Isolation
resistance measurements for voltage class B electric circuits
Prior to the measurement, the device under test (DUT)
shall be subjected to a preconditioning period of at least 8 h at (5+/- 2) °C, followed by a
conditioning period of 8 h at a temperature of (23+/- 5) °C, a humidity of 90 (+10%, -5%), and an atmospheric
pressure of between 86 kPa and 106 kPa.
Alternative preconditioning and conditioning parameters
may be selected provided transition across the dew point occurs shortly after
the beginning of the conditioning period. The isolation resistance shall be
measured during the conditioning period at a rate from which the lowest value
can be determined.
Isolation
resistance measurements of the balance of electric power systems
The test voltage shall be a d.c. voltage of at least the
maximum working voltage of the voltage class B power system and be applied for
a time long enough to obtain stable reading. If the system has several voltage
ranges (e.g. because of boost converter) in conductively connected circuit and
some of the components cannot withstand the maximum working voltage of the
entire circuit, the isolation resistances of components can be measured
separately by applying their own maximum working voltages after those
components are disconnected.
The following test procedure combines the measurement of
the isolation resistance of the live parts of the voltage class B balance of
electric power systems against the vehicle electric chassis and against the
live parts of the voltage class A balance of auxiliary electric systems.
- Traction batteries shall be disconnected at
their terminals from the power system.
- Electric power sources of the voltage class B
power systems other than the traction batteries (fuel cell stacks, capacitors)
may be disconnected at their terminals from the power system; if they remain connected,
power generation shall be deactivated.
- Barriers and enclosures shall be included unless
evaluations prove otherwise.
- All live parts of the balance of electric power
systems (voltage class B) shall be connected to each other.
- All exposed conductive parts of the balance of
electric power system shall be connected to the electric chassis.
- Batteries
of the auxiliary electric systems (voltage class A) shall be disconnected at
their terminals from the auxiliary circuits.
- All
live parts of the balance of auxiliary electric systems (voltage class A) shall
be connected to the electric chassis.
Then
the test voltage shall be applied between the connected live parts of the
voltage class B balance of electric power systems and the electric chassis.
The
measurements shall be performed using suitable instruments that can apply d.c.
voltage (e.g. megohmmeter, provided they deliver the required test voltage). Alternatively
the isolation resistance may be measured using the test procedure for the
measurement of the RESS as given in ISO 6469-1 with the balance of electric
power system connected to an external power source.
Isolation resistance
measurement of the voltage class B electric power sources
The
measurement of the isolation resistance of an RESS, if any, shall be in
accordance with ISO 6469-1. The
measurement of the isolation resistance of a fuel cell stack, if any, shall be
in accordance with ISO
6469-1 with the fuel cell stack in operation.
Alternatively
for the measurement of the isolation resistance of a fuel cell stack, the
entire mechanical structure of the fuel cell system (including the cooling
system with its cooling medium) shall be considered.
Prior
to the measurement, stop power generation after operation at maximum output
according to the manufacturer's specification. The voltage across the fuel-cell
stack power terminals shall be discharged. All cables shall be disconnected
from the fuel-cell stack power terminals, and all other cables from other
electric terminals of the fuel-cell stack. All cooling pipes, fuel pipes, and
air pipes shall remain connected. The applied test voltage shall be at least
the maximum open circuit voltage of the fuel cell stack. Apart from these
specific conditions, the procedure shall be performed as given in Isolation resistance measurements of the balance of electric power
systems.
Isolation resistance
measurement of entire voltage class B electric circuits
The
isolation resistance of entire conductively connected voltage class B electric
circuits may be measured using the test procedure for the measurement of the
RESS given in ISO 6469-1 with the balance of electric power system connected to
the voltage class B power sources.
Alternatively,
the isolation resistance of entire conductively connected voltage class B
electric circuits may be measured using an isolation resistance monitoring
system, if installed on the vehicle, provided that its accuracy
is sufficiently high.
In
case electric or electronic switches exist in the circuit (e. g. transistors in
power electronics), these switches shall be activated. If these switches cannot
be activated, the relevant part of the circuit may be measured separately in
accordance Isolation resistance measurements of the balance of electric power
systems.
Instead
of being measured, the isolation resistance of the entire conductively
connected circuit may be calculated using the measured resistances of the power
sources and the balance of electric power system.
Christian Rosu