TxProtection 280904 PART 2

Institut Latihan TNB - ILSAS

Unit Perlindungan, Seksyen Latihan Penghantaran 2007 Zulkarnain Ishak

KURSUS LATIHAN KEKOMPETENAN

Unit PerlindunganSeksyen Latihan Penghantaran

Institut Latihan Sultan Ahmad Shah (ILSAS)

PERLINDUNGAN PENGHANTARAN(SETAKAT 132kV)



SKIM PERLINDUNGAN ALATUBAH.

RESTRECTED EARTH FAULT(REF)



Institut Latihan Sultan Ahmad Shah(ILSAS)

ObjektifPada akhir pengajaran, pelatih-pelatih akan dapat 1. Mengenal pasti dan melukis litar skimatik

perlindungan geganti REF.2. Mengira tatahan perlindungan geganti REF 3. Mengaturkan prosidur pengujian skim

perlindungan geganti REF.4. Melukis litar pengujian “secondary”, “primary”

dan “stability”.dengan betul apabila skim perlindungan REF

digunakan pada alatubah.



RESTRICTED EARTH FAULT SCHEME FOR STAR WINDING

Relay operates for earth fault within protected zone.

Use high impedance principle

Transformer fed from an earthed source on the star side of transformer.

Stability level : usually max.through fault current of transformer.



RESTRICTED EARTH FAULT SCHEME

For resistance grounded transformer- base on the typical Fault Current vs. Winding Impedance curve, it shows that

1. Small fault current on HV side of Tx for single phase to ground at LV star.

- HV side O/C relay at cannot detect and clear the fault.

2. The differential relay detect fault < 40% of transformer winding (from transformer terminal).

- Fault current become smaller as the fault closer to the star point (Neutral).



RESTRICTED EARTH FAULT SCHEME

For solidly grounded transformer, >> fault current, differential possible to detect ≈ 100% of transformer winding.

REF protection better then Bias Differential scheme to protect Tx star winding . It can detect up to ≈ 80% – 90% of winding fault (E/F) i.e. from TX terminal.

Another 10% - 20% of the winding can be detected by Bucholz relay. - very low fault current



Rs

64 Is = 0.1AVo

REF Zone of protection

REF using Kichoff current principle

“Total current enter a network must be same as total current living it”. It operation using circulating current

2 side of CT req. (Line CT & Neutral CT)– measure input vs output

HI-IMPEDANCE RESTRICTED EARTH FAULT PROTECTION SCHEME.



HI-IMPEDANCE RESTRICTED EARTH FAULT PROTECTION SCHEME. Cont.

RCT = Internal CT resistance

Rl = Wiring / lead resistance

RS = Stabilizing Resistance

VS = Stabilizing Voltage

Stabilizing resistance use to limit the operating current.

To calculate the stabilizing resistor, assumption made that one of the CT saturated with heaviest through fault current.

Vsetting = IF (2Rl + RCT) , where IF normally= 15 X MVA√3 X kV

Highest value of Rl (loop resistance ) and RCT are chosen so to give maximum voltage across the relay under maximum through fault current.

Choose that the minimum operating current = IsAlso that Vs = Is (RS + R64 )Stabilizing resistor RS = (VS / IS ) – R64




For stability Vs > V. Hence the stability of REF depends upon Vs voltage setting across the relay circuit during high through fault current that cause one of the CT saturated.

Vkp req. = 2 x Vs = 2 x IF (2Rl + RCT)

Factor 2 Vs is to ensure that during fault the CT used still can derive output current.

V

Im

Vs

Vkp

Selection of CT Knee point Voltage Vkp



RS

64

VS

R Y B N

ImR ImY ImBImN

IR

EFFECTIVE PRIMARY OPERATING CURRENT (POC).

The relay operates with IR and Vr. During in zone fault the magnetizing current required to develop voltage Vr across the relay or Vs across the relay circuit are

ImR + ImY + ImB + ImN

Therefore effective POC = N (ImR + ImY + ImB + ImN + IR)POC implies the sensitivity of the scheme.

Example:IR = 20mA, CT Ratio N = 500/1 and Vs = 80V and all CT required 10mA to develop the setting voltage. Then

The effective POC = 500/1 (4x10mA + 20mA)= 30A




REF Setting - Current operating REF Relay


Rs

64Vs

i). Determine the voltage setting Vs using

Vs = (IF. /N).(2Rl + RCT)

Where - N = CT ratio- IF = Max. through fault current desired before unstable which normally set to 15 times of transformer rated current.- Rl = max. CT pilot lead resistance.- RCT = CT internal resistance.

Normally,Iop fix to 200mA



REF Setting - Current operating REF Relay


ii). Determine the magnetizing current for all CTs at setting Voltage Vs (using CT mag. Curve result). So the total magnetizing current at VS

Im = ImR + ImY + ImB + ImN

iii). Relay current setting IR should be

IR = (IPOC/N) - Im

Typical Setting for REF Protection: Solidly earthed - 10-60% of winding rated

current. (From ESI 48-3 1977)

Resistance earthed - 10-25% of minimum earth fault current for fault at transformer terminals.

iv). Required stabilizing resistor RS will be

VS = IR (RS + R64)RS = (VS/ IR) - R64 Ω

RS power rating P = IR2 . RS (watt)



REF Setting - Voltage operating REF Relay


i). Determine the voltage setting Vs using

Vs = (IF. /N).(2Rl + RCT) Where - N = CT ratio- IF = Max. through fault current desired before unstable which normally set to 15 times of transformer rated current.- Rl = max. CT pilot lead resistance.- RCT = CT internal resistance.

Rs

64Vs

IR Is

Normally, Iop fix to 20mA,Vset = 200V



REF Setting - Voltage operating REF Relay


ii). Determine the magnetizing current for all CTs at setting Voltage Vs (using CT mag. Curve result). So the total magnetizing current at VS

Im = ImR + ImY + ImB + ImN

iii). If desire effective IPOC > IR + Im then required shunt stabilizing resistor.

iv). Required stabilizing resistor RS will be

Normally relay operating current IR is fix for voltage operated relay

Let IS = (IPOC/N) – (Im+ IR)RS = (VS/ IS) Ω

RS = VS/ ((IPOC/N) – (Im+ IR)) Ω

RS rating P = IS2 . RS (watt)



REF SCHEME TEST.


R S

64

R S64

A

V

A

V

a. Relay secondary Injection test.To ensure relay in good working condition with

- operate at setting values with acceptable tolerance- correct connection

1). Relay Operation Test (secondary)

Current Operated Voltage Operated



REF SCHEME TEST.


a. Relay secondary Injection test.

i. Injection without stabilizing resistor Rs.

ii. Measure operating current and voltage.iii. Injection with stabilizing resistor.iv. Measure operating current and voltage.v. Compare the measured values with setting values.

i.e. Operating voltage between i. and iii, Vo (iv) > Vo (ii)Operating current Io ≈ Is (setting)Operating voltage Vo ≈ Vs (setting)Vo / Io ≈ Rs (Stabilizing Resistor Value)Secondary test Operating

Voltage Vo (V)Operating

Current Io (A)Resistance

Value

Without Stabilizing Resistor

With Stabilizing Resistor



REF SCHEME TEST.


a. Secondary Injection test.

Primary Operating Current Check (Secondary Injection)

Primary Operating Current IPOC = N. IS (where N = CT ratio).Note: The IPOC for future check.

RS

64

VS

R Y B NImR

ImY

ImB

ImNIR

A Is

SecondaryInjectionTest Set.



REF SCHEME TEST.


b. Primary Injection test

Primary Injection – To check relay operation using secondary output current from CT.

Using Primary Injection Test Equipment.

Injection involve all CTs connected to the scheme.

1000/1Primary Injection

Rs

64 Is = 0.1AVo

Operating current I(primary) = Is x N

CT ratio = N/1



REF SCHEME TEST.


c. REF Scheme Stability test.

Rs

64Vo

Fault

Rs

64Vo

Fault

Stable Condition for External Fault. Unstable Condition for Internal Fault.



REF SCHEME TEST.


c. REF Scheme Stability test.

-Using 1Ø primary test set.

-Injection can be done at phase side or neutral side of Txmer.

-Hi Txmer impedance. Bypass winding req.

-Measure current that flow though all branches-Phase current-Neutral current-Relay current

- Measure voltage across the relay and stabilizing resistor.

1Ø Primary Injection

Rs

64VoBypass Tx. winding

1Ø Primary Injection

Rs

64Vo

Stable Condition Unstable Condition



REF SCHEME TEST.


REF Scheme – Current Flow

RS

64VS

Stable: REF Secondary connection and current flow for out zone fault.



REF SCHEME TEST.



Unstable: Due to wrong connection at Neutral CT side.

RS

64

VS

Wrongconnection



REF SCHEME TEST.



Unstable: Due to wrong connection at Line or Phase CT side.

RS

64

VS

Wrongconnection



REF SCHEME TEST.



Unstable: Due to primary equipment defect. Fault current by passing Neutral CT.

VSRS

64



Rumusan

- Pengetahuan terhadap skim perlindungan REF penting untuk diketahui oleh Jurutera / Juruteknik Perlindungan yang berkecekapan didalam memastikan pepasangan skim perlindungan tersebut beroperasi didalam keadaan yang diharapkan.

TxProtection 280904 PART 2

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Transcript of TxProtection 280904 PART 2