EPS AND RES Flashcards
Batteries convert _____ energy into _____ energy
Chemical
Electrical
When several cells are connected together this equals a ?
Battery
The output of a battery depends on?
Material within
How they are connected
Each battery cell is made of two different materials called?
Electrodes
The battery electrodes are immersed in a conductive liquid called?
Electrolyte
When cells are connected in series a higher _____ is achieved?
Voltage
When cells are connected in parallel a higher ______ is acheived?
current
Batteries are rated in ?
Voltage and Ampere-hours (Ah)
Primary cell energy comes from?
Consuming electrodes (no re-charge)
Secondary cells also called ____ ____ have no _________ and must be _______.
Storage cells
Energy at the beginning
Charged
Large capacity rechargeable batteries are called?
Wet cells
Recharging of secondary cells is done by ?
Passing current through in the opposite direction of discharge
All batteries have _______?
Internal resistance
Open circuit voltage is ?
No-load terminal voltage
Charged battery chemical reaction
Lead Dioxide + Sulphuric Acid
Discharged battery chemical reaction
Lead Sulphate + Lead Dioxide + Water
The lead sulphate causes the internal resistance to increase during and when the battery is discharged, this is called?
Sulphation
The amp hour spec provides a measurement of battery ?
Capacity or how much energy can be stored by the battery
A dead battery voltage is considered to be ?
10.5V
Another measurement of battery capacity is?
Reserve Capacity
Reserve capacity is the number of ______ a battery @____C can supply a _____A load until it’s voltage drops to ______VPC
Minutes
20C
25A
1.75VPC
The __________ spec provides a measurement of the starting power of a battery at -18C under a load for 30 seconds with the end voltage maintained at 1.20VPC.
Cold Cranking Amps
Start batteries are manufactured with _____ plates which can convert chemical energy to electrical energy much _____ than deep cycle.
Softer
Faster
Deep cycle batteries do not work well for ______ applications because they are constructed with _____ plates for lengthy discharge times.
Starting
Hard
Marine cranking amps is similiar to cold cranking amps bit is performed at a _______ instead of -18C
Warmer 0C
For any specific battery the MCA will be about ___% greater than the CCA.
20%
Separators are used between plates of lead acid batteries to prevent?
Short circuits
Ribs at the bottom of lead acid batteries are used to?
Catch shed material from the plates
List 3 types of lead acid batteries?
- Flooded or Wet type
- Gel cells
- AGM (Absorbed glass mat) cells
Charging process
- Run a current through the battery in the opposite direction, the chemical action is reversed
- The plates go back to their original material and the electrolyte gets stronger
- For a 12V battery, charging V is usually 14.2V to 14.5VDC
- During charging, hydrogen gassing may occur through vents
To determine the level of charge in a battery we check the?
Specific gravity (SG) of the electrolyte
Specific gravity is the measure of?
The amount of acid contained in the water
Water has a SG of _____ and a _____ is the tool used to measure?
1.000
Hydrometer
Fully charged battery SG and open circuit voltage?
1280 or 1.28 … 12.7V open circuit
Fully discharged battery SG and open circuit voltage?
1150 (1.15) or less … 11.9V open circuit
SG readings should be taken at ____ C
25C
When the temp falls we ____ our SG readings and when the temp rises we ____ our SG readings.
Decrease
Increase
For each degree away from 25 we increase or decrease our SG reading by ____
0.7
High ambient temp battery operating specs
Reduced life and voltage
Low ambient temp battery operating specs?
Shelf life increases
The plates in a battery should always be covered with?
Electrolyte
When mixing electrolyte, always add ___ to the ____?
Acid to the water
Batteries should be cleaned with?
Baking soda and water
Nickel-Iron (Ni-Fe) Battery pros
Robust (virtually indestructible)
Long battery life (+30 years)
Used in mining operations
Environmentally benign
Nickel-Iron (Ni-Fe) Battery cons
Hard time keeping a charge
Bulky
Very expensive to make
Operates poorly in low temps
How to test a Nickel-iron battery?
Use a DC volt meter on cells while under load to determine state of charge (can not use hydrometer as the electrolyte density never changes)
Nickel-Cadmium Battery cons
Suffer from “memory effect”
Cadmium is a disaster environmentally
Lithium-Ion Battery benefits
High energy density
Tiny memory effect
Low self discharge
Comes in many shapes and sizes including lightweight options
(Charging Terms) Initial
First charge after battery is filled with electrolyte
(Charging Terms) Normal
Restores battery after it has been used or sitting
(Charging Terms) Trickle
Maintains battery fully charged with no load connected
(Charging Terms) Float
Supplies charge to batteries and connected loads
(Charging Terms) Bulk
Restores battery after deep discharge (constant current)
(Charging Terms) Absorption
Ensures plates are de-sulphated after bulk (constant voltage)
(Charging Terms) Equalization
Elevated charge voltage to equalize cells and remove residual sulphation
Constant current
Outputs rated current allowing charge to build fast
Voltage increases as charge builds
Preferred method for nickel cadmium
Constant Voltage
Outputs preset voltage level to prevent over charging
Current decreases as charge builds
Used for “basic” charging of lead acid batteries
Stand alone AC PV systems include an?
Inverter
High quality inverters can give conversion efficiencies of ___ %
90
For a hybrid system what is the most common back-up?
Diesel or propane generator
Two mai types of grid connected PV systems?
Utility interface
Utility Interactive
Utility Interface specs
Solar energy is stored in battery bank
Provides some or all of buildings electrical needs
Low batteries = building transfer to utility
Utility Interactive specs
No storage
Excess energy fed to utility grid
What is Islanding?
The undesirable condition where a distributed generation power source such as a PV system, continues to transfer power to the utility grid during a utility outage.
Three factors that determine any PV modules power output?
- Load impedance
- Solar Irradiance
- Cell Temperature
Meter bases
4-jaw: single phase
5-jaw: single phase but has 5th connection for neutral
7-jaw: 3 phase
Modern inverter two types?
Modified square wave
Sine wave
What kind of modern inverter is seen on PV systems?
Modified square wave (cheaper than sine wave, not as efficient)
Notes: cause more harmonic distortion, sine wave inverters will cost 2 to 3 times as much but are superior
What is a Pyranometer?
is used to measure solar irradiance on a planar surface and is a sensor that is designed to measure the solar radiation flux density from a field of view of 180 degrees.
What is a Pyrheliometer?
an instrument used for direct measurement of solar irradiance
What three things should you check for when you first receive a new generator?
Intake sealed
Exhaust sealed
Coolant intact
For servicing a gen-set do not rely on the OFF button of the ATS, you should?
Remove the battery cable from the start battery (negative first)
Starting KVA for a motor =
Locked rotor KVA
“Stand by” power systems come in three forms?
Dual radial feeds
Batteries and UPS
Emergency Generators
Generators can be started then switched to critical loads using an?
Automatic transfer switch (ATS)
ATS typically take __ - __ seconds to bring “online”
8 to 15
Generator fuel options?
Propane - bad w/ extreme temps
Gasoline - faster start (8s) time but unstable
Diesel - most popular, slow start (12s)
Generator connections are typically?
Three phase, 60Hz and almost all incorporate a 4-wire grounded neutral
Generators should be installed?
As close as possible to main power supply
On vibration pads
Not in areas of abnormally high/low temps
With adequate fuel for outages and exercising
AVR =
Automatic Voltage Regulator
What 4 things must be the same for generators to parallel?
- Terminal voltage
- Frequency
- Phase sequence
- Phase displacement
Synchronized generators must have what type of protection?
Reverse Power Relays (RPR)
Generators should be run for at least ___ minutes/week and is preferred to do so under __% load
30mins
40% load, full if possible
What does exercising a generator accomplish? (6 things)
- Booster charge to the batteries
- Cleans carb sediment
- Keeps all parts lubed
- Brings engine up to operating temp
- Removes any condensation from crankcase
- Restores residual magnetism
During the exercising period of a gen, observe and record?
Oil pressure Battery charging ammeter Fuel level Voltage and current levels Frequency under load Crank time
Transfer switches are ____ before _____
Break before make
The purpose of a transfer switch is to?
Switch the load from normal supply to emergency power either manually or automatically
What type of transfer switch would be used when a load could be affected by a slight bump in the line when transferring power?
Closed transition transfer switch (CTTS)
Typically a PV cell has an efficiency of?
20% or less (converted into electrical energy)
When paralleling generators if the lights are flashing out of sync what does this indicate and how is it rectified?
Wrong phase sequence
Interchange 2 leads of incoming alternator or change direction of prime mover
When paralleling generators if the lights are flashing at the same time but very fast what does this indicate and how is it rectified?
Incorrect frequency (too low). Changing the primer mover speed (DC motor excitation)
When paralleling generators if the lights stay on dim to bright what does this indicate and how is it rectified?
Phase displacement off.
Tweak the excitation of the primer mover to change the position within the revolution.
When paralleling generators and they lights are fully on bright or dim what does this indicate and how is it rectified?
Voltage does not match.
Adjust the field excitation of the alternator
Paralleled alternators share KW by varying the ______ and share KVARS by varying the _______?
Power of the prime mover
Field excitation of the alternator
What is “hunting”
Surging or oscillating of power between 2 alternators
How can “hunting” be rectified?
- “Damping” the governor
- Heavy fly wheels
- Amortisseur windings
The difference between a primary cell and a secondary cell is?
Secondary cell is rechargeable, primary is not
To determine the state of charge for a lead acid battery, could use a?
Voltmeter with a load connected to the battery
The no-load terminal voltage of a fully-charged, 6 cell lead acid battery would measure as?
13.2V
The internal resistance of a storage battery will _______ during charging?
Decrease
“Sulfation” is most likely caused by?
too low of water level
What type of genset is usually used with microhydro and wind power?
Asynchronous
Pressure x volume power lost at a PRV can be recovered by replacing the valves with a ?
Pump as a Turbine (PAT)
A _______ is essential for disconnecting the turbine in the event of loss of grid or phase (hydropower)
Intelligent relay
Advantages of hydro kinetic power?
- More predictable output than wind power
- No retaining structure
- Discreet or invisible due to the turbine components near total immersion
Disadvantage of hydro kinetic power?
Winter operations problematic
3 Main types of hydro kinetic turbines?
- Vertical axis
- Horizontal axis
- Oscillating-foil
5 types of renewable energy?
Sunlight Wind Hydro Tides Geothermal heat
A wind turbine is a rotating device used to convert?
Kinetic energy into electrical energy
2 types of wind turbines?
Horizontal axis
Vertical axis
The electrical machine of a wind power source is basically a ?
SCIM
A doubly fed induction machine is basically a ?
WRIM
A doubly fed induction generator has very good?
Efficiency
What strategies are employed to extract maximum power from the wind?
Blade pitch control
Variable pulley drive
Doubly fed induction generator
The nacelle is equipped with two devices to keep account of its angular position?
A turn counter
A limit detector
What is the purpose of an accumulator?
Store energy and be can used to supplement and regularize the flow rate of a pump
Wind power brake systems?
Rotor brake = hydraulic released, spring applied
Yaw brake - hydraulic applied, spring released
What does an Anemometer do?
Wind speed monitor
What are the 2 purposes of a UPS?
- An electrical apparatus that supplies emergency power to a load when the input power source or mains power fails.
- Enhance the quality of regular power by providing surge suppression and filtering noise
Off-line UPS specs
UPS is in “stand by”
Inverter not in primary path to the load normally
Time delay in the switching operation (2-12msec)
Very inexpensive
On-line UPS specs
- Batteries always connected to inverter = no power transfer switch.
- Charger/converter larger
- Units larger and generate more heat
- Shorter lifespan for unit and batteries
What is the simplest and most economical UPS?
On line UPS with no bypass
Ferro-Resonant UPS specs
- Same as off-line but when AC fails a special detector circuit switches inverter on and opens transfer switch
- This transformer essentially holds energy long enough to cover transfer time = eliminates it
- Transformer filters output
- Limited to 15KVA
Line interactive UPS specs
- Power is normally taken from utility with more active filtering for better waveform output
- Similar to off-line but utility power fed through tap-changer
- Tolerates continuous under voltage brown outs and over voltage surges without consuming battery reserve
Rotary UPS specs
- Uses high inertia of flywheel provide short term power in event of power loss (15-40sec) until generator picks it up
Rotary UPS advantages?
- High current output
- Long lasting (30 + years)
- Provide PF correction
Rotary UPS disadvantages?
- Expensive and much larger
- Maintenance required and extensive
- Can not be hot swapped
All UPS provide protection from surges, spikes and noise using a ?
Metal Oxide Varistor (MOV)
Second line of defence for a UPS?
Static bypass switch
Good field practice is to ______ bypass the UPS first then _____ bypass
Internal
External
Internal resistance of a battery increases due to?
Sulphation
What batteries are pressurized?
AGM and sealed lead acid
A fully charged lead acid battery has ___ V per cell and a hydrometer would measure ____ specific gravity and would freeze around ____ C
2.2V
1280
-60C
A lower depth of charge battery means the battery is ____ charged?
More
Which battery rating gives the best indication of how much energy it stores?
Amp-hours
After maintenance, the battery charger should be set to?
Equalization
The charging state where the battery is at a voltage where it will have the longest lifespan is?
Float/trickle
2 timed stages when normal power is restored?
- Ensure NP is returned to stay
2. Engine cool down
When is the electrical brake solenoid on the transfer switch on?
Only during load transfer
Another device used for synchronizing alternators which uses a single needle indicator influenced from a coil connected to each alternator is called?
Synchroscope
What is home portable generators commonly referred to as?
Back up power
What is the difference between a “nonseparately derived system” and a “separately derived system”?
The neutral is disconnected by the transfer switch on a separately derived system and must be re grounded.
