Most often, in electrical installations, a dead-grounded neutral is used to protect people from electric shock. As a result, in an emergency, the potentials are quickly equalized and the protective equipment works more efficiently. For the competent use of this mechanism, it is necessary to know well and be able to apply in practice the norms of the PUE.
Content
- Advantages and Disadvantages of Isolated Neutral
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The principle of operation of a solid-grounded neutral
- Pros and cons of the method
- PUE requirements
Advantages and Disadvantages of Isolated Neutral
Today, electrical installations use two protective mechanisms - isolated and solidly grounded neutral. The main advantage is that there is no need for emergency shutdown of the first single-phase earth fault. It should also be remembered that a small current is generated in the area of damage to the mains, but this is only true with a low current capacitance to ground.. However, there are several disadvantages due to which isolated neutral is used relatively rarely:
- Intermittent arc voltage may occur.
- The likelihood of occurrence of a greater amount of damage due to breakdown of the insulation of conductors in places of occurrence of arc overvoltage is not excluded.
- All electrical equipment must be isolated to line voltage with respect to earth.
- The effects of arc overvoltage on insulation are long-term.
- It is often difficult to locate damage sites.
- In the event of a single-phase fault, the correct operation of the relay protection systems cannot be guaranteed.
All these disadvantages completely negate the advantages of this method of neutral grounding. At the same time, this method of protection in some situations continues to be effective and does not contradict the rules of the PUE.
For example, an isolated neutral can be a good solution for protecting high voltage lines, as it avoids tripping. In turn, it does not meet the requirements of protecting the networks of the end consumer of electricity.
The principle of operation of a solid-grounded neutral
First, you need to understand what is the definition of a dead-grounded neutral. According to the PUE, this method involves a direct connection of the neutral of the transformer with the grounding element. In electrical engineering, this method of grounding is usually called a worker. It should also be remembered that in electrical installations designed for a voltage of 220-380 volts, the resistance of the grounding elements should not exceed 4 ohms.
The principle of operation of a grounded neutral can be demonstrated using the example of a three-wire electrical circuit connecting an energy source to a residential building. When it is created, the neutral is simply distributed over the shield, and all consumer grounding circuits are connected to it. Such a chain does not imply the presence of various devices that can disrupt its unity.
If we assume that, due to frequent vibrations in the refrigerator, the phase conductor has disconnected from the attachment point and has come into contact with the body, then this situation is emergency. All this leads to the appearance of a short circuit and a rapid increase in current strength. However, the circuit breaker quickly copes with the task and opens the circuit. If a person accidentally touches the wire, then an electric shock will not occur, because the resistance R0 will be less in comparison with that arising when passing through the human body.
Pros and cons of the method
A deafly grounded neutral has more advantages and fewer disadvantages in comparison with an isolated one. Among the advantages are:
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It becomes possible to use equipment with such a level of isolation, which was originally planned. - There is no need to use special protective circuits.
- Copes effectively with overvoltage suppression.
However, this is not an ideal method and has some disadvantages. To begin with, the risks of injury from electric shock remain, although they can be considered insignificant. In addition, due to a large current to ground, interference and even damage to the network can occur.
PUE requirements
Today, both methods are actively used in electrical engineering - solidly grounded and isolated neutral. The differences between them primarily lie in the way the transformer is connected to the grounding element. All the necessary information on the choice of the method of protection is set out in the PUE.
If we talk about a 220 volt household network, then the grounding point can be located near the transformer, and a separate conductor is used to solve the problem. This will reduce the current path while reducing costs. In a country house, it is allowed to connect to the metal frame of the building located in the depths of the earth.
If the grounding element is the foundation, then it is necessary to connect to its reinforcement at least at two points.
