Download EVSTF09-32-TF2-04

EVSTF09-32-TF2-04
Personnel protection during charging
2016/9/13, T.Miki / Toyota
During charging, personnel protection against electrical shock is ensured mainly by EV supply equipment
(charger) and/or fixed installation (electric power supply network) with the basic protection in an EV, similar
to the case for a washing machine.
When an EV is connected to a grounded AC supply network (almost all AC supply networks are grounded
at one pole) by an EV supply equipment, the vehicle electrical chassis is connected to the earth/ground
through earthing/grounding conductor. The insulation resistance between the high voltage live parts and the
vehicle electrical chassis is almost zero (earthing/grounding resistance) in this case.
Protection against electrical shock during charging is achieved by the combination of
- basic insulation (protection against direct contact with high voltage live parts), and
- equipotential bonding (earthig/grounding in this case)
- in addition, automatic disconnection of supply operated by the fault current that disconnects one or more
of the line conductors (e.g. RCD/ CCID) is provided
EV supply equipment is provided with
- earthing/grounding conductor between the electrical chassis of a vehicle and the earth/ground
- earthing/grounding continuity monitor (except mode 1 charging, which is not allowed in US)
- RCD/CCID (either in EV supply equipment or fixed electrical installation, or both)
for personnel protection according to the relevant standards/regulations (e.g. IEC 61851, SAE J1772, UL
2231, GB/T 18487)
If the electrical insulation is lost during charging, the leakage current flows through earthing/grounding
conductor to the earth/ground. The current that flows between the vehicle electrical chassis and the
earth/ground is limited. In addition, the RCD/CCID opens the circuit to interrupt the supply of energy within
specified time if the residual/differential current (= leakage current) reaches or exceeds the specified safety
threshold due to the fault/deterioration of the electrical insulation. The characteristics of the RCD/ CCID are
specified in the relevant standards as well as according to a national electrical code of each country.)
Grid
RCD/
CCID
Fault current
AC/DC
Insulation fault!
Earth/ground
Electrical chassis
The residual current at 500 Ω/VAC isolation resistance between the high voltage bus and the electrical
chassis when the charger coupler is disconnected is sufficiently lower than the residual current to trip the
RCD/CCID. The same requirement as proposed by OICA has been already adopted in ISO 17409 as the
consensus of IEC experts and ISO experts.
Current requirement of 1 MΩ came from IEC 61851-1 that exists more than 15 years ago. At that time,
there was some discussion that the European Low Voltage Directive to cover the EV during charging
among electrical installation experts. Automobile industry picked the IEC requirement up without deep
consideration on its rationale, to instantly show them that automobile regulation already covers the safety
requirement during charging. As of now, the rationale behind the IEC requirement is unclear …
Note:
residual current device (RCD)
mechanical switching device designed to make, carry and break currents under normal service conditions
and to cause the opening of the contacts when the residual current attains a given value under specified
conditions
Note 1 to entry: A residual current device can be a combination of various separate elements designed to
detect and evaluate the residual current and to make and break current.
[Source: IEC 61851-1, IEV 442-05-02]
charging circuit interrupting device (CCID)
A device that continuously monitors the differential current among all of the current-carrying line conductors
in a grounded system and rapidly interrupts the circuit under conditions where the differential current exceeds
the rated Measurement Indication Unit (MIU) value of a charging circuit interrupting device. The device is
identified by the letters CCID followed by the differential trip current rating of either 5 or 20 indicating the
tripping rating in MIU.
[Source: UL 2231-1]
Bibliography
IEC 61851-1: Electric Vehicle Conductive Charging System – Part 1: General requirements
IEC 62752: In-Cable Control and Protection Device for mode 2 charging of electric road vehicles (IC-CPD)
IEC 60364-7-722: Requirements for special installations or locations – Supplies for electric vehicles
ISO 17409: Electrically propelled road vehicles – Connection to an external electric power supply — Safety
requirements
SAE J1772: SAE Electric Vehicle and Plug in Hybrid Electric Vehicle Conductive Charge Coupler
UL 2231-1: Personnel Protection Systems for Electric Vehicle Supply Circuits: General Requirements
UL 2231-2: Personnel Protection Systems for Electric Vehicle Supply Circuits: Particular Requirements for
Protection Devices for Use in Charging Systems
GB/T 18487.1: 电动汽车传导充电系统 第 1 部分：通用要求 (Electric vehicle conductive charging system
Part 1: General requirements )