GB 20840.2-2014Instrument transformers -- Part 2: Additional requirements for current transformers (English PDF)

3.1 General definitions

3.1.201

Current Transformer Under normal conditions, the secondary current is proportional to the primary current reality, and in the right way when the coupling phase difference close to zero Transformers.

[GB/T 2900.15-1997, the definition 3.4.5] 3.1.202 Measuring current transformer Information transfer current transformer signal for measuring instruments and meters.

[GB/T 2900.15-1997, the definition 3.4.8, modified] 3.1.203 Protective current transformer to protect and control means for transmitting information signals current transformer.

[GB/T 2900.15-1997, the definition 3.4.7, modified] 3.1.204 P-level protection current transformer classPprotectivecurrenttransformer no residual magnetic flux limit of protective current transformer, under the symmetrical short-circuit current conditions its provisions saturation characteristics.

3.1.205

PR level protection current transformer classPRprotectivecurrenttransformer Having a residual magnetic flux limit protection current transformers, short-circuit current in symmetrical conditions set its saturation characteristics.

3.1.206

PX-level protection current transformer classPXprotectivecurrenttransformer no residual magnetic flux leakage reactance low limit protective current transformer, which is known as the secondary excitation characteristic, secondary winding resistance, secondary load electricity Resistance and turns ratio, then it is sufficient to determine the associated protection system performance.

3.1.207

PXR-level protection current transformer classPXRprotectivecurrenttransformer Having a residual magnetic flux limit protection current transformer, which is known as excitation characteristics, the secondary winding resistance, secondary load resistance and turns ratio when, that is sufficient to determine the relay contact associated with their performance.

201 Note. When the current transformer primary current contains a DC component, the situation will be more complicated. Therefore, in order to prevent the current transformer into saturation, using Current transformer with an air gap, but the same performance level and PX.

202 Note. reduce remanence air gap does not necessarily become a high leakage reactance current transformers (see Appendix 2C).

3.1.208

TPX-level transient characteristics of protective current transformer classTPXprotectivecurrenttransformerfortransientper-formance no residual magnetic flux limit of protective current transformer, the peak instantaneous error in transient short-circuit current conditions its provisions saturation characteristics.

3.1.209

TPY-level transient characteristics of protective current transformer classTPYprotectivecurrenttransformerfortransientper-formance Having a residual magnetic flux limit protection current transformer, the peak instantaneous error in transient short-circuit current conditions its provisions saturation characteristics.

3.1.210

TPZ-level transient characteristics of protective current transformer classTPZprotectivecurrenttransformerfortransientper-formance the protection of a secondary time constant predetermined value of current transformers to the peak AC component of the error specified in the transient short-circuit currents its saturation characteristics.

3.1.211

Optional current transformer ratio selectable-ratiocurrenttransformer Using a winding line for access or access to a variety tapped secondary winding turns ratio of the current transformer.

About 3.3 Current Rating Definition 3.3.201 Rated primary current Ipr as the performance of the current transformer primary current reference value.

[GB/T 2900.15-1997, the definition 2.3.28] 3.3.202 Rated secondary current Isr as the current transformer secondary current value of performance benchmarks.

[GB/T 2900.15-1997, the definition 2.3.30] 3.3.203 Rated short-time thermal current Ith in the case of short-circuit the secondary winding of the current transformer can withstand without damage a current maximum root mean square value in a short time stipulated.

[GB/T 2900.15-1997, definitions 2.3.18, modified] 3.3.204 Rated dynamic current Idyn in the case of short-circuit the secondary winding of the current transformer can withstand the electromagnetic force without electrical or mechanical damage to the maximum primary current Peak.

[GB/T 2900.15-1997, the definition 2.3.20] 3.3.205 Rated continuous thermal current Icth in the secondary winding is connected with the rated load, allowing continuous flow through the primary winding and the temperature does not exceed a predetermined value of the current value.

[GB/T 2900.15-1997, definitions 2.3.19, modified] 3.3.206 Rated primary short-circuit current Ipsc A transient short-circuit current side AC component rms value of the reference current transformer accuracy performance.

Note 201. Ith limits associated with fever, Ipsc related to the accuracy limits, usually Ipsc less than Ith.

3.3.207

Excitation current excitingcurrent Ie when the primary winding and other windings open circuit current transformer nominal frequency sine wave voltage is applied to the second terminal of the secondary winding the current drawn by the root-mean-square value.

[GB/T 2900.15-1997, the definition 2.3.9, modified]

3.4 Concerning the definition of accuracy

3.4.3

The ratio difference ratioerror GB 20840.1-2010 3.4.3 and the following are applicable.

Current transformer ratio difference (current error) according to equation (1) expressed as a percentage.

epsilon =

krIs-Ip

× 100% (1)

Where.

kr --- rated transformation ratio;

Ip --- the actual primary current;

Is --- under the measurement conditions, the actual flow through the secondary current when Ip.

201 Note. the amount of interpretation phase is shown in Figure 2D.1.

3.4.4

Retardation phasedisplacement deltaphi GB 20840.1-2010 3.4.4 and the following are applicable.

201 Note. the amount of interpretation phase is shown in Figure 2D.1.

3.4.201

Rated resistive load ratedresistiveburden Rb Resistive load rating of the secondary connected in ohms (ohm).

3.4.202

Secondary winding resistance Rct Actual secondary winding DC resistance in ohms (ohm), corrected to 75 °C or other temperature as may be prescribed.

Note 201. Rct actual values. Not to be confused Rct upper limit, which can otherwise specified.

3.4.203

Composite error epsilonc at steady state, when a predetermined primary current and the secondary current in the positive direction of the terminal signs agreement following the difference between the root mean square value.

a) the instantaneous value of the primary current;

b) the instantaneous value of the actual secondary current multiplied by the rated transformation ratio.

Composite error epsilonc usually according to formula (2) percentage root mean square value of the primary current representation.

epsilonc =

Tintegral

(Kr × is-ip) 2dt

× 100% (2)

Where.

kr --- rated transformation ratio;

Ip --- primary current rms value;

ip --- primary current instantaneous value;

is --- secondary current instantaneous value;

T --- a cycle of time.

201 Note. See further explanation 2D.4.

[GB/T 2900.15-1997, definitions 2.3.17, modified] 3.4.204 Rated instrument limit primary current IPL Measuring current transformer secondary load equal to the rated load, the composite error is equal to or greater than the minimum primary current value at 10%.

3.4.205

Safety factor instrumentsecurityfactor FS Primary current and rated primary current ratio of rated instrument limit.

201 Note. It should be noted that the actual instrument security factor is the impact of the load. When the load is significantly lower than the nominal value, the short-circuit current in the secondary side will produce more High Current.

202 Note. If the system fault current through the current transformer primary winding, the rated instrument security factor FS is lower, by a transformer power supply means more safety.

[GB/T 2900.15-1997, definitions 2.3.22, modified] 3.4.206 to measure the second limit potential secondarylimitinge.mfformearsuringcurrenttransformers current transformer EFS Instrument security factor FS, rated secondary current and the rated load impedance of the secondary winding and the three vector product.

Note 201. Measuring current transformer secondary limit potential EFS according to equation (3) Calculated.

EFS = FS × Isr × (Rct Rb) 2 X2b (3) where.

Rb --- resistance portion of the rated load;

The reactance Xb --- rated load.

The resulting value is higher than the actual value of this method. So the choice is to use the same protective current transformer test methods. See 7.2.6.202 and 7.2.6.203.

[GB/T 2900.15-1997, definitions 2.3.25, modified] 3.4.207 Rated accuracy limit primary current Maximum current transformer primary current to meet the requirements of the composite error value.

[GB/T 2900.15-1997, the definition 2.3.23] 3.4.208 Accuracy limit factor ALF Rated accuracy limit primary current and rated primary current ratio of.

[GB/T 2900.15-1997, the definition 2.3.27] 3.4.209 Protective current transformer secondary limit potential secondarylimitinge.mfforprotectivecurrenttransformers EALF Accuracy limit factor, rated secondary current and the rated load impedance of the secondary winding and the three vector product.

Note 201. P and PR potential EALF level protection according to formula (4) with a current transformer secondary limit calculated as follows.

EALF = ALF × Isr × (Rct Rb) 2 X2b (4) where.

Rb --- resistance portion of the rated load;

The reactance Xb --- rated load.

3.4.210

Saturation flux Psisat the maximum value of the current transformer secondary turns the flux linkage, corresponding to a magnetic saturation of the core material.

201 Note. saturation flux Psisat determine the most appropriate method is 2E.2.3 in the DC saturation method.

202 Note. In previous GB 16847 in, Psis defined as the inflection point value, it is characterized by a non-core saturation to saturation changes. This definition because the saturation value Too low to be recognized, and cause misunderstandings and conflicts. Thus, the replacement of Psisat, defined as complete saturation.

3.4.211

Residual magnetic flux remanentflux Psir After cutting the core excitation current 3min remaining turns of the secondary flux linkage value, the magnetizing current should be large enough to produce the saturation flux (Psisat).

3.4.212

Remanence factor KR the ratio of the residual magnetic flux and the saturation flux, expressed as a percentage.

3.4.213

Secondary circuit time constant secondarylooptimeconstant Ts Current transformer secondary circuit time constant value determined by the magnetizing inductance and leakage inductance sum (Ls) and the secondary loop resistance (Rs), According to equation (5) Calculated.

3.4.214

Excitation characteristics excitationcharacteristic when the current transformer primary winding and other windings open circuit, it is applied to the second terminal of the root mean square value of sinusoidal voltage and excitation current the relationship between the root mean square value, expressed as a curve or table column values. Coverage data should be sufficient to determine the value of the field from a low of 1.1 times until Abduction Point excitation characteristics of potential value.

3.4.215

Knee voltage kneepointvoltage Rated frequency sinusoidal voltage side of the current transformer when all other terminals are open, is applied to the second terminal of the root-mean-value increase the field current rms value increased by 50% plus 10%.

[GB/T 2900.15-1997, definitions 2.3.36, modified] 3.4.216 Inflection potential kneepointe.mf the field current rms value increased by 50% of current transformer rated frequency potential, the value increased 10%.

201 Note. the inflection point voltage can be applied to the current transformer secondary terminals, and the potential turning point can not be directly manipulated. Inflection point and the inflection point voltage potential can be considered the number Values are equal, because the impact of the secondary winding resistance voltage drop is small.

3.4.217

Rated inflection potential ratedkneepointe.mf Ek Inflection point lower limit electric potential.

201 Note. Rated knee-level potential inclusion PX and PXR-level protection technology specification for current transformer. According to equation (6) Calculated.

Ek = Kx × Rct R () b × Isr (6) 3.4.218 Rated turns ratio A turns ratio of the numerical value of the secondary turns provisions.

Example 1. 1/600 (1 turn represents a number of turns, the secondary turns is 600 turns).

Example 2. 2/600 (expressed as a number of turns 2 turns, the secondary turns is 600 turns).

201 Note. inclusion rated turns ratio PX and PXR grade-level protection with the technical specifications of the current transformer.

202 Note. Rated turns ratio and are rated transformation ratio is a secondary requirement. If comparing the two nominal ratio should be reciprocal.

3.4.219

Turns ratio error epsilont the actual turns ratio represents the difference between the nominal turns ratio, the...