What are the checks on CT & PT?

What are the checks on CT & PT?
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1 Answer

Answer :

a) Polarity checks

b) Insulation checks

c) Ratio checks

d) Knee point voltage (only for PS class CT)- magnetising characteristic test. 


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Related questions

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. 

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

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.

Pt. with long hix of hyperthyroidism to screen about the complication of hyperthyroidism do: liver us Ct brain Bone scan (for osteoporosis)

Description : Pt. with long hix of hyperthyroidism to screen about the complication of hyperthyroidism do: liver us Ct brain Bone scan (for osteoporosis)

Last Answer : Bone scan (for osteoporosis)

How can we use CT and PT for protection purpose?

Description : How can we use CT and PT for protection purpose?

Last Answer : CT and PT for Protection purpose: Current transformer (CT) and Potential transformer (PT) are instrument transformers, which are used in conjunction with protective relays for protection purpose. The CT ... from the healthy part. In this way the CT and PT can be used for protection purpose.

Mention the precautions to be taken while connecting CT and PT in the circuit.

Description : Mention the precautions to be taken while connecting CT and PT in the circuit. 

Last Answer : Precautions to be taken while using instrument transformers: 1. Secondary of CT is never kept open circuited when it is energized. 2. Secondary of PT is never kept short circuited when it ... of the instrument transformers unless they are properly grounded. 8. Never connect to DC circuits.

Write any four differences between CT and PT.

Description : Write any four differences between CT and PT.

Last Answer : CT PT CT corresponds to current transformer PT corresponds to potential transformer CT primary is connected in series with load and secondary winding is connected to a low range ammeter. PT ... ) x PT ratio It is a step-up transformer. It is a step-down transformer

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 

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

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. 

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 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 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.  

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  

Where core balance CT is used?

Description : Where core balance CT is used?

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

Why PT fuse fails protection?

Description : Why PT fuse fails protection?  

Last Answer : Mho relays will mal-operate if PT voltage is lost to the relay, so tripping blocked by sensing PT fuse failure. 

What is the equation for resistance measurement of PT 100 thermocouple?

Description : What is the equation for resistance measurement of PT 100 thermocouple? 

Last Answer : °C = (R-100) / 0.39  

What is the rating of generator PT fuse?

Description : What is the rating of generator PT fuse?

Last Answer : 24 kV, 3.15 Amps.  

Why AVR changes over to manual on AVR PT fuse failure?

Description : Why AVR changes over to manual on AVR PT fuse failure? 

Last Answer : Because loss of feedback to voltage corrector.  

What is the difference between PT and normal transformer?

Description : What is the difference between PT and normal transformer?  

Last Answer : Burden of PT is less and burden of normal transformer is high.  

To achieve low PT error, the burden value should be ____________. (A) low (B) high (C) medium (D) none of the above

Description : To achieve low PT error, the burden value should be ____________. (A) low (B) high (C) medium (D) none of the above

Last Answer : Ans: A In a Potential transformer, burden should be in permissible range to maintain errorless measurement.

Complete maintenance of electrical motors should include periodic checks for machine _____________. A. vibration B. watertight integrity C. speed droop D. reactive power

Description : Complete maintenance of electrical motors should include periodic checks for machine _____________. A. vibration B. watertight integrity C. speed droop D. reactive power

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What are the checks on the motor during the preventive maintenance?

Description : What are the checks on the motor during the preventive maintenance?

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What are the tests to be carried during PM checks of IPBD?

Description : What are the tests to be carried during PM checks of IPBD?  

Last Answer : a) Physical inspection of bus for any spark or overheating or discoloration. b) Physical inspection of copper braided flexibles for discoloration. c) Physical inspection of inspection window gaskets, seal off ... Tan-delta test of IPBD m) IR value measurement n) Cleanliness checks entire IPBD. 

What are the routines checks on slip rings?

Description : What are the routines checks on slip rings?

Last Answer : a. Correct mV drops brush to be used. b. Brush tension adjustment. c. Air cleaning to reduce leakage current. d. Brush bedding before use. e. Field polarity change every 6 months. 

What maintenance checks you will do for an MCC cells and MCC panel?

Description : What maintenance checks you will do for an MCC cells and MCC panel?

Last Answer : Maintenance checks on MCC cells a. Ensure that the load is tripped from control room and switch is in off position. Switch off the isolator at MCC cell. b. Open the door and rack ... See for proper earthing connection and tightness of the earthing connections. l. See for proper house keeping. 

Mention the initial commissioning checks on CT’s, PT’s and relays.

Description : Mention the initial commissioning checks on CT’s, PT’s and relays.

Last Answer : Commissioning checks on CT a) Terminal marking correctness. b) Polarity of terminals. c) Insulation resistance between primary and secondary. d) Insulation resistance between primary to earth and secondary ... h) Burden check of relay. i) Primary injection test. j) Secondary injection test. 

does medicare cover a PET scan CT scans done & were inconclusive .s Additional testing is required to obtain a diagnosis ?

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Last Answer : Yes Medicare does cover PET scans but only under the following 5 related applications: 1.Solitary Pulmonary Nodule 2.Staging of lung cancer. 3. Staging of Lymphoma. 4. Staging of Melanoma and ... cancer. In your case that a diagnosis is still inconclusive Medicare will not cover the test.

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Description : what does return reason -b.....uncollected funds hold- mean, if you have enough in your acct for the check, & you also pay for having "NO Checks returned"...please explain.....?

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