# US 2014/0156212 A1 · Method and apparatus for testing the excitation characteristic of current transformer > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2014/0156212 A1 - Document ID: US20140156212A1 - Status: Published application - Kind: A1 - Application number: 13/869,546 - Filed: 2013-04-24 - Published: 2014-06-05 - Earliest claimed: 2012-12-05 - Assignees: Ponovo Power Co., Ltd - Applicants: Ponovo Power Co., Ltd - Inventors: Yake LI; Wei CHEN; Sen ZHANG; Jingfeng ZHAO - Web page: https://patentgrep.com/patent/US20140156212A1 ## CPC - G01R 31/62: Testing of transformers - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) ## Abstract This disclosure relates to the field of current transformers, for testing the excitation characteristic of a current transformer is disclosed. The method comprise applying alternately positive and negative DC voltages across terminals of secondary winding of a CT to be tested and acquiring a secondary current; constructing a mathematical model of the relationship between the secondary current and a root mean square (rms) equivalent voltage at rated frequency of the CT from the relationship between a magnetic flux of a secondary winding iron-core of the CT and the rms equivalent voltage; and generating an excitation characteristic curve according to the mathematical model. The method and apparatus of the embodiments may test CTs requiring lower testing voltage as well as CTs with knee-point up to tens of kV by supplying a relatively low voltage and power, which makes the embodiments widely applicable. ## Claims ### Claim 1 A method for testing excitation characteristic of a current transformer (CT), characterized in that the method comprises the steps of: applying alternately positive and negative DC voltages across terminals of secondary winding of a CT to be tested, and acquiring a secondary current; constructing a mathematical model of a relationship between the secondary current and a root mean square (rms) equivalent voltage at rated frequency of the CT from a relationship between a magnetic flux of a secondary winding iron-core of the CT and the rms equivalent voltage; and generating an excitation characteristic curve according to the mathematical model. ### Claim 2 (depends on 1) The method of claim 1, wherein the mathematical model is: Uc = 2  π   f 2 * { ∫ 0 t  [ U  ( t ) - Rct * Ict  ( t ) ]   t + Φ  ( 0 ) } where Uc is the rms equivalent voltage at the rated frequency of the CT, f is the rated frequency of the CT, U(t) is an amplitude of the DC voltage applied to the terminals of the secondary winding at time t, Rct is a DC resistance of the secondary winding, Ict(t) is the secondary current acquired at time t, and Φ(0) is the magnetic flux of the secondary winding iron-core when time t=0. ### Claim 3 (depends on 2) The method of claim 2, wherein the step of acquiring the secondary current each time the positive or negative DC voltage is applied across the terminals of the secondary winding of the CT to be tested comprises: setting a target secondary current; applying the positive or negative DC voltage across the terminals of the secondary winding of the CT to be tested; and acquiring the secondary current, and once the acquired secondary current reaches the target secondary current, the positive or negative DC voltage is stopped from being applied to the terminals of the secondary winding of the CT to be tested. ### Claim 4 (depends on 3) The method of claim 3, wherein in the step of applying alternately the positive and negative DC voltages across the terminals of the secondary winding of the CT to be tested and acquiring the secondary current, the positive and the negative DC voltage are applied for at least one time. ### Claim 5 (depends on 3) The method of claim 3, wherein the target secondary current set each time is the same or not all the same; the amplitude of the positive and negative DC voltage applied each time is the same or not all the same. ### Claim 6 (depends on 4) The method of claim 4, wherein the target secondary current set each time is the same or not all the same; the amplitude of the positive and negative DC voltage applied each time is the same or not all the same. ### Claim 7 (depends on 2) The method of claim 2, wherein the method further comprises: supplying a DC current to the terminals of the secondary winding of the CT to be tested, and measuring the voltage across the terminals of the secondary winding as well as the secondary current; and obtaining the DC resistance (Rct) of the secondary winding from the measured voltage across the terminals of the secondary winding and the measured secondary current. ### Claim 8 (depends on 3) The method of claim 3, wherein the method further comprises: supplying a DC current to the terminals of the secondary winding of the CT to be tested, and measuring the voltage across the terminals of the secondary winding as well as the secondary current; and obtaining the DC resistance (Rct) of the secondary winding from the measured voltage across the terminals of the secondary winding and the measured secondary current. ### Claim 9 (depends on 4) The method of claim 4, wherein the method further comprises: supplying a DC current to the terminals of the secondary winding of the CT to be tested, and measuring the voltage across the terminals of the secondary winding as well as the secondary current; and obtaining the DC resistance (Rct) of the secondary winding from the measured voltage across the terminals of the secondary winding and the measured secondary current. ### Claim 10 (depends on 5) The method of claim 5, wherein the method further comprises: supplying a DC current to the terminals of the secondary winding of the CT to be tested, and measuring the voltage across the terminals of the secondary winding as well as the secondary current; and obtaining the DC resistance (Rct) of the secondary winding from the measured voltage across the terminals of the secondary winding and the measured secondary current. ### Claim 11 (depends on 6) The method of claim 6, wherein the method further comprises: supplying a DC current to the terminals of the secondary winding of the CT to be tested, and measuring the voltage across the terminals of the secondary winding as well as the secondary current; and obtaining the DC resistance (Rct) of the secondary winding from the measured voltage across the terminals of the secondary winding and the measured secondary current. ### Claim 12 (depends on 7) The method of claim 7, wherein the amplitude of the positive and negative DC voltage applied each time is larger than Rct*Icttarget, where Icttarget is the set target secondary current. ### Claim 13 (depends on 8) The method of claim 8, wherein the amplitude of the positive and negative DC voltage applied each time is larger than Rct*Icttarget, where Icttarget is the set target secondary current. ### Claim 14 (depends on 9) The method of claim 9, wherein the amplitude of the positive and negative DC voltage applied each time is larger than Rct*Icttarget, where Icttarget is the set target secondary current. ### Claim 15 (depends on 10) The method of claim 10, wherein the amplitude of the positive and negative DC voltage applied each time is larger than Rct*Icttarget, where Icttarget is the set target secondary current. ### Claim 16 (depends on 11) The method of claim 11, wherein the amplitude of the positive and negative DC voltage applied each time is larger than Rct*Icttarget, where Icttarget is the set target secondary current. ### Claim 17 An apparatus for testing excitation characteristic of a current transformer comprising: a testing unit configured to apply alternately positive and negative DC voltages across terminals of secondary winding of a CT to be tested, and acquire a secondary current; a model constructing unit configured to construct a mathematical model of a relationship between the secondary current and a rms equivalent voltage at rated frequency of the CT from a relationship between a magnetic flux of a secondary winding iron-core of the CT and the rms equivalent voltage; and an excitation characteristic curve generating unit configured to generate the excitation characteristic curve according to the model constructed by the model constructing unit. ### Claim 18 (depends on 17) The apparatus of claim 17, wherein the testing unit comprises: a power output subunit configured to apply alternately the positive and negative DC voltage across the terminals of the secondary winding of the CT to be tested; and a current acquiring subunit configured to acquire the secondary current of the secondary winding of the CT to be tested after applying the DC voltage across the terminals of the secondary winding of the CT to be tested by the power output subunit. ### Claim 19 (depends on 18) The apparatus of claim 18, wherein the power output subunit is further configured to supply a DC current to the terminals of the secondary winding of the CT to be tested; the testing unit further comprises: a voltage acquiring subunit configured to acquire the voltage across the terminals of the secondary winding of the CT to be tested after the DC current is supplied; wherein the current acquiring subunit is further configured to acquire the secondary current of the CT to be tested after the DC current is supplied; and a computation subunit configured to compute the DC resistance of the secondary winding, according to the voltage across the terminals of the secondary winding acquired by the voltage acquiring subunit and the secondary current acquired by the current acquiring subunit.