition, electric vehicles for people going up and down mines and mining and production all rely on reliable power sources. The use of IT systems can ensure uninterrupted power supply.

• Glass Factory

Glass Factory If there is an accidental power outage and the power outage lasts too long, the glass solution will solidify in the glass furnace, causing the glass to The furnace was scrapped.

Some electric furnaces and testing equipment

If the power supply to hot-processed parts in some electric furnaces is interrupted, the heating parts will be scrapped or the quality will be reduced. If the power supply of important test equipment is interrupted, the previous long test work will be scrapped.

• Metallurgical factory

There are many equipments in such factories that may cause serious danger if the power supply is interrupted. For example, if a metallurgical furnace in a steel plant loses power and stops supplying cooling water, there will be a risk of furnace collapse.

• The power supply of the power plant

If the power supply of the power plant is interrupted by an accident, it will affect the safe power supply of the entire region.

• Chemical Plant

If an accident interrupts the power supply and disrupts the complex production process, it will take a long time to resume normal production. resulting in huge economic losses.

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