Where core balance CT is used?

Where core balance CT is used?
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1 Answer

Answer :

Core balance CT is used in earth fault protection.  
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Related questions

Why core balance CT is preferred over residual connected CT’s to sense earth fault in 6.6 kV feeders?

Description : Why core balance CT is preferred over residual connected CT’s to sense earth fault in 6.6 kV feeders?

Last Answer : a) To avoid relay mal-operation due to CT saturation b) Better sensitivity is got. c) High pickup and TMS avoided in IDMT earth fault relay. 

Explain with simple diagram the core balance CT.

Description : Explain with simple diagram the core balance CT.

Last Answer : In core balance CT all the three phases go through the core and the resultant magnetic flux is zero. Because the flux of three phases cancel each other. So the secondary output of CT is zero and ... energised to trip the circuit. Saturation is no problem because the core size is very big.  

Where core balance CT’s are used?

Description : Where core balance CT’s are used? 

Last Answer : In earth fault protection used. It senses the zero sequence current.  

Before servicing the device indicated as 'A' in panels #1 and #3 of the illustration, the device labeled 'CT' must __________. EL-0003 A. have the disconnected leads taped to prevent short circuiting. B. only be connected to multimeter on the ammeter setting C. be short circuited D. have one lead grounded to discharge static electricity for the prevention of damage to electronic components

Description : Before servicing the device indicated as 'A' in panels #1 and #3 of the illustration, the device labeled 'CT' must __________. EL-0003 A. have the disconnected leads taped to prevent ... D. have one lead grounded to discharge static electricity for the prevention of damage to electronic components

Last Answer : Answer: C

Difference between Current Transformer (CT) and Potential Transformer (PT)

Description : Difference between Current Transformer (CT) and Potential Transformer (PT)

Last Answer : Current Transformers (CT) and Potential Transformers (PT) are used to measure the current and voltage in a circuit of the order of hundreds of amperes and volts respectively. A CT has large number of ... and flux density vary over a wide range whereas in PT, they vary over a limited range only

What are the errors in CT?

Description : What are the errors in CT?

Last Answer : (a) Ratio error Percentage ratio error = [(Nominal ratio – Actual ratio)/Actual ratio] x 100 The value of transformation ratio is not equal to the turns ratio. (b) Phase angle error: Phase angle =180/ [(ImCos -I1Sin )/nIs]

Where wound type CT used and where not used?

Description : Where wound type CT used and where not used?

Last Answer : Used where low CT ratio req. Not used where high short ckt. Current exists.

Give the details of switchyard 220 kV CB, Isolator, CT, CVT and lightning arrestor.

Description : Give the details of switchyard 220 kV CB, Isolator, CT, CVT and lightning arrestor.  

Last Answer : 220 kV SF6 Circuit Breaker 1. Make - ABB 2. Air pressure blocking a. Close Block - 17.3 bar. b. Open block - 16.7 bar. c. Auto reclose block - 19 bar. 3. SF6 pressure block a. Alarm - 5. ... , storage and erection. Rated voltage : 216 kV rms. Operating voltage : 184 kV rms. 

Why CT operated over load relay is using for loads of high acceleration time upto 30 seconds? How it getting back?

Description : Why CT operated over load relay is using for loads of high acceleration time upto 30 seconds? How it getting back?

Last Answer : The saturable current transformers linearly transforms the current upto twice the set current, but above this value the transformer core gets saturated and the secondary current is proportionally less. Thus ... overload. When current reduces the core gets de-saturated, as material design is such. 

How CT is connecting in ckt?

Description : How CT is connecting in ckt? 

Last Answer : If the primary of CT is delta connected load the CT will be in star connection and vice versa. This is because to have square root 3 time compensation. 

Why ICT are used?(INTERPOSING CT)

Description : Why ICT are used?(INTERPOSING CT)

Last Answer : To correct the system primary CT errors in case of high current faults out side CT zone (ICT’s primary CT is 800/1, but in fault current may go to thousands of amps. This ICT will take care of those errors. a) Matching the ratios. b) Matching the phase angle differences. 

What are the checks on CT & PT?

Description : What are the checks on CT & PT?

Last Answer : a) Polarity checks b) Insulation checks c) Ratio checks d) Knee point voltage (only for PS class CT)- magnetising characteristic test. 

Where CT secondary of 1A we are using?

Description : Where CT secondary of 1A we are using?

Last Answer : For long distance current transmission, to reduce the IR drop.  

What is the purpose of CT & PT?

Description : What is the purpose of CT & PT?

Last Answer : For transformation of current, voltage to a lower level for the purpose of Measurement, Protection and Control. 

What is the standard CT polarity?

Description : What is the standard CT polarity?

Last Answer : Primary current enters at P1 and secondary current leaves at S2.  

But is it advisable to keep the secondary of CT in open conditions? Will not induce very high voltage?

Description : But is it advisable to keep the secondary of CT in open conditions? Will not induce very high voltage?

Last Answer : If the CT has only one secondary winding, we should keep it always short cktd for safety, but if the CT has multiple secondary, then if one secondary voltage is kept limited by suitable loading, then the other secondary voltage is eventually limited proportionately. 

A CT has 2 – secondary windings. If we use only one secondary winding can we keep the unused secondary winding short circuited?

Description : A CT has 2 – secondary windings. If we use only one secondary winding can we keep the unused secondary winding short circuited?

Last Answer : No. If it is short-circuited then the ratio will not get correctly. The turns of primary winding will be shared between 2 secondary windings. So the unused secondary winding should kept open. 

What is over voltage interturn test for CT?

Description : What is over voltage interturn test for CT?

Last Answer : With secondary open, pass rated current in primary for 1 min. Then check secondary for insulation. 

What is the operating point in the Magnetising characteristic of protection CT & measuring CT?

Description : What is the operating point in the Magnetising characteristic of protection CT & measuring CT? 

Last Answer : Protection CT – Operation at ankle point only. Measuring CT – Operation from ankle to knee point 

What are the errors of the following CT’ s 5p. 10p. 15p. At rated current?

Description : What are the errors of the following CT’ s 5p. 10p. 15p. At rated current?  

Last Answer : 5p - 1 % Ratio error ± 60 min phase error 10p - 3 % Ratio error ± 60 min phase error 15p - 5 % Ratio error ± 60 min phase error 

What are the specifications of CT?

Description : What are the specifications of CT? 

Last Answer : Protection CT - Error. Alf. KpV. Metering CT - Error. Burden. Differential CT - Class PS. Core balance or E/F CT - 5-p type. Primary current - Rating of CT - 1. 15 ( full load current ) Short time rating - 1 sec. 

Why CT should not be open circuited?

Description : Why CT should not be open circuited?

Last Answer : Very high voltage will be induced in secondary due to less back emf resulting in the failure of the insulation. 

How can you de-saturate the CT?

Description : How can you de-saturate the CT? 

Last Answer : Pass ac current through the primary and vary the current from zero to maximum with secondary in shorted condition. Pass dc current in the secondary and vary it from zero to maximum.

What is the problem anticipated due to CT saturation?

Description : What is the problem anticipated due to CT saturation?  

Last Answer : The CT will not be able to drive the current through the circuit causing nonoperation of relays. In some other case when the currents in the two phases are compared for relay operation the relay may operate due to unbalance. 

When will you say that the CT is saturated?

Description : When will you say that the CT is saturated?

Last Answer : When checking the CT with the secondary injection method a 10% increases in the voltage causes a 50% increase in the current the CT is said to be saturated. 

Show the CT characteristics.

Description : Show the CT characteristics.

Last Answer : CT characteristics :  

How to reduce the CT error?

Description : How to reduce the CT error? 

Last Answer : Error reduces if load increases.  

Explain the procedure for finding out the polarity and ratio test in a CT with circuit diagram.

Description : Explain the procedure for finding out the polarity and ratio test in a CT with circuit diagram. 

Last Answer : Polarity test: Connect the circuit as shown in figure with a battery, switch and AVOmeter. Now momentarily close the switch S and see the deflection in the AVOmeter. If it is in the direction as shown in the ... A2. Then see whether it confirms to reading of nameplate. Ratio = A1/A2. 

Define knee point voltage of a CT.

Description : Define knee point voltage of a CT.

Last Answer : When the primary of a CT is open circuited and supply (variable) of system frequency is given to secondary, then a 10% increase in voltage constitutes 50% increase in current. That voltage is the knee point ... Above kpv the ratio of transformer will not be applicable. kpv = RCT + RLEADS + RRELAY  

Draw a neat sketch and explain the use of CT and PT for measurement of power in a single-phase circuit?

Description : Draw a neat sketch and explain the use of CT and PT for measurement of power in a single-phase circuit?

Last Answer : If wattmeter of proper range is not available or if voltage and current ranges are high we can usr CT and PT of suitable ratio. Connect the CT and PT as shown in figure. The reading of wattmeter can be multiplied by the ratio to get the actual power.   

The boundary of the protective zone is determined by the (A) Location of CT (B) sensitivity of relay used (C) Location of PT (D) None of these

Description : The boundary of the protective zone is determined by the (A) Location of CT (B) sensitivity of relay used (C) Location of PT (D) None of these

Last Answer : Ans: B The boundary of the protective zone is determined by the sensitivity of relay used. If the relay is more sensitive, the protective zone will be increased.

The harmonic currents in a power transformer does not cause increase in: a) Secondary voltage b) Core loss c) Copper loss d) Magnetic interference with protective relays

Description : The harmonic currents in a power transformer does not cause increase in: a) Secondary voltage b) Core loss c) Copper loss d) Magnetic interference with protective relays

Last Answer : Ans: A

Which of the following losses is/are present in every direct current generator armature? A. Winding copper loss B. Core eddy current loss C. Magnetic hysteresis loss D. All of the above.

Description : Which of the following losses is/are present in every direct current generator armature? A. Winding copper loss B. Core eddy current loss C. Magnetic hysteresis loss D. All of the above.

Last Answer : Answer: D

Hysteresis in a direct current generator is indicated by _____________. A. arcing at the brushes B. pulsating terminal current C. heating of the armature core D. hunting and over control

Description : Hysteresis in a direct current generator is indicated by _____________. A. arcing at the brushes B. pulsating terminal current C. heating of the armature core D. hunting and over control

Last Answer : Answer: C

Which of the listed electrical devices is represented by the symbol shown in the illustration? EL-0055 A. Fixed resistance resistor B. Coil with magnetic core C. DC motor or generator shunt field D. Transformer

Description : Which of the listed electrical devices is represented by the symbol shown in the illustration? EL-0055 A. Fixed resistance resistor B. Coil with magnetic core C. DC motor or generator shunt field D. Transformer

Last Answer : Answer: D

Brush sparking during commutation may be caused by ________. A. eddy currents in the armature core B. laminations in the generator field pieces C. induced current opposite to coil inductance D. coil inductance discharge occurring at commutation

Description : Brush sparking during commutation may be caused by ________. A. eddy currents in the armature core B. laminations in the generator field pieces C. induced current opposite to coil inductance D. coil inductance discharge occurring at commutation

Last Answer : Answer: D

In replacing a defective transformer with a new one, which of the following actions must be carried out to insure proper operation of the equipment it serves? A. The secondary leads must be grounded for 10 minutes to remove static charges. B. The transformer connections must be made as before with regard to the indicated polarity. C. The iron core of the transformer must be flashed to pre-magnetize it. D. The iron core must be grounded for 10 minutes to remove any residual magnetism.

Description : In replacing a defective transformer with a new one, which of the following actions must be carried out to insure proper operation of the equipment it serves? A. The secondary leads must be grounded ... magnetize it. D. The iron core must be grounded for 10 minutes to remove any residual magnetism.

Last Answer : Answer: B

The hook-on AC volt-ammeter consists essentially of a split-core and a rectifiertype instrument connected to the secondary winding of a _____________. A. potential transformer B. control transformer C. current transformer D. reactance transformer

Description : The hook-on AC volt-ammeter consists essentially of a split-core and a rectifiertype instrument connected to the secondary winding of a _____________. A. potential transformer B. control transformer C. current transformer D. reactance transformer

Last Answer : Answer: C

In D.C. motor construction, the armature coils' ends are _______________. A. soldered to the commutator bar risers B. imbedded into core slots C. crimped together with brush pigtails D. spliced with the field windings

Description : In D.C. motor construction, the armature coils' ends are _______________. A. soldered to the commutator bar risers B. imbedded into core slots C. crimped together with brush pigtails D. spliced with the field windings

Last Answer : Answer: A

In D.C. motor construction, commutating windings are wound on _________________. A. opposite main poles B. interpoles C. adjacent main poles D. the rotor core

Description : In D.C. motor construction, commutating windings are wound on _________________. A. opposite main poles B. interpoles C. adjacent main poles D. the rotor core

Last Answer : Answer: B

In the construction of D.C. motors, parts of both the series and shunt fields are wound on the _____________. A. opposite main pole B. rotor core C. interpole D. same main pole

Description : In the construction of D.C. motors, parts of both the series and shunt fields are wound on the _____________. A. opposite main pole B. rotor core C. interpole D. same main pole

Last Answer : Answer: D

When a transformer is used to step down voltage, the low voltage winding is _____________. A. part of the core B. the primary coil C. not insulated D. the secondary coil

Description : When a transformer is used to step down voltage, the low voltage winding is _____________. A. part of the core B. the primary coil C. not insulated D. the secondary coil

Last Answer : Answer: D

In a three-phase, squirrel-cage type, induction motor the rotating magnetic field is established by the _____________. A. current induced in the rotor windings B. application of a three-phase voltage supply to the stator windings C. laminated steel core and aluminum conductors in the rotor D. interaction of the magnetic field caused by the induced current in the squirrel-cage bars with the magnetic field of the stator

Description : In a three-phase, squirrel-cage type, induction motor the rotating magnetic field is established by the _____________. A. current induced in the rotor windings B. application of a three-phase voltage ... caused by the induced current in the squirrel-cage bars with the magnetic field of the stator

Last Answer : Answer: B

If a transformer is connected to a DC source, the transformer will overload at the ____________. A. contacts B. primary coil C. secondary coil D. core

Description : If a transformer is connected to a DC source, the transformer will overload at the ____________. A. contacts B. primary coil C. secondary coil D. core

Last Answer : Answer: B

Although saturable reactors are extremely useful in some applications, their gain is low because of ____________. A. core hysteresis losses B. inductive reactance in the control winding C. IR drop throughout the load winding D. all of the above

Description : Although saturable reactors are extremely useful in some applications, their gain is low because of ____________. A. core hysteresis losses B. inductive reactance in the control winding C. IR drop throughout the load winding D. all of the above

Last Answer : Answer: A

The horizontal line which cuts across 'L1' shown in figure 'A' of the illustration indicates a/an ______________. EL-0091 A. iron core B. saturable core C. air gap D. capacitive coupling

Description : The horizontal line which cuts across 'L1' shown in figure 'A' of the illustration indicates a/an ______________. EL-0091 A. iron core B. saturable core C. air gap D. capacitive coupling

Last Answer : Answer: B

Figure 'B' shown in the illustration represents a/an ____________. EL-0091 A. magnetic amplifier B. Scott-T transformer C. saturable-core reactor D. oil-filled toroid

Description : Figure 'B' shown in the illustration represents a/an ____________. EL-0091 A. magnetic amplifier B. Scott-T transformer C. saturable-core reactor D. oil-filled toroid

Last Answer : Answer: A

A saturable-core reactor operates on the principle of controlling a load winding's inductance by varying the core's _____________. A. dielectric B. permeability C. reactance D. inductance

Description : A saturable-core reactor operates on the principle of controlling a load winding's inductance by varying the core's _____________. A. dielectric B. permeability C. reactance D. inductance

Last Answer : Answer: B

Figure 'A' shown in the illustration represents a/an _______________. EL-0091 A. magnetic amplifier B. Scott-T transformer C. saturable-core reactor D. oil-filled toroid

Description : Figure 'A' shown in the illustration represents a/an _______________. EL-0091 A. magnetic amplifier B. Scott-T transformer C. saturable-core reactor D. oil-filled toroid

Last Answer : Answer: C

The basic control action of a magnetic amplifier depends upon _____________. A. variations in the load capacitance B. changes in inductance C. type of core material D. construction of the core

Description : The basic control action of a magnetic amplifier depends upon _____________. A. variations in the load capacitance B. changes in inductance C. type of core material D. construction of the core

Last Answer : Answer: B