Emerg Power & Renewable Energy Flashcards
(108 cards)
1
Q
As a battery discharges, the internal resistance ______?
A
Rises
2
Q
As a battery becomes more loaded, the terminal voltage will ________?
A
fall
3
Q
Where are EP systems neccessary?
A
in any facility where a large number of people congregate
4
Q
What is a cell?
A
devices that convert chemical energy into electric energy
5
Q
What is a battery?
A
when several cells are connected together
6
Q
What does the output of a battery depend on?
A
the material within and how they are connected
7
Q
What is each cell made out of, are they connected and what are they immersed in?
A
- Made of two different materials called electrodes
- Not connected but immersed in a conductive liquid called electrolyte
8
Q
What happens when cells are connected in series?
A
Higher voltage is achieved
9
Q
What happens when cells are connected in parallel?
A
Higher current is achieved
10
Q
What are batteries rated in?
A
voltage & ampere-hours
11
Q
What are characteristics of primary cells? What is a dry cell?
A
- Energy comes from consuming electrodes
- No recharge
- Energy is built into these cells
- Great for portable equipment
- Dry cell = electrolyte is solid or molten
12
Q
What are characteristics of secondary cells?
A
- Also called storage cells, no energy at the beginning
- Rechargeable
13
Q
What is a wet cell?
A
a secondary cell which has a large capacity
14
Q
How is a cell recharged?
A
Passing current through in the opposite direction of discharge
15
Q
What do all batteries have?
A
internal resistance
16
Q
What is the chemical reaction between charged and discharged batteries?
A
Charged = Lead dioxide + Sulphuric Acid Discharged = Lead sulphate + Lead dioxide + Water
17
Q
What causes the internal resistance to increase during and when the battery is discharged?
A
“Sulphation”
18
Q
What happens with every discharge cycle?
A
Some residual sulphation is left on the plates causing it to cummulate
19
Q
What is the best way to test a battery?
A
Load test
20
Q
What does the Amp Hour specification provide
A
A measurement of battery capacity
21
Q
How is the Amp Hour calculated?
A
Maximum sustained ampacity drawn from a fully charged battery over a time of 20 hours, to a point where its 100% depth of discharge
22
Q
What is reserve capacity?
A
another measurement of battery capacity, or how much energy can be stored by the battery
23
Q
What are cold cranking amps?
A
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
24
Q
What are start batteries manufactured with? Why?
A
Softer plates which can convert chemical energy to electrical energy much faster than deep cycle batteries
25
Why do deep cycle batteries not work well for starting applications?
they are constructed with hard plates for lengthy discharge times
26
What is within lead-acid batteries?
Lead & Lead dioxide immersed in sulphuric acid
27
What do both electrodes do when discharging in lead-acid batteries
Both turn into Lead Sulphate
28
What is SLI
Starting
Lighting
Ignition
29
Specific Gravity = ?
Relative Density
30
What happens when charging batteries?
- Plates go back to original material & electrolyte gets stronger
- Hydrogen gassing may occur thru vents
31
What would be the charging voltage for a 12V battery?
14.2 - 14.5 VDC
32
How do you determine the level of charge in a battery?
check the specific gravity of the electrolyte
33
what is the specific gravity?
amount of acid contained in the water
34
What tool is used to measure specific gravity?
a hydrometer
35
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
36
What is the temperature effect on batteries?
High temp. = reduced life and voltage
| Low temp = overall shelf life increases
37
Should plates always be covered in electrolyte? What should you do if battery electrolyte is low due to normal evaporation?
- Yes
| - Add distilled water
38
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
39
How should terminals be cleaned?
While wearing rubber gloves and goggles, cleans regularly using baking soda and water
40
What do you use for representation of health of large battery banks?
use pilot cells, 5-7 selected and tested
41
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
42
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
43
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
44
Lithium-Ion (Li) battery characteristics?
- Battery of the future
| - High energy density, tiny memory effect & low discharge
45
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
46
What do Li battery packs contain?
Fail-safe circuitry that disconnects battery when voltage is above cell "safe range"
47
what is normal in charging terms?
restores battery after it has been used or sitting
48
what is trickle in charging terms?
maintains battery fully charged with no load connected
49
what is float in charging terms?
supplies charge to batteries and connected loads
50
what is Bulk in charging terms?
restores battery after deep discharge (constant current)
51
what is absorption in charging terms?
ensures plates are de-sulphated after bulk (constant voltage)
52
What is equalization in charging terms?
elevated charge voltage to equalize cells and remove residual sulphation
53
what is the preferred method of charging for Nickel Cadmium batteries?
Constant Current (Bulk)
54
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
55
What does the bulk stage provide?
desired current until a user preset absorption voltage is reached
56
What happens in Absorption mode?
charger goes to constant voltage mode and current tapers off as battery plates become restored and de-sulphated
57
what would continued charging at Absorption do?
excessively gas the battery and evaporate the electrolyte
58
Level 1 electric vehicle charger characteristics?
- typically 120V
- slowest charger (8kms/hour)
- considered Trickle
59
Level 2 electric vehicle charger characteristics?
- High voltage and current
- 5-7 times faster than level 1
- 24-40 km/hour
60
What is the added component in stand-alone AC PV systems?
the inverter
61
High quality inverters can give conversion efficiencies of _____?
90%
62
What is the most common backup for PV systems?
Diesel or Propane generator
63
What are the two types of Grid Connected PV systems?
- Utility Interface
| - Utility Interactive
64
Characteristics of Utility Interface?
- Solar energy stored in battery bank
- Provides some or all of buildings electrical needs
- Low batteries = building transfer to utility
65
Utility Interactive characteristics?
- No storage
| - Excess energy fed to utility grid
66
What is islanding?
the undesirable condition where a PV system continues to transfer power to the utility grid during a utility outage
67
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
68
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
69
cons of grid connected PV systems?
- more expensive inverter required
| - utility approval process
70
What is net metering?
Utility buys power at the same rate they sell it
71
What is dual metering?
- utility may buy power at a different rate than they sell it
- Records energy flow in both directions seperately
72
What are 4-jaw meter bases used for?
single phase applications
73
what are 5-jaw meter bases used for?
single phase applications but have a 5th jaw for neutral
74
what is a 7-jaw meter base used for?
3-phase applications
75
what are the 3 factors that determine any PV module's power output?
- load impedance
- solar irradiance
- cel temperature
76
What is solar irradiance? How is it measured?
- solar power available per unit area
| - measured in watts per square meter
77
what is 'one sun' ?
Peak irradiance at sea level = 1000 watts/meter squared
78
What are the two conditions modern inverters come in?
- Sine wave
| - Modified Square wave
79
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
80
What is a solar tracker?
a generic term used to describe devices that orient various payloads towards the sun
81
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
82
What is a closed freon system?
a passive tracker that requires no power and accurately tracks the sun throughout the day
83
How much can 10% shade coverage of an array reduce the output by?
90%
84
How is Azimuth measured?
from the north
85
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
86
What is a pyranometer used to measure?
solar irradiance on a planar surface
87
What is a pyrheliometer?
an instrument for direct measurement of solar irradiance
88
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
89
Stand-by power supplies come in three forms, what are they?
1. Dual Radial Feeds
2. Batteries & UPS
3. Emergency Generators
90
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
91
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
92
Where are control panels typically mounted?
Alternator end of generator
93
What should have alarms?
everything (oil, coolant)
94
What 4 things must be the same for generators to be paralleled?
1. Terminal Voltage
2. Frequency
3. Phase Sequence
4. Phase displacement
95
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
96
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
97
What do Automatic Transfer switches provide?
"break before make" switching
98
What does break before make switching ensure?
the two sources are always isolated
99
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"
100
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
101
What components does a typical MicroHydro power system contain? (6)
1. Water Intake
2. Canal
3. Forebay tank
4. Penstock
5. Powerhouse
6. Tailrace
102
What does the turbine control do?
ensures power always flows out from the generator to the system
103
What is a benefit of run of river generation?
requires much less flooding
104
What is SCADA?
supervisory control and data aquisition
105
what does wild AC in micro-hydro power generation allow?
low speed / low head water turbines to be competitive
106
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
107
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
108
What are the 3 types of hydrokinetic turbines?
1. Vertical-axis
2. Horizontal-axis
3. Oscillating-foil
