The reactive power compensation controller is a critical component of the reactive power compensation system. It plays a central role in ensuring efficient and stable operation. Most manufacturers of such devices rely on third-party controllers, assembling them into their own units. Only a few companies have the expertise to design and manufacture these controllers internally. Those that can develop high-performance controllers are even rarer.
One of the key requirements for a good reactive power compensation controller is accurate current measurement. While voltage measurement is important for protection purposes—such as overvoltage or undervoltage detection—it is not always necessary for achieving effective compensation. Typically, a 1% accuracy in voltage measurement is sufficient. However, current measurement requires higher sensitivity. For low-end controllers using 8-bit microcontrollers, a sensitivity of at least 1% is acceptable. This means the controller can detect a 1% change in current, such as distinguishing between 100A and 105A in a 500A primary current transformer.
For high-end controllers utilizing DSP or 32-bit microcontrollers, the current measurement sensitivity should be at least 0.1%, which implies a need for four significant digits in the measured value. However, absolute accuracy is not always practical or necessary. Instead, the controller’s measurements should be calibrated in the field to ensure reliability.
The power factor measurement also needs careful consideration. A sensitivity of 0.001 is ideal, but it's more precise to focus on phase difference measurement rather than power factor itself. Reactive current is calculated using the formula Iq = I × sinφ, where sinφ must be derived directly from the phase angle. Using sinφ = √(1 - cos²φ) can introduce errors, especially when cosφ is close to 1. For example, if cosφ = 0.99, the corresponding phase angle is about 8.1 degrees, and sinφ is only 0.14. Any small changes in cosφ near this range could lead to large discrepancies in the calculated sinφ.
The controller must also be able to measure the full phase difference range of -180° to +180°. Some controllers have an automatic CT polarity detection feature, which limits the range to -90° to +90°. This can cause issues, such as incorrect load classification during power generation or when dealing with purely inductive or capacitive loads. For instance, if the active current is nearly zero, a pure capacitor may be misidentified as an Inductor, leading to overcompensation and potential system instability.
In terms of display options, LED digital tubes are commonly used due to their low cost and reliability. Multi-position LED displays can simplify circuit board design and reduce assembly effort. While liquid crystal displays (LCDs) offer better readability and energy efficiency, they are not suitable for cold environments. LCDs typically fail below -10°C, so they should only be used if the ambient temperature is guaranteed to stay above that threshold.
Parameter setting is essential for most reactive power controllers. Since parameters like capacitor rated capacity and CT ratio vary depending on the application, the controller must allow for user-defined settings. These settings should be stored securely, even after power loss. EEPROM chips like 24C02 are commonly used, or some microcontrollers have built-in EEPROM. In cases where flash memory is used, special care must be taken to avoid corruption during runtime.
Protection functions are crucial for preventing capacitor damage from overvoltage or harmonic distortion. Overvoltage protection and harmonic detection help avoid thermal overload, eliminating the need for separate thermal relays. This reduces both size and failure points.
Capacitor switching strategies should follow a step-by-step approach to avoid sudden current surges. Capacitors should not be switched all at once. For example, if the required reactive power is 40 kVAR, the 40 kVAR capacitor should be directly engaged. Similarly, if excess reactive power is detected, the same capacitor should be removed immediately.
The output circuit usually controls AC contactors or solid-state switches. Common outputs include 220V AC signals, with up to 10 channels typically sufficient. Electromagnetic relays are widely used, but it’s important to ensure that the relay armature is not electrically connected to the contacts to prevent voltage leakage. When the relay opens, an RC snubber circuit is needed to suppress arc voltage. Alternatively, electronic relays with thyristors can be used, offering lower driving requirements and better control. However, quality is important, as poor-quality units may cause false triggering. Bidirectional thyristors are another option, offering a cost-effective and reliable solution.
Ring Common Mode Inductor,UU Common Mode Inductor,Vertical Plug-in Common Mode Inductor,Power Line Common Mode Choke
Xuzhou Jiuli Electronics Co., Ltd , https://www.xzjiulielectronic.com