Frequently Asked Questions
1. Q: The MCR type static var compensator adopts iron core reactor while the TCR type SVC uses air core reactor. Is the loss of the former higher than that of the latter?
A: The loss of the MCR type SVC is seemingly higher than that of the TCR type SVC due to the iron loss of the former. However, if we do not stare at the iron loss but analyze the loss of the TCR SVC and MCR SVC more accurately, detailedly, and comprehensively, we will get more rational and more correct results.
a. Iron loss accounts for a small proportion of the total loss of the entire equipment
The loss of the whole equipment includes iron loss, line loss, and SCR heat loss. Iron loss accounts for less than 5% of the total loss. Iron loss of common transformers includes hysteresis loss and eddy current loss. The former accounts for 80% while the latter accounts for 20%. Since the working state of the magnetic valve saturable reactor deviates from the zero flux point, the loss caused by hysteresis is avoided. So, only the 20% eddy current loss is left. From the above analysis, we can see the iron loss of MCR SVC is very small.
b. Actually, most of the loss of SVC is line loss and SCR heat loss. Now let's analyze the line loss of MCR SVC and TCR SVC.
Firstly, TCR air core reactor uses aluminum wires while the MCR iron core reactor adopts copper wires. Aluminum has larger resistance than copper, so it generates more heat than copper.
Secondly, in terms of wire length, we can see from the impedance formula of reactor, X=ω×μ×N2×S/L, that the square of wire length is inversely proportional to the medium magnetic permeability under the same voltage and capacity. Since the magnetic permeability of iron core is 2000~8000 times of air magnetic permeability, the aluminum wire of air core reactor is much longer than the copper wire of iron core reactor under the same capacity. (MCR also has air gap, but it is very small, about several centimeters in length). The longer the aluminum wire, the greater the line loss. If you want to reduce the line loss, you have to increase the conductor cross-section. But this is completed by a lot of investment. The cost performance is too low.
c. The SCR of TCR SVC is connected in series to the high voltage main circuit. Its capacity is required to be large, so the generated heat is great. Consequently, large complex and expensive cooling equipment is required. By contrast, the SCR of MCR SVC works under low voltage and low power, so little heat is produced and cooling device is almost unnecessary, except for the MCR SVC with the capacity exceeding 50MVar, a low-power air-cooled cooling device is needed.
In conclusion, the loss of MCR type SVC is lower than that of the TCR type SVC. It is less than 1/2 of the latter.
2. Q: Since the MCR type Static Var Compensator adopts saturated iron core reactor, does it produce large noise?
A: Whether it is a transformer or reactor, it will produce noise. But the main reason of producing noise does not lie in whether the device is saturated (but of course, the higher the magnetic flux density of the iron core, the larger the noise produced; but the noise can be reduced by technique improvement). It depends on the manufacturing process.
Currently, China's transformer technology is becoming more and more advanced, especially in the aspect of reinforcing the overall structure, strengthening the wholeness of the iron core and the support, as well as reducing the vibration of the iron core. The noise level of large transformer is decreased below 70dB, which meets the requirements of national environmental protection standards. Our company adopts transformer and reactor from domestic well-known manufacturers and these devices fully comply with the national environmental noise emission standards, so nearly no noise pollution will be caused to the surrounding environment.