Flashcards in 18 Month Test Deck (76):
Fleish Generator Voltage
2200 volts and 2300 volts
Verdi Generator Voltage
Washoe Generator Voltage
Fleish Generator Amps
Verdi Generator Amps
Finding RPM of generator
3600/number of pairs of poles
Finding pairs of poles in generator
Fleish number of pairs of poles
24 total poles
Verdi number of pairs of poles
26 total poles
Washoe number of pairs of poles
20 total poles
2 types of DC circuits
Current only has one path
Current has more than one path
rpm = 60 (frequency/number of pairs of poles)
Fleish Transformer Protection
-745 Transformer Protection Relay
-between 2 sets of CT's (differential or negative sequence overcurrent) will isolate the transformer by opening the 2000 VCB and the 52 Generator Breaker.
Verdi Transformer Protection
-745 Transformer Protection Relay
-between 2 sets of CT's (differential or negative sequence overcurrent) will isolate the transformer by opening the 204 recloser and the 52 Generator Breaker.
Washoe Transformer Protection
-No transformer protection.
-Store current for short term use
Cells and Batteries
-Source of direct current to an electrical circuit.
-Come in 2 types: disposable and rechargeable.
-Hold charges of between 1.5 and 2 volts, although larger voltage can be achieved by connecting batteries together.
-has similar purpose to a fuse
-protects the circuit from faults
-can be reset even once they have broken the circuit
-used to transfer ac into dc and allow current to flow in only one direction.
-work like a valve. A valve in the system of pipes can stop liquid flowing in the opposite direction, just like a _______ can ensure that current in a circuit only flows one way.
-has 2 electrodes: anode and cathode
-a thin wire which melts when too much current flows through it.
-protect units from faults.
-an electrical component that can store energy from the circuit in a magnetic field.
-usually a wire shaped as a coil, which creates a magnetic field as the current passes through it.
-used to limit the build up of alternating current in a circuit and to keep the circuit running when the supply I switched off.
-output devices which produce motion.
-ex. electric fan - when current runs through the circuit, the motor moves and turns the blades of the fan.
-another kind of switch.
-under the control of another electrical circuit, which tells it when to open and close.
-2 types: 1. Electromechanical relays are controlled by a coil which generates an electromagnetic current. 2. Solid state relays use a semiconductor switching device.
-opposes the current running through an electric circuit.
-value of resistance can be set by user or variable.
-control the flow of current in a circuit.
-they are binary, which means they can only be one of two things: open or closed.
-a semiconductor device used to amplify or switch electronic signals.
-can amplify because its output can be much bigger than its input.
-designed to convert alternating current from one voltage to another.
-used to transfer electrical energy between 2 circuits.
-consists of two wire coils wrapped around a core.
-the wire coils create electromagnetic fields and the changes in these fields help to transfer energy.
5 Main Parts of a Transformer
1. Primary Winding
2. Secondary Winding
3. Iron Core
6. Nitrogen Blanket
Different Types of Transformers
1. Power Transformers
2. Distribution Transformers
3. Instrument Transformers
-a device used on electrical power systems to protect the insulation and conductors of the system from the damaging effects of lightning.
-has a high voltage terminal and a ground terminal.
-essentially a discharge gap with one side connected to the line at the primary side of the transformer and the other side connected to earth ground.
Line of Demarcation for Fleish
-right after the 2001 disconnects
Line of Demarcation for Verdi
-right after the fused disconnects
Line of Demarcation for Washoe
-right after our transformer
Most Common Faults
1. Short Circuits
3. Open Circuits
Why is an Iron Core used in transformers?
-provides an intense magnetic field
-cores are always laminated (made of thin steel sheets) to help reduce eddy currents
-used at electrical generating stations for stepping the generated voltage up to the value desired for transmission.
-Also used at substations for stepping voltages back down for distribution in geographical areas.
-used to step the distribution voltage down to values needed in geographical areas.
-Industrial - stepped down to 2400, 600, 480, 240
-Residential - down to 240, 120
-pole and pad mounted
-smaller than power and distribution transformers
-Current type or potential type
-used to lower voltage so measuring instruments (meters and relays) can be used
What determines the size of the transformer?
How is voltage ratio determined in a transformer?
-by the number of turns in the windings
-when a steady current flows in one coil and a magnetic filed is produced in the other coil.
-When 2 conductors or coils are paced near each other and a current is set up in one of them, the magnetic flux produced by the current in the fist conductor will cut the second conductor and induce a voltage in it.
Can a transformer transform DC voltage?
Types of Conductors
Types of Semiconductors
Types of Non-conductors
Types of Grounding Rods
-several alloys combined
-it breaks down before the shaft
-regulates the induced voltage
-Allows a variable number of turns to be selected.
-Changes output voltage in a transformer.
Can a tap changer be used when the transformer is energized?
No, transformer must be de-energized.
2 types of lubrication
3 Types of Loads
1. Resistive - current and voltage are in phase
2. Inductive - current lags voltage
3. Capacitive - current leads voltage
3 Types of Power
1. Real - measured in watts
2. Reactive - measured in VARs
3. Apparent - measured in volt amps (sum of real and reactive power)
3 things that determine amount of voltage a generator produces
1. number of coils in the stator
2. the speed of the rotor
3. strength of the magnetic field
How do you get Power Factor?
real power/apparent power
3 things needed to make electricity
1. Magnetic Field
2. Relative Motion
Protection Devices for Transformers
1. Lightning arrestors
2. Spark gaps
4. Circuit Breakers
5. Grounding Equipment
Core Form vs. Shell Form Transformer
Core Form - windings surround the core
Shell Form - windings are surrounded by the core
Things that determine the capacitance of a capacitor
1. area of the plates
2. distance between the plates
3. material of the dielectric
What voltage does a potential transformer usually step down to?
What secondary current does a current transformer usually step down to?
-occurs as the result of a break in a conductor
-a low resistance path around a component
Things Distribution substations contain
4 Types of grounding systems in distribution equipment
1. Solid grounds
2. Low resistance ground
3. high resistance ground
4. Ungrounded (floating) circuits
-have the neutral connections firmly tied to earth with no resistance between them
Low Resistance Grounds
-small resistance is placed in the ground circuit to limit current value between 25 and 1000 amps
High Resistance Grounds
-uses higher resistance to limit the ground fault current to about 10 amps
-don't use a connected ground but rather allow the phases to float.
-forms a barrier between moving surfaces
-Thick film of lubricant
-stops friction, heat, and wear