How to Choose the Power Transducer Correctly?
With the increasing degree of automation of the electrical system, the detection requirements for the electrical system are getting higher and higher and the function of the power transducer is very important. A power transducer is used to collect various signals, such as current, voltage, power, frequency, power factor, etc., and convert these signals into Standard signals, transmitted to the control system.
What is the power transducer function?
The power transducer is a device that converts various signals in the electrical system into standard signals and transmits them to the control system. Common power transducers include AC current transducers, AC voltage transducers, frequency transducers, power transmitters, power factor transmitters, power transmitters, DC current transducers, and DC voltage transducers device. This article will introduce the common questions in the selection of power transducers according to the type of measured power parameters, and help you easily grasp the selection method of power transducers.
How to choose the power transducer correctly?
1. AC voltage transducer and AC current transducer
The AC voltage transducer/AC current transducer is to convert a certain range of AC voltage or current into a standard analog signal or digital signal output in proportion. The selection is relatively simple, and the correct model can be selected by providing the measurement range, output signal, and working power parameters; the following points should be paid attention to when selecting the type:
When measuring AC voltage/current, there will be different requirements for detecting single-phase or three-phase, so pay attention to distinguishing when selecting models;
To measure AC voltage or current signals with distorted waveforms and non-standard sine waves, a transmitter with a true RMS measurement method is required;
Conventionally, when the voltage is higher than 500V and the current is higher than 5A, it is necessary to connect the transmitter through the secondary side of the transformer; if the current is required to directly measure the primary current without passing through the transformer, a perforated current transducer can be used.
In a word, you should choose AC voltage transducer and AC current transducer based on current transducer function and voltage transducer function.
2. Frequency transducer
The frequency transducer measures the frequency of the grid or power system and linearly converts a certain frequency range into a standard analog signal or digital signal output. When selecting a model, you need to know the frequency measurement range, output signal, and working power parameters, and you need to determine the voltage level of the input signal. The voltage level can be a range; for high-voltage systems, the frequency transducer needs to be connected to the secondary side of the voltage transformer.
3. Power transducer
The power transducer calculates the active/reactive power value after measuring the input voltage and current signal and converts it into a standard analog output or digital output that is linear with a certain power range. Including single-phase active power transducers or reactive power transducers, three-phase three-wire active or reactive power transducers, and three-phase four-wire active power transducers or reactive power transducers. When selecting the model, it is necessary to determine the wiring mode, input current or voltage range, working power supply, output signal, and power range of the system under test.
Transform the electrical energy in the power system into a linear proportional pulse output or digital output. Electric energy is divided into active electric energy and reactive electric energy. When selecting a model, it is necessary to confirm the wiring method, input current/voltage range, working power supply, output signal, and pulse constant of the system under test; the issues that need attention are:
Pulse output, one-way or two-way pulse output can be selected, and the two-way pulse output is for the output of forward electric energy and reverse electric energy respectively;
The pulse output constant is the number of pulses of a certain amount of electric energy, such as 5000imp/kWh, which means 5000 pulses per kilowatt-hour of active energy. Like other transmitters, when the input current and voltage signals are connected through the secondary side of the transformer When using a transmitter, the electric energy of the transmitter represents the secondary electric energy, and the electric energy of the primary side = the electric energy of the secondary side * the transformation ratio of the current transformer (CT) * the transformation ratio of the voltage transformer (PT);
4. power factor transducer
The effective value of voltage and current is directly multiplied to indicate the maximum power that the power supply can supply or the circuit can absorb. We call it apparent power. The ratio of active power to apparent power PF=P/S=cosφ is the power factor. The power factor transmitter is an instrument that converts the power factor into a standard analog signal output or digital output. Including single-phase power factor transducers, three-phase three-wire power factor transducers, and three-phase four-wire power factor transducers. When selecting the type, it is necessary to determine the wiring mode, input current/voltage range, working power supply, output signal, and power factor measurement range of the system under test; similar to the power transducer, the measurement of power factor is difficult to understand and confirm during type selection range, the following points should be noted:
Determined according to the formula power factor PF=P/S=cosφ, the power factor is the cos function relationship of the phase angle difference φ, and the phase angle difference is determined by the inductive and capacitive loads contained in the system.
Because the power system has certain standard requirements for power factor, the measurement range of the most commonly used power factor transducer is 0.5(C)~1~0.5(L), which can meet the requirements of most systems for power factor measurement. There are also ranges: 0(C) ~1~0(L) and 0~1;
In addition, it should be noted that sometimes there is a need to measure the phase angle difference of the system, so since the power factor is the cost function of the phase angle difference φ, it is generally recommended to directly replace it with a corresponding power factor transducer.
Other FAQs about selecting a power transducer
The selection of a DC current transducer/ dc voltage transducer is relatively simple, one only needs to provide the measurement range, output signal, and working power parameters. Usually, when the DC current is greater than 10A, an external shunt can be installed, or a DC current transformer with perforated wiring can be selected. Transmitters, such as Hall current transducers;
The AC system generally defaults to a power system with a power frequency of 50/60Hz. If it is an AC system with other special frequencies, it must be proposed separately when selecting the model;
In addition to single-function power transducers, you can also choose some combined-function power transducers, such as combined current and power transducers, power and electric energy combination transmitters, etc., the selection method and single-function transmitters The transmitter is consistent;
For transducers with digital output, the most common one is RS485 communication output, which can measure a single power value, or multiple power or full power data;
The input, output, and power supply of most power transducers are mutually isolators. For power systems with different voltage levels, it is necessary to pay attention to whether the isolation voltage level of the power transducer meets the requirements;
The measurement accuracy of the power transducer will be one of the considerations in the design of the power system. When selecting the model, it is necessary to confirm whether the accuracy of the transmitter meets the design requirements;
In addition to the above power data, there will also be some special power data to be measured, such as negative sequence current transmitter, negative sequence voltage transmitter, zero sequences current transducer, dual output current transducer, etc., according to the corresponding transducer selection table when selecting, specify the specific parameters respectively.