Boundary control

Boundary Control Process

  • Used when RIPC (Renewable In-Plant Clearance) alone is inappropriate due to equipment restrictions (batteries, photovoltaics) that cannot be de-energized.
  • Energy is isolated from the work location.
  • Verifies absence of voltage, but photovoltaics & batteries are always live and cannot be turned off.
  • Used to isolate different circuit parts before performing verification under RIPC (hot, cold, hot).
  • Not a replacement for renewables in plant clearance; energy potential remains at the work location.
  • Used as a sole energy control source only when batteries, photovoltaics, or other equipment cannot be de-energized during work or replacement.
  • Appropriate PPE and current verification are vital when working on live components.
  • Executed before RFEC on equipment isolated from batteries/solar panels that cannot be confirmed de-energized.
  • Involves disconnecting the battery module/solar panel/equipment, then releasing boundary control to confirm de-energization and proceed to RIPC.

Boundary Control Application

  • First, perform boundary control and verify no current flow, isolating what is possible, including disconnection.

  • After boundary control, an RIPC can be performed to verify absence of voltage.

  • Combiner Box Example

    • Multiple strings feed into, and are combined in parallel within a combiner box.
    • Multiple combiner boxes then feed an inverter, also connecting in parallel.
    • Opening the disconnect in the combiner box leaves both the top and bottom terminals live, since downstream components remain connected at that inverter.
    • Shutting down the inverter (stopping it from drawing current) allows the disconnects feeding that inverter to be opened. After verifying no current flow, one can open the DC side of the inverter.
    • Multimeter checks on the positive and negative terminals can verify complete isolation of the DC field from the inverter, allowing RIPC on the inverter and downstream combiner boxes, since it has been fully disconnected from all of the DC field.
      Clarification
    • Opening all combiner box disconnects is essential for RIPC. Leaving even one closed keeps all combiner boxes hot on both terminals.
    • Replacing a combiner box requires disconnecting live leads at some point.

Order of Operations for Combiner Box Replacement

  1. Shut down the inverter to stop current draw.
  2. Open all combiner boxes to separate the DC field from the inverter.
  3. If replacing a combiner box, live DC voltage will be present on the upstream side, requiring disconnection.
  4. Verify no current flow with appropriate PPE.

Current Verification

  • Clamp meter use is essential to ensure conductors leading to the combiner box are not passing current before disconnection, allowing for a safer disconnection process.

Arcing Considerations

  • Isolating DC strings is crucial. Without isolation, an arc can occur between positive and negative terminals of each DC string, providing a path for current to flow.
  • Analogy: Unplugging a lamp. When switched off, unplugging is uneventful. When on, unplugging causes a small arc.
  • Higher voltage and current increase the risk and danger of arcing.

Safe Disconnection Practices

  • Open the disconnect and then open the MC4 connectors.
  • Verify no current flow before disconnection.
  • Potential danger: Up to 1,500V1,500V may be present on a lead even with no current flow.

Exposed Conductors and Safety
Damaged MC4 Connectors: If a cable pulls out of a damaged MC4 connector, leaving an exposed 1,500V1,500V conductor, protect it with electrical tape to prevent contact.

Boundary Control Tags

  • Different from RIPC tags (no QR code).
  • No official iPad app or formal clearance process.
  • Process: Verify absence of current, apply tag with name, date, and initials on the isolation point.

Tag Usage
Disconnection Indication: Indicate disconnect is open for a reason and should not be tampered with.

Disconnect Switch Tagging

Preventing Backfeed: Replacing damaged DC disconnects (not entire combiner box) requires tagging every DC disconnect switch to prevent backfeed.

SMS 301.4 - Shock & Arc Flash Hazard Mitigation

  • Circuits at the boundary control point must be tested for zero current flow using a clamp meter (or multimeter if current is low enough).

Potential Hazard: Current Leakage

  • Difficulties: Physically verifying the absence of current flow is impossible if a conductor is touching a frame, torque tube or post, creating a leakage path.
  • Resolution: Finding and fixing the issue involves cutting/disconnecting a live conductor, potentially causing an arc.
  • Mitigation: Wait until nighttime to minimize current flow through solar panels and circuitry.

Documentation and procedures

Office Paperwork: Become familiar with SMS 301 and SMS 214, found on Horizon.

Battery Systems Discussion

Current State and Future Plans
  • Current: Large-scale batteries are becoming more important, especially with advancements in technology.
  • Future: NextEra plans to pair all wind and solar with battery storage.
Benefits of Battery Storage
  • Objective: Batteries pair with renewable sources (wind and solar) to address intermittency.
  • Mechanism: Overbuilt sites generate extra energy, stored in batteries rather than curtailed.
  • Grid Regulation: Like a glass of water, power generation must match supply/demand. Batteries help regulate, preventing blackouts/waste.
  • Traditional Regulation: Power plants constantly monitor demand, adjusting generation assets (fossil, steam, natural gas).
  • Renewables Integration: Batteries help regulate supply and demand, particularly with renewables.
Use cases

Simplification Batteries charge when demand is low and discharge when demand is high, based on time of day.

  • Four main categories:

    1. Solar Firming: Batteries paired with photovoltaics store excess energy during the day, extending output duration, especially at night.

    2. Solar Smoothing: Batteries act as accumulators, smoothing erratic photovoltaic output caused by cloud cover, equipment, or weather conditions.

    3. Peak Shaving: Standalone battery systems charge during low demand (e.g., night) when energy is cheap, then discharge during peak demand (e.g., morning) to sell high.

    4. Contingency Reserves (Frequency Response): Batteries provide backup power when a generator trips offline, allowing time to start large generation assets, stabilize grid frequency.

Reliability and Backup
  • Importance of Traditional Generation: Large steam generators and combined-cycle natural gas plants set grid frequency standard, ensuring consistency.

Backup Mechanism When large assets fail, batteries act as a backup power source, averting blackouts.

Black Start Machines

Diesel Generators: Often used to reform the grid during failures, now being replaced by battery backups.

Smaller Scale: Small generators can trip offline due to over-demand from too many devices (drills, battery chargers).

Alternative Storage Solutions
  • Hydrogen: NextEra has a hydrogen generation plant in Florida, using renewable sources to produce hydrogen and reduce emissions in natural gas plants.
Electrolysis Process
  • Uses electricity to split water into hydrogen and oxygen.
  • The hydrogen is captured and stored.
Hydrogen Storage
  • Must be compressed to increase energy density. Liquefaction requires extremely low temperatures which requires energy.
  • Requires special tanks (composites, carbon fibers), as it can seep through metal.
Hydrogen as Vehicle Fuel
  • Toyota explores hydrogen fuel for vehicles.
  • Fuel Cells: Hydrogen EVs use fuel cells to recombine hydrogen with oxygen, generating electricity and producing only water vapor.

Other Potential Battery Technologies

Lithium based is not the only storage Medium.

Non-Lithium Options
  • Zinc Bromide/Sodium: Alternatives to lithium, offering potentially higher energy density and safety.
  • Resource Availability: Alleviates concerns about lithium resource limitations.
    Inherent Dangers: There's a less intrinsic risk with zinc bromide batteries.
    Thermal Management: They generally involve less thermal control in zinc bromide, compared to lithium ion.
EOS Technologies
  • Utilizes zinc bromide technology.
  • May require specific thermal conditions (e.g., constant high temperature).
Inverter Operation
  • Flexible Input: Inverters accept voltage and current from various sources (batteries, photovoltaics), as long as requirements are met.
Battery Management Systems (BMS)
  • Lithium Ion Sensitivity: Critical, since lithium ion batteries are highly temperature-sensitive.
  • Battery Monitoring: These systems are used to ensure proper function of these batteries.

Battery Container

External Setup: Connects to the grid via an inverter, step-up transformer, and substation protection.

Battery safety in the work place

Always be aware of surroundings when working, even with general site safety, such as snakes, bugs and scorpions.

General safety
  • ESOP usage, if able
  • If possible, GTFO- egress as far as possible from the site
  • Contacting outside services- 911 to help contain any situation
  • In an battery emergency, it is possible batteries may vent as a safety measures
  • Many sites are externally protected, but in any container site , you would want to do any training such as that
Battery Module Internal Structure

General Module Setup: Contains cells, modules, racks, and container-level organization, analogous to photovoltaic systems.

Component Cell Voltages: Battery cells have voltages from 4.5-10 volts.

Module configuration in series, 56 cells, build to 50 to 80 volts

modules in racks to scale 800 to 1500 volts, with paralleled racks to increase power.

Calculations: Voltage increases in series, while current increases in parallel.

Example series, modules in 80 volts: + to negative is two forty, parallel 30V.

Quick Maths recap of concepts from former trainings.

Baghdad battery chemical battery from artifacts of the past.

Electrochemical potential for electricity that uses Chemicals and materials that generate that electricity.

Anode cathode and separated with chemicals materials.

Accidental battery cell- brisket in steel pan.

How many lasagna cells are our batteries:130

Capacity and power of energy units for the energy inside batteries and how it is utilized

  • C rating: How quick can battery discharge or recharge
  • AA battery last quite a while at low demand
  • Over working lithium and batteries will heat, expand and degrade overtime
    C rate, for discharge or recharge, name plate on a device.

Duty cycle as percent of use.

There will be software and hard ware fail safes on a lithium battery, so that it doesn't cause thermal failure. Tesla batteries are zero to 100 use and battery is on all of our devices, just as with the Samsung note thermal case, Samsung changed batteries and fail safe system. With lithium , that's how can make a safety container