The diesel generator set's ungrounded output switch will trip. According to relevant public information, we learned that the diesel generator must be grounded. There must be a suitable ground wire. Once a leak occurs, a loop will occur with the earth, seriously affecting human safety. Diesel generator protective earthing is used in three-phase power supply neutral point ungrounded systems.
Diesel generator set belongs to TT power system, which is generally called three-phase four-wire and grounding power system. This system is commonly used when equipment is powered by the public electricity network. It is more common in suburban areas.
The characteristic of TT power system is that there is no electrical connection between the neutral wire N and the protective earth wirePE, that is, the grounding of the neutral N wire and the PE wire are separated. , so the equipment shell and the grounding of the power supply are not in direct contact. The equipment shell is at ground potential and will not generate sparks or arcs, making it safer. However, when a ground fault occurs, the ground current must pass through the equipment ground resistance and the power supply neutral line ground resistance R. The loop impedance is large and the fault current is lower than that of the TN power system, which reduces the action sensitivity of the line protection device. When the system operates normally, whether the three-phase load is balanced or not, when the neutral line N is loaded, the PE line is not loaded.
When the insulation of a phase line of the equipment is damaged, the shell of the equipment will be charged. At that time, if whatWhether one touches the neutral line or the equipment shell connected to the neutral line, it will be charged. dangerous and easy. An electric shock accident has occurred. In addition, the potential of the remaining two phase lines with respect to earth will increase by more than 300 V, causing accidents in insulation installations due to high voltage. Therefore, this power system should pay special attention to the reasonable configuration of high sensitivity overcurrent. protective devices.
When the live wire collides with the shell, because the line resistance is very small, the voltage U is almost completely added to the two grounding resistances (grounding resistance ground of the neutral point of the power supply, protective earthing resistance), in accordance with the earthing resistance regulations, the two resistances must not exceed 4 Ω (some areasdo not actually require more than 10 Ω).
The current of 27.5A can melt the fuse with a rated current of 1OA (the fuse can be quickly blown by more than 3 times the rated current) and cut off the power supply; the fuse with the rated current of 4A quickly cuts off the power, which avoids electric shock accidents. However, for electrical equipment with a rated current greater than 1OA, the short circuit current of 27.5A cannot quickly melt the fuse, so the resistor has a voltage of 110V, i.e. say the metal shell of all electrical equipment connected to the grounding device has a voltage of 110V to ground. When the human body comes into contact with the metal casing of the equipment, electric shock is likely to occur. This type of system can only be used in a small power range. For example, the TT power system is reliablee for equipment with a power not exceeding 1 kW.
As the above shows, protective earthing is suitable for electrical equipment in power systems where the neutral line is not earthed. For power networks where the neutral line of the power supply is grounded, protection is used. Grounding has limits. To protect electrical equipment and ensure reliable operation of protective devices such as fuses to avoid the risk of electric shock, a protective zero connection is used when the neutral line is grounded, such as in a system TN power supply.
Protected zero connection is to connect the metal shell or frame of electrical equipment to the neutral line (neutral line) of the power supply in a low-voltage system where the neutral line of the power supply is grounded. After using the z connectionero protection, if the insulation of electrical equipment is damaged and a short circuit occurs due to hull collision, almost all the voltage will be applied to the phase line and neutral line since the impedance of the phase line and the neutral. The line is very small, the short circuit current will be very large. The circuit protection switch or fuse will be quickly disconnected, thereby cutting off the power supply and eliminating the risk of electric shock.
At present, generators generally use single-phase power supply with two-wire system for power supply, and three-phase power supply with three-phase four-wire system for power supply, namely l TN-C power supply. Power system and TT power system. The TN-S power system should be gradually implemented, that is, single-phase three-wire power supply and three-phase five-wire power supplythey. During military field training, if local electrical resources are used, correct power supply and grounding methods should be ensured according to the local electrical power system in order to increase reliability and security of the communication system.