# More the transformer impedance less the fault current... so is a high value of transformer impedance good for it?

It depends a lot on the application, i would go with low impedance transformers if am using the transformers for distribution as it will really increase the the maximum fault current. If am using the transformers as step up specially for generators or to charge capacitors, using a high impedance transformer is a good idea as it will decrease the inrush current of the system.

you have to see your application and decide what fit that best.

Mohammad Jaradat

Power Generation Project Manager

### Relation between kva and fault level?

There isn't enough information here. Available short circuit fault level can be given as a KVA value for different types of faults, but I assume the questioner is looking for a relationshiop between (transformer?) KVA and available short circuit current - If my assumption is correct, there is no direct correlation without knowing the transformer positive and zero sequence impedances. If these are known, you can assume the source impedance is infinite, and calculate the… Read More

### What is the reason for using a neutral current transformer on a transformer?

A current transformer is primarily used at the neutral point of a transformer for earth fault protection. A neutral current transformer will measure any ground fault current which will essentially flow from the star point of the transformer. A fault-detection device other devices is connected to the current transformer and, if the fault current exceeds a certain trigger value, the fault-detection device will give a trip command to an earth-fault relay to disconnect the supply… Read More

### Why is the neutral current transformer?

A current transformer is primarily used at the neutral point of a transformer for earth fault protection. A neutral current transformer will measure any ground fault current which will essentially flow from the star point of the transformer. A fault-detection device other devices is connected to the current transformer and, if the fault current exceeds a certain trigger value, the fault-detection device will give a trip command to an earth-fault relay to disconnect the supply… Read More

### What is neutral earth compensator?

For earth fault protection on the windings of a delta connected transformer. Used in MV distribution. An earth fault current return path is provided by connecting a Neutral Earthing Compensator (NEC) between the three phases of the power system and the earth system. This is done at the source of the supply. The NEC transformer winding has a Zig-zag configuration with no secondary winding. The impedance of the winding is high when there is no… Read More

### What is the reason for using a current transformer in an electrical service substation?

A current transformer is primarily used at the neutral point of a transformer for earth fault protection. A neutral current transformer will measure any ground fault current which will essentially flow from the star point of the transformer. A fault-detection device other devices is connected to the current transformer and, if the fault current exceeds a certain trigger value, the fault-detection device will give a trip command to an earth-fault relay to disconnect the supply… Read More

### If impedance of power transformer is increase from 8 to 10 percentage then what will effect?

if the designed value of percentage impedance is change, for general this should affect tow things * if the percentage impedance is decrease this should increase the fualt level current *if the percentage impedance is increase this should increase the transformer losses and tempreture rise so the designed value of percentage impedance is determined according IEC if it is less than or equal 10% the margin should be + or_ 15%, if it is more… Read More

### What is earth fault loop impedance?

is actual of earth loop impendance for maximum value. for comprisoner the current through the cicruit

### If a 240V circuit is protected by a 15A simi-enclosed fused and has an electrical earth-fault loop impedance of 1.9 ohms determine the earth fault current in the event of a zero impedance earth fault?

I am assuming that its a 240 Volt AC circuit supplying an inductive load with a fault loop impedance of 1.9 ohms at the time of the short circuit. The power factor is assumed to be 0.8 The instantaneous earth fault current value would be; Current = (Voltage x Power Factor) / Impedance (240 x 0.8) / 1.9 192 / 1.9 = 101 Amps. However this may be a trick question as it doesn't ask… Read More

### When 440 volts and 300 amps is given as an input to the transformer the output obtained is 11 kva in this secondary current will decrease or not?

Your question reveals a misunderstanding of how a transformer works. The primary current of a transformer is determined by the secondary current, not the other way around. When the secondary voltage is applied to a load, a secondary current flows, and its value is determined by the secondary voltage and the load impedance. This secondary current then determines the value of the primary current.

### How do you calculate current on secondary side of transformer?

The secondary current is calculated by dividing the secondary current by the impedance of the load. This value shouldn't exceed the secondary-winding's rated current except for short periods of time.

### HOW TO CALCULATE THE IMPEDANCE FOR THE TRANSFORMER?

The simple impedance is measured by running the transformer on load and off load. The on-load voltage is less than the off-load voltage, and the impedance is equal to the change in voltage divided by the load current. Another Answer You are probably referring to the transformer's 'percentage impedance', which is one of the characteristics listed on its nameplate data. Percentage impedance is rather confusing because it is expressed in terms of voltages! To conduct… Read More

### Why do you need to measure ground resistance value?

The whole point of earthing or grounding is to provide a low-impedance path back to the supply transformer in the event of an earth fault within a wiring installation, which will then enable sufficient earth-fault current to flow in order to operate the circuit's protective device (circuit breaker or fuse). When designing the circuit's protection system, it is therefore necessary to determine the resistance of the earth (ground) as it determines the value of this… Read More

### How do you convert percent impedance of transformer to impedance value?

The apparent impedance looking into a transformer from one side will not be the same as looking in it from the other, which is why percent impedance is used. If you are looking from the high voltage winding (I'm labeling #1) to the low voltage winding (#2), you must scale the percent impedance as follows: (% impedance) x (Winding #1 nominal voltage)^2 / (transformer base VA)

### Why impedance relay is called as distance relay?

because the distance is propotional to the impedance of the line ,so the operation of the impedance relay comes into picture when the impedance seen by the relay is less than the pre-setting value.When a fault occurs ,the current increases to a high value and so the Impedence decreases and the relay actuates

### Why ELCB are measured in terms of milliampere. how will we measure the capacity required for any application. how do we calculate it?

ELCB's are "earth leakage circuit breakers". They are used in situations where high impedance grounding is used, meaning a phase to ground fault has very low current levels. This results in standard overcurrent/breaker protection not necessarily "seeing" the fault. And I do not believe ELCBs are usually rated in milliamperes. Their interrupting rating, and load is usually similar to MCCBs. They include a leakage current rating, which is in mA (leakage current is current to… Read More

### What is defrential protection relay?

I am going to assume that you are asking about a differential relay. It is basically just that- it compare two different sources and will trip at a set value value of the difference. These can be directional as well. A couple of examples are transformer protective relays and bus differential. A transformer relay will measure the amount of current coming into the transformer and the amount of current going out. If there is a… Read More

### How do you size zigzag transformer in ETAP software how to find the impedance value in the device coorination mode?

http://www.etap.com/faqs.htm

### Is a capacitor used to change an AC voltage to a lower or higher value?

Yes.... capacitors offer impedance to flow of ac current.. But since the value of impedance is inversly proportional to the frequency of source therefore the impedance offered generally is much lesser than in case of dc current

### Effect of winding resistance with respect to EHV transformers voltage levels and their MVA rating?

The MVA rating will have an effect on the winding resistance - the higher the rating, the bigger current flows, thus the larger winding wire must be, which lowers the resistance. Generally, EHV transformers impedance (the resistance value you're thinking of) is specified when ordering the transformer, and can range from 4-20% (on the transformer base rating). When heavily loaded, on a weak system (high source impedance), the impedance of the transformer can impact the… Read More

### How do you calculate impedance on power transformer?

Impedance is based on the thickness and type of wire used, the number of turns, type of core, etc. To calculate, you have to have all this information. On large transformers, short circuit tests are performed to determine the impedance. Another Answer I assume you are referring to a transformer's 'percentage impedance'? The term, 'percentage impedance', is a little misleading, as it is defined as 'the value of primary voltage that will cause rated current… Read More

### How designing stabilizing resistor in restricted earth fault relay?

To determine the value of Stabilizing resistor Rs = Vs/Is = If(Rct +2Rl)/Is Where, Rs = resistance value of the stabilizing resistor Vs = voltage at which the relay will operate Is = current flowing through the stabilizing resitor and the relay If = maximum secondary fault current magnitude Rct = internal resistance of the current transformer Rl = resistance of attached wire leads

### What is the current in the secondary coil if current in primary is 5.0A?

It depends on the turns ratio between the primary and the secondary. If the ratio were 10:1, a step-down transformer, for instance, the current in the secondary would be about 50A. If it were 1:10, a step-up transformer, however, the current in the secondary would be about 0.5A. Answer The primary current doesn't determine the secondary current. The secondary current is entirely-dependent on the secondary voltage and the impedance of the load. It is this… Read More

### What is the difference between a transformer and a rectifer?

A transformer is used to change the value of a voltage applied to the transformer's primary winding to a different voltage value taken from the transformers secondary winding. A rectifier is used to change an alternating current value to a direct current value.

### How does a current transformer work?

A current transformer (CT) works just like any other transformer. It is important to note it is not referenced to ground. It reflects current flow, not phase to ground voltage, so it attempts to hold current constant, not voltage. There is usually one primary "winding": one large cable through a donut CT, and multiple secondary windings. If a secondary winding is shorted (a wire placed across its terminals), the voltage built up in the secondary… Read More

### What is the difference between neutral earthing resistance and solid earth?

The star point of a primary*-transformer's secondary winding is frequently connected to earth via an impedance, in order to limit the return current in the event of an earth fault close to the transformer. The impedance may be a resistor or an inductor, (choke) depending on the nature of the earth return. In general, if the earth resistance is low, then resistive earthing is used; if the earth resistance is high, then inductive earthing is… Read More

### How calculate primary current in transformer the 50kva rating and 11kvprimary voltage?

The primary current is determined by the secondary current. So, if you don't know the secondary current, you cannot work out the primary current. If the secondary isn't connected to the load, then the primary current is simply the primary voltage divided by the impedance of the primary winding. You can, though, work out the 'rated' primary current (i.e. the value of current the primary can carry, continuously). For a single-phase transformer, this will be… Read More

### How do you calculation of selecting Neutral Earthing Transformer?

iT IS ISMILAR TO THE GROUND RESITOR CALCULATION FOR TRANSFOMER THE TYPICAL EXAMPLE WAS ANSWERED EARLIER FOR TRANSFORMER DT.19-06-2009 Neutral of transformer can be grounded solidly earthed OR with Neutral Grounded with Resistance. Typical shunt calculations fro 5 MAV 11/6.6 kv transformer neutral are as :_ Transformer rating = 5 MVA Voltage ratio = 11/6.6 KV Vector Group = Dyn11 (6.6 KV ground through Resistor) During Earth fault voltage between Neutral & Earth = 6.6/âˆš3… Read More

### What is the difference between resistance and impedance?

Resistance is a concept used for DC (direct currents) whereas impedance is the AC (alternating current) equivalent. Resistance and impedance have different fundamental origins even though the calculation for their value is the same: R=V/I

### What Ac to ac step up transformer?

its a simple transformer which converts say 110volt 60hz ac current to 220 volt 60hz ac current. such change in magnitude of ac current from lower value to higher value is know as step up operation. if it vice versa then its called step down

### How do you do the loop impedance test?

The earth-fault loop includes the consumer's line conductor, the consumer's protective conductor, and the earth parth external to the consumer's installation (including the low-voltage winding of the transformer, the distribution line conductors to the installation, and the earth return path. The purpose of this test is to measure the actual value of the earth-fault loop impedance and to confirm that its value complies with the tabulated maximum values listed in BS 7671:2008 Regulations for Electrical… Read More

### What is the relation between surge current and fault current?

Fault/short circuit current is the available current from the source when a short circuit occurs. It is the maximum current the source can provide, defined as an RMS value, usually without any DC offset. Surge current is the maximum instantaneous current that is drawn by "turning on" or energizing a device such as a motor or transformer. Surge current will be less than fault current. If you assume a very strong source relative to the… Read More

### Is current ratio of transformer constant on loads?

the current ratio I1/I2 is a constant for all loads. the total current drawn on the secondary winding of a transformer depends on the total circuit impedance as seen by the transformer output terminals. considering that the power in primary is equal to the power in the secondary and is a constant (assuming no losses as per the principle of conservation of energy). The input voltage(primary) is a constant i.e equal to the primary distribution… Read More

### What is current trandformers?

I believe you meant transformer. If so it is a transformer used in high voltage circuits to reduce the current to a safer measurable value. It can be used as a direct input to a metering or protective relay to covert high currents to a lower value. It is used in AC circuits and typically encircles the conductor(s) it is monitoring, then works by using the expanding/ collapsing field which is the theory of induction… Read More

### What is a current transformer and how can a current transformer be used to extend the range of a wattmeter?

A current transformer (CT) works just like any other transformer. It is important to note it is not referenced to ground. It reflects current flow, not phase to ground voltage, so it attempts to hold current constant, not voltage. There is usually one primary "winding": one large cable through a donut CT, and multiple secondary windings. If a secondary winding is shorted (a wire placed across its terminals), the voltage built up in the secondary… Read More

### What is the current in the secondary coil if the current in the primary coil is 5.0?

If I am not wrong then you have asked about a transformer. And its a current transformer. By theory of voltage transformer we know that Vs/Vp = Ns/Np So for answering your question we need the value of number of turns in primary and secondary coil. But you can use this equation to find your answer if you have other values. By using ohmic law you can convert voltage to current.

### What is distance really?

The most common form of protection on high voltage transmission systems is distance relay protection. Power lines have set impedance per kilometre and using this value and comparing voltage and current the distance to a fault can be determined. The ANSI standard device number for a distance relay is 21

### What is a bus fault?

When a fault occurs in the electric bus (electric lines and intersections) due to short circuit between the phases or between 1 or more phase and ground, the current value mounts up to a very high value, which is known as bus fault current. This high value of current may cause damages to the transformers and could also rupture the other electric lines connected to the bus.

### Why ngt or ngr used in transformer?

Criteria-in order to protect the stator core from damage during internal earth fault it is necessary to limit the stator earth fault current al low as possible.may be upto 10amp for generator. Basis for selection of ngtr- if generator is connected to the system through generator transformer then generator can be treated as an isolated system which is not influenced by the distribution earthing system. In this case you can select earth fault current as… Read More

### What is the voltage if the current is 10Ampere?

Basic Ohm's law.... V = I x R Multiply the current (10 Ampere) by the resistance (or impedance) of the load to get the voltage. Comment: You cannot work out the value of the voltage by simply having the value of the current. V=I x R Or V=P/I

### What does a transformer transform?

A transformer transforms one level of voltage and current into another. A step up transformer raises voltage and lowers current, usually to make long power lines more efficient, and a step down transformer raises current and lowers voltage, usually to make it safe for homes and appliances. There are other more specialized transformers as well. Isolation transformers provide galvanic (DC) isolation between primary and secondary. They may step the voltage up or down, or not… Read More

### Why ohms low is not applicable for transformers?

Ohm's law gives a relation between Voltage, Current, and Resistance of circuit. Namely, V=IR, or Voltage = Current x Resistance Note that this equation states that when Voltage goes up, current goes up. A transformer is used to change the voltage of an AC circuit - a 1:10 transformer increases the voltage to 10x its old value, while a 10:1 transformer decreases it to 1/10th its old value.

### How does a transformer change voltage and current?

A transformer works through mutual induction, whereby a changing current in one coil induces a voltage into a second coil. The transformer winding (coil) connected to the supply is termed the primary winding, while the winding connected to the load is termed the secondary winding, and it is the ratio of the turns in each of these winding that determines whether the transformer is a step-up transformer or a step-down transformer. For example, if the… Read More

### Does a transformer convert the current from 240 volts to 120 volt?

Transformers are rated in KVA or VA (volt-amps). They transform voltages from one value to another. The current in a transformer is inverse to the voltage. This is why transformers are rated in KVA and smaller ones in VA.

### How do you measure neutral current on primary of transformer?

It depends on the voltage level. For low voltages, an ammeter could be used. For high voltages it is necessary for the ammeter to be electrically isolated from the current you wish to measure, so a current transformer (CT) will have to be used. A CT might also be necessary if the value of current to be measured is very high.

### Why transformers unit is rated as kva?

Power rating of any equipment depends on power consumed by that equipment, in other wordspower depend on Voltage, Current & Phase angle between Voltage & Current vactor. P = V * I * cosÃ˜ In case of transformer, there are two types of losses occure in transformer one is iron loss & other is copper loss. Iron loss occcure in core of the transformer and its value depends on supply voltage, whereas copper loss occures… Read More

### What is dynamic impedance?

The impedance of a circuit having an inductance and a capacitance in parallel at the frequency at which this impedance has a maximum value. Also known as rejector impedance.

### What is impedance analyzer?

Measurement of electrical conductivity by knowing the impedance value.

### Why is an alternating current out-of-phase with the voltage when connected to a capacitive or an inductive circuit?

Because the impedance of the inductor and capacitor is not a real resistance / has an imaginary value that causes voltage and current to be out of phase. An inductor's impedance is equivalent to j*w*L (j = i = imaginary number, w = frequency in radians, L = inductance), while a capacitor's impedance is 1/ (j*w*C). The 'j' causes the phase shift.

### How percentage impedance in transformers calculated?

The term, 'percentage impedance', is a little misleading, as it is defined as 'the value of primary voltage that will cause rated current to flow in the secondary winding, expressed as a percentage of the rated primary voltage'. So, the test is carried out as follows: the secondary winding is short-circuited through an ammeter capable of reading the rated secondary current. A variable voltage is applied to the primary winding. The primary voltage is gradually… Read More

### What do you mean by fault MVA?

This describes what is known as the 'fault level' at a particular point in an electricity transmission or distribution system, expressed in megavolt amperes, enabling the theoretical value of fault current to be calculated at that point in the system, in order to ensure that the relevant switchgear is capable of interrupting that level of fault current.