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Ref Formula

The document provides calculations for determining the stabilizing resistor value for a transformer protection relay. It includes formulas and values for short circuit MVA, current, voltage ratios, required operating voltage for through fault stability, voltage across the resistor, and selecting the resistor value so that the voltage is sufficient to operate the relay coil. Input values provided are for a 25 MVA, 132kV transformer with 0.1043% impedance and a 150A primary current transformer. The calculated stabilizing resistor value is 252.1244 ohms.

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Gnanavel G
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408 views10 pages

Ref Formula

The document provides calculations for determining the stabilizing resistor value for a transformer protection relay. It includes formulas and values for short circuit MVA, current, voltage ratios, required operating voltage for through fault stability, voltage across the resistor, and selecting the resistor value so that the voltage is sufficient to operate the relay coil. Input values provided are for a 25 MVA, 132kV transformer with 0.1043% impedance and a 150A primary current transformer. The calculated stabilizing resistor value is 252.1244 ohms.

Uploaded by

Gnanavel G
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as XLS, PDF, TXT or read online on Scribd
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POWER FORMULA FOR 3-PHASE SYSTEM

KV I PF POWER IN MVA

132000 109.37 1 25.00460688

AMPS FORMULA

POWER KV PF HV AMPS

25000000 132000 1 228624 109.349849535

SHORT CIRCUIT MVA

MVA X% SHORT CIRCUIT MVA

25 9.02 277.1618625277

SHORT CIRCUIT CURRENT

Sc MVA KV ROOT KV*ROOT Sc A

400000 132 1.732 228.624 1749.59759255

TRANSFORMER

IMPEDENCE VOLTAGE FORMULA


% IMP BASE KV IMP V

9.02 132000 11906.4

IMPEDENCE RATIO
IMP V APP V RATIO
11906 415 28.689156627

I1 RATIO
HV-A IMP-RATIO I1-RATIO

82.668 45.06 1.834620506

I2 RATIO
I1 I2 RATIO

82.668 2598.15 57.659786951

VOLTAGE RATIO FOR CVT


Sec.V Appiled.V Base KV ratio
110 2000 400000 0.55
STABILIZING RESISTOR SELECTION CALCULATION

INPUTS
Base MVA of Transformer

Impedence

Amps

CT-primary-A

Rct*

Loop RL*

HV/LV-V

RELAY COIL VA

Id MIN

RELAY OPERATING CURRENT*

SHORT CIRCUIT MVA


MVA X%

25000000 0.1043

SHORT CIRCUIT CURR


Sc MVA KV

23969319271.3327 132000

Calculation of required operating voltage UR for through fa

UR = Ifmax/CT P-A (Rct +2 Rl)

Ifmax Rct

6.989443882 2.22

Relay operating Voltage

VA/I = burden/current

RELAY COIL VA SETTING A

0.04 0.0726666667

Voltage across stabilizing resistor:

UR RELAY OPERATING V
18.8714984815 0.5504587156

Voltage across resistor


Stabilizing resistance = Current through resistor

VOLTAGE ACROSS RESISTOR CURRENT THROUGH RESISTOR

18.3210397659 0.0726666667

select stabilizing resistor 252.1244004485

Rct= is a winding resistance of aCT secondary core

RI= loop resistance of connecting cables

standerd = 8.0ohm/km * 2run


G

Before enter please see the note

CALCULATION
ENTER YOUR INPUTS HERE

VA 25000000

%IMP/100 0.1043
RESISTOR VALUE
HV/LV 109

PRIMARY-A 150

WINDING RESISTANCE-OHM 2.22 1


150
WIRE RESISTANCE 0.48 0.0066666667
10.9

VOLTAGE 132000

0.04
VA

10% OF HV/LV -A 10.9

0.0726666667

T CIRCUIT MVA
SHORT CIRCUIT MVA

23969319271.3327

SHORT CIRCUIT CURRENT


ROOT KV*ROOT Ifmax

1.732 228624 1048 6.989443882

UR for through fault stability.

2RI UR

0.48 18.8714984815

RELAYOPERATING- V

0.5504587156

VOLTAGE ACROSS RESISTOR


18.3210397659

STEBILIZING RESISTANCE

252.1244004485

ohms

econdary core
NOTE:

1.CT RATIO IS EXAMPLE 500/1 1/500=.002

2.WIRE REISTANCE

252.1244 OHMS 8.8OHMS/KM YOU COLLECT HOW MUCH DISTANCE FROM YAR
FOR EXAMPLE 300M 8.8/300

RI= 2*2.8=5.6
3. MVA VALUE CONVERT TO VA
4. KV VALUE CONVERT TO V
5.ENTER ANY ONE OF HV OR LV VOLTAGE WHICH SIDE THE H
6.ENTER ANY ONE OF HV OR LV AMPS
7.* MARKING OF INPUT Automatly GENERATED

8. it is suitable for 2Winding and 3Winding transfomer

auto transformer ref stabilizing resistor calculation

relay coil VA for REx670 = 0.25VA


1/500=.002

HOW MUCH DISTANCE FROM YARD TO PANEL


2.8

LV VOLTAGE WHICH SIDE THE HIGH IMP REF WILL COME

atly GENERATED

ng and 3Winding transfomer only

bilizing resistor calculation under progress

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