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Distance Protection Relay Setting Calculations
Distance Protection
•
A distance protection element measures the quotient impedance (V/I), considering the phase angle between the voltage V and the current I.
•
In the event of a fault, sudden changes occur in measured voltage and current, causing a variation in the measured impedance.
• •
The measured impedance is then compared against the set value.
• •
Distance protection is used to protect transmission lines .
Distance element will trip the relay (a trip command will be issued to the CB associated with the relay) if the measured value of the impedance is less then the value set. It is a non unit protection.
Why Distance Protection ? Why not Overcurrent relay?
•
The reach of over current relay is function of Source Impedance which varies considerably, making it difficult to get fast and Selective tripping. So , distance protection is used as a primary protection.
Distance Protection
Distance protection principle of operation In Fig. the impedance measured at the relay point A is Zin , where x is the distance to the fault (short circuit), and R and X are transmission line parameters in per unit length. The line length is l in the fig. Operating characteristics of distance protection elements are usually represented using R-X diagrams.
Required information for Protective Setting Line Parameters:
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Line length, voltage level, conductor size and conductor type used for local as well as remote substations.
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This information is used to calculate the parameters (positive and zero sequence resistance, reactance) for each section.
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Maximum load current or apparent power (MVA) corresponding to the emergency line which can be obtained from the table of standard conductor rating (available in each utility).
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The number of conductors in a bundle has to be taken into consideration.
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Conductor Specifications if not available, refer to CEA manual ‘Annexure-V, Table 1(a), Line parameters’
…required information for Protective Setting Transformer Parameters:
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The manufacturer's positive and zero sequence impedance test values have to be obtained.
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The transformer nameplate normally provides manufacturer's positive sequence impedance values.
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Voltage ratio, MVA rating, %Impedance value
the
CT & PT Ratios :
•
Obtain the CT & PT ratios as indicated on the protection diagrams.
•
For existing circuits, it is possible to verify the ratios indicated on the diagrams by measuring the load currents on site and comparing with a known ratio.
Arc & Tower footing resistance:
•
Used in resistive reach calculation.
Various operating Characteristics
•
Protective relays respond and operate according to defined operating characteristic and applied settings.
•
Each type of protective relay has distinctive operating characteristic to achieve implementation objective: sensitivity, selectivity, reliability and adequate speed of operation.
MHO characteristics
X Line Q
Region of non-operation outside the circle
120%
B 80% Zone 2 Line P
Z RS Region of operation Zone 1
A
Load region
R
1. Mostly used 2. Resistive and reactive reach can be set independently
Zone protection
* Generally
zones Z1, Z2, Z3 are taken as forward direction and Z4 is taken as reverse direction with time settings as T1, T2, T3 and T4 respectively.
* Settings adopted depends on their respective Regional Power Committees and CBIP recommendation or guidelines.
Adopted Philosophy for Transmission Line Protection
* Stepped distance scheme is followed. * 3 Forward Zones + 1 Reverse Zone is kept Zone 1: * Set to cover 80% of the protected line. There is no intentional time delay for this zone.
Why 80% ? The under-reach setting is set to avoid overreaching into the next protected line & to avoid unwanted tripping. Reasons for inaccuracy of distance relay reach * Inaccuracy in CT & PT ratios. * Line parameter errors. * Variation of line parameters according to atmospheric conditions.
It should isolate the fault instantaneously.
Adopted Philosophy for Transmission Line Protection Zone 2: * Set to cover (120% of the protected line) Or (Protected line impedance + 50% of adjacent shortest line impedance) or (Protected line + 50% transformer impedance). * 150% of the protected line (for Double circuit ) * Time delay- 300-500 milli seconds. * Provides Backup protection for a part of the adjacent line. * Should be set in such a way that Zone-2 setting should not encroach into LV side of the transformer as this leads to unwanted tripping of HV side for a fault in LV side. * Trip the faulty line instantaneously using carrier aided tripping (POTT). Consideration for time delay: • Downstream Co-ordination (100ms) • Circuit Breaker Operation(100ms) • Safety margin(100ms)
Adopted Philosophy for Transmission Line Protection Zone 3:
* Set to cover (120% of the protected line + adjacent longest line) or (Protected line impedance + 100% of adjacent longest line impedance + 25% of second adjacent longest line) or (Protected line + 100% transformer impedance). * Time delay- 800-1200milli seconds . * Provides Backup protection for a the next adjacent line. * Should be set in such a way that Zone-3 setting should not encroach into LV side of the transformer as this leads to unwanted tripping of HV side for a fault in LV side.. Zone-4: * Reverse Zone * Provides backup protection for station faults. (Acts as Busbar zone backup) * Time delay is normally 1-1.3sec if Bus bar protection available else 450-500ms.
Conversion of primary values into secondary values * Distance relays are fed from the secondary's of line CT’s & Bus PT’s /Line CVT’s. * The line parameters are to be converted into secondary values Zsec = Zpri / (Impedance ratio) Where Impedance ratio = PT ratio / CT ratio. * The CT and PT ratios are inter related. Hence any changes in CT ratio has to be effected along with revision of relay settings only. RCA (Relay Characteristics Angle) * Represents the characteristics of entire transmission line * Angle range : KV
Line Angle
132kV
60-70 Deg
220kV
70-80 Deg
400kV
80-85 Deg
* Formula – Inverse of
tan'(X/R).
Load Encroachment : * While protecting long lines the necessary reach may be large so that the minimum service impedance (load impedance) falls with the region. This results in tripping without there being any fault.
* How to identify Load encroachment? Conditions
Phase angle
Heavy load
+30 to -30 Deg
Short circuits
60 to 80 Deg
…Load Encroachment : How to reduce Load encroachment problem?
* Use Lenticular or elliptical shape characteristics (Limitation: Fault resistance coverage reduced)
* Shaping the characteristic of the relay to avoid load . Zone-3 reach should be set less than maximum load coverage. (Limitation: More complex shapes become hard to define)
What to do?
* Define the load regions in the impedance plane and block operation of distance elements if the impedance in either of the load region.
Resistive reach: * This setting is used for setting the resistive coverage. * Separate resistive settings are kept for Phase-Phase faults & Phase-Earth faults. * Arc resistance & tower footing resistance are required to calculate resistive reach settings.
…Resistive reach: In general , reach is calculated ..
* Phase-Phase fault Resistance
= Arc resistance . Phase-Earth fault Resistance = Arc resistance + Tower footing resistance.
* R ph-ph = R(Zone) + Phase-Phase fault Resistance R ph-e = R(Zone) + Phase-Earth fault Resistance
* R ph-e >> Rph-ph. Notation: * R1PH-R1G ( MiCOM) * R(Z)-RE(Z) (SIEMENS) * RFPP-RFPE (ABB)
Power swing
* Power
Swing which is basically caused by the large disturbances in the power system which if not blocked could cause wrong operation of the distance relay and can generates wrong or undesired tripping of the transmission line circuit breaker.
* Power swing is a variation in three-phrase power flow which occurs when
the generator angles are advancing or retarding relative to each other in response to changes in load magnitudes, line switching, loss of generation, faults, and other system disturbance.
* It can cause major power outages, even power blackout or severe damage to the machine.
* Thereby, a Power Swing Block (PSB) function is adopted in modern relays to prevent unwanted distance relay element operation during power swing.
* The
main purpose of the PSB function is to differentiate between power faults and power swings, and block distance or other relay elements from operations during a power swing.
Power swing effect on distance relay
* Power swings can cause the load impedance to enter into the relay’s operating characteristic which under steady state conditions is not within the relay’s operating characteristic as shown in figure.
* Distance
or other relays should not trip during such as stable or unstable power swings, and allow the power system to return to a stable operating condition.
* Faults that occur during a power swing must be detected and cleared with a high degree of selectivity and dependability.
Power Swing * A fault on the system results in the measured impedance crossing rapidly crossing the R Band, en route to a tripping zone. * Power swing is detected when three phase-phase impedances remained within the R band for a time delay. * It is recommended to block all the zones in the distance relay for a time delay of 2 seconds to avoid unwanted tripping. (For stable power swing)
How to identify power swings?
* The rate of change of impedance phasor is slower during power swings whereas faster for short circuit faults.
* Power swing impedances vectors will normally enter the protection zones at an angle of 90 deg to the line angle.
* Direction of current flow will remain same during the power swing event. Only voltages change with respect to one another.
* Causes severe oscillations in power flow.
Power swing detection methods
* Traditional Method •
We can distinguish a Power Swing condition or OSS condition by the difference in the rate of change of the positive-sequence impedance vector.
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This detection method is based on the fact that it takes a certain time for the rotor angle to advance because of system inertias.
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Practical implementation of measuring the rate of change of the impedance is normally performed through the use of two impedance measurement elements together with a timing device.
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If the measured impedance stays between the settings of the two impedance measurement elements for a predetermined time, the relay declares a power swing condition and issues a blocking signal to block the distance relay element operation.
*Advanced Method • The advent of digital technology has given relay design engineers the ability to develop and realize new methods for detecting power swings.
• Some
of these new methods determine a power swing condition based on a continuous impedance calculation.
• For
example, an impedance calculation is performed for each 5ms step, and compared with the previous 5ms’ result. Thus two continuous deviations can be predicted as traveling impedance because of power swing.
• Synchro
phasor-based Out-of-Step Relaying measurement has also been used to detect and take action for power swings.
• Many
utilities are currently evaluating the use and application of synchronized phasor measurement systems.
Auto Reclose Element Types of faults:
* 1.Transient faults
2. Semi permanent faults 3. Permanent faults
Transient faults:
* Disappear after Short dead time Various Transient Faults
• Lightning strokes resulting in flashovers • Conductor swinging due to high winds • Bird fault • Temporary contact with foreign objects like tree etc.
* 80%-90% of
faults on any overhead line network are transient in nature. The remaining 20%-10% of faults are either semipermanent or permanent.
…Auto reclose : Advantages: * Decreases outage time * Improves reliability * Improves system stability * Reduces maintenance time. Dead time: The time between the auto reclosing scheme being energised and the operation of the contacts which energise the circuit breaker closing circuit. Range: 0.3- 1.2 sec ; 1 Sec (NRPC & CBIP-274 for both 220 kV and 400kV) Reclaim time: The time between 1st and 2nd Auto reclosure. Range: 10-30 sec ; 25 Sec (NRPC)
•Single phase , Single pole Auto reclosing is recommended.(CBIP) •Auto reclose function should be kept for Zone-1.(CBIP) •The recommended operating cycle as per IEC publication 56.2 is O-0.3s-CO-3min-CO
… Auto reclose : Protections which block AR : * CB internal problems * Local Breaker protection relay operates * Bus bar protection operates
Auto-reclosing on EHV Transmission Networks
* The most important consideration in the application of auto-reclosing to EHV transmission lines is the maintenance of system stability and synchronism.
* The
problems involved are dependent on whether the transmission system is weak or strong.
• With a weak system, loss of a transmission link may lead quickly to an excessive phase angle across the CB used for re-closure, thus preventing a successful re-closure.
• In a relatively strong system, the rate of change of phase angle will be slow, so that delayed auto-reclose can be successfully applied.
Single-phase Auto-reclosing
* Single phase to earth faults are the majority of faults in overhead lines. * When three-phase auto-reclosing is applied to single circuit interconnectors between two power systems, the tripping of all three phases may cause the two systems to drift apart in phase resulting no interchange of synchronising power during the dead time.
* If
only the faulty phase is tripped, synchronising power can still be interchanged through the healthy phases leading to the reduction in the disturbance on the system when the circuit breaker recloses.
* On
the occurrence of a phase-earth fault, single-phase auto-reclose schemes trip and reclose only the corresponding pole of the circuit breaker.
* Modern
numerical relays often incorporate the logic for combined single and three-phase auto-reclosing where single phase to earth faults initiate single-phase tripping and reclosure, and phase-phase faults initiate three-phase tripping and reclosure.
* Advantages of Single Phase Auto-reclosing • The maintenance of system continuity. • The particular faulty phase is restored by maintaining the stability and synchronism.
* Disadvantages of Single Phase Auto-reclosing • The main disadvantage is the longer de-ionisation time resulting from capacitive coupling between the faulty and healthy lines. This leads to a longer dead time being required.
SOTF (Switch Onto Fault)
* Line is switched on to a close by fault (say after line clear with earth
switch closed, accidental energization), the voltage at the relaying point will be zero. * Voltage applied to the relay will be low. * SOTF relay will trip instantaneously. * SOTF feature will be effective only for about 200 ms after the line is charged and if fault is presents the relay will operate as a simple O/C relay and its isolate the healthy section from faulty detection. * This function is very useful in a case when maintenance of any machinery is done in a switchyard and the line to be energised. * Faults occurring after this time will be measured in normal way.
How is SOTF sensed? If the voltage does not rise to 50-60% of rated voltage in one cycle & if the current is more than the set current.
Broken Conductor
* Type of unbalanced fault which is a open circuit fault or series fault. * Series
faults will not cause an increase in phase current on the system and are not readily detectable by standard overcurrent relays.
* A resultant level of negative phase current can be detected. * An
element is incorporated which measures the ratio of negative phase sequence to positive phase sequence (I2/I1).
* Setting: I2/I1 ≥ 0.2 ; Time delay 3-5secs. (NRPC)
* This element is given for alarm only.
Fuse failure protection
* Distance
relays being voltage restrained overcurrent relay, loss of voltage due to PT fuse failure will cause mal-operation of the relay operation.
* This element will block the distance element not to operate.
* The relays senses the condition by the presence of residual voltage. * Normally set to 15% unbalance. * Given for alarm .
Settings Calculation
Setting calculations for ABB REL-521 Data Required *Positive Sequence Line Impedance = R1+jX1 *Zero Sequence Line Impedance = R0+jX0 *CT Ratio *PT Ratio *Protected line length (PLL) *Adjacent shortest line length (ASLL) *Adjacent longest line length (ALLL) *Second adjacent long line length (SALLL) *MVA, %Impedance of Transformer, No. of Transformers connected *Maximum load on the Feeder (Refer from CEA Tr. Lines Guidelines) *Phase-Phase fault resistance (Arc resistance) *Phase-Earth fault resistance (Arc resistance + Tower footing resistance)
.....setting calculations for ABB REL-521 Calculations 1.Protected Line (P.L)
*Positive Sequence Resistance of P.L (Primary) = R1 (Ω/Km) *Total Positive sequence resistance of P.L (Primary) = R1x PLL *Total Positive Sequence resistance wrt secondary (R1 Sec) = R1 x PLL x (CT/PT ratio) *Positive Sequence Reactance of P.L (Primary) = X1 (Ω/Km) *Total Positive sequence reactance of P.L (Primary) = X1x PLL *Total Positive Sequence reactance wrt secondary (X1 Sec) = X1 x PLL x (CT/PT ratio) *Zero Sequence Resistance of P.L (Primary) = R0 (Ω/Km) *Total Zero sequence resistance of P.L (Primary) = R0x PLL *Total Zero Sequence resistance wrt secondary (R0 Sec) = R0 x PLL x (CT/PT ratio) *Zero Sequence Reactance of P.L (Primary) = X0 (Ω/Km) *Total Zero sequence reactance of P.L (Primary) = X0x PLL *Total Zero Sequence reactance wrt secondary (X0 Sec) = X0 x PLL x (CT/PT ratio)
.....setting calculations for ABB REL-521 Calculations 2.Adjacent Short Line (A.S.L) *Positive Sequence Resistance of A.S.L (Primary) = R1 (Ω/Km) *Total Positive sequence resistance of A.S.L (Primary) = R1x ASLL *Total Positive Sequence resistance wrt secondary (R1 Sec) = R1 x ASLL x (CT/PT ratio)
*Positive Sequence Reactance of A.S.L (Primary) = X1 (Ω/Km) *Total Positive sequence reactance of A.S.L (Primary) = X1x ASLL *Total Positive Sequence reactance wrt secondary (X1 Sec) = X1 x ASLL x (CT/PT ratio) *Zero Sequence Resistance of A.S.L (Primary) = R0 (Ω/Km) *Total Zero sequence resistance of A.S.L (Primary) = R0x ASLL *Total Zero Sequence resistance wrt secondary (R0 Sec) = R0 x ASLL x (CT/PT ratio) *Zero Sequence Reactance of A.S.L (Primary) = X0 (Ω/Km) *Total Zero sequence reactance of A.S.L (Primary) = X0x ASLL *Total Zero Sequence reactance wrt secondary (X0 Sec) = X0 x ASLL x (CT/PT ratio) 3.Adjacent Long Line (A.L.L) 4.Second Adjacent Long Line (S.A.L.L)
.....setting calculations for ABB REL-521 Calculations Transformer Impedance *Total transformer Impedance ZT (Pri) = Imp.of Tranf.1 + Imp. of Transf. 2 +............... = > ZT =[ 1/ { %Imp.* (KV²/MVA)}] + [ 1/ { %Imp.* (KV²/MVA)}] +............... *Total transformer Impedance ZT (Sec) = ZT (Pri) x (CT/PT ratio) Loadablity *Max Load current *Max apparent power Smax= 1.732 x 1.2 x V L-L x Max load current *As per “Reliability Standard PRC-023” for 0.85per unit voltage and max current is Zloadmin (Pri.)=(0.8*V L-L* V L-L)/(Smax) Zloadmin (Sec.) = Zload max (Pri.) * (CT/PT ratio)
*Angle of Positive sequence impedance ZPL = tan-1(X1/R1) *Angle of Zero sequence impedance ZPL = tan-1(X0/R0)
.....setting calculations for ABB REL-521 Zone Settings Zone 1 Phase- Phase
*X1PP = 80% of PLL *R1PP = 80% of PLL *RFPP = Min[ (Ph-Ph fault resistance in Sec),(3 times of Zone 1 reach) & (1.6*Zloadmin*(cos 30-(R1PP/X1PP)*Sin 30))] Phase-Earth *X1PE=X1PP *R1PE=R1PP *RFPE = Min[ (Ph-Ph fault resistance in Sec),(4.5 times of Zone 1 reach) & (0.8*Zloadmin*(cos 30-(2*R1PP+R0PE/2*X1PP+X0PE)*Sin 30))] Zero Sequence *X0PE = 80% of PLL (X0) *R0PE = 80% of PLL (R0)
*Time Setting = 0 Seconds
.....setting calculations for ABB REL-521 Zone Settings Zone 2 Phase- Phase
*X1PP = Min[Max { (PLL+0.5*ASLL),(1.2*PLL)} & (PLL+0.5 Trans. Impedance)] *R1PP = Min[Max { (PLL+0.5*ASLL),(1.2*PLL)} & (PLL+0.5 Trans. Impedance)] *RFPP = Min[ (Ph-Ph fault resistance in Sec),(3 times of Zone 2 reach) & (1.6*Zloadmin*(cos 30-(R1PP/X1PP)*Sin 30))] Phase-Earth *X1PE=X1PP *R1PE=R1PP *RFPE = Min[ (Ph-Ph fault resistance in Sec),(4.5 times of Zone 2 reach) & (0.8*Zloadmin*(cos 30-(2*R1PP+R0PE/2*X1PP+X0PE)*Sin 30))] Zero Sequence *X0PE = Min[Max { (PLL+0.5*ASLL),(1.2*PLL)} & (PLL+0.5 Trans. Impedance)] *R0PE = Min[Max { (PLL+0.5*ASLL),(1.2*PLL)} & (PLL+0.5 Trans. Impedance)]
*Time Setting = 0.35- 0.5 Seconds
.....setting calculations for ABB REL-521 Zone Settings Zone 3 Phase- Phase
*X1PP = Min[ (1.2*PLL+ALLL),(PLL+ALL+0.25*SALL)} & (PLL+Trans. Impedance)] *R1PP = Min[ (1.2*PLL+ALLL),(PLL+ALL+0.25*SALL)} & (PLL+Trans. Impedance)] *RFPP = Min[ (Ph-Ph fault resistance in Sec),(3 times of Zone 3 reach) & (1.6*Zloadmin*(cos 30-(R1PP/X1PP)*Sin 30))] Phase-Earth *X1PE=X1PP *R1PE=R1PP *RFPE = Min[ (Ph-Ph fault resistance in Sec),(4.5 times of Zone 3 reach) & (0.8*Zloadmin*(cos 30-(2*R1PP+R0PE/2*X1PP+X0PE)*Sin 30))] Zero Sequence *X0PE = Min[ (1.2*PLL+ALLL),(PLL+ALL+0.25*SALL)} & (PLL+Trans. Impedance)] *R0PE = Min[ (1.2*PLL+ALLL),(PLL+ALL+0.25*SALL)} & (PLL+Trans. Impedance)]
*Time Setting = 0.7 – 1.0 Seconds
.....setting calculations for ABB REL-521 Zone Settings Zone 4 Phase- Phase
*X1PP = 0.25 * Zone 1 Impedance *R1PP = 0.25 * Zone 1 Impedance *RFPP = Min[ (Ph-Ph fault resistance in Sec),(3 times of Zone 4 reach) & (1.6*Zloadmin*(cos 30-(R1PP/X1PP)*Sin 30))] Phase-Earth *X1PE=X1PP *R1PE=R1PP *RFPE = Min[ (Ph-Ph fault resistance in Sec),(4.5 times of Zone 4 reach) & (0.8*Zloadmin*(cos 30-(2*R1PP+R0PE/2*X1PP+X0PE)*Sin 30))] Zero Sequence *X0PE = 0.25 * Zone 1 Impedance *R0PE = 0.25 * Zone 1 Impedance
*Time Setting = 1.0 – 1.2 Seconds
.....setting calculations for ABB REL-521 Power Swing
*Inner Reactive Boundary Forward (X1InFw)
= 1.1 x X1PP of Zone 3
*Inner Reactive Boundary Reverse (X1InRv) = 1.1 x X1PP of Zone 3 *Line resistance for inner characteristics angle (R1In) =1.1 x R1PP of Zone 3 *X1OUT = KX x (X1In/100) where KX= 0.125 *R1OUT = KX x (R1In/100) where KX= 0.125 *Time for detection of Initial Power Swing (tp1) = 0.045 sec *Time for detection of subsequent Power Swing (tp2) = 0.015 sec *Waiting time for activation of tp2 timer (tw) = 0.25 sec *Time for giving Power Swing start output (tH) = 0.5 sec *Timer giving delay to inhibit by the residual current (tR1) = 0.3 sec *Timer giving delay to inhibit by very slow Swing (tR2) = 2 Sec
Setting calculations for Siemens 7SAXXX Data Required *Positive Sequence Line Impedance = R1+jX1 *Zero Sequence Line Impedance = R0+jX0 *CT Ratio *PT Ratio *Protected line length (PLL) *Adjacent shortest line length (ASLL) *Adjacent longest line length (ALLL) *Second adjacent long line length (SALLL) *MVA, %Impedance of Transformer, No. of Transformers connected *Maximum load on the Feeder (Refer from CEA Tr. Lines Guidelines) *Phase-Phase fault resistance (Arc resistance) *Phase-Earth fault resistance (Arc resistance + Tower footing resistance)
.....setting calculations for Siemens 7SAXXX Calculations 1.Protected Line (P.L)
*Positive Sequence Impedance of P.L (Primary) Z = √ (R12+X12 ) (Ω/Km) *Total Positive sequence Impedance of P.L ( Primary) = Z x PLL *Total Positive Sequence Impedance wrt secondary (PL .Z Sec) = Z x PLL x (CT/PT ratio)
2.Adjacent Shortest Line (A.S.L)
*Positive Sequence Impedance of
A.S.L (Primary) Z = √ (R12+X12 )
(Ω/Km)
*Total Positive sequence Impedance of A.S.L ( Primary) = Z x ASLL *Total Positive Sequence Impedance wrt secondary (ASL.Z Sec) = Z x ASLL x (CT/PT ratio)
.....setting calculations for Siemens 7SAXXX Calculations 3.Adjacent Longest Line (A.L.L)
*Positive Sequence Impedance of
A.L.L (Primary) Z = √ (R12+X12 )
(Ω/Km)
*Total Positive sequence Impedance of A.L.L ( Primary) = Z x ALLL *Total Positive Sequence Impedance wrt secondary (ALL.Z Sec) = Z x ALLL x (CT/PT ratio)
4.Second Adjacent Longest Line (S.A.L.L)
*Positive Sequence Impedance of
S.A.L.L (Primary) Z = √ (R12+X12 )
(Ω/Km)
*Total Positive sequence Impedance of S.A.L.L ( Primary) = *Total Positive Sequence Impedance wrt secondary (SALLL.Z Sec) = Z x SALLL x(CT/PT ratio)
Z x SALLL
.....setting calculations for Siemens 7SAXXX Calculations Transformer Impedance *Total transformer Impedance ZT (Pri) = Imp. of Tranf.1 + Imp. of Transf. 2 +............... = > ZT =[ 1/ { %Imp.* (KV²/MVA)}] + [ 1/ { %Imp.* (KV²/MVA)}] +............... *Total transformer Impedance ZT (Sec) = ZT (Pri) x (CT/PT ratio) Loadablity *Max Load current *Max apparent power Smax= 1.732 x 1.2 x V L-L x Max load current *As per “Reliability Standard PRC-023” for 0.85per unit voltage and max current is Zmax (Pri.)=(0.8*V L-L* V L-L)/(Smax) Zmax (Sec.) = Zload max (Pri.) * (CT/PT ratio)
*Angle of Positive sequence impedance ZPL = tan-1(X1/R1) *Angle of Zero sequence impedance ZPL = tan-1(X0/R0)
.....setting calculations for Siemens 7SAXXX Calculations Loadablity
* The Resistance reach & Reactance reach corresponding to Zmax w.r.t Secondary is R = Zmax *Cos (30) & X= Zmax *Sin (30)
*The New impedance for Parallel line drawn parallel to the Line impedance passing through Zmax to the point at which the parallel line cuts
*The Resistance axis is Znew= X(at Zmax) /Sin(Line angle) *The New Resistance from known Reactance Rnew = Znew* Cos (Line angle)
*Resistance
reach of Relay Characteristics obtained from maximum loadability condition Resistive Reach R=(R correspond to Zmax – Rnew)
.....setting calculations for Siemens 7SAXXX Zone Settings Zone 1
*Zone 1 Impedance Z1= 80% x P.L.Z Sec *Zone 1 Resistance R1= Z1 x Cos(Line angle) *Zone 1 Reactance X1= Z1 x Sin(Line angle) *Phase to phase resistive reach R(Z1) = R1+Arc Resistance/2 *Phase to earth resistive reach RE(Z1)=R1+Arc Resistance +Tower footing resistance
*Time settings T1= 0 Seconds
.....setting calculations for Siemens 7SAXXX Zone Settings Zone 2
*Zone 2 Impedance
Z2
= Min[Max {(PLL.Z Sec+0.5*ASLL.Z Sec),(1.2*PLL.Z Sec)} & (PLL.Z Sec+0.5 Trans. Impedance)]
*Zone 2 Resistance R2= Z2 x Cos(Line angle) *Zone 2 Reactance X2= Z2 x Sin(Line angle) *Phase to phase resistive reach R(Z2) = R2+Arc Resistance/2 *Phase to earth resistive reach RE(Z2)=R2+Arc Resistance + Tower footing resistance
*Time settings T2= 0.35- 0.5 Seconds
.....setting calculations for Siemens 7SAXXX Zone Settings Zone 3
*Zone 3 Impedance
Z3
= Min[(1.2*PLL.Z Sec +ALLL.Z Sec),(PLL.Z Sec+ ALL.Z Sec+0.25*SALL.Z Sec)} & (PLL.Z Sec+ Trans. Impedance)]
*Zone 3 Resistance R3= Z3 x Cos(Line angle) *Zone 3 Reactance X3= Z3 x Sin(Line angle) *Phase to phase resistive reach R(Z3) = R3+Arc Resistance/2 *Phase to earth resistive reach RE(Z3)=R3+Arc Resistance + Tower footing resistance
*Time settings T3= 0.7- 1.0 Seconds
.....setting calculations for Siemens 7SAXXX Zone Settings Zone 4
*Zone 4 Impedance Z4= 0.25 * Zone 1 Impedance (Z1) *Zone 4 Resistance R4= Z4 x Cos(Line angle) *Zone 4 Reactance X4= Z4 x Sin(Line angle) *Phase to phase resistive reach R(Z4) = R4+Arc Resistance/2 *Phase to earth resistive reach RE(Z4)=R4+Arc Resistance +Tower footing resistance
*Time settings T4=
1.0 -1.2 Seconds
.....setting calculations for Siemens 7SAXXX Power Swing Blocking
*Power Swing Operating mode = All zones to be blocked (As per CEA protection committee guidelines, all zones to be blocked till study is carried out to selectively block or unblock logic)
*Power swing trip = No tripping * Trip delay timing = 2 Sec