6th Comprehensive Protection Training Program at Pearl Continental L AHORE in 2012
A TYPICAL POWER SYSTEM NETWORK
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SIEMENS LECTURE ON
OVER CURRENT & EARTH FAULT RELAY SETTING CALCULATIONS AT
PEARL CONTINENTAL HOTEL LAHORE ON 04-09-2012
BY SIEMENS PAKISTAN ENGINEERING COMPANY LTD Slide 2
RELAY SETTING CALCULATIONS
A guide for the calculations of the Relay Settings for: Over current and Earth fault Relays a) Definite Time Relays b) Inverse Time Relays For Power Transformers & 11kv feeders
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RELAY SETTING CALCULATIONS 1. Enlist the technical data required in network study and calculations of relay settings. 2. Ask from client\consultant to provide essential technical data relating to the existing network and equipment needed in the subject matter. 3. Study carefully the protection schemes designed for the project. 4. Enlist the protection relays with their functions to be used. 5. Chalk out which type of documents are agreed to submit to consultant/client. 6. Arrange the content/index sheet of the relays, need to settings' calculations. 7. Submission of proposed relay settings to the consultant\client for approval. 8. Arrange a meeting to clarify technical and disputed points regarding to the submitted document for the approval. 9. Finalize the relays setting calculations with duly signed from client\consultant\contractor. 10. Upload the parameters in the relays according to the calculations at site for pre-commissioning and testing. Slide 4
RELAY SETTING CALCULATIONS Please note that - Minimum generation is considered for relay setting calculations. (pick up,trip) & - Circuit Breaking capacity is calculated for maximum generation possible.
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PROTECTION IN SMALL ZONES USING OVERLAPPING PRINCIPLE 2
1
G
G
3
POWER HOUSE
STATION A 132 kV
4
STATION B 132 kV
Boundary of Protection Zones are decided by Location of CT’s
PAKISTAN
X
Circuit Breaker
1
Generator Protection Zone
2
Generator Transformer Unit Protection Zone
3
Bus Bar Protection Zone
4
Transmission Line Protection Zone Slide 6
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Definite Time Over current Characteristic
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Inverse time Over current Characteristic
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Normal Inverse time characteristic of relay 7SJ60
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SETTING DEFINITE TIME OVERCURRENT RELAYS Over current Relays has a wide range of applications. It can be applied where there is an abrupt change of current due to faulty condition. These relays are used for protection of Motors, Transformers, Generators and Transmission Lines etc. In distribution networks these are the main protection whereas in HV and EHV systems, these are used as back up protection. Although there is no hard and fast rule for use of definite time or inverse time relays and one can decide by looking into the site requirements.
NTDC and the utilities in Pakistan however have standard practice to use Inverse time relays for back up of Motors, Transformers and Generators. For HV and EHV lines, definite time over current relays are used for back up purpose. Slide 12
SETTING DEFINITE TIME OVERCURRENT RELAYS Definite time over current relays have adjustable over current elements. When an element picks up, it energizes a built in time element which initiates a tripping signal after elapse of set time. In definite time over current Relays, we have to set, The over current element for its pick up value, the high set element for its pick up value along with the time delays required. The instantaneous element pick up value for the current is to be selected whereas time setting is instantaneous.
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7SJ602 SETTING POSSIBILITIES OVERCURRENT RELAY 7SJ602 PHASE FAULTS
EARTH FAULTS
STAGE I>
DEFINITE TIME OR IDMTL
DEFINITE TIME OR IDMTL
STAGE I>>
DEFINITE TIME OR INSTANTANEOUS
DEFINITE TIME OR INSTANTANEOUS
STAGE I>>>
INSTANTANEOUS
------------
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OVERCURRENT RELAY SETTINGS
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OVERCURRENT RELAY SETTINGS The relay at the far end B is set with shortest operating time. The Relay on upstream which is at end A has to be time graded against relay at end B with a minimum time difference of 200-300mSec for numerical relays and of 400-500mSec for electro-mechanical relays. The relay at end B is required to be set with the minimum operating time IDMTL mode and to be set for TMS of 0.1or 0.05 Time Dial whichever setting is available. The relay at end A has to be set accordingly. Slide 16
SETTING OF OVER CURRENT RELAYS
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OVERCURRENT RELAY SETTINGS In the previous diagram, the relay at far end (D) is set with shortest operating time. Relays on the upstream are to be time graded against the next down stream relay in steps of 0.2 Secs. Definite time characteristic is selected where Source Impedance is quite larger compared to the line impedance. This means small current variation between near and far end faults. The inverse mode is selected where fault current is much less at the far end of the line than at the local end. (Selection also depends on the utility preference looking into their operational requirements.)
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7SJ602 SETTING CALCULATIONS FOR AUTOTRANSFORMER 3x200 MVA 500KV 3 × 200 MVA Auto-transformer HV Winding Circuit Time Over Current Relay Type: CT Ratio : Rated power: Rated voltage: (at minimum tap)
7SJ6021-5EB20-1FA0 N = 3250/1 S = 600MVA U = 472.5KV
Required Settings: Plug Setting Characteristic to be selected Time Multiplier Setting (TMS) High Set Element Settings, I >> Instantaneous Element Setting, I >>>
Plug Setting: Autotransformer HV winding rated current IN = S ÷ ( 3 × U ) Allowed overloading Relay's resetting ratio = Drop off ÷ Pick up Relay's setting current = (IN + IN ) ÷R Corresponding secondary current = Is ÷ N
IN = 733A = 5% R = 0.95 Is = 810A = 0.25A
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7SJ602 SETTING CALCULATIONS FOR AUTOTRANSFORMER 3x200 MVA 500KV Characteristic to be selected: Normal Inverse Characteristic is selected according to the NTDC System practice. Usually for inductive loads, inverse time characteristics are selected. For line feeders, definite time characteristics are suggested. Time Multiplier Setting: Fault current at HV Connection of autotransformer IF =11548A Multiples of Fault Current (PSM) = IF ÷ Is =14.25 As per IEC Normal Inverse characteristic =0.14÷{(14.25)0.02-1} Operating time at TMS = 1 A =2.565 sec. For selectivity as backup, tripping time chosen B =1.200 sec. Required time multiplier setting, = B ÷ A TMS = 0.47 High Set Element setting = to be blocked Instantaneous setting (Ipick up = 5 × IN ) =5.00 I/In Settings recommended: Over current plug setting TMS setting Characteristic Instantaneous setting (Ipick up = 5 × IN ) High Set Element Settings, I >> IE >>
=0.25 I/In =0.47 = Normal Inverse =5.00 I/In = Blocked Slide 20
7SJ602 SETTING CALCULATIONS FOR AUTOTRANSFORMER 3x200 MVA 500KV 3 × 200 MVA Auto-transformer HV Winding Circuit Earth Fault Time Over Current Relay Type: 7SJ6021-5EB20-1FA0 CT Ratio : N = 3250/1 Rated power: S = 600MVA Rated voltage: (at minimum tap) U = 472.5KV
Required Settings: Plug Setting Characteristic to be selected Time Multiplier Setting (TMS) High Set Element Settings, IE >> Instantaneous Element Setting, IE >>>
Plug Setting: Autotransformer HV winding rated current IN = S ÷ 3 × U ) IN = 733A Minimum fault current considered as percentage of rated current = 5% (for purpose of pick up of relay) Relay's resetting ratio = Drop off ÷ Pick up R = 0.95 Relay's setting current = ( )×(IN ÷ R) =.05x733 ÷.95=38.57 or Is = 39A Corresponding secondary current = Is ÷ N = 0.01A
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7SJ602 SETTING CALCULATIONS FOR AUTOTRANSFORMER 3x200 MVA 500KV Characteristic to be selected: Normal Inverse Characteristic is selected according to the NTDC System practice. Usually for inductive loads, inverse time characteristics are selected and For line feeders, definite time characteristics are suggested. Time Multiplier Setting: Fault current at HV Connection of autotransformer IF =1469A Multiples of Fault Current (PSM) = IF ÷ Is =38.07 As per IEC Normal Inverse characteristic =0.14÷{(38.07)0.02-1} Operating time at TMS = 1 A =1.854 sec. For selectivity as backup, tripping time chosen B =1.100 sec. Required time multiplier setting, = B ÷ A TMS = 0.59 High Set Element Setting = to be blocked Instantaneous setting (Ipick up = 5 × IN ) =5.00 I/In Settings recommended: Over current plug setting TMS setting Characteristic Instantaneous setting (Ipick up = 5 × IN ) High Set Element Settings, I >> IE >>
=0.01 I/In =0.59 = Normal Inverse =5.00 I/In = Blocked Slide 22
OVER CURRENT RELAY SETTINGS FOR 11KV FEEDER 11 kV Outgoing Panel CT Ratio = 400/5 = 80
Relay 7SJ602 O/C Settings Calculations
Load Current = 360 A Relay Nominal Current = 5A ___________________________________________________________________________
Settings Required
1) Characteristic to be chosen 2) Plug Setting 3) Time Multiplier Setting TMS 4) High Set elements settings I >> IE >> 5) Instantaneous element setting I >>> ___________________________________________________________________________
PHASE FAULT: Ip > (Pick Up)
1) Characteristic = Normal Inverse (IEC) 2) Plug Setting Considering Full Load Current. Permissible over loading Relays Resetting ratio = Drop off/Pick up Relay setting current Secondary Current Selected Pick Up Setting 3) Time Multiplier Setting Assuming fault current Multiple of Fault Current (PSM)
= 360 A = 10 % = 0.95 = 360x1.1 .95 = 417 = 5.2 A 80 = 1.04
= 417 A
= 1350 A (an hypothetical value) = 3.23 = 1350 417
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OVER CURRENT RELAY SETTINGS FOR 11KV FEEDER (continues) Operating time as per IEC NI Characteristics = 0.14 = 0.02 (3.23 – 1)
0.14 0.0267
= 5.24
Time required for Relay Operation is = 300 mSec ( Normally site requirements should be considered. ) Therefore: TMS = _0.3_ = 0.057 5.24
PHASE FAULT: Ip >> (High Set) 1) Characteristic = Definite Time _ 2) Plug Setting Considering 4.0 times the Pick up Current. Secondary Current = 1668 = 20.85 A 80(ct ratio) Selected Pick Up Setting = 20.85/ 5 =4.17 3) Time Setting = 0.1 s (to be chosen by the engineer as per requirement)
PHASE FAULT: Ip>>> (Instantaneous) 1) Characteristic = Instantaneous 2) Plug Setting Considering 5.0 times the Pick up Current. Secondary Current = 417x5 = 26.05 A 80 Selected Pick Up Setting = 26.05/5 = 5.2 (or we can calculate from I pick up which will be 1.04 x 5 = 5.20) (Please note that the fault current is to be calculated based on fault calculation study on HT side and considering the secondary impedance of the Transformer installed )
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EARTH FAULT SETTINGS FOR 11KV FEEDER Relay 7SJ602 E/F Settings Calculations EARTH FAULT: Ie> (Pick Up) CHARACTERISTIC SELECTED = NORMAL INVERSE (IEC)
Plug Setting Considering NTDC practice to set the E/F element pick up at 20% of ct sec. rated current. = 0.2 x 5 = 1 (effective value in amps = 80 Amps) (Utilities normally select earth fault element pick up from 10% to 20%. At lower pick up values, sensitivity increases and stability reduces. At higher pick up, the sensitivity is reduced but stability is increased. Normally time of operation is set equal to phase operation time.)
Time Multiplier Setting Assuming single phase to ground fault current = 650 Amps Multiple of Fault Current = 650 = 7.71 84.2 Operating time as per IEC NI Characteristics = 0.14 = 0.14 (7.71 0.02 – 1) 0.0416
= 3.365
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EARTH FAULT SETTINGS FOR 11KV FEEDER Time required for Relay Operation is = 0.3 Sec ( to be selected considering site conditions) Therefore: TMS = 0.3 = 0.089 3.365 EARTH FAULT: Ie>> (Instantaneous element setting) 1) Characteristic = Instantaneous 2) Plug Setting Considering fault Current = 650A = 650 = 8.125 80 Pick Up Setting for instantaneous element = 8.125/5=1.625 (It is to be noted that settings are selected keeping in view the site conditions and past experience. No hard and fast rules can be chalked out. These examples are to show the procedure only. ) Slide 26
Thank you for your Attention
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CONSTRUCTION OF ELECTROMECHANICAL RELAYS
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Protection Co ordination of inverse time relays & Disc emulation Disc emulation evokes a dropout process, which begins after de energization. This Process corresponds to the back turn of a Ferraris Disc. In case several faults occur successively, it is ensured that due to the inertia of the Ferraris Disc, the history is taken into consideration. Consider the main over current relay of electro mechanical type and the feeder relay of numerical type. There are chances that the Main relay may operate unnecessarily on repeated feeder fault. To avoid this Disc emulation feature is introduced. The Disc emulation feature Offers its advantages when the grading co ordination chart of the time over current protection is combined with other devices (elect. Mech or induction base) connected to the system.
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SLAVE POINTER AND MEAN VALUES Slave pointer and Mean values is basically a measuring technique to measure the Maximum , Minimum and average values of waveform. The waveform can be of current or voltage.
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THERMAL OVER LOAD PROTECTION The thermal Over load protection prevents the protected object ( cables, motors and transformers etc) from damage caused by thermal over loading. This protection operates independent on the time over current and unbalanced load protection. It can work with memory or without memory. OVER LOAD PROTECTION WITHOUT MEMORY If the overload protection without memory is selected, the tripping time is calculated according to a formula. When the current in any phase exceeds threshold value, timer picks up. Trip command is given after the time has elapsed. This method is easy in handling. t=
35x tL (I/ IL )2 - 1 where t is tripping time I is over load current IL parameterized threshold value tL parameterized time multiplier (tripping time with 6 times the threshold value IL)
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THERMAL OVER LOAD PROTECTION OVER LOAD PROTECTION WITH MEMORY The unit computes the temperature rise according to a thermal single body model (thermal replica). This method requires some knowledge of the protected object, its ambient context and its cooling temperature etc. This method is used when the object is to be operated at the limit of its performance.
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CONCEPT OF I/IN IN is the rated current of the relay and also the secondary current of the Current Transformer. They should match with each other so that correct setting and pick up values could be selected. Example: In the 7SJ602 relay, the phase current pick up I range has been defined as 0.1 IN ------4.0 IN If IN is 1 amp then it is easy to understand that the pick up range will be from 0.1 amp to 4.0 amp However if IN is 5 amp then the pick up range will be from 0.5 to 20 amps To make it simpler we can write the above pick up range as I/ IN from 0.1 to 4.0(10% to 400%) This statement is independent of amps. We have to always look at I/IN and set the relay from 0.1 to 4.0 Assume ct 100/1,relay rated current 1, the relay pick up set at 1 means relay will pick up at 100 Amps in primary And if we assume ct of 100/5, relay rated current 5, the relay pick up set at 1 means that relay will pick up at 100 Amps (ct 100/5 relay 1 amp- relay pick up setting possible 2 to 80 Amp) (100/5 means 20 relay can be set 20 x 0.1-4.0 i.e. 2-80 Amps) Slide 33
