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First, the classification of leakage current

Generally, there are four types of leakage currents: semiconductor component leakage current, power supply leakage current, capacitor leakage current and filter leakage current.

1. Leakage current of semiconductor components

The very small current that flows through the PN junction when it is turned off. D-S is forward biased, G-S is reverse biased, and after the conductive channel is opened, current will flow from D to S. But in fact, due to the existence of free electrons, free electrons are attached to SIO2 and N+, resulting in leakage current of D-S.

2. Power leakage current

In order to reduce the interference in the switching power supply, according to the national standard, an EMI filter circuit must be provided. Due to the relationship of the EMI circuit, there is a small current to the ground after the switching power supply is connected to the mains, which is the leakage current. If it is not grounded, the shell of the computer will have a voltage of 110 volts to the ground, and it will feel numb when you touch it with your hands, and it will also affect the work of the computer.

3. Capacitor leakage current

The capacitor medium cannot be absolutely non-conductive. When the capacitor is applied with a DC voltage, the capacitor will have a leakage current. If the leakage current is too large, the capacitor will heat up and be damaged. Except for electrolytic capacitors, the leakage current of other capacitors is extremely small, so the insulation resistance parameter is used to represent their insulation performance; while electrolytic capacitors have large leakage current, so the leakage current is used to represent their insulation performance (proportional to capacity).
When the rated DC working voltage is applied to the capacitor, it will be observed that the change of the charging current starts to be large, and it decreases with time. When it reaches a certain final value, it reaches a relatively stable state. This final value current is called leakage current. i=kcu(μa); where k is the leakage current constant in μa(v·μf)

4. Filter leakage current

The leakage current of the power filter is defined as: the current from the filter housing to any end of the AC incoming line under the rated AC voltage.
If all the ports of the filter are completely insulated from the housing, the value of the leakage current mainly depends on the leakage current of the common mode capacitor CY, that is, it mainly depends on the capacity of CY.
Due to the size of the leakage current of the filter, which involves personal safety, all countries in the world have strict standards for it. For 220V/50Hz AC power supply, the leakage current of the noise filter is generally required to be less than 1mA.

2. Principle of system leakage detection

Most technicians are very familiar with GFCI sensors for ground fault current detection. The detection principle is as follows:

In a three-phase system, the chip RCMU (leakage current monitoring unit) is placed on the busbar, and the most important thing is that all three busbars randomly pass through the middle wire hole of the RCMU. The system shown in the figure has no neutral line and is a three-phase three-wire AC system. If it is a three-phase four-wire system, if the neutral wire does not carry current, the neutral wire does not need to pass through the RCMU. Assuming a 10A load connected to a 480/277vac system, the RCMU will measure it simultaneously. According to Kirchhoff's law, incoming and outgoing currents cancel each other out. The current vector sum of the three bus bars should be zero. As can be seen from the figure, regardless of the direction: 10A - 5A - 4A = 1A, that is, the leakage current value on the line of the system is 1A. RCMU is based on the design principle of chip type, and the difference from passive transformer is that it can detect different leakage components, and belongs to Type-B RCMU. Having said that, a brief review of leakage current types.
1) AC type leakage protector:
The AC type leakage protector is developed and designed for the power frequency sinusoidal leakage current, and can reliably protect the sinusoidal leakage current that is applied suddenly and slowly rising.
2) Type A leakage protector:
In addition to the reliable protection of the sinusoidal leakage signal, the A-type leakage protector can also reliably protect the leakage signal containing the pulsating DC component.
3) Type B leakage protector:
Type B leakage protector can reliably protect sinusoidal AC signals, pulsating DC signals and smooth signals

3. Application of leakage current protection in electric vehicle charging piles

1. There are 4 modes of electric vehicle charging piles:
1) Mode 1:

Uncontrolled charging
Power interface: ordinary power socket
Charging interface: dedicated charging interface
In≤8A;Un:AC 230,400V
Conductors for phase, neutral and earth protection on the mains side
The electrical safety depends on the safety protection of the power supply grid, and the safety is poor, which is eliminated in the GB/T 18487.1-2 standard

2) Mode 2:

Uncontrolled charging
Power interface: ordinary power socket
Charging interface: dedicated charging interface
In<16A;Un:AC 230
Power and current: 2Kw(1.8Kw) 8A 1Ph; 3.3Kw(2.8Kw) 13A 1Ph
Ground protection, over current (over temperature)
Conductors for phase, neutral and earth protection on the mains side
Function with protection device/control
Electrical safety depends on the safety basic protection of the power supply grid and the protection of IC-CPD

3) Mode three:

Input Power: Low Voltage AC
Charging interface: dedicated charging interface
In<63A;Un:AC 230,400V
Power and current 3.3Kw 16A 1Ph; 7Kw 32A 1Ph; 40Kw 63A 3Ph
Ground protection overcurrent
Conductors for phase, neutral and earth protection on the mains side
With protective device/control function, the plug is integrated on the charging station
Electrical safety is based on dedicated charging piles and guidance detection between piles and vehicles

4) Mode four:

control charging
Station charger
Power 15KW, 30KW, 45KW, 180KW, 240KW, 360KW (charging voltage and current depend on the size of the module)
Functions with monitoring protection/control integrated into the pile
Built-in charging station charging cable
Figure 3.1.7 The leakage current protection points in the four charging modes:

2. The structure of the charging pile is divided into:

1) Modular leakage protection design method
For example, discuss the charging pile of Mode 2, also known as IC-CPD (online charging guide box) and the leakage protection application of Mode 3, as shown in Figure 3.2.1

According to the current leakage protection requirements of IEC62752, it can be protected by a Type A module + DC 6mA module or a direct Type B leakage current sensor. For the design volume requirements of Mode 2 IC-CPD, Type B RCMUs are basically used for design. Figure 3.2.2 RCMU design application scheme of MAGTRON Type B

For mode three AC piles, for single-phase piles with low power, a modular Type B leakage current sensor can also be used for protection, and its effect is equivalent to B type RCCB. Figure 3.2.3

2) RCD circuit breaker protection design method
For charging piles with high power, the modular leakage current sensor cannot meet the high current passing on the primary side bus. Since the internal volume of the high-power pile is not high, the B-type RCCB can be directly used for protection as shown in Figure 3.2 .4. However, the current common B-type RCCB is relatively expensive, and the mode of Type A/Type F+DC 6mA can also be temporarily selected for protection as shown in Figure 3.2.5.

Fourth, the classification of RCD

 

1. According to the number of series and the number of current loops
Single stage two current loops, two stage, three stage, three stage four current loops, four stage RCD
2. RCDs are classified as follows according to the anti-malfunction performance
RCD with normal resistance to false tripping (general type)
RCD (S type) with enhanced resistance to false tripping
3. According to (when residual current occurs) delay points
Delayless RCD
Delayed RCD
4. According to the working condition with DC component
AC type RCD
Type A RCD
5. Single-phase 220V circuit, choose 2P or 1P+N type

6. For electrical equipment powered by three-phase three-wire system 380V power supply, use three-phase three-wire system (3P) RCD

3P type RCD can only be used in three-phase three-wire power distribution system without neutral wire
7. For electrical equipment with a three-phase four-wire 380V power supply, or a circuit common to single-phase equipment and three-phase equipment, a three-pole four-wire (3P+N) or four-pole four-wire (4P) RCD should be used.
All in all, the final protection method in the electric vehicle charging pile will strictly implement the protection requirements of Type B.
Magtron is a global leader in All Programamble PGA Sensor and magnetoelectric sensing SoC, dedicated to realizing a new generation of smarter, higher power density and differentiated magnetoelectric sensing system solutions. Driven by the general trend of the entire industry towards industrial Internet of Things and sensing intelligence, Magtron's innovative technologies such as Quadcore, RCMU, iShunt and other innovative technologies make magnetoelectric sensing, especially current sensor applications, highly integrated and easy to use, while achieving high The power density is also the first to realize the high-speed software of the sensor.