Neutral is ... Definition, device and purpose

The power industry is a complex industrial complex, which consists of many components. In order for each element to work correctly and fulfill its tasks, accurate knowledge and understanding of the physical processes that occur in power equipment are necessary. Some of them are easy to explain, so we offer to get acquainted with such a concept as "neutral".

General purpose of the neutral wire in the transformer windings

Neutral is a common, zero point conductor connection in three-phase transformers or generators. Currently, there are 4 main varieties of joining the zero point:

1. Isolated. This type is characterized by a lack of neutrality. The main connection diagram for the presented network is a triangle. With single-phase earth faults at the operating phases, they do not feel changes in energy consumption. A similar variety is used in distribution networks 6-35 kV.
2. Resonance-earthed. This option involves the use of grounding the zero point of the transformer or generator windings through arc suppression coils or reactors (DGK, DGR). The availability of specialized equipment compensates for the increasing current level, avoiding more complex, interfacial damage.
3. Deaf earthed. The most common type of neutral used in consumer networks. The transformer winding on the low side is made by an open star connection, and the zero point is grounded through the ground loop of the transformer or transformer substation. In case of damage on the line or the occurrence of a single-phase circuit, a potential is created relative to the ground, which activates the protection that disconnects the line.
4. Effectively grounded. A kind of grounded neutral, which is used in high-voltage networks of 110 kV and higher. The zero point of the power transformers and the potential of the circuit are carried to the ground. To increase the efficiency of the protection, additional equipment is used, a single-column neutral grounding conductor (ZON). The position of the switching device is determined by operating instructions. For distribution networks of 6-35 kV, grounding is used through a low-resistance resistor.

Types of connection of power transformer windings

As noted above, neutral is the connection of the neutral conductor of a three-phase power transformer or generator. To determine the type of grounding, just look at the diagram of power equipment. For isolated neutral, the circuit diagram is a triangle.

Other options are implemented through grounding of the neutral conductor to ground, DHA, low-resistance resistor. The latter are mainly used in substations that convert high-voltage electrical energy to low, consumer. The concept is a star.

Isolated neutral in electrical networks

It is used in distribution networks of 6-35 kV. As for the physical manifestations of isolated neutral, the voltage rises to linear. The main purpose of this type is associated with the following points:

1. The network does not turn off, continues to work. Consumers in non-short-circuited phases use single-phase home appliances until the line shuts down. There is no voltage imbalance in 0.4 kV networks; in 6-35 networks it increases to linear.
2. The implementation of such networks is many times cheaper in maintenance, which saves significant funds on the distribution of electric energy.
3. High reliability, especially on overhead power lines. The fall of the branch will not disable the feeder and ensure its operability.

The main disadvantages of isolated networks are:

1. With a single-phase circuit, the network continues to work, the protections do not work, which sometimes leads to accidents with the population.
2. The presence of ferroresonant processes and the emergence of reactive power, which affects the quality of electrical energy.

Resistor and voltage of 110 kV and higher: how is the zero point executed?

Effective grounding is a special type of neutral conductor connected to specialized equipment, which is used in electrical installations above 1 kV. For distribution networks, the option is used with grounding through low-resistance resistors, which provide disconnection of the line with a single-phase earth fault without delay.

High voltage lines of 110 kV and higher also use the presented type of neutral, which ensures quick response of the protections. To increase the sensitivity of the “relay” operation, each power transformer has special ZON equipment. A single-column neutral earthing switch also provides overload protection.

Grounding through low resistance resistors

The use of low-resistance resistors is considered an ideal solution in terms of the safety of people in distribution networks, as well as in matters of maintaining the insulation of cable lines. The implementation of protections involves the removal of the zero point on specialized equipment, which has less ohmic resistance and gives a signal to turn off the line. The feeder is disconnected with a minimum delay time, which is one of the advantages. Among others, it is necessary to include:

• The first is neutral, which when the “earth” appears accurately determines the damaged direction and turns off the desired line.
• Second: there is no need for additional calculations and compilation of regime maps with limited possibilities of banding distribution networks.

Important disadvantages of this type of grounding:

1. It is not effective at high earth fault currents, as problems appear in substations where low-resistance resistors are installed.
2. Low efficiency on overhead lines, as well as on long lines. In the first case, the smallest approximation of tree branches will cause the feeder to turn off. Especially relevant with consumers of the 1st special, 1 and 2 categories.
3. Extra shutdowns that occur due to improper protection operation (absence of automatic reclosure), involves downtime in consumption, material losses of the energy supplying organization.

Blind earth ground power transformers

All that is connected with the 0.4 kV distribution network is neutral with dead ground to the ground. The presented type has a special place and role in terms of security. When a short circuit to ground occurs, protection is triggered, in particular, the PN-2 burns out or the machine is turned off. With regard to such a network, protection for wiring in houses and apartments is also being developed. A striking example is the action of RCDs, which ensures the detection of leakage currents.

The main advantages of this type of neutral are:

1. Ideal for distribution of electrical energy, ensures the operability of domestic and specialized single-phase / three-phase equipment.
2. The protection scheme does not require specialized and expensive equipment. Technical means such as fuses or circuit breakers can easily cope with a dead earth fault.

The disadvantages include:

1. Protections are insensitive in case of a short-circuit. An accurate calculation of the ohmic resistance of the phase-zero loop and the correct choice of circuit breakers or fuses are necessary.
2. Tripping does not occur if there is no earth fault. This is a danger to humans, which is corrected through the use of insulated wires.

Resonant-earthed or compensated neutral

Resonant-grounded neutrals are mainly used in distribution networks with a voltage of 6-35 kV, where the connection diagram is made by cable lines. Zero point connection is carried out through special plunger or adjustable RUOM transformers. Such a system allows you to determine the inductance in the network with a single-phase circuit, which provides compensation for the current level.

This type of neutral reduces the risk of an accident, the transition of a single-phase circuit to interphase. Advantages for voltage of 6-35 kV are:

1. The main advantage is associated with the appointment of equipment. High degree of protection for the insulation of cable lines with proper adjustment.

The disadvantages of a network with this type of neutral are:

1. Difficulty setting. Undercompensation or overcompensation may occur, which will prevent proper use of the equipment. For alignment, it is necessary to calculate the inductance of the currents depending on the length of the line, the power of the transformers. In the event of a change in the circuit or the addition of power equipment, plunger transformers do not always cope with the tasks.
2. Improperly configured equipment and high wear of cable lines leads to a chain reaction, which involves the failure of several weak sections of the network.
3. Increased technical losses that occur during operation, as well as safety problems. The current compensation at the substation is realized relative to the ground.
4. Inability to determine the line where the fault occurred. The process of selecting a feeder with ground is carried out by comparing the harmonics currents, which is not always considered an effective means of obtaining reliable information.

Zero conductor and arc suppression coil, reactor

The difference of the resonant-grounded neutral is associated with the equipment used. As noted above, the zero point can be located on an arcing coil of a plunger type or in a controlled reactor. The main differences are associated with the following points:

1. DHA involves compensation through a rebuilt plunger transformer system. The configuration is implemented through the calculations of a real network by the relay protection service. When an earth fault occurs, current compensation based on inductance occurs. The process is not regulated and does not adjust, which is an unpleasant moment in the case of the appearance of "earth" at several points of different lines.
2. GDR - more modern equipment, which involves the use of automatic systems for determining the inductance of the network. Among the popular options are considered reactor type "RUOM" with tuning "SAMUR". Implementation of the survey is performed in real time, which ensures operability even with several faults with earth faults.

It doesn’t matter whether it is neutral or isolated, the application of each type will find its place in modern electric power industry. A knowledge of the features will allow you to understand the physical nature of the issue.