GBT 18487.1-2015 defines the term residual current protector as follows: Residual current protector (RCD) is a mechanical switchgear or combination of electrical appliances that can switch on, carry and break the current under normal operating conditions, as well as disconnect the contacts when the residual current reaches a specified value. It is a mechanical switchgear or combination of electrical appliances that can switch on, carry and break current under normal operating conditions and that can break the contacts when the residual current reaches a specified value under specified conditions.
Different types of residual current protector are available for different protection scenarios and the appropriate type of residual current protection should be selected for the scenario to be protected.
According to the standard classification of residual current containing DC component action characteristics, residual current protectors are mainly divided into AC type residual current protectors, A type residual current protectors, F type residual current protectors and B type residual current protectors. Their respective functions are as follows.
AC type residual current protector: sinusoidal AC residual current.
Type A residual current protector: AC type function, pulsating DC residual current, pulsating DC residual current superimposed on 6mA of smooth DC current.
Type F residual current protector: Type A, compound residual current from circuits powered by phase and neutral or phase and earth intermediate conductors, pulsating DC residual current superimposed on a smooth DC current of 10mA.
Type B residual current protector: Type F, sinusoidal AC residual current at 1000Hz and below, AC residual current superimposed on 0.4 times the rated residual action current or 10mA smooth DC current (whichever is greater), pulsating DC residual current superimposed on 0.4 times the rated residual action current or 10mA smooth DC current (whichever is greater), DC residual current from rectified circuits, smooth DC residual current.
The basic architecture of the EV on-board charger generally includes EMI filtering for the input section, rectification and PFC, power conversion circuit, EMI filter for the output section, etc. The red box in the figure below shows a two-stage power factor correction circuit with an isolation transformer, where Lg1, lg2 and auxiliary capacitors form the input EMI filter, L1, C1, D1, C3, Q5 form the step-up type The front stage PFC circuit, Q1, Q2, Q3, Q4, T1, D2, D3, D4, D5 form the power conversion circuit of the rear stage, Lg3, lg4 and auxiliary capacitors form the output EMI filter to reduce the ripple value.
During the use of the vehicle, there will inevitably be bumps and vibrations, device aging and other problems that may make the insulation within the vehicle charger problematic, so that for the vehicle charger in the AC charging process in different locations of the failure mode analysis can be obtained as follows failure modes.
(1) ground fault on the AC side of the municipal network input, at which point the fault current is an industrial frequency AC current.
(2) Ground fault in the rectifier section, where the fault current is pulsating DC current.
(3) DC/DC ground fault on both sides, when the fault current is smooth DC current.
(4) isolation transformer ground fault, the fault current is non-frequency AC current.
From the A type residual current protector protection function can be known, it can protect the AC type function, pulsating DC residual current, pulsating DC residual current superimposed less than 6mA smooth DC current, and the vehicle charger DC fault current ≥ 6mA, A type residual current protector may appear hysteresis or will not act, resulting in the normal work, then the residual current protector will lose the protection function.
The European standard IEC 61851 does not mandate Type B, but for EVSEs with Type A residual current protectors, it is necessary to additionally ensure that a fault circuit with a DC content of more than 6mA is cut off, one or the other. Combined with the analysis of the above residual current protector selection, it is clear that if the above fault protection is to be met, from a safety point of view, a type B residual current protector is required
Post time: Jan-20-2022
