How to configure reactive power compensation for impact loads?
What’s impact load?
Impact load usually refers to the electrical equipment with large rated capacity (30% greater than the system power supply transformer capacity) and frequent input and cut demand.The impact load accounts for a large proportion in the grid, and the difficult to control the rapidly changing electric energy quality problems has a great impact on the grid, which has become a hot issue of attention and research.
What’s the Characteristics of the impact load?
Impact load is involved in the wide variety of electrical equipment in many industries.According to the fluctuation frequency of impact load and the possible power quality problems, it is roughly divided into the following three types:
-The first typical representative is inverter welding equipment, the inversion program leads to current amplitude distortion which leads to a variable Thdi.
-The second type is frequent start and stop motors, such as punch, paper cutters, grain carts and other equipment.The frequent power outage opportunities will cause rapid changes in the grid load.The active power and reactive power not only change the amplitude of the motor but also the direction.
-The third type of load is the arc furnace type load.The load change of the arc furnace is completely random, and the load change of each phase is not correlated, and there is no rule for the load change.
Power quality problem of impact load and its harm
Impact loads power quality problems mainly include reactive power, harmonic, voltage fluctuation and flash change, three-phase load imbalance, etc. Due to its fast change speed and large amplitude, some even reverse phase, so it is very difficult to deal with.It also causes the generator end structure damage and metering error.The reactive power and three-phase load imbalance will increase grid loss and increase grid operating costs.Especially for the small-capacity power grid, it is difficult to compensate the reactive power of the impact load through traditional means, resulting in a higher electricity price of power users and a greater loss.
How to configure reactive power compensation for impact loads?
The traditional scheme is to configure a capacitor banks.But due to the impact load change too fast, some changes or even irregular, traditional capacitor compensation can’t react quickly, and a frequent input and cut off will also reduce the capacitor’s service life . Meanwhile, due to the steps compensation characteristics of the capacitor compensation, it’s prone to result in a over compensation with -PF ,which may casues a penalty.
How to solve the rapid response problem, reduce the capacitor input/cut frequency, and avoid over compensation?
As a new I G B T inversion based technology, SVG responds ultra-fast usually within 10ms . In a hybrid SVG capacitor banks reactive power compensation system, SVG takes the role of quickly response and adjust the peak compensation, thus will not only reduce the cutting frequency but also extend the service life of the capacitors.
As SVG compensation range is from capacitive to inductive -1 to 1, Hence the hybrid compensation system will be enabled from capacitive to inductive .
For example,if we configure 100kvar SVG with 400kvar capacitor banks for a ordinary load , the hybrid compensation capability will ranges from -100kvar to +500kvar,If there is a over compensation from capacitors, SVG will automatically output reverse reactive power to offset it,In this way, the user’s requirement for the target power factor will be realized.
But for fast impact load SVG sizing,the vital SVG size should be equal to capacitor banks.That’s to say ,400kvar capacitor banks should be equiped with 400kvar SVG. Because for a peak compensation,capacitor banks takes longer time to cut off ,this will leads to a over compensation after the peak come down,SVG will react faster and output an equal reverse reactive value to offset,when a peak compensation requirement is needed, SVG will react faster before capacitors input to avoid under copensation occurs.
How to do the wiring for hybrid SVG Capacitor banks compensation?
In hybrid compensation system, SVG CT access point should be upstream of capacitor banks,thus ,SVG will output corresponding reactive power subject to the remainig reactive power compensated by capacitor banks,SVG will also amend the under compensation and over compensation problem caused by capacitor steps compensation. In this way SVG will improve the compensation performance and achieve a vital PF on grid metering device.
