Reactive power compensation is a concern that many new construction and renovation projects need to consider when designing electromechanical systems. Due to the fact that most countries in the world have requirements for user to control the output of reactive power, they require companies to ensure a power factor at 0.8 or above. Some countries even require industrial and commercial user to have a power factor of no less than 0.9, otherwise fines will be imposed based on their electricity consumption.
In the design process of power line systems, engineers need to comprehensively consider multiple aspects such as compensation methods, capacity calculations, installation locations, and equipment selection. The compensation method and capacity calculation determine the investment budget of the owner, the service life and return cycle of the equipment, so they are crucial.
The way of compensation
Select one or more compensation methods in combination based on load characteristics and compensation objectives
1. Random compensation: Connecting capacitors in parallel with the motor is suitable for compensating for the reactive power consumption of the motor, and has the advantages of low investment and simple maintenance
2. Accompanying compensation: Connecting capacitors to the secondary side of distribution transformers to compensate for transformer no-load reactive power is one of the most effective means of compensating for transformer no-load
3. Tracking compensation: Controlled by reactive power compensation switching device, the capacitor bank is compensated on the large user 0.4KV busbar, suitable for dedicated distribution transformer users above 100KVA, with flexible operation and high reliability
4. Centralized compensation: Install compensation devices in substations or low-voltage busbars to compensate for the reactive power losses of the main transformer and the higher-level power grid
The way of capacity calculation
The determination of compensation capacity needs to be based on the compensation purpose and load characteristics. Common methods include:
1. Calculated based on increasing power factor:
Fixed compensation capacity: Qc=Px (tan ∼ i-tan ∼), where P is the average active power, and ∼ 1 and ∼ 2 are compensation, respectively
The power factor angle after. Automatic switching compensation capacity: It needs to be grouped according to the characteristics of load reactive power changes to avoid overcompensation during light loads.
2. Calculated based on suppressing voltage fluctuations:
The compensation capacity c is related to the maximum reactive power variation △ Q of the load and the allowable voltage variation △ U.
3. Calculate according to the adjusted operating voltage:
estimate the compensation capacity based on the demand for voltage increase at the end of the line.
The above principles are the basic technical principles of reactive power compensation devices. If it is not a professional electrical engineer, but a procurement personnel or owner of a certain project. So, the following points can help you make simple and quick decision making
Example:
A large ceramic factory with a wiring system of 400V/50Hz. After a 2-week analysis using a power quality tester, the average power factor of the factory was found to be 0.75, and the total harmonic distortion rate THDi was 4.2%. The power of the transformer is 1MW, and the actual total operating power of the load is about 6200KW. The minimum requirement for power factor by the power supply bureau is 0.9. The customer has a relatively sufficient budget and hopes to receive precise compensation and a longer equipment lifespan.
Technical Solution:
Harmonics Issue: As the harmonic content is not serious (THDi 4.2%), there is no need to use independent harmonic filtering equipment, such as active harmonic filter(AHF) cabinets. Even so, we still need to understand that in the operation of large industrial equipment, dynamic power line systems may experience harmonic resonance during reactive power compensation, resulting in power line overload. Therefore, we will equip capacitors with a reactance coefficient of 7% to effectively suppress harmonics in the circuit and reduce the possibility of harmonic resonance.
Switching control: The nature of the project's load and budget are the fundamental reasons for determining which switching method we should use. At present, there are two main control methods for capacitor switching:
Option 1: Capacitor+reactor(7%)+contactor+capacitor controller
Option 2: Capacitor+reactor(7%)+Thyristor controlled switch+capacitor controller
Count on all the above conditions and the specific requirements of the customer, we can obtain a preliminary technical solution for reactive power compensation:
Capacity: 2500kVar
Technical solution: capacitor+reactance (7%)+Thyristor controlled switch+capacitor controller
Compensation solution: 500kVar capacitor cabinet * 5units, shared BUSBAR, ACB*1* 5000A+MCCB*5*1000A
The technical solution for reactive power compensation is not the only optimal solution. Technicians can provide a relatively good technical solution based on the nature, complexity, and investment budget of the load. Even with the same technical solution, components from different brands will have significant differences in service life and performance. In addition, the temperature, humidity, altitude, and other factors on site need to be considered by designers. For example, if the altitude exceeds 2000 meters, the compensation effect will be reduced. To ensure the compensation effect, we need to increase the compensation capacity accordingly. Contact us for professional guidance.
