Test Flashcards
Describe the operation of a diode
Diodes allow current to flow when the anode ( > ) is positive in relation to the cathode ( | )
What happens to a circuit with 3 resistors connected in parallel when one of the resistors is open circuited?
Each parallel branch offers another path for current to flow, resulting in less resistance. If one parallel branch is opened, current can no longer flow in that branch. Circuit resistance is therefore increased.
Efficiency formula
Efficiency = (output/input) x 100
Power Factor formula
PF = True Power/Apparent Power
Formula for frequency
f = 1 / t (time)
Parallel circuit formulas
R t = 1 / ( 1/R1 + 1/R2 + 1/R3 )
Vt = V1 = V2 = V3
I t = I 1 + I 2 + I 3
In a parallel circuit, resistance total uses the reciprocal formula. Voltage is the same across all branches. Current total is the sum of all branch currents.
Series circuit formulas
R t = R 1 + R 2 + R 3
V t = V r1 + V r2 + V r3
I t = I 1 = I 2 = I 3
In series circuits, total resistance is the sum of all resistors. Total voltage is the sum of all voltage drops across each resistor. Current remains the same throughout the whole circuit
What is Kirchoffs current law?
Current flowing into a junction must be equal to the current flowing out
What is kirchoffs voltage law?
The sum of all voltage drops in a circuit equals the total source voltage
Define impedance
Impedance is the effective resistance of an electric circuit or component to alternating current; the combined effects of ohmic resistance and reactance
What causes Iron Loss in transformers
Iron losses are caused by the alternating flux in the core of the transformer, as this loss occurs in the core it is also known as core loss.
What is hysteresis loss in a transformer
The core of the transformer is subjected to an alternating magnetizing force, and for each cycle of EMF, a hysteresis loop is traced out. Power is dissipated in the form of heat known as hysteresis loss.
What is eddy current loss in a transformer
Since the core is made of a conducting material, EMFs circulate currents within the body of the material. They occur when the conductor experiences a changing magnetic field. These produce a loss known as Eddy current loss. The eddy current loss is minimized by making the core with thin laminations.
What is copper loss (ohmic loss)?
Losses due to the ohmic resistance of the transformer windings
What is stray loss in transformers?
The occurrence of stray losses is due to the presence of leakage field. The percentage of these losses are very small as compared to the iron and copper losses so they can be neglected.
What is dielectric loss in transformers?
Dielectric loss occurs in the insulating material of the transformer that is in the oil of the transformer, or in the solid insulations.
What does a full wave bridge rectifier do?
Converts Ac input voltage to pulsating Dc voltage.
Left diodes - ass to ass
Right diodes - head to head
Load connected to left and right side of diamond.
Ac Source connected to the top and bottom of diamond
In a purely inductive or capacitive circuit, voltage and current are how many degrees apart?
90 degrees
How many watts are in 1HP
1HP = 745.699 Watts approx 746 Watts
A shorted circuit has less or more than normal resistance
A shorted circuit will have less than normal resistance
Diodes allow current to flow when the anode is positive or negative in relation to the cathode?
Positive
In a purely resistive circuit with Ac voltage and current applied, the Ac voltage and the AC current are in or out of phase?
In phase. It is reactance (capacitors, inductors) that cause voltage and current to be out of phase.
Efficiency formula
Efficiency = (power out/ power in) x 100
Ac rms formula
V rms = V peak x .707
V rms = V ave x 1.11
Ac peak formula
V peak = V rms x 1.414
V peak = V ave x 1.57
V ave formulas
V ave = V peak x .637
V ave = V rms x .9
True power is measured in?
True power is measured in Watts
Apparent power is measured in?
Apparent power is measured in volt amps VA
Reactive power is measured in?
Reactive power is measured in VAR
What does a 7 pole CT shorting switch do?
A 7 pole CT shorting switch allows isolation and maintenance of one half of the CT circuit while keeping the other half in service
What do Voltage transformers do?
Voltage transformers reduces the primary voltage proportionally to a secondary voltage that is usable for meters and relays.
On a PT, to get the lowest secondary voltage, do you want full or half tap? (600:1 full, 1040:1 half)
To get the lowest secondary voltage you want the half tap. The bigger the ratio, the smaller the secondary.
