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Harmonic Analysis Flashcards

1
Q

When harmonics are involved what percentage of Breaker settings is advisable for Other load breakers and capacitor bank breaker?

A

As per IEEE standard

Considering harmonics :
Capacitor bank breakers pick up= 1.4 times *full load amps

And add additional 20 % margin which is

1.6 times *full load amps

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2
Q

Capacitor bank voltage should be equal to

A

Bus voltage it is connected ,otherwise kvar value varies

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3
Q

What equipment is needed for 12 pulse converter?

A

Transformer

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4
Q

In this circuit or device current leads voltage by 90 degree and power factor is zero

A

Pure capacitor because true power equal to zero

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5
Q

In this circuit or device current lags voltage by 90 degree and power factor is zero

A

Pure inductive circuit because true power qual to zero and no dissipitative resistive component in circuit and circuit is reactive

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6
Q

In this circuit current and voltage are in phase and Power factor is one

A

Resistive circuit because reactive power equals to zero

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7
Q

Average power is zero in

A

Inductive load which leads to current is flowing without no work done by inductive load but current circulates in line thereby increasing losses and voltage

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8
Q

Average power is not zero in

A

Resistive load

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9
Q

Frequency of power is double of its voltage frequency in which load?

A

Pure inductive load

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10
Q

Real power is positive or unidirectional in which load ?

A

Resistive load

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11
Q

Power is negative for small duration and power is positive for longer duration for which power factor?

A

Cos(0.8)

Power factor=0.80

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12
Q

True power factor formula

A

Cos pi* sqr root of 1/1+(thd)^2

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13
Q

When try power factor and thd are used

A

When non linear load are present

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14
Q

Which is voltage harmonic devices?

A

Arc furnace and all other devices are current harmonic device

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15
Q

What are harmonic sources?

A

A devices which changes the nature of voltage and current waveforms

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16
Q

If inductive reactance increases?frequency?

A

Frequency increases

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17
Q

When capacitive reactance increases?frequency?

A

Frequency decreases

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18
Q

Which equipment provides low impedance path for high frequency harmonics?

A

Shunt capacitance so harmonic current goes to capacitance instead of source

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19
Q

Which equipment opposes high frequency harmonics?

A

Inductor

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20
Q

Formula for peak value

A

Square root of 2 * rms value

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21
Q

If source impedance of grid is increased what happens to source short circuit current and voltage thd? And current THD?

A

Source short circuit current decrease which results in increase in voltage THD

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22
Q

If source impedance of grid is decreased what happens to source short circuit current and voltage thd?

A

Source short circuit current increases which results in decrease in voltage THD

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23
Q

If x/R ratio of source increases?

A

THD increase

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24
Q

If x/R ratio of source decreases?

A

THD decreases

R value remains same while X value varies

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25
If Transformer impedance is increased
THD below Transformer increases and THD above Transformer decreases
26
If transformer impedance is decreased
THD below TRANSFORMER decreases and THD above transformer increase
27
When connecting capacitor bank in Down stream system filled with harmonic source?
Smart thing is add reactor with capacitor bank because reactor limits harmonic current
28
cable selections is depends on what factors?
1) voltage drop 2) short circuit withstand capacity 3) current carrying capacity
29
what is formula for MIN cross sectional area of cable
A= SHORT CIRCUIT CUURENT * (SQRT ROOT OF t)/K ``` t= FAULT CLEARING TIME OR DURATION OF SHORT CIRCUIT k= S.C TEMP RISE CONSTANT ```
30
WHAT IS K VALUE FOR XLPE AL CABLE AND XLPE CU CABLE?
K=0.094(FOR XLPE AL) | K=0.143(FOR XLPE CU)
31
FLA FORMULA?
KVA/1.732*V
32
VOLTAGE DROP FORMULA?
I*R*COS(PI)+ j*X*SIN (PI)
33
WE NEED GRID DATA FOR HARMONIC STUDY OR NOT?IF WE DON'T HAVE GRID DATA?
YES WE NEED GRID DATA.IF WE DONT HAVE GRID WE SHOULD SEE SWITCH GEAR DATA OR SLD
34
THE WORST CASE SCENERIO FOR HARMONIC ANALYSIS OCCURS DURING
MIN SHORT CIRCUIT CURRENT
35
HARMONIC ANALYSIS SHOULD BE DONE AT WHAT SC CURRENT?
MIN SHORT CIRCUIT CURRENT
36
AC RESISTANCE OF CONDUCTOR SHOUL BE CONSIDERED AT WHAT TEMPERATURE?
1) AC RESISTANCE OF CONDUCTOR SHOULD BE CONSIDERED AT MINIMUM TEMP FOR SHORT CIRCUIT STUDY 2) AC RESISTANCE OF CONDUCTOR SHOULD BE CONSIDERED AT MAXIMUM TEMP FOR LOAD FLOW STUDY AND HARMONIC STUDY AND TRANSIENT STABILITY
37
IF TEMPERATURE RISES WHAT HAPPENS TO RESISTANCE
RESISTANCE INCREASES
38
R t FORMULA
R t = R o(1+ ALPHA*(t - t o) AL[PHA FOR CU CABLE ALPHA FOR AL CABLE
39
YOU HAVE TO GET DC RESISTANCE OF CONDUCTOR AT WHAT TEMP
AT ALL TEMP
40
KVA FORMULA
KVA= 1.732 *V*I
41
FOR HARMONICS WHAT THREE LIMITS OR THINGS COME INTO PICTURE?
1) VOLTAGE DROP LIMIT 2) STABILITY LIMIT 3) THERMAL LIMIT
42
WHY WE CANT GET PARAMETER SUCH AS LINE REACTANCE AND CAPACITANCE?
BECAUSE LINE REACTANCE AND CAPACITANCE DEPENDS UPON 1) TOWER STRUCTURE AND HEIGHT 2) SPACING BETWEEN CONDUCTORS 3) HOW MANY GROUND WIRES 4) SPACING BETWEEN GROUND WIRES
43
IF WANT TO CONSIDER RLC PARAMETERS FOR BUSDUCT MODELLING.WHAT YOU HAVE TO DO
MODEL BUSDUCT AS AN IMPEDENCE(MODEL) IN ETAP
44
HOW TO FIND CABLE TYPE WHENT IS MENTIONED?
YOU CAN FIND CABLE TYPE BY SEEING MIN CROSS SECTIONAL AREA OF CONDUCTOR (A= I sh * SQRT OF t/K)
45
(REG 5 WINDING INTO 3 WINDING TRAFO) | WHAT IS IMPEDANCE VOLTAGE (U k) OF WINDING UNDER TEST(SC TEST)?
PRIMARY WINDING VOLTAGE AT WHICH YOU GET RATED CURRENT AT SHORTED SECONDERY WINDING
46
PER UNIT IMPEDANCE FORMULA
IMPEDANCE VOLTAGE/RATED VOLTGE (IF NECESSCARY MULTIPLY TIS VALUE BY 100%)
47
Z P.U NEW FORMULA
Z p.u OLD * (KVA OLD/KVA NEW)^2 * | MVA NEW/MVA OLD
48
X/R RATIO FORMULA
LOAD LOSS or Cu loss/BASE MVA
49
HOW WILL DETERMINE MAX LOAD VALUE (i.e of trafo)IF IT IS NOT KNOWN
ASSUME LOAD VALUE AS 80% OF TRAFO MVA
50
HOW PF OR KVAR CAN BE IMPROVED AT SOURCE(BUS)?
IMPROVED BY ADJUSTING GENERATING VOLTAGE(AVR) OR ADJUSTING OLTC
51
WHAT IS A STANDARD FOR HARMONIC ANALYSIS?
IEEE 519 2014
52
WHAT IS TDD
TOTAL DEMAND DISTORTION
53
AS WHICH BUS GRID WILL ACT AS ALWAYS
GRID WILL ALWAYS BE SWING BUS WHATEVER MISMATCH HAPPENS THAT WILL BE HANDLED SWING BUS
54
WHEN GRID(SYSTEM )CONSIDERED WEAK.
WHEN IT HAS 1) LESSER S.C CURRENT 2) HIGH SOURCE IMPEDANCE 3) HARMONICS IS HIGH
55
WHAT IS Q VALUE
QUALITY FACTOR
56
WHAT IS FORMULA FOR h?
h = n*P *(+ OR - 1) n- INTEGER P- NO OF PULSE (i.e 6 PULSE CONVERTOR )
57
WHY WE AVOID ADD HARMONIC FILTER TO HV AND EHV LINES
BECAUSE IT IS EXTREMELY EXPENSIVE
58
SHOULD WE PERFORM HARMONIC ANALYSIS IF TOTAL THD VALUE IS WITHIN LIMIT AND ONE PARTICAL HARMONICS(i.e ; 5th HARMONIC) THD VALUE EXCEEDS LIMIT?
WE SHOULD PERFORM HARMONIC ANALYSIS
59
IN HARMONIC SITUATION WHAT YOU ARE NEEDED TO FIND OUT?
1) WHERE THIS HARMONICS COMES FROM | 2) WHAT ORDER HARMONICS
60
PURPOSE OF IMPEDANCE SCANNING
TO FIND OUT WHERE YOUR IMPEDANCE IS MAXIMUM AND AT THIS(IMP MAX POINT) POINT WHICH HARMONIC IS PREDOMINANT (IN GRAPH)
61
HOW TO MODEL CABLE LINE FOR HARMONIC ANALYSIS IF IT IS LESS THAN ONE KM?
SHOULD BE MODEL AS DISTRIBUTED PARAMETER OR FREQUENCY DEPENDANT MODEL FOR HARMONIC ANALYSIS
62
HOW TO MODEL CABLE LINE FOR HARMONIC ANALYSIS IF IT IS MORE THAN ONE KM?
MODEL IT AS A DISTRBUTED PARAMETER .BECAUSE NOMINAL PI METHOD WONT WORK IF CABLE IS MORE THAN ONE KM AND FREQUENCY OF HARMONICS AND RESONANCE FREQUENCY OF NETWORK ALMOST COINCIDES(VERIFY)
63
IF SYSTEM IS NOT GRID CONNECTED SHOULD WE PERFORM HARMONIC ANALYSIS?
HARMONIC ANALYSIS IS NECCESSARY | TO LOOK AT HARMONIC DISTORTION,RESONANCE POINT AND IMPACT OF ELEMENT
64
WHEN WE SHOULD SUGGEST INSTALLING FILTER AT PCC?
1) AFTER MEASURING HARMONICS AT SIT | 2) DURING DESIGN ANALYSIS PROCESS
65
OTHER PURPOSE OF HARMONIC ANALYSIS
TO FIND WHERE RESONANCE FREQUENCY OCCURS
66
RESONANT FREQUENCY
?`
67
WHERE SHOULD BE HARMONIC FILTER PLACED
FILTERSHOUL BE PLACED NEAR TO HARMONIC SOURCE
68
DOES SATURATION OF TRAFO CAUSE HARMONICS
YES BUT FOR SHORT PERIOD OF TIME
69
DO WE NEED TO PERFORM HARMONIC ANALYSIS FOR ISLANDED SYSTEM?WHY?
YES BECAUSE SHORT CIRCUIT CURRENT AT ISLANDED SYSTEM IS LOW WHICH LEADS INCREASE IN HARMONICS.ALSO YOU NEED TO PERFORM HARMONIC ANALSIS TO CHECK WHETER DEISEL GENERATOR ARE CAPABLE OF WITHSTANDING HARMONICS
70
HARMONICS ORDER TYPE AND ITS RESULTING CURRENT
``` 1ST ORDER- +VE SEQUENCE CURRENT 2ND ORDER- -VE SEQUENCE CURRENT 3RD ORDER- ZERO SEQUENCE CURRENT 4TH ORDER- +VE SEQUENCE CURRENT 5TH ORDER- -VE SEQUENCE CURRENT 6TH ORDER- ZERO SEQUENCE CURRENT ETC ```
71
WHAT IS EFFECT OF NEGATIVE SEQUENCE CURRENT IN GENERATORS?
GENERATOR ROTATES IN OPPOSITE DIRECUTION .SO TORQUE(BREAKING) IS GENERATOR WHICH CAUSES THE HEAT TO INCREASE
72
What can harmonics do to transformers?
Harmonics generate additional heat in transformer thus reducing the life expectancy of trafo
73
Why is low voltage side generators are solidly earthed?
We are going for solidly earthed because fault current will be higher and it could be easily detectable by current principle by over system protection devices. Lv side has ACB ,MCCB,MCB.now except electronic devices all other like thermal magnetic or mcb cannot detect earth fault

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