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The primary side of one distribution power transformer with DYn connection was protected by three HRC fuses.
Author : Hamid - From: Iran
Imagine a hypothetical substation with a standard differential protection scheme that has been used to protect one of transmission power transformer with DYn connection.
Author : Hamid - From: Iran
The high voltage substation of power plant is usually built near it and the generated electrical energy in each power generation unit is transferred to substation by one short transmission line.
Author : Hamid
After one sever earthquake happened in the hypothetical nuclear power plant area, following observations were reported by special investigation committee that were authorized to estimate earthquake demolition in power plant.

Author : Hamid
In an extra high voltage substation, the output overhead lines protected by standard protection system.
Author : Hamid
In 3-Phase  over current protection scheme sometimes 2 no of Current Transformers used for overcurrent relay activation.
Author : VATKARI from INDIA
500MW power station under erection. Generator Transformer comes in separate phase banks.

Author : UKB from CANADA

Recently the commissioning part of our company started a new project in a gas turbine power plant with six individual power generation units, each 160 MW.
Author : Hamid
In a bus bar protection scheme applied for a double bus high voltage substation, protection systems design group have chosen high speed trip relay with operation time equal to 4 ms and a 2.5W DC bobbin;
Author : Hamid - From: Iran
In a low voltage substation, including two incomings and a coupling circuit breakers, incoming C.Bs are connected to two individual power transformers which are fed from upstream medium voltage system.
Author : Hamid - From: Iran
In an industrial power plant including four individual power generation units and related step up power transformers, the delta side of transformers is connected to generators and star side to main substation busbars via relevant incoming circuit breakers.
Author : Hamid - From: Iran
As you know, for earth fault protection of electrical system, the residual current measurement is often performed using the three line CTs.
Author : Hamid - From: IRAN
A 20 KV switchgear have equipped with one zig-zag earthing transformer. As you know, A grounding transformer must handle the unbalanced load on the circuit as well as the duty during line-to-ground faults.
Author : Hamid - From: IRAN
I want to know how will we set the earth fault setting of a earthfault relay? is it depends on load or on load pattern?
Author : GUEST
Why the stator winding of the generator cannot be protected 100%.  What is the reason? Kindly clarify.
Author : T.Kailash Kumar - From: INDIA
What is the difference between earth fault & restricted earth fault?  
Please explain.
Author : T.Kailash Kumar - From: INDIA

I have been reviewing the configuration of some multi-function protection relays. The relay settings file for a Feeder Protection relay shows a Minimum Operating Voltage for Bus Undervoltage protection but it is currently set to 0.00 x VT.

Author : GUEST
In Large Generators,for providing 100% Stator Earth Fault protection,low Frequency Injection voltage at 20HZ IS WIDELY USED.
Author : GUEST

the interposing VTs are used for incoming and running busses in synchronising scheme why these two VTs are used? what are advantages?

Author : GUEST
If the star point of a transformer is earthed and one phase develops a fault to earth can anyone provide a link with a detailed explanation to the resultant effect on the healthy phases with respect to earth ?
Author : GUEST
What is the role of secondary grounding protection in luminous tube?
Author : EHSAN - From: IRAN
What is the control and protection dc voltage selection philosophy in substations?
Author : Ahmad - From: IRAN

One of my friends participated in an interesting power network test recently. They intended to evaluate the ability of one of separated power generation unit in islanding mode operation.
Author : Hamid - From: IRAN
What happens when ct  secondary gets open while selecting through ampere meter selector switch for metering function why dont it get burst/burn when secondary is open momentarally?
Author : bipul pandey - From: INDIA
Please let me know the function of neutral ground resistance sytem of transformer protection and how it is different from restricted eath fault protection.
Author : bipul pandey - From: INDIA
In an industrial plant, electrical heaters are derived by suitable contactor and MCCB. Also a standard earth fault relay has considered for as earth leakage detector.
Author : Hamid - From: IRAN
What points shall be considered in circuit breaker choosing?
Author : NADER - From: Iran
Why saturation phenomenon in current transformers cannot prevent the CTs secondary overvoltage?
Author : NASER - From: IRAN
Is there any relation between electrical contact melting and amount of through current or voltage drop in switching condition?
Author : Bita - From: IRAN
In protective relay selection, what terms of reliability or availability are important?  Please explain.
Author : Hamid
What facility or anticipation shall be considered in design stage for reduction of fire risk in substations?
Author : Habibi - From: IRAN
how does directional overcurrent work ? and how do i go about testing it ?
Author : atiqun nabi - From: England
under normal condition why is the bus coupler protection switched on
Author : MONICA MAHLANGU - From: South African

For suitable thermal protection of induction motor, I need its time constant. How can I calculate it?
Author : AFRA
Can a 3500 KVA, 6.3/11 KV power transformer HV side be protected against all faults by installing protection relays only on its primary 6.3 KV side? Overhead line is directly connected at 11 KV side of transformer.
i 'd like to know the mechanizm of SF6 CB working.
Author : Mohammed - From: Libya
There are 2 generators in parallel and they are coupled to a common busbar where there is a stepup transformer.
Author : Guest - From: Unknown
As you know, the inrush current just appears in one side of transformer when we energize power transformers.
Author : Hamid - From: IRAN
what is dead machine protection of an alternator?
Author : YOGI - From: India
Is there reverse KVAR relay similar to reverse power protection relay in power system?
Author : Ahmed - From: Egypt
how differential relay's setting is calculated? calculation given in book doesnt match with actual setting.....
Author : Yogi - From: India
Have a property in Spain with spasmodic tripping on the RCD.  I have found a neutral to earth fault with a voltage reading of 378 volts!,  there is no cross bonding in the houses over here and all the earth wires are in connector blocks throughout the house.  
Author : Brian Thurlborn - From: Spain
what is out of step protection of an alternator?
Author : Yogi - From: India
The lubrication oil pumps of turbo generator bearing are fed by outgoing of an emergency panel in power plant as illustrated in below figure. The control circuit of mentioned AC panel is supplied by power station safe (of course not very safe) uninterruptable DC system.
Author : Hamid - From: Iran
A ring of transformers supplied from main substation using 2 feeders. The main substation feeding from 15MVA transformer.
Author : Ahmad - From: Iran
What is difference between 50N and 50G protection? And related advantage and disadvantages?
Author : Alfredo - From: Spain
Are there any criteria or normal practice for setting calculation of earth leakage protection in impedance earthed electrical systems?
Author : abbas - From: Iran
Earth fault tripping on starting of Large 3 phase motor.  Can current imbalance and CT connection scheme explain this. Or other reason?
Author : Brett Welsh - From: Australia
what are the advantages of internal fault protection in transformer?
Author : Shital - From: India
In our industrial plant, the power electronic convertor devices such as industrial frequency convertor, variable speed drives and ac to dc convertors have used, and we concern to voltage and current distortion and its bad affects on electrical protection systems.
Author : Bahula - From: India
During CT's primary injection testing why we cannot inject 80%-90% of primary current in to CT?
Author : Rohana - From: Sri Lanka
want to know details about it and a diagram and circuit.....
Author : Nitin - From: India
I want to know the criteria of setting calculation of phase unbalance protections such as 46, or 47 devices.
Author : Gustaw - From: Poland
Studious groups were commanded to harmonic affect on protective relay investigation in a power plant substation. Ali as youngest member of group should be gather field data and information.
Author : Hamid - From: Iran
Are there any over voltage limitation for electro motors operation?
Author : Reza - From: Iran
Please tell me for REf Protection, the induction relay is being used?....
And Lots about details of relay
Author : Nitin - From: India
A protection design group which their company had fronted to budget problems, for pecuniary saving, decided to use of one set differential relay with three input current instead of two differential relay for protection of two same power transformers as indicated in below figure.
Author : Hamid - From: Iran
Why they are not much sensitive at for 1phase to earth fault close to the earth point in solidly earthed X'mers & ref is being used in place of that?
Author : Nitin chavda - From: India
What is difference of low and high impedance relay and their advantage in practical cases?
Author : Ashkan
What is the reason of using resistor in high impedance relay?
Author : alireza - From: Iran
what happen when a CT become saturated?
is the secondary of CT like a short circuit?
Author : alireza - From: Iran
Why the primary side of distribution transformers usually is not grounded?

Author : Hamid - From: Iran
In an executed REF protection, the neutral CT No.1 after many years of system operation is fronted to burning due to unknown accident (see below figure).
Author : Hamid - From: Iran
Why we Eliminate the 5th harmonic in differential protection?
Author : Mohammad - From: Iran-Esfahan
Please  find attached  image for REF low impedance protection for 2MVA , 11KV/ 0.415 KV , %Z = 7 %  .
Author : ASAD - From: Saudi Arabia
numerical restricted  EFR whether it is a low impedence or high impedence ref.
Author : Radhakrishna hn - From: Bengaluru
I want to know  about solid state relay..............
And Any Project In Earth fault........
Author : Nitsworld
How can I calculate eartfault in distribution feeders?
Author : Tag - From: Iran
Please inform me about G.59 protection in diesel generator protection system.
Author : Rahim - From: Iran
How can be verified the transformer differential relay connections to CTs and be sure correct CT polarity in commissioning stage?
Author : Sara - From: Iran
I would like to know about the safety Co-efficient of transformer named as FS of a transformer. what does this signifies and how to choose between them.
Author : Mirza Shoaib - From: Pakistan
What is the difference between restricted earth fault & standby earth fault?
Is the setting of the both relays are kept equal?
Author : Bashir Varsi
I know locked rotor current, of an induction motor, how can be calculated/chosen the suitable setting current of 50 (instantaneous over current ANSI code) of specified motor protective relay?
Author : H.S - From: Qatar
Advantages  of providing REF protection on 2MVA,22KV/433v Dyn11 Transformer,Having Z% 6.25.What should be ideal CT specs on transformer neutral and in LT panel.
Author : Manish Naha - From: S N Joshiconsultants,Pune, India
CT Equipotential connection and its requirment.
Author : Abdul Hameed
Rating of the CT provided in the neutral of the transformer/generator for the earth fault protection is 1/5 of the rated current of the transformer/generator. How this 1/5 is arived? why?
Author : Deepa
I need some help. In our 50MVA, 132/33 kV star/star transformer, at the time of charging from HV side, the transformer trips on REF (restricted earth fault) due to magnetizing inrush current.
Author : Sreelatha - From: India
In one of our transformer 100 MVA, 220/132 kV Auto, only Hydrogen generation is increasing, other fault gases are absent.
Author : Gajjala Sreelatha - From: India
According to NEMA/NEC/ANSI/UL/... etc should there be an indication in the SPD when its service life is over
Author : Sinnadurai Sripadmanaba - From: Srilanka
If surge protectors are used should we disconnect home appliances,
In homes people disconnect antenna and power connections to TV,Telephone,Radio etc during thunderstorm in the fear that lightning can harm appliances as well as persons....
Author : Sinnadurai Sripadmanaba - From: Srilanka
What are the frequencies(HZ) of surges/impulses including lightening and switching which travels along transmission lines and pass to ground via SPDs?
Author : Sinnadurai Sripadmanaban - From: Srilanka
During a surge will the air gap between contacts in light switches and receptacles breakdown and cause damage to connected equipment.What is the magnitude and duration of surge required for it to happen?...
Author : Sinnadurai Sripadmanaban - From: Srilanka
We have experienced unduly trips of a Stand By Earth Fault relay which uses the residual connection of the three phase CT's on primary side of 6.5 MVA 11/3.3KV Dyn11 transformer. ...
Author : Claudio - From: Italy
In IEC-364 it is specified that operating time of protective devices for protection against Indirect Contact as 5 second How this value is arrived
Author : V.K.Nambiathiri - From: India
Pls assist with full details and schematic drawings of standby earth fault protection
Author : Unknown
Dear i just remove N wire from 4 pole Elcb but still no triping, and as we know our system is never balanced so ir,iy,ib never equal to each other and never in=0  so at which condition 4pole Elcb trip???
Author : asad - From: pakistan
Please guide for the protection scheme of transformer with four winding.
following transformer specifications, ...
Author : Anirudh patel - From: India
For high impedance restricted earth fault protection it is known the neutral CT ratio of the power transformer must much with the line CT, But during Test and commisining i have got a problem, ...
Author : Addis - From: Ethiopia
Can lightning arrestor of BIL1050 KVp  be used for 11/235 KV 150 MVA generator transformer of BIL 950 KVp? Is there a chance of damage to transformer due to  lightning impulse of voltage peak greater than 950 but less than 1050?
Author : Purnendu Pradhan - From: India
I would like to know more about testing methods of Directional Earth fault Protection. Also mainly in which system Directional earth fault is mandatory?
Author : Pramod - From: India
We have a fault in one of our 13,8 kv outgoing feeder , the faults cleare by the stuck breaker protection , when we energize normlize all the feeders , the faulty feeder tripped by it is own portection ( o/c) . ...
CBCT is used as REF protection for Tranformers. How?
Author : Soman - From: India
Explain high speed  bus bar differential protection of above 132 kv substations
Author : SOMAN - From: India
2 MVA Oil filled Tr. with OLTC and RTCC panel, Functiong of oil surge relay with primary tripping mechanisem
Author : Unknown - From: India
What will happen if Field excitation is provided at 1000 rpm to the generator having synchronous speed is 3000 rpm . Is there any protection provided to avoid this?
Author : rakesh kumar - From: India
how differential protection of bus bar works? how outgoing feeders ct is connected to differential protection relay?
Author : george.v.sebastian - From: India
I would like to know how short circuit limiter works.
Author : george.v.sebastian - From: India
Explain and determination of Grading Time  in High set and low set  stages  of Numerical relays Protection ( Delta t DT  And Delta t IDMT )
Author : soman - From: India
I was wondering why REF is set to time delayed tripping of around 200 ms as REF will only cause tripping when the part of winding has grounded and obviously REF wont trip for imbalance and ....
Author : Why - From: Pakistan
Suppose that we have autotransformer of 250 MVA whose tertiary was initally Grounded at one point and no load was there on tertiary. ...
Author : Unknown
In  small ratings of transformers,  Over current protection is also give the internal fault protection of transformers. How?
Author : soman - From: India
Can you inform why we can not use the parallel combination of field breaker 52a contact & Field U/V relay's NC contact ....
Author : Imran Mushtaque - From: India
Can anyone tell what is the dead Zone?
2ndly how to calculate the I Burden of Current Transformer?
Author : Unknown
The standard current transformer secondary winding rating is always kept in 5 amps. Why?
Author : soman - From: India
Can anyone explain what is the 'I" burden and "V" burden of C.T and how to calculate it?
Author : Unknown
Protection CT for REF protection - How minimum knee point voltage & maximum magnetising current calculated.
Author : Unknown
what is the recommended setting on the directional over current relay in ring / mesh network  & for coordination how can we set between two relays like 0.3 sec time discrimination.
Author : Ikhan - From: UK
The instantaneous earth fault relay provided at 11kV side of 1000kVA, 11kV/433V relay trips when load on transformer reaches approximatly 400kVA. IDMT earth fault relay at 433V side does not act.Much obliged if the reason given.
Author : V.K.Nambiathiri - From: India
How to calculate Earth Fault relay current& time setting for 160 KW motor with softstarter?
Author : birendra singh mehta - From: India
Whether ELCBs are available for pure tripple free DC circuits? If so the principle of working.
Author : V.K.Nambiathiri - From: India
What is the difference between 5P20 & PS class CT, How to decide which one shall suitable?
Author : Deepak
how to determine the knee point voltage of ct  for motor differential protection protection?
Author : Aditya
how and why malopration is ocuure? is it advantageable or not
Author : arslan
In one of our MCC we have encountered a problem tat whenever there is flashover or any motor burnt, the fuse blows out but ....
Author : Kailash - From: India
Please provide setting calculations for ( GE ) MiFII over current & Earth fault relay.
Author : Faizullah Bajwa - From: Pakistan
how to calculate MCCB size  for motor load.if there is thumb rule please advice me
Author : tajuddeen - From: India
Does IEC endorse NFC regarding Early Streamer Emission Arresters?
Recently , I heard that at last ,  IEC confirmed NFC 17 102 Std . Regarding correctness and usage of Early Streamer Emission Surge Arrester . I haven't found any article to confirm it yet .
Author : PEGAH - From: IRAN
Subject We have 11kv bus for distribution of power. Our breaker no.1 tripped on sensitive earth fault with a fault current of 240amps in CBCT. But with ....
Author : Indrajeet
What should be the setting of undervoltage in a multifunction relay of incoming 33kv in a 33/11kv substation. The transformer is with a auomatic tap changer controller with T1 = 150 sec and T2 = 10 sec in 85% undervoltage
Author : Mubarak - From: Tunis
Design of protection scheme to detect earth fault and isolate the faulty source in multiple 11kv generators connected to common bus through dedicated breakers.
Author : Muhammad Waqas - From: Pakistan
Distance relay  has to be acted at all the times of lightning protection .But , in some cases , it is not acting at  all the times. Please explain the reasons.
Author : soman - From: India
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