What is over voltage interturn test for CT?

What is over voltage interturn test for CT?
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1 Answer

Answer :

With secondary open, pass rated current in primary for 1 min. Then check secondary for insulation. 
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Related questions

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. 

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  

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. 

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. 

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 is the output voltage of a CT when it is set on electrical zero?

Description : What is the output voltage of a CT when it is set on electrical zero?

Last Answer : Zero or minimum voltage.

What is the amplitude and voltage induced into the rotor when the CX is turned 90º while the CT remains on electrical zero?

Description : What is the amplitude and voltage induced into the rotor when the CX is turned 90º while the CT remains on electrical zero?

Last Answer : The voltage is maximum and in phase with the ac excitation voltage to the CX.

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. 

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.  

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 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 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 is used?

Description : Where core balance CT is used?

Last Answer : Core balance CT is used in earth fault protection.  

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.

my husband had a colon test,and they found a tumor a piece was sent for testing, now he will be having a ct scan, should we be worried?

Description : my husband had a colon test,and they found a tumor a piece was sent for testing, now he will be having a ct scan, should we be worried?

Last Answer : what is my answer?

Following is the most sensitive test to detect the DNA. C A. ELISA B. Magnetic Resonance Imaging C. PCR D. CT Scanning

Description : Following is the most sensitive test to detect the DNA. C A. ELISA B. Magnetic Resonance Imaging C. PCR D. CT Scanning

Last Answer : PCR

A three-phase electrical system is equipped with ground detecting lamps. If one of the lamp goes dark and the other two burn normally before and after the test switch is operated, this indicates _______________. A. the dark lamp must be replaced B. there is a ground in the line with the dark lamp C. there are grounds in two of the three phases D. the voltage to the dark lamp is less than that of the system

Description : A three-phase electrical system is equipped with ground detecting lamps. If one of the lamp goes dark and the other two burn normally before and after the test switch is operated, this indicates _______________. ... of the three phases D. the voltage to the dark lamp is less than that of the system

Last Answer : Answer: A

In a three-phase electrical system, three ground detecting lamps are provided. If all three lamps REMAIN at half-brilliance when the ground detecting test switch is operated, ______________. A. there is a slight ground on all three phases B. the switch must be replaced C. there are no grounds present D. the light bulbs are of improper voltage

Description : In a three-phase electrical system, three ground detecting lamps are provided. If all three lamps REMAIN at half-brilliance when the ground detecting test switch is operated, ______________. A. there is a ... must be replaced C. there are no grounds present D. the light bulbs are of improper voltage

Last Answer : Answer: C

If reading AC current with the illustrated device and unsure of the range as a precaution , the first step should be to _________. EL-0047 A. secure power and test for voltage B. disconnect the lead to be tested and connect the meter in series C. connect the meter to measure resistance and use Ohm's law to calculate current D. unable to safely measure current with the device

Description : If reading AC current with the illustrated device and unsure of the range as a precaution , the first step should be to _________. EL-0047 A. secure power and test for voltage B. disconnect the ... resistance and use Ohm's law to calculate current D. unable to safely measure current with the device

Last Answer : Answer: A

In the illustrated test, if the lamp fails to light on any of the three windings then _________. EL-0027 A. all three windings are grounded and the motor should be sent out for repair B. the brushes should be set back on the commutator and the test redone C. the ground is not in the windings and the connections to the motor controller and the controller should be checked D. the test should be redone at a higher voltage

Description : In the illustrated test, if the lamp fails to light on any of the three windings then _________. EL-0027 A. all three windings are grounded and the motor should be sent out for repair B. ... the motor controller and the controller should be checked D. the test should be redone at a higher voltage

Last Answer : Answer: C

When using a multimeter for resistance measurements, it should be calibrated by clipping the loose ends of the leads together and _____________. A. setting the instrument pointer at 'zero' ohms B. adjusting the line voltage to calibrate the instrument C. plugging each end of one test lead into the plus and minus terminals D. using a special purpose resistance measuring instrument (a bridge)

Description : When using a multimeter for resistance measurements, it should be calibrated by clipping the loose ends of the leads together and _____________. A. setting the instrument pointer at 'zero' ohms B. ... the plus and minus terminals D. using a special purpose resistance measuring instrument (a bridge)

Last Answer : Answer: A

When a megohmmeter is being used to test insulation resistance, current leakage along the surface of the insulation is indicated by the megohmmeter pointer _____________. A. fluctuating around a constant resistance reading B. dipping towards 'zero', then rising slowly C. kicking slightly downscale as voltage is applied D. continually rising as the test voltage is applied

Description : When a megohmmeter is being used to test insulation resistance, current leakage along the surface of the insulation is indicated by the megohmmeter pointer _____________. A. fluctuating around a ... slightly downscale as voltage is applied D. continually rising as the test voltage is applied

Last Answer : Answer: C

You are using a mechanical voltage tester to check the fuses in a three-phase circuit supplying an electric motor. For which of the following reasons must the motor be stopped during the test? A. Testing an energized circuit presents a hazard to the testing personnel. B. A faulty fuse could go undetected with the motor energized. C. Reversed polarity of the circuit would be indicated by the voltage tester with the circuit energized. D. All of the above.

Description : You are using a mechanical voltage tester to check the fuses in a three-phase circuit supplying an electric motor. For which of the following reasons must the motor be stopped during the test? A. ... circuit would be indicated by the voltage tester with the circuit energized. D. All of the above.

Last Answer : Answer: B

When troubleshooting a lead-acid storage battery, a weak or dead cell is best detected by _________________. A. measuring and comparing all cells' specific gravity B. taking an open circuit voltage test of individual cells C. visually inspecting the electrolyte levels of each cell D. taking each cell's temperature with a calibrated mercury thermometer

Description : When troubleshooting a lead-acid storage battery, a weak or dead cell is best detected by _________________. A. measuring and comparing all cells' specific gravity B. taking an open circuit ... electrolyte levels of each cell D. taking each cell's temperature with a calibrated mercury thermometer

Last Answer : Answer: A

Under which of the following conditions will a lead-acid battery be given a 'test discharge'? A. To determine its capacity. B. Whenever a cell cannot be brought within 10 points of full charge specific gravity. C. When one or more cells is found to have less than normal voltage after an equalizing charge. D. All of the above.

Description : Under which of the following conditions will a lead-acid battery be given a 'test discharge'? A. To determine its capacity. B. Whenever a cell cannot be brought within 10 points of full charge ... cells is found to have less than normal voltage after an equalizing charge. D. All of the above.

Last Answer : Answer: D

Normally, the FIRST step in troubleshooting a transistor circuit card is to _____________. A. carefully remove the transistors from the card B. give the circuit an initial test with a signal generator C. test for continuity with a low voltage DC supply D. visually inspect the card

Description : Normally, the FIRST step in troubleshooting a transistor circuit card is to _____________. A. carefully remove the transistors from the card B. give the circuit an initial test with a signal generator C. test for continuity with a low voltage DC supply D. visually inspect the card

Last Answer : Answer: D

Which of the following actions must be carried out before a voltage tester can be used to test the three line fuses to a three-phase motor? A. The fuses must be removed from the circuit. B. The starter must be placed in the STOP position to stop the motor. C. The three line connections in the motor terminal box must be disconnected and tagged. D. Nothing need be done as long as the motor is running under a light load.

Description : Which of the following actions must be carried out before a voltage tester can be used to test the three line fuses to a three-phase motor? A. The fuses must be removed from the circuit. B. The ... disconnected and tagged. D. Nothing need be done as long as the motor is running under a light load.

Last Answer : Answer: B

To test fuses in an energized circuit, you should use a ____________. A. low voltage light bulb B. megohmmeter C. voltmeter D. resistance meter

Description : To test fuses in an energized circuit, you should use a ____________. A. low voltage light bulb B. megohmmeter C. voltmeter D. resistance meter

Last Answer : Answer: C

When a megohmmeter is being used to test insulation resistance, current leakage along the surface of the insulation is indicated by the megohmmeter's pointer _____________. A. dipping toward zero then raising slowly B. continually rising as test voltage is applied C. kicking slightly down scale as voltage is applied D. fluctuating around a constant resistance reading

Description : When a megohmmeter is being used to test insulation resistance, current leakage along the surface of the insulation is indicated by the megohmmeter's pointer _____________. A. dipping toward ... kicking slightly down scale as voltage is applied D. fluctuating around a constant resistance reading

Last Answer : Answer: C

In testing a three-phase delta winding for an open circuit using a megohmmeter, you must ______________. A. test each phase with all connections intact B. measure the voltage across the open connections while testing C. test the windings as parallel groups to avoid short circuiting D. open the delta-connections to avoid shunting the phase being tested

Description : In testing a three-phase delta winding for an open circuit using a megohmmeter, you must ______________. A. test each phase with all connections intact B. measure the voltage across the open ... groups to avoid short circuiting D. open the delta-connections to avoid shunting the phase being tested

Last Answer : Answer: D

One method of testing for a reversed shunt field coil in a DC generator or motor is by connecting the field to a direct current source, at reduced field rated voltage, and test for polarity using a/an ____________. A. iron bar across each field B. magnetic compass placed near each field C. test lamp across adjacent fields D. copper jumper across the interpole connections

Description : One method of testing for a reversed shunt field coil in a DC generator or motor is by connecting the field to a direct current source, at reduced field rated voltage, and test for ... placed near each field C. test lamp across adjacent fields D. copper jumper across the interpole connections

Last Answer : Answer: B

As a general rule, the first troubleshooting action to be taken in checking faulty electric control devices is to _____________. A. draw a one line diagram of the circuitry B. test all fuses and measure the line voltage C. take megger readings D. insulate the apparatus from ground

Description : As a general rule, the first troubleshooting action to be taken in checking faulty electric control devices is to _____________. A. draw a one line diagram of the circuitry B. test all fuses and measure the line voltage C. take megger readings D. insulate the apparatus from ground

Last Answer : Answer: B