The Madshen monophasic AC current transmitter is an important component of the power monitoring system. Its function is to convert the AC current into DC voltage or DC current. At the same time, it also undertakes the isolation function of the strong current system and the weak current system (for example, the computer system), so as to protect the input of the computer acquisition system from being breakdown by the high voltage alternating voltage.
In addition, by converting the current transmitter, the DC or DC voltage proportional to the input alternating current is more convenient for long-distance transmission, enabling remote monitoring devices or monitoring instruments to receive the precise current signals conveniently.
Because current is the most important index reflecting the load size of electric power system, the current transmitter is the most automated instrument used in electric power monitoring system.
How to select the current transmitter is the key to the accurate detection and conversion of the AC current. If it is not reasonable to choose the appropriate current transmitter, it will cause the error and distortion of the monitoring system in the future.
The following problems should be paid attention to in selecting current transmitter:
1. is a single phase current or a three-phase current - a current transmitter usually has 2 forms, which can be used to detect single phase or three-phase current.
2., the range of the input current of the transmitter. Because the wide range of actual load current changes, in order to adapt to this situation, we usually use current transformer to convert large current to 1A or 5A small current. Therefore, the input of the current transducer is usually selected according to the two current of the current transformer. For example, the two current current transformer is 5A, then the input current of the current transducer can also be 0-5A. The variation range of the output DC signal - the standard of the international output signal is usually used in DC 4-20mA. Of course, DC output can also be operated by DC voltage (for example, DC 0-10V, etc.), matching with the input of instrument or automatic control device behind the current transmitter.
3., the specifications of auxiliary power, the AC current transmitter, in order to accurately detect the change of input current and output DC signals that are linearly changed with input current, usually need an auxiliary power supply, which is the most current source of current transmitter. Usually, the most selected is the easy to get AC 220V. It can also choose DC power, such as DC 24V and so on. It is important to note that there are some current transmitters that claim that no auxiliary power is needed, that is, the so-called &ldquo, passive &rdquo, and current transmitter. The current transducer should be carefully selected. The so-called “ passive ” not a power supply is not needed, but a power supply by the instrument behind the output signal of the current transmitter. It's “ eat the instrument power &rdquo behind the transmitter; Nature increases the burden of collecting instruments behind the transmitter. Another kind of &ldquo, passive current transmitter &rdquo, is the power of the transmitter using the two current of the current transformer. This transmitter disadvantage is that when the load current is low, the output current natural small current transformer, provided to the transmitter energy is also reduced, at the same time, current transducer will produce nonlinear error, and according to current signal transmission error, so that the transmitter is needed to be used.
4., the overload and overload capacity of the current transmitter, when the load current is overloaded or when the system fails, the current transmitter usually has a very large overload current. In this case, the ability to withstand the large overload current becomes an important indicator of the performance of the current transmitter.
