Classification of Protective Measures
Classification Of Protective Measures
Protective measures are divided into three areas. This multi-level concept illustrates the takeover function adopted by the most important protective measures when a protective measure fails.
Basic protection
- Protection from direct contact
This category includes the basic insulation of active high-voltage components in the vehicle. This protection type classifies the degree to which equipment is protected from contact, foreign bodies and water. In this case basic protection is provided. The standardised classification of protection types is specified in ISO 20653 (International Standards Organization) and DIN 40050/EN 60529. The IP code includes the degrees of protection and defines the protection type.
Protection types according to ISO 20653
Two-digit protection types originating exclusively from the electrical engineering sector (such as IP 54) have been extended especially for road vehicles (high-voltage technology). These extensions affect single-digit degrees of protection which have been replaced by two digits ending with a K.
A third and fourth digit were also added to take into account workshop requirements and the testing of moving parts. Standardisation according to DIN or EN deviates from the international standard in certain cases.
In high-voltage technology, the different variations are heavily restricted by the minimum requirements for shock-hazard protection.
Examples for shock-hazard protection
IPXXB
Equipment is protected against access with fingers.
IPXXD
Equipment is protected against access with a wire (> 1 mm). Contact/Water protection according to DIN is not specified.
The classification of high-voltage components used by Porsche
NOTE: At Porsche, degree of protection IPXXB is also valid for contact surfaces on disconnected plugs. Degree of protection IPXXD is the minimum protection type for all operational high-voltage components.
Fault protection
- Protection against indirect contact
Indirect contact exists if faults (e.g. ground fault) on system components that are usually free of voltage connect voltage potentials to other components.
Protective measures are divided into two groups with and without protective conductors.
Measures without protective conductors
Total insulation
All devices from protection class 2 fall into this category (see "Classification of devices into protection classes").
Safety or functional extra-low voltage (SELV/FELV)
See "Classification of devices into protection classes".
Protective separation
An isolating transformer galvanically isolates the primary end connected to the reference potential from the secondary end. In the event of a fault, current cannot flow towards the reference potential. Isolating transformers are marked with a corresponding symbol. Refer to the chapter on protective separation.
Measures with protective conductors
The protective conductor (PE - protective earth) connects conductive, touchable inactive system components to one another and may only be used for this purpose. The green-yellow color is permitted exclusively for protective conductors.
Protective ground
The protective conductors on the system are connected to the PEN/neutral conductors. In the event of a ground fault, the fault current generated is so large that the high-current protection mechanisms (fuses) can trigger within 0.2 s. The fuses integrated in the protective measures are designed to protect the line. The ground fault then becomes a short circuit.
Grounding wire system (IT network with isolation monitoring)
The grounding wire system (not to be confused with the protective conductor system) consists of the protective measures used in hybrid vehicles.
The IT system (see Network types) is combined with a function that monitors the isolation of the producer from the reference potential (body).
All elements on the high-voltage system are connected with one another (equipotential bonding). Generated contact voltages are diverted to the vehicle body.
For other versions, see IT network and equipotential bonding.
The area 2 fault protection measures become ineffective if another fault occurs in addition to the first fault.
Protective separation
Protective separation prevents contact resistances from occurring between different energized areas or current circuits and is usually achieved through an isolating transformer (galvanic isolation) that disconnects the active parts (i.e. live under normal conditions) from the reference potential completely. Reference potential refers to the vehicle body here. A technician is also "connected" to the body when working normally on the vehicle (leaning, supporting, etc.). The additional connection to ground can be ignored because motor vehicles are already regarded as being isolated.
The protective isolator is integrated in the DC/DC converter between the 288-volt and the 12-volt areas.
If a ground fault occurs on a high-voltage component, impermissible contact voltages are not generated between a housing and the reference potential or the remaining 12-volt potential. Without this protective isolator, it would not be possible to isolate the high-voltage area from the reference potential.
Additional protection
- If the basic protection and fault protection fail
Additional protection measures prevent dangerous contact voltages from occurring if the measures for area 1 and 2 fail.
Residual-current device protection
The residual-current circuit breaker measures the sum of the currents flowing in both directions within the system. If a current flows to ground through a person, for example, the two currents are no longer the same. If this differential current exceeds the trigger current (e.g. 30 mA), the residual-current circuit breaker shuts down the system at all terminals within 0.2 s.
Pilot line
The pilot line is a ring line that loops through all high-voltage components.
Open circuits in the line are identified by the battery management system (BMS) and the high-voltage system is actively discharged as a consequence.
Active discharge
Controlled by the battery management system, active discharging reduces residual voltages in the high-voltage system and is performed every time the system is switched off or an open circuit is detected in the pilot line.
Passive discharge
High voltage-components discharge without intervention from the battery management system so that residual voltages in the capacitances are discharged rapidly after the power electronics are removed, for example.
Equipotential bonding
Equipotential bonding is a connection between all touchable, conductive and inactive parts (i.e. live under normal conditions) of an electrical system. All housings on the high-voltage components are connected to the vehicle body.
The main task of equipotential bonding is to prevent impermissible contact voltages caused by induction or faults within the system and the failure of basic and fault protection measures, and divert these voltages to the shared potential (vehicle body).
In Porsche hybrid vehicles, equipotential bonding safely discharges contact voltages in conjunction with the relevant IT network. Combined with other measures, this system fulfils the requirements for intrinsically safe high-voltage vehicles.
In the following example, which does not include equipotential bonding, a second ground fault occurs in the IT network and connects the housing with the negative terminal on the battery. 288 volts are present between the housings. The fuse does not trigger.
The equipotential bonding in the illustration below short circuits these voltages and discharges them via the body.
A connection established between the two terminals on the high-voltage battery causes the fuse to trigger. Dangerous contact voltages do not occur, even momentarily, if the contact resistances involved in equipotential bonding are small enough in relation to the resistance of the body.
Implementation
Equipotential bonding is realized by way of a conductor with black insulation. This connects the components and the vehicle body. The main elements of the equipotential bonding system are the housings from the following components:
- Power electronics
- High-voltage battery
- Electric machine
- High-voltage air-conditioning compressor
The ground straps are secured on both sides with grounding bolts. The following illustrations show the configuration of the power electronics and the high-voltage battery.
NOTE:
- The effectiveness of equipotential bonding depends directly on the quality of the configuration. All contact surfaces must be clean and free of grease. The battery manager evaluates the contact resistances as isolation faults.
- See Workshop Data.
Safety and functional extra-low voltage (SELV/FELV)
Even the safety and functional extra-low voltages offer effective additional protection. Please refer to "Classification of devices into protection classes" for details on the SELV and FELV.