Power quality problems in the power grid

(1) Wind power grid connection problem

(2) Bus voltage fluctuation

(3) Reactive power reverse

(4) Poor voltage control and stability

(5) Insufficient damping under small interference

(6) Low transient steady-state limit

Causes of grid harmonics

1. Harmonics generated at the power supply end.

In the production of three-phase generator windings, it is difficult to achieve absolute symmetry. Due to the manufacturing process, it is difficult to achieve absolute uniformity even in the core part. For other reasons, such as the stability of the generator, some harmonics occur, but usually fewer.

2. Harmonics that occur in power transmission and distribution.

Power transformers are important sources of harmonics in power transmission and distribution. Since the design of the transformer must be economical, the magnetization curve of its core is nonlinear saturated, which gives the acting magnetization current a sharp peak, producing simple harmonics.

3. Harmonics generated by electrical equipment.

Grid harmonic hazards

The harm caused by harmonics is very serious. Harmonics can reduce the efficiency of power generation, transmission and consumption, cause electrical equipment to overheat, cause vibration and noise, make equipment aging, shorten the service life, and even cause failures or safety accidents. Harmonics cause localized parallel or series resonances in electrical systems, amplifying the harmonic content and causing capacitors and other equipment to burn. Harmonics can also cause relay protection and automatic equipment failure, leading to confusion in power measurements. In the case of external power systems, harmonics can cause serious interference to electronic and communication equipment.

Damage caused by harmonics in public networks and other systems typically includes

1. Increased operating costs for energy companies

Since harmonics cannot be eliminated without treatment, a large number of harmonic voltages and currents are displaced and accumulated in the power grid, resulting in increased line losses and overheating of electrical equipment, thereby increasing the operating cost of electricity and raising the price.

2. The reliability of supply is reduced

In many cases, harmonic voltages produce sharper sine waves, which not only increase latency and stray current losses in electrical equipment such as transformers and capacitors, but also increase the electrical load on the insulating material. Harmonic current increases the copper loss of the transformer, resulting in local overheating of the transformer, increased noise under high harmonic load, accelerating the aging of the insulation and greatly reducing the life of the transformer and motor. The reliability of supply is reduced, and during the production process, supply failure is likely to have serious consequences.

3. Power supply accidents

Power systems contain many sources of harmonics (frequency converters or rectifiers), as well as capacitors, transformers, cables, motors, and other loads that are constantly moving, which can easily create resonant conditions in series or parallel. If the network parameters do not match, harmonic oscillations occur at a certain frequency, resulting in overvoltage or overcurrent. If left unchecked, they can threaten the safe operation of the network and can easily lead to transmission and distribution failures.

4. Equipment failure cannot work

In generators and rotating motors, harmonic currents or harmonic voltages cause additional losses in stator windings, rotor circuits and cores, reducing the efficiency and energy consumption of the transmission equipment. More importantly, harmonic oscillations can easily cause vibration of turbine generators, causing mechanical resonance, causing turbine blade deformation, fatigue cycle and equipment failure.

5. Cause destructive accidents

Automation of relay protection plays an important role in ensuring the safe operation of power systems. However, due to the large number of harmonics, it is easy to make various network protection and automation equipment abnormal action or action failure, especially in the widely used microcomputer protection and performance of excellent comprehensive automation equipment, resulting in regional (field) network failure, resulting in large-scale power outages and other harmful reasons.

6. Short circuit

Harmonics in the network lead to errors in the measuring instrument and measurements that do not correspond to the correct instructions (errors in the measuring instrument are mainly reflected on the meter). When a circuit breaker cuts off a current with a high harmonic content, the locking capacity of the circuit breaker is greatly reduced, resulting in arcing, short circuits and even explosions.

7. Product quality declines

Due to the long-term presence of resonance waves, the operation of motors and other equipment increases vibration, increases production errors, and reduces product quality.

8. The normal operation of the communication system is interfered with

When the transmission line and the communication line are parallel or close, due to the static electricity and electromagnetic induction between them, electric field coupling and magnetic field coupling are generated, and the harmonic components cause noise interference to the communication system, reduce the quality of signal transmission, and destroy the forward signal transmission. This not only affects the clarity of conversation, but also endangers communication equipment and personal safety in severe cases.

Harmonics interfere with adjacent communication systems, generate noise in the lungs, reduce the quality of communication, and hinder the normal operation of the communication system.

Solution

The existence of power quality problems has brought serious harm to the power grid, for this reason, Bowo provides a complete set of solutions, as follows: