Emergency Power Flashcards
What is the composition of a singular cell?
Contains two conductive electrodes (plates) of different material, and an electrolyte solution. The electrolyte reacts chemically with the electrodes, and acts as a medium for transferring electrons, creating potential difference between two electrodes.
What is open circuit voltage?
When no load is connected to the cell, the open circuit terminal voltage is equal to the voltage produced by that specific type of cell.
What is closed circuit voltage?
When current is drawn, there will be voltage drop across the cell due to internal resistance. The terminal voltage on the cell will be much less than emf.
What are the two fundamental types of batteries?
Primary, and Secondary
What is the most common type of primary cell?
Dry cell (doesn’t use liquid electrolyte. Uses powder)
- Chemical reaction during discharging destroys the electrodes, when battery is fully discharged the cell must be replaced.
- ex) one time use battery like a key fob battery or basic AA battery
What is another name for a secondary battery?
Storage cell or wet cell
What is the difference between a primary and secondary cell?
Primary cell (dry cell) cannot be recharged. Secondary cell (wet cell) can be recharged by passing current through the opposite direction of discharge.
What are the most common types of dry cells?
Carbon-zinc, zinc-chloride, alkaline, mercury, silver oxide, lithium.
What is the most common primary type battery?
lithium-manganese dioxide cell
What is the main practical use of secondary cells?
Used in emergency power systems because they are rechargeable
What voltage is a lead acid cell?
About 2.1V per cell
What is the most common primary cell?
Lithium-manganese dioxide cell
What is the open circuit voltage of a lithium cell (primary)?
3V, remains virtually constant throughout it’s operating life.
What are the main categories of secondary batteries?
SLI - engine starting, lighting, and ignition
Motive power - for electric vehicles
Standby batteries - for emergency power equipment and alarms
Portable batteries - for tools and equipment
What are the two long-life storage battery types?
Lead-acid, nickel-cadmium
What is an advantage of the primary lithium cell battery?
Can operate at a wide range of temperatures (-20 - +55), has a constant voltage of 3V
What are the main categories of secondary batteries?
- SLI (for engine starting, lighting, and ignition)
- motive power for electric vehicles
- standby for emergency power equipment and alarms
- portable for tools and equipment
What are the two types of long-life storage batteries?
lead-acid, nickel-cadmium
What is the general makeup of a lead acid battery?
positive-plate electrodes of lead dioxide, negative-plate electrodes of sponge lead, supported within lead alloy grid structure. Electrolyte is sulphuric acid and water.
What is a hydrometer?
A tool that measures the density of the electrolyte, shows the condition of the battery
How does a hydrometer work?
The float will rise with an increase in relative density or charge. Float will indicate red, white, or green.
Red is poor condition or completely discharged.
White needs charging
Green is good condition, and charged.
What are the full charge amounts for stationary batteries?
Full charge: between 1210-1225
Fully discharged: between 1180 and 1195
What are the full charge amounts for portable batteries?
Full charge: between 1280 - 1300
Fully discharged: between 1100 - 1130
What types of batteries are sealed/maintenance free?
Absorbed Glass Mat (AGM), and Gel type.
Which battery types need maintenance?
Wet cells/flooded cells, with venting and electrolytes
Why should stored batteries be kept on concrete?
Cold concrete can act as a heat sink, extended the life of the battery.
What are some applications for a nickel-cadmium battery?
- Small applications like rechargeable tools, laptop computers, camera.
- Medium applications like UPS system and emergency lighting
- Large applications like solar or wind power generation and utility backup power
What are some advantages of ni-cad batteries over lead-acid batteries?
higher energy to weight ratio, low internal resistance, good terminal voltage throughout discharge cycle, faster recharge rate, long storage life without maintenance charging
What is the difference between a lithium and lithium ion battery?
Lithium is primary, lithium-ion is secondary
What is the main caution to be taken with battery maintenance?
Suphuric acid burns. Rubber gloves, apron, and eye goggles are necessary.
What is the gas that is vented from batteries?
Hydrogen gas
How should batteries be connected and disconnected for testing?
Disconnect negative terminals first, then positive terminals. When reconnecting connect positive first, negative second
What is a battery cycle?
Charge and discharge
How is battery health measured?
Through a load test. Voltmeter is not sufficient
What are the aH rating based off of?
a 20 hour discharge
How much heavier is a fully charged battery than water?
1.28 times heavier than water, or 1280
What is the open circuit voltage of a fully charged lead acid battery?
12.7V
What is the open circuit voltage of a fully discharged lead acid battery?
11.9V
What are specific gravity readings?
What a hydrometer measures.
Based off of 25 degrees C
When temp falls, we decrease readings, when temp rises we increase readings.
Each degree away from 25, increase or decrease SG reading by 0.7
ex) 1280 reading is taken at room temp of 12 degrees. What is the true reading? 1280 -(13degrees x 0.7) = 1270.9
Which battery has a long life of 30+ years?
Nickel - Iron (Ni-Fe)
Which battery suffers from ‘memory effect’?
Nickel Cadmium
Why are nickel iron and nickel cadmium batteries no longer used?
Disasterous to humans and environment
What are the battery charging types?
Initial, Normal, Trickle, Float
What is the initial battery charge?
First time a secondary battery is charged, done at factory
What is normal battery charging?
-Routine charge
- Current starts high and gradually falls
- Overcharge is possible so shouldn’t leave it plugged in constantly
- Inexpensive
What is trickle charging?
- Continues to charge battery when it is full and keeps it fully charged
- Low constant current used while battery is in stand by mode
- can cause overcharge, should not be left plugged in
What is float charging?
- Low current charger with battery and load connected in parallel
- Charger shuts off automatically when battery is fully charged
- Tops up battery and never overcharges
What are the three forms of stand-by power supplies?
Dual Radial feeds, batteries & UPS, emergency generators
What are standby generators?
Started then switched to critical loads using ATS, takes about 8-15 seconds to bring online
Typically all generators are what the of wired system?
4-wire with grounded neutral (wye)
Who are generator regulations monitored by?
Municipality & Fire Marshall
What are some main features of a generator control panel?
Frequency meter, voltage adjust rheostat, water temp gauge, cranking limiter
What three things must match for generators to be paralleled?
Terminal voltage, frequency, phase sequence
Synchronized generator units must have _____ protection.
Reverse Power Relays (RPR)
What is the purpose of exercising a standby generator?
Switch to test, at least 40% load, 30 minutes
-Booster charges batteries
- Cleans carburetor of sediment
- Keeps all parts lubricated
- Brings engine up to operating temp
- Removes condensation from crankcase
What is one requirement for transfer switches and generators?
The switch ampacity must match the ampacity of the generator
What is positive interlocking?
ATS arrangement of ‘break before make’ switching. Ensures two sources are always isolated before switching
What are the ATS controller functions?
- Sense voltage and HZ variations. Looks for troubles in generator circuit
- Starts generator, retransfers load when normal AC returns
- Monitors generated voltage, allows for momentary AC bumps
What is a UPS?
Uninterruptible Power Supply, provides emergency power to a load when input power source or main power fails
What are the four main components of a UPS?
Battery source, converter, inverter, control equipment
What does a converter do?
converts AC to DC
What does an inverter do?
Converts DC to AC
What is an offline UPS system?
UPS is in standby mode, power to loads is straight from utility, batteries are in charge level three (flow).
What is an online UPS system?
Batteries are always connected to the inverter, power to loads is coming from inverter even during normal operation. Transfer switch is in place incase inverter fails. Acts as a bypass
What is another purpose for UPS other than backup power supply?
Filters the power quality issues on lines
What is a live interactive UPS?
Power goes from transfer switch to inverter, DC from inverter charges batteries, AC from inverter powers loads
What are the three modes of a UPS?
Normal, test, and bypass
What is power outage protection?
UPS and generator combination for backup power. UPS will keep critical loads energized, generator will eventually kick on and energize essential loads
What is the best way to visually inspect a UPS fault?
Thermal imaging camera
What is reference grounding?
Any conducting piece of electrical component but have its own ground wire run to it, not daisy chained.
Sulphation within a lead-acid battery occurs due to ______ charging
Incomplete
What is the internal resistance of your average dry cell battery?
0.2-0.4ohms
