This is for power system engineers and consultants
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Koor Koordi din nasi asi Aru Arus Lebi Lebih h Pada Pada Jaring ingan Rad Radial
Dr. Ir. Redy Mardiana Labo Laborat rator oriu ium m Tekn Teknik ik Tega Tegang ngan an dan dan Arus Arus Tingg Tinggii Seko Sekola lah h Tekn Teknik ik Elek Elektro tro dan dan Info Inform rmat atik ika a Institut Teknologi Bandung
Radial System
• R1 provides primary protection to line 1 • R2 provides primary protection to line 2 & remote backup for line 1 • Farthe Farthest st rel relay ay from from the source source is set first first • Relays Relays locate located d on on source source side side of of the the line line – Trip Trip direct direction ion towar towards ds the the line – The radial radial system system is is inherently inherently directional directional Dr.Ir. Redy Mardia Mardiana na - STEI ITB
Inverse Characteristic
Time-Current Characteristic of overcurrent relay PSM = Pickup Setting Multiplier (know also as Plug Setting Multiplier)
PSM
=
=
Primary current (fault current) Primary seting current (pickup) I F I PU
Pickup can be changed using Tap I PU =I TAP Dr.Ir. Redy Mardiana - STEI ITB
Adjustable Setting of Inverse Relay •
Time Dial Setting (TDS) also known as Time Multiplier Setting (TMS) – To set relay operating time
•
Pickup Current which relate to Pickup Setting Multiplier (PSM) (also known as Plug Multiplier Setting) – To set pickup current for relay to operate
Dr.Ir. Redy Mardiana - STEI ITB
Time Multiplier Setting (TMS) TDS =
T T m
T = the required time of operation T m= the time obtained from the relay characteristic curve at TDS = 1.0
Example: If the time obtained from relay characteristic curve (TDS=1.0) is 4.0 , while the required time to operate the relay is 0.4s , then TDS is set to 0.4/4.0 = 0,1.
Dr.Ir. Redy Mardiana - STEI ITB
Pickup Setting Multiplier (PSM) PSM
=
=
Primary Current (Fault Current) Primary setting current (pickup)
=
F PU
Primary Current (Fault Current) Relay current setting
×
CT Ratio
Example: If fault current I F is 3000A and primary pickup current is 200A, then PSM = 3000/200=15. If the installed CT has a ratio of 400/5 then the relay current setting is 200 x 5/400 = 2.5A. (or the relay tap = 2.5A)
PSM
=
3000 200
=
3000 2.5 × (400 / 5)
=
15
* Pickup current sometimes refers to relay current setting if it is seen from secondary side of CT Dr.Ir. Redy Mardiana - STEI ITB
To determine Pickup and Time Dial setting of Time Overcurrent R1 • Determine minimum fault current (IF-MIN) and full load current (IFL) • Determine primary pickup IPU IFL< IPU< IF-MIN • Determine relay current setting (= I PU /CTR ) – Relay current setting also known as pickup current at secondary side • TDS is set at the lowest value (e.g. 0.5) – No coordination is necessary for R1
I
< FL
I
PU
I = F MIN
I F MIN
1.3
I
2
I FL< I PU
;
I
=
3 1.3 × 2 × 2
3 2 3I
To determine Pickup and Time Dial setting of Time Overcurrent R1
5.
=
0.33
Handbook recommendation, the effect of arc resistance has been considered
Dr.Ir. Redy Mardiana - STEI ITB
1. 2. 3. 4.
I 3
Coordination for all currents is done at maximum multiple of pickup. It is achieved at IF-MAX Calculate IPU Calculate IF-MAX Calculate PSM Set TDS at 0.5 (the lowest) Determine time from curves (=tOP-R1) Dr.Ir. Redy Mardiana - STEI ITB
3I
To determine Pickup and Time Dial setting of Time Overcurrent R2 t OP-R2 ' t OP-R1 + t CTI – t CTI is the coordinating time interval (known as time margin) – t B1 is the CB time to operate – t OT is the over-travel time – t SF is safety factor
1. Choose t CTI and calculate t OP-R2 2. Calculate IPU 3. Calculate IF-MAX (at closest to R1) 4. Calculate PSM 5. Determine TDS time from curves
Dr.Ir. Redy Mardiana - STEI ITB
Coordinating Time Interval (CTI) The CTI Consists of: 1.
CB fault-interruption or fault-clearing time, typically 2–8 cycles (0.033–0.133 sec). 2. Relay overtravel time: The energy stored in the electromechanical induction disk or solid-state circuitry will continue operation after the initiating energy is removed. Typically, this is not more than 0.03–0.06 sec for electromechanical units; less, but not zero, for solid-state units. 3. Safety factor (safety margin) for errors or difference s in equipmentoperating time, fault current magnitudes , CT ratios, and so on. The CTI values frequently used in relay coordination range between 0.2 and 0.5 sec, depending on the degree of confidence or the conservatism of the protection engineer—0.3 sec, is the frequently used CTI value. Dr.Ir. Redy Mardiana - STEI ITB
Selection of Time Characteristic
• •
•
Inverse – used when IF is dependent on generation – not fault location Very Inverse – used when I F is dependent on fault location – used when I F independent of normal changes in generating capacity Extremely Inverse – used when I F is dependent on fault location – used when I F independent of normal changes in generating capacity – Ease coordinates with fuses and reclosers Dr.Ir. Redy Mardiana - STEI ITB
• Upstream relay has longer t OP than downstream relay • Very undesirable – for the fault closes to the source, I F will be very large but the relay operating time is longer. This will damages the equipment (the source) • Combine inverse and instantaneous overcurrent relay to reduce fault clearing time Dr.Ir. Redy Mardiana - STEI ITB
Reduction of Operating Times With Instantaneous Overcurrent Relays
• The most significant reduction in operating time is on line section 4 • Instantaneous relay provides primary protection mainly for close-in faults Dr.Ir. Redy Mardiana - STEI ITB
Instantaneous Overcurrent Relays (IOC)
F1 is the closest to R1
• Use to reduce fault clearing times • Provide no backup protection • IOC relay must NEVER operate for faults beyond line section end • Setting Pickup for IOC: I
=PUk× I3
(at F1)
MAX
1.25 k 1.5 Dr.Ir. Redy Mardiana - STEI ITB
RELE ARUS LEBIH Pengaman Hubung Singkat Relai dialiri oleh Arus Fasa, Tetapi Juga Dialiri oleh Arus Beban, maka Iset > Ibeban Cara 2
Cara 1 R
R
S
S
T
T
Jika terjadi gangguan ke tanah dimana I gangguan < Ibeban , maka relay tak beroperasi Dr.Ir. Redy Mardiana - STEI ITB
RELE ARUS LEBIH Pengaman Hubung Singkat 1 Fasa Ketanah Arus gangguan (1 fasa ketanah) < (arus beban max.), karena : - Gangguan lewat tahanan gangguan - Pentanahan Netral Lewat Impedansi Oleh sebab itu relai gangguan tanah tidak dipasang di arus fasa tetapi mengambil arus residu dari arus ke tiga fasa. Cara 1
OC
Cara 2
OC
R
R
S
S
T
T
GF
OC
OC
OC
GF
*Setting pickup ground fault relay jauh lebih rendah dari overcurrent. Dr.Ir. Redy Mardiana - STEI ITB
Residual Earth Fault Relays • There are two types: – Residual Current Relay (also known as zero sequence current relay) – Residual Voltage Relay (also known as zero sequence voltage relay)
• Residual current and voltage only exists when a fault current flows to earth, • Need to coordinate with similar relays downstream. Dr.Ir. Redy Mardiana - STEI ITB
Residual Earth Fault Relays Residual Current Relay •
Commonly used for :
•
Current flowing on relay is quite high due to solidly or low resistance groundings. Rarely used for high resistance grounding system. Fault current is higher compared to ungrounded or high resistance grounding systems.
• •
– Solidly grounding system – Low resistance grounding system.
Dr.Ir. Redy Mardiana - STEI ITB
Residual earth fault (EF) connection: a) b) c)
Single ground relay Combine ground and 3 phase relays Combine ground and 2 phase relays
Configuration (c) consists of two phases since these will detect any interphase fault; the connections to the earth-fault relay are unaffected by this consideration. The typical settings for earth-fault relays are 30%-40% of the full-load current or minimum earth-fault current on the part Dr.Ir. Redy Mardiana - STEI ITB of the system being protected.
Residual Earth Fault Relays Residual Voltage Relay • Commonly used for ungrounded neutral system and sometimes high resistance grounding system. • Voltage provides the best indication of ground fault because the current is low due to ungrounded neutral syatem. • The circuit uses a wyebroken-delta potential transformer with an overvoltage relay connected across the opening in the delta. Dr.Ir. Redy Mardiana - STEI ITB
