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EV.5.3 Maintenance Plugs
EV.5.3.1 Maintenance Plugs must allow electrical separation of the Accumulator Segments to meet:
a. The separated Segments meet voltage and energy limits of EV.5.1.2
b. The separation must affect both poles of the Segment
Picture - Amphenol SurLok Series
Picture - Amphenol SurLok Series
First of all, what are Maintenance Plugs used for?
High Voltage Maintenance Plugs are used to safely isolate sections of electrical circuits or equipment during repair work. By inserting these plugs into designated sockets, it is safe to assume that sections which you are working on are completely de-energized and isolated from the rest of the electrical system. Maintenance Plugs also provide a secure and insulated connection point for monitoring and testing.
As stipulated by EV.5.3.1.a, configuration of these maintenance plugs must allow teams to justify that their individual segments are compliant with EV.5.1.2. Not only must the maximum voltage of each segment be under 120V DC, but the maximum energy of the segment must also be under 6 MJ.
To calculate the static voltage of our stack, we use Nodal Analysis on a schematic of our Segment Layout. To calculate the contained energy of our stack, we multiply the findings of our static voltage with a Nominal Capacity calculated using an Equivalent Capacitance Analysis within our Segment Layout, and converting from Amp-Hours to Joules.
Rules Reference - EV.5.1.2
Rules Reference - EV.5.1.2
EV.5.1.2 Each Accumulator Segment must contain:
Maximum static voltage of less than 120 V DC
Maximum energy of 6 MJ
The contained energy of a stack is calculated by multiplying the maximum stack voltage with the nominal capacity of the used cell(s).
Additionally, as per EV.5.3.1.b, the plugs must separate both the positive and negative terminals of each Accumulator Segment. In addition to for the sake of redundancy, this rule works to prevent teams from bypassing energy limits by potentially bolting segments together on one end and putting a Maintenance Plug at the other end so that there would be greater than 120V DC across the Disconnect Pins.
EV.5.3.2 Maintenance Plugs must:
a. Require the physical removal or separation of a component. Contactors or switches are not acceptable Maintenance Plugs
b. Have access after opening the Accumulator Container and not necessary to move or remove any other components
c. Not be physically possible to connect in any configuration other than the design intended configuration
d. Not require tools to install or remove
e. Include a positive locking feature which prevents the plug from unintentionally becoming loose
f. Be nonconductive on surfaces that do not provide any electrical connection
EV.5.3.2.a determines that teams are not allowed to use contactors or switches as Maintenance Plugs, but instead must use a design that requires a component to be physically separated. Contactors and switches do not suffice because there is no component being removed. Instead, they either use electromagnets or physical actuation to open-or-close a set of contacts.
EV.5.3.2.b states that the Maintenance Plugs should be accessible from a top-view of the Accumulator Container (with the lid off, of course). Because these components electrically isolate each segment, it is important that they can be accessed without having to sift through components which might not yet be isolated and could potentially carry higher levels of energy.
EV.5.3.2.c requires that no incorrect connection be mechanically allowable by the team's design. This is to prevent teams from accidentally shorting the high voltage batteries by connecting incompatible terminals.
EV.5.3.2.d specifies that tools should not be used to install or remove these plugs. Ultimately, these isolation plugs should be immediately accessible at any time, and should not require access to insulated tools to engage or disengage.
As mentioned in EV.5.3.2.e, the Maintenance Plugs must be equipped with a positive locking feature. Positive locking is a mechanism used to ensure that two or more components are securely locked together in a specific position or configuration, and often involves physical components that interlock or engage with each other in a way that prevents movement or separation. This can include mechanisms such as pins, bolts, clips, or hooks that physically secure components together and help them to withstand high forces and vibrations.
In our manufacturing process, we use the concept of "Poka-yoke" in positive locking devices. This term roughly means "avoid unexpected surprises" or "avoid blunders" in Japanese. In English, a poka-yoke is sometimes referred to as "mistake-proof" or "foolproof." Essentially, a poka-yoke is a safeguard that prevents a process from proceeding to the next step until the proper conditions have been met.
Graphic - Poka-Yoke
Graphic - Poka-Yoke
Finally, EV.5.3.2.f requires that surfaces of the maintenance plugs must be non-conductive except as required to make the electrical connection, mainly to prevent shorting within the internal housing and to prevent unexpected arcs within a high-energy path.
EV.5.3.3 When the Accumulator Containers are opened or Segments are removed, the Accumulator Segments must be separated by using the Maintenance Plugs. See EV.11.4.1
This rule states that in the case where the Accumulator Container is open and exposes the segments or teams need to remove their segment(s), each Accumulator Segment must be electrically isolated using the Maintenance Plugs. This is necessary because whether charged or not, the Accumulator is a High Energy System that is always live. When cells are connected, they have the capacity to carry High Voltages which could be dangerous if worked around. Isolating the Accumulator Segments reduces the maximum voltage ceiling from 600V to 120V, which is much less hazardous.
EV.11.4 states that any energized electrical work or High-Voltage work must be done in the "Hot-Tent" (or designated area) at Competition.
Rules Reference - EV.11.4
Rules Reference - EV.11.4
EV.11.4 Accumulator
EV.11.4.1 The following work activities at competition are allowed only in the designated area and during Electrical Technical Inspection IN.4 See EV.5.3.3
a. Opening Accumulator Containers
b. Any work on Accumulators, cells, or Segments
c. Energized electrical work
Rules Reference - IN.4 (Referenced in EV.11.4)
Rules Reference - IN.4 (Referenced in EV.11.4)
IN.4 ELECTRICAL TECHNICAL INSPECTION (EV ONLY)
IN.4.1 Inspection Items
Bring these to Electrical Technical Inspection:
Charger(s) for the Accumulator(s) EV.8.1
Accumulator Container Hand Cart EV.4.10
Spare Accumulator(s) (if applicable) EV.5.1.4
Electrical Systems Form (ESF) and Component Data Sheets EV.2
Copies of any submitted Rules Questions with the received answer GR.7
The following basic tools in good condition:
Insulated cable shears
Insulated screw drivers
Multimeter with protected probe tips
Insulated tools, if screwed connections are used in the Tractive System
Face Shield
HV insulating gloves which are 12 months or less from their test date
Two HV insulating blankets of minimum 0.83 m² each
Safety glasses with side shields for all team members that might work on the Tractive System or Accumulator
IN.4.2 Accumulator Inspection
The Accumulator(s) and associated equipment (Hand Cart, Chargers, etc) may be inspected during Electrical Technical Inspection, or separately from the rest of Electrical Technical Inspection.
IN.4.3 Accumulator Access
IN.4.3.1 If the Accumulator Container(s) is not easily accessible during Electrical Tech Inspection, provide detailed pictures of the internals taken during assembly
IN.4.3.2 Tech inspectors may require access to check any Accumulator(s) for rules compliance
IN.4.4 Insulation Monitoring Device Test
IN.4.4.1 The Insulation Monitoring Device will be tested by connecting a resistor between the Tractive System Measuring Points (EV.5.8), and several electrically conductive vehicle parts while the Tractive System is active
IN.4.4.2 The test passes if the IMD shuts down the Tractive System in 30 seconds or less at a fault resistance of 50% below the response value corresponding to 250 Ohm / Volt
IN.4.5 Insulation Measurement Test
IN.4.5.1 The insulation resistance between the Tractive System and GLV System Ground will be measured.
IN.4.5.2 The available measurement voltages are 250 V and 500 V. All vehicles with a maximum nominal operation voltage below 500 V will be measured with the next available voltage level. All teams with a system voltage of 500 V or more will be measured with 500 V.
IN.4.5.3 To pass the Insulation Measurement Test the measured insulation resistance must be minimum 500 Ohm/Volt related to the maximum nominal Tractive System operation voltage.
IN.4.6 Ready to Drive Sound
The sound level will be measured with a free field microphone placed free from obstructions in a radius of 2 m around the vehicle against the criteria in EV.9.5
IN.4.7 Electrical Inspection Completion
IN.4.7.1 All or portions of the Tractive System, Charger and other components may be sealed IN.2.6
IN.4.7.2 Additional monitoring to verify conformance to rules may be installed. Refer to the Event Website for further information.
IN.4.7.3 Electric Vehicles must pass Electrical Technical Inspection and Mechanical Technical Inspection before the vehicle may attempt any further Inspections. See EV.11.3.2
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