Emerg Power & Renewable Energy Flashcards
As a battery discharges, the internal resistance ______?
Rises
As a battery becomes more loaded, the terminal voltage will ________?
fall
Where are EP systems neccessary?
in any facility where a large number of people congregate
What is a cell?
devices that convert chemical energy into electric energy
What is a battery?
when several cells are connected together
What does the output of a battery depend on?
the material within and how they are connected
What is each cell made out of, are they connected and what are they immersed in?
- Made of two different materials called electrodes
- Not connected but immersed in a conductive liquid called electrolyte
What happens when cells are connected in series?
Higher voltage is achieved
What happens when cells are connected in parallel?
Higher current is achieved
What are batteries rated in?
voltage & ampere-hours
What are characteristics of primary cells? What is a dry cell?
- Energy comes from consuming electrodes
- No recharge
- Energy is built into these cells
- Great for portable equipment
- Dry cell = electrolyte is solid or molten
What are characteristics of secondary cells?
- Also called storage cells, no energy at the beginning
- Rechargeable
What is a wet cell?
a secondary cell which has a large capacity
How is a cell recharged?
Passing current through in the opposite direction of discharge
What do all batteries have?
internal resistance
What is the chemical reaction between charged and discharged batteries?
Charged = Lead dioxide + Sulphuric Acid Discharged = Lead sulphate + Lead dioxide + Water
What causes the internal resistance to increase during and when the battery is discharged?
“Sulphation”
What happens with every discharge cycle?
Some residual sulphation is left on the plates causing it to cummulate
What is the best way to test a battery?
Load test
What does the Amp Hour specification provide
A measurement of battery capacity
How is the Amp Hour calculated?
Maximum sustained ampacity drawn from a fully charged battery over a time of 20 hours, to a point where its 100% depth of discharge
What is reserve capacity?
another measurement of battery capacity, or how much energy can be stored by the battery
What are cold cranking amps?
provides a measurement of the starting power of a battery at -18°C under a load (amps) for 30 seconds with the end voltage maintained at 1.20 VPC
What are start batteries manufactured with? Why?
Softer plates which can convert chemical energy to electrical energy much faster than deep cycle batteries
Why do deep cycle batteries not work well for starting applications?
they are constructed with hard plates for lengthy discharge times
What is within lead-acid batteries?
Lead & Lead dioxide immersed in sulphuric acid
What do both electrodes do when discharging in lead-acid batteries
Both turn into Lead Sulphate
What is SLI
Starting
Lighting
Ignition
Specific Gravity = ?
Relative Density
What happens when charging batteries?
- Plates go back to original material & electrolyte gets stronger
- Hydrogen gassing may occur thru vents
What would be the charging voltage for a 12V battery?
14.2 - 14.5 VDC
How do you determine the level of charge in a battery?
check the specific gravity of the electrolyte
what is the specific gravity?
amount of acid contained in the water
What tool is used to measure specific gravity?
a hydrometer
Explain using a hydrometer and temperature?
- SG readings should be taken at 25°C
- When temp. falls, we decrease our readings
- When temp rises, we increase our readings
- For each degree away from 25, we change our SG reading by 0.7
What is the temperature effect on batteries?
High temp. = reduced life and voltage
Low temp = overall shelf life increases
Should plates always be covered in electrolyte? What should you do if battery electrolyte is low due to normal evaporation?
- Yes
- Add distilled water
What should you do if electrolyte is low due to spillage? How should acid and water be mixed?
- Add sulphuric acid ( 3:1 mixture)
- Always add acid to water
How should terminals be cleaned?
While wearing rubber gloves and goggles, cleans regularly using baking soda and water
What do you use for representation of health of large battery banks?
use pilot cells, 5-7 selected and tested
Nickel-Iron (Ni-Fe) battery characteristics?
- Indestructible
- Long life (30+ years)
- Used in mining operations
- Do not contain hazardous materials
- Hard time keeping a charge
- Operate poorly in low temps
Maintenance and testing for Ni-Fe batteries?
- When overcharges, it gasses and loses electrolytes
- Keep distilled water above plate line
- Use a DC voltmeter on cells while under load to test
Nickel-Cadmium (Ni-Cd) battery characteristics?
- Improvement from Ni-Fe
- Hold charge, good life cycle & perform at low temps
- Thinner plate design made for portable size batteries
- More expensive than Lead-acid
- Suffer from memory effect (hold less charge over time)
- Cadmium is a disaster to humans & environment
Lithium-Ion (Li) battery characteristics?
- Battery of the future
- High energy density, tiny memory effect & low discharge
Why can Li batteries be dangerous?
- contain a flammable electrolyte that is kept pressurized
- Prolonged exposure to heat reduces battery life & can lead to “thermal runaway” and cell combustion
What do Li battery packs contain?
Fail-safe circuitry that disconnects battery when voltage is above cell “safe range”
what is normal in charging terms?
restores battery after it has been used or sitting
what is trickle in charging terms?
maintains battery fully charged with no load connected
what is float in charging terms?
supplies charge to batteries and connected loads
what is Bulk in charging terms?
restores battery after deep discharge (constant current)
what is absorption in charging terms?
ensures plates are de-sulphated after bulk (constant voltage)
What is equalization in charging terms?
elevated charge voltage to equalize cells and remove residual sulphation
what is the preferred method of charging for Nickel Cadmium batteries?
Constant Current (Bulk)
What does constant voltage charging do? What is it used for?
- outputs preset voltage level to prevent overcharging
- current decreases as charge builds
- used for ‘basic’ charging of Lead-acid batteries
What does the bulk stage provide?
desired current until a user preset absorption voltage is reached
What happens in Absorption mode?
charger goes to constant voltage mode and current tapers off as battery plates become restored and de-sulphated
what would continued charging at Absorption do?
excessively gas the battery and evaporate the electrolyte
Level 1 electric vehicle charger characteristics?
- typically 120V
- slowest charger (8kms/hour)
- considered Trickle
Level 2 electric vehicle charger characteristics?
- High voltage and current
- 5-7 times faster than level 1
- 24-40 km/hour
What is the added component in stand-alone AC PV systems?
the inverter
High quality inverters can give conversion efficiencies of _____?
90%
What is the most common backup for PV systems?
Diesel or Propane generator
What are the two types of Grid Connected PV systems?
- Utility Interface
- Utility Interactive
Characteristics of Utility Interface?
- Solar energy stored in battery bank
- Provides some or all of buildings electrical needs
- Low batteries = building transfer to utility
Utility Interactive characteristics?
- No storage
- Excess energy fed to utility grid
What is islanding?
the undesirable condition where a PV system continues to transfer power to the utility grid during a utility outage
what must be done if the utility experiences an outage? Why?
- utility-interactive inverters must stop supplying power to the grid
- it is an extreme electrocution hazard to any line workers
What are benefits of grid connected PV systems?
- Home powered by PV during the day
- simple to install
- low capital cost
- could possibly be paid back for extra energy
cons of grid connected PV systems?
- more expensive inverter required
- utility approval process
What is net metering?
Utility buys power at the same rate they sell it
What is dual metering?
- utility may buy power at a different rate than they sell it
- Records energy flow in both directions seperately
What are 4-jaw meter bases used for?
single phase applications
what are 5-jaw meter bases used for?
single phase applications but have a 5th jaw for neutral
what is a 7-jaw meter base used for?
3-phase applications
what are the 3 factors that determine any PV module’s power output?
- load impedance
- solar irradiance
- cel temperature
What is solar irradiance? How is it measured?
- solar power available per unit area
- measured in watts per square meter
what is ‘one sun’ ?
Peak irradiance at sea level = 1000 watts/meter squared
What are the two conditions modern inverters come in?
- Sine wave
- Modified Square wave
Modified square meter characteristics?
- most commonly seen on PV systems
- Cheaper than sine wave inverters
- Not as efficient
- cause more harmonic distortion in a system due to the extra step produced
What is a solar tracker?
a generic term used to describe devices that orient various payloads towards the sun
What is a maximum power point tracker (MPPT) ?
a high efficiency DC to DC converter that presents an optimal electrical load to a solar panel or array and produces a voltage suitable for the load
What is a closed freon system?
a passive tracker that requires no power and accurately tracks the sun throughout the day
How much can 10% shade coverage of an array reduce the output by?
90%
How is Azimuth measured?
from the north
What is a pyranometer? what is it measured in?
a sensor that measures the solar radiation flux density from a field of view of 180°
Measured in watts per square meter
What is a pyranometer used to measure?
solar irradiance on a planar surface
What is a pyrheliometer?
an instrument for direct measurement of solar irradiance
What are building-integrated photovoltaics (BIPV) ?
photovoltaic materials used to replace building materials in parts of the building envelope such as the roof, skylights or facades
Stand-by power supplies come in three forms, what are they?
- Dual Radial Feeds
- Batteries & UPS
- Emergency Generators
How are generators brought online? What is the best fuel?
They can be started, then switched to critical loads using an automatic transfer switch
Can take 8-15 seconds to be brought online
Best fuel is Diesel
What are some installation tips to be considered when installing generators?
- Locate as close as possible to main supply
- Mount on vibration pads
- Avoid areas of high or low temps.
- Adequate fueling must be available
Where are control panels typically mounted?
Alternator end of generator
What should have alarms?
everything (oil, coolant)
What 4 things must be the same for generators to be paralleled?
- Terminal Voltage
- Frequency
- Phase Sequence
- Phase displacement
What must synchronized units have? Why?
Reverse Power Relays
If one generator goes into speed droop, it will be unable to pick up its share of the load and will act like a load itself
How often should the generator be ran in preparation for a real emergency?
at least 30 mins per week and at least under 40% load-full is possible
What do Automatic Transfer switches provide?
“break before make” switching
What does break before make switching ensure?
the two sources are always isolated
How does a Closed Transition Transfer Switch work?
overlaps the two sources for .1 seconds, not long enough to do any damage and no line “bump”
How do you lockout a generator and transfer switch for maintenance?
- Place ATS selector switch in STOP
- Disconnect batteries at generator
- Open and lock-out the CB of generator
- Turn off normal power and perform shutdown
What components does a typical MicroHydro power system contain? (6)
- Water Intake
- Canal
- Forebay tank
- Penstock
- Powerhouse
- Tailrace
What does the turbine control do?
ensures power always flows out from the generator to the system
What is a benefit of run of river generation?
requires much less flooding
What is SCADA?
supervisory control and data aquisition
what does wild AC in micro-hydro power generation allow?
low speed / low head water turbines to be competitive
What is a Hydrokinetic power system?
a system consisting of one or more hydrokinetic turbines that convert kinetic energy of flowing water into electrical energy
What are some advantages and disadvantages of hydrokinetic systems?
Advantages:
- More predictable than wind power
- No retaining structure
- Discreet or even invisible
Disadvantages:
- Winter operations possibly problematic
What are the 3 types of hydrokinetic turbines?
- Vertical-axis
- Horizontal-axis
- Oscillating-foil
