EV Charging
Residual Current Protection for AC EV Charging
The following picture shows the electrical diagram of a typical onboard charging system(OBC). In the use of the electrical vehicle (EV), it is inevitable to have vibration and aging for components and parts, which might result in an OBC insulation fault. The smooth DC residual current resulting from the insulation fault of an OPC can impair the proper function of type-A 30 mA RCD installed at the power line supplying AC EV charging piles or installed in the AC EV charging piles. In other words, both the response time and the response level of type-A RCD can be negatively affected in the occurrence of DC fault currents above 6 mA. In the worst scenario, a type-A RCD will no longer be tripped in the occurrence of an electrical accident.
According to IEC61851-1: 2017 and IEC60364-7-222:2018, the appropriate measures for Mode-3 EV charging systems shall be
- Option 1: RCD Type B (IEC60947-2 type-B mRCD/CBR or IEC62423 type-B RCCB)
- Option 2: RCD Type A (IEC61008-1 type-A RCCB, IEC61009-1 type-A RCBO or IEC60947-2 type-A mRCD/CBR ) and RDC-DD (IEC62955 RDC-PD / RDC-MD)
RCDs and RDC-DD shall comply with the standards in the brackets. Also, it is explicitly stated by IEC60364-7-222:2018 that RCD shall disconnect all live conductors. Therefore, we highly recommend installing a type-A RCD outside the EV charger housing, even though EV chargers are already built-in AC and DC protection.
The standard of IEC IEC/EN 62752:2016 specifies the request for AC and DC residual current protection for mode-2 EVSE (IC-CPDs). Although it seems similar to the requirement for mode-3 EV charging, a high-level robust design is needed for IC-CPDs.
Residual Current Sensors
Bituo offers a wide range of high-performance AC / DC residual current sensors compliant with IEC 62752, IEC 62955, and UL 2231 standards. Our sensors have been widely used by EV charger manufacturers in Asia and Europe with a proven track record.
Typical Configurations for Mode-3 EV Chargers
Configuration 1
- AC / DC residual current sensor (also called AC / DC leakage current sensor) can be used to configure an RDC-PD (IEC 61008-1 / IEC60947-2-Annex M and IEC 62955) and RDC-MD (IEC 62955) together with a specifically designed EV charging controller, to meet the protection request defined in IEC 61851-1: 2017 and IEC 60364-7-722:2018.
- Protection against the fatal AC residual current in this configuration – via coordinated activities of the sensor, charging controller, and relays/contactors – is less reliable than RCBOs or RCCBs detecting and trips independently. Therefore, we strongly advocate installing at least a type-A RCDs upstream of the EV charger, even if your chargers declare a built-in type-A 30 mA protection.
Configuration 2
- Type EV RCD (Integrated Type-A RCBO/RCCB + RDC-PD) is a very safe and reliable protective measure because it disconnects all live conductors in the occurrence of both AC and DC fault currents, as well as works independent of charging controller and relays/contactors.
- Type EV RCDs also benefit installers and end users in terms of a very low risk of the wrong installation. Electricians have been using RCBOs/RCCBs for years without electrical accidents. Moreover, the end users can quickly notice the tripping of their type-EV RCBOs/RCCBs in the distribution boards.
- Both Type EV and Type B RCDs can provide sufficient protection for Mode-3 EV charging applications. Their differences are introduced in this article.
Compact AC EV Charger
Compact AC EV chargers- either mode-2 IC-CPDs or mode-3 wall boxes- are favored by end users. Thus, EV charger engineers have been trying hard to design EV chargers as small as possible. To meet their request, our team has created BRCS-04 two-in-one sensor with patented two-deck housing containing a CT, a ZCT, and a vertically standing PCBA.
BRCS-04 two-in-one sensor complies with IEC/EN 62752 and IEC/EN 61851-1. There are only six pins at the sensor – S1/S2 for current measurement and Vcc / GND / Trip / Test for residual current detection. The BRCS-04 sensor is very fast at detecting both AC and DC fault currents, which facilitates the wide selection of main-circuit relays.
