Why CT should not be open circuited?

Why CT should not be open circuited?
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1 Answer

Answer :

Very high voltage will be induced in secondary due to less back emf resulting in the failure of the insulation. 
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Related questions

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

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. 

Booster transformer should never: a) Have fuse in the HV winding b) Be left open circuited c) Be left closed circuited d) None of the above

Description : Booster transformer should never: a) Have fuse in the HV winding b) Be left open circuited c) Be left closed circuited d) None of the above

Last Answer : Ans: B

If the field circuits of an unloaded salient pole synchronous motor gets suddenly open circuited, then (A) The motor stops. (B) It continues to run at the same speed. (C) Its runs at the slower speed. (D) It runs at a very high speed.

Description : If the field circuits of an unloaded salient pole synchronous motor gets suddenly open circuited, then (A) The motor stops. (B) It continues to run at the same speed. (C) Its runs at the slower speed. (D) It runs at a very high speed.

Last Answer : Ans: B The motor continues to run at the same speed because synchronous motor speed does not depend upon load, Nα f.

A 220/440 V, 50 Hz, 5 KVA, single phase transformer operates on 220V, 40Hz supply with secondary winding open circuited. Then (A) Both eddy current and hysteresis losses decreases. (B) Both eddy current and hysteresis losses increases. (C) Eddy current loss remains the same but hysteresis loss increases. (D) Eddy current loss increases but hysteresis loss remains the same.

Description : A 220/440 V, 50 Hz, 5 KVA, single phase transformer operates on 220V, 40Hz supply with secondary winding open circuited. Then (A) Both eddy current and hysteresis losses decreases. (B) Both ... same but hysteresis loss increases. (D) Eddy current loss increases but hysteresis loss remains the same.

Last Answer : (A) Both eddy current and hysteresis losses decreases.

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. 

If your multimeter gives a reading in ohms when testing each end of each conductor of a three-conductor cable, this indicates ______________. A. continuity of the conductor B. an infinite resistance C. the presence of a partial ground D. that the conductor is not short circuited

Description : If your multimeter gives a reading in ohms when testing each end of each conductor of a three-conductor cable, this indicates ______________. A. continuity of the conductor B. an infinite resistance C. the presence of a partial ground D. that the conductor is not short circuited

Last Answer : Answer: A

If the illustrated device is fully discharged, what will be the result? EL-0061 A. The battery will be short circuited because the mud space will be filled with lead sulfate B. The electrolyte will be maximum sulfuric acid minimum water C. The electrolyte will be maximum water minimum sulfuric acid. D. The plates will be maximum lead oxide and sponge lead minimum lead sulfate.

Description : If the illustrated device is fully discharged, what will be the result? EL-0061 A. The battery will be short circuited because the mud space will be filled with lead sulfate B. The electrolyte ... minimum sulfuric acid. D. The plates will be maximum lead oxide and sponge lead minimum lead sulfate.

Last Answer : Answer: C

In the illustration, the chemical reaction depicted indicates that the _________. EL-0061 A. battery is being charged at a high rate B. cell is short circuited C. cell is discharging D. battery is attached to a trickle charger

Description : In the illustration, the chemical reaction depicted indicates that the _________. EL-0061 A. battery is being charged at a high rate B. cell is short circuited C. cell is discharging D. battery is attached to a trickle charger

Last Answer : Answer: C

If many turns of an alternating current coil for a contactor become short circuited, the coil _____________. A. will continue to operate B. will probably burn out immediately C. will operate on reduced current D. temperature will drop

Description : If many turns of an alternating current coil for a contactor become short circuited, the coil _____________. A. will continue to operate B. will probably burn out immediately C. will operate on reduced current D. temperature will drop

Last Answer : Answer: B

If many turns of an alternating current coil for a contactor become short circuited, the coil _____________. A. temperature will drop B. will probably burn out immediately C. will continue to operate D. will operate on reduced current

Description : If many turns of an alternating current coil for a contactor become short circuited, the coil _____________. A. temperature will drop B. will probably burn out immediately C. will continue to operate D. will operate on reduced current

Last Answer : Answer: B

Which of the following conditions indicates a short circuited capacitor when checking its condition with an ohmmeter? A. The capacitor shows charging, but the final resistance reading is appreciably less than normal. B. The reading is practically zero and remains there. C. The capacitor shows no charging action, but indicates a very high resistance. D. The pointer moves quickly to the low resistance side of the scale, then slowly recedes toward infinity.

Description : Which of the following conditions indicates a short circuited capacitor when checking its condition with an ohmmeter? A. The capacitor shows charging, but the final resistance reading is appreciably less ... moves quickly to the low resistance side of the scale, then slowly recedes toward infinity.

Last Answer : Answer: B

If you disconnect and arrange both ends of a three conductor cable, without any contact between the individual conductors, an indicated ohmic value between the ends of a single conductor would indicate ______________. A. continuity of the conductor B. an infinite resistance C. the presence of a partial ground D. that the conductor is not short circuited

Description : If you disconnect and arrange both ends of a three conductor cable, without any contact between the individual conductors, an indicated ohmic value between the ends of a single conductor would indicate ... resistance C. the presence of a partial ground D. that the conductor is not short circuited

Last Answer : Answer: A

Which parameter indicates the rotor short-circuited turns (Not involving earthfault)?

Description : Which parameter indicates the rotor short-circuited turns (Not involving earthfault)? 

Last Answer : Vibration increases.  

A dc cumulatively compounded motor delivers rated load torque at rated speed. If series field is short circuited, then the armature current and speed will a) Both increases b) Both decreases c) Increases and decreases d) Decreases and increases

Description : A dc cumulatively compounded motor delivers rated load torque at rated speed. If series field is short circuited, then the armature current and speed will a) Both increases b) Both decreases c) Increases and decreases d) Decreases and increases

Last Answer : Ans: Both increases

The standing wave ratio of short circuited and open circuited lines will be a) 0 b) 1 c) -1 d) ∞

Description : The standing wave ratio of short circuited and open circuited lines will be a) 0 b) 1 c) -1 d) ∞

Last Answer : d) ∞

The reflection co-efficient at the open circuited end of a transmission line. (a) zero (b) infinity (c) unity (d) none of the above

Description : The reflection co-efficient at the open circuited end of a transmission line. (a) zero (b) infinity (c) unity (d) none of the above

Last Answer : (c) unity

The phenomenon qf rise in voltage at the receiving end of the open-circuited or lightly loaded line is called the (a) Seeback effect (b) Ferranti effect (c) Raman effect (d) none of the above

Description : The phenomenon qf rise in voltage at the receiving end of the open-circuited or lightly loaded line is called the (a) Seeback effect (b) Ferranti effect (c) Raman effect (d) none of the above

Last Answer : (b) Ferranti effect

At what point on an open-circuited rf line do voltage peaks occur?

Description : At what point on an open-circuited rf line do voltage peaks occur?

Last Answer : At 1/2 wavelength from the end and at every 1/2 wavelength along the line

Short-circuited stubs are preferred to open-circuited stubs because thelatter are a. more difficult to make an connect b. made of a transmission line with a different characteristic impedance c. liable to radiate

Description : Short-circuited stubs are preferred to open-circuited stubs because thelatter are a. more difficult to make an connect b. made of a transmission line with a different characteristic impedance c. liable to radiate

Last Answer : c. liable to radiate

Impedance inversionmaybe obtainedwith a. a short-circuited stub b. an open-circuited stub c. a quarter-wave line d. a half-wave line

Description : Impedance inversionmaybe obtainedwith a. a short-circuited stub b. an open-circuited stub c. a quarter-wave line d. a half-wave line

Last Answer : c. a quarter-wave line

The phenomenon qf rise in voltage at the receiving end of the open-circuited or lightly loaded line is called the (a) Seeback effect (b) Ferranti effect (c) Raman effect (d) none of the above

Description : The phenomenon qf rise in voltage at the receiving end of the open-circuited or lightly loaded line is called the (a) Seeback effect (b) Ferranti effect (c) Raman effect (d) none of the above

Last Answer : (b) Ferranti effect

Explain standing waves with load terminal open circuited and short circuited.

Description : Explain standing waves with load terminal open circuited and short circuited. 

Last Answer : Standing waves with load terminal open circuited   Standing waves: The forward and reflected waves on the incorrectly terminated transmission line produce an interference pattern known as Standing ... , the load impedance will not be equal to the transmission line (characteristic)impedence.

A quarter wave line open circuited at far end behaves as:

Description : A quarter wave line open circuited at far end behaves as:  (1) Inductance (2) L and C in parallel (3) Capacitance (4) L and C in series

Last Answer : A quarter wave line open circuited at far end behaves as: L and C in series.

Open circuited armature coil of a D.C. machine is?

Last Answer : Open circuited armature coil of a D.C. machine is identified by the scarring of the commutator segment to which open circuited coil is connected and indicated by a spark completely around the commutator.

If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will?

Last Answer : If the field winding of an unloaded salient pole synchronous motor is open circuited, the motor will stop.

When secondary of a current transformer is open-circuited its iron core will be?

Description : When secondary of a current transformer is open-circuited its iron core will be?

Last Answer : When secondary of a current transformer is open-circuited its iron core will be hot because of heavy iron losses taking place in it due to high flux density.

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. 

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. 

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.  

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. 

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.